Title Effects of spectral and temporal disruption on cortical encoding of gerbil vocalizations Running Head Slow envelopes dominate vocalization encoding in AI Authors

2 3 Animal communication sounds contain spectrotemporal fluctuations which provide 4 powerful cues for detection and discrimination. Human perception of speech is 5 influenced both by spectral and temporal acoustic features, but is most critically 6 dependent on envelope information. To investigate the neural coding principles 7 underlying the perception of communication sounds, we explored the effect of disrupting 8 the spectral or temporal content of 5 different gerbil call types on neural responses in the 9 awake gerbil's primary auditory cortex (AI). The vocalizations were impoverished 10 spectrally by reduction to 4 or 16 channels of band-passed noise. For this acoustic 11 manipulation, a neuron's average firing rate did not carry sufficient information to 12 distinguish between call types. In contrast, the discharge patterns of individual AI 13 neurons reliably categorized vocalizations composed of only 4 spectral bands with the 14 appropriate natural token. The pooled responses of small populations of AI cells 15 classified spectrally disrupted and natural calls with an accuracy that paralleled human 16 performance on an analogous speech task. To assess whether discharge pattern was 17 robust to temporal perturbations of an individual call, vocalizations were disrupted by 18 time-reversing segments of variable duration. For this acoustic manipulation, cortical 19 neurons were relatively insensitive to short reversal lengths. Consistent with human 20 perception of speech, these results indicate that the stable representation of 21 communication sounds in AI is more dependent on sensitivity to slow temporal 22 envelopes than on spectral detail.