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.

The purpose of this study was to investigate the influence of frequency of blinking on creating a personal impression. The subjects were 88 Japanese university students, 35 males and 53 females, who rated stimulus persons on a seven-point semantic differential scale. The stimulus persons, two males and two females, were presented on a 20-second video simulating various blink rates, i.e., 3, 6, 9, 12, 18, 24, 36, 48, 72, and 96 blinks/min. A factor analysis of the ratings yielded three factors, interpreted as Nervousness, Unfriendliness, and Carelessness. As the frequency of the stimulus persons'blinking increased, so did the tendency to rate them as more nervous and more careless. As for Unfriendliness, there was a U-shaped relation between the frequency of blinking and the impressions formed. Present results provide evidence that frequency of blinking plays an important role in impression formation. Further implications of the findings are discussed.

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Aim This cross‐sectional study aimed to investigate the associations between salivary testosterone concentrations and cognitive function in 70‐year‐old Japanese elderly people without dementia and stroke. Methods Participants were 197 Japanese community‐dwelling people aged 69–71 years. Their salivary samples were collected, and their cognitive function was assessed using the Japanese version of the Montreal Cognitive Assessment (MoCA‐J). Participants were also administered a 10‐item recall and a 24‐item recognition test. The data for 179 (106 men and 73 women) individuals were analyzed, excluding individuals with a past history of stroke and dementia. Multivariate logistic regression analyses were performed after adjusting for lifestyle factors and analyzing data separately for men and women. Results MoCA‐J scores showed that men with low testosterone concentrations had a significantly greater risk of low cognitive performance than those with high testosterone concentrations (adjusted odds ratio: 4.72, 95% confidence interval: 1.06–21.00), while no significant association was found in women. The 10‐item recall test scores showed that higher testosterone concentrations were significantly associated with greater recall in the second trial in women (standardized beta = 0.24, P = 0.040), whereas no significant association was found in men. Salivary testosterone concentrations were positively associated with better cognitive performance in older men and women. Conclusions The associations between salivary testosterone concentrations and cognitive function were shown by different tasks for men and women. Geriatr Gerontol Int 2022; 22: 1040–1046.

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