Friends of the Nonverbal Communication Blog, this week we present the paper “Pupil dilation reflects the authenticity of received nonverbal vocalizations” by Cosme, G.; Rosa, P. J.; Lima, C. F.; Tavares, V.; Scott, S.; Chen, S.; Wilcockson, T. D.; Crawford, T. and Prata, D. (2021), in which authors wonder whether a reaction by the autonomic nervous system exists when we listen nonverbal vocalizations and we judge if they are genuine or not.

Lie detection is one of the more controversial areas of study in nonverbal communication.

Not only body movements are studied when it comes about discover lies, but also the authenticity of the emotions showed.

This process is something we do voluntarily and involuntarily too, because the emotions we express and receive in social interactions are extremely important to stablish bonds. From a biological and evolutive point of view, they mark the difference between surviving or not.

Emotions can be expressed with nonverbal vocalizations and yet they can provide valuable information.

Crying, for example, is an intense emotional expression of a negative state often accompanied by lacrimation. In a social context, is assumed to have the purpose of eliciting help from listeners, or, in an interpersonal context, is understood to function as relief and improve mood after shed tears.

On the contrary, laughter is an emotional expression of a positive state and has the role of promoting and maintaining social bonding.

Authors say that previous studies have shown that some differences exist between real and faked laughter and cries. Authentic ones are often more highly pitched and longer in duration. Moreover, they have more variable pitch, lower harmonicity and less regular temporal structure.

On one hand, whereas genuine laughter is a reaction to a positive and surprising stimulus, acted laughter is associated with polite agreement and fake appreciation in formal contexts.

On the other hand, authentic crying is a genuine reaction to a negative stimulus, while acted crying is associated with manipulative social deception.

Authors explain that, according to previous works, interpreting non-authentic stimuli, and solving its ambiguity, is cognitively demanding. This is when pupil dilation comes into play.

Pupil size is used as proxy of arousal and cognitive effort in emotion research, and it depends on autonomic nervous system activity.

The pupil dilates with higher arousal elicited by a stimulus, thus, emotionally charged vocalizations evoke higher pupil dilation compared to the others. In addition, the pupil also dilates with cognitive effort, which is something we have already mentioned.

Considering what has been explained, authors wonder, for the first time, if the process of authenticity recognition in nonverbal emotional cues indues an autonomic nervous system response in the listener. The response would be the pupil dilation or contraction.

To carry out their study, authors have two hypotheses. The first prediction is that authentic vocalizations would elicit higher pupil dilation compared to acted, because they have been found to be more arousing in general, and pupil dilation increases with arousal.

Secondly, they ask themselves if authentic vocalizations would elicit lower pupil dilation, because authenticity discrimination, at least in laughter, has been found to decrease the cognitive effort.

A total of 28 people participated in the study. They were filmed while they listened to cries and laughter that were genuine or fake.

Results were interesting, because has been proved for the first time that authenticity recognition in human vocalizations has effects on pupil dilation.

Authors observed that fake laughter elicit higher pupil dilation than authentic ones. The opposite was observed with cries, genuine ones provoke higher pupil dilation that fake cries.

These consequences are explained by authors in the following way.

We must bear in mind that they work with the ideas that cognitive effort is related to pupil dilation and that is possible that the same happens if we talk about intensity in the listened emotions.

Authors comment that is possible that the reason why obtained results are like this, is that the discriminating authenticity in laughs depends more on cognitive effort than on emotional arousal, whilst in cries, the discrimination of authenticity may depend more on the level of emotional arousal they elicit.

Besides, there are more things that may influence these results. For instance, the fact that a fake laugh is considered a more recent cultural tool from an evolutive point of view, whereas fake cries are thought to have a manipulative role. Plus, genuine crying has a biological function of alarm and provokes an intense emotional response when it is heard.

One of the limitations of this study is that information about pupil dilation may be lost with the blinks. Authors say they will try to improve this in future research.

The most important thing in this experiment, it is that it is confirmed that a pupilar response exists, and thus, a response from the autonomic nervous system, when it comes about distinguish which nonverbal vocalizations are true or faked.

Nevertheless, as this is a novel study, authors point out the need of delve into this topic.

NonVerbal Communication Blog