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Neuropsychologia 48 (2010) 1115–1124

Contents lists available at ScienceDirect

Neuropsychologia

journa l homepage: www.e lsev ier .com/ locate /neuropsychologia

mitation of para-phonological detail following left hemisphere lesions

uliane Kappesa,∗, Annette Baumgaertnerb, Claudia Peschkec, Georg Goldenbergd, Wolfram Zieglera

Clinical Neuropsychology Research Group, Neuropsychological Dept., Clinic Bogenhausen, Dachauer Str. 164, 80992 Munich, GermanyHochschule Fresenius, Department of Speech and Language Therapy, Hamburg, GermanySchool of Engineering and Science, Jacobs University Bremen, Bremen, GermanyNeuropsychological Dept., Clinic Bogenhausen, Munich, Germany

r t i c l e i n f o

rticle history:eceived 12 October 2009eceived in revised form6 November 2009ccepted 7 December 2009vailable online 7 January 2010

eywords:

a b s t r a c t

Imitation in speech refers to the unintentional transfer of phonologically irrelevant acoustic–phoneticinformation of auditory input into speech motor output. Evidence for such imitation effects has beenexplained within the framework of episodic theories. However, it is largely unclear, which neural struc-tures mediate speech imitation and how imitation is related with verbal repetition. Two experimentswere conducted, a standard repetition task, and a transformation task requiring phonetic manipula-tion of the presented auditory nonword stimuli. Nonword materials varied sub-phonemically in wordstress (pitch elevation magnitude; PEM) and in a parameter related to speaking style, i.e., the explicit-

uditory–motor integrationerbal repetitionchwa-syllableord stress

honological impairmentpisodic theory

ness of final schwa-syllables (SSE). We examined speech imitation in 10 healthy participants, 10 patientswith phonological impairments after left hemisphere lesions, and 11 patients with right hemispherelesions. In repetition, significant imitation of SSE and PEM was observed in all groups of participants.In transformation, imitation occurred in healthy participants and in the patients with right hemispherelesions, whereas no imitation was observed in the patient group with left hemisphere lesions. Voxel-based lesion–symptom mapping revealed that different areas within the left temporal plane influenced

f phon

the degree of imitation o

. Introduction

Imitation is an ubiquitous phenomenon in human social inter-ctions and comprises a wide range of behaviors, such as imitationf body postures, mannerisms, or facial expressions (Chartrand &argh, 1999). Imitation often occurs unintentionally and automati-ally (Tessari, Rumiati, & Haggard, 2002). Meltzoff, Kuhl, Movellan,nd Sejnowski (2009) regard imitation as one of the fundaments ofuman development and learning. Moreover, imitative behavior isonsidered to enhance affiliation and empathy between interactionartners (Paukner, Suomi, Visalberghi, & Ferrari, 2009).

Vocal imitation plays an important role in language acquisitionnd was described to occur in infants between 12 and 20 weeks ofge (Kuhl & Meltzoff, 1996). Auditory-oral matching capabilities,s a precursor to vocal imitation, were found in newborns (Chen,triano, & Rakoczy, 2004), and it is known that imitation of speech

ontinues to exist even if language acquisition has been completedDelvaux & Soquet, 2007).

Considering imitation in speech it is important to distinguishmitation from repetition. Repetition refers to the intentional repro-

∗ Corresponding author. Tel.: +49 89 154058.E-mail address: Juliane.Kappes@extern.lrz-muenchen.de (J. Kappes).

028-3932/$ – see front matter © 2009 Elsevier Ltd. All rights reserved.oi:10.1016/j.neuropsychologia.2009.12.012

etic and prosodic detail in repetition.© 2009 Elsevier Ltd. All rights reserved.

duction of the phonemic content of a word or nonword, whichcomprises production of the correct phonemes in the right order.Whether, for example, the repeated item matches the fundamentalfrequency of the stimulus is normally not considered relevant forjudging a response as correct or false.

