Interaction Studies Voice features of telephone operators predict auditory preferences of consumers. --Manuscript Draft-Manuscript Number:
IS-D-15-00008R3
Full Title:
Voice features of telephone operators predict auditory preferences of consumers.
Short Title:
Voice features of operator predict auditory preferences
Article Type:
Original Article
First Author:
Vanessa André
Other Authors:
Christine Petr Nicolas André Martine Hausberger Alban Lemasson
Corresponding Author:
Vanessa André Rennes, Bretain FRANCE
Funding Information: Section/Category:
Social behaviour & interaction
Keywords:
acoustic structure, human, phone interaction, prosody, voice perception
Manuscript Classifications:
10.03.01: Animal social behaviour; 20.01: Experimental; 10.05.06: Psycholinguistics
Abstract:
What makes a human voice agreeable is a matter of scientific discussion. Whereas prosody was shown to play a role regarding "male-female" attraction, the impact of frequency modulations in "non-sexual", notably commercial, contexts has attracted little attention. Another point unaddressed in the literature is auditory sensitivity to shortterm frequency modulations as current studies focus more on sentence. Thirty French female operators were recorded over the phone. All "bonjour" greeting words were classified in terms of frequency modulation linearity and orientation at the syllable and word levels. Then, the different voices were played back to students and seniors who had to rate each voice according to their degree of agreeableness. Listeners preferred non-monotonous voices. Differences between age-classes were greater than between sex-classes. Results suggest that short-term frequency changes are important for auditory evaluation of voice agreeableness. This study opens new research perspectives concerning the importance of prosody during consumer-seller interactions.
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Voice features of telephone operators predict auditory preferences of consumers. André, Vanessa;a Petr, Christine;b André, Nicolas;a Hausberger, Martine;a Lemasson, Albanc C.N.R.S., Ethologie animale et humaine, U.M.R. 6552 - Université de Rennes 1 –, Campus de Beaulieu 263 Avenue du General Leclerc, Bâtiment 25, 35042 Rennes, France a
Institut d’études politiques, Université de Rennes 1, 104 bd de la Duchesse Anne, 35700 Rennes, France b
c
Université de Rennes 1, Ethologie animale et humaine, UMR6552 - C.N.R.S., Station Biologique, 35380, Paimpont, France What makes a human voice agreeable is a matter of scientific discussion. Whereas prosody was shown to play a role regarding “male-female” attraction, the impact of frequency modulations in “non-sexual”, notably commercial, contexts has attracted little attention. Another point unaddressed in the literature is auditory sensitivity to shortterm frequency modulations as current studies focus more on sentence. Thirty French female operators were recorded over the phone. All “bonjour” greeting words were classified in terms of frequency modulation linearity and orientation at the syllable and word levels. Then, the different voices were played back to students and seniors who had to rate each voice according to their degree of agreeableness. Listeners preferred non-monotonous voices. Differences between age-classes were greater than between sex-classes. Results suggest that short-term frequency changes are important for auditory evaluation of voice agreeableness. This study opens new research perspectives concerning the importance of prosody during consumer-seller interactions. Key words: acoustic structure, human, phone interaction, prosody, voice perception Corresponding author: André Vanessa
[email protected] UMR 6552, Bâtiment 25, Campus de Beaulieu, 263 Avenue Général Leclerc 35042 Rennes, France +33670856489
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1. Introduction
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Regardless of the syntactic and the semantic content of speech, the phonetic
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organization of voices is commonly used by conversing interlocutors to assess each
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other’s identity, personality, arousal state and motivation (Bruckert, Lienard, Lacroix,
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Kreutzer and Leboucher, 2006; Collins, 2000; Feinberg, Jones, Little, Burt and Perrett,
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2005; Jones, Feinberg, DeBruine, Little and Vukovic, 2010; Scherer, 1972; Scherer,
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1978; Smith, Brown, Strong and Rencher, 1975). Thus, the interpretation of a word by a
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receiver is based first on facial expressions (55%), second on voice features (38%), and
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only third on lexical content (7%) (Mehrabian and Ferris, 1967), suggesting that in the
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absence of any visual clues, prosody plays a role in auditory perception. However, most
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studies have focused on women – men auditory sexual attraction and evaluation
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(Bruckert et al., 2006; Collins, 2000; Jones, Feinberg, DeBruine, Little and Vukovic,
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2008; Jones et al., 2010; Klofstad, Anderson and Peters, 2012; Re, O’Connor, Bennett
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and Feinberg, 2012; Simmons, Peters and Rhodes, 2011). Interestingly, a few studies
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also investigated vocal attractiveness in other social contexts (e.g. Bruckert et al, 2010).
