When an adapting shape and a test shape (backward masked) are presented briefly (e.g., 30 ms each) and in rapid succession (e.g., 200 ms ISI), global shape aftereffects occur in some basic geometric dimensions (e.g., skew, taper, curvature, convexity, and aspect ratio; Suzuki & Cavanagh, 1998, JEPHPP; Suzuki, 1999; 2000, ARVO). Recently, using overlapping outline shapes as adaptors, Suzuki (2001, Vision Research) reported that these shape aftereffects are strongly modulated by selective attention under appropriate conditions. In this study, the operational loci of this attentional selection were investigated by considering two distinct hypotheses. First, attention might linearly weight contour signals at an early stage of processing; signals from attended contours would receive a larger weight, whereas signals from ignored contours would receive a smaller weight - the early-contour-weighting hypothesis. Alternatively, attention might operate at the stage of (opponent) population coding of global shape attributes underlying shape aftereffects, such that attending to a particular shape attribute (e.g., a concave pattern) might primarily inhibit responses of neural units tuned to the opponent shape attribute (e.g., a convex pattern) - the opponent-shape-suppression hypothesis. These two hypotheses were contrasted by using pairs of overlapping adaptor shapes that were either opponent (producing opposite aftereffects) or non-opponent (producing orthogonal aftereffects). The results favored the early-contour-weighting hypothesis. Furthermore, the linear attention weights obtained (w[attended] - w[ignored] ∼ 60%), using shape aftereffects as the dependent measure, was comparable to those previously reported by Reynolds et al. (1999, J Neurosci), using responses of V4 neurons as the dependent measure, suggesting that attentional selection of an overlapping shape is potentially mediated by attentional modulations of neural activity through V4.
ASJC Scopus subject areas
- Sensory Systems