The behavioural cues of familiarity during social interactions among human adults: A review of the literature and some observations in normal and demented elderly subjects.

The present paper deals with the non-verbal expression of individual recognition in normal and pathological populations. In the first part, the literature on non-verbal communication is surveyed with a selective attention given to observational studies comparing encounters between friends and between strangers in young adult subjects. To begin with, it is shown that in some cases external observers can discriminate above chance level silent films showing interactions between familiar and unfamiliar persons. Then, potential cues enabling such a performance are searched for by analysis of familiarity effects on interpersonal distance, touching gesture, visual and postural orientation, and facial or manual movements expressing affiliation or reticence. Finally, these observations are discussed in relation to several underlying processes: learning of interaction rules, involvement of an affiliative motivational system, and regulation of arousal. The problem of assessing the directionality of the familiarity effects is also raised. The second part of the paper addresses the issue of non-verbal expression of recognition in subjects who show impaired person recognition in the verbal modality. A pilot study compares the behaviour of older institutionalised women, either normal or suffering from senile dementia of the Alzheimer's type, during conversations with a member of the medical team and with another unfamiliar person. The methodological problems raised by the planning of the experimental situation are discussed.