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Previously, we discovered that the broadband cells in the two magnocellular (large cell) layers of the monkey lateral geniculate nucleus (LGN) are much more sensitive to luminance contrast than are the color-sensitive cells in the four parvocellular (small cell) layers. We now report that this large difference in contrast sensitivity is due not to LGN(More)
Stimulation outside the receptive field of a primary visual cortical (V1) neuron reveals intracortical neural interactions. However, previous investigators implicitly or explicitly considered the extent of cortical spatial summation and, therefore, the size of the classical receptive field to be fixed and independent of stimulus characteristics or of(More)
We studied the steady-state orientation selectivity of single neurons in macaque primary visual cortex (V1). To analyze the data, two measures of orientation tuning selectivity, circular variance and orientation bandwidth, were computed from the tuning curves. Circular variance is a global measure of the shape of the tuning curve, whereas orientation(More)
Spatial and temporal properties of illusory contours and amodal completion were investigated using a shape discrimination task. Performance was characterized as accuracy of angular discrimination of the inducing figures ("pacmen") in a two-alternative forced choice (2AFC) paradigm. First, we compared performance when four "pacmen" were organized into(More)
Orientation tuning of neurons is one of the chief emergent characteristics of the primary visual cortex, V1. Neurons of the lateral geniculate nucleus, which comprise the thalamic input to V1, are not orientation-tuned, but the majority of V1 neurons are quite selective. How orientation tuning arises within V1 is still controversial. To study this problem,(More)
1. Variation in stimulus contrast produces a marked effect on the dynamics of the cat retina. This contrast effect was investigated by measurement of the responses of X and Y ganglion cells. The stimuli were sine gratings or rectangular spots modulated by a temporal signal which was a sum of sinusoids. Fourier analysis of the neural response to such a(More)
1. Cells of the lateral geniculate nucleus (l.g.n.) in macaque monkeys were sorted into two functional groups on the basis of spatial summation of visually evoked neural signals. 2. Cells were called X cells if their responses to contrast reversal of fine sine gratings were at the fundamental temporal modulation frequency with null positions one quarter of(More)
Perceptually, color is used to discriminate objects by hue and to identify color boundaries. The primate retina and the lateral geniculate nucleus (LGN) have cell populations sensitive to color modulation, but the role of the primary visual cortex (V1) in color signal processing is uncertain. We re-evaluated color processing in V1 by studying single-neuron(More)
The classification of cat retinal ganglion cells as X or Y on the basis of linearity or nonlinearity of spatial summation has been confirmed and extended. Recordings were taken from optic tract fibres of anaesthetized, paralysed cats. 2. When an alternating phase sine wave grating was used as a stimulus, X cells had null positions and Y cells responded at(More)
1. The mechanism which makes Y cells different from X cells was investigated. 2. Spatial frequency contrast sensitivity functions for the fundamental and second harmonic responses of Y cells to alternating phase gratings were determined. 3. The fundamental spatial frequency response was predicted by the Fourier transform of the sensitivity profile of the Y(More)