Orientation discrimination independent of retinal matching by blowflies

Blowflies, Phaenicia sericata, can be trained to discriminate in a learning paradigm in which one of the two visual cues is positively rewarded. Retin otopic matching of a learned visual image to the same retinal location from viewing to viewing has been hypothesized to underlie visual pattern learni ng and memory in insects. To address the theory of retinotopic matching, a detailed analysis was made of the flies' body orientations during learned d iscriminations between +45 degrees and -45 degrees gratings. Initial approa ches to the positive rewarded visual cue did not originate from the same sp atial location within the behavioral arena with respect to the visual cues; thus, individual flies approached the positive cue from a different vantag e point from trial to trial. During initial approaches to the rewarded visu al cue, the distributions of body angles with respect to the cue were diffe rent from trial to trial for each individual. These data suggest that Phaen icia sericata can learn a visual pattern with one eye region and later reco gnize the same pattern with another eye region. Thus, retinotopic matching is not necessary for the recognition of pattern orientation in the experime ntal paradigm used here. The average amount of head turning in the yaw plan e was too small to compensate for the changes in body orientation exhibited by the flies. Flies view the visual patterns with distinct retinal regions from trial to trial during orientation discrimination.