Initial stages of visual information processing

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ITERATIVE-REENTRY MODEL. Advances in neuroscience have pointed to reentrant signalling as the main form of communication between brain regions. Yet, theories of perception continue to be couched in feed-forward sequences. In our alternative account, perceptions emerge from iterative exchanges between brain regions. That account is based on Object-Substitution Masking (OSM) in which an initial combined display of target and mask continues with the mask alone. OSM implicates reentrant processing because it cannot be explained by 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: perception of form based on stimuli defined by luminance contours, relative motion, segregated texture, and binocular disparity. EXPLORING ******THE REJUVENATION EFFECT. The onset of a new object triggers a chain of processing events from sensory encoding to consolidation and memory storage. In contrast, the same object does not keep on being reprocessed if it remains on view beyond a critical duration. Instead, it causes signals to be sent to higher centres indicating that nothing of consequence has changed. I have found that the visual system can treat “old” objects as though they were “new” for a period of about 200 ms following a visual or auditory transient event. We refer to this as the rejuvenation effect, as it denotes a process by which old contours acquire some of the attributes of new contours. Further experiments have pointed to phasic activation of the Locus CoeruleusNorepinephrine (LC-NE) system as the determinant of rejuvenation. Many sets of experiments need to be done to explore this novel phenomenon.******TEMPORAL INTEGRATION IN VISION. To study temporal integration in vision, two halves of a dot-matrix are displayed successively, separated by an inter-stimulus interval (ISI). Integration deteriorates at ISIs beyond 100 ms. In a pilot study, I varied the duration of the two halves between 20 and 100 ms and found that at exposure durations beyond about 60 ms a NEGATIVE ISI 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. Main objective: to encompass all results in terms of iterative reentrant processing.*****