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, 19 (2), 417-28

Do Monkeys Compare Themselves to Others?

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Do Monkeys Compare Themselves to Others?

Vanessa Schmitt et al. Anim Cogn.

Abstract

Social comparisons are a fundamental characteristic of human behaviour, yet relatively little is known about their evolutionary foundations. Adapting the co-acting paradigm from human research (Seta in J Pers Soc Psychol 42:281-291, 1982. doi: 10.1037//0022-3514.42.2.281), we examined how the performance of a partner influenced subjects' performance in long-tailed macaques (Macaca fascicularis). Using parallel testing in touch screen setups in which subjects had to discriminate familiar and novel photographs of men and women, we investigated whether accuracy and reaction time were influenced by partner performance and relationship quality (affiliate vs. non-affiliate). Auditory feedback about the alleged performance of the co-actor was provided via playback; partner performance was either moderately or extremely better or worse than subject performance. We predicted that subjects would assimilate to moderately different comparison standards as well as to affiliates and contrast away from extreme standards and non-affiliates. Subjects instantly generalized to novel pictures. While accuracy was not affected by any of the factors, long reaction times occurred more frequently when subjects were tested with a non-affiliate who was performing worse, compared to one who was doing better than them (80% quantile worse: 5.1, better: 4.3 s). For affiliate co-actors, there was no marked effect (worse: 4.4, better: 4.6 s). In a control condition with no auditory feedback, subjects performed somewhat better in the presence of affiliates (M = 77.8% correct) compared to non-affiliates (M = 71.1%), while reaction time was not affected. Apparently, subjects were sensitive to partner identity and performance, yet variation in motivation rather than assimilation and contrast effects may account for the observed effects.

Keywords: Co-acting paradigm; Evolution; Inequity aversion; Meta-cognition; Monkeys; Non-human primates; Social comparison processes; Social relationships.

Figures

Fig. 1
Fig. 1
Experimental setup used to test the monkeys. Two touch screen boxes placed next to each other were attached to the separation cages. TC touch screen computer, S subject, P partner
Fig. 2
Fig. 2
Examples of stimuli used in the discrimination tasks and experimental setup. In the first training phase, the monkeys learned to discriminate between images of triangles (a) and circles (b) in six different colours on the touch screen (f). In the pre-test and test phase, pictures of male and female humans had to be discriminated. In each session, whole-body pictures (c), images of the upper half of the body (d), and face-only pictures (e) were presented on the touch screen (g)
Fig. 3
Fig. 3
a Effect of standard extremity and direction of comparison. Individual mean proportions of correct responses in relation to extremity (moderate vs. extreme) and direction (circle: better; triangle: worse). Bars indicate overall means per condition. b Effect of relationship and direction of comparison. Individual mean proportions of correct responses in relation to relationship (affiliate vs. non-affiliate) and direction (circle: better; triangle: worse) are given. Bars indicate overall means per condition
Fig. 4
Fig. 4
Differences in performance in the two experimental blocks. Individual mean proportion correct responses in the first block (B1) and second block (B2) are given. Bars indicate overall means per condition
Fig. 5
Fig. 5
Effect of the key predictor variables on the location of the quantiles. A positive shift in the location of the upper quantiles indicates that long RTs occur more frequently. Shaded areas indicate 95 % confidence intervals; nonzero effects can be inferred when confidence intervals do not overlap with the null value
Fig. 6
Fig. 6
Comparison of social control and feedback conditions. Individual mean proportion correct responses in the social control (open circles) and the experimental feedback conditions (light grey circles) separately for sessions with an affiliate (A) and a non-affiliate (NA) present as co-actor. Bars indicate overall means per condition

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