Evidence for cognitive restoration of time-reversed speech by a language-trained chimpanzee (Pan troglodytes)

Previously, we reported on the ability of Panzee, a language-trained chimpanzee, to identify sine-wave and noise-vocoded speech by attending to the amplitude and frequency modulations in the altered signals. Here, we report on her ability to perceive phoneme-length information in words reproduced in time-reversed form. While this manipulation preserves the amplitude of frequency components, it reverses the pattern of energy changes within each reversal window. Listeners easily recognize speech at reversal windows up to 100-ms length, but at longer reversal lengths unintelligibility begins to occur (Saberi and Perrott, 1999). The theoretical interpretation is that individual phonetic segments range from 50 to 100 ms (Crystal and House, 1988), and reversal-windows less than 100 ms provide for restoration of phoneme perception. Hypothesizing that Panzee also perceives speech based on phonemic segments, we tested her and humans with words in eight reversal forms ranging from 25 to 200 ms. Results revealed tim...