Computer-aided studies of vision in crabs

Abstract

A system for the back projection of computer-generated visual images onto a screen or screens that cover 240 of the horizontal visual field is described. Its applicability for the study of crab vision is tested by comparing the frequency response of the optokinetic response of the land crab, Cardisoma guanhumi, to sinusoidal oscillation of computer-generated striped patterns and a real striped drum. Significant differences were observed only at the low end of the frequency spectrum. The flexibility of computer-generated visual stimulation and its advantages for the study of optic flow are illustrated by experiments that: (a) demonstrate how well crabs separate the translational and rotational components of optic flow by showing compensatory eye movements to only the latter; (b) show that the ability to compensate for rotation is not impaired by combinations of rotation and translation; (c) show that motion parallax cues are used in addition to previously-described global cues for making the distinction between rotation and translation. Finally, the use of these methods in a successful search for visual interneurones sensitive to optic flow stimuli is demonstrated for the shore crab, Carcinus maenas.

Mechanisms of homing in the fiddler crabUca rapax2. Information sources and frame of reference for a path integration system

“…Yet free-walking crabs use eye movements to separate the rotational and translational components of optic flow, a necessary step in making its information content more available (Barnes, 1990;Paul et al, 1998). There are also visual interneurones within the crab optic tract specifically tuned to components of optic flow (Barnes et al, 2002). The evidence provided by this study that the rotational component of optic flow is involved in the maintenance of a straight course despite external influences is thus especially welcome.…”

Receptive-field structure of optic flow responsive Purkinje cells in the vestibulocerebellum of pigeons

“…RF mapping studies in the parietal cortex of primates and in optic flow neurons in invertebrate species have typically utilized relatively small stimuli moving throughout the visual field to map visually responsive areas~e.g., primates, Schaafsma & Duysens, 1996;Duhamel et al, 1997;Ben Hamed et al, 2001;Bremmer et al, 2002;Avillac et al, 2005;blowfly, Krapp & Hengstenberg, 1996;Krapp et al, 1998; shore crab, Barnes et al, 2002!. A larger stimulus was used in the present study, as small visual stimuli are not effective modulators of CSA in the VbC~Simpson & Alley, 1974!. Thus, to determine the local motion sensitivity and local preferred direction in different areas of the RFs of expansion, contraction, and rH45c neurons~simply referred to as rotation neurons hereafter!, 24 units were tested with a 45 deg ϫ 37.5 deg square-wave grating drifting in different subfields.…”

“…In the visual system of invertebrates, there are neurons responding to optic flow resulting from either self-rotation or self-translatioñ e.g., Krapp & Hengstenberg, 1996;Krapp et al, 1998;Barnes et al, 2002!. Like neurons in the AOS, pretectum, and VbC, these optic flow cells are responsible for generating the optokinetic Receptive-field structure in the pigeon vestibulocerebellum response~Hengstenberg, 1993;Simpson, 1984!. In blowflies and shore crabs, RF organization was assessed using intracellular recording in response to small moving visual stimuli~blowfly, Krapp & Hengstenberg, 1996;Krapp et al, 1998;crab, Barnes et al, 2002;Johnson et al, 2002!, and it was determined that the RFs are precisely tuned to the preferred optic flowfield. Comparison to the present study is rather tenuous due to very different recording conditions and stimuli.…”

Burrow surveillance in fiddler crabs II. The sensory cues

“…Krapp et al, 1998). Barnes et al (2002) have recently recorded from large-field interneurons in the crab lobula, the local directional motion sensitivities of which are arranged across the receptive field in such a way that they are likely to respond to translatory optic flow fields. However, in contrast to these examples, the neurones that we suggest to be involved in burrow surveillance in the fiddler crab should only respond to small objects and not to global image motion.…”