Mental transformations of spatial stimuli in humans and in monkeys: Rotation vs. translocation

Rhesus monkeys manipulate mental images

Humans form mental images and manipulate them in ways that mirror physical transformations of objects. Studies of nonhuman animals will inform our understanding of the evolution and distribution among species of mental imagery. Across three experiments, we found mostly converging evidence that rhesus monkeys formed and rotated mental images. In Experiment 1, monkeys discriminated rotations of sample images from mirror images, and showed longer response latencies with greater rotation as is characteristic of human mental rotation. In Experiment 2 monkeys used a rotation cue that indicated how far to mentally rotate sample images before tests, indicating a precision of better than 30° in discriminating rotations. Experiment 3 yielded mixed evidence on whether the rotation cue shortened decision times as has been found in humans. These results show that rhesus monkeys manipulate mental images.

Spontaneous color preferences in rhesus monkeys: What is the advantage of primate trichromacy?

Color perception and color signaling play an important role in various aspects of animal behavior. However, in mammals, trichromatic vision characterized by three retinal photopigments tuned to peak short, middle and long wavelengths is limited only to some primate species. In Old and New World primates a second photopigment has appeared repeatedly during phylogeny, allowing red colors to be distinguished from yellows and greens. Several hypotheses aspire to explain the adaptive benefits of trichromatic vision for primates. The predominant one is foraging adaptation for facilitation visual detection of fruits or young leaves. Alternative explanations are based on the function of red color in aposematic signaling or its role in socio-sexual communication. We tested spontaneous color preference in macaque monkeys (Macaca mulatta) for both food and non-food objects in a laboratory environment. We hypothesized that preference for or avoidance of red color together with the context of such behavior may help us to understand what the adaptive advantage leading to a rapid expansion of a gene for a second pigment in the long-wavelength region was. We found neither preference nor avoidance toward red color in non-food objects, but we found a significant preference for red color in food; therefore, we suggest that the results support the foraging hypothesis in macaque monkeys.

Reactions to novel objects in monkeys: what does it mean to be neophobic?

Animals' reactions to novel objects vary not only with zoological taxa and their ecology but also in the types of presented stimuli, the context, and individual characteristics. Behavioral reactions can vary from extremely neophobic (avoiding novel objects) to extremely neophilic (intense exploration of novel objects); most often, a mixture of these behavioral patterns appears. In primates, reactions toward novel objects vary according to species, age, sex, population, and the types of objects. Most experiments in this field have used a free exploration design with food or non-food objects. Here, we tested the reactions of captive male rhesus macaques using various stimuli, motivation levels, rewards, and time limits. We found that the monkeys explored and manipulated novel objects in various contexts, with little evidence of a neophobic response; however, environment, types of stimuli, and other parameters of the test can significantly affect monkeys' reactions.

Spatial Navigation: Implications for Animal Models, Drug Development and Human Studies

Spatial navigation and memory is considered to be a part of the declarative memory system and it is widely used as an animal model of human declarative memory. However, spatial tests typically involve only static settings, despite the dynamic nature of the real world. Animals, as well as people constantly need to interact with moving objects, other subjects or even with entire moving environments (flowing water, running stairway). Therefore, we design novel spatial tests in dynamic environments to study brain mechanisms of spatial processing in more natural settings with an interdisciplinary approach including neuropharmacology. We also translate data from neuropharmacological studies and animal models into development of novel therapeutic approaches to neuropsychiatric disorders and more sensitive screening tests for impairments of memory, thought, and behavior.