In contrast, speech imitation refers to the unintended copyingof phonologically irrelevant parts of the acoustic–phonetic infor-mation contained in an auditory stimulus, such as fundamentalfrequency, speaking rate, or other fine phonetic detail.

A range of studies have focused on imitation of such “para-phonological” properties. For example, Shockley, Sabadini, andFowler (2004) gradually manipulated the voice onset times (VOT1)of stop consonants without altering their phonemic categories.During repetition, speakers adapted their VOTs to those of thestimuli. Similarly, Gentilucci and Bernadis (2007) reported femalesubjects to imitate gender-specific aspects of the voice spectrum ofa male speaker by lowering their first and second formant.

More recent studies examined further acoustic signatures ofspoken words, e.g., voice fundamental frequency (F0), for imitation.F0 varies within subjects, e.g., as a function of prosody or of psy-chological factors like stress or effort, and between subjects, e.g.,

1 VOT distinguishes voiced from voiceless plosive consonants, e.g., /d/ from /t/.

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116 J. Kappes et al. / Neuropsy

s a function of age and gender. Therefore, on purely physiologi-al grounds absolute imitation of F0 cannot generally be expectedo occur. However, in a combined behavioral and functional brainmaging study Peschke, Ziegler, Kappes, and Baumgaertner (2009)eported that imitation of F0 occurred in repetition with very shortelays (“shadowing”). In this study, participants shadowed non-ords spoken by children, women, and men who varied in their

peaking rates and fundamental frequencies. Significant imitationf speaking rate was present in all participants, imitation of F0 inwo-thirds of them.

In a further study imitation of F0 was investigated in dif-erent repetition paradigms (Kappes, Baumgaertner, Peschke, &iegler, 2009). This study for the first time also included a param-ter reflecting speaking style, more specifically, the degree tohich schwa-syllables are reduced. Schwa-syllable reduction (e.g.,

fogəl/, engl. bird pronounced as /fogl/) is an option which Germanpeakers frequently use in conversational speech. This process doesot alter the meaning of a word, but signals a certain degree of

nformal attitude. In their study, Kappes et al. (2009) used model-timuli which were systematically varied with respect to F0 and tohe explicitness of schwa-syllable expression (SSE). In a standardepetition task, healthy subjects imitated both stimulus aspects, F0nd SSE, with stronger effects for the latter. The imitation behaviorf an aphasic patient with an anterior left hemisphere lesion resem-led that of the healthy subjects, whereas imitation was stronglyeduced in another aphasic patient with a posterior lesion.

The evidence reviewed above supports exemplar-basedpproaches to word repetition. Exemplar theories would assumehat in repetition the idiosyncrasies contained in an auditorytimulus, e.g., voice features, prosody, or specific properties ofrticulation, may survive the transfer into the speech motor outputf another speaker. In a purely abstractionist view, on the contrary,uch para-phonological information would be considered irrele-ant and stripped-off from the stimulus before reproduction, withnly the phonologically relevant information being conveyed.

The neural structures mediating speech repetition have beeniscussed extensively over many decades. Left peri-sylvian cor-ex and the arcuate fascicle are classically thought to be involvedGeschwind, 1965; Wernicke, 1874). More modern stances, like theual stream model (Hickok & Poeppel, 2004), propose a left lateral-

zed dorsal stream for mapping auditory to motor representation, asequired in speech repetition, whereas a ventral stream maps audi-ory representations onto meaning. The dorsal stream is proposedo run from superior-temporal gyrus (STG) via the inferior-parietalobe to frontal speech areas. In a different approach, Warren,

ise, and Warren (2005) evaluated evidence from humans andon-human primates to develop a model of the dorsal (auditory)athway as an auditory “do-system”, which is proposed to medi-te the translation of auditory input into vocal motor output. A keyole in this process is attributed to the posterior superior-temporallane (STP), where input signals are matched onto auditory tem-lates representing traces from recent or from remote auditoryxperience (Warren et al., 2005; Wise et al., 2001).

