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Eva Chadnova, Alexandre Reynaud, Simon Clavagnier, Robert Hess; Dichoptic imbalance of luminance affects the phase component of steady-state MEG signals. Journal of Vision 2016;16(12):433. doi: 10.1167/16.12.433.
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© ARVO (1962-2015); The Authors (2016-present)
Interocular interaction in a normal visual system occur under dichoptic conditions when contrast and luminance are imbalanced between the eyes. Psychophysically such interaction are well described by a contrast normalization model. However the neural processing underlying such interactions within the visual cortex are still unclear. We set to investigate how an interocular imbalance in contrast or luminance affects visual processing. We used magnetoencephalography to record SSVEP and fMRI to obtain individual retinotopic maps that we used for source computation for each participant. Monocular and dichoptic stimuli (binary noise patterns) were frequency-tagged at 4 and 6 Hz (contrast modulated) and presented at a range of contrasts from 0 to 32%. Monocularly, we reduced the luminance by placing a 1.5 ND filter over one eye in the maximal contrast condition. We used amplitude component of SSVEP averaged per region of interest to describe monocular responses and dichoptic interaction. Phase component (phase angle and its variance) of the strongest vertex per region of interest was used to obtain the temporal estimate of the response. Monotonic increase in SSVEP amplitude reflected the experimental change in contrast from 0 to 32% in V1, V2, V3 and V4. Interocular suppression was seen in both eyes as a decrease in SSVEP amplitude and was well approximated by the normalization model (r2 =0.9). Reducing the mean luminance delayed monocular processing by approximately 35 ms across the areas of interest and increased phase variance. A dramatic increase in phase variance was observed in dichoptic condition for a monocular reduction in luminance. Delaying monocular input also increased suppression from the fellow-fixing eye to the delayed filtered eye and a release of suppression was seen in the opposite direction. Temporally filtering the monocular input prior to binocular combination stage of the normalization model provided a good fit to our experimental data.
Meeting abstract presented at VSS 2016
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