Spontaneous pattern preferences of Drosophila melanogaster to black areas in various parts of the visual field

Abstract

Spontaneous preferences of freely moving, de-winged flies, Drosophila melanogaster, to rectangular black areas of varying pattern parameters were tested within a cylindrical white drum. The black, but not the white, areas cause spontaneous preferences of the flies. All three pattern parameters taken into account—the lower ( h 1) and upper ( h 2) limit as well as the width ( w) of the black area—contribute to the stimulatory value, which thus does not only depend on the size of the black area. The correlation, however, between the stimulatory value of the black area and one special pattern parameter (f.e. h 1) is not an invariant against variations of the other two stimulus parameters (f.e. h 2 and w). The stimulus values were separately tested for the black area and the vertical edges (contrast lines) of that area. With increasing height of a black stripe presented at the horizon, the maximum of the reaction frequency distribution shifts from the centre of the black area towards the contrast line. Black areas more than 30° in height receive maximal reaction frequencies at the edges when they are more than 180° wide. With decreasing width, the vertical contrast lines have to increase correspondingly in length in order to maintain a constant reaction frequency. From these findings two main conclusions can be drawn: (1) that the visual environment must be topologically represented within the visual system of the fly and (2) that different parts of the visual field are of unequal importance for pattern recognition. Referring to form perception, the visual system of Drosophila is not isotropic in function.