Polarization contrast and motion detection

The polarisation of light is used by many species of cephalopods and crustaceans to discriminate objects or to communicate. Most visual systems with this ability, such as that of the fiddler crab, include receptors with photopigments that are oriented horizontally and vertically relative to the outside world. Photoreceptors in such an orthogonal array are maximally sensitive to polarised light with the same fixed e-vector orientation. Using opponent neural connections, this two-channel system may produce a single value of polarisation contrast and, consequently, it may suffer from null points of discrimination. Stomatopod crustaceans use a different system for polarisation vision, comprising at least four types of polarisationsensitive photoreceptor arranged at 0, 45, 90 and 135 deg relative to each other, in conjunction with extensive rotational eye movements. This anatomical arrangement should not suffer from equivalent null points of discrimination. To test whether these two systems were vulnerable to null points, we presented the fiddler crab Uca heteropleura and the stomatopod Haptosquilla trispinosa with polarised looming stimuli on a modified LCD monitor. The fiddler crab was less sensitive to differences in the degree of polarised light when the e-vector was at −45 deg than when the e-vector was horizontal. In comparison, stomatopods showed no difference in sensitivity between the two stimulus types. The results suggest that fiddler crabs suffer from a null point of sensitivity, while stomatopods do not.

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Null point of discrimination in crustacean polarisation vision

How

Christy

Roberts

et al. 2014

“…(3) Earlier experiments with modified screens have shown that viewing angle and edge effects from the contour of the stimuli are two additional factors that can potentially give rise to secondary cues (Glantz and Schroeter, 2006;Hanke et al, 2013). Therefore, we standardized the viewing angle during the entire study by presenting the stimuli to the birds only when they were located directly in front of the screens, thus constraining the maximal horizontal and vertical viewing angles to about 10 and 24 deg, respectively.…”

Section: Exclusion Of Secondary Cuesmentioning

confidence: 99%

“…1). This allowed for controlled rotation of the direction of polarization without changing intensity or spectral composition (Glantz and Schroeter, 2006;Pignatelli et al, 2011;Hanke et al, 2013;Temple et al, 2012). Initially, the birds were trained to associate food rewards with visible stimuli to produce a generalized behavioural response to any stimulus shown on the screens.…”

Section: Introductionmentioning

confidence: 99%

No response to linear polarization cues in operant conditioning experiments with zebra finches

Melgar

Lind

Muheim

2015

Many animals can use the polarization of light in various behavioural contexts. Birds are well known to use information from the skylight polarization pattern for orientation and compass calibration. However, there are few controlled studies of polarization vision in birds, and the majority of them have not been successful in convincingly demonstrating polarization vision. We used a two-alternative forced choice conditioning approach to assess linear polarization vision in male zebra finches in the 'visible' spectral range (wavelengths >400 nm). The birds were trained to discriminate colour, brightness and polarization stimuli presented on either one of two LCD-screens. All birds were able to discriminate the colour and brightness stimuli, but they were unable to discriminate the polarization stimuli. Our results suggest that in the behavioural context studied here, zebra finches are not able to discriminate polarized light stimuli.

“…Lizards meeting learning criteria under white polarized light were then tested for orientation under plane-polarized light of different wavelengths. Plane-polarized light was produced and regulated by an LCD screen connected to a computer and dedicated software (Glantz and Schroeter, 2006). For the first time, an LCD system was used to study compass orientation behaviour in a terrestrial vertebrate (Parretta et al, 2011).…”

Section: Introductionmentioning

confidence: 99%

The lizard celestial compass detects linearly polarized light in the blue

Beltrami

Parretta

Petrucci

et al. 2012

SUMMARYThe present study first examined whether ruin lizards, Podarcis sicula, are able to orientate using plane-polarized light produced by an LCD screen. Ruin lizards were trained and tested indoors, inside a hexagonal Morris water maze positioned under an LCD screen producing white polarized light with a single E-vector, which provided an axial cue. White polarized light did not include wavelengths in the UV. Lizards orientated correctly either when tested with E-vector parallel to the training axis or after 90deg rotation of the E-vector direction, thus validating the apparatus. Further experiments examined whether there is a preferential region of the light spectrum to perceive the E-vector direction of polarized light. For this purpose, lizards reaching learning criteria under white polarized light were subdivided into four experimental groups. Each group was tested for orientation under a different spectrum of plane-polarized light (red, green, cyan and blue) with equalized photon flux density. Lizards tested under blue polarized light orientated correctly, whereas lizards tested under red polarized light were completely disoriented. Green polarized light was barely discernible by lizards, and thus insufficient for a correct functioning of their compass. When exposed to cyan polarized light, lizard orientation performances were optimal, indistinguishable from lizards detecting blue polarized light. Overall, the present results demonstrate that perception of linear polarization in the blue is necessary -and sufficient -for a proper functioning of the sky polarization compass of ruin lizards. This may be adaptively important, as detection of polarized light in the blue improves functioning of the polarization compass under cloudy skies, i.e. when the alternative celestial compass based on detection of the sun disk is rendered useless because the sun is obscured by clouds. Supplementary material available online at