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Journal articles on the topic 'Spatial response function'
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1
Frans, E. P., and R. A. Schowengerdt. "Improving Spatial-Spectral Unmixing with the Sensor Spatial Response Function." Canadian Journal of Remote Sensing 25, no. 2 (June 1999): 131–51. http://dx.doi.org/10.1080/07038992.1999.10874712.
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Lindsley, Richard D., Craig Anderson, Julia Figa-Saldana, and David G. Long. "A Parameterized ASCAT Measurement Spatial Response Function." IEEE Transactions on Geoscience and Remote Sensing 54, no. 8 (August 2016): 4570–79. http://dx.doi.org/10.1109/tgrs.2016.2544835.
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Lei, Xuefeng, Shuangshuang Zhu, Zhenyang Li, Jin Hong, Zhenhai Liu, Fei Tao, Peng Zou, Maoxin Song, and Congfei Li. "Integration model of POSP measurement spatial response function." Optics Express 28, no. 17 (August 14, 2020): 25480. http://dx.doi.org/10.1364/oe.393897.
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Williford, Tori, and John H. R. Maunsell. "Effects of Spatial Attention on Contrast Response Functions in Macaque Area V4." Journal of Neurophysiology 96, no. 1 (July 2006): 40–54. http://dx.doi.org/10.1152/jn.01207.2005.
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Previous single-unit studies of visual cortex have reported that spatial attention modulates responses to different orientations and directions proportionally, such that it does not change the width of tuning functions for these properties. Other studies have suggested that spatial attention causes a leftward shift in contrast response functions, such that its effects on responses to stimuli of different contrasts are not proportional. We have further explored the effects of attention on stimulus-response functions by measuring the responses of 131 individual V4 neurons in two monkeys while they did a task that controlled their spatial attention. Each neuron was tested with a set of stimuli that spanned complete ranges of orientation and contrast during different states of attention. Consistent with earlier reports, attention scaled responses to preferred and nonpreferred orientations proportionally. However, we did not find compelling evidence that the effects were best described by a leftward shift of the contrast response function. The modulation of neuronal responses by attention was well described by either a leftward shift or proportional scaling of the contrast response function. Consideration of differences in experimental design and analysis that may have contributed to this discrepancy suggests that it was premature to exclude a proportional scaling of responses to different contrasts by attention in favor of a leftward shift of contrast response functions. The current results reopen the possibility that the effects of attention on stimulus-response functions are well described by a single proportional increase in a neuron's response to all stimuli.
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Kabara, Joseph F., and A. B. Bonds. "Modification of Response Functions of Cat Visual Cortical Cells by Spatially Congruent Perturbing Stimuli." Journal of Neurophysiology 86, no. 6 (December 1, 2001): 2703–14. http://dx.doi.org/10.1152/jn.2001.86.6.2703.
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Responses of cat striate cortical cells to a drifting sinusoidal grating were modified by the superimposition of a second, perturbing grating (PG) that did not excite the cell when presented alone. One consequence of the presence of a PG was a shift in the tuning curves. The orientation tuning of all 41 cells exposed to a PG and the spatial frequency tuning of 83% of the 23 cells exposed to a PG showed statistically significant dislocations of both the response function peak and center of mass from their single grating values. As found in earlier reports, the presence of PGs suppressed responsiveness. However, reductions measured at the single grating optimum orientation or spatial frequency were on average 1.3 times greater than the suppression found at the peak of the response function modified by the presence of the PG. Much of the loss in response seen at the single grating optimum is thus a result of a shift in the tuning function rather than outright suppression. On average orientation shifts were repulsive and proportional (∼0.10 deg/deg) to the angle between the perturbing stimulus and the optimum single grating orientation. Shifts in the spatial frequency response function were both attractive and repulsive, resulting in an overall average of zero. For both simple and complex cells, PGs generally broadened orientation response function bandwidths. Similarly, complex cell spatial frequency response function bandwidths broadened. Simple cell spatial frequency response functions usually did not change, and those that did broadened only 4% on average. These data support the hypothesis that additional sinusoidal components in compound stimuli retune cells' response functions for orientation and spatial frequency.
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Frey, E. C., and B. M. W. Tsui. "Spatial properties of the scatter response function in SPECT." IEEE Transactions on Nuclear Science 38, no. 2 (April 1991): 789–94. http://dx.doi.org/10.1109/23.289392.
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Sun, Kang, Lei Zhu, Karen Cady-Pereira, Christopher Chan Miller, Kelly Chance, Lieven Clarisse, Pierre-François Coheur, et al. "A physics-based approach to oversample multi-satellite, multispecies observations to a common grid." Atmospheric Measurement Techniques 11, no. 12 (December 18, 2018): 6679–701. http://dx.doi.org/10.5194/amt-11-6679-2018.
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Abstract. Satellite remote sensing of the Earth's atmospheric composition usually samples irregularly in space and time, and many applications require spatially and temporally averaging the satellite observations (level 2) to a regular grid (level 3). When averaging level 2 data over a long period to a target level 3 grid that is significantly finer than the sizes of level 2 pixels, this process is referred to as “oversampling”. An agile, physics-based oversampling approach is developed to represent each satellite observation as a sensitivity distribution on the ground, instead of a point or a polygon as assumed in previous methods. This sensitivity distribution can be determined by the spatial response function of each satellite sensor. A generalized 2-D super Gaussian function is proposed to characterize the spatial response functions of both imaging grating spectrometers (e.g., OMI, OMPS, and TROPOMI) and scanning Fourier transform spectrometers (e.g., GOSAT, IASI, and CrIS). Synthetic OMI and IASI observations were generated to compare the errors due to simplifying satellite fields of view (FOVs) as polygons (tessellation error) and the errors due to discretizing the smooth spatial response function on a finite grid (discretization error). The balance between these two error sources depends on the target grid size, the ground size of the FOV, and the smoothness of spatial response functions. Explicit consideration of the spatial response function is favorable for fine-grid oversampling and smoother spatial response. For OMI, it is beneficial to oversample using the spatial response functions for grids finer than ∼16 km. The generalized 2-D super Gaussian function also enables smoothing of the level 3 results by decreasing the shape-determining exponents, which is useful for a high noise level or sparse satellite datasets. This physical oversampling approach is especially advantageous during smaller temporal windows and shows substantially improved visualization of trace gas distribution and local gradients when applied to OMI NO2 products and IASI NH3 products. There is no appreciable difference in the computational time when using the physical oversampling versus other oversampling methods.
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Manahilov, V. "Multiphasic Spatial Response to Flickering Stimuli." Perception 26, no. 1_suppl (August 1997): 255. http://dx.doi.org/10.1068/v970259.
