Music-Induced Arousal and Individual Differences Predict Pupillary Responses

12 Pages·2015·0.94 MB·English

by  Bruno Gingras

ORIGINALRESEARCH
published:10November2015
doi:10.3389/fnhum.2015.00619
The Eye is Listening: Music-Induced
Arousal and Individual Differences
Predict Pupillary Responses
BrunoGingras1*,ManuelaM.Marin2,EstelaPuig-Waldmüller3 andW.T.Fitch3
1InstituteofPsychology,UniversityofInnsbruck,Innsbruck,Austria,2DepartmentofBasicPsychologicalResearchand
ResearchMethods,UniversityofVienna,Vienna,Austria,3DepartmentofCognitiveBiology,UniversityofVienna,Vienna,
Austria
Pupillary responses are a well-known indicator of emotional arousal but have not yet
been systematically investigated in response to music. Here, we measured pupillary
dilations evoked by short musical excerpts normalized for intensity and selected for
their stylistic uniformity. Thirty participants (15 females) provided subjective ratings of
music-induced felt arousal, tension,pleasantness, and familiarity for80 classical music
excerpts.Thepupillary responsesevokedbytheseexcerptsweremeasured inanother
thirty participants (15 females). We probed the role of listener-specific characteristics
suchasmood, stress reactivity, self-reported role of music in life,liking fortheselected
excerpts, as well as of subjective responses to music, in pupillary responses. Linear
mixed model analyses showed that a greater role of music in life was associated
with larger dilations, and that larger dilations were also predicted for excerpts rated
as more arousing or tense. However, an interaction between arousal and liking for the
excerpts suggested that pupillary responses were modulated less strongly by arousal
Editedby:
DanielJ.Graham, when the excerpts were particularly liked. An analogous interaction was observed
HobartandWilliamSmithColleges,
between tension and liking. Additionally, males exhibited larger dilations than females.
USA
Overall, these findings suggest a complex interplay between bottom-up and top-down
Reviewedby:
JosephPlazak, influencesonpupillaryresponsestomusic.
IllinoisWesleyanUniversity,USA
Yune-SangLee, Keywords:music,emotion,arousal,individualdifferences,pupillometry
UniversityofPennsylvania,USA
*Correspondence:
INTRODUCTION
BrunoGingras
[email protected]
Music is a powerful elicitor of emotions (Blood et al., 1999), and there is cumulative empirical
Received:26July2015 evidence that emotions induced by music share many components typical of emotions induced
Accepted:27October2015 by other types of sensory stimuli (Scherer, 2004; Juslin and Västfjäll, 2008). Musical emotions
Published:10November2015 can be evoked by various mechanisms that vary in their degree of relatednessto acoustical and
Citation: musicalproperties(JuslinandVästfjäll,2008).Emotion-inducingmechanismssuchasevaluative
GingrasB,MarinMM, conditioning or episodic memory donot depend on the music’sacoustical and musical features
Puig-WaldmüllerEandFitchWT but rather on the type of emotions induced by real-life events that were coupled with the
(2015)TheEyeisListening: experience of music (Juslin and Västfjäll, 2008). Conversely, emotion induction by emotional
Music-InducedArousalandIndividual
contagion is a mechanism that largely depends on the musical signal itself. Musical emotions
DifferencesPredictPupillary
areperceived,trigger physiological responses, andconcurrently induce emotions in the listener.
Responses.
Musically induced emotions are conveyed by two types of cues, comprising basic acoustic cues,
Front.Hum.Neurosci.9:619.
doi:10.3389/fnhum.2015.00619 such as those related to intensity (Juslin and Laukka, 2003; Ilie and Thompson, 2006), timbre
FrontiersinHumanNeuroscience|www.frontiersin.org 1 November2015|Volume9|Article619
Gingrasetal. Pupillaryresponsestomusiclistening
(Scherer and Oshinsky, 1977; Hailstone et al., 2009), pitch, illuminationcaninducepupillarydilationscorresponding toan
and tempo (Hevner, 1937; Ilie and Thompson, 2006), and increase of up to 4 mm, changes that are cognitively driven
culturally determined cues associated with a specific musical are more modest and are rarely greater than 0.5 mm (Beatty
system (Meyer, 1956). In particular, subjective arousal induced and Lucero-Wagoner, 2000), corresponding to a size increase
bymusichasbeenassociatedwithintensity,tempo,andspectral of approximately 20%. Additionally, pupillary responses seem
parameters such as spectral flux and spectral entropy (Gingras to be affected by the interaction between emotional influences
etal.,2014). and cognitive load. An earlier study by Stanners et al. (1979),
There is a growing body of research on psychophysiological which manipulated both cognitive load and arousal, concluded
indices of music-induced emotions, such as skin conductance, thatarousalaffectedpupillaryresponsesonlywhencognitiveload
heart rate, and facial electromyography (e.g., Gomez and was low. This finding is congruent with the fact that studies
Danuser, 2004; Rickard, 2004; Khalfa et al., 2008; Lundqvist reporting effects of emotion in terms of sympathetic activation
et al., 2009). However, very few studies have been published employed low cognitive-load tasks such as passive viewing or
on pupillary responses in relation to music, as pointed out in listening(PartalaandSurakka,2003).
