Initial stages of visual information processing

点击翻译按钮获取中文摘要

I plan to work in three distinct but related areas:ITERATIVE-REENTRY MODEL. Advances in neuroscience have called attention to reentrant signalling as the main form of communication between brain regions connected by two-way pathways. Yet, theories of perception continue to be couched in feed-forward sequences. We have developed an alternative account in which perceptions are held to emerge from iterative exchanges between brain regions. That account emerged from the discovery of Object-Substitution Masking (OSM) in which an initial combined display of target and mask continues with the mask alone. The target is identified easily when all display elements terminate together. When the mask alone remains on view, masking occurs, with its strength increasing with the duration of the mask. OSM implicates reentrant processing because it cannot be explained on the basis of feed-forward processes alone. The main objective of the research programme is to explore systematically the perceptual domains in which iterative reentrant processes mediate visual perception, and how that mediation is modulated by the distribution of attention in space and time. These domains include the perception of form based on stimuli that are defined by luminance contours, by relative motion, by segregated texture, and by binocular disparity.EFFICIENCY OF VISUAL SEARCH DURING THE AB. Is the efficiency of visual search in “pop-out” displays, as indexed by the slope of the search function (reaction time over set size), modulated by attention? Earlier work sought to answer this question by presenting the search array while attention was depleted during the period of the AB. For various methodological reasons, that work failed to produce an unequivocal answer. For example, in one case, the search array that acted as the second target (T2) in the AB sequence remained on the screen until response, thus allowing the array to be searched with full attention after T1 had been processed. In another case, search efficiency could not be assessed because only a single set size was used. In a pilot study that avoided the flaws in the earlier work, I found that the efficiency of pop-out search, as indexed by the search slope, is impaired while attention is depleted during the AB. I will examine this finding with different types of search (feature, compound, conjunction search), and will pursue its implication that the establishment of a feature gradient (e.g., texture segmentation) requires attention.TEMPORAL INTEGRATION IN VISION. Quite some time ago, my then graduate student John Hogben and I devised a method of studying temporal integration in vision. Two halves of a dot-matrix pattern are displayed successively, separated by a blank inter-stimulus interval (ISI). Perceptual integration of the two halves deteriorates, and eventually breaks down, as the ISI is increased to 100 ms. In a pilot study, I varied the duration of the two halves of the pattern from 20 to 100 ms, and used a staircase threshold-tracking procedure (PEST) that adjusted the ISI dynamically so as to converge on a critical ISI that yielded an accuracy of 80%. I found that, at exposure durations beyond about 60 ms, a NEGATIVE ISI of up to 100 ms was required to achieve an accuracy of 80%. Namely, a pattern that was easily perceived when displayed briefly as a whole, was destroyed when it was preceded and followed by parts of itself. I plan to pursue this fascinating and counterintuitive finding.The first two projects will also involve the recording of event-related potentials to study the brain’s electrical activity triggered by various stimulus sequences. The ultimate objective is to encompass the results of all three projects within a comprehensive theory based on iterative reentrant processing.