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If it is assumed that the weighting function of early vision can be described by a spatiotemporal Gabor-like function (Manahilov, 1995 Vision Research35 227 – 237), the spatial impulse response to flickering stimuli would consist of more alternating phases than that to a brief stimulus. To test this prediction, the Westheimer paradigm and the brightness matching technique were used. The effect of a flickering inducing disk (temporal frequency 7.7 Hz, duration 195 ms, zero starting phase) of variable radius on the apparent brightness of an incremental test stimulus (1.2 min arc radius, duration 14.25 ms) was measured in foveal photopic vision. The test stimulus was superimposed on the centre of the inducing disk and presented 142 ms after the onset of the inducing stimulus. When the radius of the inducing stimulus was increased, the test brightness was enhanced, reaching a maximum at a radius of 3 min arc, then diminished below the control level at radii of 9 – 11 min arc and was enhanced again at radii of 14 – 17 min arc. This finding differed from the unimodal effect of a brief inducing disk on test brightness and suggested a multiphasic profile of the spatial impulse response to a flickering stimulus. This suggestion was supported by the dependence of the apparent brightness of a test line on the distance between the test and two flanking inducing lines. The temporal conditions were similar to those of the previous experiment. The brightness of the test line was increased above the control level at distances of 0 – 2 min arc, decreased at distances of 3 – 6 min arc and again increased to a smaller extent at distances of 10 – 13 min arc. Brief inducing lines evoked only the initial enhancement of the test-line brightness and its decrease at lateral positions. The data obtained are in line with the predictions of the model of the visual weighting function.
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Tong, Lillian, William Guido, Nina Tumosa, Peter D. Spear, and Susan Heidenreich. "Binocular interactions in the cat's dorsal lateral geniculate nucleus, II: Effects on dominant-eye spatial-frequency and contrast processing." Visual Neuroscience 8, no. 6 (June 1992): 557–66. http://dx.doi.org/10.1017/s0952523800005654.
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AbstractThe present study tested the hypothesis that nondominant-eye influences on lateral geniculate nucleus (LGN) neurons affect the processing of spatial and contrast information from the dominant eye. To do this, we determined the effects of stimulating the nondominant eye at its optimal spatial frequency on the responses of LGN cells to sine-wave gratings of different spatial frequency and contrast presented to the dominant eye. Detailed testing was carried out on 49 cells that had statistically significant responses to stimulation of the nondominant eye alone.Spatial-frequency response functions to nondominant-eye stimulation indicated that the responses were spatially tuned, as reported previously (Guido et al., 1989). Optimal spatial frequencies through the nondominant eye were significantly correlated with the optimal spatial frequencies through the dominant eye (r = 0.54; P < 0.0001), and the optimal spatial frequencies were fairly similar for the two eyes.Nondominant-eye stimulation changed the maximal amplitude of the fundamental (Fl) response to dominant-eye stimulation for only about 45% (22 of 49) of the cells that responded to nondominant-eye stimulation alone. The response vs. contrast function through the dominant eye was altered for 73% of the cells (51% independent of spatial frequency). Three types of effects were observed: a change in the initial slope of the response vs. contrast function (contrast gain), a change in the response amplitude at which saturation occurred, or an overall change in response at all contrasts. The incidence of these changes was similar for X and Y cells in LGN layers A, Al, and C (only four W cells were tested).Nondominant-eye stimulation had little or no effect on the sizes or sensitivities of the receptive-field centers or surrounds for the dominant eye. In addition, nondominant-eye stimulation had little or no effect on optimal spatial frequency, spatial resolution, or the bandwidth of spatial-frequency contrast sensitivity curves for the dominant eye.Possible functions of binocular interactions in the LGN are considered. The present results suggest a role in interocular contrast-gain control. Interocular contrast differences can occur before the acquisition of binocular fusion, when the two eyes are viewing different aspects of a visual stimulus. Psychophysical and physiological studies suggest that an interocular mechanism exists to maintain relatively constant binocular interactions despite differences in interocular contrast. The present results suggest that at least part of this mechanism occurs in the LGN.
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Pouget, Alexandre, and Terrence J. Sejnowski. "Spatial Transformations in the Parietal Cortex Using Basis Functions." Journal of Cognitive Neuroscience 9, no. 2 (March 1997): 222–37. http://dx.doi.org/10.1162/jocn.1997.9.2.222.
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Sensorimotor transformations are nonlinear mappings of sensory inputs to motor responses. We explore here the possibility that the responses of single neurons in the parietal cortex serve as basis functions for these transformations. Basis function decomposition is a general method for approximating nonlinear functions that is computationally efficient and well suited for adaptive modification. In particular, the responses of single parietal neurons can be approximated by the product of a Gaussian function of retinal location and a sigmoid function of eye position, called a gain field. A large set of such functions forms a basis set that can be used to perform an arbitrary motor response through a direct projection. We compare this hypothesis with other approaches that are commonly used to model population codes, such as computational maps and vectorial representations. Neither of these alternatives can fully account for the responses of parietal neurons, and they are computationally less efficient for nonlinear transformations. Basis functions also have the advantage of not depending on any coordinate system or reference frame. As a consequence, the position of an object can be represented in multiple reference frames simultaneously, a property consistent with the behavior of hemineglect patients with lesions in the parietal cortex.
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RAITZA, THOMAS, HEIDI REINHOLZ, and GERD RÖPKE. "DYNAMICAL SPATIALLY RESOLVED RESPONSE FUNCTION OF FINITE 1-D NANO PLASMAS." International Journal of Modern Physics B 24, no. 25n26 (October 20, 2010): 4961–78. http://dx.doi.org/10.1142/s0217979210057134.
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The dynamical response of one dimensional chains containing 55 till 309 atoms is investigated using a restricted molecular dynamics simulation scheme. The total momentum correlation function of an electron cloud shows resonances that are related to different collective excitation modes of the nano plasma. Spatially resolved cross correlation functions are calculated to deduce the spatial structure and strength of these resonance modes. The dependence of the corresponding resonance frequencies on temperature, density and chain size is investigated. The width of the resonances is analyzed in terms of a mode dependent collision frequency.
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Bradley, Joshua P., and David G. Long. "Estimation of the OSCAT Spatial Response Function Using Island Targets." IEEE Transactions on Geoscience and Remote Sensing 52, no. 4 (April 2014): 1924–34. http://dx.doi.org/10.1109/tgrs.2013.2256429.
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Müller, Sven, and Knut Haase. "Local revenue response to service quality: spatial effects in seasonal ticket revenue data." European Journal of Marketing 49, no. 9/10 (September 14, 2015): 1391–416. http://dx.doi.org/10.1108/ejm-10-2013-0531.
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Purpose – This paper aims to consider spatial effects in the analysis of the relationship of revenue and service quality. When firms’ customers are located in spatially dispersed areas, it can be difficult to manage service quality on a geographically small scale because the relative importance of service quality might vary spatially. Moreover, standard approaches discussed so far in the marketing science literature usually neglect spatial effects, such as spatial dependencies (e.g. spatial autocorrelation) and spatial drift (spatial non-stationarity). Design/methodology/approach – The authors propose a comprehensive but intelligible approach based on spatial econometric methods that cover spatial dependencies and spatial drift simultaneously. In particular, they incorporate the spatial expansion method (spatial drift) into spatial econometric models (e.g. spatial lag model). Findings – Using real company data on seasonal ticket revenue (dependent variable) and service quality (independent variables) of a regional public transport service provider, the authors find that the elasticity for the length of the public transport network is between 0.2 and 0.5, whereas the elasticity for the headway is between −0.2 and 0.6, for example. The authors control for several socio-economic, socio-demographic and land-use variables. Practical implications – Based on the empirical findings, the authors show that addressing spatial effects of service data can improve management’s ability to implement programs aimed at enhancing seasonal ticket revenue. Therefore, they derive a spatial revenue response function that enables managers to identify small-scale areas that are most efficient in terms of increasing revenue by service improvement. Originality/value – The paper addresses the need to account for spatial effects in revenue response functions of public transport companies.
