Visual Discrimination of Pattern Orientation by Honeybees: Performance and Implications for `Cortical' Processing

The ability of honeybees (Apis mellifera) to discriminate pattern orientation was evaluated by examining their choice behaviour in a twin-choice Y-maze apparatus which offered two differently oriented patterns, one of which was associated with a reward. The distinctive feature of this experimental arrangement was that it forced the freely flying bees to choose between the two patterns at a distance, thus preventing the bees from fixating the patterns and discriminating between them on the basis of an eidetic (`photographic') image. Training and testing experiments using a number of different pairs of patterns, such as gratings, stripes and plaids, led to the following results: (i) bees perform well at discriminating the orientation of unidirectional patterns, such as single stripes or gratings; (ii) trained bees learn to prefer the orientation that is associated with the reward, as well as to avoid the unrewarded orientation; (iii) bees perform poorly at discriminating the orientation of right-angled crosses or plaids, but well at discriminating the orientation of 45 degrees crosses or plaids; and (iv) orientation discrimination appears to be mediated primarily by signals from the green-receptor channel of the bee's visual system. These findings, together with recent work (Srinivasan et al. Nature, Lond. 362, 539-540 (1993)), suggest that the honeybee's visual system analyses orientation in much the same manner as the mammalian cortex. Our data suggest the participation of at least three orientation-sensitive channels with different preferred orientations, and broad tuning curves with half-widths of ca. 90 degrees.