a recent review (Hodges, 2010, Table 11.2), even though the To our knowledge, the earliest published study on music-
influence of emotional processing on pupillary responses has induced pupillary responses is that of Slaughter (1954), which
been clearly established with both pictures (Steinhauer et al., used a subjective,observational methodology to determine that
1983; Bradley et al., 2008) and environmental sounds (Partala stimulative music led to pupil dilation, while sedative music
and Surakka, 2003). Considering that music is recognized induced pupil constriction. Mudd et al. (1990) reported an
as a potent inducer of emotions in everyday life (Sloboda, associationbetweenpupilresponsestomusicandnoiseexcerpts
2010), especially with respect to emotional arousal (Khalfa and preference ratings. Using stimuli from the International
et al., 2002; Gomez and Danuser, 2004; van den Bosch et al., Affective Digitized Sounds(IADS) database (Bradleyand Lang,
2013), it would seem to be an ideal stimulus for investigating 1999), Partala and Surakka (2003) showed that pupil size
pupillary responses. In contrast to visual stimuli, auditory was larger during emotionally negative or positive stimuli
stimuli present an important advantage for the study of than during neutral sounds. Roy et al. (2009) observed
pupillary responses, in that methodological problems related that the startle eye blink reflex occurred faster and attained
to color, luminance, and contrast are circumvented (Hess and a larger amplitude for unpleasant music than for pleasant
Petrovich, 1987). Moreover, pupillometry is less invasive than music.
other psychophysiological measurements such as electrodermal In the present study, we investigated pupillary responses
activity, respiratory patterns, and heart rate. An additional to music within the context of the multicomponent model of
benefitofusingpupillaryresponsestoinvestigatemusic-induced musicalresponsesproposedbyHargreavesetal.(2005).Intheir
emotionsisthatpupillarydilationsinresponsetoexternalstimuli reciprocal feedback model, Hargreaves et al. (2005) describe
ormentaleventscannotbevoluntarilysuppressed(Loewenfeld, three main determinants of emotional responses to a musical
1993). stimulus: the music, the listening situation and the listener.
Variationsinpupilsizeareconsideredtobeareliableindicator Here, we focused more specifically on the combined influence
of autonomic nervous system (ANS)activity (Andreassi, 1995). of affective characteristics specific to a musical excerpt (such as
Importantly, pupil diameter is affected not only by changes arousalpotential)andtraitsassociatedwithaparticularlistener
in ambient light (the pupillary light reflex), but also by non- (such aspersonality traits ororientation tomusic) onpupillary
visual stimuli as well as cognitive load and affective processing responsestomusic.Modernstatisticalapproachessuchaslinear
(Goldwater,1972;Laengetal.,2012).Indeed,pupillary dilation mixed models (Laird and Ware, 1982) allow the estimation
has been observed in response to emotionally relevant visual of such excerpt-specific and listener-specific effects in a single
(Hess and Polt, 1960; Hess et al., 1965) or auditory (Dabbs, statisticalmodel.Inordertoinvestigatebotheffects,wecollected
1997;PartalaandSurakka,2003)stimuli,aswellastoincreased pupillary responses to a large set of short musical stimuli for
working memory (Kahneman and Beatty, 1966), or executive whichsubjectiveemotionandfamiliarityratingshadpreviously
loads(HessandPolt,1964;AhernandBeatty,1979). been collected (Gingras et al., 2014), and invited participants
Changes in pupil diameter are controlled by two muscles, to complete a series of questionnaires to assess their personal
the pupil dilator muscle and the pupillary sphincter. The characteristics.
activity of the dilator muscle is mediated by the sympathetic Because gender effects for psychophysiological arousal
pathway, whereas the pupillary sphincter is under control of measureshavebeenpreviouslyreported,withfemalesdisplaying
theparasympatheticsystem,mediatedbytheEdinger–Westphal stronger responses to highly arousing stimuli (Bradley et al.,
complex of the oculomotor nucleus (Steinhauer et al., 2004). 2001;PartalaandSurakka,2003;Nateretal.,2006),wepredicted
Although pupillary responses to increased cognitive load are that females would show greater pupillary dilation in response
primarily mediated by the parasympathetic system (Steinhauer to highly arousing stimuli. Since Nater et al. (2006) proposed
et al., 2004), pupil dilations observed in response to emotional that stress reactivity, for which females generally report higher
stimuli may involve activation of the dilator muscle by the values, may explain these gender effects, we also assessed
sympatheticsystem(Bradleyetal.,2008). participants’ stress reactivity. Moreover, stress reactivity has
Pupil diameter can react to stimulation in as little as also been discussed in relation to emotion regulation and
0.2 s (Lowenstein and Loewenfeld, 1962). Although changes in physiological functioning during music listening (Thoma etal.,
FrontiersinHumanNeuroscience|www.frontiersin.org 2 November2015|Volume9|Article619
Gingrasetal. Pupillaryresponsestomusiclistening
2012). Here, stress reactivity was evaluated using the German 2011). Additionally, to minimize potential confounds due to
StressReactivity Scale (SRS),which isbased onthe assumption effects of familiarity on emotion ratings (Witvliet and Vrana,
that four personality characteristics underlie stress reactivity: 2007; Marin and Leder, 2013; van den Bosch et al., 2013),
high intrusiveness, low self-efficacy, high arousability of the we chose a musical style with which most listeners are likely
central nervous system, and high negative affectivity (Schulz to be unaccustomed but which is still rooted in familiar
etal.,2005). Western major–minor tonality. The use of recordings of actual
Temporary mood states may affect emotion processing performancesensuredthatlistenershadaccesstoanyecologically
(Eerola and Vuoskoski, 2010; Schmid and Schmid Mast, relevant acoustic information that may play a role in eliciting
2010; Vuoskoski and Eerola, 2011; Cummings and Rennels, emotionalresponses.