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Irish, Jennifer L., Donald T. Resio, and Mary A. Cialone. "A surge response function approach to coastal hazard assessment. Part 2: Quantification of spatial attributes of response functions." Natural Hazards 51, no. 1 (March 20, 2009): 183–205. http://dx.doi.org/10.1007/s11069-009-9381-4.
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Frazor, Robert A., Duane G. Albrecht, Wilson S. Geisler, and Alison M. Crane. "Visual Cortex Neurons of Monkeys and Cats: Temporal Dynamics of the Spatial Frequency Response Function." Journal of Neurophysiology 91, no. 6 (June 2004): 2607–27. http://dx.doi.org/10.1152/jn.00858.2003.
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We measured the responses of striate cortex neurons as a function of spatial frequency on a fine time scale, over the course of an interval that is comparable to the duration of a single fixation (200 ms). Stationary gratings were flashed on for 200 ms and then off for 300 ms; the responses were analyzed at sequential 1-ms intervals. We found that 1) the preferred spatial frequency shifts through time from low frequencies to high frequencies, 2) the latency of the response increases as a function of spatial frequency, and 3) the poststimulus time histograms (PSTHs) are relatively shape-invariant across spatial frequency. The dynamic shifts in preferred spatial frequency appear to be a simple consequence of the latency shifts and the transient nature of the PSTH. The effects of these dynamic shifts on the coding of spatial frequency information are examined within the context of several different temporal integration strategies, and pattern-detection performance is determined as a function of the interval of integration, following response onset. The findings are considered within the context of related investigations as well as a number of functional issues: motion selectivity in depth, “coarse-to-fine” processing, direction selectivity, latency as a code for stimulus attributes, and behavioral response latency. Finally, we demonstrate that the results are qualitatively consistent with a simple feedforward model, similar to the one originally proposed in 1962 by Hubel and Wiesel, that incorporates measured differences in the response latencies and the receptive field sizes of different lateral geniculate nucleus inputs.
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Adolph, Alan R., Charles L. Zucker, Berndt Ehinger, and Anders Bergström. "Function and Structure in Retinal Transplants." Journal of Neural Transplantation and Plasticity 5, no. 3 (1994): 147–61. http://dx.doi.org/10.1155/np.1994.147.
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Embryonic mammalian donor retina transplanted into the subretinal space of a mature host develops into a graft with wellorganized, but atypical retinal structure. We tested the effect of this organization on rabbitto-rabbit graft functional properties, isolating the graft to avoid contamination of graft responses by host retinal activity. Transient ON or ON-OFF spike-like responses and local electroretinograms (L-ERGs) were recorded simultaneously via a single electrode on the graft surface. These response components depended on stimulus diameter, sometimes in a way indicating antagonistic center-surround receptive field organization and spatial tuning (43%). Other times, the responses were an increasing function of stimulus diameter which saturated for large spots (57%). Response amplitudes were transplantation surgery is to be done with therapeutic aims.
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Chey, Jeanyung, Junghee Lee, Yong-Sik Kim, Suk-Man Kwon, and Young-Min Shin. "Spatial working memory span, delayed response and executive function in schizophrenia." Psychiatry Research 110, no. 3 (July 2002): 259–71. http://dx.doi.org/10.1016/s0165-1781(02)00105-1.
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Chu, D. P., and M. G. Dowsett. "Dopant spatial distributions: Sample-independent response function and maximum-entropy reconstruction." Physical Review B 56, no. 23 (December 15, 1997): 15167–70. http://dx.doi.org/10.1103/physrevb.56.15167.
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Spitzer, H., and S. Hochstein. "A complex-cell receptive-field model." Journal of Neurophysiology 53, no. 5 (May 1, 1985): 1266–86. http://dx.doi.org/10.1152/jn.1985.53.5.1266.
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The time course of the response of a single cortical neuron to counterphase-grating stimulation may vary as a function of stimulation parameters, as shown in the preceding paper (19). The poststimulus-time histograms of the response amplitudes against time are single or double peaked, and where double peaked, the two peaks are of equal or unequal amplitudes. Furthermore, the spatial-phase dependence of cortical complex-cell responses may be a function of spatial frequency, so that the receptive field appears to have linear spatial summation at some spatial frequencies and nonlinear spatial summation at others (19). In the first part of this paper, we analyze a model receptive field that displays this behavior, and in the second part experimental data are presented and analyzed with regard to the model. The model cortical receptive field in its simplest form contains (two rows) of geniculate X-cell-like, DOG (difference-of-Gaussians)-shaped, center-surround antagonistic, circular-input subunits. We propose nonlinear summation between these two subunits, by introducing a half-wave rectification stage before pooling. The model is tested for the responses it predicts for the application of counterphase-grating stimulation. This simple model predicts the appearance of three response forms as a function of counterphase-stimulation parameters. At periodic spatial frequencies the expected-response histogram has a single peak, whose amplitude has a sinusoidal dependence on spatial phase. At spatial frequencies halfway between these, the expected-response histogram has two equal peaks whose amplitudes have a full-wave rectified sinusoidal dependence on spatial phase. At all intermediate spatial frequencies the expected-response histogram has a "mixed" form; the histogram appears sometimes with one peak, sometimes with two equal peaks, and generally with two peaks of unequal amplitude, as a function of spatial phase. Null responses are expected to appear at specific spatial phases only for the periodic spatial frequencies that give "pure" response time courses as in paragraph 5 above, and not in the more common mixed response case of paragraph 6. The analysis procedure described in the preceding paper (19) is used, separating the odd and even Fourier components of the response histograms reflecting the receptive-field intrasubunit linear summation and intersubunit nonlinear summation, respectively. We propose that this model may be used as a working hypothesis for the analysis of these aspects of the various cortical receptive-field types. Experimental data are described and discussed in terms of the model.(ABSTRACT TRUNCATED AT 400 WORDS)
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Porciatti, V., R. Alesci, and P. Bagnoli. "Evoked responses to sinusoidal gratings in the pigeon optic tectum." Visual Neuroscience 2, no. 2 (February 1989): 137–45. http://dx.doi.org/10.1017/s0952523800011998.
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AbstractTectal evoked potentials (TEPs) in response to sinusoidal gratings of different contrast, spatial and temporal frequency have been recorded from the tectal surface of the pigeon. Responses have been digitally filtered in order to isolate transient oscillatory (fast) potentials (50–150 Hz), transient slow potentials (1–50 Hz), and the steady-state second-harmonic component (16.6 Hz). Transient slow potentials, as well as the steady-state second-harmonic component, are band-pass spatially tuned with a maximum at 0.5 cycles/deg and attenuation at higher and lower spatial frequencies. The high spatial frequency cutoff is 4–5 cycles/deg. Both transient slow potentials and the steady-state second-harmonic component increase in amplitude as a function of log contrast and saturate at about 20% contrast. The contrast sensitivity, as determined by extrapolating TEP amplitude to 0 V is 0.1–0.2%. These characteristics of spatial-frequency selectivity and contrast sensitivity are similar to those reported for single tectal cells. Unlike slow potentials, oscillatory potentials are not band-pass spatially tuned. In addition, their contrast response function does not saturate at moderate contrast. These differences suggest that tectal evoked slow and fast potentials reflect the activity of different neuronal mechanisms.
