Our research consisted of two studies focusing on the probability of humans being able to perceive the difference between faces expressing pain versus pleasure. As controls, we included: smile, neutral facial expression, and expression of fear. The first study was online and was conducted using a large sample (n=902) of respondents. The second study was conducted in a laboratory setting and involved a stress induction procedure. For both, the task was to categorize whether the facial expression was rated positive, neutral or negative. Stimuli were faces extracted from freely downloadable online videos. Each rating participant (rater) was presented with five facial expressions (stimuli) of five females and five males. All raters were presented with the stimuli twice so as to evaluate the consistency of the ratings. Beforehand, we tested for stimuli differences using specialized software and found decisive differences. Using a Bayesian statistical approach, we could test for consistencies and due-to-chance probabilities. The results support the expectation that the results are not repeatable but indeed solely due to chance, diminishing the communication value of the expressions of pain and pleasure. The expression of fear was also rated due to chance, but not neutral and smile. Stress induction did have an impact on the perception of pleasure.

No abstract

Our research consisted of two studies focusing on the probability of humans being able to perceive the difference between faces expressing pain versus pleasure. As controls, we included: smile, neutral facial expression, and expression of fear. The first study was conducted online and used a large sample (n = 902) of respondents. The second study was conducted in a laboratory setting and involved a stress induction procedure. For both, the task was to categorize whether the facial expression was rated positive, neutral or negative. Stimuli were faces extracted from freely downloadable online videos. Each rating participant (rater) was presented with five facial expressions (stimuli) of five females and of five males. All raters were presented with the stimuli twice so as to evaluate the consistency of the ratings. Beforehand, we tested for stimuli differences using specialized software and found decisive differences. Using a Bayesian statistical approach, we could test for consistencies and due-to-chance probabilities. The results support the prediction that the results are not repeatable but are solely due to chance, decreasing the communication value of the expressions of pain and pleasure. The expression of fear was also rated due to chance, but neither neutral nor smile. Stress induction did have an impact on the perception of pleasure.

No abstract

Our study focused on the ability of humans to correctly rate the valence of human facial expressions and vocalizations of high (pain and pleasure) and low intensity (laugh and neutral expression/speech) affective states. The study was conducted online and used a large sample (n=902) of respondents. The task was to categorize whether the human vocalization and facial expression as positive, neutral, or negative. The stimuli were audio records and pictures of facial expressions extracted from freely downloadable online videos and can be considered semi-naturalistic. Each rating participant was presented simultaneously with the facial expression and the vocalization of the affective states. Two of these with high intensity (pain and pleasure) and two of low intensity (laugh/smile and neutral). Each affective state was expressed and rated by female and male expressers. Using a Bayesian statistical approach, we could test due-to-chance probabilities (guessing). The outcomes support the prediction that affective states with higher intensity are harder to correctly rate, even with a bimodal presentation. Furthermore, in comparison with previous unimodal studies using the same stimuli, the results provide novel insight into systematic perception. Adding the vocalizations to the facial expressions results in the participants being more convinced in their choices independently of the correctness of the assessment as previously shown in auditory stimuli perception.