Gotowa bibliografia na temat „Foveaux Strait”

Saccades are fast conjugate eye movements that move both eyes quickly in the same direction, so that the image of an object of interest is brought on the foveae. Saccades can be made not only toward visual targets, but also toward auditory and tactile stimuli, as well as toward memorized targets. Saccades can be generated reflexively, and they are responsible for resetting the eyes back to the mid-orbital position during vestibulo-ocular or optokinetic stimulation. Saccades need to be fast to get the eyes on the target as soon as possible. They also need to be fast because our eyes act like cameras with slow shutters—vision is so blurred during saccades that the eyes have to move quickly to minimize the time during which no clear image is captured on the foveae. Indeed, saccades are the fastest type of eye movements, and they are among the fastest movements that the body can make. Saccade speed is not under voluntary control but depends on the size of the movement, with larger saccades attaining higher peak velocities. It has been estimated that we make more than 100,000 saccades per day. The burst neuron circuits in the brainstem provide the necessary motor signals to the extraocular muscles for the generation of saccades. There is a division of labor between the pons and the midbrain, with the pons primarily involved in generating horizontal saccades and the midbrain primarily involved in generating vertical and torsional saccades. However, because eye movements are a component of cognitive and purposeful behaviors in higher mammals, the process of deciding when and where to make a saccade occurs in the cerebral cortex. Not only does the cortex exert control over saccades through direct projections to the burst neuron circuits, it also acts via the superior colliculus. The superior colliculus is located in the midbrain and consists of seven layers: three superficial layers and four intermediate/ deep layers. The three superficial layers receive direct inputs from both the retina and striate cortex, and they contain a retinotopic representation of the contralateral visual hemifield.

Descriptions of all radial and ulnar fossils from Sterkfontein are presented. The relatively large sample of forelimb bones from Sterkfontein provide information about the elbow, wrist, and forearm of Australopithecus africanus. The proximal orientation of the olecranon process and anterior orientation of the trochlear notch suggest that the forelimb was used in flexed position, as in humans. The bones are small relative to other hominins, and have relatively straight diaphysis and small muscle attachment markings like other australopiths, suggesting the presence of reduced forearm muscularity relative to apes. Diaphyseal cross-sectional shape suggests a pattern of forearm muscle use that may be neither completely human-like nor ape-like but somewhat intermediate, perhaps reflecting a reduced use in locomotion and an increased use in manipulation. In contrast to the diaphysis, the proximal radius is more clearly ape-like, with beveled heads and constricted and relatively long necks comparable to the Hadar specimens, which underscores the unique morphology of the elbow (neither completely human-like nor ape-like) in these hominins. The distal ulna, with the well-marked tendon groove, deep fovea, and a head shape intermediate between apes and humans, like A. afarensis specimens, suggest that stability was required during loading and use of the hand and wrist, although possibly less so than in extant apes. The overall picture of the Sterkfontein forelimb is that of a taxon that had powerful arms, but less powerful than apes, and that they were using them for tasks such as manipulation and probably less so for locomotion.