Perceptual Determinants of Gaze Aversion By the Lesser Mouse Lemur (Microcebus Murinus), the Role of Two Facing Eyes

Abstract

AbstractCaptive lesser mouse lemurs (Microcebus murinus) were observed to avert their heads during face-to-face encounters. Based on evidence obtained from other vertebrate species, predominantly among the Primates, it was assumed that the facing orientation and direction of gaze of an adversary was the provocative agent eliciting gaze aversion by mouse lemurs. A more precise examination of the perceptual determinants of gaze aversion employed models presenting various combinations of eyelike concentric circles. Presented side-by-side in paired comparisons, it was predicted that a model presenting two horizontally placed concentric circles, which schematically resemble two facing eyes, would elicit less visual inspection, i.e., more visual avoidance, than models presenting less physiognomic arrangements of concentric circles. Using a special model-viewing apparatus, Experiment I examined the gaze behavior of 28 mouse lemurs in their peak activity period to determine the response-eliciting effectiveness of 5 models varying in the number of concentric circles. Experiment 2 examined 50 lemurs, some of which were in seasonally and artificially induced torpor. Three models differing in the spatial orientation of two concentric circles were investigated in an attempt to control for contour complexity. Both the bout frequency and duration of model fixation were measured using head orientation as the response criterion. The following results were obtained: 1. For the over-all paired comparisons in both experiments, the model presenting two horizontally positioned concentric circles was the only model which elicited significantly fewer bouts of longer fixation. 2. Because of a lack of homogeneity in model fixation, due to intense fear in some lemurs, the lemurs were separated into homogeneous subgroups using statistical criteria in the first experiment and behavioral criteria in the second. Only the largest subgroups comprising relatively calm mouse lemurs exhibited differential model fixation at a significant level. In both experiments, these particular subgroups looked significantly less at the critical model exhibiting two schematic facing eyes than at any of the other models. In conjunction with observations of dyadic interactions among mouse lemurs, the experimental findings suggest the following: 1. Two schematic facing eyes viewed out of context with a predator or conspecific are a provocative source of stimulation eliciting less visual inspection which could be considered analogous to bouts of gaze aversion observed among interacting lemurs. 2. In concordance with laboratory observations of attenuated gaze aversion by frightened mouse lemurs, the more fear-motivated lemurs in the present experiments exhibited reduced differential model inspection. The affinity between these findings implies, perhaps, that fear-motivation increases the tendency to engage in less selective investigative gazing as the animal shifts into a protective behavior mode. This as well as any other functional interpretation of the role of gaze behavior during agonistic encounters, however, awaits further experimental support.