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Mark Vergeer, Juraj Mesik, Yihwa Baek, Kelton Wilmerding, Stephen Engel; Contrast adaptation reduces SSVEP amplitude. Journal of Vision 2017;17(10):485. doi: 10.1167/17.10.485.
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© ARVO (1962-2015); The Authors (2016-present)
Contrast adaptation can dramatically alter neural response to the adapted orientation. However, measuring adaptation with EEG has proven challenging, as the large number of test presentations required can reduce the effects of adaptation. Here, we measured changes in neural response due to adaptation using steady-state evoked potentials (SSVEP) and a frequency tagging technique. Stimuli were presented on a head-mounted display and EEG signals were recorded using a dry electrode system. The test stimulus was a plaid consisting of horizontal and vertical gratings that reversed their contrast at different frequencies (6 and 15 Hz, respectively). A pilot experiment showed that increasing the contrast of the vertical grating in the test plaid, with the contrast of the horizontal grating fixed, produced a monotonic increase in occipital 15 Hz SSVEP amplitude. Next, eight volunteers performed the main experiment, in which they adapted to full-contrast vertical gratings, contrast reversing at 15 Hz. During each 1.5 sec trial, the test plaid was presented with 5% vertical contrast and 25% horizontal contrast. Trials were presented in blocks that began with 30 seconds of adaptation, and each trial was preceded by 6 seconds of "top-up" adaptation. A baseline recording session, preceding the adaptation session was identical, except it lacked presentation of the adapting gratings. Adaptation to vertical significantly reduced occipital response to the adapted orientation; amplitude of the 15 Hz response decreased by 62% from baseline, p < 0.05. Effects were orientation specific; response to the 6 Hz horizontal grating increased non-significantly in amplitude following adaptation, and the ratio of the two responses (15 Hz / 6 Hz) decreased significantly following adaptation (by 60%, p < 0.05). In demonstrating that contrast adaptation leads to a strong reduction in SSVEP response, these results highlight the potential of SSVEPs to powerfully address questions of visual plasticity.
Meeting abstract presented at VSS 2017
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