Abstract

Can the photochemical processes involved in light transduction perform linearly under extreme levels of illumination? The space between each outer segment disk appears to act as an independent transduction unit, and there are about 600 disks in human peripheral cones. Thus linearity would be expected up to levels of ~300 quanta absorbed per cone (50% of the independent processing units) within the cone response time (i.e., simultaneously). Beyond this level, increasing numbers of quanta must be processed simultaneously within each interdiscal space. We measured human light response properties at flux levels up to nine million quanta per cone per millisecond [15 million trolands (Td) incident on peripheral cones]. We used conditions in which brief flashes at this intensity were at psychophysical threshold: a 30′ field of 660 nm at 35° eccentricity with an equiluminant white surround. Temporal integration for pulses of different durations was measured in these conditions to determine the response linearity as stimulus duration was reduced. Complete linearity was obtained for durations down to 100 ps, where about one million quanta were absorbed at threshold (more than 1000 quanta absorbed for each outer segment disk).

© 1988 Optical Society of America