Abstract
Research on colour preferences in humans and non-human primates suggests similar patterns of biases for and avoidance of specific colours, indicating that these colours are connected to a psychological reaction. Similarly, in the acoustic domain, approach reactions to consonant sounds (considered as positive) and avoidance reactions to dissonant sounds (considered as negative) have been found in human adults and children, and it has been demonstrated that non-human primates are able to discriminate between consonant and dissonant sounds. Yet it remains unclear whether the visual and acoustic approach–avoidance patterns remain consistent when both types of stimuli are combined, how they relate to and influence each other, and whether these are similar for humans and other primates. Therefore, to investigate whether gaze duration biases for colours are similar across primates and whether reactions to consonant and dissonant sounds cumulate with reactions to specific colours, we conducted an eye-tracking study in which we compared humans with one species of great apes, the orangutans. We presented four different colours either in isolation or in combination with consonant and dissonant sounds. We hypothesised that the viewing time for specific colours should be influenced by dissonant sounds and that previously existing avoidance behaviours with regard to colours should be intensified, reflecting their association with negative acoustic information. The results showed that the humans had constant gaze durations which were independent of the auditory stimulus, with a clear avoidance of yellow. In contrast, the orangutans did not show any clear gaze duration bias or avoidance of colours, and they were also not influenced by the auditory stimuli. In conclusion, our findings only partially support the previously identified pattern of biases for and avoidance of specific colours in humans and do not confirm such a pattern for orangutans.
Highlights
The capacity for trichromatic colour vision has evolved in many primates, including humans
We examined gaze fixation durations for the four colours blue, red, yellow and green, both separately and in combination with an auditory stimulus comprising a consonant or dissonant triad and chord
The likelihood ratio test between model 4 and model 5 indicated that including the cross-level interaction between Colour and Group in model 5 significantly improved the fit of the model to the data, which means that species-specific differences existed in relation to the factor Colour
Summary
The capacity for trichromatic colour vision has evolved in many primates, including humans. Two hypothesized functions for the evolution of trichromatic colour vision are that this capability provided advantages in detecting ripe fruits and in detecting young leaves [2, 7]. There does not seem to be a consistent difference between fruit predominantly consumed by dichromats and that predominantly consumed by trichromats [2, 8] Another hypothesized function of trichromatic colour vision is the advantage of being able to discriminate modulations in the skin colour of conspecifics for extracting information about emotional states, socio-sexual signals and threat displays [9]. Sensitivity to signal colours probably influences preferences for specific colours This raises the question, in regard to humans and non-human great apes, whether shared colour biases could have evolved together with the evolution of colour vision. Osorio and Vorobyev [8] noted that there are different perspectives regarding the evolution of sensory systems: “One is that communication signals evolve in response to a fixed sensory system [14], the other is that senses and signals co-evolve as a specialised communication system.” If senses and signals co-evolved, it could be that biases for specific colours are linked to this communication system
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