Contextual modulation in human vision

Increased visual task difficulty enhances attentional capture by both visual and auditory distractor stimuli

A visual stimulus can be made invisible, i.e. masked, by the presentation of a second stimulus. In the sensory cortex, neural responses to a masked stimulus are suppressed, yet how this suppression comes about is still debated. Inhibitory models explain masking by asserting that the mask exerts an inhibitory influence on the responses of a neuron evoked by the target. However, other models argue that the masking interferes with recurrent or reentrant processing. Using computer modeling, we show that surround inhibition evoked by ON and OFF responses to the mask suppresses the responses to a briefly presented stimulus in forward and backward masking paradigms. Our model results resemble several previously described psychophysical and neurophysiological findings in perceptual masking experiments and are in line with earlier theoretical descriptions of masking. We suggest that precise spatiotemporal influence of surround inhibition is relevant for visual detection.

Whole brain event-related functional magnetic resonance imaging (fMRI) techniques were employed to elucidate the cerebral sites involved in processing rare target and novel visual stimuli during an oddball discrimination task. The analyses of the hemodynamic response to the visual target stimuli revealed a distributed network of neural sources in anterior and posterior cingulate, inferior and middle frontal gyrus, bilateral parietal lobules, anterior superior temporal gyrus, amygdala, and thalamus. The analyses of the hemodynamic response for the visual novel stimuli revealed an extensive network of neural activations in occipital lobes and posterior temporal lobes, bilateral parietal lobules, and lateral frontal cortex. The hemodynamic response associated with processing target and novel stimuli in the visual modality were also compared with data from an analogous study in the auditory modality ( Kiehl et al., 2001 ). Similar patterns of activation were observed for target and novel stimuli in both modalities, but there were some significant differences. The results support the hypothesis that target detection and novelty processing are associated with neural activation in widespread neural areas, suggesting that the brain seems to adopt a strategy of activating many potentially useful brain regions despite the low probability that these brain regions are necessary for task performance.

Perception Matches Selectivity in the Human Anterior Color Center

A moving visual field can induce the feeling of self-motion or vection. Illusory motion from static repeated asymmetric patterns creates a compelling visual motion stimulus, but it is unclear if such illusory motion can induce a feeling of self-motion or alter self-motion perception. In these experiments, human subjects reported the perceived direction of self-motion for sway translation and yaw rotation at the end of a period of viewing set visual stimuli coordinated with varying inertial stimuli. This tested the hypothesis that illusory visual motion would influence self-motion perception in the horizontal plane. Trials were arranged into 5 blocks based on stimulus type: moving star field with yaw rotation, moving star field with sway translation, illusory motion with yaw, illusory motion with sway, and static arrows with sway. Static arrows were used to evaluate the effect of cognitive suggestion on self-motion perception. Each trial had a control condition; the illusory motion controls were altered versions of the experimental image, which removed the illusory motion effect. For the moving visual stimulus, controls were carried out in a dark room. With the arrow visual stimulus, controls were a gray screen. In blocks containing a visual stimulus there was an 8s viewing interval with the inertial stimulus occurring over the final 1s. This allowed measurement of the visual illusion perception using objective methods. When no visual stimulus was present, only the 1s motion stimulus was presented. Eight women and five men (mean age 37) participated. To assess for a shift in self-motion perception, the effect of each visual stimulus on the self-motion stimulus (cm/s) at which subjects were equally likely to report motion in either direction was measured. Significant effects were seen for moving star fields for both translation (p = 0.001) and rotation (p<0.001), and arrows (p = 0.02). For the visual motion stimuli, inertial motion perception was shifted in the direction consistent with the visual stimulus. Arrows had a small effect on self-motion perception driven by a minority of subjects. There was no significant effect of illusory motion on self-motion perception for either translation or rotation (p>0.1 for both). Thus, although a true moving visual field can induce self-motion, results of this study show that illusory motion does not.

