Wide-field direction-selective neurones from the optic lobes of the butterfly Papilio aegeus show some properties similar to those displayed by the large neurones of the fly lobula plate. Temporal and spatial frequency threshold tuning curves show that butterfly optic lobe neurones sensitive to different directions of image motion are fed by presynaptic subunits similar to those of the fly. However, unlike fly lobula plate neurones, the butterfly optic lobe neurones show a steep low-spatial-frequency roll-off which persists even at high temporal frequencies. Also exceptional is the temporal resolution of rapid changes in image speed by the butterfly neurones. When the cells are adapted to continuous motion their responses indicate a further increase in temporal resolution. Evidence is provided that in any one state of adaptation the neurones may be thought of as piece-wise linear and, thus, their responses can be predicted by convolution with a velocity kernel measured for that adaptation state. Adaptation to continuous motion results in the cells responding to motion in proportion to the mean motion signal. Motion in the non-preferred direction also appears to adapt the cells. Velocity impulse responses of both butterfly and blowfly neurones were determined with one-dimensional gratings and two-dimensional textured patterns and the results for the two stimuli are shown to be very similar.

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