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Wolk, Fabian, Hidekatsu Yamazaki, Hua Li, and Rolf G. Lueck. "Calibrating the Spatial Response of Bio-Optical Sensors." Journal of Atmospheric and Oceanic Technology 23, no. 3 (March 1, 2006): 511–16. http://dx.doi.org/10.1175/jtech1863.1.
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Abstract This article describes an experimental method used to establish the spatial wavenumber response of in situ fluorometers. The method is applied to a fluorometer developed to measure the structure of the fluorescence field at high spatial wavenumbers. This fluorometer detects fluorescence variations on centimeter scales by creating a sampling volume in the undisturbed flow region, outside of the sensor housing. The sampling volume is created by intersecting beams of blue excitation light. To establish the size of the sampling volume and the amount of spatial averaging, the fluorometer and a fast response thermistor are towed repeatedly through a warm, fluorescent plume in a tow tank. The ratio of the measured fluorescence and temperature spectrum determines the wavenumber response of the fluorometer. The measured spectral ratio is well described by the transfer function of a first-order, low-pass filter with a half-power point at 22 cpm. The equivalent spatial resolution is 7 mm. The transfer function model can be used to correct measured fluorescence spectra for the limited wavenumber response of the sensor.
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Bayerl, Jeanne P., David R. Millen, and Steven H. Lewis. "Consistent Layout of Function Keys and Screen Labels Speeds User Responses." Proceedings of the Human Factors Society Annual Meeting 32, no. 5 (October 1988): 344–46. http://dx.doi.org/10.1177/154193128803200524.
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Personal-computer applications-software often requires people to navigate and select options using their keyboard's function keys where context-dependent meanings for these keys are assigned by guides or menus labeled on the screen. The physical layout of function keys on standard PC-compatible keyboards differs from the most common layouts of screen labels. This study examined user performance consequences of this simple, spatial, inconsistency. In a simulated order entry task, 36 participants each completed 240 trials, 40 with each of six different combinations of two keyboards and three screen guides with different spatial arrangements of function keys and screen labeling. One keyboard used the standard 5×2 function key pad and one used a single horizontal row of function keys; the screen guides were either a horizontal row, a vertical list, or a grid consistent with the standard key pad. We collected measures of response time, errors, and user preferences. Analysis of errors showed no reliable results. Analysis of response times showed several significant effects. Responses were faster with the two combinations of key pad and screen-guide layouts that were spatially consistent than with the four inconsistent layouts. Response times were also faster with the keyboard with horizontal function keys than with the standard layout, and slower with the vertical screen guide than with either of the other two guides. Over 80% of the participants thought the task was easiest when the screen guide matched the function key layout.
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Shao, Lin, Jiarui Liu, Chong Wang, Ki B. Ma, Jianming Zhang, John Chen, Daniel Tang, Sanjay Patel, and Wei-Kan Chu. "Response function during oxygen sputter profiling for deconvolution of boron spatial distribution." Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms 219-220 (June 2004): 303–6. http://dx.doi.org/10.1016/j.nimb.2004.01.073.
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KASAHARA, Naoto, and Hideki TAKASHO. "Frequency Response Function of Thermal Stress to Spatial Fluctuations of Fluid Temperature." Proceedings of the JSME annual meeting 2002.2 (2002): 239–40. http://dx.doi.org/10.1299/jsmemecjo.2002.2.0_239.
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Park, Soon-Yong. "Effects of nonlinear camera response function in spatial domain depth-from-defocus." Journal of Electronic Imaging 16, no. 3 (July 1, 2007): 033021. http://dx.doi.org/10.1117/1.2774830.
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Li, Xiaoling, Guangping Hu, and Zhaosheng Feng. "Pattern Dynamics in a Spatial Predator–Prey Model with Nonmonotonic Response Function." International Journal of Bifurcation and Chaos 28, no. 06 (June 15, 2018): 1850077. http://dx.doi.org/10.1142/s0218127418500773.
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In this paper, we study a diffusive predator–prey system with the nonmonotonic response function. The conditions on Hopf bifurcation and Turing instability of spatial systems are obtained. Near the Turing bifurcation point we apply the weakly nonlinear analysis to derive the amplitude equations of stationary pattern, to investigate the selection of spatiotemporal pattern. It shows that different types of patterns will occur in the model under various conditions. Numerical simulations agree well with our theoretical analysis when control parameters are in the Turing space. This study may provide some deep insights into the formation and selection of patterns for diffusive predator–prey systems.
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Hu, Yuping, Siyu Wu, Sanying Feng, and Junliang Jin. "Estimation in Partial Functional Linear Spatial Autoregressive Model." Mathematics 8, no. 10 (October 1, 2020): 1680. http://dx.doi.org/10.3390/math8101680.
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Functional regression allows for a scalar response to be dependent on a functional predictor; however, not much work has been done when response variables are dependence spatial variables. In this paper, we introduce a new partial functional linear spatial autoregressive model which explores the relationship between a scalar dependence spatial response variable and explanatory variables containing both multiple real-valued scalar variables and a function-valued random variable. By means of functional principal components analysis and the instrumental variable estimation method, we obtain the estimators of the parametric component and slope function of the model. Under some regularity conditions, we establish the asymptotic normality for the parametric component and the convergence rate for slope function. At last, we illustrate the finite sample performance of our proposed methods with some simulation studies.
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Gravuer, Kelly, Anu Eskelinen, Joy B. Winbourne, and Susan P. Harrison. "Vulnerability and resistance in the spatial heterogeneity of soil microbial communities under resource additions." Proceedings of the National Academy of Sciences 117, no. 13 (March 12, 2020): 7263–70. http://dx.doi.org/10.1073/pnas.1908117117.
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Spatial heterogeneity in composition and function enables ecosystems to supply diverse services. For soil microbes and the ecosystem functions they catalyze, whether such heterogeneity can be maintained in the face of altered resource inputs is uncertain. In a 50-ha northern California grassland with a mosaic of plant communities generated by different soil types, we tested how spatial variability in microbial composition and function changed in response to nutrient and water addition. Fungal composition lost some of its spatial variability in response to nutrient addition, driven by decreases in mutualistic fungi and increases in antagonistic fungi that were strongest on the least fertile soils, where mutualists were initially most frequent and antagonists initially least frequent. Bacterial and archaeal community composition showed little change in their spatial variability with resource addition. Microbial functions related to nitrogen cycling showed increased spatial variability under nutrient, and sometimes water, additions, driven in part by accelerated nitrification on the initially more-fertile soils. Under anthropogenic changes such as eutrophication and altered rainfall, these findings illustrate the potential for significant changes in ecosystem-level spatial heterogeneity of microbial functions and communities.
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Albrecht, Duane G. "Visual cortex neurons in monkey and cat: Effect of contrast on the spatial and temporal phase transfer functions." Visual Neuroscience 12, no. 6 (November 1995): 1191–210. http://dx.doi.org/10.1017/s0952523800006817.
