Equiluminous red-green sine-wave gratings were drifted at a uniform rate in the bottom half of 10-deg field. In top display was sinusoidal-luminance grating same spatial frequency and 95% contrast that opposite direction. Observers, while fixating point center, adjusted speed this upper comparison so it appeared to match velocity chromatic below. At low frequencies, equiluminous appreciably slowed sometimes stopped even though individual bars could be easily resolved. The amount slowing...

Humans often create and appreciate visual symmetry in their environment, the underlying brain mechanisms have been a topic of increasing interest. Here, symmetric versus random dot stimuli produced robust functional MRI (fMRI) activity higher-order regions human cortex (especially areas V3A, V4, V7, LO) but little elsewhere brain. This fMRI response was found both with without attention controls. Moreover, it highly correlated psychophysical perception symmetry. Similar responses were by...

The human visual system devotes a significant proportion of its resources to very small part the field, fovea. Foveal vision is crucial for natural behavior and many tasks in daily life such as reading or fine motor control. Despite size, this cortex rarely investigated limited data have resulted competing models layout foveal confluence primate species. Specifically, how V2 V3 converge at central fovea subject debate primates has remained "terra incognita" humans. Using high-resolution fMRI...

Visual sensitivity to stimuli with sinusoidal movement was examined under a number of conditions binocular stimulation. Sensitivity stereoscopic in depth reduced comparison that for monocular movement. The appeared be due the presence movement, as opposed stimulation, or fusion images.

The spatial limitations of stereoscopic vision were studied by using vertical line stimuli containing sinusoidal disparity variations such that different parts the appeared at depths. Stimuli with a finer grain than about 3 cycles per degree did not elicit depth perception, even though curvature was clearly visible monocularly. At low frequencies curvature, stereoacuity limited to same extent as monocular sensitivity. limiting for Panum's fusional region and upper limit are subject scaling...

It has been commonly reported that the temporal integration of grating contrast proceeds more slowly as spatial frequency is increased. Such results have based on critical duration for sensitivity to pulses varying in duration, but analyses not assumed full at short durations and neglected effects probability summation over time. To take such into account, we discuss a class analytical models nonlinear integration. On assumption impulse response visual system determines time, develop both...

Temporal-frequency characteristics were measured as a function of retinal location, with test-field size scaled to provide equivalent sensitivity at each eccentricity. The results showed that the temporal-frequency limits increased uniformly by about factor 2 between fovea and 45° eccentricity, corresponding decrease in response-time constant from 70 35 msec. These data compared change inner- outer-segment diameters cones across same range. conform hypothesis visual time varies inversely...

Direction selectivity of synaptic potentials in simple cells the cat visual cortex. J. Neurophysiol. 78: 2772-2789, 1997. The direction cortex is generated at least part by nonlinear mechanisms. If a neuron were spatially linear, its responses to moving stimuli could be predicted accurately from linear combinations stationary presented different positions within receptive field. In extracellular recordings, this has not been found case. Although experiments demonstrate presence nonlinearity,...

Primate visual cortex contains a set of maps space. These are fundamental to early processing, yet their form is not fully understood in humans. This especially true for the central and most important part field--the fovea. We used functional magnetic resonance imaging (fMRI) measure mapping geometry human V1 V2 down 0.5 degrees eccentricity. By applying automated atlas fitting procedures parametrize average retinotopic measurements eight brains, we provide reference standard two-dimensional...

Critical flicker frequency (CFF) and modulation sensitivity were measured throughout the visual field as a function of meridian, eccentricity, luminance. The stimulus conditions designed to excite preferentially long-wavelength-sensitive (R) cones in equal numbers at each retinal location. Temporal-frequency responses under these can be partitioned into two components by following analysis Kelly [ J. Opt. Soc. Am.51, 422 ( 1961)]: high-frequency linear component unaffected mean luminance...