2014), thus participants’ mood was assessed prior to the Finally, we considered the possible effect of sound intensity
experiment using the multidimensional mood questionnaire on pupil dilation. Stelmack and Siddle (1982) observed similar
(Mehrdimensionaler Befindlichkeitsfragebogen, MDBF; Steyer pupillaryresponsesforthreeintensitylevels(60,75,and90dB)
et al., 1997). Furthermore, we obtained overall liking ratings of a 1000-Hz pure tone and concluded that tone intensity had
for the music excerpts used in the experiment to account for noreliableeffectontheamplitudeofpupillarydilation.However,
individual differences regarding preferences for musical styles otherresearchersfound thatlouderpuretones(Nunnallyetal.,
(Kreutzetal.,2008)aswellasforthelinkbetweenphysiological 1967; Hirano et al., 1994) or broadband noise (Antikainen and
arousalandliking(Berlyne,1971;SchäferandSedlmeier,2010). Niemi, 1983) led to larger pupillary dilations. Because sound
Finally, participants were asked to estimate the frequency with intensity has been linked to subjective arousal (Scherer, 1989;
whichtheyexperiencedemotionswhilelisteningtotheexcerpts IlieandThompson,2006)andtomeasurementsofphysiological
during the experiment, andmore generallyto assessthe role of arousal such as skin conductance (Gomez and Danuser, 2007),
musicintheir livesasabroad measureofmusical engagement, we used amplitude-normalized excerpts for this study and
i.e.,involvementwithandinterestinmusic. verifiedthatourexcerptswereadequatelymatchedforperceptual
Both Partala and Surakka (2003) and Bradley et al. (2008) loudnessaswell(Gingrasetal.,2014).Amplitudenormalization
suggested, on the basis of their results, that pupil dilation is a procedure routinely used in psychoacoustic research (e.g.,
was determined mostly by emotional arousal. Bradley et al. Bigandetal.,2011),andspecificallytocontrolfordifferencesin
(2008)additionallyreportedastrongconcordancebetweenpupil arousalinductionmodulatedbysoundintensity(e.g.,Royetal.,
dilationandskinconductance,anothermeasureofphysiological 2009).
arousal. Thus, we hypothesized that subjective arousal ratings
should predict pupillary responses to musical stimuli, with a
MATERIALS AND METHODS
larger pupil dilation for excerpts judged as highly arousing.
However, there was a potential confound in both studies cited
Stimuli
above:neutralstimuliweresubjectivelyratedassignificantlyless
arousing than either positively or negatively valenced stimuli, Eighty-four 6-s excerpts were selected from commercial
and therefore effects of valence could not be disentangled recordings (lossless audio) of piano trios from the Romantic
from those of arousal. Here, we addressed these issues by also period, corresponding to the early to middle 19th-century.
includingneutrallyvalencedstimuliwithabroadrangeofarousal All three instruments of the trio (piano, violin, and cello)
ratings. could be heard at least once during each excerpt. To avoid
Previousstudieson pupillary responses induced by auditory intra-opus familiarity effects (Krumhansl, 1995), only one
stimuli did not consider emotion models incorporating other excerpt per movement was chosen. Following Hevner’s (1935)
affective dimensions such as tension, which have been argued recommendation, only excerpts with a uniform emotional
tobemoresuitabletomusicemotionresearch(Schimmackand expression were selected. Linear fade-in and fade-out were
Grob, 2000; Schimmack and Reisenzein, 2002). Here, we used applied to the first and last 22 ms of each excerpt. A list of the
a three-dimensional emotion model(pleasantness, arousal, and excerpts is provided in the Appendix in the Supplementary
tension) to predict pupillary responses. To do so, we invited Material.
a second group of participants to rate the music excerpts for Excerptsweregloballynormalizedatthemeanintensitylevel
arousal (calm versus aroused), tension (relaxed versus tense), of all original excerpts, such that the average intensity was the
andpleasantness(unpleasantversuspleasant),followingWundt’s same for all excerpts (details are provided in the “Materials
(1896) model, and compared these ratings with the pupillary and Methods” section of Gingras et al., 2014). Because the
responses observed in response to the same excerpts, but in a normalization wasdoneonthe meanintensity levelscomputed
differentgroupofparticipants. overtheentireexcerpts,intensitycontourswerepreservedintact
Carefulattentionwaspaidtotheselectionofmusicalstimuli. foreachexcerpt.Fourexcerptswithmeanfamiliarityratingsover
Allmusicexcerptsusedinthepresentstudywereobtainedfroma 4 (middleof scale)wereexcluded from this analysis,leaving80
selectionofRomanticpianotrios,arelativelyunfamiliarmusical excerpts.Notethat,whereasparticipantswhoratedtheexcerpts
genre characterized by a high stylistic and timbral uniformity. for arousal and valence in Gingras et al. (2014) heard all 84
Weusedasetofexcerptsmatchedfortimbreandcompositional excerpts, the two groups of participants recruited for this study
style because the relationship between emotional ratings and (see below) heard only the 80 excerpts selected as described
acousticcueshasbeenshowntobepartlygenre-specific(Eerola, above.
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Gingrasetal. Pupillaryresponsestomusiclistening
Participants 10.6.7 operating system. Musical excerpts were played using an
ThirtyGerman-speakingpsychologystudents(15females,mean Edirol FA-66 FireWire Audio Capture audio interface (Roland,
age = 23.1 years, SD = 2.6, range: 19–30) rated the musical Shizuoka, Japan), at a fixed intensity level, on Sennheiser HD
excerpts for arousal, tension, valence, and familiarity. Another 280 headphones. The mean intensity across all excerpts was
thirtyGerman-speakingparticipants,forthemostpartuniversity 70 dB SPL, based on audiometric measurements taken at the
students (15 females, mean age = 26.1 years, SD = 5.8, range: headphones using a Voltcraft SL-400 decibel meter that was
19–39), participated in the pupillary response experiment. All calibratedimmediatelypriortousage.Thestimuliwerepresented
participantsforbothexperimentshadlessthan3yearsofmusical and the experiment was controlled using Psychtoolbox-3.0.9
training,werenotmusicallyactiveatthetimeoftheexperiment, (Brainard,1997;Pelli,1997;Cornelissenetal.,2002)runningon
andreportednormalhearingandnohistoryofhearingdisorders. MATLABR2010a(Mathworks,Natick,MA,USA).
