Gesture refers to a nonlocomotory movement with communicative value of the forearm, hand, wrist, or fingers (cf. ref. 14). Leg and foot movements are included, because these movements have been observed to be communicative in bonobos (11). Excluded from this definition are any other movements that are sometimes labeled gestures in the literature (e.g., ref. 53), such as body postures, head movements, and locomotion patterns. The movement must be directed at another individual. Directed means that the performer of the gesture must potentially be in the recipient's view. This applies only to nontactile gestures; for a tactile gesture the recipient simply needs to be within touching proximity. A tactile action is considered a gesture only if it lasts 2 s and visibly lacks the mechanical force to bring about the reaction shown by the recipient, and also does not include any attempt to grab or extensively hold a body part of the other. For example, the gesture hard touch applied to the leg neither moves the other's leg in any observable direction nor does it visibly, forcibly change the other's physical position (if a positional change does result, it must appear ″voluntary″). Play movements are repeated and exaggerated, usually leading to tickling, play hitting, or wrestling. Movements during play are not considered gestures in this study, except for those that initiate play. These gestures must occur at least 0.5 s before any play is observed between two individuals. |
