Purpose: We measured the chromatic impulse response function (IRF) of an isolated human S-cone pathway. In the last Fall Vision Meeting (2002), we described S-cone increment IRFs measured with bluish pulses (equi-luminous chromatic change to the bluish direction on each individual tritan line). In this research, we measured S-cone decrement IRFs using yellowish pulses, and compare quantitatively S-cone increment and decrement IRFs. Method: IRFs were derived from thresholds for a series of double-pulses in which the pulses were chromatically modulated at constant luminance (based on 18 Hz heterochromatic flicker photometry). Chromatic stimuli were presented as a Gaussian patch (+-1 SD = 2.3 deg) in one of four quadrants around a central fixation cross on a CRT screen. Each of the two pulses (6.67 ms) was separated by an interstimulus interval (ISI) from 20 to 360 ms. Chromaticity of the pulses was changed from the equal-energy white of the background to a bluish or yellowish color along individually determined tritan lines (based on color matching under strong S-cone adaptation from a 420 nm background superimposed in Maxwellian view). Chromatic detection thresholds were determined by a four-alternative forced-choice method with staircases for each ISI interleaved in each session. Measurements were repeated in at least four sessions for each observer. Results and Discussion: IRFs were calculated by varying four parameters of an exponentially-damped sinewave (Burr and Morrone, JOSA A 10, 1993). Both S-cone increment and decrement IRFs are characterized by a single excitatory phase and a much longer time course compared with luminous IRFs, which were measured using the same apparatus and observers(Shinomori and Werner, Vision Res. 43, 2003). S-cone decrement IRFs are much longer than S-cone decrement IRFs. The time to peak amplitude of S-cone decrement IRFs is about 100∼120 ms whereas the duration of S-cone increment IRFs is about 50∼70 ms.
- Impulse response
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