Fig. 3. The response of V1 neurone to stimulation of the ocelli (A-C) and compound eyes (D-F) before (blue curves) and after (red curves) cauterisation of the ocellar nerve. The coloured curves show instantaneous spike rates (ISRs) averaged over 563 trials, and overlay extracellular recordings of V1's spike activity during a single trial. (A) ISR and representative recording before cauterising the ocellar nerve (scale bar, 15 µV). The grey shading indicates variability of ISR, ±1 s.e.m. The baseline of the extracellular recording indicates the mean spontaneous spike rate. (B) Stimulus presented to the right and left lateral ocelli. LED intensity difference=(left LED output-right LED output); I_max, max LED output. The dots show illumination switching between left and right ocelli as the LED intensity difference switches from I_max to -I_max. (C) Greatly reduced activity in V1 after cauterising the ocellar nerve, traces as in A. (D) ISR recorded in response to compound eye stimulation before cauterisation of the ocellar nerve. Traces as in A and C, but variability (±1 s.e.m.) is shown as a white band against the background of recorded spikes. (E) Compound eye stimulus: a horizontal sinusoidal grating (spatial frequency=0.63 cycles deg.^-1) moving in V1's preferred direction, vertically downwards at 40 deg. s^-1. Grating contrast was progressively increased over each trial to drive V1 over its full range of spike rate. (F) Response to compound eye stimulus after cauterisation of the ocellar nerve. The complete set of experiments was performed with five animals, giving a total of 563 trials for each stimulus protocol.