Evaluación Diagnóstica:

In order to investigate the signaller’s likelihood of using another gesture based on whether or not their goal had been fulfilled, I analysed the probability of persisting following gestures meaning “affiliate/play.” This meaning was used for analysis as it was the most common meaning of gestures and showed a high fidelity of meaning from first to second gestures in a sequence, thus raising the likelihood that “affiliate/play” gestures used as 2nd, 3rd, or 4th gestures would be parts of sequences directed towards the same meaning. The likelihood of performing another gesture was calculated for gestures in positions 1-4 in a sequence following either responses that met the goal “affiliate/play,” responses that didn’t meet the goal, or no response at all (Figure 10).

Figure 10: CHANCE OF CONTINUING TO GESTURE AT DIFFERENT POINTS IN A SEQUENCE FOLLOWING GESTURES MEANING “AFFILIATE/PLAY” BASED ON WHETHER RECIPIENT’S RESPONSE FULFILLS GOAL.

didn’t meet goal met goal

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When the orangutans used gestures meaning “affiliate/play,” the chance of the signaller’s using another gesture was highest following no recipient response (77% ± 3.5%), lower following responses that did not fulfil the goal of the gesture (49% ± 4.3%), and lowest following responses that fell within the definition of affiliation or play (18% ± 4.2%). As the probability of continuing to gesture did not vary greatly over the four positions in the sequence, data from all four positions were pooled for analysis.

Following no response, orangutans continued to gesture a total of 231 times and stopped gesturing 65 times. Following a response that did not meet the goal “affiliate/play,” orangutans continued to gesture a total of 136 times and stopped gesturing 125 times. Following a response that was consistent with the goal “affiliate/play,” orangutans continued to gesture a total of 29 times and stopped gesturing 114 times. These observed frequencies were compared to one another using a chi-squared test. The type of recipient response was found to significantly affect the signaller’s chance of using another gesture (χ2=134.31, df=2, p<0.0001).

The likelihood of a signaller’s attempting another gesture following a response that matched the meaning of the gesture was lower than the likelihood following other types of responses, but if the signaller’s goal had been fulfilled, one would expect them to never persist. The persistence rate (18% ± 4.2%) following responses that corresponded to the meaning of the previous gesture may be a product of the breadth of the category of meaning assigned to both the gestures and responses. All types of affiliation and play were combined into a single category that included actions as diverse as chasing,

cuddling, wrestling, playing with objects, and sitting in contact. Perhaps the cases where the signaller continued to gesture following an affiliative response represent cases where the recipient responded generally in the right way, but did not meet the precise

expectations of the signaller. If the signaller wanted to wrestle with the recipient and the recipient responded to the first gesture by touching or embracing the signaller, the signaller would likely continue to gesture in an attempt to engage the recipient in a wrestling bout.

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Orangutans were more likely to continue gesturing when the recipient did not respond than when the recipient responded in a way that did not fulfil the goal of the previous gesture. Though the practical outcome of the two conditions was the same (i.e. the signaller’s goal was not met), the recipient’s behaviour suggests in one case that the recipient may not have perceived the gesture, and in the other that the recipient has either misunderstood the goal or rejected the signaller’s attempt to affiliate. To humans, there is an important difference between a recipient who has not yet responded and one who has actively rejected a communicative attempt. Similar distinctions in the cooperative nature or willingness of the recipient have been tested using human experimenters and

chimpanzee subjects. These studies have produced mixed results. Some found that chimpanzees are unable to distinguish intentions (Povinelli et al. 1998), while others suggested that chimpanzees are able to distinguish intentions, particularly in competitive contexts (Call 2003; Tomasello et al. 2003; Call et al. 2004; Hare and Tomasello 2004). The most recent studies suggest that chimpanzees have some ability to act according to the intentions of others, but there are no comparable studies of this ability in orangutans. Our finding that orangutans are less likely to persist when the recipient has responded with an action that does not meet their goal than when the recipient has not responded at all suggests that orangutans may make a distinction between an active rejection or misunderstanding and a failure to communicate.

Before any conclusions can be drawn regarding the ability of orangutans to discriminate between failed communication and communication that has not yet been successful (i.e. a lack of response), it is necessary to ensure that there is a true distinction between the two conditions. It is possible that in cases where the human observer has recorded a lack of response from the recipient, the recipient is merely responding in a more subtle way. In an observational study using conspecific recipients, it is difficult to determine whether there is actually no response from the recipient. In the present analysis, the recipient met the criteria for demonstrating no response when he continued the behaviour in which he was engaged before the gesture with no noticeable changes in attention or orientation. The term “any noticeable changes” avoided the difficulty in assessing subtle changes in temperament and gaze. It was almost impossible to determine

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from the video gathered whether the recipient glanced sideways at the recipient, tensed their body slightly, or otherwise acknowledged the gesture but did not respond with a large behaviour change. In order to determine whether orangutan signallers are able to determine and act in response to the recipient’s understanding of their gestures, it is therefore desirable to examine sequences made by orangutans in situations where the recipient’s responses can be controlled (see Chapter 5). The question of whether or not the recipient has perceived the signaller’s gesture however, can be addressed by examining the signaller’s use of different gestural modalities in response to the recipient’s visual attention (see section 4.6).