Abstract
The impulse response function (IRF) means a response of entire visual system measured by a psychophysical method. As we reported in the FVM 2003, IRFs for S-cone increments in excitation were slower than for luminance modulation, but faster than IRFs for S-cone decrements. In this research, we measured IRFs possibly reflecting interactions between these putative pathways with one bluish pulse and one yellowish pulse. 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 HFP) along individually determined tritan lines from an equal-energy white background. Chromatic stimuli were presented as a Gaussian patch (SD = 2.3 degree) in one of four quadrants around a central fixation cross on a CRT screen (a 4AFC method). When S-cone increments and decrements were combined in a pulse pair, there was an interaction that resulted in a threshold reduction. This is consistent with model assumptions that flash interactions between increments and decrements result from the same response to the first flash as obtained under isochromatic conditions, plus a (weaker) response component in the opposite polarity with a time delay. Model analysis indicated that S-cone increment IRFs are faster than S-cone decrement IRF (in terms of the time of peak amplitude and delay for the other polarity phase).
This work was supported by a National Institute of Health grant (NIA AG04058) to J.S. Werner and Graduate School Sophistication Special Promotion Support by the Promotion and Mutual Aid Corporation for Private Schools of Japan to K. Shinomori. We would like to thank Susan Garcia for help collecting the data.