Participants in the pupillary response experiment had normal Participantsfirstsignedtheinformedconsentformandfilled
or corrected-to-normal vision. All experiments conformed to out the MDBF mood questionnaire. They were then seated in
the institutional guidelines of the University of Vienna for a comfortable chair with their head stabilized in a chin rest,
experimentswithhumansubjects.Writteninformedconsentwas facing the computer monitor ata distance of 60 cm,in aquiet,
givenbyallparticipantswhocouldwithdrawatanytimeduring moderatelylitroom(ambientlightlevelsof200luxasmeasured
the experiment without further consequences. All experimental justbelowtheforeheadsupportusinganX-Ritei1Proluxmeter).
datawerecollectedbetweenNovember2012andJuly2013. Arandomizedtargetorder5-point(HV5)calibrationroutinewas
performed(5-pointcalibrationwasdeemedsufficientsincepupil
Procedure for the Subjective Rating diameterwastheonlymeasurementofinterestandparticipants
wereaskedtocontinuously fixatetheareacorresponding tothe
Experiment
center of the screen), followed by a separate validation using
Theprocedureforthesubjectiveratingexperimentwasidentical
theEyeLink1000software.Participantswereaskednottomove
to the procedure described in Gingras et al. (2014), except
their head during the experiment and to look at the fixation
that participants also rated the excerpts for tension. Briefly,
crosslocatedatthecenterofthescreenandtrytoavoidblinking
participantsfirstfilledouttheMDBFmoodquestionnaire(short
whenitwasdisplayed(theywereshownanimageofthecross).
formversionA)andwereinstructedtoratetheirfamiliaritywith
Participants were also told that they could blink or close their
the musical excerpts, as well as their felt arousal, felt tension,
eyeswhen a “smileyface” was shown on the screen in-between
and felt pleasantness, using 7-point scales. The scales ranged
trials.Thecrosscolorwasdarkgray(RGB:75,75,75).Thesizeof
from “very unfamiliar” to “very familiar” for familiarity, “very thefixationcrosswas168×168pixels,correspondingto4.5◦of
calm” to “very aroused” for arousal, “very relaxed” to “very
visualangleataviewingdistanceof60cm.Thesmileyfacewas
tense” for tension, and “very unpleasant” to “very pleasant”
thesamecolorasthecrossandapproximatelythesamesize.
for pleasantness. In order to familiarize participants with the
Aswiththeratingexperiment,participantsfirstpracticedwith
procedure, they first practiced with three excerpts not included
three excerpts not included in the actual stimulus set and were
intheactualstimulussetandwerethenexposedtoall80excerpts
thenexposedtoall80excerptsfromthestimulusset.Theorder
from thestimulusset.Theorderofpresentationoftheexcerpts
ofpresentationoftheexcerptswasrandomized.Foreachexcerpt,
was randomized. Ratings were entered on the computer (by
thefixationcrosswasfirstshownfor2s,thenthemusicplayed
clickingonorderediconsonthescreencorrespondingtothescale
for 6 s, then the cross wasdisplayed for another 2 s,for a total
ratings)onlyoncetheentireexcerptwasplayed.Afterallratings
of 10 s of recording of the pupillary response per trial. Similar
wereentered,therewasa5-sdelaybeforethenextexcerptbegan
tothe ratingprocedure,therewasa5-sdelaybetweenexcerpts,
playing.ExcerptswerepresentedusinganE-MU0204USBaudio
indicatedbya“smileyface”displayedonthescreen,duringwhich
interface (E-MU, Scotts Valley, CA, USA), at a fixed intensity
participants could close their eyes or blink. Four seconds after
level,onSennheiserHD380headphones.Stimuluspresentation
theendofatrial(1sbeforethecrossindicatingthebeginningof
andratingscollectionwerecontrolledusingacustomMATLAB
thenexttrialwouldappear),asoft“beep”sound(a400Hzpure
interface.Theentireexperimentlastedapproximately45min.
toneplayedfor0.1s)wasplayedtoindicatethattheparticipants
shouldpreparetoopentheireyesandlookatthefixationcross.
Procedure for the Pupillary Response
After40stimuli(midwaythrough theexperiment),participants
Experiment
were allowed to take a pause. Upon resuming the experiment,
TheEyeLink1000 head-supported infrared optical eye-tracking calibration correction wasperformed (complete calibration was
system (SR Research, Ottawa, ON, Canada), which includes a performedifnecessary).
1000-Hz infrared camera,illuminator, and proprietary software Once all excerpts had been played, participants were invited
running on a custom workstation, was used to collect pupil to fill in a post-experiment paper questionnaire about their
data. The screen used for the experiment was a Samsung socio-demographic background and musical interests. This
SyncMaster 2233 (21.5 inches, 60 Hz refresh rate), with a questionnaire included three questions, all on a 7-point scale,
resolution of 1680 × 1050 pixels. The background color of the about the role that music plays in their life (ranging from
screen was gray, RGB (150,150,150), following Kuchinke et al. “no role” to “a very important role”; the German acceptation
(2007). The computer was an Apple Mac Mini 4.1, with an of the term refers to the general importance of music in
IntelCoreDuo22.4GHzprocessor,runningontheMacOSX participants’lives),theirgenerallikingfortheexcerptspresented
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Gingrasetal. Pupillaryresponsestomusiclistening
in the experiment (ranging from “not at all” to “very much”) (Tremblay and Ransijn, 2015) and the Anova function from
and the frequency with which they felt emotions during the packagecartoobtainsignificancetests(FoxandWeisberg,2011).
