Achromatic and chromatic perceived contrast are reduced in the visual periphery.

The loss of contrast sensitivity with eccentricity is well documented, and is steeper for higher spatial frequencies, and for L/M cone-opponent stimuli compared to achromatic or S-cone-opponent. Here, we ask how perceived contrast depends on eccentricity when stimuli are presented at suprathreshold contrasts, and test two opposing predictions. Contrast constancy predicts no loss in perceived contrast across the visual field regardless of changes in detection threshold - appearance depends only on physical contrast.

Magnetoencephalography contrast adaptation reflects perceptual adaptation.

Contrast adaptation is a fundamental visual process that has been extensively investigated and used to infer the selectivity of visual cortex. We recently reported an apparent disconnect between the effects of contrast adaptation on perception and functional magnetic resonance imaging BOLD response adaptation, in which adaptation between chromatic and achromatic stimuli measured psychophysically showed greater selectivity than adaptation measured using BOLD signals. Here we used magnetoencephalography (MEG) recordings of neural responses to the same chromatic and achromatic adaptation conditions to characterize the neural effects of contrast adaptation and to determine whether BOLD adaptation or MEG better reflect the measured perceptual effects.

Linking perceived to physical contrast: Comparing results from discrimination and difference-scaling experiments.

Psychophysical approaches that allow us to estimate how perceived stimulus intensity is linked to physical intensity are import tools for studying nonlinear transformations of visual signals within different visual pathways. Here, we investigated how stimulus contrast is encoded in achromatic and chromatic pathways using simple grating stimuli. We compared two experimental approaches to this question: contrast discrimination (increment detection thresholds measured on contrast pedestals) and the maximum likelihood difference scaling (MLDS) approach introduced by Maloney and Yang (2003).

Enhanced luminance sensitivity on color and luminance pedestals: Threshold measurements and a model of parvocellular luminance processing.

Psychophysical interactions between chromatic and achromatic stimuli may inform our understanding of the cortical processing of signals of parvocellular origin, which carry both luminance and color information. We measured observers' sensitivity in discriminating the luminance of circular patch stimuli with a range of baseline ("pedestal") luminance and chromaticity. Pedestal stimuli were defined along vectors in cone-contrast space in a plane spanned by the red-green cone-opponent (L-M) and achromatic (L + M + S) axes.

Laminar Differences in Responses to Naturalistic Texture in Macaque V1 and V2.

Most single units recorded from macaque secondary visual cortex (V2) respond with higher firing rates to synthetic texture images containing "naturalistic" higher-order statistics than to spectrally matched "noise" images lacking these statistics. In contrast, few single units in V1 show this property. We explored how the strength and dynamics of response vary across the different layers of visual cortex by recording multiunit (defined as high-frequency power in the local field potential) and gamma-band activity evoked by brief presentations of naturalistic and noise images in V1 and V2 of anesthetized macaque monkeys of both sexes.

Asymmetric Dichoptic Masking in Visual Cortex of Amblyopic Macaque Monkeys.

In amblyopia, abnormal visual experience leads to an extreme form of eye dominance, in which vision through the nondominant eye is degraded. A key aspect of this disorder is perceptual suppression: the image seen by the stronger eye often dominates during binocular viewing, blocking the image of the weaker eye from reaching awareness. Interocular suppression is the focus of ongoing work aimed at understanding and treating amblyopia, yet its physiological basis remains unknown.

Altered Balance of Receptive Field Excitation and Suppression in Visual Cortex of Amblyopic Macaque Monkeys.

In amblyopia, a visual disorder caused by abnormal visual experience during development, the amblyopic eye (AE) loses visual sensitivity whereas the fellow eye (FE) is largely unaffected. Binocular vision in amblyopes is often disrupted by interocular suppression. We used 96-electrode arrays to record neurons and neuronal groups in areas V1 and V2 of six female macaque monkeys () made amblyopic by artificial strabismus or anisometropia in early life, as well as two visually normal female controls.

Population representation of visual information in areas V1 and V2 of amblyopic macaques.

Amblyopia is a developmental disorder resulting in poor vision in one eye. The mechanism by which input to the affected eye is prevented from reaching the level of awareness remains poorly understood. We recorded simultaneously from large populations of neurons in the supragranular layers of areas V1 and V2 in 6 macaques that were made amblyopic by rearing with artificial strabismus or anisometropia, and 1 normally reared control.

High-capacity, transient retention of direction-of-motion information for multiple moving objects.

The multiple-object tracking paradigm (MOT) has been used extensively for studying dynamic visual attention, but the basic mechanisms which subserve this capability are as yet unknown. Among the unresolved issues surrounding MOT are the relative importance of motion (as opposed to positional) information and the role of various memory mechanisms. We sought to quantify the capacity and dynamics for retention of direction-of-motion information when viewing a multiple-object motion stimulus similar to those used in MOT.

Role of task-directed attention in nonconscious and conscious response priming by form and color.

Prior research on visual priming suggests that during nonconscious processing attention can be directed to single stimulus dimensions such as form or color. In the current experiment, nonconscious priming was compared to conscious priming by employing masking techniques that render primes invisible (masked) or visible (unmasked) to the observers. Observers were asked to respond to the form, the color, or the combination of form and color of the mask-probe that followed either a masked or an unmasked prime.