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Leonardo Chelazzi
Department of Neurological and Vision Sciences, Section of Physiology, University of Verona – Medical School, Verona, ITALY
Wednesday 22 February 2006
16:00
Seminar Room B10 (Basement)
Alexandra House, 17 Queen Square, London, WC1N 3AR
Breaking down the unity of perceptual objects: Neural correlates of feature-selective attention in primate area V4
Psychologists and psychophysicists have distinguished two types of feature-based attention. A first type is engaged in visual search tasks any time feature information can be used to select one or multiple items across the visual array possessing a designated feature value (e.g., the red items), as proposed for instance by the Guided Search model of Wolfe and coworkers (Wolfe et al., 1989). An entirely different type of feature-based attention, perhaps more properly defined as feature-selective attention, is engaged when an observer must process one elemental feature of an object (e.g., its color) while other features of the same object (e.g., its shape and texture) must be actively ignored in order to eliminate potential conflict (e.g., Kanwisher et al., 1995; Fanini et al., in press; Nobre et al., in press). This second type of feature selective processing is tapped in a number of behavioral tests, including the Stroop test and the Wisconsin card-sorting test. The fundamental difference between the two types of feature-based attention is that only the latter requires that the perceptual unity of objects (or feature binding) be broken down by attention mechanisms in order to resolve potential conflict for perceptual decisions and behavioral control.
So far, such clear-cut distinction has not been made at the neurophysiological level. While a number of studies have begun to uncover the mechanisms underlying the former type of feature-based attention by measuring the activity of single neurons from extrastriate visual cortical areas of the behaving macaque (Motter, 1994; Treue and Martinez Trujillo, 1999; Martinez Trujillo and Treue, 2004; Bichot et al., 2005), no solid work so far has explored the second type of feature-based attention at the cellular level. In my talk I will review and discuss the results of a series of experiments conducted in my laboratory aimed at uncovering the neuronal mechanisms of feature-selective processing in area V4 of the macaque monkey.