∗
experiment(ranging from “never”to“veryoften”). Participants StatisticalpowerestimateswerecomputedwithG Power3.1.9.2
also completed the SRS (Schulz et al., 2005), in which each (Fauletal.,2007).
item describes a potentially stressful situation with three
answer options representing possible stress responses. Finally,
RESULTS
participants were paid 5 Euros for their participation, thanked,
and debriefed. The entire experiment lasted approximately
Mood Questionnaire
30min.
The MDBF mood questionnaire includes subscales for
Data Analysis positive/negative mood, alertness/fatigue, and quietude/
Thelefteye’spupildiameterandgazecoordinatesweresampled disquietude. Subscale scores were analyzed using a MANOVA
at 1,000 Hz with an average spatial resolution of 20 min arc design, with experimental group (subjective ratings versus
(range across participants: 11–39 min arc). Pupil diameter is pupillary response) as a between-subject factor. Except for a
measured in arbitrary units which are linear in true diameter marginaltendencyforpositive/negativemoodscorestobelower
(Einhäuseretal.,2008).Gazecoordinateswerealsorecordedin for the subjective rating group, F(1,58) = 3.45, p = 0.069, no
order to track the gaze position and exclude samples for which significantdifferenceswereobservedbetweenthetwogroupson
the participants did not fixate the screen area corresponding to thesubscales(allotherp-values>0.3).
thecentercross.
Blinks were identified by the proprietary algorithm of the Subjective Ratings of the excerpts
Eyelink 1000 eye-tracking system, using default settings. Data Familiarity
samplesfrom50msbeforethebeginningofblinksto50msafter Theoverallmeanfamiliarityratingforthe 80excerptswas2.76
theendofblinkswerediscardedtoexcludepre-andpost-blink (range:2.00–3.73,SD=0.41)ona7-pointscale,whichisslightly
artifacts(1.7%ofallsamples;range:0.1–5.0%perparticipant).In lowerthantheratingsobtainedonthesameexcerptsinGingras
addition, given that pupil size estimation is less accurate when etal.(2014)andsuggeststhatnoneoftheexcerptssoundedvery
participantsarenotfixatingthecenterofthescreen(Gagletal., familiartotheparticipants.
2011), all samples for which the screen coordinates of the gaze
Arousal,Tension,andPleasantness
were outside a circle centered on the fixation cross and with
diameterequaltothesizeofthecross(168pixels)wereexcluded To evaluate whether participants rated the excerpts in a
(0.3%ofallsamples;range:0.0–4.7%perparticipant).Following consistent manner, inter-rater reliability was assessed by
Einhäuser et al. (2008), all discarded samples were treated as computingtheaveragemeasureintraclasscorrelationcoefficient
missing data rather than interpolated (Einhäuser et al., 2008 (ICC) using the ICC(2,k) form (Shrout and Fleiss, 1979),
obtained verysimilar results with both methods). Trials during which corresponds to a two-way random effects model for
whichparticipants blinked ordidnotfixatethecentercrossfor consistency(McGrawandWong,1996).ICCvaluesindicatethat
morethan15%ofthetotaltrialdurationwereexcluded.Atotal inter-rater agreement was high for arousal, ICC(2,30) = 0.92,
of 50 of 2400 trials(2.1%) werethus excluded (range:0.0–8.8% and tension ratings, ICC(2,30) = 0.91, but only moderate
perparticipant). for pleasantness, ICC(2,30) = 0.67. The ICC values obtained
Frequencyresponsesinpupilsizevariationthatoccuratrates for arousal and pleasantness were nearly identical to those
faster than 2 Hzare considered to be noise (Richer and Beatty, reported in Gingras et al. (2014). Moreover, the mean arousal
1985; Privitera and Stark, 2006). Accordingly, pupil diameter and pleasantness ratings obtained here were also consistent
datawerelow-passedusingafourth-orderButterworthfilterwith with those obtained on the same excerpts, but with different
a cutoff frequency of 4 Hz. The baseline pupil diameter was participants (Gingras et al., 2014), with a rank correlation of
measured as the averagepupil diameterfor a period of 200 ms r (78) = 0.88 (p < 0.001) for arousal, and a slightly weaker
s
immediately preceding the stimulus onset. Baseline-corrected correlationofr (78)=0.74(p<0.001)forpleasantnessbetween
s
pupildiameterswerecomputedbysubtractingthebaselinepupil bothexperimentalgroups(Spearman’scorrelationcoefficientwas
diameter from the raw pupil diameter after stimulus onset. To usedbecausethedistributionofthemeanarousalratingsdeviated
allow for comparisons between participants and to correct for significantlyfromnormalityasindicatedbyShapiro–Wilk’stest,
possible tonic changesin pupil diameterover the course of the W=0.963,p=0.023,seeFigure1).
