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Nestor Matthews, Jenna Kelly; Bilateral attentional advantage in Gabor detection. Journal of Vision 2009;9(8):214. doi: 10.1167/9.8.214.
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Introduction: In principle, visual performance could be uniform within (unilateral) and across (bilateral) the left and right hemifields. However, previous research has revealed bilateral advantages on relatively high level visual tasks, such as letter identification (Awh & Pashler, 2000; Chakravarthi & Cavanagh, 2006), and motion tracking (Alvarez & Cavanaugh, 2005). Last year we reported that this bilateral advantage extends even to the elementary task of detecting Gabor targets among Gabor distracters (Matthews, 2008). Here we investigated whether this bilateral superiority reflects attention or surround suppression. Method: Thirteen Denison University undergraduates completed a 2×2×3 within-subject experiment. The independent variables were laterality (bilateral versus unilateral), Gabor distracter (present versus absent), and foveal letter duration (67, 117, or 167 msec). Each trial began with a pair of bilateral or unilateral cues indicating the peripheral positions (14.55 deg diagonally from fixation) at which a Gabor target (183 msec) would appear, if present. Half the trials contained Gabor distracters horizontally or vertically displaced (by 7.1 deg) from the cued target positions. After correctly identifying a foveally flashed letter, participants judged whether a Gabor target had been present or absent at either cued peripheral position. Results: Peripheral Gabor detection (d') increased with foveal letter duration. At the briefest letter duration, false alarm rates were significantly higher unilaterally than bilaterally. This difference was more pronounced when distracters were present, and declined as foveal letter-duration increased. By contrast, bilateral and unilateral hit rates were statistically indistinguishable from each other across duration-by-distracter pairings. Discussion: The data indicate that a neural resource shared by the fovea and the periphery constrained performance. Relative to the bilateral response, the unilateral response exhibited a failure to exclude distracters -not a failure to detect contrast. This pattern implicates bilateral superiority in attention, even on this most elementary visual task.
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