A macaque remembers pictures briefly viewed six months earlier

Abstract

While there are several studies documenting the enduring nature of memory for acquired discriminatory ‘habits’ or ‘skills’ in animals, comparable data on memory for visual scenes, i.e., ‘events’, are essentially non-existent, and difficult to obtain even in man. An opportunity to assay this question in macaques arose in the early stages of training an animal on a running recognition task. It had previously been trained on trial-unique delayed matching to sample, and its past experience with this visual material was precisely known. When some of these images which had not been seen by the monkey for at least 6 months were intermingled with comparable material during its training on the running recognition task, with a high degree of statistical reliability ( P < 0.005) it distinguished about one-third of the earlier images, many of which had been seen for a total of only 30 s or less. A medical student, who had previously trained the animals and had had more exposure to the material than did this macaque, and certainly had more precise instruction on how to perform, recognized two-thirds of these same images, also after a hiatus of 6 months. It thus appears likely that the permanence of mnemonic storage for briefly encountered scenes is comparable for the central visual systems of macaque and man.