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Elise Piazza, Michael Silver; The time course of hemispheric asymmetries in perceptual selection of spatial frequency information. Journal of Vision 2011;11(11):307. doi: 10.1167/11.11.307.
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© ARVO (1962-2015); The Authors (2016-present)
Structural and functional differences between the brain's two hemispheres result in asymmetries in sensory processing. The Double Filtering by Frequency (DFF) theory (Ivry & Robertson, 1998) proposes two sequential stages of spatial and temporal frequency information processing. First, a subset of task-relevant frequencies is selected from the environment. Second, these frequencies are divided asymmetrically such that the right hemisphere processes relatively lower frequencies more efficiently and the left hemisphere preferentially processes relatively higher frequencies. Support for this theory comes primarily from measurements of reaction times to individual stimuli. Thus, it remains unclear whether this hemispheric asymmetry applies to perceptual selection from multiple stimuli containing a range of frequencies. In addition, the precise time course of the proposed two-stage filtering process has not been empirically assessed. We used binocular rivalry to measure perceptual selection of spatial frequencies from among competing alternatives over time. In binocular rivalry, conflicting images presented to the two eyes result in a perceptual alternation between the images. During each 30-second trial, subjects viewed two rivaling orthogonal gratings, one with a spatial frequency of 1 cyc/deg and the other with 3 cyc/deg, and they continuously reported which of the grating orientations they perceived. Trials were blocked based on whether the rivalrous gratings were presented to the left or right visual hemifield. At the onset of stimulus presentation, subjects were more likely to perceptually select (i.e., report seeing) the lower spatial frequency grating in the left hemifield (right hemisphere) condition, and they were more likely to select the higher spatial frequency grating in the right hemifield condition. These results support the DFF theory. However, this interaction of spatial frequency and hemisphere dissipated after the first few seconds of viewing, suggesting that perceptual selection is initially asymmetric but that over time, the two hemispheres transition into more symmetric processing.
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