Distinct dorsal and ventral streams for binocular rivalry dominance and suppression revealed by magnetoencephalography.

Binocular rivalry is an example of bistable visual perception extensively examined in neuroimaging. Magnetoencephalography can track brain responses to phasic visual stimulations of predetermined frequency and phase to advance our understanding of perceptual dominance and suppression in binocular rivalry. We used left and right eye stimuli that flickered at two tagging frequencies to track their respective oscillatory cortical evoked responses.

Interocular Grouping in Perceptual Rivalry Localized with fMRI.

Bistable perception refers to a broad class of dynamically alternating visual illusions that result from ambiguous images. These illusions provide a powerful method to study the mechanisms that determine how visual input is integrated over space and time. Binocular rivalry occurs when subjects view different images in each eye, and a similar experience called stimulus rivalry occurs even when the left and right images are exchanged at a fast rate.

Tagged MEG measures binocular rivalry in a cortical network that predicts alternation rate.

Binocular rivalry (BR) is a dynamic visual illusion that provides insight into the cortical mechanisms of visual awareness, stimulus selection, and object identification. When dissimilar binocular images cannot be fused, perception switches every few seconds between the left and right eye images. The speed at which individuals switch between alternatives is a stable, partially heritable trait.

Transcranial magnetic stimulation to visual cortex induces suboptimal introspection.

Blindsight patients with damage to the visual cortex can discriminate objects but report no conscious visual experience. This provides an intriguing opportunity to allow the study of subjective awareness in isolation from objective performance capacity. However, blindsight is rare, so one promising way to induce the effect in neurologically intact observers is to apply transcranial magnetic stimulation (TMS) to the visual cortex.

Children's Brain Responses to Optic Flow Vary by Pattern Type and Motion Speed.

Structured patterns of global visual motion called optic flow provide crucial information about an observer's speed and direction of self-motion and about the geometry of the environment. Brain and behavioral responses to optic flow undergo considerable postnatal maturation, but relatively little brain imaging evidence describes the time course of development in motion processing systems in early to middle childhood, a time when psychophysical data suggest that there are changes in sensitivity. To fill this gap, electroencephalographic (EEG) responses were recorded in 4- to 8-year-old children who viewed three time-varying optic flow patterns (translation, rotation, and radial expansion/contraction) at three different speeds (2, 4, and 8 deg/s).

Comparison of stimulus rivalry to binocular rivalry with functional magnetic resonance imaging.

When incompatible images are presented to each eye, a phenomenon known as binocular rivalry occurs in which the viewer's conscious visual perception alternates between the two images. In stimulus rivalry, similar perceptual alternations between rival images can occur even in the midst of fast image swapping between the eyes. Here, we used functional magnetic resonance imaging to directly compare brain activity underlying the two types of perceptual rivalry.

Individual peak gamma frequency predicts switch rate in perceptual rivalry.

Perceptual rivalry-the experience of alternation between two mutually exclusive interpretations of an ambiguous image-provides powerful opportunities to study conscious awareness. It is known that individual subjects experience perceptual alternations for various types of bistable stimuli at distinct rates, and this a stable, heritable trait. Also stable and heritable is the peak frequency of induced gamma-band (30-100 Hz) oscillation of a population-level response in occipital cortex to simple visual patterns, which has been established as a neural correlate of conscious processing.

Cortical responses to optic flow and motion contrast across patterns and speeds.

Motion provides animals with fast and robust cues for navigation and object detection. In the first case, stereotyped patterns of optic flow inform a moving observer about the direction and speed of its own movement. In the case of object detection, regional differences in motion allow for the segmentation of figures from their background, even in the absence of color or shading cues.

Long range grouping mechanisms for object perception.

The case made by Kogo and Wagemans for border ownership of surface boundaries to explain modal completion of illusory contours is well argued, and is compatible with psychophysical and physiological research on configural interactions with stereoscopic depth processing. However, it is important to contextualize such a mechanism of surface interpolation with related object grouping mechanisms in visual cortex, such as those not necessarily related to depth. Additionally, it's worth considering how the BOWN model can be generalized beyond Kanizsa shapes to more complex volumetric surface interpolations.

Linking brain to behavior for the visual perception of figures and objects.

The dissociation of a figure from its background is an essential feat of visual perception, as it allows us to detect, recognize, and interact with shapes and objects in our environment. In order to understand how the human brain gives rise to the perception of figures, we here review experiments that explore the links between activity in visual cortex and performance of perceptual tasks related to figure perception. We organize our review according to a proposed model that attempts to contextualize figure processing within the more general framework of object processing in the brain.

Distinct cortical responses to 2D figures defined by motion contrast.

Motion contrast contributes to the segregation of a two-dimensional figure from its background, yet many questions remain about its neural mechanisms. We measured steady-state visual evoked potential (SSVEP) responses to moving dot displays in which figure regions emerged from and disappeared into the background at a specific temporal frequency (1.2Hz, F1), based on regional differences of dot direction and global direction coherence.

Defective motion processing in children with cerebral visual impairment due to periventricular white matter damage.

Aim: We sought to characterize visual motion processing in children with cerebral visual impairment (CVI) due to periventricular white matter damage caused by either hydrocephalus (eight individuals) or periventricular leukomalacia (PVL) associated with prematurity (11 individuals).

Method: Using steady-state visually evoked potentials (ssVEP), we measured cortical activity related to motion processing for two distinct types of visual stimuli: 'local' motion patterns thought to activate mainly primary visual cortex (V1), and 'global' or coherent patterns thought to activate higher cortical visual association areas (V3, V5, etc.).