Stimulation with a temporally reversed echolocation sequence indicates a role of forward suppression shaping the time course of cortical responses.
(a) Stimulus oscillogram and raster plots of a unit stimulated in the ”natural situation” (top) and “reversed situation” (bottom). Colored stars signal to specific call-echo elements leading to weaker responses in the “natural” than in the “reversed situation”. (b) Contrast response curve of the same unit. The normalized PSTH in the “natural situation” was subtracted from the temporally-mirrored normalized PSTH of the “reversed situation”. Positive values indicate more spikes while negative ones less spikes in the “reversed” than in the “natural situation”. Stars indicate the starting point of the corresponding stimulus (black and white for ”natural” and “reversed situation”, respectively). Blue and red arrowheads indicate the time point of best response in the “reversed” and “natural situation”, respectively. Note that the best response temporally shifts by 346 ms between the two situations. (c) Color-map of contrast response curves from each unit (organized with decreasing best delays along the y-axis). (d) Median contrast response curve calculated from temporally aligned contrast response curves of each unit. Bins without changes (values = 0) were excluded. Response curves were aligned so that the best responses in the “natural situation” correspond to time point 0. Note that negative values are dominant before and positive values after the zero point. (e) Values from period 1 and period 2 in (d) have medians that are statistically different from 0 (Sign test; ***p < 10−5, n = 129) and are also different from each other (Mann-Whitney test; ***p < 10−5; n = 129). See also Supplementary Fig. 4.