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Jean-Baptiste Leca, Ph.D.

Associate Professor

Department of Psychology

University of Lethbridge


Eye covering play in Balinese long-tailed macaques

Eye covering play in Balinese long-tailed macaques is another form of non-instrumental object manipulation which consists of deliberately covering one’s eyes with various objects (e.g., half coconut shell, leaf, cloth, plastic bag) during a play sequence. [VIDEO]

Even though eye covering play has social and cognitive implications, little is known about the mechanisms and function of this intriguing behavior.

The “surplus energy” hypothesis holds that play enables the expenditure of excess metabolic energy, which occurs more often in young individuals. Moreover, eye covering behavior is a form of object play in macaques.

Thus I hypothesize that intragroup variation in eye covering play will reflect more age than sex differences. Eye covering play should be more frequent, longer, and riskier in young than in older individuals, regardless of sex.

In line with the “play and safety” hypothesis, the contagious nature of play activities, and the occasional integration of eye covering behavior into social interactions (e.g., an individual using an object to cover another individual’s eyes, or contest competition over objects to cover one’s eyes, I predict that an individual’s probability (per unit of time) of engaging in eye covering play will increase as more and more group members are already performing this behavior.

Does eye covering play in Balinese long-tailed macaques involve pretence?

Pretence play is defined as entertaining simultaneously two mental representations of a situation – one experiential/real and one imagined – and being efficient at switching from an imaged to an experiential representation in anticipation of an upcoming difficulty (via “cheating”, that is through groping or peeking).

To explore pretence from a cognitive perspective, I will investigate eye covering play patterns, including

(1) evidence of planning travel routes before covering one’s eyes,

(2) the duration and complexity of blind travels (e.g., long, curved, bumpy, off ground),

and (3) the occurrence, timing (before difficulties to avoid them versus after errors to correct them), and form (aimed groping/peeking) of cheating.

Simpler alternative mental processes may involve voluntary means of self-stimulation or autotelic play. To explore pretence from an evolutionary perspective, I will compare these data with reports of eye covering play in other macaque species.