Recently, the fiber tracts of the auditory dorsal stream systemere investigated using diffusion tensor imaging (DTI) methodol-

gy. Catani, Jones, and ffytche (2005) argued for a separation ofhe arcuate fascicle into a direct component (connecting temporalith frontal areas) and an indirect component (via parietal areas).lasser and Rilling (2008) suggested that fiber tracts within the leftrcuate fascicle connecting middle temporal gyrus (MTG) and STGith frontal areas mediate phonological processing, and they also

escribed a connection with the right MTG which they proposed toupport prosodic processing (Glasser & Rilling, 2008).

Breier, Hasan, Zhang, Men, and Papanicolaou (2008) relatedamage of white matter tracts in patients with left hemisphere

esions to their language deficits and found the superior longitu-

gia 48 (2010) 1115–1124

dinal and arcuate fascicles to be important in speech repetition. Bycombining an activation study with fiber tracking, Saur et al. (2008)tested the neuroanatomical basis of the dual stream model. Consis-tent with Breier et al. (2008), repetition was found to be subservedby a dorsal stream connecting temporal and frontal lobes via thearcuate fascicle and the superior longitudinal fascicle (Saur et al.,2008).

While the structures subserving verbal repetition have beeninvestigated extensively, the neural correlates of speech motorimitation are largely unknown. Lesion studies focussing on ver-bal repetition abilities in aphasic patients have neglected the issueof imitation. As an exception, a recent pilot study of two aphasicpatients revealed perfectly retained imitation in a nonfluent patientwith a left anterior lesion sparing temporal and parietal areas,whereas imitation was almost entirely abolished in a fluent apha-sic with a lesion encompassing, among others, superior-temporaland inferior-parietal regions (Kappes et al., 2009). Functional imag-ing studies of verbal repetition likewise have neglected imitationaspects. In a recent fMRI-study, Peschke et al. (2009) administered aspeech shadowing task and found right inferior-parietal activationto correlate with the imitation of speaking rate. In contrast, thestrength of F0-imitation was not related to any localizable increaseof activation.

In the present study, our aim was to replicate earlier findingsof vocal imitative behavior in repetition, and, for the first time, totransfer the question of unintended vocal imitation into a groupstudy of patients with left and right hemisphere lesions in theregion of the supposed dorsal stream structures. Imitation wasstudied using two different phonetic paradigms: one relating tosegmental aspects of word shape, i.e., the degree of schwa-syllableexpression, and one relating to prosodic aspects of word produc-tion, i.e., the degree to which vocal pitch is raised on the stressedsyllable of a word. Both paradigms are built on naturally occurringphonetic variations which do not alter the phonemic content of aword. While the schwa-syllable paradigm has been used in two ear-lier studies (Kappes et al., 2009; Peschke et al., 2009), the prosodicparadigm has, to our knowledge, not been used so far.

A specific issue considered in the experiments presented herewas whether imitation is bound to conditions with a one-to-one correspondence between input and output, as it occurs inword repetition tasks. To examine this question we introduced atransformation paradigm in which participants were required tointentionally transform a heard stimulus before overt production,with the aim of analysing the degree to which imitation takes placedespite the fact that some mental operation has to be performedon the input stimulus.

The experiments developed here were administered to nor-mal participants and to two groups of patients with right and lefthemisphere lesions in the territory of the middle cerebral artery. Aquestion relating to imitation behavior in the left hemisphere sub-jects, all of whom were aphasic, was if imitation in these patientsdepends on their verbal repetition abilities. The right hemispherepatients were included, first, as a clinical control group, and sec-ond, to examine whether RH-lesions interfere with the imitationof prosodic detail, as suggested by Glasser and Rilling (2008). Wefurther sought to identify factors that may influence imitationof phonologically irrelevant segmental and prosodic information,such as lesion size, and – in a first, preliminary attempt – also theintra-hemispheric localization of brain lesions.