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Nevertheless, little is still known about voice agreeableness and its impact on social
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interactions and notably in contexts where voices play a crucial role as in commercial
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interactions over the phone.
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A key acoustic feature playing a general role in auditory perception and evaluation
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is the pitch of a voice. Auditory recognition of gender and age is frequency-dependent;
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the voices of men and seniors are lower-pitched than those, respectively, of women and
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juniors (Bruckert et al., 2006; Latinus and Belin, 2011). Regardless of the age and the
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gender of both receivers and emitters, people with low-pitched voices are perceived as
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more dominant than people with high-pitched voices (Jones et al., 2010; Klofstad et al., 2
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2012). Conversely, men judge women with high-pitched voices to be more feminine
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than women with low-pitched voices (Collins and Missing, 2003; Jones et al., 2008).
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Similarly, men with low-pitched voices are considered to be more masculine, more
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corpulent (larger and taller) and more attractive to women than men with high-pitched
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voices (Collins, 2000; Feinberg et al., 2005; Jones et al., 2010). Higher pitches are
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associated with anger, joy and anxiety, whereas lower pitches are associated with
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sadness and indifference (Zetterholm, 1998).
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Voice variations in both temporal and frequency domains appear even more crucial
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for evaluation than pitch (Besson, Magne and Schon, 2002; Latinus and Belin, 2011).
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Some people with clinical disorders, such as schizophrenia or depression, are unable to
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detect these so-called prosodic variations in their interlocutors’ voices and thus have
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difficulties holding a proper conversation (Alpert, Pouget and Silva, 2001; Bach,
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Buxtorf, Grandjean and Strik, 2009; Péron et al., 2011). Among the different prosodic
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features, voice rhythm is of primal importance. For example, reasonably fast-speaking
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people are considered more competent and more persuasive than slow-speaking people
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in occidental cultures (Peng, Zebrowitz and Lee, 1993). However, speakers with very
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low or very high rhythms are considered less benevolent than speakers with
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intermediate rhythms (Brown, Strong and Rencher, 1973; Brown, Strong and Rencher,
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1974; Brown, William and Alvin, 1975; Smith et al., 1975). Frequency variations can
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also play a crucial role. In general, less monotonous voices (i.e. with frequent frequency
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changes for instance while reading a speech) are associated with more positive
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personalities (Zukerman and Miyake, 1993). However, most of the past studies focus on
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rhythm variations or frequency changes at the sentence or the word level (Brown et al.,
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1973; Brown et al., 1974; Brown et al., 1975; Peng et al., 1993; McAleer et al, 2014; 3
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Smith et al., 1975), and comparatively little is known concerning the impact of subtle
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frequency variations such as sudden within-word changes (at the syllable level). Subtle
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frequency variations concern both frequency linearity (linear vs non-linear frequencies
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within the syllable) and orientation (upward vs flat vs downward frequencies across the
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syllable), but again, to our knowledge, nothing is known concerning the relative
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importance of frequency modulations for evaluation by listeners.
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Unfamiliar interlocutors are frequently engaged in oral non-visual conversation,
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notably over the phone. A lot of companies use phone platforms to approach potential
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clients, so there is no visual signaling during conversations. Direct oral exchanges are
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rated more positively than electronically-written messages (Dillma et al., 2009),
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probably because they allow a better evaluation of the interlocutor. Reports suggest that
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prosody plays a role during phone interviews. Questionnaire survey results indicate that
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people say that they would agree more easily to answer questions over the phone when
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the caller’s voice was not monotonous in terms of sentence intonation (Oksenberg,
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Coleman and Cannell, 1986; Benkí, Broome, Conrad, Groves and Kreuter, 2011).
