Learned discrimination of pattern orientation in walking flies

To determine the pattern-orientation discrimination ability of blowflies, P haenicia sericata, a learning/memory assay was developed in which sucrose s erved as the reward stimulus and was paired with one of two visual gratings of different orientations. Individual, freely walking flies with clipped w ings were trained to discriminate between pairs of visual patterns presente d in the vertical plane. During training trials, individual flies learned t o search preferentially at the rewarded stimulus. In subsequent testing tri als, flies continued to exhibit a learned preference for the previously rew arded stimulus, demonstrating an ability to discriminate between the two vi sual cues. Flies learned to discriminate between horizontal and vertical gr atings, +45 degrees (relative to a 0 degrees vertical) and -45 degrees grat ings, and vertical and +5 degrees gratings. Individual patterns of learning and locomotive behavior mere observed in the pattern of exploration during training trials. The features of the visual cue critical for discriminatio n of orientation are discussed.