Abstract # 1955 Event # 50:

Scheduled for Thursday, August 17, 2006 03:45 PM-04:00 PM: Session 6 (Regency East #3) Oral Presentation


J. Vonk
Department of Psychology, University of Southern Mississippi, Gulf Coast, 730 East Beach Blvd. , Long Beach , MS 39560 , USA
     It is unclear whether orangutans are capable of estimating numerosities with the same degree of accuracy displayed by other primate species. Here, an adult male orangutan (Pongo abelii) was presented with a series of delayed matching-to-sample (DMTS) tasks in which he was to match images based on a) the number of individuals depicted in the photograph (from 1-4), b) the number of abstract shapes presented in the stimulus (from 1-4), or c) the number of dots presented in the stimulus (from 1-4, 4-7, and 7-10). The size of the dots was manipulated to control for overall ratio of foreground to background. In addition, the spatial arrangement of the dots and the background color of the stimuli varied within each set of stimuli depicting the same number of dots. ANOVAs revealed that this orangutan’s performance was not affected by these irrelevant variables suggesting that he attended to the number of objects depicted in each stimulus. Moreover, he achieved above chance performance levels by the second session with all but one of the six novel stimulus sets as revealed by binomial tests (p < .05). He showed a high degree of transfer to novel numerosities and performed at 100% correct on the first session with 7 to 10 dots, indicating that orangutans are capable of numerical estimation for a greater number of items than can presumably be quantified without enumeration (i.e., subitized).