Laboratory Assessment of Temperament and Postrotary Nystagmus Responses in Rhesus Monkey Infants (Macaca Mulatta)

Abstract

The relationship between temperamental expressions of emotionality and postrotary nystagmus responses was investigated in infant rhesus monkeys. Thirty-three infants were tested on nine occasions during the first months of life using instruments adapted from human developmental tests. Assessments included a laboratory assessment of temperament and an adaptation of the Southern California Postrotary Nystagmus Test. Correlations among the nine postrotary nystagmus sessions were consistently high and positive indicating high test-retest stability of the postrotary nystagmus test for rhesus monkey infants. Infants with high rating on early laboratory assessments of fearfulness were found to exhibit shortened durations of postrotary nytagmus, shortened excursion lengths of postrotary nystagmus, more variance or day-to-day fluctuation in postrotary nystgmus, and less stability of rank order across the nine testing sessions when compared to infants categorized as bold. Possible mechanisms underlying the suggested ling between temperament and postrotary nystagmus responses in monkeys, as well as directions for future research, are discussed.