Grant: Discovery Grants Program - Individual

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 Coeruleus-Norepinephrine (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.