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Development of a cognitive bias methodology for measuring low mood in chimpanzees.

Bateson M, Nettle D - PeerJ (2015)

Bottom Line: There was a significant difference between subjects in their relative latencies to touch intermediate cones (pessimism index) that emerged following the second test session, and was not changed by the addition of further data.The most dominant male subject was least pessimistic, and the female most pessimistic.We argue that the task has the potential to be used to assess longitudinal changes in sub-clinical levels of low mood in chimpanzees, however further work with a larger sample of animals is required to validate this claim.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre for Behaviour and Evolution and Institute of Neuroscience, Newcastle University , Newcastle upon Tyne , UK.

ABSTRACT
There is an ethical and scientific need for objective, well-validated measures of low mood in captive chimpanzees. We describe the development of a novel cognitive task designed to measure 'pessimistic' bias in judgments of expectation of reward, a cognitive marker of low mood previously validated in a wide range of species, and report training and test data from three common chimpanzees (Pan troglodytes). The chimpanzees were trained on an arbitrary visual discrimination in which lifting a pale grey paper cone was associated with reinforcement with a peanut, whereas lifting a dark grey cone was associated with no reward. The discrimination was trained by sequentially presenting the two cone types until significant differences in latency to touch the cone types emerged, and was confirmed by simultaneously presenting both cone types in choice trials. Subjects were subsequently tested on their latency to touch unrewarded cones of three intermediate shades of grey not previously seen. Pessimism was indicated by the similarity between the latency to touch intermediate cones and the latency to touch the trained, unreinforced, dark grey cones. Three subjects completed training and testing, two adult males and one adult female. All subjects learnt the discrimination (107-240 trials), and retained it during five sessions of testing. There was no evidence that latencies to lift intermediate cones increased over testing, as would have occurred if subjects learnt that these were never rewarded, suggesting that the task could be used for repeated testing of individual animals. There was a significant difference between subjects in their relative latencies to touch intermediate cones (pessimism index) that emerged following the second test session, and was not changed by the addition of further data. The most dominant male subject was least pessimistic, and the female most pessimistic. We argue that the task has the potential to be used to assess longitudinal changes in sub-clinical levels of low mood in chimpanzees, however further work with a larger sample of animals is required to validate this claim.

No MeSH data available.


Related in: MedlinePlus

Choice data.Proportion of choices of the POS cone in each choice session for each of the three chimpanzees. The dotted line shows the criterion for choice to be significantly different from random (p < 0.05).
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fig-2: Choice data.Proportion of choices of the POS cone in each choice session for each of the three chimpanzees. The dotted line shows the criterion for choice to be significantly different from random (p < 0.05).

Mentions: The period of testing spanned 13 days for Bobby, 6 for ET and 12 for Nicky. Of note, both Bobby and Nicky had a gap of 6 days during which they were neither trained nor tested between test sessions 3 and 4. In the first set of analyses, we tested whether the chimpanzees retained the discrimination between POS and NEG learnt during training in the test phase of the experiment. Figure 2 summarises performance in the choice trials. All three chimpanzees showed a highly significant preference for touching the POS cone first in all choice sessions (binomial tests: all p < 0.01), with all three animals showing perfect performance in at least two of the five sessions. A general linear mixed model on the proportion of POS choices in a session (square-root transformed), with session number as a continuous predictor, and chimpanzee as a random effect, showed that the chimpanzees’ preference for the POS cone became stronger over the six choice sessions (effect of session: B ± se = 0.015 ± 0.004, X2(1) = 11.38, p < 0.001). Although the NEG cones never concealed peanuts, and the chimpanzees had clearly acquired the POS-NEG discrimination perfectly by the end of the testing, all three chimpanzees continued to pick up both cones on the majority of choice trials (data not shown).


Development of a cognitive bias methodology for measuring low mood in chimpanzees.

Bateson M, Nettle D - PeerJ (2015)

Choice data.Proportion of choices of the POS cone in each choice session for each of the three chimpanzees. The dotted line shows the criterion for choice to be significantly different from random (p < 0.05).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4465942&req=5

fig-2: Choice data.Proportion of choices of the POS cone in each choice session for each of the three chimpanzees. The dotted line shows the criterion for choice to be significantly different from random (p < 0.05).
Mentions: The period of testing spanned 13 days for Bobby, 6 for ET and 12 for Nicky. Of note, both Bobby and Nicky had a gap of 6 days during which they were neither trained nor tested between test sessions 3 and 4. In the first set of analyses, we tested whether the chimpanzees retained the discrimination between POS and NEG learnt during training in the test phase of the experiment. Figure 2 summarises performance in the choice trials. All three chimpanzees showed a highly significant preference for touching the POS cone first in all choice sessions (binomial tests: all p < 0.01), with all three animals showing perfect performance in at least two of the five sessions. A general linear mixed model on the proportion of POS choices in a session (square-root transformed), with session number as a continuous predictor, and chimpanzee as a random effect, showed that the chimpanzees’ preference for the POS cone became stronger over the six choice sessions (effect of session: B ± se = 0.015 ± 0.004, X2(1) = 11.38, p < 0.001). Although the NEG cones never concealed peanuts, and the chimpanzees had clearly acquired the POS-NEG discrimination perfectly by the end of the testing, all three chimpanzees continued to pick up both cones on the majority of choice trials (data not shown).

Bottom Line: There was a significant difference between subjects in their relative latencies to touch intermediate cones (pessimism index) that emerged following the second test session, and was not changed by the addition of further data.The most dominant male subject was least pessimistic, and the female most pessimistic.We argue that the task has the potential to be used to assess longitudinal changes in sub-clinical levels of low mood in chimpanzees, however further work with a larger sample of animals is required to validate this claim.

View Article: PubMed Central - HTML - PubMed

Affiliation: Centre for Behaviour and Evolution and Institute of Neuroscience, Newcastle University , Newcastle upon Tyne , UK.

ABSTRACT
There is an ethical and scientific need for objective, well-validated measures of low mood in captive chimpanzees. We describe the development of a novel cognitive task designed to measure 'pessimistic' bias in judgments of expectation of reward, a cognitive marker of low mood previously validated in a wide range of species, and report training and test data from three common chimpanzees (Pan troglodytes). The chimpanzees were trained on an arbitrary visual discrimination in which lifting a pale grey paper cone was associated with reinforcement with a peanut, whereas lifting a dark grey cone was associated with no reward. The discrimination was trained by sequentially presenting the two cone types until significant differences in latency to touch the cone types emerged, and was confirmed by simultaneously presenting both cone types in choice trials. Subjects were subsequently tested on their latency to touch unrewarded cones of three intermediate shades of grey not previously seen. Pessimism was indicated by the similarity between the latency to touch intermediate cones and the latency to touch the trained, unreinforced, dark grey cones. Three subjects completed training and testing, two adult males and one adult female. All subjects learnt the discrimination (107-240 trials), and retained it during five sessions of testing. There was no evidence that latencies to lift intermediate cones increased over testing, as would have occurred if subjects learnt that these were never rewarded, suggesting that the task could be used for repeated testing of individual animals. There was a significant difference between subjects in their relative latencies to touch intermediate cones (pessimism index) that emerged following the second test session, and was not changed by the addition of further data. The most dominant male subject was least pessimistic, and the female most pessimistic. We argue that the task has the potential to be used to assess longitudinal changes in sub-clinical levels of low mood in chimpanzees, however further work with a larger sample of animals is required to validate this claim.

No MeSH data available.


Related in: MedlinePlus