Publication Type: Individual Poster
Abstract: Gergely, Bekkering, and Király (2002) used an imitation paradigm to show that 14-month-old infants imitate rationally: Infants who observed an adult freely choose to switch on a lamp with her head were more likely to copy that action than infants who observed the adult having to use this unusual means because of some constraint. One interpretation of this finding is that infants understand not just others’ goals but also others’ intentions as rational plans for actions. Now that there is some evidence that apes, too, understand something about others’ goals (Call, Hare, Carpenter, & Tomasello, 2004) it is important to investigate whether apes understand this additional component of others’ intentional action as well.
We modified Gergely and colleagues’ (2002) procedure to directly compare 14-month-old human infants (n=28) and nonhuman primates (chimpanzees, bonobos, gorillas, and orangutans, n=28).
All participants watched as a human experimenter (E) used an unusual tool (a wooden block) to pull in a platform with a reward (a toy or food) on it. For half of the participants E first tried unsuccessfully to use a nearby, more usual tool, a rope (E had to use the unusual tool). For the other half of the participants, E first visually explored and rejected the more usual tool and then chose the unusual tool to bring in the reward (E wanted to use the unusual tool). There were two blocks of trials with one demonstration and three response periods each for a total of six trials.
As in Gergely and colleagues’ (2002) study, infants copied E’s action significantly more often when E wanted to use the unusual tool than when E had to use it, t(26)= -2.18, p<.04. They showed this discrimination from their very first trial, χ2 (1,26)= 5.60, p<.02. Apes, in contrast, used the unusual tool equally often in both conditions, t(26)= -0.54, p=.59. Similar results were found in a follow-up task using different tools t(26)=0.20, p=0.85, and within-subjects comparisons across the two tasks also confirmed these results, t(27)= -0.21, p=0.84. Testing on the follow-up task with infants is still in progress but preliminary results support those of the first task.
These findings suggest that whereas 14-month-old infants seem to understand others’ intentions as rational choices of action plans, there is currently no evidence of this ability in great apes.