Action spectrum of photomechanical cone contraction in the catfish retina.

The action spectrum for the photomechanical contraction of catfish single cones was found to fit the absorbance spectrum of the visual pigment they contain (determined by microspectrophotometry). This indicates that cone contraction is brought about by a direct effect of light on the cones themselves and not, as is the case for the epithelial pigment, by an indirect effect via the rods.