Abstract
ABSTRACTStomatopods have an extraordinary visual system, incorporating independent movement of their eyes in all three degrees of rotational freedom. In this work, we demonstrate that in the peacock mantis shrimp, Odontodactylus scyllarus, the level of ocular independence is task dependent. During gaze stabilization in the context of optokinesis, there is weak but significant correlation between the left and right eyes in the yaw degree of rotational freedom, but not in pitch and torsion. When one eye is completely occluded, the uncovered eye does not drive the covered eye during gaze stabilization. However, occluding one eye does significantly affect the uncovered eye, lowering its gaze stabilization performance. There is a lateral asymmetry, with the magnitude of the effect depending on the eye (left or right) combined with the direction of motion of the visual field. In contrast, during a startle saccade, the uncovered eye does drive a covered eye. Such disparate levels of independence between the two eyes suggest that responses to individual visual tasks are likely to follow different neural pathways.
Highlights
It is not unusual for animals to have eyes that move independently of one another
We investigated the extent to which the two eyes of the peacock mantis shrimp, Odontodactylus scyllarus, are independent in each degree of rotational freedom, and whether the level of independence depends on the type of visual task
The median relative velocity ratio during the slow phase of optokinesis across both eyes was Sy=0.87±0.18, demonstrating good gaze stabilization performance
Summary
It is not unusual for animals to have eyes that move independently of one another. Chameleons are perhaps the most famous example (Tauber and Atkin, 1967), but there are examples of ocular independence in teleost fish (Land, 1999a; Pettigrew et al, 1999; Fritsches and Marshall, 2002), reptiles (Pettigrew et al, 1999) and crustaceans (Land et al, 1990; Cronin and Marshall, 2001), to name but a few. A chameleon’s eyes will behave independently whilst surveying its general surroundings, but during tracking or ocular pursuit of a target, the two eyes can become yoked together to display conjugate eye movements (Katz et al, 2015). The eyes of the pipefish Corythoichthyes intestinalis show disconjugate movement during scene surveying, yet the two eyes move conjugately during gaze stabilization (Fritsches and Marshall, 2002). The sandlance Limnichthyes fasciatus has eyes that are apparently completely independent, even during gaze stabilization (Fritsches and Marshall, 2002)
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