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Stephen Engel, Juraj Mesik, Mark Vergeer; Long-term contrast deprivation increases neural gain in early visual cortex. Journal of Vision 2018;18(10):765. doi: https://doi.org/10.1167/18.10.765.
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Prolonged exposure to a visual feature, such as a particular orientation or color, generally causes the visual system to adjust its sensitivity to the adapted feature. Such effects of visual adaptation have predominantly been investigated on short timescales of seconds to minutes. Recently, we reported perceptual effects of long-term adaptation, on a timescale of hours to days, using a deprivation paradigm. However, the neural bases of such effects remain unknown. Here we measured neural effects of long-term adaptation using steady-state visually evoked potentials (SSVEPs). Participants adapted to a visual environment that contained little to no vertical energy for a period of 4 hours. They wore a head-mounted display (HMD) with a video camera mounted on top. The video stream was filtered in real-time to remove vertical energy, and the filtered images were presented on the HMD. During EEG recordings, subjects viewed a test plaid comprised of a horizontal and a vertical grating, each contrast reversing at a different temporal frequency. In 90 test trials, 6 sec adaptation "top-up", using pre-recorded filtered natural video, was followed by a 2.5 sec test plaid presentation. Six dry electrodes integrated into the HMD recorded occipital SSVEPs. The FFT of the signal during each plaid presentation was computed, and the amplitude of the FFT at the two stimulus frequencies quantified the response to each component grating. Recordings were made after 3 minutes of adaptation and after 240 additional minutes in the visually deprived world. The average response amplitude for the vertical component increased after long-term adaptation, while no reliable change in response amplitude for the unadapted horizontal component was observed. These results indicate that long-term contrast deprivation increased neural response selectively for the deprived orientation. The gain changes likely arise in early visual cortex, which is the dominant source of SSVEP response to gratings.
Meeting abstract presented at VSS 2018
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