Neural processing of orientation differences between the eyes’ images

The aim of this study was to explore the neural mechanisms underlying visual processing of brief stimuli that were either the same in the two eyes or differed in orientation between the two eyes. To examine the neural mechanisms, I measured event-related potentials (ERPs) to 200-ms sine-wave gratings differing in orientation between the eyes from 08 to 908. The gratings were either both of high contrast or both of low contrast. They elicited typical ERPs at occipital electrodes, with a first major component (P100) 100 ms after stimulus onset and a second major component (N170) 170 ms after stimulus onset. Global electrical field strength and focal amplitudes of both components were affected by grating contrast: Highcontrast gratings elicited larger amplitudes than low-contrast gratings, confirming that neural responses depend on stimulus salience. P100 amplitude followed a U-shaped function: It was larger when the orientations were the same in the two eyes (yielding binocular fusion), intermediate when the orientations were maximally different between the eyes (leading to binocular rivalry), and smallest for in-between orientation differences. N170 amplitude followed a linear function: It was smallest when the orientations were the same and increased with orientation difference between the eyes. These results suggest that the P100 reflects processes in which the binocular input are offset against each other, and that the N170 reflects binocular rivalry. I argue that the N170 shows the effects of reciprocal inhibition and adaptation-both critical factors in theories of binocular rivalry

Gottfried Wilhelm Osann (1833, 1836) on Simultaneous Color Contrast:Translation and Commentary

Gottfried Wilhelm Osann (1796–1866) was a German scientist most renowned for his work in chemistry and physics. However, inspired by Goethe’s work on color, he published a paper on simultaneous color contrast in 1833 using a method that is similar to that of later authors: reflection of an achromatic spot from an angled piece of glass. He wrote at least four more papers on color contrasts, in 1836 using essentially the same method as credited to others. We provide a description and translation of Osann’s 1833 paper and the relevant part of his 1836 paper, say why these papers are interesting and important, give some biographical information about Osann, comment on the fate of Osann’s papers, and describe Osann’s other papers on color

On the Role of Attention in Binocular Rivalry: Electrophysiological Evidence

During binocular rivalry visual consciousness fluctuates between two dissimilar monocular images. We investigated the role of attention in this phenomenon by comparing event-related potentials (ERPs) when binocular-rivalry stimuli were attended with when they were unattended. Stimuli were dichoptic, orthogonal gratings that yielded binocular rivalry and dioptic, identically oriented gratings that yielded binocular fusion. Events were all possible orthogonal changes in orientation of one or both gratings. We had two attention conditions: In the attend-to-grating condition, participants had to report changes in perceived orientation, focussing their attention on the gratings. In the attend-to-fixation condition participants had to report changes in a central fixation target, taking attention away from the gratings. We found, surprisingly, that attending to rival gratings yielded a smaller ERP component (the N1, from 160–210 ms) than attending to the fixation target. To explain this paradoxical effect of attention, we propose that rivalry occurs in the attend-to-fixation condition (we found an ERP signature of rivalry in the form of a sustained negativity from 210–300 ms) but that the mechanism processing the stimulus changes is more adapted in the attend-to-grating condition than in the attend-to-fixation condition. This is consistent with the theory that adaptation gives rise to changes of visual consciousness during binocular rivalry

Processing of Abstract Rule Violations in Audition

The ability to encode rules and to detect rule-violating events outside the focus of attention is vital for adaptive behavior. Our brain recordings reveal that violations of abstract auditory rules are processed even when the sounds are unattended. When subjects performed a task related to the sounds but not to the rule, rule violations impaired task performance and activated a network involving supratemporal, parietal and frontal areas although none of the subjects acquired explicit knowledge of the rule or became aware of rule violations. When subjects tried to behaviorally detect rule violations, the brain's automatic violation detection facilitated intentional detection. This shows the brain's capacity for abstraction – an important cognitive function necessary to model the world. Our study provides the first evidence for the task-independence (i.e. automaticity) of this ability to encode abstract rules and for its immediate consequences for subsequent mental processes

