Figure 9. OSDNs exhibited two types of luminance response in Manduca sexta: (1) what would be predicted based upon their response to an expanding and contracting disc, and (2) the opposite of what would be predicted. The traces above the response plots indicate the luminance of the stimulus, which was a 5 cm disc centered on the moth’s field of view. The response plots show spikes per second (calculated in 10 ms bins) plotted against time. (A) Two examples of OSDNs responding to a luminance test as would be predicted from their response to looming axis motion. Both units B and H responded to an expanding disc and increasing luminance. (B) Unit K responds to an expanding disc and decreasing luminance, while Unit N responds to a contracting disc and increasing luminance.