experiment, raw pupil diameters were converted into relative Figure 1 shows the two-dimensional emotion spaces
pupil diameter by expressing them as a proportional difference corresponding to the set of 80 excerpts, displaying the mean
fromthebaselinediameter(vanRijnetal.,2012). arousal, tension, and pleasantness ratings obtained on each
All data analyses were conducted in MATLAB R2012b excerpt.Meanpleasantnessratings(range:3.47–5.30,M=4.41,
(Mathworks, Natick, MA, USA), except for the linear mixed SD=0.41)exhibitedamorerestrictedrangethanmeanarousal
modelanalysiswhichwasimplementedinR3.1.1(RCoreTeam, ratings (range: 2.43–6.00, M = 3.80, SD = 0.82), in line with
2015) using the lmer function from package lme4 to build the the ratings reported for the IADS database (Bradley and Lang,
models (Bateset al., 2015), the fitLMER function from package 2007) and with other studies using Romantic music (Marin
LMERConvenienceFunctions to select the best-fitting models et al., 2012). Mean arousal and mean tension ratings (range:
FrontiersinHumanNeuroscience|www.frontiersin.org 5 November2015|Volume9|Article619
Gingrasetal. Pupillaryresponsestomusiclistening
FIGURE1|Meansubjectivearousal,tension,andpleasantnessratingsfor80six-secondexcerptsselectedfromRomanticpianotrios.Thenumbers
identifytheexcerpts(foracompletelistingoftheexcerpts,seeAppendixintheSupplementaryMaterial).Thefullscaleforallthreeratingsrangedfrom1to7,buta
restrictedrangeisdisplayedheretofacilitateviewing.
2.30–5.60,M =3.58,SD=0.76)werehighly correlated,with a non-unimodal distribution, D = 0.1167,p = 0.001), M = 4.40,
rankcorrelationofr (78)=0.93(p<0.001). SD=1.25(Figure2D).Nosignificantdifferenceswereobserved
s
between male and female participants for any of these three
Characteristics of the Participants in the questions (Wilcoxon rank-sum tests,allp-values>0.1), nor for
Pupillary Response Experiment the mood subscale scores (MANOVA with gender as between-
SRSTotalScores subjectsfactor,allp-values>0.2).
Mean SRS total scores (M = 55.5, SD = 9.0) are shown
Pupillary Responses
in Figure 2A. Female participants obtained higher scores
(M = 57.4) than male participants (M = 53.6), in line with To visualize whether the time course of pupillary responses is
earlierstudies(Nateretal.,2006),butthisdifferencedidnotreach similar for low- and high-arousing stimuli, we categorized the
significance,t(14)=1.21,p=0.25. excerpts into low- and high-arousal brackets. The time course
displayed a similar pattern for the 40 excerpts rated as most
AttitudestowardMusic
arousingandthe40ratedasleastarousing,althoughtherelative
Threequestionsfromthepost-experimentquestionnaireprobed dilation was larger for the high-arousing excerpts (Figure 3).
the participants’ attitudes toward music, both generally and in A sharp increase in pupil size occurs about 400 ms after the
regardstotheexperiment.Althoughmostparticipants reported stimulus onset. The peak dilation is reached around 1.5 s after
thatmusicplaysalargeroleintheirlife(roleofmusic:M=5.53, stimulusonset(and maintained fora fewseconds for the high-
SD = 1.25), a sizable minority judged its role to be relatively arousing excerpts), followed by a smooth constriction until the
modest(Figure2B).Mostparticipantsreportedlikingthemusic stimulus offset. A small dilation occurs 400 ms after the offset,
excerpts,M=5.37,SD=1.10(Figure2C),whereasthefrequency followed by a rapid constriction. These observations are in line
of felt emotions during the experiment exhibited a bimodal with earlier investigations of pupillary responses to affective
distribution (Hartigan’s dip test for unimodality indicated a sounds(PartalaandSurakka,2003).
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Gingrasetal. Pupillaryresponsestomusiclistening
FIGURE2|Histogramsofthestressreactivityscoresandratingspertainingtoparticipants’attitudestowardmusic.(A)SRStotalscores(Schulzetal.,
2005).(B)Participants’ratingsregardingtheroleofmusicintheirlife.(C)Participants’overalllikingforthemusicexcerptspresentedduringtheexperiment.
(D)Participants’frequencyoffeltemotionsduringtheexperiment.
Becausethe subjective ratings obtained on the excerpts were mean pupillary response observed for each excerpt (Table 1).
retrospective ratings of the entire excerpts, pupillary responses Moreover,listeners’self-reportedevaluationoftheroleofmusic
wereaveragedovertheentire6-sdurationoftheexcerpts(Partala in their life was significantly correlated with their pupillary
andSurakka,2003)inordertoallowameaningfulinvestigation responses,averagedoverallexcerpts(Table2).
of the association between ratings and pupillary responses. As A more refined analysis combined the subjective ratings
apreliminaryanalysisofthisassociation,wefirstcomputedthe associated witheachexcerpt with the participants’ self-reported
correlations betweenthemeanpupillaryresponsesobservedfor mood subscales, SRS scores, and attitudes toward music in a
each excerpt and the mean subjective ratings obtained for each singlestatisticalmodeltopredictthepupillaryresponseforeach
excerpt (treating each excerpt as the unit of analysis) on the excerpt and participant. In doing so, we sought to quantify
one hand (Table 1), and between the meanpupillary responses the contribution of excerpt-specific affective characteristics and
observedforeachparticipantandtheparticipant-specificfeatures listener-specific traits to the observed variance in pupillary
(i.e.,moodsubscales,SRSscoresandratedattitudestowardmusic response among excerpts and participants using maximum-
obtained,treatingeachparticipantastheunitofanalysis)onthe likelihood linear mixed models. Given that each excerpt was
otherhand(Table2).Theseanalysesshowedthatmeansubjective heardbyeachparticipant,excerptsandparticipantsweretreated
arousal and tension ratings were positively correlated with the as fully crossed random effects (Baayen et al., 2008; Judd
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Gingrasetal. Pupillaryresponsestomusiclistening
FIGURE3|Timecourseofthepupillaryresponseforhigh-andlow-arousingexcerpts.Pupildilationiscalculatedasapercentageofthemeanpupil
diameterobservedduringthe200msbeforetheonset(baseline).High-arousingexcerptscorrespondtothe40excerptsratedasmostarousing,whereas
low-arousingexcerptsarethe40ratedasleastarousing.
