Methods

In order to identify movements that potentially held meaning as gestures for the signalling orangutans, I began by selecting all non-functional movements I observed orangutans perform when oriented towards other individuals and classifying them according to their forms. The movements were categorized according to their modality, direction, speed, force, and whether or not they were performed with an object (according to the classification in Table 3). These distinctions allowed movements to be sorted into potential gestures through similarity of form.

Similarity of form does not necessarily imply similarity of meaning, as English homophones and homonyms demonstrate. In order to demonstrate that two potential gestures that were similar in form were distinct signals, it was necessary to ascertain that 1) the same individuals could use both gestures (ensuring one gesture was not a reflection of the movement preferences of certain individuals), and 2) that the two gestures were not used interchangeably towards the same goal. If one of the two potential gestures was always used first and the other always followed, or if one were used to initiate a

particular kind of interaction with an adult and the other with a juvenile, then it would be possible to argue that the two potential gestures were indeed different from one another. In these cases, however, one would have to be careful that one of the two forms was not an exaggeration of the other, following the other as a necessity because it was used when the first gesture failed to achieve its goal and was repeated in a bigger or slower way. If this second form could precede the other or be used independently, it would indicate that

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it was a distinct gesture, but I tried to ensure that gesture types were defined more often as categorical distinctions than gradations of the same movement along one particular variable.

In order to investigate the choices orangutan signallers make and what variables they take into account when attempting to communicate, I first had to establish that the potential gestures they produced towards other orangutans were, in fact, intentionally communicative signals. As I planned to investigate orangutans’ use of gesture as a way to gain insight into their understanding of communicative failure and the minds of other individuals, it was important that the signallers actively chose the gestures they exhibited. Intentional use was therefore essential in determining which movement forms (i.e.

potential gestures) could be considered to be gestures in this study. To this end, I identified likely markers of intentional communication (i.e. waiting for a response, looking at the recipient following a potential gesture, using a modality that can be

perceived by the recipient, persisting and elaborating when there is no response) and gave each occurrence of each potential gesture a rating to indicate how strongly it was

accompanied by these markers.

In the analysis of the forms and meaning of gestures presented in this chapter, I focused on gestures that were produced in an intentional manner at least once by each individual observed to use that gesture (see Chapter 2.5 for a full description of

intentionality criteria). It is possible that though a particular movement may be the same in two individuals, one may use the movement with an intent to communicate and one may not. It is for this reason that before I claimed that an individual had a specific gesture in her repertoire, she must have used that gesture at least once in a manner that suggested intentional use.

Non-functional movements that were performed towards other individuals (or at least in the presence of other individuals) were initially divided into potential gestures based on the modality and overall form of the movement (Table 2). Once I had identified the gestures that were used in a manner suggestive of intentional communication, I then

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examined the contextual use, presumed goal of the signaller, and response of the recipient of each example in order to determine whether the gestures that I had defined through structural similarity were also distinct from one another in their contextual use as signals.

The presumed goal of a gesture was taken to be the action of the recipient that caused the signaller to stop trying to communicate. I assumed that the goal was always to elicit an active response from the recipient (e.g. movement towards or away from the signaller, sharing an item, or interacting in an affiliative way). Thus, a lack of response of the recipient, or a rejection of the signaller (by averting gaze or turning away) was never assumed to be the signaller’s goal. These presumed goals were compared within and between gestures in order to best categorize them into potential gestures. Some gestures, which had appeared distinct in form, were combined into larger units because they were used interchangeably. Others were divided into more than one gesture if the variance in their use could be explained by separating out a subgroup defined by a commonality along a structural variable such as handshape or location on the recipient’s body. These combinations and divisions helped to ensure that the observed movements grouped into potential gestures were similar in form but were used to convey as few goals as possible.

If gestures were used interchangeably towards any goal, then gestures could not be said to carry any specific information about the signaller’s goal. If this were the case, all the gestures would signal is intent to communicate rather than providing any specific information about the goal of the signaller. Following one of these gestures, the recipient would have to discern the signaller’s goal from non-gestural cues such as context. This is the case in the deictic1 gestures (such as pointing) produced by adult humans and children (McNeill 1992). When a young child points to an object or individual, the recipient must interpret the child’s specific meaning from the context. Apes are capable of similarly ambiguous attention-directing gestures, though the nature and form of “pointing”

1 _{A deictic signal is one in which meaning is dependent on the context. Pointing is} perhaps the most common instance of deixis; the movement itself does not transmit information, but through using the signal in conjunction with the context, an observer can infer meaning. English deictics exhibit similar traits, including words such as “there” and “that.”

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gestures in apes is debated (see Leavens and Hopkins 1999 for review). Other attention- directing signals may be more common in ape gestural communication. One study of human-reared gorillas found that they would use “contact gestures” (e.g. directing the human’s hand to a location of desired food) in situations where human infants would have used pointing to indicate intent (Gómez et al. 1993)

In contrast to deictic gestures that rely on the context for meaning, gestures that are used most frequently to initiate one type of interaction likely contain information about the signaller’s specific goals in the form of the gesture. I attempted to define gestures so that they corresponded to as few goals as possible. This was done to raise the specificity of each gesture so that meaningful gestures could be identified whilst ensuring that the definitions were not so narrow as to render most gestures idiosyncratic.