Visual properties of the crustacean eye

Abstract

Four aspects of the crustacean visual system are investigated:1. the molecular basis of polarized light sensitivity. Discrete transient membrane potentials (bumps) were recorded from retinula cells of a crab, in response to single polarized photons. An analysis of bump rates versus the E-vector of the polarized light stimulus reveals that the rhabdomere's dichroism accounts for the photoreceptor's sensitivity to polarized light.2. The mechanism underlying the shore crab's ability to perceive slow movement, The temporal properties of the photoreceptor were characterized, establishing that the photoreceptors are not sluggish. The results indicate higher-order neural specialization accounts for the crab's resolution of slow movement. 3. The absolute sensitivity of an apposition type of compound eye. A behavioural study of the optokinetic response demonstrated an absolute-intensity threshold considerably better than previous theoretical estimates. The experimental finding provide the first definitive proof that na animal possessing a compound eye can see a star, contrary to widely accepted views that compound eyes are a poor device for the detection of point sources.4. Visual adaptation to a dark two-dimensional world. An electrophysiological and behavioural study of the Ghost crab eye illustrated the selective pressure a narrow visual ecological niche can make on eye design. The findings reveal a fundamental strategy employing oversampling and higher-order spatial summation of photoreceptor signals to overcome the problems associated with dim light vision.