et al., 2012; Brieber et al., 2014). Here, we began with a full The best-fitting model included the following predictors:
model including all fixed and random effects of interest, and listeners’gender,b=–1.31(withmalesasthereferencecategory),
implemented a backward stepwise model selection procedure. SE = 0.63,χ2(1) = 4.29, p = 0.038, the reported role of music
Hence, our initial model included arousal, pleasantness, and in their lives, b = 0.61, SE = 0.25, χ2(1) = 5.95, p = 0.015,
familiarity ratings as excerpt-specific features (tension ratings and the arousal ratings of the excerpts, b = 0.31, SE = 0.11,
were not included to reduce multicollinearity), and gender, χ2(1) = 8.46, p = 0.004. Additionally, a significant interaction
moodsubscales,SRSscores,andattitudestowardmusic(roleof between arousal ratings and liking for the excerpts was found,
music,likingfortheexcerpts,andfrequencyoffeltemotions)as b = –0.29, SE = 0.10, χ2(1) = 8.41, p = 0.004, meaning
listener-specific features. Additionally, all two-way interactions that the pupillary responses of listeners who liked the excerpts
between each excerpt-specific feature and listener-specific trait greatly were modulated less strongly by arousal than those of
were considered (i.e., arousal × gender, pleasantness × SRS listenerswhodidnotliketheexcerptsasmuch.Thefinalmodel
scores, etc...). Participant, excerpt, and gender were coded as also included a random intercept associated with each listener,
categorical factors, whereas all other predictors were treated as χ2(1)=203.28,p<0.001,butnorandominterceptforexcerpts
covariatesandgrandmeancentered(EndersandTofighi,2007). asitsinclusiondidnotimprovethemodelfit.
According to the model, males were predicted to show
stronger pupillary dilations than females (1.31% on average),
TABLE1|Correlationscomputedoverthemeanvaluesobtainedforeach whereas each additional unit increment in a listener’s reported
musicexcerpt. role of music in their life predicted an increase of 0.61% in the
dilationobservedforthatlistener(acrossallexcerpts).Moreover,
Arousal Tension Pleasantness Familiarity
each additional unit increment in the mean arousal ratings
Arousal predicted an increase of 0.31% in the dilation observed for
Tension 0.93∗∗∗ a specific excerpt (across all listeners). However, the effect of
Pleasantness –0.24∗ –0.43∗∗∗ arousal was much weaker for listeners who liked the excerpts
Familiarity 0.16 –0.04 0.40∗∗∗ greatly,withaSpearmancorrelationcoefficientbetweenarousal
Pupillaryresponse 0.29∗∗ 0.27∗ –0.02 0.17 ratings and pupillary responses of 0.39, p < 0.001, for the 18
Rankcorrelations(Spearman;df=78)areshownbecausesomevariablesarenot listenerswhogavelikingratingsof5orless,comparedto–0.02
normallydistributed.∗p<0.05;∗∗p<0.01;∗∗∗p<0.001.Thestatisticalpower forthe12listenerswhogaveratingsof6ormore.
todetectalargeeffectsize(|r| >0.50)forasampleofthissize(N=80)was Ananalogousmodelwasobtainedwhenpredictingpupillary
estimatedat0.998fortwo-tailedbivariatecorrelationswithasignificancethreshold
responses using tension ratings instead of arousal ratings,
of0.05.
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Gingrasetal. Pupillaryresponsestomusiclistening
TABLE2|Correlationscomputedoverthevaluesobtainedforeachparticipant.
Positivemood Alertness Quietude SRSscores Roleofmusic Likingexcerpts Feltemotions
Positivemood
Alertness 0.37∗
Quietude 0.62∗∗∗ 0.43∗
SRSscores 0.32† 0.07 0.16
Roleofmusic 0.06 0.17 –0.19 0.02
Likingexcerpts 0.02 –0.01 0.08 0.09 0.02
Feltemotions 0.14 0.17 0.19 0.20 –0.20 0.27
Pupillaryresponse 0.24 –0.08 0.12 0.14 0.42∗ 0.05 0.06
Meanvalueswereusedforthepupillaryresponse.Rankcorrelations(Spearman;df=28)areshownbecausesomevariablesarenotnormallydistributed.∗p<0.05;
∗∗p<0.01;∗∗∗p<0.001;†p<0.10.Thestatisticalpowertodetectalargeeffectsize(|r| >0.50)forasampleofthissize(N=30)wasestimatedat0.828fortwo-tailed
bivariatecorrelationswithasignificancethresholdof0.05.
with significant effects of gender, reported role of music, emotional arousal, independently of the perceived pleasantness
tension ratings, and a significant interaction between tension of the stimuli (Bradley et al., 2008). Furthermore, we
and overall liking for the excerpts. The coefficients and note that pleasantness ratings are not as consistent across
statistical tests also yielded very similar values to those participants as arousal and tension ratings, and are also
obtained for the arousal model, which is to be expected more difficult to predict from the acoustical features of
considering the very high correlation between arousal and the stimuli (Schubert, 2004; Eerola, 2011; Gingras et al.,
tensionratings. 2014).
