In the late 1960s and early 1970s David Marr produced three astonishing papers in which he gave a detailed account of how the fine structure and known cell types of the cerebellum, hippocampus and neocortex perform the functions that they do. Marr went on to become one of the main founders of Computational Neuroscience. In his classic work 'Vision' he distinguished between the computational, algorithmic, and implementational levels, and the three early theories concerned implementation. However, they were produced when Neuroscience (...) was in its infancy.Now that so much more is known, it is timely to revisit these early theories to see to what extent they are still valid and what needs to be altered to produce viable theories that stand up to current evidence. This book brings together some of the most distinguished scientists in their fields to evaluate Marr's legacy. (shrink)

The neural substrate of early visual processing in the macaque is used as a framework to discuss recent progress towards a precise anatomical localization and understanding of the functional implications of the syndromes of blindsight, achromatopsia and akinetopsia in humans. This review is mainly concerned with how these syndromes support the principles of organization of the visual system into parallel pathways and the functional hierarchy of visual mechanisms.

Several authors have characterized a striking phenomenon of perceptual learning in visual discrimination tasks. This learning process is selective for the stimulus characteristics and location in the visual field. Since the human visual system exploits symmetry for object recognition we were interested in exploring how it learns to use preattentive symmetry cues for discriminating simple, meaningless, forms. In this study, similar to previous studies of perceptual learning, we asked whether the effects of practice acquired in the discrimination of pairs of (...) shape with a specific orientation of the symmetry axis would transfer to the discrimination of shapes with different orientation of symmetry axis, or to shapes presented in different areas of the visual field. We found that there was no learning transfer between forms with very different axes of symmetry (90° apart). Interestingly, however, we found a transfer of learning effect to horizontally oriented symmetry axis from a condition with an axis of symmetry differing by 45°. Also it appears that some subjects took a longer time to learn than the typical fast learning paradigm would predict. Data showed that when observers practice discrimination of meaningless symmetric forms, consistent improvement in the performance occurs. This improvement is lasting over days, and it tends to be specific for the area of the visual field trained. We will discuss results from some of the observers whose learning was not fast, but who actually improved with more practice and with large time intervals (1 day) between training sessions. (shrink)

A single case study of a patient, D.M., with a lesion in the region of the right occipito-temporal gyrus is presented. D.M. had well-preserved language and general cognitive abilities. Colour discrimination, contrast sensitivity, gross depth perception, spatial localization, and motion appreciation were within normal limits.On the evaluation of perceptual abilities, he failed to identify two-dimensional shapes from stereoscopic vision, motion, and texture although in all cases he was able to identify the rough area subtended by the shape. These findings are (...) considered in relation to the current anatomical-physiological functional models of vision and it is suggested that D.M. 's deficits provide evidence for the existence in man of a functional pathway involved in the computation of texture and fine aspects of shape, which is distinct from the pathways involved in motion and stereopsis processing on one hand and colour and coarse aspects of form on the other hand. (shrink)

Twenty-four aphasic and fifteen right brain-damaged subjects were compared on their ability to identify the objects whose use was depicted in a series of twenty videotaped pantomimes. Aphasics were inferior to right brain-damaged patients in inferring object use. Success was correlated with Performance IQ, but not with language measures. Analysis of movement features contributing to subjects' choices reveal speed of movement and object weight to be the most robust and hand shape and size to be the most fragile.