The Experts below are selected from a list of 18 Experts worldwide ranked by ideXlab platform
Daniel L. Schacter - One of the best experts on this subject based on the ideXlab platform.
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The nature of memory related activity in Early Visual Areas
Neuropsychologia, 2006Co-Authors: Scott D. Slotnick, Daniel L. SchacterAbstract:Memory for Visual items can evoke activity in Visual processing regions, which is typically assumed to reflect conscious remembering. However, based on previous findings, we hypothesized that such activity in Early Visual Areas (BA17, BA18) may reflect priming, a form of nonconscious memory. We tested this hypothesis in two fMRI experiments with similar stimulus protocols, but explicit or implicit task instructions. During initial runs, abstract shapes were presented to either side of fixation, filled with parallel lines of random orientation and color. In subsequent runs, old and new shapes (plus related shapes in Experiment 2) were presented at fixation. In Experiment 1, participants were instructed to remember each shape and its spatial location during initial runs; during subsequent runs they classified each shape as old and on the "left", old and on the "right", or "new". A right fusiform gyrus region (BA18) and a left lingual gyrus region (BA18) were preferentially associated with shapes previously presented on the left and right, respectively. In support of our hypothesis, this Early Visual Area activity was independent of response accuracy for spatial location. In Experiment 2, for each shape, participants identified parallel line orientation relative to horizontal. Consistent with our hypothesis, specific neural activity was observed in Early Visual regions (BA17, BA18, extending into BA19), with old activity greater than related and new activity (likely reflecting priming). The results of these experiments provide convergent evidence that memory related Early Visual Area activity (BA17, BA18) can reflect nonconscious processing.
Scott D. Slotnick - One of the best experts on this subject based on the ideXlab platform.
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The nature of memory related activity in Early Visual Areas
Neuropsychologia, 2006Co-Authors: Scott D. Slotnick, Daniel L. SchacterAbstract:Memory for Visual items can evoke activity in Visual processing regions, which is typically assumed to reflect conscious remembering. However, based on previous findings, we hypothesized that such activity in Early Visual Areas (BA17, BA18) may reflect priming, a form of nonconscious memory. We tested this hypothesis in two fMRI experiments with similar stimulus protocols, but explicit or implicit task instructions. During initial runs, abstract shapes were presented to either side of fixation, filled with parallel lines of random orientation and color. In subsequent runs, old and new shapes (plus related shapes in Experiment 2) were presented at fixation. In Experiment 1, participants were instructed to remember each shape and its spatial location during initial runs; during subsequent runs they classified each shape as old and on the "left", old and on the "right", or "new". A right fusiform gyrus region (BA18) and a left lingual gyrus region (BA18) were preferentially associated with shapes previously presented on the left and right, respectively. In support of our hypothesis, this Early Visual Area activity was independent of response accuracy for spatial location. In Experiment 2, for each shape, participants identified parallel line orientation relative to horizontal. Consistent with our hypothesis, specific neural activity was observed in Early Visual regions (BA17, BA18, extending into BA19), with old activity greater than related and new activity (likely reflecting priming). The results of these experiments provide convergent evidence that memory related Early Visual Area activity (BA17, BA18) can reflect nonconscious processing.
David C. Bradley - One of the best experts on this subject based on the ideXlab platform.
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Early Visual cortex: Smarter than you think
Current biology : CB, 2001Co-Authors: David C. BradleyAbstract:A recent study has provided elegant evidence that the Early Visual Area V2 plays an important role in image segmentation, piecing together parts of an object with the help of stereoscopic clues.
George Mather - One of the best experts on this subject based on the ideXlab platform.
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The neural basis of form and form-motion integration from static and dynamic translational Glass patterns: a rTMS investigation
NeuroImage, 2017Co-Authors: Andrea Pavan, Filippo Ghin, Rita Donato, Gianluca Campana, George MatherAbstract:A long-held view of the Visual system is that form and motion are independently analysed. However, there is physiological and psychophysical evidence of Early interaction in the processing of form and motion. In this study, we used a combination of Glass patterns (GPs) and repetitive Transcranial Magnetic Stimulation (rTMS) to investigate in human observers the neural mechanisms underlying form-motion integration. GPs consist of randomly distributed dot pairs (dipoles) that induce the percept of an oriented stimulus. GPs can be either static or dynamic. Dynamic GPs have both a form component (i.e., orientation) and a non-directional motion component along the orientation axis. GPs were presented in two temporal intervals and observers were asked to discriminate the temporal interval containing the most coherent GP. rTMS was delivered over Early Visual Area (V1/V2) and over Area V5/MT shortly after the presentation of the GP in each interval. The results showed that rTMS applied over Early Visual Areas affected the perception of static GPs, but the stimulation of Area V5/MT did not affect observers’ performance. On the other hand, rTMS was delivered over either V1/V2 or V5/MT strongly impaired the perception of dynamic GPs. These results suggest that Early Visual Areas seem to be involved in the processing of the spatial structure of GPs, and interfering with the extraction of the global spatial structure also affects the extraction of the motion component, possibly interfering with Early form-motion integration. However, Visual Area V5/MT is likely to be involved only in the processing of the motion component of dynamic GPs. These results suggest that motion and form cues may interact as Early as V1/V2.
Stephen A. Engel - One of the best experts on this subject based on the ideXlab platform.
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Perceptual Learning Increases the Strength of the Earliest Signals in Visual Cortex
The Journal of neuroscience : the official journal of the Society for Neuroscience, 2010Co-Authors: Min Bao, Lin Yang, Cristina Rios, Stephen A. EngelAbstract:Training improves performance on most Visual tasks. Such perceptual learning can modify how information is read out from, and represented in, later Visual Areas, but effects on Early Visual cortex are controversial. In particular, it remains unknown whether learning can reshape neural response properties in Early Visual Areas independent from feedback arising in later cortical Areas. Here, we tested whether learning can modify feedforward signals in Early Visual cortex as measured by the human electroencephalogram. Fourteen subjects were trained for >24 d to detect a diagonal grating pattern in one quadrant of the Visual field. Training improved performance, reducing the contrast needed for reliable detection, and also reliably increased the amplitude of the earliest component of the Visual evoked potential, the C1. Control orientations and locations showed smaller effects of training. Because the C1 arises rapidly and has a source in Early Visual cortex, our results suggest that learning can increase Early Visual Area response through local receptive field changes without feedback from later Areas.
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Activity in Visual Area V4 correlates with surface perception.
Journal of Vision, 2008Co-Authors: Seth E. Bouvier, Kristen S. Cardinal, Stephen A. EngelAbstract:The neural mechanisms responsible for unifying noncontiguous regions of a Visual image into a percept of a single surface remain largely unknown. To investigate these mechanisms, we used a novel stimulus in which local luminance was the only cue for surface segmentation. Subjects viewed an array of small adjoining elements that were randomly assigned as either surface or noise every 100 ms. On each trial, the luminance of surface elements was fixed to a single value and the luminance of noise elements was randomly assigned. As the ratio of surface to noise elements changed, subjects perceived either a surface embedded in noise or noise alone. In three functional magnetic resonance imaging (fMRI) experiments, Early Visual Area V1 responded most strongly during trials with a low surface-to-noise ratio while later Areas responded most strongly during trials with a high ratio. Furthermore, even at identical surface-to-noise ratios, responses in Area V4 were higher during trials in which the subject perceived a surface than during trials in which the subject did not. Early Visual Areas did not show this pattern. These results suggest that Visual Area V4 contains neurons critical for the representation of surfaces.
