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Brent R. Beutter, Miguel P. Eckstein, Leland S. Stone; Classification images reveal that saccades and perception use similar shape information in a visual search task.. Journal of Vision 2004;4(8):672. doi: 10.1167/4.8.672.
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Some researchers have suggested that action and perception are controlled by separate independent pathways (Goodale & Milner, 1992). Others have suggested that perception and voluntary eye movements rely on shared visual processing (Krauzlis & Stone, 1999). Here we investigate whether saccades and perception share visual processing of shape information by measuring classification images for both perceptual and eye-movement decisions in a visual search task. Methods: Two observers performed an 8-AFC contrast-discrimination search task. The target (contrast=18%) and distractors (contrast (15%) were blurred (8′) circles (radius 57′) presented equally spaced at an eccentricity of 5.8 deg with added external noise (gaussian, white, 24% rms contrast). The task was to locate the bright target circle among dimmer distractor circles. Classification images were computed by averaging the noise fields from all incorrect trials. In the saccadic condition (duration 4s), observers searched the display using eye movements. We defined the 1st saccadic 8-AFC decision as the element location nearest to the saccade's endpoint. In a separate perceptual condition, stimulus duration (117–150 ms) was chosen to match saccadic and perceptual processing times. Observers made an 8-AFC perceptual decision. Results: Saccadic and perceptual accuracies were similar (mean: 36 and 40%). The classification images show that both saccades and perception used shape information to perform the task. Both images had a circular excitatory region similar to the target, but also contained circular inhibitory surrounding regions suggesting that lateral inhibition contributed to the decisions. The radially-averaged images for saccades and perception were not significantly different (chi2 test, p > 0.05). Conclusion: The neural information driving search saccades can include relatively precise shape information. Furthermore, saccades and perception are guided by visual mechanisms with similar receptive fields.
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