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Abstract

Many animals use relative motion to segregate objects from their background [21, 26, 28, 31, 33]. Nerve cells tuned to this visual cue have been found in various animal groups, such as insects [3, 4, 6, 24, 25], amphibians [32], birds [12, 13] and mammals [1, 14]. Well examined examples are the figure detection (FD) cells in the visual system of the blowfly [6, 11]. The mechanism that tunes a particular FD-cell, the FD1-cell, to small-field motion is analyzed by injecting individual visual interneurons with a fluorescent dye and ablating them by illumination with a laser beam. In this way, it is shown that the FD1-cell acquires its specific spatial tuning by inhibitory input from an identified GABAergic cell, the ventral centrifugal horizontal (VCH)-cell which is most sensitive to coherent large-field motion in front of both eyes. For the first time, the detection of small objects by evaluation of their motion parallax, thus, can be attributed to synaptic interactions between identified neurons.