Abstract

Silent cone substitution was exploited by Estévez & Spekreijse¹ to measure presumed photoreceptor temporal modulation sensitivity. Kelly and van Norren² emphasized the role of higher-order neural elements sensitive to achromatic and chromatic modulation. We tested the Kelly and van Norren hypothesis using 556- and 642-nm stimuli. We first collected temporal MTF data for chromatic and achromatic sine—waves of time-average luminance 1256 td and chromaticity 595 nm. We defined silent M and silent L substitution in two ways: (1) We reduced peak modulation depth (642-nm LED for silent L and 556-nm LED for silent M) to maintain time-average luminance and chromaticity. (2) We reduced the luminance of the 642-nm LED for silent L (1047 td, 589.5 nm) and increased it for silent M (4358 td. 622 nm). We defined achromatic modulation as (L + M) and chromatic modulation as (L - kM), where L and M are the Smith-Pokomy fundamentals and k normalized the chromatic channel to the time average chromaticity. We calculated the residual modulation depth for the four silent conditions and used these values to weight the sine wave temporal MTFs. Silent L revealed chromatic processing; silent M revealed chromatic processing at low frequencies and achromatic processing at high frequencies.

© 1991 Optical Society of America