AIRS 1st Annual Meeting: 2009

Title: The speech-to-song illusion: experimental evidence
Authors: Simone Falk (Ludwid-Maximilians-Universitat, Germany), Tamara Rathcke

Abstract

We are exploring the boundaries of speech and song in an acoustic-perceptive perspective. We
investigate a musical illusion first described by Diana Deutsch (1995, Deutsch et al. 2008). In this
"speech-to-song illusion" a phrase read by Diana Deutsch shifts to be heard as sung without
changing any acoustic characteristics of the signal. This illusion is achieved by simply repeating
the phrase several times in exactly the same way. As far as we know, the effect was found only
with this single phrase as piece of evidence. We assume that some acoustic characteristics of this
read phrase supported the perceptive shifting from speech to song in a specific way. Our
assumption is that the shifting will occur earlier, i.e. after fewer repetitions, when specific
acoustic characteristics are present in a sound signal. We have set up a reaction time experiment
using the speech-to-song illusion as a method to test several hypotheses about the nature of the
acoustic characteristics that will support the perceptive drift. Our hypotheses are as follows: We
suggest that the drift will occur earlier if (i) pitch accents occur isochronically (ii) if intervocalic
intervals are equalized in duration resembling note durations, (iii) the targets of pitch accents
are level-like (as opposed to contour-like targets as in natural speech) and (iv) if scalar tonal
relations are suggested by the melody especially at the phrase boundary. In the experiment, we
manipulate these factors individually and cumulatively to assess their relative importance for
the perceptual shift. This study is still in progress. It will give useful evidence for modeling the
acoustic basis of speech and song perception and will reveal shared resources.