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The current study evaluated the impact of subtle frequency changes (i.e. variation of
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frequency linearity and orientation) in phone operators’ voices (at the syllable and word
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levels) on their agreeableness rating by potential consumers. First, we phoned different
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grocery stores in order to record the voices of various female telephone operators and
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then classified the recorded voices in terms of frequency modulation linearity and
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orientation. Second, the different voices were played back to a panel of junior (students)
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and senior men and women for evaluation. Third, we crossed acoustic and
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agreeableness data. The impacts of the sex and the age of the listener were assessed.
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The sex of the listener is supposed to play a role in evaluation ratings (Collins, 2000; 4
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Feinberg et al., 2005; Jones et al., 2010), but it is not known whether this is also true in
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a commercial context. Although reports show that age impacts differently adult and
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children listeners’ agreeableness evaluations (Saxton, DeBruine, Jones, Little and
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Roberts, 2009), we do not know whether age impacts adults’ evaluations.
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2. Methods
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2.1 Participants
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The group of participants (listeners) included 30 biology and psychology students at
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Rennes universities (France), between 18 and 26 years old (13 men, 17 women), and 30
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retired persons from various socio-professional categories, between 60 and 75 years old
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(12 men, 18 women). There was no age difference between males and females in each
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of the two age groups (Mann Whitney tests; students: U=92.500, Z=-0.756, P=0.457 /
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retired persons: U= 88.000, Z=0.829, P=0.415). All participants were French native
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speakers, living in Rennes city, and were naive to playback experiments.
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2.2 Protocol
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2.2.1 Voice recording of telephone operators
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The voices of 30 women operators, working in grocery stores in Rennes (France) were
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recorded during a phone conversation in February 2011. One experimenter (N. A.)
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phoned the reception of the store and inquired about their opening schedule. The
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conversation was recorded directly on a PC computer (Dell ® Latitude D600) using
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Audacity® (sampling rate 11kHz, resolution 16bit, .wav format). From these
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conversations, only the first greeting word pronounced by the operator was saved. As
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the study focused on the pronunciation of a single word with post-recording
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anonymized files, speaker identification was not possible. Hence, no approval was
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necessary. Hence, we collected a data set of 30 “Bonjour” ([bɔʒ̃ uʀ], meaning ‘Good 5
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morning’ in French) that was used for subsequent acoustic and playback analyses. The
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30 recordings were homogenized in intensity using ANA® software (Richard, 1991) so
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that the acoustic stimuli were comparable.
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2.2.2 Playback to participants and evaluation of the agreeableness of the voices
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To avoid any bias in our interpretation, we first made sure that all the seniors passed a
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cognitive test (MMSE “mini mental state examination” - Fostein, Folstein and McHugh,
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1975) and a test for geriatric depression (Yesavage et al., 1983). All the seniors
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successfully passed the screening tests. The Mini Mental State Examination (MMSE) is
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an 11-question measure. The maximum score is 30. A score of 23 or lower is indicative
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of cognitive impairment (Kurlowicz and Wallace, 1999). The students were exposed to
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playbacks in a quiet room of our laboratory and the seniors were tested at home. All
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raters declared to have no hearing problem. Each participant was informed in oral and
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written forms that this study aimed to determine the agreeableness of a person according
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to its vocal features. Participants were also informed: that they were going to listen to
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several recordings of telephone operator voices pronouncing a particular word; that each
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voice will be broadcast only once; that they had to rate each voice by responding to the
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question “Did you find this voice agreeable?” and by using the following rating scale: 1
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(not agreeable at all), 2 (No), 3 (neither-yes-nor-no), 4 (Yes), 5 (Yes very agreeable);
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and that there was no time restriction to answer. During the test, all the participants
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were in front of the researcher in the isolated experimental room. All participants
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completed all trials. We choose a five choice scale to make it comparable with what was
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used in comparative studies about evaluation of human feelings (Johnson, 1996;
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Kokkinos, 2007; Nagy, 2002; Trout, Magnusson and Hedges, 2000). The 30 voice
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stimuli were proposed to each participant in a different (random) order. Sounds were 6
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played back using a Hewlett Packard® house dv9000 computer connected to same
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Sennheiser® HD 25-1 II noise-cancelling headphones. In order to homogenize the
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amplitude of the different recorded voices, we used the function "Normalizer" of
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Audacity software to homogenize the amplitude of the different recorded voices.
