Assessing generalization within and between trap tasks in the great apes

Abstract

Considerable research has been devoted to investigate the type of information that subjects use to solve tool-using tasks in which they have to avoid certain obstacles (e.g., traps) to retrieve a reward. Much of the debate has centered on whether subjects simply use certain stimulus features (e.g., the position of the trap) or instead use more functionally-relevant information regarding the effect that certain features may have on a moving reward. We tested eight apes (that in a previous study had succeeded in a trap-tube task) with one functional and two nonfunctional traps to investigate the features that they used to solve the task. Four of the eight subjects used functional features. Additionally, we presented 31 apes with a trap task that did not involve tools but required subjects to make an inference about the position of a hidden reward based on its displacement over a substrate with or without a trap. Subjects performed above chance levels (including from the first trial) in the experimental condition (unlike in the control conditions), suggesting that they took into account the effect that a trap may have on a reward. Third, we correlated the subjects performance in four trap tasks (3 involving tool-use and one without tool-use) and found positive correlations between some of the tasks. Our results suggest that apes possess some knowledge about the effects that traps have on slow moving unsupported objects. However, this knowledge was not robust enough to prevent the influence of certain practice and task effects. Moreover, subjects’ knowledge may not have been abstract enough to allow them to establish broad analogies between tasks.