The neural basis of pattern recognition is a central problem in visual neuroscience. Responses single cells were recorded area V4 macaque monkey to three classes periodic stimuli that are based on spatial derivative operators: polar (concentric and radial), hyperbolic, conventional sinusoidal (Cartesian) gratings. Of 118 tested, 16 percent responded significantly more or hyperbolic (non-Cartesian) gratings than Cartesian only 8 showed significant preference for Among selective non-Cartesian...

Gender differences in brain activation during working memory tasks were examined with fMRI. Seventeen right-handed subjects (nine males, eight females) studied four different verbal of varying difficulty using whole echo-planar Consistent prior studies, we observed the lateral prefrontal cortices (LPFC), parietal (PC), and additionally, caudate both sexes. The volume activated tissue increased increasing task difficulty. For all tasks, male showed bilateral or right-sided dominance (LPFC, PC...

<b><i><i>Objectives:</i></i></b> To evaluate the neural correlates of attention and working memory deficits in patients with HIV-1. <b><i><i>Method:</i></i></b> fMRI was used to brain activity 11 HIV age-, sex-, education-, handedness-matched seronegative subjects, while performing a battery tasks that required different levels for memory. <b><i><i>Results:</i></i></b> Patients showed greater activation (blood oxygenation level dependent signal changes) some regions compared control subjects...

Abstract Although visual attention is known to modulate brain activity in the posterior parietal, prefrontal, and sensory areas, unique roles of these areas control attentional resources have remained unclear. Here, we report a dissociation response profiles areas. In parametric functional magnetic resonance imaging (fMRI) study, subjects performed covert motion-tracking task, which manipulated “attentional load” by varying number tracked balls. While strong effects attention—independent...

In more than one respect, visual search for the most salient or least item in a display are different kinds of tasks. The present work investigated whether this difference is primarily perceptual difficulty, it fundamental and relates to attention. Display items salience were produced by varying either size, contrast, color saturation, pattern. Perceptual masking was employed and, on average, mask onset delayed longer item. As result, two types presented comparable as judged psychophysical...

We propose a novel explanation for bistable perception, namely, the collective dynamics of multiple neural populations that are individually meta-stable. Distributed representations sensory input and perceptual state build gradually through noise-driven transitions in these populations, until competition between alternative is resolved by threshold mechanism. The perpetual repetition this race to renders perception bistable. This - which largely uncoupled from time-scales govern individual...

We report that multi-stable perception operates in a consistent, dynamical regime, balancing the conflicting goals of stability and sensitivity. When visual display is viewed continuously, its phenomenal appearance reverses spontaneously at irregular intervals. characterized perceptual dynamics individual observers terms four statistical measures: distribution dominance times (mean variance) novel, subtle dependence on prior history (correlation time-constant). The known to reflect several...

The timing of perceptual decisions depends on both deterministic and stochastic factors, as the gradual accumulation sensory evidence (deterministic) is contaminated by and/or internal noise (stochastic). When human observers view multistable visual displays, successive episodes culminate in repeated reversals appearance. Treating reversal a "first-passage time" problem, we ask how observed densities constrain underlying accumulation. Importantly, mean times (i.e., factors) differ enormously...

When visual space is densely populated by elements of random orientation, which happen to be aligned may form a perceptually salient 'contour' (Field et al., 1993; Kovacs and Julesz, 1993). Here we further characterize human performance for detecting this type Gestalt grouping. We find that detectability contours reaches plateau when they comprise at least 10 are presented 200 ms. It has been suggested the detection mediated intrinsic connectivity striate cortex several computational models...

We report contrast detection, increment, masking, orientation discrimination, and spatial frequency discrimination thresholds for spatially localized stimuli at 4° of eccentricity. Our stimulus geometry emphasizes interactions among overlapping visual filters differs from that used in previous threshold measurements, which also admits distant filters. quantitatively account all measurements by simulating a small population interacting through divisive inhibition. depart models this kind the...

Many ambiguous patterns elicit spontaneous alternations of phenomenal appearance. Attention is known to influence these reversals, as do several other factors. We asked whether a shift attention individually prompts each reversal By combining intermittent presentation with proven method control, we monitored in the complete absence shifts. found that reversals become less frequent but continue even when observers neither report on nor an pattern. The statistical variability remains...

It is well known that pauses in the presentation of an ambiguous display may stabilize its perceptual appearance. Here we show this stabilization depends on extended history spanning several dominance periods, not merely most recent period. Specifically, appearance after a pause often reflects less (but longer) periods rather than more shorter) periods. Our results imply existence short-tem memory for builds up over seconds, decays minutes, and robust to reversals. Although evident paused...

Neural adaptation plays an important role in multistable perception, but its effects are difficult to discern sequences of perceptual reversals. Investigating the appearance kinetic depth and binocular rivalry displays, we introduce cumulative history as a novel statistical measure adaptive state. We show that history-an integral past states, weighted toward most recent states-significantly consistently correlates with future dominance durations: larger measure, shorter times, revealing...