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AbstractThe responses of simple cells (recorded from within the striate visual cortex) were measured as a function of the contrast and the frequency of sine-wave grating patterns in order to explore the effect of contrast on the spatial and temporal phase transfer functions and on the spatiotemporal receptive field. In general, as the contrast increased, the phase of the response advanced by approximately 45 ms (approximately one-quarter of a cycle for frequencies near 5 Hz), although the exact value varied from cell to cell. The dynamics of this phase-advance were similar to the dynamics of the amplitude: the amplitude and the phase increased in an accelerating fashion at lower contrasts and then saturated at higher contrasts. Further, the gain for both the amplitude and the phase appeared to be governed by the magnitude of the contrast rather than the magnitude of the response. For the spatial phase transfer function, variations in contrast had little or no systematic effect; all of the phase responses clustered around a single straight line, with a common slope and intercept. This implies that the phase-advance was not due to a change in the spatial properties of the neuron; it also implies that the phase-advance was not systematically related to the magnitude of the response amplitude. On the other hand, for the temporal phase transfer function, the phase responses fell on five straight lines, related to the five steps in contrast. As the contrast increased, the phase responses advanced such that both the slope and the intercept were affected. This implies that the phase-advance was a result of contrast-induced changes in both the response latency and the shape/symmetry of the temporal receptive field.
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Baro, John A., and Stephen Lehmkuhle. "The effects of a luminanace-modulated background on the grating-evoked cortical potential in the cat." Visual Neuroscience 3, no. 6 (December 1989): 563–72. http://dx.doi.org/10.1017/s0952523800009895.
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AbstractAveraged grating-evoked cortical potentials were recorded from area 17 of awake cats. Peak latency of early components of the visual-evoked potential (VEP) response to stimulus onset increased as a function of spatial frequency, while amplitude tended to be largest at intermediate spatial frequencies. Latency increased and amplitude generally decreased to lower spatial-frequency stimuli (<0.25 cycle/deg) in the presence of a uniform flickering field (UFF). The UFF had a relatively small or opposite effect on peak latency and amplitude for higher spatial-frequency stimuli (>0.50 cycle/deg). The VEP response to stimulus offset was present only at low spatial frequencies and was virtually eliminated by the presence of the UFF. The effects were similar whether the target and UFF background were simultaneously presented or briefly separated; however, the UFF had no effect when the two were spatially separated. The effects of the UFF background on VEP onset response increased with increasing temporal frequency from 2–8 Hz; offset responses were affected similarly at all temporal frequencies. These effects are similar to those observed in humans and suggest that two spatio-temporally tuned mechanisms contribute to the early VEP response. In the cat, the mechanisms seem to correspond to X and Y cells in the dorsal lateral geniculate nucleus.
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KORTH, MATTHIAS, RAINER RIX, and OTTO SEMBRITZKI. "The sequential processing of visual motion in the human electroretinogram and visual evoked potential." Visual Neuroscience 17, no. 4 (July 2000): 631–46. http://dx.doi.org/10.1017/s0952523800174127.
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Mechanisms of motion vision in the human have been studied extensively by psychophysical methods but less frequently by electrophysiological techniques. It is the purpose of the present investigation to study electrical potentials of the eye (electroretinogram, ERG) and of the brain (visual evoked potential, VEP) in response to moving regular square-wave stripe patterns spanning a wide range of contrasts, spatial frequencies, and speeds. The results show that ERG amplitudes increase linearly with contrast while VEPs, in agreement with the literature, show an amplitude saturation at low contrast. Furthermore, retinal responses oscillate with the fundamental temporal stimulus frequency of the moving pattern while brain responses do not. In both the retina and the brain, the response amplitudes are tuned to certain speeds which is in agreement with the nonlinear correlation-type motion detector. Along the ascending slopes (which means increasing amplitudes) of the tuning functions, the ERG curves overlap at all spatial frequencies if plotted as a function of temporal stimulation frequency. The ascending slopes of the tuning functions of the VEP overlap if plotted as a function of speed. The descending slopes (which means decreasing amplitudes) of the tuning functions show little (ERG) or no (VEP) overlap and the waveforms at high speeds approach pattern-offset-onset responses. These observations suggest that in the retina motion processing along the ascending slopes of the tuning curves takes place by coding the temporal stimulation frequency which depends on the spatial frequency of the moving pattern. In the brain, however, motion processing is by speed independent of spatial frequency. Simple calculations show that the VEP information is decoded from the ERG signal into a speed signal.
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Cooper, Bonnie, Barry B. Lee, and Dingcai Cao. "Macaque retinal ganglion cell responses to visual patterns: harmonic composition, noise, and psychophysical detectability." Journal of Neurophysiology 115, no. 6 (June 1, 2016): 2976–88. http://dx.doi.org/10.1152/jn.00411.2015.
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The goal of these experiments was to test how well cell responses to visual patterns can be predicted from the sinewave tuning curve. Magnocellular (MC) and parvocellular (PC) ganglion cell responses to different spatial waveforms (sinewave, squarewave, and ramp waveforms) were measured across a range of spatial frequencies. Sinewave spatial tuning curves were fit with standard Gaussian models. From these fits, waveforms and spatial tuning of a cell's responses to the other waveforms were predicted for different harmonics by scaling in amplitude for the power in the waveform's Fourier expansion series over spatial frequency. Since higher spatial harmonics move at a higher temporal frequency, an additional scaling for each harmonic by the MC (bandpass) or PC (lowpass) temporal response was included, together with response phase. Finally, the model included a rectifying nonlinearity. This provided a largely satisfactory estimation of MC and PC cell responses to complex waveforms. As a consequence of their transient responses, MC responses to complex waveforms were found to have significantly more energy in higher spatial harmonic components than PC responses. Response variance (noise) was also quantified as a function of harmonic component. Noise increased to some degree for the higher harmonics. The data are relevant for psychophysical detection or discrimination of visual patterns, and we discuss the results in this context.
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Pang, J. C., P. A. Robinson, and K. M. Aquino. "Response-mode decomposition of spatio-temporal haemodynamics." Journal of The Royal Society Interface 13, no. 118 (May 2016): 20160253. http://dx.doi.org/10.1098/rsif.2016.0253.
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The blood oxygen-level dependent (BOLD) response to a neural stimulus is analysed using the transfer function derived from a physiologically based poroelastic model of cortical tissue. The transfer function is decomposed into components that correspond to distinct poles, each related to a response mode with a natural frequency and dispersion relation; together these yield the total BOLD response. The properties of the decomposed components provide a deeper understanding of the nature of the BOLD response, via the components' frequency dependences, spatial and temporal power spectra, and resonances. The transfer function components are then used to separate the BOLD response to a localized impulse stimulus, termed the Green function or spatio-temporal haemodynamic response function, into component responses that are explicitly related to underlying physiological quantities. The analytical results also provide a quantitative tool to calculate the linear BOLD response to an arbitrary neural drive, which is faster to implement than direct Fourier transform methods. The results of this study can be used to interpret functional magnetic resonance imaging data in new ways based on physiology, to enhance deconvolution methods and to design experimental protocols that can selectively enhance or suppress particular responses, to probe specific physiological phenomena.
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Heil, Peter. "Auditory Cortical Onset Responses Revisited. II. Response Strength." Journal of Neurophysiology 77, no. 5 (May 1, 1997): 2642–60. http://dx.doi.org/10.1152/jn.1997.77.5.2642.
