Behavioral signatures of Y-like neuronal responses in human vision

Abstract

Retinal ganglion cells (RGCs) initiating the magnocellular/Y-cell visual pathways are distinguished by responding nonlinearly to high spatial frequencies (SFs) and temporal frequencies (TFs). This nonlinearity is implicated in the processing of contrast modulation (CM) stimuli in cats and monkeys, but its contribution to human visual perception is not well understood. Here we formulated an approach to reveal the function of human Y-like RGCs by leveraging the Y-like carrier response properties of cortical neurons to CM stimuli consisting of a high SF contrast-reversing grating carrier whose contrast is modulated by a low SF drifting sinewave envelope. Subjects reported the direction of motion of CM envelopes or luminance modulation (LM) gratings, presented at different eccentricities. The dependence of task performance on SF (for LMs) or carrier SF (for CMs) was measured for different TFs (LMs) or carrier TFs (CMs). The best performance for LM stimuli was at lower TFs and SFs, which decreased systematically with eccentricity. However, performance with CM stimuli was bandpass with carrier SF, largely independent of carrier TF, and at the highest carrier TF (20 Hz) decreased minimally with eccentricity. Since the nonlinear subunits of Y-cells respond better at higher TFs compared to the linear response components, and respond best at higher SFs that are relatively independent of eccentricity, these results suggest that behavioral tasks employing CM stimuli with high spatiotemporal carrier frequencies can reveal the nonlinear contributions of retinal Y-like cells to human perception.