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. 2013 May 31;8(5):e66018.
doi: 10.1371/journal.pone.0066018. Print 2013.

Eye-blink behaviors in 71 species of primates

Hideoki Tada  1 , Yasuko Omori, Kumi Hirokawa, Hideki Ohira, Masaki Tomonaga
Affiliations

Eye-blink behaviors in 71 species of primates

Hideoki Tada et al. PLoS One. .

Abstract

The present study was performed to investigate the associations between eye-blink behaviors and various other factors in primates. We video-recorded 141 individuals across 71 primate species and analyzed the blink rate, blink duration, and "isolated" blink ratio (i.e., blinks without eye or head movement) in relation to activity rhythms, habitat types, group size, and body size factors. The results showed close relationships between three types of eye-blink measures and body size factors. All of these measures increased as a function of body weight. In addition, diurnal primates showed more blinks than nocturnal species even after controlling for body size factors. The most important findings were the relationships between eye-blink behaviors and social factors, e.g., group size. Among diurnal primates, only the blink rate was significantly correlated even after controlling for body size factors. The blink rate increased as the group size increased. Enlargement of the neocortex is strongly correlated with group size in primate species and considered strong evidence for the social brain hypothesis. Our results suggest that spontaneous eye-blinks have acquired a role in social communication, similar to grooming, to adapt to complex social living during primate evolution.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Two examples of eye-blinking behaviors in nonhuman primates.
Left: Black-and-white ruffed lemur (Varecia variegata); right: the drill (Mandrillus leucophaeus).
Figure 2
Figure 2. Mean blink rate as a function of activity rhythms.
Error bars show standard deviations.
Figure 3
Figure 3. Three eye-blink measures and body weight as functions of habitat type.
SD: standard deviation.
Figure 4
Figure 4. Scatterplots of the three measures for eye-blinking behaviors in primates as a function of body size and group size factors.
Red lines indicate the simple regression lines. ***: P < 0.001, **: P < 0.01, *: P < 0.05. A: arboreal; sA: semiarboreal; T: terrestrial.
Figure 5
Figure 5. Regression coefficients for body weight and group size factors for each eye-blink measure.
Error bars show 95% confidence intervals.
See this image and copyright information in PMC

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