Topography of vision and behaviour

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SUMMARYHabituation is an active process that allows animals to learn to identify repeated, harmless events, and so could help individuals deal with the trade-off between reducing the risk of predation and minimizing escape costs. Safe habituation requires an accurate distinction between dangerous and harmless events, but in natural environments such an assessment is challenging because sensory information is often noisy and limited. What, then, comprises the information animals use to recognize objects that they have previously learned to be harmless? We tested whether the fiddler crab Uca vomeris distinguishes objects purely by their sensory signature or whether identification also involves more complex attributes such as the direction from which an object approaches. We found that crabs habituated their escape responses after repeated presentations of a dummy predator consistently approaching from the same compass direction. Females habituated both movement towards the burrow and descent into the burrow, whereas males only habituated descent into the burrow. The crabs were more likely to respond again when a physically identical dummy approached them from a new compass direction. The crabs distinguished between the two dummies even though both dummies were visible for the entire duration of the experiment and there was no difference in the timing of the dummiesʼ movements. Thus, the position or approach direction of a dummy encodes important information that allows animals to identify an event and habituate to it. These results argue against the traditional notion that habituation is a simple, nonassociative learning process, and instead suggest that habituation is very selective and uses information to distinguish between objects that is not available from the sensory signature of the object itself.

Section: Discussionmentioning

confidence: 67%

Habituation under natural conditions: model predators are distinguished by approach direction

Raderschall

Magrath

Hemmi

2011

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“…Another possibility is that the results demonstrate an actual difference in the behavioural sensitivity of these two animal groups to polarised cues. Fiddler crabs are known to respond to very weak intensity cues in the dorsal part of the visual field, corresponding to the retinal position of small avian predators such as terns (Smolka and Hemmi, 2009;Smolka et al, 2011;Smolka et al, 2013). Given that polarisation is likely to act as a contrast enhancer for the intensity channel, it would seem logical that these animals should also respond well to small differences in polarised light.…”

Section: Research Articlementioning

confidence: 99%

Null point of discrimination in crustacean polarisation vision

How

Christy

Roberts

et al. 2014

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.

“…they see an oscillating change in object luminance) rather than reacting to the dummies' internal motion. This result is not surprising considering the crabs' visual acuity (Smolka and Hemmi, 2009). At typical response distances, dummies only occupied a visual angle of approximately 0.6 to 2.3deg (at approximately 4 and 1m, respectively).…”

Section: Flicker As a Response Cuementioning

confidence: 62%

Flicker is part of a multi-cue response criterion in fiddler crab predator avoidance

Smolka

Raderschall

Hemmi

2012

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SUMMARYPredator avoidance behaviour costs time, energy and opportunities, and prey animals need to balance these costs with the risk of predation. The decisions necessary to strike this balance are often based on information that is inherently imperfect and incomplete because of the limited sensory capabilities of prey animals. Our knowledge, however, about how prey animals solve the challenging task of restricting their responses to the most dangerous stimuli in their environment is very limited. Using dummy predators, we examined the contribution of visual flicker to the predator avoidance response of the fiddler crab Uca vomeris. The results illustrate that crabs let purely black or purely white dummies approach significantly closer than black-andwhite flickering dummies. We show that this effect complements other factors that modulate escape timing such as retinal speed and the crabʼs distance to its burrow, and is therefore not due exclusively to an earlier detection of the flickering signal. By combining and adjusting a range of imperfect response criteria in a way that relates to actual threats in their natural environment, prey animals may be able to measure risk and adjust their responses more efficiently, even under difficult or noisy sensory conditions.