Differentiation of VEP intermodulation and second harmonic components by dichoptic, monocular, and binocular stimulation

Abstract

Modulation by two temporal frequencies differentiates visual processing at the fundamentals (lFs), second harmonics (2Fs), and second-order intermodulation components (IMCs), the latter created neurally as the sum or difference of the two modulation frequencies. Steady-state VEPs were recorded while stereo-normal adults viewed luminance or grating stimuli modulated by up to three temporal frequencies under dichoptic, monocular, or ordinary (binocular) viewing conditions arranged using liquid crystal light shutters. In Experiment 1, modulation of luminance by a single temporal frequency produced strong IF and 2F VEP components, but modulation of gratings produced only 2Fs. Modulation by two temporal frequencies resulted in IMCs, often in the absence of evoked activity in the EEG at the lFs. IMCs were generally larger during pattern as compared to luminance modulation. Amplitudes of lFs and IMCs were smaller, but 2Fs were larger, during dichoptic as compared to ordinary viewing. Although the 2F to a single modulation presented to one eye was not reduced when a second frequency was added to the opposite eye, monocular IMCs were diminished when a frequency was added to the opposite eye. We conclude that 2Fs and IMCs are associated with different neural substrates. Results are consistent with a two pathway model with one pathway having a nonlinear filter prior to binocular combination, the other pathway having a nonlinearity following binocular linear summation. Implications of these data for binocular function are discussed.

From Intermodulation Components to Perception and Cognition- a Review

“…First, they demonstrated how IMs provide a direct physiological measure of neural signal integration in the human brain. For example, several studies investigating early integration from both eyes demonstrated large differences in IM responses when the two eyes receive the same input (monoptic presentation), when only one eye receives input (monocular presentation) and when the two eyes receive different inputs (dichoptic presentation) (Suter et al, 1996) or, when comparing between healthy and stereoblind patients (Baitch and Levi, 1988). Second, they demonstrated how plausible their models of neural processes can be by examining the response spectrum across frequencies (including harmonics and high order IMs, as detailed above in the section 3.3) (Regan and Regan, 1988a).…”

Contrast Normalization Accounts for Binocular Interactions in Human Striate and Extra-striate Visual Cortex

“…In addition to self-term responses, the interaction between the two unique frequency components presented to each eye also evokes intermodulation (IM) terms (nF1 Ϯ mF2) (Baitch and Levi, 1988;Suter et al, 1996;Brown et al, 1999;Sutoyo and Srinivasan, 2009;Baker and Wade, 2017;Cunningham et al, 2017). The presence of such IM components constitutes objective neural evidence for interocular interaction (Brown et al, 1999; for review, see Norcia et al, 2015).…”

Disparity Tuning of Binocular Facilitation and Suppression after Normal versus Abnormal Visual Development

“…Other techniques use distinct temporal frequencies in each eye 12, 35, 37 . With these latter methods, responses of each eye are recorded simultaneously at harmonics of the respective eye-tagging frequencies and definitive evidence for binocular interaction can be obtained by detecting responses at frequencies equal to sums and difference of the eye-tag frequencies.…”