Origin of Perceptually Measured Phase Shifts in the Visual System

Abstract

De Lange (1958) first remarked that a pair of heterochromatic lights in temporal sinusoidal counterphase modulation show residual flicker after adjustment to the minimum flicker percept consistent with equiluminance. He used long wavelength (“red”) and mid wavelength (“green”) lights and suggested that the residual flicker could be cancelled by adjusting the relative physical phase of the “red” and “green” component lights. De Lange ascribed the phenomenon to a latency difference between the cones. The phase adjustment for minimal flicker required that the “green” light lead the “red” light at the heterochromatic transition. De Lange concluded that the long wavelength sensitive (LWS) cones had shorter latencies than the middle wavelength sensitive (MWS) cones. De Lange’s findings and subsequent data of Walraven & Leebeck (1964) and Vos & Walraven (1965) were subsequently attributed to rod intrusion in the flicker match and to a difference between rod and cone latencies rather than to latency differences between LWS and MWS cone types (von Grunau, 1977; van der Berg & Spekreijse, 1977). However, Cushman & Levinson (1983) working at high luminance levels and with high temporal frequencies were able to confirm the existence of residual flicker which could be cancelled by phase adjustment of one of the component lights. Their data also required a phase adjustment to “green” leads “red” at the heterochromatic transition. Thus they established that perceptual phase shifts can be mediated within LWS and MWS cone pathways.