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Heil, Peter. Auditory cortical onset responses revisited. II. Response strength. J. Neurophysiol. 77: 2642–2660, 1997. Most neurons of the auditory pathway discharge spikes locked to the onset of an acoustic stimulus, but it is largely unknown in which way the acoustic parameters of sound onsets shape the neuronal responses. In this paper is analyzed the number of spikes discharged by single neurons in primary auditory cortex of barbiturate-anesthetized cats to the onsets of tones of characteristic frequency. The time course of the peak pressure (i.e., the envelope) was altered by parametrically varying sound pressure level (SPL), rise time, and rise function (linear or cosine-squared). For both rise functions, rise time had manifold, and in some cases dramatic, effects on conventional spike count–level functions. In general, threshold SPL, dynamic range, and the lowest SPL at which monotonic spike count functions saturated increased with prolongation of the rise time. In neurons with mostly nonmonotonic spike count–level functions, “best SPL” increased and the descending high-SPL arms flattened, so that functions obtained with long rise times were often monotonic whereas those obtained with shorter rise times were highly nonmonotonic. Consequently, the “tuning” to SPL was less sharp for longer rise time tones, and spike count versus rise time functions changed from “short-pass” to “long-pass” with an increase in SPL. Systematic effects of rise time persisted when spike counts were plotted against the rate of change of peak pressure or against the maximum acceleration of peak pressure. However, when spike counts were plotted as a function of the instantaneous peak pressure at the time of response initiation, the functions obtained with different rise times, and even with different rise functions, were in close register. This suggests that the stimulus-dependent component of first-spike latency can be viewed as an integration window, during which rate of change of peak pressure is integrated. The window commences with tone onset and its duration is inversely related to the maximum acceleration (or, for linear rise functions, the rate of change) of peak pressure and the neuron's transient sensitivity. The present findings seriously question, for onset responses, the usefulness of the spike count–level function and measures derived from it, such as threshold SPL, dynamic range, best SPL, or degree of nonmonotonicity. They further cast doubt onto the validity of current concepts of intensity coding at cortical levels, because most neurons' onset responses are not indicative of a signal's steady-state SPL. However, they suggest a mechanism by which a neuronal population will sample a given transient in an orderly, sensitivity-dependent, temporal sequence. The sampling rate is automatically adjusted to, and adjusted by, the rapidity of the signal's change. And the instantaneous properties of the transient could be represented by the ratios and spatial distribution of responses across the simultaneously active subpopulation. Such a mechanism could provide the basis for the demonstrated capability of discrimination of rapid transients.
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Forgays, Donald G., and Gary McClure. "Heart-Rate Response to Water-Immersion Isolation as a Function of Spatial Orientation." Perceptual and Motor Skills 67, no. 1 (August 1988): 163–67. http://dx.doi.org/10.2466/pms.1988.67.1.163.
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The present study investigates the effect of spatial orientation of the body on heart rate during conditions of water-immersion sensory isolation. Two groups of three men and three women each were exposed to one of two isolation conditions. In one condition the subject was suspended in a buoyant but vertical attitude; in a second condition the subject was suspended in a buoyant but horizontal attitude. Heart-rate data were obtained continuously during each session. There was no significant difference in mean heart rate between the two conditions. The data were interpreted as providing support for the position that studies comparing recumbent subjects in air isolation with underwater subjects in a vertical suspension attitude are valid, at least for some measures, and are not an artifact of spatial bodily orientation. The possible importance of neutral buoyancy in accounting for the nonsignificant effect of body attitude on heart rate is discussed.
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Goodkind, Andrew L., Jay S. Coggins, and Julian D. Marshall. "A Spatial Model of Air Pollution: The Impact of the Concentration-Response Function." Journal of the Association of Environmental and Resource Economists 1, no. 4 (December 2014): 451–79. http://dx.doi.org/10.1086/678985.
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Štěpánek, Petr, and Sonia Coriani. "Spatial localization in nuclear spin-induced circular dichroism – a quadratic response function analysis." Physical Chemistry Chemical Physics 21, no. 33 (2019): 18082–91. http://dx.doi.org/10.1039/c9cp01716j.
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Miller, William E. B., and Alan L. Kastengren. "Measurements of spatial variations in response of ionization chambers." Journal of Synchrotron Radiation 20, no. 1 (November 10, 2012): 160–65. http://dx.doi.org/10.1107/s0909049512041337.
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Measurements of the spatial variations in the response of three ionization chamber (IC) designs were tested as a function of chamber bias voltage, incident X-ray flux and fill gas. Two components of spatial variation are seen. When the ionization chambers are near saturation, spatial variations exist that are tied to the chamber geometry. While the response of some chambers is relatively flat, others show significant variation across the IC. These variations appear to be inherent in the response of each IC at saturation. When the chamber is far from saturation, large spatial variations in response are present when N2is used as a fill gas, but not when ambient air is used as a fill gas. These appear to be tied to space charge effects.
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Bilgili, Ecevit, Barry Bernstein, and Hamid Arastoopour. "Influence of Material Non Homogeneity on the Shearing Response of a Neo Hookean Slab." Rubber Chemistry and Technology 75, no. 2 (May 1, 2002): 347–63. http://dx.doi.org/10.5254/1.3544983.
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Abstract Vulcanized rubber components possess material non-homogeneities due to either non-uniform vulcanization during their fabrication or attack of thermal and oxidative environments during their service life. The primary objective of this paper is to theoretically investigate the effect of a material non-homogeneity on the shearing response of an isotropic, incompressible neo-Hookean slab. The non-homogeneity considered in the slab is the spatially varying shear modulus that is approximately described by a spatial-distribution function. A parabolic and a boundary layer-like spatial-distribution function are assumed; then exact solutions for the stress—strain fields in the slab are obtained by solving the linear momentum balance equations based on a postulated inhomogeneous shearing deformation. Our theoretical results show that the shear strain is more inhomogeneous and localized for the slabs with a greater degree of spatial non-homogeneity. In the non-homogeneous slabs, we have also determined the existence of a uniform shear stress and an inhomogeneous first normal-stress difference whose variation is similar to that of the shear strain. The implications of these results are considered in terms of the fabrication, performance and mechanical characterization of the rubber-elastic materials.
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Beech, John R. "Spatial Visualization: Running Visualization for Empty Squares." Perceptual and Motor Skills 85, no. 3 (December 1997): 1028–30. http://dx.doi.org/10.2466/pms.1997.85.3.1028.
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A technique is reported in which an oral description of empty squares had to be visualized. A tone signaled completion, and a response was made whether the last square had touched a previous square. The chain lengths varied from 10 to 19 squares at closure. Local closure sizes consisted of 4 to 10 squares. Closures up to 6 squares produced the least errors. There were biases in response as a function of response type and chain length. The technique could be useful for monitoring continuous spatial visualization.
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Leigh, Andrea, Ross Hill, and Marilyn C. Ball. "Leaf shape influences spatial variation in photosynthetic function in Lomatia tinctoria." Functional Plant Biology 41, no. 8 (2014): 833. http://dx.doi.org/10.1071/fp13334.
