Impaired generalization of speaker identity in the perception of familiar and unfamiliar voices

In 2 behavioral experiments, we explored how the extraction of identity-related information from familiar and unfamiliar voices is affected by naturally occurring vocal flexibility and variability, introduced by different types of vocalizations and levels of volitional control during production. In a first experiment, participants performed a speaker discrimination task on vowels, volitional (acted) laughter, and spontaneous (authentic) laughter from 5 unfamiliar speakers. We found that performance was significantly impaired for spontaneous laughter, a vocalization produced under reduced volitional control. We additionally found that the detection of identity-related information fails to generalize across different types of nonverbal vocalizations (e.g., laughter vs. vowels) and across mismatches in volitional control within vocalization pairs (e.g., volitional laughter vs. spontaneous laughter), with performance levels indicating an inability to discriminate between speakers. In a second experiment, we explored whether personal familiarity with the speakers would afford greater accuracy and better generalization of identity perception. Using new stimuli, we largely replicated our previous findings: whereas familiarity afforded a consistent performance advantage for speaker discriminations, the experimental manipulations impaired performance to similar extents for familiar and unfamiliar listener groups. We discuss our findings with reference to prototype-based models of voice processing and suggest potential underlying mechanisms and representations of familiar and unfamiliar voice perception. (PsycINFO Database Record (c) 2016 APA, all rights reserved

Impoverished encoding of speaker identity in spontaneous laughter

Our ability to perceive person identity from other human voices has been described as prodigious. However, emerging evidence points to limitations in this skill. In this study, we investigated the recent and striking finding that identity perception from spontaneous laughter - a frequently occurring and important social signal in human vocal communication - is significantly impaired relative to identity perception from volitional (acted) laughter. We report the findings of an experiment in which listeners made speaker discrimination judgements from pairs of volitional and spontaneous laughter samples. The experimental design employed a range of different conditions, designed to disentangle the effects of laughter production mode versus perceptual features on the extraction of speaker identity. We find that the major driving factor of reduced accuracy for spontaneous laughter is not its perceived emotional quality but rather its distinct production mode, which is phylogenetically homologous with other primates. These results suggest that identity-related information is less successfully encoded in spontaneously produced (laughter) vocalisations. We therefore propose that claims for a limitless human capacity to process identity-related information from voices may be linked to the evolution of volitional vocal control and the emergence of articulate speech

Flexible voices : Identity perception from variable vocal signals

Human voices are extremely variable: The same person can sound very different depending on whether they are speaking, laughing, shouting or whispering. In order to successfully recognise someone from their voice, a listener needs to be able to generalize across these different vocal signals (‘telling people together’). However, in most studies of voice-identity processing to date, the substantial within-person variability has been eliminated through the use of highly controlled stimuli, thus focussing on how we tell people apart. We argue that this obscures our understanding of voice-identity processing by controlling away an essential feature of vocal stimuli that may include diagnostic information. In this paper, we propose that we need to extend the focus of voice-identity research to account for both “telling people together” as well as “telling people apart.” That is, we must account for whether, and to what extent, listeners can overcome within-person variability to obtain a stable percept of person identity from vocal cues. To do this, our theoretical and methodological frameworks need to be adjusted to explicitly include the study of within-person variability

Trait evaluations of faces and voices: Comparing within- and between-person variability

Human faces and voices are rich sources of information that can vary in many different ways. Most of the literature on face/voice perception has focussed on understanding how people look and sound different to each other (between-person variability). However, recent studies highlight the ways in which the same person can look and sound different on different occasions (within-person variability). Across three experiments, we examined how within- and between-person variability relate to one another for social trait impressions by collecting trait ratings attributed to multiple face images and voice recordings of the same people. We find that within-person variability in social trait evaluations is at least as great as between-person variability. Using different stimulus sets across experiments, trait impressions of voices are consistently more variable within people than between people – a pattern that is only evident occasionally when judging faces. Our findings highlight the importance of understanding within-person variability, showing how judgements of the same person can vary widely on different encounters and quantify how this pattern differs for voice and face perception. The work consequently has implications for theoretical models proposing that voices can be considered ‘auditory faces’ and imposes limitations to the ‘kernel of truth’ hypothesis of trait evaluations

Neural correlates of the affective properties of spontaneous and volitional laughter types

Previous investigations of vocal expressions of emotion have identified acoustic and perceptual distinctions between expressions of different emotion categories, and between spontaneous and volitional (or acted) variants of a given category. Recent work on laughter has identified relationships between acoustic properties of laughs and their perceived affective properties (arousal and valence) that are similar across spontaneous and volitional types (Bryant & Aktipis, 2014; Lavan et al., 2016). In the current study, we explored the neural correlates of such relationships by measuring modulations of the BOLD response in the presence of itemwise variability in the subjective affective properties of spontaneous and volitional laughter. Across all laughs, and within spontaneous and volitional sets, we consistently observed linear increases in the response of bilateral auditory cortices (including Heschl's gyrus and superior temporal gyrus [STG]) associated with higher ratings of perceived arousal, valence and authenticity. Areas in the anterior medial prefrontal cortex (amPFC) showed negative linear correlations with valence and authenticity ratings across the full set of spontaneous and volitional laughs; in line with previous research (McGettigan et al., 2015; Szameitat et al., 2010), we suggest that this reflects increased engagement of these regions in response to laughter of greater social ambiguity. Strikingly, an investigation of higher-order relationships between the entire laughter set and the neural response revealed a positive quadratic profile of the BOLD response in right-dominant STG (extending onto the dorsal bank of the STS), where this region responded most strongly to laughs rated at the extremes of the authenticity scale. While previous studies claimed a role for right STG in bipolar representation of emotional valence, we instead argue that this may in fact exhibit a relatively categorical response to emotional signals, whether positive or negative

Speaker Sex Perception from Spontaneous and Volitional Nonverbal Vocalizations.

In two experiments, we explore how speaker sex recognition is affected by vocal flexibility, introduced by volitional and spontaneous vocalizations. In Experiment 1, participants judged speaker sex from two spontaneous vocalizations, laughter and crying, and volitionally produced vowels. Striking effects of speaker sex emerged: For male vocalizations, listeners' performance was significantly impaired for spontaneous vocalizations (laughter and crying) compared to a volitional baseline (repeated vowels), a pattern that was also reflected in longer reaction times for spontaneous vocalizations. Further, performance was less accurate for laughter than crying. For female vocalizations, a different pattern emerged. In Experiment 2, we largely replicated the findings of Experiment 1 using spontaneous laughter, volitional laughter and (volitional) vowels: here, performance for male vocalizations was impaired for spontaneous laughter compared to both volitional laughter and vowels, providing further evidence that differences in volitional control over vocal production may modulate our ability to accurately perceive speaker sex from vocal signals. For both experiments, acoustic analyses showed relationships between stimulus fundamental frequency (F0) and the participants' responses. The higher the F0 of a vocal signal, the more likely listeners were to perceive a vocalization as being produced by a female speaker, an effect that was more pronounced for vocalizations produced by males. We discuss the results in terms of the availability of salient acoustic cues across different vocalizations