Scotopic and photopic components of the rat electroetinogram.

1. Increment thresholds were measured on the albino rat retina using the e.r.g. as an indicator of visual sensitivity.2. Light adaptation produces a change in b-wave spectral sensitivity independently of whether brief or steady adapting backgrounds are used. This shows that the changed spectral sensitivity is not directly associated with the bleaching of visual pigment.3. Light adaptation does not appear to alter the spectral sensitivity of the ordinary a-wave. Consequently, after light adaptation a- and b-waves have different spectral sensitivities.4. B-wave increments determined with a blue test stimulus on a red adaptive background show rod saturation. Background levels which saturate the rods cause the a-wave mechanism to cease responding to incremental stimuli.5. A background intense enough to saturate the rods evokes a maximum a-wave response. If a light is sufficiently bright to saturate the rods then the isolated a-wave fails to signal the termination of the stimulus.6. Scotopically equated blue and orange stimuli produce equal early receptor potentials.