Society for Experimental Biology Annual Main Meeting 6th – 10th July 2008, Marseille, France A9 — NEUROBIOLOGY POSTER SESSION A9.1 Varying the sign and gain of optomotor feedback provides insights into mechanisms of course control in walking land crabs, Cardisoma guanhumi J. Barnes (University of Glasgow); M. Macauley (University of Glasgow); J. Neidhardt (University of Applied Sciences, Bremen); J. Layne (University of Cincinnati) This study used a walking compensator consisting of a hollow styrofoam ball supported on a cushion of air. The crab, held above the ball, is unable to rotate or translate, but instead moves the ball under its feet. Visual stimuli, mimicking rotational optic flow, are generated by computers and projected onto two screens that cover 240° of the crab's visual field. Optical computer mice monitor movements of the ball about all three axes, and the signals from ball rotation about a vertical axis are fed back to the computers generating visual stimuli. In this way, the visual consequences of turns can be fed back to the visual system, with experimenter control of gain and sign. Eye movements are recorded using a capacitative position-sensing device. This apparatus was used to analyse the control systems that govern both optomotor body turns, used in course control, and compensatory eye movements. Results demonstrate that the optomotor system has a high gain and long time constant. Thus, responses to sinusoidal visual inputs with positive rather than negative feedback do not, as might be expected, simply generate body turns in the opposite direction to the visual input. Instead, they are dominated by the direction of turning that the crab initially makes, so that the turning movement is unidirectional and no longer follows the sinusoidal component of the visual input. Modelling such responses using Simulink (a Matlab package) allows us to test different models of the control system. doi:10.1016/j.cbpa.2008.04.306 Comparative Biochemistry and Physiology, Part A 150 (2008) S130 Contents lists available at ScienceDirect Comparative Biochemistry and Physiology, Part A journal homepage: www.elsevier.com/locate/cbpa

Varying the sign and gain of optomotor feedback provides insights into mechanisms of course control in walking land crabs, Cardisoma guanhumi

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Page 1: Varying the sign and gain of optomotor feedback provides insights into mechanisms of course control in walking land crabs, Cardisoma guanhumi

Comparative Biochemistry and Physiology, Part A 150 (2008) S130

Contents lists available at ScienceDirect

Comparative Biochemistry and Physiology, Part A

j ourna l homepage: www.e lsev ie r.com/ locate /cbpa

Society for Experimental Biology Annual Main Meeting6th – 10th July 2008, Marseille, France

A9 — NEUROBIOLOGY POSTER SESSION

A9.1Varying the sign and gain of optomotor feedback provides insightsinto mechanisms of course control in walking land crabs,Cardisoma guanhumi

J. Barnes (University of Glasgow); M. Macauley (University ofGlasgow); J. Neidhardt (University of Applied Sciences, Bremen);J. Layne (University of Cincinnati)

This study used a walking compensator consisting of a hollowstyrofoam ball supported on a cushion of air. The crab, held above theball, is unable to rotate or translate, but instead moves the ball underits feet. Visual stimuli, mimicking rotational optic flow, are generatedby computers and projected onto two screens that cover 240° of thecrab's visual field. Optical computer mice monitor movements of theball about all three axes, and the signals from ball rotation about avertical axis are fed back to the computers generating visual stimuli. In

this way, the visual consequences of turns can be fed back to the visualsystem, with experimenter control of gain and sign. Eye movementsare recorded using a capacitative position-sensing device. Thisapparatus was used to analyse the control systems that govern bothoptomotor body turns, used in course control, and compensatory eyemovements. Results demonstrate that the optomotor system has ahigh gain and long time constant. Thus, responses to sinusoidal visualinputs with positive rather than negative feedback do not, as might beexpected, simply generate body turns in the opposite direction to thevisual input. Instead, they are dominated by the direction of turningthat the crab initially makes, so that the turning movement isunidirectional and no longer follows the sinusoidal component of thevisual input. Modelling such responses using Simulink (a Matlabpackage) allows us to test different models of the control system.

doi:10.1016/j.cbpa.2008.04.306

http://dx.doi.org/10.1016/j.cbpa.2008.04.306

http://www.sciencedirect.com/science/journal/10956433