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Darren Cunningham, Daniel Baker, Jonathan Peirce; Measuring Selective Responses to Coherent Plaids Using the Intermodulation Term. Journal of Vision 2016;16(12):304. doi: 10.1167/16.12.304.
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© 2017 Association for Research in Vision and Ophthalmology.
The visual system combines information that is propagated from the retina in order to generate a coherent percept of the environment. While much is known about how primary visual cortical mechanisms encode for low-level image features, relatively little is known about how this encoded information is then processed by mid-level mechanisms. By frequency tagging the components of a stimulus at different temporal frequencies and measuring steady-state visual evoked potentials (SSVEPs), we can examine the individual responses to each of the components at their fundamental component frequencies as well as various nonlinear interactions. Responses at the intermodulation frequencies (the sum and difference of the component frequencies) indicate nonlinearities at or after the point of combination. These can arise from either suppressive effects or combination effects such as AND responses to the compound. We have used the multi-component frequency-tagging technique to study responses to the combination of gratings into various plaid patterns. We combined two components (1cpd and 3cpd, respectively) into orthogonal plaid patterns with either matched spatial frequencies ('coherent' plaids) or non-matched ('non-coherent' plaids). Grating components were simultaneously flickered at different frequencies (2.3Hz, 3.75Hz) resulting in fundamental component-based responses at these frequencies, as well as intermodulation responses at their difference (1.45Hz) and sum (6.05Hz). The nonlinearities generated in response to the gratings and plaids were investigated by comparing several response frequencies. These included the component frequencies, the first-order intermodulation responses, and the various harmonic responses associated with these. The technique provides a rich set of data that we can investigate with a family of computational models. From this we can determine how the various nonlinearities (suppressive, additive etc.) contribute towards different response patterns. In particular, the harmonic of the sum intermodulation frequency appears in this case to differentiate second-order mechanisms from suppressive interactions in V1.
Meeting abstract presented at VSS 2016
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