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N. Tsuchiya, G. Rees, J. Braun, C. Koch; Attentional modulation of visual motion perception using novel wavelet stimuli. Journal of Vision 2001;1(3):84. doi: 10.1167/1.3.84.
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We have previously characterized the effects of withdrawing attention on detection and discrimination of static visual stimuli (Lee et al. Nature Neuroscience 1998). Here we report attentional modulation of motion perception. A novel motion stimulus comprising spatiotemporally contrast-modulated Gabor wavelets was used to distinguish attentional effects on mechanisms sensitive to component motion from those sensitive to pattern motion (Schrater et al Nature Neuroscience 2000). Methods: Multiple moving wavelets were presented as a composite patch (1degree diameter) 4degrees away from fixation. Each wavelet had a random orientation and phase, and moved orthogonally to its orientation. A local wavelet mask of different orientation and contrast was superimposed on each target wavelet. This composite stimulus is expected to selectively activate component motion mechanisms located in primary visual cortex. A concurrent letter discrimination task presented at fixation was used to withdraw attention from the peripheral motion stimulus. 3 observers performed a 2AFC target detection task on the peripheral stimulus, while contrast and local direction of the mask wavelets was systematically manipulated. Results: Novel moving wavelet stimuli can be successfully used to characterize the effects of withdrawing attention on component-motion sensitive mechanisms. 1) Contrast increment thresholds for motion detection showed a ‘dipper’ function 2) Withdrawing attention led to elevation of motion detection thresholds that depended systematically on mask contrast but had little dependence on mask direction. 3) Motion detection thresholds with full attention (or without attention) were surprisingly similar whether the mask wavelets moved locally in either the same or opposite directions as the target.
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