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A relationship exists between the two-dimensional shape of leaves and their venation architecture, such that broad or broad-lobed leaves can have leaf tissue far from major veins, potentially creating stronger gradients in water potential – and associated photosynthetic function – than found across narrow counterparts. We examined the spatial patterns of photosynthetic efficiency (ΔF/Fm′) and non-photochemical quenching (NPQ) in response to increased vapour pressure deficit (VPD) using two morphs of Lomatia tinctoria (Labill.) R.Br: those with broad-lobed and those with narrow-lobed leaves. Stomatal conductance (gs), instantaneous water use efficiency (WUE), stomatal and minor veins density also were measured. ΔF/Fm′ decreased with stress but was higher and less spatially heterogeneous across broad than narrow lobes. The strongest depression in ΔF/Fm′ in broad lobes was at the edges and in narrow lobes, the tips. Non-photochemical quenching was spatially more varied in broad lobes, increasing at the edges and tips. Variation in photosynthetic function could not be explained by gs, WUE or minor vein density, whereas proximity to major veins appeared to mitigate water stress at the tips only for broad lobes. Our findings indicate that the relationship between venation architecture and water delivery alone can partially explain the spatial pattern of photosynthetic function.
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Zoccatelli, D., M. Borga, A. Viglione, G. B. Chirico, and G. Blöschl. "Spatial moments of catchment rainfall: rainfall spatial organisation, basin morphology, and flood response." Hydrology and Earth System Sciences Discussions 8, no. 3 (June 21, 2011): 5811–47. http://dx.doi.org/10.5194/hessd-8-5811-2011.
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Abstract. This paper provides a general analytical framework for assessing the dependence existing between spatial rainfall organisation, basin morphology and runoff response. The analytical framework builds upon a set of spatial rainfall statistics (termed "spatial moments of catchment rainfall") which describe the spatial rainfall organisation in terms of concentration and dispersion statistics as a function of the distance measured along the flow routing coordinate. The introduction of these statistics permits derivation of a simple relationship for the quantification of storm velocity at the catchment scale. The paper illustrates the development of the analytical framework and explains the conceptual meaning of the statistics by means of application to five extreme flash floods occurred in various European regions in the period 2002–2007. High resolution radar rainfall fields and a distributed hydrologic model are employed to examine how effective are these statistics in describing the degree of spatial rainfall organisation which is important for runoff modelling. This is obtained by quantifying the effects of neglecting the spatial rainfall variability on flood modelling, with a focus on runoff timing. The size of the study catchments ranges between 36 to 982 km2. The analysis reported here shows that the spatial moments of catchment rainfall can be effectively employed to isolate and describe the features of rainfall spatial organization which have significant impact on runoff simulation. These statistics provide essential information on what space-time scales rainfall has to be monitored, given certain catchment and flood characteristics, and what are the effects of space-time aggregation on flood response modeling.
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Yan, Shanyong, and Changhong Wang. "Horizontal spatial correlation of reverberation for rough sea-bottom interface." MATEC Web of Conferences 283 (2019): 07005. http://dx.doi.org/10.1051/matecconf/201928307005.
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Correlation sonar, which estimates the velocity of vessel utilizing the principle of waveform invariance, can achieve the sampling of the horizontal spatial correlation of sea-bottom reverberation. The horizontal spatial correlation can be expressed as a correlation function and is affected by sea-bottom characteristics. The expression of the correlation function of the sea-bottom reverberation is derived, which is written as the convolution of the autocorrelation function of transmitted signal, the cross-correlation function of the backscattered impulse response from a plane interface, and the autocorrelation function of the probability density function of the sea-bottom roughness. The isotropic interface roughness of the sea-bottom leads to a circular planform of the correlation function whose width varies with roughness. The anisotropic interface roughness of the sea-bottom leads to an elliptical planform of the correlation function whose major axis is in the direction of weaker roughness. Simulation of submarine reverberation and correlation function verifies this conclusion. The model for the spatially covariant field is used to estimate the backscattering cross section which varies with azimuth angle under the condition of anisotropic seafloor roughness. It should be noted that the horizontal spatial correlation of reverberation is also related to sonar parameters and other sea-bottom characteristics.
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van Orden, Karl F., and John F. House. "Spatial Frequency-Dependent Asymmetry of Visual Evoked Potential Amplitudes." Perceptual and Motor Skills 82, no. 3 (June 1996): 1011–18. http://dx.doi.org/10.2466/pms.1996.82.3.1011.
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The extent to which pattern reversal evoked potential amplitudes are distributed symmetrically over the scalp was investigated as a function of stimulus spatial frequency. Nine right-handed male subjects viewed sinusoidal grating stimuli of 4.0 and 0.5 c/deg phase reversed every 900 msec. A visual half-field configuration enabled selective stimulation of the right- or left-hemisphere visual cortex. Evoked responses were recorded from the 2 cm above the inion (Oz) and at 7 and 13 cm lateral to Oz. Analyses of normalized evoked response amplitudes showed a significant asymmetry for the 4.0 c/deg stimulus; right-hemisphere amplitudes declined as a function of distance from the midline, while left-hemisphere amplitudes were greatest at the 7 cm recording site. No hemispheric differences were observed for the 0.5 c/deg stimulus; amplitudes for both hemispheres declined as a function of distance from the midline. The data are discussed in terms of hemispheric differences in morphology and functional asymmetries at early levels of sensory processing.
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Goodyear, Bradley G., David A. Nicolle, G. Keith Humphrey, and Ravi S. Menon. "BOLD fMRI Response of Early Visual Areas to Perceived Contrast in Human Amblyopia." Journal of Neurophysiology 84, no. 4 (October 1, 2000): 1907–13. http://dx.doi.org/10.1152/jn.2000.84.4.1907.
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In this study, we used a temporal two-alternative forced choice psychophysical procedure to measure the observer's perception of a 22% physical contrast grating for each eye as a function of spatial frequency in four subjects with unilateral amblyopia and in six subjects with normal vision. Contrast thresholds were also measured using a standard staircase method. Additionally, blood-oxygenation-level–dependent (BOLD) functional magnetic resonance imaging (fMRI) was used to measure the neuronal response within early visual cortical areas to monocular presentations of the same 22% physical contrast gratings as a function of spatial frequency. For all six subjects with normal vision and for three subjects with amblyopia, the psychophysically measured perception of 22% contrast as a function of spatial frequency was the same for both eyes. Threshold contrast, however, was elevated for the amblyopic eye for all subjects, as expected. The magnitude of the fMRI response to 22% physical contrast within “activated” voxels was the same for each eye as a function of spatial frequency, regardless of the presence of amblyopia. However, there were always fewer “activated” fMRI voxels during amblyopic stimulation than during normal eye stimulation. These results are consistent with the hypotheses that contrast thresholds are elevated in amblyopia because fewer neurons are responsive during amblyopic stimulation, and that the average firing rate of the responsive neurons, which reflects the perception of contrast, is unaffected in amblyopia.
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Zoccatelli, D., M. Borga, A. Viglione, G. B. Chirico, and G. Blöschl. "Spatial moments of catchment rainfall: rainfall spatial organisation, basin morphology, and flood response." Hydrology and Earth System Sciences 15, no. 12 (December 20, 2011): 3767–83. http://dx.doi.org/10.5194/hess-15-3767-2011.
