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Gravity bias in young and adult chimpanzees (Pan troglodytes): tests with a modified opaque-tubes task
Masaki Tomonaga1, Tomoko Imura, Yuu Mizuno
1Language and Intelligence Section, Primate Research Institute, Kyoto University, Inuyama, Aichi, Japan. tomonaga@pri.kyoto-u.ac.jp
Insights
Young chimpanzees exhibit a
Area of Science:
- Primate cognition
- Developmental psychology
- Comparative psychology
Background:
- Young children, dogs, and monkeys exhibit a 'gravity bias', incorrectly predicting object location when dropped through tubes.
- This bias involves searching below the release point, contrary to physical reality.
Purpose of the Study:
- To investigate the presence of a gravity bias in young and adult chimpanzees.
- To determine if developmental stage or learning influences this bias in chimpanzees.
Main Methods:
- A modified opaque-tube task was used, requiring prediction before object drop.
- Chimpanzees (young: 1.5-2.5 years; adult) were tested with straight and crossed tubes.
- Experiment 2 involved simultaneous presentation of straight and crossed tubes to assess learning and development.
Main Results:
- Both young and adult chimpanzees predicted the object's location below the release point, demonstrating a gravity bias.
- This bias persisted even with crossed tubes and extensive experience.
- Results were consistent across experiments, indicating no significant effect of development or learning.
Conclusions:
- Chimpanzees, like young humans and other primates, show a gravity bias.
- This cognitive bias appears robust and is not significantly altered by age or learning within the tested range.
Abstract:
Young human children at around 2 years of age fail to predict the correct location of an object when it is dropped from the top of an S-shape opaque tube. They search in the location just below the releasing point (Hood, 1995). This type of error, called a 'gravity bias', has recently been reported in dogs and monkeys. In the present study, we investigated whether young and adult chimpanzees also show such a gravity bias in a modified version of the original opaque-tube task. The original task by Hood and colleagues required the subject to search in a location after the object had fallen, while in the task reported here, subjects were required to predict the location before the object was dropped. Thus the present procedure does not involve explicit invisible displacement operations, one of the important components of the original procedure. In Experiment 1 both young (1.5-2.5-year-old) and adult chimpanzees predicted the location of falling food items below the releasing point even when crossed tubes were used. These gravity errors remained after the extensive experience of using the tubes themselves. Experiment 2 further tested adult and 4-year-old chimpanzees under the set-up in which the straight and crossed tubes were simultaneously presented. The results were the same as those in the previous test, suggesting that developmental changes and learning effect do not affect the gravity bias in chimpanzees.