Decision letter: Visual and motor signatures of locomotion dynamically shape a population code for feature detection in Drosophila

Categorical perception was first demonstrated in studies of speech sounds (Liberman, Harris, Hoffman, & Griffith, 1957). The present work employed visual stimuli to explore categorical responding in relation to the context in which the stimuli were embedded. The target stimulus was a vertical line whose length was varied from 20 to 31 min (approximately) in steps of 1.2 min. Experiment 1 examined the effect of a geometrical context on the subjects' ability to discriminate between pairs of lines. The context improved performance, but produced no evidence of categorical responding. In Experiment 2 a graphemic context depressed performance, but failed to show clear evidence of categorization. By contrast, strong evidence of categorical responding was obtained in Experiment 3, in which the graphemes used in Experiment 2 were embedded in meaningful words. From this pattern of results it is argued that categorical responding is reflective not of relatively peripheral perceptual activity, but of higher-order decision processes.

The perceived duration of a target visual stimulus is shorter when a brief non-target visual stimulus precedes and trails the target than when it appears alone. This time compression requires spatiotemporal proximity of the target and non-target stimuli, which is one of the perceptual grouping rules. The present study examined whether and how another grouping rule, stimulus (dis)similarity, modulated this effect. In Experiment 1, time compression occurred only when the preceding and trailing stimuli (black-white checkerboard) were dissimilar from the target (unfilled round or triangle)with spatiotemporal proximity. Incontrast, it was reduced when the preceding or trailing stimuli (filled rounds or triangles) were similar to the target. Experiment 2 revealed time compression with dissimilar stimuli, independent of the intensity or saliency of thetarget and non-target stimuli. Experiment 3 replicated the findings of Experiment 1 by manipulating the luminance similarity between target and non-target stimuli. Furthermore, time dilation occurred when the non-target stimuli were indistinguishable from the target stimuli. These results indicate that stimulus dissimilarity with spatiotemporal proximity induces time compression, whereas stimulus similarity with spatiotemporal proximity does not. These findings werediscussed in relation to the neural readout model.

Perceptual organization concerns the organization of people’s perception into meaningful, structured entities—often wholes containing parts, with specific interrelationships among the parts as well as specific relationships between the parts and the wholes. It embraces a wide variety of distinct processes, which often occur together in everyday life and lead to interesting perceptual experiences by their interactions. The best-known perceptual organization processes are perceptual grouping and figure-ground organization, which appear to be determined by characteristic principles or laws, such as grouping by proximity, similarity, good continuation, area, convexity, symmetry, and so forth. Other important phenomena of perceptual organization include perceptual multi-stability (i.e., the fact that the same stimulus can give rise to multiple competing percepts that switch over time), visual illusions, the role of reference frames, and the role of context. Gestalt psychology has contributed deep insights into the way people’s perception of the world is organized, although it has also been criticized for its emphasis on subjective experiences and its sometimes vague and non-quantitative descriptions of the Gestalt principles. Because perceptual organization essentially concerns visual awareness, however, phenomenology is needed to describe what is experienced. This ultimately remains the basis for research on perceptual organization even when it is aimed at quantifying the principles of perceptual organization and identifying the neural correlates or mechanisms underlying perceptual organization.

Previous research indicates that people respond fastest when the motor response is (spatially, functionally, anatomically, or otherwise) congruent to the visual stimulus. This effect, called ideomotor compatibility, is thought to be expressed in motor areas. Congruence occurs when the stimulus and response share some dimensions in their internal representations. If the ideomotor compatibility hypothesis were true, we would expect facilitation when right hand stimuli are presented to the left hemisphere, or left hand stimuli are presented to the right hemisphere. To address this issue, we conducted a simple reaction time experiment with lateralized targets. Participants were instructed to press a button as soon as a target was observed. The target stimulus was a left hand, a right hand, or a neutral control. Each hemisphere showed faster responses to contralateral hand stimuli as compared with ipsilateral hand stimuli, consistent with the ideomotor compatibility hypothesis. The results support an automatic and implicit processing of visual stimuli within motor representations even when no recognition of, or decision about, the stimulus is necessary.

