Intelligibility of time-reversed speech

Time-reversed speech has the same long-term amplitude spectrum as natural speech, but is largely unintelligible.
However, Saberi & Perrott ("Cognitive restoration of reversed speech," Nature 398: 760, 1999) recently showed that
local time reversal does not destroy intelligibility, if the time reversal window is brief. They divided everyday English
sentences into segments of fixed duration, and each segment was time reversed.  Near-perfect intelligibility was
found for windows less than 50 ms and performance declined progessively as the time reversal window length was
increased to 300 ms.

The effects of local time reversal are illustrated with audio examples below. The example is of a male voice saying
"The watchdog gave a warning growl." In each case the waveform of the sentence was divided into successive,
non-overlapping time-reversal windows of progressively longer duration: 0 ms (unaltered original),
10 ms, 20 ms, 50 ms, 100 ms, 250 ms, 500 ms, and in the final example, 1 second. The figure shows
the waveform of a time-reversed sentence using a 0-ms time reversal window (unaltered original, top);
a 1-s time reversal window (middle); and a 50-ms window (bottom).


              .WAV format                         .AU format




        Email: assmann@utdallas.edu
      Peter Assmann
      School of Human Development
      The University of Texas at Dallas, Richardson, Texas, 75083, USA
      Tel: (972) 883-2435
      FAX: (972) 883-2491