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Participants informed the experimenter when they were ready to listen to the first voice,
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and had to rate the voice just heard before to ask for listening to the next one. The
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experimenter controlled the playbacks.
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2.2.3 Acoustic analyses
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The complexity of the frequency modulation (FM) of each voice stimulus was qualified
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using an acoustic classification, based on visual and audio analysis of spectrograms
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(Sampling frequency 11kHz, FFt-length 1024), commonly used in animal bioacoustics
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(Datta and Sturtivant, 2002; Hausberger, 1997; Lemasson and Hausberger, 2011;
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McCowan and Reiss, 1997): (1) FM linearity (linear vs non-linear), (2) FM orientation
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(upwards vs flat vs downwards) (Fig. 1). Hence, both syllables (‘bon’ vs ‘jour’) were
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blindly (i.e. the experimenter did not know the identity of the speaker or the score given
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to his/her voice) and independently scored in terms of linearity and orientation by a
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second experimenter (V. A.) (See examples in Fig. 2). In addition to this latter
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experimenter (A), two other persons (B and C, both were naive with the experiment and
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the second one was also naive with bioacoustics) were ask to rate all sonograms
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according to above-defined criteria of classification. Then, Cohen’s kappa were
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calculated to measure the agreement between raters (A-B: 0.97 / A-C: 0.88). This
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confirms the reproducibility of our rating as Cohen’s kappa greater than 0.85 is
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typically considered to be high (Cicchetti and Heavens, 1981).
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2.2.4 Data crossing and statistical analyses 7
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From the 1800 rates collected (i.e. 60 participants rated 30 voices each), we
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collected the following total of scores: 66 times “1”, 252 times “2”, 776 times “4” and
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154 times “5”.
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A first Binomial (agreeable vs disagreeable: when subjects gave a score equal to
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respectively ‘4 or 5’ vs ‘1 or 2’) Generalized Linear Model (GLM) compared the
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agreeableness scores of participants from the different age-sex classes in terms of FM
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linearity and orientation patterns for each syllable separately.
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Another Binomial (agreeable vs disagreeable) GLM evaluated the relative importance
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of FM orientation and linearity on the agreeableness scores given by participants from
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the different age-sex classes at the word level. For instance, a word was considered flat
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when both syllables were flat. Words were classified as follows (with L=linear,
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NL=non-linear, F=flat, NF=non-flat for each syllable): non-linear and non-flat (NLNL
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NFNF / LNL NFNF / LNL FNF / NLNL FNF), linear and non-flat (LL NFNF / LL
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NFF), non-linear and flat (NLNL FF / LNL FF), linear and flat (LL FF). Analyses were
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run with R software with FDR (False Discovery Rate) correction for multiple
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comparisons.
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3. Results 3.1 Analyses at the syllable level
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The agreeableness scores given by subjects showed that 69.70% and 30.30% of
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the voices heard were considered agreeable and disagreeable respectively. However,
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appreciations varied according to the listeners’ characteristics as well as to the acoustic
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pattern of frequency modulations (FM). While the listener’s sex did not influence voice
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appreciation scores (Table 1), age appeared a major factor as the seniors found the
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voices in general more agreeable than did the students (Fig. 3). 8
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Analyses of voice acoustic structures showed that both linearity and orientation
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of frequency modulations in the two syllables “bon” (1) and “jour” (2) were determinant
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(Table 1). Non-linear FM was preferred to linear FM, but only for syllable 1 (Fig. 4).
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Agreeableness scores regarding FM orientation patterns differed between the two
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syllables. Syllables 1 with an upward orientation were allocated the highest scores,
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whereas syllables 2 with a downward orientation were preferred (Fig. 5). Among non-
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flat voices, 81/90% were going upward and 19/10% were going downward on the
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first/second syllable. Significant interactions among factors were limited to sex and age
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with FM orientations (Table 1). Women found upward FM in syllable 2 more agreeable
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than men did (Fig. 6). The students found downward syllable 1 and upward syllable 2
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less agreeable than did the seniors. Flat syllables 1 and 2 were also found less agreeable
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by younger listeners (Fig. 7).
