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Nestor Matthews; Bilateral superiority in detecting gabor targets among gabor distracters. Journal of Vision 2008;8(6):140. doi: https://doi.org/10.1167/8.6.140.
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Introduction: Previous research has suggested separate limited-capacity attentional tracking systems for the left and right visual hemifields (Alvarez & Cavanaugh, 2005). Evidence for this possibility comes from the finding that the ability to attentionally track three seconds of target-motion is significantly greater for bilateral than for unilateral stimuli (Alvarez & Cavanaugh, 2005). The present study addressed whether similar bilateral superiority occurs at much briefer stimulus durations ([[lt]]200 msec) when detecting briefly flashed Gabor targets. Method: Twenty-four Denison University undergraduates completed a 2x2 within-subject experiment in which the independent variables were laterality (bilateral versus unilateral) and Gabor distracter (present versus absent). Each trial began with a pair of either bilateral or unilateral attentional cues indicating the peripheral positions (12 deg from fixation) at which the Gabor targets (diagonal orientation, 183 msec) would appear, if present. In an attempt to overwhelm the neural resources dedicated to detecting Gabor targets in each lateral visual field, half of the trials (randomly) contained irrelevant Gabor distracters presented between the attentionally cued Gabor-target positions. After correctly identifying a foveally flashed letter that controlled fixation, participants judged whether Gabor targets had been present or absent at the attentionally cued positions. Results: When distracters were absent, bilateral and unilateral detection (d') were statistically indistinguishable (F(1,23)=1.29, p=0.268, n.s., partial eta squared = 0.053). By contrast, when distracters were present, detection (d') was significantly greater bilaterally than unilaterally (F(1,23)=23.266, p[[lt]]0.001, partial eta squared = 0.503). Discussion: Like the previous attentional-tracking data (Alvarez & Cavanaugh, 2005), the present distracter-dependent bilateral superiority in detection is consistent with independent capacity limits for the left and right visual hemifields. Because crowding effects and masking effects are distinguished by distracter-induced impairments in detection (Pelli, Palomares, & Majaj, 2004), the present distracter-induced reduction in unilateral detection is consistent with masking but not with crowding.
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