Neural processing of orientation differences between the eyes\u27 images

The aim of this study was to explore the neural mechanisms underlying visual processing of brief stimuli that were either the same in the two eyes or differed in orientation between the two eyes. To examine the neural mechanisms, I measured event-related potentials (ERPs) to 200-ms sine-wave gratings differing in orientation between the eyes from 0° to 90°. The gratings were either both of high contrast or both of low contrast. They elicited typical ERPs at occipital electrodes, with a first major component (P100) 100 ms after stimulus onset and a second major component (N170) 170 ms after stimulus onset. Global electrical field strength and focal amplitudes of both components were affected by grating contrast: High-contrast gratings elicited larger amplitudes than low-contrast gratings, confirming that neural responses depend on stimulus salience. P100 amplitude followed a U-shaped function: It was larger when the orientations were the same in the two eyes (yielding binocular fusion), intermediate when the orientations were maximally different between the eyes (leading to binocular rivalry), and smallest for in-between orientation differences. N170 amplitude followed a linear function: It was smallest when the orientations were the same and increased with orientation difference between the eyes. These results suggest that the P100 reflects processes in which the binocular input are offset against each other, and that the N170 reflects binocular rivalry. I argue that the N170 shows the effects of reciprocal inhibition and adaptation—both critical factors in theories of binocular rivalry

Encoding into Visual Working Memory: Event-Related Brain Potentials Reflect Automatic Processing of Seemingly Redundant Information

Encoding and maintenance of information in visual working memory in an S1-S2 task with a 1500 ms retention phase were investigated by means of event-related brain potentials (ERPs). Participants were asked to decide whether two visual stimuli were physically identical (identity comparison (IC) task) or belonged to the same set or category of equivalent patterns (category comparison (CC) task). The stimuli differ with regard to two features. (1) Each pattern can belong to a set of either four (ESS 4) or eight (ESS 8) equivalent patterns, mirroring differences in the complexity with regard to the representational structure of each pattern (i.e., equivalence set size (ESS)). (2) The set of patterns differ with regard to the rated complexity. Memory performance obtained the effects of the task instructions (IC versus CC) and the ESS (ESS 4 versus ESS 8) but not of the rated complexity. ERPs in the retention interval reveal that the stimulus-related factors (subjective complexity and ESS) affect the encoding of the stimuli as mirrored by the pronounced P3b amplitude in ESS 8 compared to ESS 4 patterns. Importantly, these effects are independent of task instructions. The pattern of results suggests an automatic processing of the ESS in the encoding phase

Neural correlates of adaptation within an episode of binocular-rivalry suppression

Binocular rivalry occurs when an observer looks at two different monocular images. One of the images is alternately suppressed, invisible, while the other is dominant, visible. Models of binocular rivalry hold adaptation responsible for these changes in visual consciousness. Alais et al. (2010, Current Biology) showed psychophysically that depth of rivalry suppression declines within an episode of suppression, consistent with the effects of adaptation. Our aim was to find a neural marker for this decline in suppression depth. We used electroencephalography (EEG) to search for this neural marker. We induced binocular rivalry with dichoptically orthogonal sine-wave gratings. Participants pressed keys to record their perception of orientation. On each trial, we changed one of the gratings to be the same as the other, either to the currently suppressed or to the currently dominant stimulus. On different trials, we made the change at an individually adjusted short time (about 200 ms), medium time (about 700 ms), or long time (about 1200 ms) after the participant signalled a new percept. We found the earliest neural correlate of suppression about 100 ms after the stimulus change, with invisible changes yielding a smaller positive deflection (P1) than visible changes. The P1 difference was pronounced for the short and medium times, and almost abolished for the long time. The decline from short and medium times to the long time is consistent with the expected reduction in suppression depth with time in the suppression interval, and consistent with the psychophysical results. We conclude that we have shown a neural correlate of the adaptation leading to changes in visibility during binocular rivalry

Predicting binocular rivalry alternations from brain activity

When each eye views a different stimulus, visual perception alternates irregularly between them: binocular rivalry. One theory is that: reciprocal inhibition between neurons processing the two stimuli yields active (dominant) and suppressed neurons—we see the stimulus processed by active neurons; adaptation of active neurons eventually reverses activity—perception changes. We know that highly active neurons adapt faster than sluggishly active neurons. Hence, if we had some way of measuring the early activity of the active population, we could predict when a rivalry alternation will take place. We used electroencephalography (EEG) to measure brain activity to a 1000-ms display of dichoptic, orthogonally oriented, sine-wave gratings. Then we turned off both gratings for a 200-ms, dark gap, before showing the same rival gratings for another 1000 ms. We followed this by a mask then an inter-trial interval (ITI). Thirteen participants pressed keys during the ITI of numerous trials to say whether perception changed at the gap or not. Each participant also responded to numerous non-rivalry trials in which the gratings had identical orientations for the two eyes and for which the orientation of both either changed physically at the gap or did not. We found, with simple averaging (rather than requiring pattern classifiers), that greater activity about 180 ms after initial onset of rival stimuli predicted a change in perception more than 1000 ms later, after the gap. We conclude that the predictive activity is consistent with adaptation’s being responsible for binocular rivalry alternations