A Model for Enhancing the Visual InformationAvailable Under Low-Level Light Conditions:Multiple Contrast Channels Created by Stepwise Changesin Detector Parameters in the Banked Ventral Retina ofthe Firefly Squid
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概要
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The structure of a specialized portion of the ventral retina of the firefly squid (FSVR) is briefly compared with the 'normal' cephalopod retina and with the structurally related rhabdom-based retina of crustaceans. The accumulating evidence fulfilling the conditions required to demonstrate the presence in the FSVR of systems of colour vision (hue discrimination) and polarization sensitivity (e-vector discrimination) is briefly summarized. While some of the necessary conditions for both systems are fulfilled, sufficient proof for the functional existence of either is still lacking (although in Octopus there is sufficient evidence for functional polarization sensitivity). Experience with these systems in other animals suggests that, where a given visual unit (e.g. rhabdom) has photoreceptor cells which differ in both visual pigment wavelength absorption and polarization sensitivity, the information passed on to higher visual processing centres is based on only one of these qualitative parameters, thus avoiding errors in information transfer. An hypothesis is proposed which accounts for the apparently conflicting evidence for the simultaneous presence of both systems in the FSVR. It is argued that sensitivity to polarization patterns is probably the basic parameter for a system of contrast discrimination, which is enhanced by progressive shifts in detector parameters (wavelength of maximum sensitivity and/or directions of maximum sensitivity to the plane of polarization of light) in the deeper lying rhabdoms, optimizing sensitivity with regard to the screening effects of the overlying distal layers. This arrangement may represent an adaptation for maximizing information extraction from the limited quantity of environmental light available in the firefly squids' deep sea habitat.
- 東北大学の論文
- 1994-11-00