Size tuning of neural response variability in laminar circuits of macaque primary visual cortex.

A defining feature of the cortex is its laminar organization, which is likely critical for cortical information processing. For example, visual stimuli of different size evoke distinct patterns of laminar activity. Visual information processing is also influenced by the response variability of individual neurons and the degree to which this variability is correlated among neurons.

Distinct Laminar Processing of Local and Global Context in Primate Primary Visual Cortex.

Visual perception is affected by spatial context. In visual cortex, neuronal responses to stimuli inside the receptive field (RF) are suppressed by stimuli in the RF surround. To understand the circuits and cortical layers processing spatial context, we simultaneously recorded across all layers of macaque primary visual cortex while presenting stimuli at increasing distances from the recorded cells' RF.

Top-down feedback controls spatial summation and response amplitude in primate visual cortex.

Sensory information travels along feedforward connections through a hierarchy of cortical areas, which, in turn, send feedback connections to lower-order areas. Feedback has been implicated in attention, expectation, and sensory context, but the mechanisms underlying these diverse feedback functions are unknown. Using specific optogenetic inactivation of feedback connections from the secondary visual area (V2), we show how feedback affects neural responses in the primate primary visual cortex (V1).

Circuits and Mechanisms for Surround Modulation in Visual Cortex.

Surround modulation (SM) is a fundamental property of sensory neurons in many species and sensory modalities. SM is the ability of stimuli in the surround of a neuron's receptive field (RF) to modulate (typically suppress) the neuron's response to stimuli simultaneously presented inside the RF, a property thought to underlie optimal coding of sensory information and important perceptual functions. Understanding the circuit and mechanisms for SM can reveal fundamental principles of computations in sensory cortices, from mouse to human.

Multiple components of surround modulation in primary visual cortex: multiple neural circuits with multiple functions?

The responses of neurons in primary visual cortex (V1) to stimulation of their receptive field (RF) are modulated by stimuli in the RF surround. This modulation is suppressive when the stimuli in the RF and surround are of similar orientation, but less suppressive or facilitatory when they are cross-oriented. Similarly, in human vision surround stimuli selectively suppress the perceived contrast of a central stimulus.

Visual interactions conform to pattern decorrelation in multiple cortical areas.

Neural responses to visual stimuli are strongest in the classical receptive field, but they are also modulated by stimuli in a much wider region. In the primary visual cortex, physiological data and models suggest that such contextual modulation is mediated by recurrent interactions between cortical areas. Outside the primary visual cortex, imaging data has shown qualitatively similar interactions.

Fovea-periphery axis symmetry of surround modulation in the human visual system.

A visual stimulus activates different sized cortical area depending on eccentricity of the stimulus. Here, our aim is to understand whether the visual field size of a stimulus or cortical size of the corresponding representation determines how strongly it interacts with other stimuli. We measured surround modulation of blood-oxygenation-level-dependent signal and perceived contrast with surrounds that extended either towards the periphery or the fovea from a center stimulus, centered at 6° eccentricity.

Different orientation tuning of near- and far-surround suppression in macaque primary visual cortex mirrors their tuning in human perception.

In primary visual cortex (V1), neuronal responses to stimuli inside the receptive field (RF) are usually suppressed by stimuli in the RF surround. This suppression is orientation specific. Similarly, in human vision surround stimuli can suppress perceived contrast of a central stimulus in an orientation-dependent manner.

The effect of mean luminance change and grating pedestals on contrast perception: model simulations suggest a common, retinal, origin.

The percept of a contrast target is substantially affected by co-occurring changes in mean luminance or underlying ("pedestal") contrast elements. These two types of modulatory effects have traditionally been studied as separate phenomena. However, regardless of different higher-level mechanisms, both classes of phenomena will necessarily also depend on shared mechanisms in the first stages of vision, starting with the primary responses of photoreceptors.

Effects of mean luminance changes on human contrast perception: contrast dependence, time-course and spatial specificity.

Background: When we are viewing natural scenes, every saccade abruptly changes both the mean luminance and the contrast structure falling on any given retinal location. Thus it would be useful if the two were independently encoded by the visual system, even when they change simultaneously. Recordings from single neurons in the cat visual system have suggested that contrast information may be quite independently represented in neural responses to simultaneous changes in contrast and luminance.

Surround suppression and facilitation in the fovea: very long-range spatial interactions in contrast perception.

Surround modulation of perceived contrast has been almost exclusively studied in short-range conditions, i.e., in situations where a tiny gap, at most, separates center from surround.

Area summation in human visual system: psychophysics, fMRI, and modeling.

Contextual modulation is a fundamental feature of sensory processing, both on perceptual and on single-neuron level. When the diameter of a visual stimulus is increased, the firing rate of a cell typically first increases (summation field) and then decreases (surround field). Such an area summation function draws a comprehensive profile of the receptive field structure of a neuron, including areas outside the classical receptive field.

Spatial frequency tuning in human retinotopic visual areas.

Human medial occipital cortex comprises multiple visual areas, each with a distinct retinotopic representation of visual environment. We measured spatial frequency (SF) tuning curves with functional magnetic resonance imaging (fMRI) and found consistent differences between these areas. Areas V1, V2, VP, V3, V4v, and V3A were all band-pass tuned, with progressively lower SF optima in V1, V2, and V3A.