Acoustic and affective comparisons of natural and imaginary infant-, foreigner- and adult-directed speech

This study evaluated the use of imagined interactions in speech research, by comparing speech addressed to imaginary speech partners with natural speech addressed to genuine interaction partners. Samples of speech directed to an imaginary infant (IDS), foreigner (FDS) and adult (ADS) produced by ten female students were acoustically analysed and also rated on positive vocal affect. Our results for vocal affect are consistent with previous findings using natural interactions, with IDS rated higher in positive vocal affect than ADS/FDS. However, acoustic analyses of IDS revealed a much smaller vowel space than ADS/FDS, with no difference between those two conditions. Unlike the findings in the natural speech samples, our IDS mean pitch was not significantly higher than ADS/FDS. Since these results are contrary to those from interactions with genuine speech partners, speech obtained from imaginary interactions should be used with caution.