Interocular binding of chromatic signals across time

The temporal dynamics of visual processing depend on the properties of the stimulus being processed. Luminance, contrast, spatial frequency, and color all influence the speed of processing and the duration of temporal integration. But it is not well understood how the visual system combines complementary signals that, when isolated, are processed with different temporal dynamics. Are processing dynamics of the combination determined by the more rapidly or more sluggishly processed component, or by some compromise between them? Psychophysics and electrophysiology have established that S-cone signals are processed with longer delays and temporal integration periods than L-cone signals. Here, we use a classic visual illusion--the Pulfrich effect—to examine how L- and S-cone isolating signals are combined across time. Six observers viewed a dichoptically presented oscillating bar. One eye’s stimulus caused pure L-cone modulation. The other eye’s stimulus caused both L- and S-cone modulations, with S-cone contrasts that were titrated with condition. In two experiments, the tasks were to report the direction of motion and the orientation of the stimulus’ perceived trajectory in depth. Seven-level psychometric functions were measured. Observers perceived anomalous Pulfrich effects consistent with the L+S stimulus being processed with a longer delay, and with a longer temporal integration period. Processing delay and integration duration increased with the contrast of the S- cone component of combined stimulus. The anomalous Pulfrich effect, a consequence of different temporal integration periods in the two eyes, is characterized by a motion trajectory that appears oriented left- or right-side back from the true direction of motion (Chin & Burge, 2022). The present results demonstrate both that the combined signal is processed more sluggishly than its fastest constituent, and that interocular color differences spanning only a fraction of the full color gamut cause processing differences that can lead to substantial misperceptions of motion in depth.