2. Methods

2.1. Subjects

Participants included 10 patients with unilateral left hemisphere damage (LHD;3 women), 11 patients with right hemisphere damage (RHD; 3 women), and 10neurologically healthy control subjects (NC; 5 women). Participants gave informed

J. Kappes et al. / Neuropsychologia 48 (2010) 1115–1124 1117

Table 1Demographic and clinical characteristics of subjects with left and right hemisphere damage.

Subject Gender Age Post-onset Aetiology Token testa Auditory nonword discriminationb Auditory span

L1 M 61 2 isch 21 10 2L2 M 41 51 isch 16 11 1L3 M 53 16 isch 7 10 2L4 F 33 7 isch 74 0 6L5 M 63 1 isch 41 6 2L6 M 53 7 isch 46 3 2L7 M 50 6 isch 94 9 6L8 F 58 2 hem 50 14 2L9 M 47 5 hem 95 2 7L10 F 34 3 isch 93 2 5

R1 F 41 7 isch – 5 6R2 M 60 6 hem – 6 7R3 M 45 7 isch – 3 6R4 M 58 4 isch – 3 7R5 M 70 2 isch – 6 5R6 M 64 3 isch – 9 7R7 F 30 3 hem – 2 5R8 M 66 3 isch – 10 7R9 F 52 7 isch – 6 7R10 M 55 4 isch – 1 7R11 M 39 3 isch – 1 5

Subject: L = LHD, R = RHD; Gender: M = male, F = female; Age: in years; Post-onset: in months; Aetiology: isch = ischemic infarction of medial cerebral artery, hem = hemorrhagici , 0–6 es

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nfarction; Token test: percentile values; Auditory nonword discrimination: n = 72yllables.

a Aachener Aphasietest (Huber et al., 1983).b Lexikon, Modell-orientiert (De Bleser et al., 2004).

onsent prior to the investigation. Control subjects were paid for their partici-ation. All participants were right-handed native German speakers and reportedormal hearing. Handedness was confirmed by the Edinburgh Handedness Inven-ory (Oldfield, 1971). The RHD, LHD and NC groups were balanced for mean agen years (LHD = 49.3 ± 10.6; RHD = 52.7 ± 12.6; NC = 50.1 ± 16.3). Lesions were docu-

ented by MRT scans.All patients suffered from infarction within the vascular territory of the middle

erebral artery. In the LHD group eight patients had an ischemic and two patientshemorrhagic infarction. The investigation took place on average 10 months post-nset (±15). In the RHD group, nine patients suffered from an ischemic, two patientsrom a hemorrhagic infarction. Subjects were tested 4 (±2) months post-onset. TheHD and the RHD group did not differ significantly in post-onset time (p > .1). Meanesion size was 89 cc (SD 78) in the LHD group and 180.4 cc (SD 138.8) in the RHDroup. This difference in lesion size was statistically significant (U = 26, p < .05.)

A series of experiments and diagnostic tests was administered in two sessions.ach session took approximately 1 h to complete. Here, we will report on two exper-ments: a transformation experiment, completed in the first session, and a repetitionxperiment, completed in the second session. Additional diagnostic testing includeduditory discrimination (subtest of the LeMo-battery; De Bleser, Cholewa, Stadie, &abatabaie, 2004) and auditory verbal span. Auditory nonword discrimination wasmpaired in five LHD patients, and unimpaired in the remaining five patients. Audi-ory span ranged from 1 to 7 syllables (mean 3.5 ± 2.2). Percentile ranks of the Tokenest (AAT; Huber, Poeck, Weniger, & Willmes, 1983) ranged between 7 and 95 (mean4 ± 34). Detailed information is given in Table 1.

Auditory nonword discrimination was impaired in two RHD patients and unim-aired in nine (De Bleser et al., 2004). Auditory span ranged from 5 to 7 syllablesmean 6.3 ± .9).

