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Nestor Matthews, Kristin Cox; Bilateral and unilateral orientation dynamics. Journal of Vision 2007;7(9):589. doi: 10.1167/7.9.589.
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© ARVO (1962-2015); The Authors (2016-present)
Introduction: Previous studies have suggested that additional neural processing time may be needed for comparisons across the vertical midline than for comparisons restricted to either lateral hemi-field (Wilson, Blake & Lee, 2001; Ringo, Doty, Demeter & Simard, 1994 ) Here, we compared bilateral and unilateral orientation discrimination to determine the extent to which orientation judgments exhibit an inter-hemispheric cost. Method: Nine participants completed a 2á2 within subject experiment in which the independent variables were laterality and stimulus duration. On each trial, one of 15 randomly generated letters was presented foveally for 192 msec while two diagonally oriented gabor patches were flashed either unilaterally or bilaterally for either 83 or 183 msec. Randomly across trials, the gabor patches were either identically or orthoganlly oriented. The letter stimuli and the gabor patches were followed by visual masks to limit neural persistence. If the foveally presented letter was correctly identified, the participant judged the orientation of the peripherally presented gabor patches as either the ‘same’ or ‘different’. Results: A 2á2 within-subject ANOVA revealed a significant main effect of stimulus duration. Specifically, orientation sensitivity was significantly greater at 183 msec than at 83 msec (p [[lt]] 0.01). Neither the main effect of laterality nor the laterality-by-duration interaction was significant. Discussion: The present orientation-discrimination data are consistent with the previous finding that there is no cost associated with inter-hemispheric comparisons on a distal misalignment task (Pillow & Rubin, 2002). It may be that an inter-hemispheric cost was not present here because the orientation task did not require low-level grouping. Other studies requiring low-level grouping have shown a within-hemi-field advantage (Pillow & Rubin, 2002; Butcher & Cavanagh, 2004). Finally, the present data on peripheral orientation discrimination extend previous work that similarly demonstrated duration-related improvements in foveal orientation discrimination for masked stimuli (Strong, Kurosawa & Matthews, 2006).
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