Fig. 7. Response of an M1 and an M2 type of movement detector neuron to the looming stimulus appearing from the right visual field. Traces exemplify individual responses from each neuronal type. The time of spike occurrence shown below the traces illustrates the consistency of the response for each neuron to nine presentations of the stimulus, separated by 1 min (the traces correspond to the last trial of these series). Peristimulus time histograms show the mean spike rate obtained from the nine trials. Data are divided into 100-ms bins and are plotted as means ± s.e.m. Angular size of the looming object is given in the lower traces of each panel. Arrowheads mark the beginning of the stimulus expansion; long arrows mark the moment at which the synaptic activity or the spike rate of neurons had clearly increased above resting level.