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.

Our research consisted of two studies focusing on the probability of humans being able to perceive the difference between valence of human vocalizations of high (pain, pleasure and fear) and low intensity (laugh and neutral speech). 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 human vocalization was rated positive, neutral or negative. Stimuli were audio records extracted from freely downloadable online videos and can be considered semi-naturalistic. Each rating participant (rater) was presented with five audio records (stimuli) of five females and of five males. All raters were presented with the stimuli twice (so as to statistically estimate the consistency of the ratings). Using a Bayesian statistical approach, we could test for consistencies and due-to-chance probabilities. The outcomes support the prediction that the results (ratings) are repeatable (not due to chance) but incorrectly attributed, decreasing the communication value of the expressions of fear, pain, and pleasure. Stress induction (in study two conducted on 28 participants) did have an impact on the ratings of male neutral and laugh – it caused decrease in correct attribution.

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