AN AC CONSTANT-RESPONSE METHOD FOR ELECTROPHYSIOLOGICAL MEASUREMENTS OF SPECTRAL SENSITIVITY FUNCTIONS

A number of methods have been used in the past to measure spectral sen sitivity (S(lambda)) functions of electric responses in the visual sys tem. We present here a microcomputer-based, AC, constant-response meth od for automatic on-line measurement of S(lambda) in cells with or wit hout a sustained tonic response. It is based on feedback adjustment of light intensity to obtain constant peak-to-peak amplitudes of respons e to a flickering stimulus as the spectrum is scanned between 300 and 700 nm in 4 nm steps. It combines the advantages of: (1) on-line prese ntation of S(lambda) curves; (2) constant light adaptation; (3) sampli ng of many points; and (4) fast data collection time. The system can b e applied to sensitivity or threshold (e.g., S(lambda), dark adaptatio n, receptive field) measurements of any electrically recorded visual r esponse.