Full textAbstract:
Abstract. This paper describes a set of spatial rainfall statistics (termed "spatial moments of catchment rainfall") quantifying the dependence existing between spatial rainfall organisation, basin morphology and runoff response. These statistics describe the spatial rainfall organisation in terms of concentration and dispersion statistics as a function of the distance measured along the flow routing coordinate. The introduction of these statistics permits derivation of a simple relationship for the quantification of catchment-scale storm velocity. The concept of the catchment-scale storm velocity takes into account the role of relative catchment orientation and morphology with respect to storm motion and kinematics. The paper illustrates the derivation of the statistics from an analytical framework recently proposed in literature and explains the conceptual meaning of the statistics by applying them to five extreme flash floods occurred in various European regions in the period 2002–2007. High resolution radar rainfall fields and a distributed hydrologic model are employed to examine how effective are these statistics in describing the degree of spatial rainfall organisation which is important for runoff modelling. This is obtained by quantifying the effects of neglecting the spatial rainfall variability on flood modelling, with a focus on runoff timing. The size of the study catchments ranges between 36 to 982 km2. The analysis reported here shows that the spatial moments of catchment rainfall can be effectively employed to isolate and describe the features of rainfall spatial organization which have significant impact on runoff simulation. These statistics provide useful information on what space-time scales rainfall has to be monitored, given certain catchment and flood characteristics, and what are the effects of space-time aggregation on flood response modeling.
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Pix, W., J. M. Zanker, and J. Zeil. "The optomotor response and spatial resolution of the visual system in male Xenos vesparum (Strepsiptera)." Journal of Experimental Biology 203, no. 22 (November 15, 2000): 3397–409. http://dx.doi.org/10.1242/jeb.203.22.3397.
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The Strepsiptera are an enigmatic group of parasitic insects whose phylogenetic relationships are hotly debated. Male Strepsiptera have very unusual compound eyes, in which each of a small number of ommatidia possesses a retina of at least 60 retinula cells. We analysed the optomotor response of Xenos vesparum males to determine whether spatial resolution in these eyes is limited by the interommatidial angle or by the higher resolution potentially provided by the extended array of retinula cells within each ommatidium. We find that the optomotor response in Strepsiptera has a typical bandpass characteristic in the temporal domain, with a temporal frequency optimum at 1–3 Hz. As a function of spatial wavelength, the optomotor response is zero at grating periods below 12 degrees and reaches its maximum strength at grating periods between 60 degrees and 70 degrees. To identify the combination of interommatidial angles and angular sensitivity functions that would generate such a spatial characteristic, we used motion detection theory to model the spatial tuning function of the strepsipteran optomotor response. We found the best correspondence between the measured response profile and theoretical prediction for an irregular array of sampling distances spaced around 9 degrees (half the estimated interommatidial angle) and an angular sensitivity function of approximately 50 degrees, which corresponds to the angular extent of the retina we estimated at the centre of curvature of the lens. Our behavioural data strongly suggest that, at least for the optomotor response, the resolution of the strepsipteran compound eye is limited by the ommatidial sampling array and not by the array of retinula cells within each ommatidium. We discuss the significance of these results in relation to the functional organisation of strepsipteran compound eyes, their evolution and the role of vision in these insects.
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Bilotta, J., and I. Abramov. "Spatiospectral properties of goldfish retinal ganglion cells." Journal of Neurophysiology 62, no. 5 (November 1, 1989): 1140–48. http://dx.doi.org/10.1152/jn.1989.62.5.1140.
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1. Responses of single ganglion cells from isolated goldfish retinas were recorded during presentation of various spatial and spectral stimuli. Each cell was classified along several spatial [spatial summation class, spatial contrast sensitivity function (CSF), and response to contrast] and spectral (Red-ON, Red-OFF or Red-ON/OFF, and spectral opponency/nonopponency) dimensions. 2. Linearity of spatial summation was determined from responses to contrast-reversal sinusoidal gratings positioned at various locations across the receptive field of the cell. CSFs were derived from responses to sinusoidal gratings of various spatial frequencies and contrasts, drifting across the cell's receptive field at a rate of 4 Hz. Response to contrast was determined from responses to variations in contrast of a sinusoidal grating of optimal spatial frequency. Spectral classifications were based on responses to monochromatic stimuli presented separately to the center and surround portions of the receptive field. 3. Linearity of spatial summation (X-, Y-, and W-like) was independent of the cell's spectral properties; for example, an X-like cell could be classified as either a Red-ON, Red-OFF, or Red-ON/OFF center cell and as spectrally opponent or nonopponent. 4. There were differences in response to contrast across spectral categories. Red-OFF center cells were very sensitive to contrast compared with Red-ON center cells. Spectrally nonopponent cells were more responsive to contrast than spectrally opponent cells. 5. There were dramatic differences across the spectral categories in relative sensitivity to low spatial frequency stimuli; however, the spatial resolution (i.e., sensitivity to high spatial frequencies) of each spectral classification appeared to be similar.(ABSTRACT TRUNCATED AT 250 WORDS)
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Linster, Christiane, Silke Sachse, and C. Giovanni Galizia. "Computational Modeling Suggests That Response Properties Rather Than Spatial Position Determine Connectivity Between Olfactory Glomeruli." Journal of Neurophysiology 93, no. 6 (June 2005): 3410–17. http://dx.doi.org/10.1152/jn.01285.2004.
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Olfactory responses require the representation of high-dimensional olfactory stimuli within the constraints of two-dimensional neural networks. We used a computational model of the honeybee antennal lobe to test how inhibitory interactions in the antennal lobe should be organized to best reproduce the experimentally measured input-output function in this structure. Our simulations show that a functionally organized inhibitory network, as opposed to an anatomically or all-to-all organized inhibitory network, best reproduces the input-output function of the antennal lobe observed with calcium imaging. In this network, inhibition between each pair of glomeruli was proportional to the similarity of their odor-response profiles. We conclude that contrast enhancement between odorants in the honeybee antennal lobe is best achieved when interglomerular inhibition is organized based on glomerular odor response profiles rather than on anatomical neighborhood relations.
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Rodriguez, Alejandro, and Pernilla Bjerling. "The links between chromatin spatial organization and biological function." Biochemical Society Transactions 41, no. 6 (November 20, 2013): 1634–39. http://dx.doi.org/10.1042/bst20130213.
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During the last few years, there has been a rapid increase in our knowledge of how chromatin is organized inside the nucleus. Techniques such as FISH (fluorescence in situ hybridization) have proved that chromosomes organize themselves in so-called CTs (chromosome territories). In addition, newly developed 3C (chromatin conformation capture) techniques have revealed that certain chromosomal regions tend to interact with adjacent regions on either the same chromosome or adjacent chromosomes, and also that regions in close proximity are replicated simultaneously. Furthermore, transcriptionally repressed or active areas occupy different nuclear compartments. Another new technique, named DamID (DNA adenine methyltransferase identification), has strengthened the notion that transcriptionally repressed genes are often found in close association with the nuclear membrane, whereas transcriptionally active regions are found in the more central regions of the nucleus. However, in response to various stimuli, transcriptionally repressed regions are known to relocalize from the nuclear lamina to the interior of the nucleus, leading to a concomitant up-regulation of otherwise silenced genes. Taken together, these insights are of great interest for the relationship between chromosomal spatial organization and genome function. In the present article, we review recent advances in this field with a focus on mammalian cells and the eukaryotic model organism Schizosaccharomyces pombe.