The integration of laughter and speech in vocal communication: A dynamic systems perspective

Laughter in infant-directed speech was examined in 13 mother-infant pairs t o investigate the possible co-occurrence of speech and laughter Contrary to previous findings in adult-adult social interaction, all mothers produced speech simultaneously with laughter in up to 50% of laughs. In most of thes e speech-laughs the onset of laugh and speech was simultaneous. Laughter oc curred on both function and content words and was more likely to occur on a pproximately 2 words and on utterances that were statements rather than que stions or exclamations. Laughter and speech are different outcomes produced from a reorganization of the same vocal/anatomical parameters. A 3rd outco me is possible in the Form of speech-laughs utilizing features from both la ughter and speech. In speech-laughs, the duration of the vocalization was m ore likely to increase, and the changes in the utterance were likely to inc lude 1 or more of the features of vowel elongation, syllabic pulsation, bre athiness, and pitch change. These findings and individual variations in the resulting vocal output are discussed from a dynamic systems perspective. I t is argued that neither speech nor laughter is dominant when both are comb ined, but that this is a more complex vocal outcome produced with idiosyncr atic flexibility within stable temporal and physiological constraints.