Logical and illogical errors made by apes and children on a cognitive task

Abstract

The purpose of this study was to analyse changes in errors made by juvenile chimpanzees, mentally retarded human children, and human children of normal intelligence who were tested on a non-verbal, Piagetian-type multiple classification task. On this task the subjects were required to select the correct object from the response tray and place it inside the empty cell of the stimulus matrix that was formed by combining two different colors with two different forms. The data were analysed to determine the degree to which absolute error rate and patterns of logical and illogical errors, that occurred on the first and second trials of each problem, influenced the multiple classification performance of non-human and human primates. Logical errors were operationally defined as the selection of objects which had one or two stimulus dimensions incorrect on the first trial, and the selection of objects which had one or two stimulus dimensions correct on the second trial. Illogical errors were operationally defined as the selection of objects which only had one stimulus dimension correct on the first trial, and the selection of objects which had both stimulus dimensions incorrect on the second trial. It was found that there was an inverse relationship between absolute error rate and the selection of objects which were correct on both color and form on the first trial. The proportion of logical errors remained constant at about 80% for all groups tested, save for the normal children who had an absolute and relative error rate that approached a value of zero for the last part of testing. These results suggest that while absolute error rate may be influenced by the specific characteristics of the stimulus items used, logical errors indicate that a similar cognitive mechanism may permit non-human and human primates to utilize the two stimulus dimensions of color and form to solve a series of unique multiple classification problems. The implication of these results to the language-cognition