Using wavelet analysis of the signals of electrical brain activity (EEG), we study the processes of neural activity, associated with perception of visual stimuli. We demonstrate that the brain can process visual stimuli in two scenarios: (i) perception is characterized by destruction of the alpha-waves and increase in the high-frequency (beta) activity, (ii) the beta-rhythm is not well pronounced, while the alpha-wave energy remains unchanged. The special experiments show that the motivation factor initiates the first scenario, explained by the increasing alertness. Based on the obtained results we build the brain-computer interface and demonstrate how the degree of the alertness can be estimated and controlled in real experiment.

Event Abstract Back to Event Changes of oscillatory activity during visual oddball task (SEEG study) Robert Roman1*, Milan Brázdil2, J. Chládek3, P. Jurák3, Ivan Rektor2 and M. Kukleta1 1 Department of Physiology, Medical Faculty, Masaryk University, Czechia 2 Department of Neurology, St. Anne Hospital, Masaryk University, Czechia 3 Institute of Scientific Instruments, Academy of Sciences, Czechia Objectives: To study intracerebral distribution and frequency spectrum of event-related desynchronization (ERD) and synchronization (ERS) recorded during discrimination task. Methods: EEG was recorded from 187 cerebral sites in 6 patients suffering from intractable epilepsy during visual oddball task. Patients were instructed to respond only to the target stimulus by pressing the microswitch button. The intertrial variance method of quantification of ERD and ERS was used separately for target and frequent stimuli in individually selected reactive frequency bands (in the theta, alfa, beta and gamma range). Results: ERD and ERS were observed both after target and frequent stimuli repeatedly in the amygdala, hippocampus, parahippocampal gyrus, cingulate gyrus, fusiform gyrus, rectus gyrus, orbitofrontal gyri, superior and middle temporal gyri, middle and inferior frontal gyri. ERD after target stimuli was found in 139 sites – 91 cases in alfa, 69 cases in theta, 86 cases in beta and 15 cases in gamma band. ERS was observed in 86 sites – 42 cases in alfa, 37 cases in theta, 42 cases in beta and 17 cases in gamma band. ERD after frequent stimuli was present in 53 sites – 21 cases in alfa, 9 cases in theta, 23 cases in beta and 5 cases in gamma band. ERS was found in 63 sites – 24 cases in alfa, 9 cases in theta, 39 cases in beta and 4 cases in gamma band. Conclusion: Widespread distribution of decreased and increased oscillatory activity in different frequency bands shows the complexity of neural networks involved in cognitive processing of visual stimuli. More frequent finding of ERD phenomena after target stimuli might probably reflect the enhanced information processing related to the executive functions. Conference: 10th International Conference on Cognitive Neuroscience, Bodrum, Turkey, 1 Sep - 5 Sep, 2008. Presentation Type: Poster Presentation Topic: Brain Electrical Oscillations in Cognition Citation: Roman R, Brázdil M, Chládek J, Jurák P, Rektor I and Kukleta M (2008). Changes of oscillatory activity during visual oddball task (SEEG study). Conference Abstract: 10th International Conference on Cognitive Neuroscience. doi: 10.3389/conf.neuro.09.2009.01.141 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 05 Dec 2008; Published Online: 05 Dec 2008. * Correspondence: Robert Roman, Department of Physiology, Medical Faculty, Masaryk University, Brno, Czechia, roman@med.muni.cz Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Robert Roman Milan Brázdil J. Chládek P. Jurák Ivan Rektor M. Kukleta Google Robert Roman Milan Brázdil J. Chládek P. Jurák Ivan Rektor M. Kukleta Google Scholar Robert Roman Milan Brázdil J. Chládek P. Jurák Ivan Rektor M. Kukleta PubMed Robert Roman Milan Brázdil J. Chládek P. Jurák Ivan Rektor M. Kukleta Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

In contradiction to the crossing of all retinal fibers in the lateral-eye species, the retinal fibers of binocular vision in frontal-eye species run either ipsilaterally or cross the midline twice to terminate the ipsilateral cerebral hemisphere.[1][1] It is hypothesized that carrying separated

Modality-specific subregions in human inferior parietal lobule: a magnetoencephalographic study during cognitive tasks

Individual differences in arithmetic ability reflected in the ERP pattern