Figure 4. Properties of Feature-Selectivity in the IC.

(a) The number of significant features each neuron is encoding shows that the majority of IC neurons in our sample were tuned for two or more spectrotemporal features of the stimulus, and only a minority of them (7%, 6/87) were tuned for a single feature that was equivalent to the STA. The remaining 81 neurons were significantly tuned for multiple features and their first feature was compared to the second in the subsequent panels. (b) Most of these features showed strong inseparability since they were usually tilted either upward or downward indicating a preference for the direction of frequency-modulated (FM) sweeps. The mean inseparability index for the first and second most informative features were both around 0.6 (n=81). (c,d) Direction-selectivity index for the first and second feature shows that they have different directional tuning. While the first feature is biased towards downward (negative) motion with a mean of −0.2, the second feature showed a bimodal distribution with a mean around zero. (e) Comparing direction-selectivity extracted from features of communication signals to selectivity for the direction of synthetic FM sweeps showed similarity to the selectivity observed in the first feature but not the second. Yet selectivity to sweeps had an even stronger bias for the downward direction with a mean of −0.3.