**3. Capacity of contagious laughter stimuli to provoke positive emotions in the listeners**

Given that not all laughter is accompanied by emotion and that laughter caused by contagious laughter can occur in the absence of a humorous situation and without the physical presence of the sender that induces this vocalization, it is not clear whether this vocalization is imitative vocal behavior not accompanied by positive emotions or whether contagious laughter is capable of eliciting these emotions in the listener. Based on this reasoning, the study by Arévalo-Pachón & Cruz [36] aimed to determine whether the acoustic stimuli of contagious laughter, in addition to generating laughter or smile behaviors [1], provoke positive emotions in receptors.

Since joy is a positive emotion compatible with the functions attributed to contagious laughter (facilitating social interaction) [30], this research selected it as

*Contagious Laughter as an Innate Acoustic Stimulus That Provokes Positive Emotions... DOI: http://dx.doi.org/10.5772/intechopen.108336*

the reference emotion. To determine the presence of this emotion in the different experimental conditions, the following dependent measures were used: (a) facial expressions: The facial expressions of the participants in the different experimental conditions were recorded using the Online video platform Hippo Video (Lyceum Technologies, Pvt. Ltd). Operationally, facial expressions were defined as the percentage of predominant emotions presented by the subjects when exposed to different laugh stimuli measured using the FaceReader software- Noldus Information Technology, bv.; (b) electromyographic (EMG) responses of the zygomatic muscle: electromyographic wave amplitude measured in volts by the "Biopack" hardware and the EMG 100-C module that allows amplifying the signals.

The two audios of female and male laughter rated as more contagious and the two audios of female and male laughter rated as less contagious were taken as laughter stimuli, according to the evaluation made by the 132 subjects of the study by Arévalo-Pachón and Cruz [29]. On the other hand, this study involved 60 university students from the city of Bogotá of both sexes (39 women and 21 men) aged between 18 and 30 years. The sample size was calculated using the GPower software (version 3.1.9.2). The research was carried out individually in the biofeedback laboratory of the Universidad de Los Andes.

The study used a within-subject experimental design in which each participant was exposed to a baseline condition and to different male and female laugh stimuli conditions. The experiment was applied using the OpenSesame program (version 3.2.7 of 2018), which made it possible to standardize the procedure and to control the confounding variables, and take the data of some dependent variables in a synchronized way in baseline and experimental conditions. The 4 contagious laughter stimuli selected were randomly presented with a duration of 12 seconds each, while the responses of the selected dependent variables were recorded. Before applying the experiment, a pilot study was carried out with six university students to whom the complete experiment was applied. This application allowed us to detect flaws in the procedure, instructions, and measurement of dependent variables.

The investigation formulated the following hypothesis: Compared with conditions of baseline and exposure to less contagious laughter stimuli, study participants will show greater facial expressions of joy and greater electromyographic (EMG) amplitude of the zygomatic muscle when exposed to more contagious male or female laughter stimuli. The data that allowed verifying this hypothesis are reported below.

The results of **Table 1** show significant differences in the expressions of joy when comparing the baseline data with those observed when the subjects are exposed to laughter stimuli classified as more contagious and when comparing the data of conditions of more contagious laughter stimuli vs. less contagious laughter stimuli of both sexes. In both comparisons, expressions of joy are significantly higher in exposures to more contagious laughter stimuli.

The significant data related to facial expression are relevant to verify the thesis that is intended to be supported in this chapter, since several authors, such as Maison and Pawlowska [37], have considered facial expression to be the most important form of emotional expression, especially in emotions that are expressed automatically. It is clear that exposure to more contagious laughter stimulus changes the percentage of joy expressions compared to baseline data. This finding indicates that contagious laughter not only has acoustic attributes that would indicate its spontaneity and, therefore, its emotional nature [29], but that the laughter caused by it would also have a clear emotional nature. On the other hand, the significant differences observed in the exposures to the more contagious versus the less contagious laughter could be


### **Table 1.**

*Statistical verification of differences between expressions of joy in different study conditions.*


### **Table 2.**

*Statistical verification of differences between EMG activity in different study conditions.*

### *Contagious Laughter as an Innate Acoustic Stimulus That Provokes Positive Emotions... DOI: http://dx.doi.org/10.5772/intechopen.108336*

interpreted as variations in the intensity of the expressions of this emotion proportional to the variations in the level of contagiousness of the laughter presented.

Based on the observed data on EMG activity in participants exposed to different conditions (**Table 2**), it can be stated that there are significant differences between (a) baseline and the most contagious male and female laughter stimuli conditions and (b) more contagious vs. less contagious laughter stimuli of both sexes.

Although EMG activity does not exactly discriminate the type of emotion experienced by an evaluated subject [27], it has been found that higher electrical activity in the zygomatic muscle is associated with positive effects and emotions (e.g., [38, 39]). Due to its high spatial resolution, facial EMG allows the detection of imperceptible emotional contractions of the zygomaticus for the observer or the emotion recognition software and due to its high temporal resolution, it can detect subtle and rapid changes in the electrical activity of the muscle [36, 38, 40]. Thus, the significant results observed in this study would confirm the emotional nature of the responses provoked by more contagious laughter stimuli and the difference in the intensity of this emotion proportional to the level of contagion of laughter presented.

The results in **Tables 1** and **2** and the observations of the subjects' responses in the different conditions showed that contagious laughter is able to induce an emotion that was not present or was minimally present in the receptors in the baseline condition. The fact that an exclusively acoustic stimulus shows such a capacity indicates its biological relevance and could be considered as supporting the thesis formulated in this chapter. It can be assumed that evolution favored this type of laughter as an inducer of positive emotions in congeners, although as occurs with other innate responses, there are differences in the susceptibility and intensity of receptor responses to this type of laughter [41].

Hatfield et al. [3] considered contagious laughter as a case of primitive emotional contagion, although they did not offer empirical evidence for this assumption; however, the data from this research would offer indirect support to the theory of emotional contagion [3, 42], since this laughter would not only induce this same vocalization in the listener, but also emotional contagion. Specifically, the reported findings would support the hypothesis of emotional contagion through exclusively acoustic stimuli. In this order of ideas, contagious laughter would have acquired an adaptive function that since ancient times would have helped human beings to increase their chances of survival [43] by favoring group cohesion and the achievement of common group goals.
