Investigating Perceptual Discrimination of Timing Cues in Synthetic Vocalizations in Rodents and Humans

Animals\u27 ability to understand and classify speech and non-speech vocalizations is highly robust, in spite of variations in tonal frequency composition (Belin et al., 2008; Shannon et al., 1995). This ability suggests that timing cues within any given sound envelope are important for discriminating such sounds. However, prior studies examining perceptual thresholds for discriminating timing cues often include tonal cues as well. In this study, we synthesized simple white noise sound burst sequences that contain the timing cues present in natural vocalizations sequences, but that are also devoid of underlying tonal cues. We then trained Long Evans rats and Humans utilizing a Two Alternative Forced Choice (2AFC) paradigm and tested their ability to discriminate these timing cues for long versus short duration sound burst sequences. Data demonstrates that rodents and humans can discriminate long versus short frequency sound burst sequences. We find that the average human subject (N=15) can perceptually discriminate sound bursts that differ by as little as 38ms. Furthermore, synthetic, smoothed square waves were constructed to determine if an additive advantage of onset slope and duration exists. Data expresses humans’ ability to discriminate short from long duration sound burst over the range of 100-200m using only plateau duration as a cue. Moreover, the use of a slower sound wave envelope onset slope enhanced discrimination. Our findings are consistent with the idea that sound integration time scales in auditory cortex determine these perceptual limits (Read et al., 2017, SFN abstract)