Sound intensity, which is one of the main predictors of
music-inducedsubjectivearousal,isknowntobecorrelatedwith
DISCUSSION physiological responses such as skin conductance (Gomez and
Danuser, 2007). However, our findings not only suggest that
Pupillary responses to musical stimuli have rarely been the range of subjective music-induced arousal ratings is largely
investigated. In this study, we collected pupillary responses of unaffected by amplitude normalization (Gingras et al., 2014),
non-musicians to a set of 80 six-second music excerpts for but also that physiological responses to music stimuli remain
which we separately obtained subjective ratings of felt arousal, correlatedwithsubjectivearousalratingsevenintheabsenceof
pleasantness, tension, and familiarity. We hypothesized that intensitycontrastsbetweenmusicstimuli.
arousal ratings of the music excerpts, as well as participants’ The relationship between the role of music in participants’
attitudes toward music, would predict pupillary responses. lives and their pupillary responses, as well as the observed
A correlational analysis showed that, as predicted, arousal and interaction between arousal ratings and participants’ liking for
tensionratingsweresignificantlycorrelatedwithmeanpupillary the excerpts, are in line with the growing body of literature
response. Among listener-specific characteristics, participants’ suggesting that emotional responses to music depend on
reported role of music in their life predicted the magnitude of individualdifferences(e.g., Liljeström etal.,2013;Mas-Herrero
the pupillary dilation. A linear mixed model analysis including et al., 2013; Park et al., 2013; Mori and Iwanaga, 2015). In
both music- and listener-specific features resulted in a best- contrasttoourfindingsregardingtheinteractionbetweenarousal
fitting model with gender, role of music and arousal ratings as ratingsandlikingfortheexcerpts,SchäferandSedlmeier(2011)
predictorsofthepupillaryresponse.Furthermore,aninteraction reportedthatskinconductancedidnotcorrelatewithpreference
between arousal ratings and liking was found. In general, for music, whereas heart and respiration rates did, suggesting
these results are in line with the hypothesized contribution of that future research will need to further investigate how the
excerpt-specific and listener-specific characteristics to pupillary preference for music style and autonomic arousal measuresare
responsestomusic.However,contrarytoourpredictions,female related.
participants showed smaller pupillary dilations than males, The finding that the role of music in people’s lives predicts
even though male and female listeners did not significantly their pupillary response to music could be interpreted as an
differ in their attitude toward music or in their scores indicator that physiological arousal varies with the level of
on the subscales of the MDBF mood questionnaire. Taken engagement with music (see Latulipe et al., 2011; Bradshaw
together, these results lend support to models that predict et al., 2012). It could be surmised that the importance
that responses to music depend on characteristics of the of music in people’s lives is associated with traits such as
listener as well as on the music itself (Hargreaves et al., absorptionaswellaswiththeirdegreeofmusicalsophistication.
2005). Therefore, the relationship between the role of music in
Regarding excerpt-specific features, it is worth noting people’slivesandphysiologicalresponses,suchaspupildilation,
that pleasantness was not significantly correlated with may be further investigated by assessing participants’ degree
pupillary responses. This is in agreement with previous of musical engagement (e.g., Müllensiefen et al., 2014) and
reports indicating that pupillary responses are determined by absorption (Sandstrom and Russo, 2013) using standardized
FrontiersinHumanNeuroscience|www.frontiersin.org 9 November2015|Volume9|Article619
Gingrasetal. Pupillaryresponsestomusiclistening
tests. Furthermore, it should be noted that the questionnaire positively related to skin conductance (van den Bosch et al.,
item regarding the self-reported role of music in participants’ 2013).
lives did not differentiate between positively or negatively
valenced influences, which is an aspect that could be explored
ingreaterdetail.Moregenerally,becausepersonalitytraits,such CONCLUSION
asneuroticism, havebeenshown to predict pupillary responses
tosoundstimuli(AntikainenandNiemi,1983),future research We show that pupillary responses to music are predicted by a
in this domain should consider the role of personality traits in combination ofexcerpt-specific affective characteristics, suchas
greaterdepth. arousal potential, and listeners’ attitudes toward music. Besides
The larger pupil dilations observed for male listeners demonstratingthatpupilsizeisapsychophysiologicalparameter
stand in contrast to earlier studies reporting stronger thatissensitivetomusicallyinduced emotionsand canthusbe
psychophysiological, but not psychological, responses to usedtoprobe listeners’ affective responses tomusic, ourresults
high-arousing, unpleasant music in females compared to alsopointmorebroadlytowardawide-rangingcomplementarity
males (Nater et al., 2006). This discrepancy with earlier between the role of individual differences at the level of music
results may be due to the fact that our musical stimuli production (Gingras et al., 2013) and at the level of music
were not selected to induce high levels of unpleasantness, reception.
which is supported by the fact that stress reactivity was
not a significant predictor of pupil dilation. Moreover, in
contrast to Nater et al. (2006), female participants were not ACKNOWLEDGMENTS
screened for the use of hormonal contraceptives in the present
study. This research was supported by ERC Advanced Grant
Although we controlled for the potential effect of familiarity SOMACCA No. 230604 and a University of Vienna startup
by selecting music excerpts from a little-known genre, we granttoW.T.Fitch.WethankAndreasGartusforhistechnical
observed a positive (but non-significant) correlation between assistance and HelmutLederfor providing laboratory space for
familiarity and pupil dilation. Because the range of familiarity collectingsubjectiveratings.
ratings was very restricted, we may suppose that the effect
of familiarity and exposure on pupillary responses would
be more evident with a set of music excerpts ranging SUPPLEMENTARY MATERIAL
from unfamiliar to very familiar. This is supported by
recent findings showing that repeated exposure to unfamiliar The Supplementary Material for this article can be found
music significantly increased skin conductance (a marker of online at: http://journal.frontiersin.org/article/10.3389/fnhum.
emotionalarousal)andthatself-reportedfamiliarityratingswere 2015.00619
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