Responses to object approach by a wide field visual neurone, the LGMD2 of the locust: Characterization and image cues |
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Authors: | Peter J Simmons F Claire Rind |
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Institution: | (1) Department of Neurobiology, University of Newcastle upon Tyne, Newcastle upon Tyne, NE2 4HH, UK Fax: +44-191/222 5227 e-mail: P.J.Simmons@ncl.ac.uk, GB |
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Abstract: | The LGMD2 belongs to a group of giant movement-detecting neurones which have fan-shaped arbors in the lobula of the locust
optic lobe and respond to movements of objects. One of these neurones, the LGMD1, has been shown to respond directionally
to movements of objects in depth, generating vigorous, maintained spike discharges during object approach. Here we compare
the responses of the LGMD2 neurone with those of the LGMD1 to simulated movements of objects in depth and examine different
image cues which could allow the LGMD2 to distinguish approaching from receding objects. In the absence of stimulation, the
LGMD2 has a resting discharge of 10–40 spikes s−1 compared with <1 spike s−1 for the LGMD1. The most powerful excitatory stimulus for the LGMD2 is a dark object approaching the eye. Responses to approaching
objects are suppressed by wide field movements of the background. Unlike the LGMD1, the LGMD2 is not excited by the approach
of light objects; it specifically responds to movement of edges in the light to dark direction. Both neurones rely on the
same monocular image cues to distinguish approaching from receding objects: an increase in the velocity with which edges of
images travel over the eye; and an increase in the extent of edges in the image during approach.
Accepted: 23 October 1996 |
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Keywords: | Key words Vision Brain Insect Collision Intracellular |
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