Photometry in goldfish by electrophysiological recording: Comparison of criterion response method with heterochromatic flicker photometry

Abstract

In everyday vision the eye commonly functions while its state of adaptation is continuously changing rather than being held constant as in most scientific studies. We measured spectral luminosity curves for goldfish by recording ERG and tectal evoked response. Continuously changing the state of adaptation had a large effect at tectal level, but comparatively little at ERG level. With changing adaptation the relation between light intensity and response amplitude showed gross hysteresis and nonlinearity at tectal level. This was not so marked at ERG level, and not at all at either level when adaptation was not changing. The widely-used criterion response method showed severe limitations when adaptation was changing. Heterochromatic flicker photometry was a more accurate, and considerably more sensitive (0.01 log unit) way of measuring the spectral luminosity curve. ERG and TER gave similar luminosity curves. These curves did not depend on flicker frequency (2.5–20 Hz), adaptation level (over 2.0 log units) or harmonic component. The luminosity curve was fitted by absorption spectra for cone photopigments: the red pigment dominated, and the blue contribution was negligible.