Can Monkeys (Macaca mulatta) Represent Invisible Displacement?

Four experiments were conducted to assess whether or not rhesus macaques (Macaca mulatta) could represent the unperceived movements of a stimulus. Subjects were tested on 2 computerized tasks, HOLE (monkeys) and LASER (humans and monkeys), in which subjects needed to chase or shoot at, respectively, a moving target that either remained visible or became invisible for a portion of its path of movement. Response patterns were analyzed and compared between target-visible and target-invisible conditions. Results of Experiments 1, 2, and 3 demonstrated that the monkeys are capable of extrapolating movement. That this extrapolation involved internal representation of the target's invisible movement was suggested but not confirmed. Experiment 4, however, demonstrated that the monkeys are capable of representing the invisible displacements of a stimulus

A Species Difference in Visuospatial Memory in Adult Humans and Rhesus Monkeys: The Concentration Game

One of the most familiar children’s games (marketed under many names including the memory game, Concentration, and Husker Du also would seem to provide an excellent test of visuospatial memory. A computerized version of this game was written in which human adults or rhesus monkeys were required to find matching pairs of pictures by “flipping over” computer-generated images of cards. Finding one of the 2 to 6 pairs of images (color patches, line drawings, letters, etc.) caused the pictures to remain visible, but errors (mismatches) caused the images to be concealed again and thus required the participants to remember which images had been seen and where each was hidden. In a series of experiments, all participants were able to locate the pairs of stimuli, but monkeys were consistently and significantly worse than the human adults. Indeed, the monkeys frequently perseverated on errors, causing them to be worse than chance in many conditions, even after training. In the present manuscript, data are presented to suggest that this species difference does not simply reflect a limitation on the monkeys’ knowledge of the “rules of the game.

A Species Difference in Visuospatial Memory: A Failure of Memory for What, Where, or What is Where?

Four experiments were conducted to determine why rhesus monkeys (Macaca mulatta) perform so poorly on a visuospatial memory test modeled after a popular children’s game (Concentration). In these studies, four different memory tasks were administered to ascertain whether monkeys show limitations in visual memory (memory for which images had been seen), limitations in spatial memory (limitations of what locations had been visited), or limitations in the coordination of these two modalities (memory for what images are located where). The data indicate that the monkeys could remember visual information when there were no spatial demands. The monkeys could also remember spatial information when there were no visual-memory demands, although performance on this spatial-memory task was not as accurate as had been predicted. However, when visual and spatial memories had to be coordinated–memory for what was where–performance was no better than chance. Hypotheses were discussed for why the monkeys, but not human participants, struggle to coordinate visual and spatial memory. Perhaps this represents and area where humans use verbal working memory—a mnemonic strategy that is presumably unavailable to nonhuman primates—to facilitate the maintenance and cross-referencing of visual and spatial information

A Species Difference in Visuospatial Working Memory:Does Language Link “What” with “Where”?

A computerized version of a popular children’s memory game (“Concentration”) was used to test the role of language in visuospatial working memory of humans, apes, and monkeys. Participants were required to find matching pairs of pictures by “flipping over” computer-generated cards, and to remember which images had been seen and where each was hidden. All participants were able to locate the pairs of stimuli, but the nonhuman animals were consistently and significantly worse than the human adults. When humans could not use language, performance declined. When the stimuli were meaningful symbols from the chimpanzees’ language keyboards, performance improved. These data suggest that language provides an important function even in visuospatial working memory, linking “memory for what” with “memory for where.

With his memory magnetically erased, a monkey knows he is uncertain

Although intelligence is associated with what one knows, it is also important to recognize and to respond adaptively when one is uncertain. This competency has been examined developmentally and comparatively, but it is difficult to distinguish between objective versus subjective cues to which organisms may respond. In this study, transcranial magnetic stimulation was used to disrupt cognitive processing by a rhesus monkey (Macaca mulatta) in a computerized divided visual field memory task. When magnetic stimulation disrupted neural activity in the cerebral hemisphere that initially processed the visual images, recognition accuracy declined and use of the uncertain response significantly increased, relative to control conditions. Thus, the monkey tended to respond adaptively when he did not know the answer—where uncertainty was produced by targeted disruption of the neural processing of a stimulus—even in the absence of external, objective cues to corroborate his subjective, metacognitive assessment of uncertainty