Investigations on human laughter and its implications for the evolution of hominid visual communication

Author(s): Loi, M., Landerer, S.

Journal/Book: Homo. 2000; 51: Villengang 2, D-07745 Jena, Germany. Gustav Fischer Verlag. 1-18.

Abstract: In order to be able to compare human and non-human primate facial expressions, e.g. For phylogenetical considerations, metric analyses of the coordination of these movements in humans are still necessary. Moreover, reliable associations between clearly defined analytic descriptions of the motor coordinations in the laughing human face on the one hand and their emotional interpretation by human raters on the other hand are still lacking. Therefore, we analysed the expressive facial movements of 58 test persons, 45 videotaped laughing adults and 13 laughing minor children. Afterwards, we showed the videos to 103 raters for the interpretation of adult laughs and to 129 raters for the laughs of children. The raters made n = 6312 judgments. We found that laughs that were judged as positive by the receptors had lasted > 3 sec andwp to 6 or 7 sec. From our results presented below we conclude, that the visual aspects of laughing faces that are judged as cheerful, winning, or as generally socially positive can be summarized as follows: 1)Positive laughs tend to last longer, i.e. > 3 sec up to 6 or 7:sec, while negative ones on the average last less than 3 sec. 2) During the first second of the expression of laughter, very rapid mouth and eye movements can be observed, but they are lacking in negatively interpreted laughs. 3) In positively interpreted laughter, mouth and eye movements (opening and closing) may be repeated two or three times. This was never observed in negative laughs. 4) Very positive and inconsistently rated laughs showed almost or fully closed eye lids, sometimes repeatedly. By contrast to moistening blinks, the duration of the closed eyes varied strongly from <0.1 sec to > 1 sec. 5) Short blinks, detectable by sharp spikes in the curve of the much less than eye angle much greater than, were most frequent at the end of the positive laughs and less frequent in the inconsistently rated ones. In the most negatively judged laughs they were lacking (Fig. 3 d-f). It is not the large eyed grin, but it is mainly the fast onset and the high dynamics of the expressive movements, sometimes combined with fast closings of the eyes, possibly combined with a long duration of the laughing expression, that is interpreted by the receiving partner as convincingly cheerful,. Closing one's eyes while laughing is emitted unconsciously and adequately decodes, as unconsciously, as a positive signal. All these findings indicate strongly the high heriditary component in human laughing behavior that has been evolutionarily aquired by prehuman ancestors. Moreover, our data quantify, how the various laughing expressions are decoded by the social partners. Since our investigations focus exclusively on the visual channel follow-up investigations should now include the acoustic component of the expression.

Note: Article Niemitz C, Free Univ Berlin, Inst Anthropol & Humanbiol, Fabeckstr 15, D-14195 Berlin, GERMANY

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