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3.2 Analyses at the word level
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None of the voices heard by subjects were linear and flat, 10% were flat and
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non-linear, 13.33% were linear and non-flat and 76.67% were non-linear and non-flat.
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Focusing the analysis on the word level showed that variations in evaluation appeared
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mostly based on orientation of frequency modulations: words with non-linear and non-
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flat frequency modulations were preferred to non-linear and flat words, whereas
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agreeableness scores of linear and non-flat words did not differ from the two other
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classes (Table 2, Fig. 8).
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Figure 9 shows spectrograms of typical agreeable (syllable 1: upwards and linear,
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syllable 2: downwards and non-linear) and disagreeable (syllable 1: flat and non-linear,
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syllable 2: flat and linear) voices.
9
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Moreover, whereas sex did not impact agreeableness scores, it varied with age (Table
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2). The seniors found non-linear words (both flat and non-flat) more agreeable than the
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students (Fig. 10).
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4. Discussion
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This study confirms that (1) subtle and sudden (at both syllable and word levels)
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frequency modulations in unfamiliar human voices impact auditory evaluation; (2) the
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voices of phone operators are not evaluated similarly by all potential consumers; (3) the
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age more than the sex of the listener impacts his/her agreeableness appreciation; and (4)
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variations in frequency orientations more than in frequency linearity determine the
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agreeableness of a voice, non-monotonous voices being allocated the highest rates of
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agreeableness. However, we first acknowledge that our conclusions are drawn from
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analyses conducted on fundamental frequencies only. Hence, further investigations on
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resonant frequencies would be interesting. Also, we used a relatively small sample size
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of raters and speakers. Hence, replicating this study with more varied speakers (e.g.
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different age-sex classes), more raters and rating contexts are now necessary.
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Our study is, to our knowledge, the first to evidence the differential impact of
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different kinds of subtle and sudden prosodic frequency modulations of human voices
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on auditory evaluation, particularly at the beginning of a word (first syllable). Hence,
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short-term prosodic changes seem as crucial as long-term changes. In line with this,
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some authors have shown that humans are able to categorize very quickly (in less than
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200ms) a voice as neutral or emotional (Chen and Yang, 2012; Paulmann, Schmidt, Pell
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and Kotz, 2008). Thus, people attribute particular emotional states to particular voice
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prosody (Bach et al., 2009; Latinus and Belin, 2011; Mehrabian and Ferris, 1967). For
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example, some authors showed that voices with large frequency variations are 10
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associated with a friendly personality, and speakers with high pitched voices are
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considered to be helpful and sincere (Brown et al., 1975; Chen and Yang, 2012;
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Zetterholm, 1998; Weirich, 2008). However, authors underline a cultural impact on the
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prosody evaluation. One study stresses that Koreans and Americans do not judge a
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given speaker in similar ways. More precisely, Americans, contrary to Koreans,
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associate a fast voice with a powerful and qualified person. However, when Korean
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participants live in the United States, their judgments converge with those of
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Americans. Indeed, they associate a fast rhythm with competence (Peng et al., 1993).
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Variations in frequency modulation orientation impact more than frequency
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modulation linearity, for each syllable as well as for an entire word. Non-flat voices are
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particularly positively evaluated. A first hypothesis predicts that changes in orientation
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are preferred to changes in linearity. A second hypothesis predicts that changes in
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orientation are more easily detectable than changes in linearity by a human ear. Indeed,
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some authors underline that some sounds (like tones) are more easily perceived by the
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human ear than others (like clicks) (Szymaszek, Szelag and Sliwowska, 2006). Even
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though linearity was not the most determining acoustic criterion, it did impact the
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evaluation of the first syllable of the word “Bonjour”. Thus we suppose that linearity
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variations are detected to some extent, and that evaluation is based more on a higher
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agreeableness score for orientation changes. Moreover, we showed that the type of
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orientation preferred in the first (upward) and in the second (downward) syllables
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differed. This should warn researchers of the difficulty to draw firm and general
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conclusions based on prosodic acoustic analyses conducted at a broad (e.g. sentence)
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level, as often found in the literature (Brown et al., 1973; Brown et al., 1974; Brown et
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al., 1975; Peng et al., 1993; Smith et al., 1975). We must acknowledge that our 11
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conclusions at the word level are based on a single greeting item and cannot be
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generalized to other words. Also, our data concern only French-speaking female phone
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operators and French student listeners. This limit is mentioned by other authors
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concerning the risk of “overgeneralization” (Montepare and Zebrowitz- McArthur,
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1987), and the important variations due to the cultural background of the subjects (Peng
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et al., 1993) and to the experimental context (Jones et al., 2008). Finally, future studies
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may want to go beyond the simple analysis of the fundamental frequency pattern and
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notably investigate variations in formants’ distribution.
