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M.D. Menz, M.K. Menz, E.E. Sutter; Orientation Specific Interocular Interactions measured with mfVEP . Invest. Ophthalmol. Vis. Sci. 2004;45(13):5484.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: To investigate interocular interactions of grating stimuli as a function of their relative orientation by evaluating the mutual kernel of the multifocal visually evoked potential (mfVEP) derived by means of dichoptic stimulation. Methods: The stimulus consisted of a single 5 degree patch with 0.5 degree achromatic bars presented dichoptically to each eye. The stimulus was placed either immediately above or below the fixation point. Each patch was contrast reversed according to a binary m–sequence using VERIS pro 5 software (EDI). Four combinations of orientations were used, parallel (i.e., both horizontal, both vertical) and two cross–orientations (one vertical, one horizontal). For each spatial configuration, responses to three different rates of pseudorandom pattern reversal were recorded, stimulus update after each video frame (base interval 13.3 ms) and update after 2 and 4 frames (base interval 26.6 ms and 40 ms). From the cortical response we extracted the self–kernel for each eye and the mutual kernel, which represents the nonlinear interocular interaction between the responses from the two eyes. Results: The size and shape of the mutual kernel varies considerably depending on the location of the stimulus patch, bar size, stimulation rate, electrode configuration, and subject. While interactions between simultaneous reversal in the two eyes were generally large, other components of the mutual kernel representing interactions between reversals one, two or more frames apart were negligible. The equal time interactions tend to have larger amplitudes and more complex, longer lasting waveforms as the stimulus is slowed down. The same holds for the self kernels of the two eyes which contain a very large induced component (effect of a reversal response on the immediately following response). As expected, the two cross–orientation conditions generally produce similar results in our normal subjects. The differences between the mutual kernels of the parallel and the cross–orientation conditions was found to be large in some cases but varied strongly between subjects, stimulus location and rate of stimulation. The differences were largest in the latter response components after about 100 ms. Conclusions: The picture that emerges suggests an unexpectedly complex interplay of self and mutual interactions between the inputs from the two eyes.
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