Perceptual enhancement and suppression correlate with V1 neural activity during active sensing.

Perception in multiple sensory modalities is an active process that involves exploratory behaviors. In humans and other primates, vision results from sensory sampling guided by saccadic eye movements. Saccades are known to modulate visual perception, and a corollary discharge signal associated with saccades appears to establish a sense of visual stability.

Transsacadic Information and Corollary Discharge in Local Field Potentials of Macaque V1.

Approximately three times per second, human visual perception is interrupted by a saccadic eye movement. In addition to taking the eyes to a new location, several lines of evidence suggest that the saccades play multiple roles in visual perception. Indeed, it may be crucial that visual processing is informed about movements of the eyes in order to analyze visual input distinctly and efficiently on each fixation and preserve stable visual perception of the world across saccades.

Saccade-based termination responses in macaque V1 and visual perception.

Neurons in visual areas of the brain are generally characterized by the increase in firing rate that occurs when a stimulus is flashed on in the receptive field (RF). However, neurons also increase their firing rate when a stimulus is turned off. These "termination responses" or "after-discharges" that occur with flashed stimuli have been observed in area V1 and they may be important for vision as stimulus terminations have been shown to influence visual perception.

Contrast sensitivity, V1 neural activity, and natural vision.

Unlabelled: Contrast sensitivity is fundamental to natural visual processing and an important tool for characterizing both visual function and clinical disorders. We simultaneously measured contrast sensitivity and neural contrast response functions and compared measurements in common laboratory conditions with naturalistic conditions. In typical experiments, a subject holds fixation and a stimulus is flashed on, whereas in natural vision, saccades bring stimuli into view.

Eye movements reset visual perception.

Human vision uses saccadic eye movements to rapidly shift the sensitive foveal portion of our retina to objects of interest. For vision to function properly amidst these ballistic eye movements, a mechanism is needed to extract discrete percepts on each fixation from the continuous stream of neural activity that spans fixations. The speed of visual parsing is crucial because human behaviors ranging from reading to driving to sports rely on rapid visual analysis.

Macaque V1 representations in natural and reduced visual contexts: spatial and temporal properties and influence of saccadic eye movements.

Vision in natural situations is different from the paradigms generally used to study vision in the laboratory. In natural vision, stimuli usually appear in a receptive field as the result of saccadic eye movements rather than suddenly flashing into view. The stimuli themselves are rich with meaningful and recognizable objects rather than simple abstract patterns.

V1 response timing and surface filling-in.

There is ample evidence from demonstrations such as color induction and stabilized images that information from surface boundaries plays a special role in determining the perception of surface interiors. Surface interiors appear to "fill-in." Psychophysical experiments also show that surface perception involves a slow scale-dependent process distinct from mechanisms involved in contour perception.

Rebounding V1 activity and a new visual aftereffect.

A serendipitous observation led to this study of V1 activity rebounds, which occur well after stimulus offset, and their relationship to visual aftereffects. We found that when a stimulus bar and background were simultaneously turned off, there was strong delayed rebounding activity (distinct from any off response). The neural rebound started 350-500 ms after stimulus offset, and its magnitude and duration were correlated with the prior visual response of the cell.

Macaque V1 activity during natural vision: effects of natural scenes and saccades.

In the present study, we examined the way that scene complexity and saccades combine to sculpt the temporal response patterns of V1 neurons. To bridge the gap between conventional and free viewing experiments, we compared responses of neurons across four paradigms ranging from less to more natural. An optimal bar stimulus was either flashed into a receptive field (RF) or brought into it via saccade and was embedded in either a natural scene or a uniform gray background.

Lightness, filling-in, and the fundamental role of context in visual perception.

Visual perception is defined by the unique spatial interactions that distinguish it from the point-to-point precision of a photometer. Over several decades, Lothar Spillmann has made key observations about the nature of these interactions and the role of context in perception. Our lab has explored the perceptual properties of spatial interactions and more generally the importance of visual context for neuronal responses and perception.

Stimulus for rapid ocular dominance plasticity in visual cortex.

Although it has been known for decades that monocular deprivation shifts ocular dominance in kitten striate cortex, uncertainty persists about the adequate stimulus for deprivation-induced losses of cortical responsiveness. In the current study we compared the effects of 2 days of lid closure and 2 days of monocular blur using an overcorrecting contact lens. Our finding of comparable ocular dominance shifts in visual cortex indicates that deprived-eye response depression is not a result of reduced retinal illumination.

The importance of modulatory input for V1 activity and perception.

To conduct well-controlled studies of visual processing in the laboratory, deviations from natural visual situations must generally be employed. In some regards, the reduced visual paradigms typically used are adequate for providing an accurate description of visual representations. However, the use of fixation paradigms and stimuli isolated within a receptive field may underestimate the richness of visual processing in area V1.

Background changes delay information represented in macaque V1 neurons.

In natural behavioral situations, saccadic eye movements not only introduce new stimuli into V1 receptive fields, they also cause changes in the background. We recorded in awake macaque V1 using a fixation paradigm and compared evoked activity to small stimuli when the background was either static or changing as with a saccade. When a stimulus was shown on a static background, as in most previous experiments, the initial response was orientation selective and contrast was inversely correlated with response latency.

Background changes delay the perceptual availability of form information.

In natural visual situations, unlike most psychophysical experiments, when a new stimulus appears in a portion of the visual field, the surrounding background changes simultaneously. In recordings from macaque V1, we found that a visual stimulus presented simultaneously with a background change evokes a response that is qualitatively different from the response to the same stimulus flashed on a static background. With the changing background, information about stimulus orientation and contrast is significantly delayed compared with the static-background situation.

Perception of brightness and brightness illusions in the macaque monkey.

Recent physiological studies show that neural responses correlated with the perception of brightness are found in cortical area V1 but not earlier in the visual pathway (Kayama et al., 1979; Reid and Shapley, 1989; Squatrito et al., 1990; Komatsu et al.

Perceptual and neuronal correspondence in primary visual cortex.

Recent findings from the study of primary visual cortex in humans and animals blur the distinction between early and late visual processing. Under some conditions, the activity of neurons in primary visual cortex appears as close or closer to perception than activity in 'higher' visual areas.