Figure 4.
Membrane potential recorded in response to different-sized black targets (Weber contrast 1.0) drifted across against a bright background on an LCD screen along a trajectory that passed through the centre of the receptive field of a single photoreceptor from the fronto-dorsal acute zone in the eye of a male blowfly, Calliphora stygia. The drift velocity was 45° s−1. As predicted by the optical model, response peaks saturate for target sizes above 5°, and decline rapidly for targets below 1°. Data shown are the average of 40 trials (targets up to 1.5°) or 10 trials (target sizes >1.5°).