Was That a Scream? Listener Agreement and Major Distinguishing Acoustic Features

Human screams have been suggested to comprise a salient and readily identified call type, yet few studies have explored the degree to which people agree on what constitutes a scream, and the defining acoustic structure of screams has not been fully determined. In this study, participants listened to 75 human vocal sounds, representing both a broad acoustical range and array of emotional contexts, and classified each as to whether it was a scream or not. Participants showed substantial agreement on which sounds were considered screams, consistent with the idea of screams as a basic call type. Agreement on classifications was related to participant gender, emotion processing accuracy, and empathy. To characterize the acoustic structure of screams, we measured the stimuli on 27 acoustic parameters. Principal components analysis and generalized linear mixed modeling indicated that classification as a scream was positively correlated with 3 acoustic dimensions: one corresponding to high pitch and roughness, another corresponding to wide fundamental frequency variability and narrow interquartile range bandwidth, and a third positively correlated with peak frequency slope. Twenty-six stimuli were agreed upon by > 90% of participants to be screams, but these were not acoustically homogeneous, and others evoked mixed responses. These results suggest that while screams might represent a salient and possibly innate call type, they also exhibit perceptual and acoustic gradation, perhaps reflecting the wide range of emotions and contexts in which they occur.