Harry S. Orbach

Learn More
We have investigated the use of optical methods for monitoring neuron activity in mammalian cortex. The cortex was stained with a voltage-sensitive dye and fluorescence was simultaneously measured from 124 areas using a photodiode array. Optical signals were detected in rat somatosensory cortex in response to small whisker movements and in visual cortex in(More)
The angular dependence of precision measurements is well established as the oblique effect in motion perception. Recently, it has been shown that the visual system also exhibits anisotropic behaviour with respect to accuracy of the absolute direction of motion of random dot fields. This study aimed to investigate whether this angular dependent, directional(More)
Pointlike object features such as line-endings, have a privileged position in the computation of the veridical direction of object motion. Experiments confirm that the human visual system relies heavily on such features if they are present. It has been proposed that units such as end-stopped cells might be necessary for the computation of feature motion(More)
We have investigated the use of voltage-sensitive dyes to monitor neuronal activity in the intact salamander olfactory bulb. After a 10- to 20-min staining period, a magnified image of an in vitro or an in vivo preparation was formed on a 124-element photodiode array. The array was used to simultaneously record absorption or fluorescence changes from 124(More)
The ability to discriminate minute deviations from circularity is dependent upon global summation mechanisms integrating information along entire contours. The aim of this study was to determine how the strength of global summation depends on various stimulus features. To determine if the strength of global summation differs between shapes, contour(More)
Several factors that affect the suitability of opticaL methods for monitoring neuron activity were evaluated in several species of gastropod molluscs. The mean cell body diameter and the total number of cells in the central nervous system were determined In 6 preparations and qualitative evaluations were made for an additional 25 species. There was a factor(More)
Change blindness--our inability to detect large changes in natural scenes when saccades, blinks and other transients interrupt visual input--seems to contradict psychophysical evidence for our exquisite sensitivity to contrast changes. Can the type of effects described as 'change blindness' be observed with simple, multi-element stimuli, amenable to(More)
Visual evoked potentials to pattern reversal (PR-VEPs) are used to assess the integrity and maturation of the visual pathways in infants and young children. To establish normal ranges and to facilitate interpolation, we consider the maturation rate of PR-VEPs using published normative data. Curves based on the logistic function (a sigmoid model) are(More)
This study investigated how the perception of a translating object is affected by rotation. Observers were asked to judge the motion and trajectory of objects that rotated around their centroid while linearly translating. The expected percept, consistent with the actual dynamics used to generate the movie sequences, is that of a translating and rotating(More)