Recent research published in Cognition and Emotion reveals how subtle changes in eye appearance can significantly affect people’s perceptions and charitable behavior towards non-human primates.
Two experimental studies led by a team of researchers found that primate portraits featuring larger pupils elicited more favorable impressions and encouraged greater donations to conservation efforts.
This effect was particularly noticeable when the irises were brighter, which accentuated the visibility of pupil size.
Eye Characteristics and Social Interaction
Eyes play a critical role in social interaction, as they are vital for nonverbal communication and forming interpersonal relationships.
Literature indicates that pupil size serves as a cue for emotions, interest, and trustworthiness—larger pupils are often associated with warmth and allure, whereas smaller pupils can indicate disinterest or sadness.
However, the impact of iris brightness on these dynamics had not been thoroughly explored until this research.
Study Design and Methodology
The research unfolded in two phases involving participants from Leiden University.
In the first study, 64 students evaluated digitally modified images of 32 distinct non-human primate species, each carefully chosen to represent a wide array of primate lineages.
This selection aimed to ensure that the findings were applicable across various primate types and minimized bias toward particularly attractive species.
Participants assessed the primates based on traits such as cuteness, approachability, and allure while deciding on monetary donations for conservation, with options ranging from zero to twenty euros.
The researchers manipulated pupil appearance to be either constricted or dilated while keeping iris brightness constant.
The second phase included 121 participants who assessed primates with both manipulated iris brightness and pupil size through digital adjustments.
Participants rated the primates and made donations, allowing the researchers to analyze how changes in these two features influenced perceptions.
Findings and Implications
To maintain the integrity of the findings, the testing was conducted individually on an online platform, with directives aimed at minimizing distractions.
The researchers implemented measures to exclude participants who recognized the changes made to the images.
The results consistently showed that larger pupils led to more favorable evaluations regarding cuteness, friendliness, and attractiveness.
In the first study, participants were more inclined to donate to primates exhibiting dilated pupils, although the effect was modest.
Notably, pupil size effects varied among species, with more pronounced outcomes for primates whose iris color made pupil size more noticeable.
Perea-García expressed surprise at these findings, noting his initial skepticism about previous studies linking pupil size to social judgments.
The second study further reinforced the initial outcomes, showing that primates with brighter irises received higher ratings for cuteness and friendliness, but only when their pupils were dilated.
Conversely, when pupils were constricted, brighter irises resulted in lower evaluations.
Donations reached their highest for primates displaying a combination of bright irises and dilated pupils, signifying that this pairing enhanced perceptions of likability and positive emotional expression.
The subtlety of these influences is significant, with Perea-García observing that seemingly trivial details can sway responses in ways that people may not consciously recognize.
While the study focused on endangered primates, it underscores a broader tendency to make judgments based on appearance, prompting a call for skepticism and delayed judgment in first impressions due to inherent biases.
Nonetheless, the research has limitations.
The digital alterations may not fully represent the natural variations observed in live environments.
Future studies could explore these variables through real-time interactions or video stimuli.
The key takeaway is that the researchers manipulated eye features beyond what typically occurs in nature, a practice referred to as “hyper stimulus.” Although common in research and not inherently compromising the findings, this remains an important consideration.
While the focus on non-human primates helps mitigate pre-existing biases, questions arise about how these findings may inform human social contexts.
Investigating these dynamics among people could yield a deeper understanding of underlying mechanisms.
Perea-García recognizes that visual perception is closely tied to environmental lighting, which varies significantly across the habitats of different primate species.
Just as human skin tones adapt to variations in light, so do the eye features of primates.
Ultimately, the desire exists to reconcile the multiple functions of eyes in both communication and visual perception, reflecting on the evolutionary pressures that shape these characteristics.
For those interested, supplementary materials are provided in the article detailing participants’ rankings of various species across different dimensions, piquing curiosity about how personal evaluations align with collective perceptions.
The study, titled “Pupil size and iris brightness interact to affect prosocial behaviour and affective responses,” was authored by Juan Olvido Perea-García, Daisy Berris, Jingzhi Tan, and Mariska E. Kret.
“`htmlStudy Details:
- Title: Pupil size and iris brightness interact to affect prosocial behaviour and affective responses
- Authors: Juan Olvido Perea-García, Daisy Berris, Jingzhi Tan, and Mariska E. Kret
- Journal: Cognition and Emotion
- Publication Date: 2024
- DOI: 10.1080/02699931.2024.2427340