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Here the listener sex effect on auditory evaluation was very limited, although
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most studies currently underline its importance, probably because they focus on the
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characteristics allowing people to attribute masculine and feminine features to speakers
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in a “sexual” attraction context (Collins, 2000; Feinberg et al., 2005; Feinberg et al.,
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2006; Jones et al., 2008; Jones et al., 2010; Little et al., 2010; Puts, 2005; Vukovic et
253
al., 2008). However, these authors found differences in the women’s preferences for
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masculine men’s voices according to their estrogen cycle, to the listening context (short-
255
term versus long-term mating contexts), and to their self-rated attractiveness (Feinberg
256
et al., 2006; Puts, 2005; Vukovic et al., 2008). As our study in a “commercial” context
257
could not evidence strong differences between men and women, the impact of prosody
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possibly varies according to the context of the conversation. It seems that,
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independently of context, men and women do not detect emotions in voices similarly.
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Men’s treatment of emotional prosody is slower than women’s (Besson et al., 2002).
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Moreover, the brain organizations for processing prosody differ between sexes
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(Imaizumi, Homma, Ozawa, Maruishi and Muranaka, 2004; Rymarczyk and
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Grabowska, 2007). These differences in perception and treatment of human voices can 12
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explain the fact that we found subtle differences in the agreeableness scores of the
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participants according to their gender. Particularly, we underlined that women allocated
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higher scores to upward frequency modulations than men did.
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Conversely to sex, age of listeners seems to be an important factor for voice
268
appreciation. Indeed, older people allocated higher scores to some voices than did
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younger people. Two hypotheses could explain this. First, because of an age-dependent
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auditory sensitivity seniors could be less sensitive than juniors to acoustic changes or to
271
the associated emotions. Several authors have reported that detection and perception of
272
prosody varies with age. Older people are less efficient and accurate in the detection of
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emotionally associated prosodic changes in a voice (Mill, Alink, Realo and Valk, 2009;
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Mitchell, 2007). The second hypothesis predicts an age-dependent acoustic preference.
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Some authors have shown that the positive or the negative valence assigned to voices
276
varies with age (Fecteau, Armony, Joanette and Belin 2005). This is confirmed by our
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data showing that seniors did not systematically rate higher all the voices, neither all the
278
modulated voices, but only some voices.
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5. Conclusion
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To summarize, this study is the first to our knowledge to evidence the impact of
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human voice prosody on a listener in a commercial context when it is particularly
282
important to use an agreeable voice, and it raises several fundamental and applied
283
perspectives. Moreover, whereas studies generally focus on long-term frequency
284
changes, our results underline the importance to focalize on subtle variations that have
285
been neglected until now.
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Acknowledgments
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The idea of this study emerged from scientific discussions among members of the
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interdisciplinary research network GIS “Cerveau, Comportement, Société”. This study
291
received financial support from the French Ministry of Research, the C.N.R.S. We
292
thank the receptionists and all the students and seniors for their participation in this
293
study. We are grateful to Ann Cloarec for correcting the English.
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Figure captions
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Fig. 1: Frequency modulation patterns used to classify syllables.
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Fig. 2: Spectrograms of frequency modulation patterns of the second syllable “jour”: (a)
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non-linear downwards, (b) non-linear upwards, (c) linear flat.
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Fig. 3: Voice agreeableness scores given by the students and the seniors (1: agreeable,
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0: disagreeable). Binomial Glm test ** P
