Abstract
Many crustaceans are sensitive to the polarization of light and use this information for object-based visually guided behaviors. For these tasks, it is unknown whether polarization and intensity information are integrated into a single-contrast channel, whereby polarization directly contributes to perceived intensity, or whether they are processed separately and in parallel. Using a novel type of visual display that allowed polarization and intensity properties of visual stimuli to be adjusted independently and simultaneously, we conducted behavioral experiments with fiddler crabs to test which of these two models of visual processing occurs. We found that, for a loom detection task, fiddler crabs process polarization and intensity information independently and in parallel. The crab's response depended on whichever contrast was the most salient. By contributing independent measures of visual contrast, polarization and intensity provide a greater range of detectable contrast information for the receiver, increasing the chance of detecting a potential threat.
Highlights
Many animals, including insects, cephalopods, fish, and crustaceans, are sensitive to the polarization of light
If polarization and intensity information are processed within either a single channel or parallel channels, several predictions can be made about the probability of an individual responding to a controlled stimulus that comprises both intensity and polarization
A patterned vertical alignment type liquid crystal display (PVA-LCD) was modified by removing the front polarizer to control the degree of polarization of transmitted light
Summary
Many animals, including insects, cephalopods, fish, and crustaceans, are sensitive to the polarization of light. The most common of these photoreceptor arrangements, which has been converged upon by at least two evolutionary lineages (arthropods and cephalopods) and forms the focus of this study, is the dipolat system, a two-channel arrangement in which photoreceptors are oriented perpendicularly to each other. In this system, an intensity-independent measure of polarization contrast may be produced through opponent processing between these two polarization-sensitive channels [6, 7]. Dipolatic receptor arrangements have been found in the image-forming eyes of many animals including insects [8,9,10], cephalopods [11], and crustaceans [12, 13]
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