Local mechanisms for the separation of optic flow-field components in the land crab, Cardisoma guanhumi: A role for motion parallax?

• Published in: Visual neuroscience Vol. 21; no. 6; pp. 905 - 911
• Main Authors: JOHNSON, AARON P., BARNES, W. JON. P., MACAULEY, MARTIN W.S.
• Format: Journal Article
• Language: English
• Published: New York, USA Cambridge University Press 01.11.2004
• Subjects: Adaptation, Physiological; Animals; Biochemistry. Physiology. Immunology; Biological and medical sciences; Brachyura - physiology; Cardisoma guanhumi; Computer-generated visual images; Contrast Sensitivity - physiology; Crab; Crustacea; Cues; Decapoda; Eye Movements; Eyes & eyesight; Fundamental and applied biological sciences. Psychology; Invertebrates; Light; Motion parallax; Motor Activity - physiology; Optic flow; Optokinetic responses; Photic Stimulation - methods; Physiology. Development; Retina; Rotation; Studies; Velocity; Vision Disparity - physiology; Vision, Ocular - physiology; Crab; Computer-generated visual images; Optic flow; Motion parallax; Optokinetic responses; Translation; Contrast; Rotation; Optokinetic response; Crustacea; Visual stimulus; Arthropoda; Parallax; Invertebrata; Optical flow
• ISSN: 0952-5238; 1469-8714
• DOI: 10.1017/S0952523804216108

Although a number of global mechanisms have been proposed over the years that explain how crabs might separate the rotational and translational components of their optic flow field, there has been no evidence to date that local mechanisms such as motion parallax are used in this separation. We describe here a study that takes advantage of a recently developed suite of computer-generated visual stimuli that creates a three-dimensional world surrounding the crab in which we can simulate translational and rotational optic flow. We show that, while motion parallax is not the only mechanism used in flow-field separation, it does play a role in the recognition of translational optic flow fields in that, under conditions of low overall light intensity and low contrast ratio when crabs find the distinction between rotation and translation harder, smaller eye movements occur in response to translation when motion parallax cues are present than when they are absent. Thus, motion parallax is one of many cues that crabs use to separate rotational and translational optic flow by showing compensatory eye movements to only the former.