Humans Need Auditory Experience to Produce Typical Volitional Nonverbal Vocalizations

Introduction

This research paper explores whether humans require auditory input to produce nonverbal emotional expressions (such as screams and cries). While these nonverbal vocalizations seem to have a strong reflexive basis, many emotional vocalizations are under our voluntary control. This suggests that these vocalizations, like language, may require auditory input for normal development. To test this hypothesis, the authors analyzed hundreds of volitional vocalizations produced by completely deaf adults and a control group with typical hearing.

Source Introduction

This article was published in “Communications Psychology” in 2024, co-authored by Katarzyna Pisanski, David Reby, and Anna Oleszkiewicz. The authors are affiliated with the ENES bioacoustics research laboratory, CRNL Center for Research in Neuroscience in Lyon, University of Saint-étienne, France; the CNRS French National Centre for Scientific Research; the Institute of Psychology, University of Wrocław, Poland; and the Department of Otorhinolaryngology, Technische Universität Dresden, Germany.

Research Process

Subjects and Experimental Design

The study included 60 completely deaf adults and 60 control subjects with normal hearing, matched by gender and age. All subjects were asked to produce nonverbal vocalizations expressing aggression, pain, and fear, with each person producing three audio samples, totaling 360 vocal samples.

Sound Collection and Analysis

Sound collection was conducted in a quiet room using 24-bit quantization and 48kHz sampling rate recording equipment. Acoustic analysis was then performed using the open-source software Praat and R package soundgen, including 15 sound parameters such as fundamental frequency (pitch), vibrato, noise, amplitude, and nonlinear phenomena.

Data Analysis

Linear Mixed Models (LMMs) were used to compare the vocal samples of deaf subjects and the control group, mainly considering the spectrotemporal structure of the vocalizations. The study also conducted a series of auditory perception experiments to assess how listeners identify and perceive these vocalizations.

Main Research Findings

Vocal Analysis Results

1. Abnormal structure of nonverbal vocalizations in deaf subjects: Vocalizations produced by deaf adults were generally high-pitched, monotonous, lacking nonlinear phenomena, and without effective phonemes. This was particularly unusual when expressing aggression and pain. In the control group, aggressive vocalizations were typically low-frequency, sharp, and contained more nonlinear phenomena, while deaf subjects’ vocalizations were the opposite, appearing overly tonal and lacking sharpness and roughness.

2. Relative normality of fear vocalizations: In comparison, the fear vocalizations of deaf subjects were relatively more typical, although they were still identified as having more high-frequency sounds but with lower overall distortion. This suggests that fear vocalizations may have a stronger inherent and biological basis, allowing them to develop normally with less auditory input.

Auditory Perception Experiment Results

1. Accuracy of emotional identification: In a forced-choice task, listeners were able to more accurately identify the emotional intent of nonverbal vocalizations from the control group, while the accuracy rate for the deaf group significantly decreased. Specifically, aggressive vocalizations from the deaf group were more often misidentified as fear or pain.

2. Authenticity judgment: Listeners found the vocalizations of deaf subjects less authentic than those of the control group, especially when expressing aggression. This is related to their lack of typical aggressive characteristics, while the authenticity assessments for pain and fear were relatively closer.

3. Identification of hearing loss: Listeners were able to auditorily determine whether the vocalizer had hearing loss, indicating that the nonverbal vocalizations of deaf subjects are structurally significantly different from those of people with normal hearing.

Additional Impact of Severe Auditory Deprivation

The study further divided deaf subjects into two groups: those with no auditory experience (congenitally deaf and never used hearing aids) and those with partial auditory experience. Results showed that subjects with no auditory experience exhibited the most severe vocal structure abnormalities and emotional recognition difficulties.

Conclusion and Significance

This study demonstrates that humans indeed need auditory input to produce typical volitional nonverbal vocalizations. This finding emphasizes the importance of auditory experience in vocal development, indicating that not only language but also nonverbal emotional sounds require sound learning to achieve their full expression. The recorded vocal abnormalities also reflect the crucial role of auditory input in emotional expression, providing new insights and intervention directions for emotional communication in people with hearing impairments.

This research not only advances our understanding of human vocalization behavior and emotional expression mechanisms but also provides valuable scientific basis and potential intervention methods for nonverbal communication in individuals with hearing impairments.