Properties of elementary movement detectors in the flyCalliphora erythrocephala

Summary

Experiments, involving sequential micro-stimulation of two (or more) adjacent neuroommatidia in the compound eye of the blowfly,Calliphora erythrocephala (Mg.), are presented. These experiments, using brief flashes of 3 ms duration with low intensities in the order of 8·10⁻³ Cd/m², are performed to isolate individual response contributions of single Elementary Movement Detectors in the input micro-circuitry of the motion-sensitive directionally-selective H1-neuron (Figs. 4 through 6). A two-dimensional mapping of single EMD contributions to the overall response will be presented for the dark adapted eye (Fig. 7). It is concluded that under such low illumination levels (when compared to normal daylight situations, where illumination typically varies between 1 and 200 Cd/m²), contributions from EMD's with sampling bases up to 8Δ φ _h, oriented along the horizontal sensitivity axis of the neuron, contribute to the total response of the neuron. In addition, results will be presented for similar experiments, in which various backgrounds with different sizes and intensities are superimposed on the sequence of stimulus flashes (Fig. 8). The dependence of the relative contributions for the smallest four sampling bases (i.e. 2, ..., 8 timesΔ φ _h) on background size, background intensity and distance of the background field to the projections of the flashes, will be discussed. Supplementary experiments (Figs. 9 through 12) will be presented, which indicate that when in addition to an ongoing sequence in (for instance) the null direction, thus inhibiting the activity of the neuron, a second sequence is presented somewhere in the receptive field of the H1-neuron, the total response is a non-linear combination of both individual responses. Interpretation in terms of a pooling correlation scheme, which, over a limited target region, sums the activities of the EMD's in a highly non-linear fashion, provides a qualitative explanation.