.2. Materials

A list of 48 bisyllabic, phonotactically legal nonwords was used for the twoxperiments. Each nonword had a trochaic stress pattern, with a closed schwa-yllable in the unstressed position, and was accompanied by a definite article. Theorms were constructed analogous to German plural forms like “die Beutel” (theags), or “die Decken” (the blankets). The first, stressed, nonword syllable was con-rolled for frequency. High and low frequency first syllables were equally distributedver the different conditions. The second, unstressed, nonword syllable was alwayshigh-frequency schwa-syllable like . In everyday speech, suchyllables are often accommodated by deleting or reducing the schwa and eventuallyssimilating the coda consonant, which is indicative of a natural or casual speakingtyle. Explicit forms may occur as well, e.g., in slow or formal speech.

The items were spoken by a professional male speaker and recorded in a sound-roof room. We used a dynamic microphone (TG-X 58, Beyerdynamic) and a digitaludio tape recorder (DAT, TCD-D3, Sony). Our study was focused on two sourcesf natural, sub-phonemic variation in these materials: first, the degree of schwa-yllable expression (SSE), and, second, the magnitude of pitch elevation (PEM)or the realization of word stress. As for SSE, the model speaker was encouraged

rrors = unimpaired, 7–22 errors = impaired, >22 errors = random; Auditory span: n

to produce explicit and reduced forms of the schwa-syllables for each item (e.g.,) to achieve the desired phonetic variation. As for the prosodic

variation, the natural variability of pitch elevation for the marking of word stress inthe spoken nonwords was exploited, without drawing the model speaker’s attentionto this property (see Section 2.5).

2.3. Procedure

In both experiments, participants were sitting in front of a computer screen.New trials were always initiated manually by the experimenter. Auditory stimuliwere conveyed via a headset (Sennheiser). The experiments were conducted usingthe UDAP presentation program (Zierdt, 1997). There were practice trials beforeeach experiment.

Participants were engaged in two tasks, repetition and transformation. All givenresponses were audio-taped via a headset (Sennheiser). Of course, participants wereblind to the goals of the study, i.e., imitation was neither instructed nor mentionedat any point during the examination.

In the repetition experiment subjects were asked to repeat the presented non-words (n = 24). Responses were prompted by a visual stimulus 800 ms after stimuluspresentation.

In the transformation experiment, the implicit task was to transform explicitschwa-syllables into reduced forms and vice versa, e.g., /di:laigəl/ into /di:laigl/ or/di: :tl/ into /di: :təl/. Each trial started with a visual cue (loudspeaker symbol),after which an explicit or a reduced nonword was presented. Again, after 800 ms par-ticipants were prompted to initiate their response. In this experiment, no explicitinstructions concerning the “transformation rule” were given. Instead, subjects wererequired to infer their task through implicit learning. The learning procedure startedwith real word examples presented by the examiner (e.g., /di:ze:gəl/ - /di:ze:gl/,engl. the sails) and subjects were then invited to complete a pair when only onestimulus was given (e.g., /di:zegl/). Only after a participant had given several cor-rect answers in a row, the learning was extended to nonword examples. No explicitinstruction was given during the learning, but most participants on their own cre-ated attributes for the property to be changed, like “clear” vs. “mumbled,” etc. Intotal, participants had to transform n = 48 items.

2.4. Perceptual analyses

Phonemic accuracy of the responses obtained in the two experiments was ana-lyzed on the basis of broad transcripts prepared by the first author. For each response,errors were counted on the first and second consonant of the nonword, resulting inzero, one or two errors per item.

Since the level of schwa-syllable expression cannot easily be captured by a sin-gle acoustic variable, responses were rated by a panel of students who had at leastcompleted a first-level course in phonetics. The listeners were required to rate eachresponse on a scale from 0 (completely reduced schwa-syllable) to 3 (completelyexplicit schwa-syllable). A short training was offered to each rater in which she/hereceived feedback about her/his ratings. Each sample was rated independently by

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118 J. Kappes et al. / Neuropsy

hree listeners. Each listener rated responses from each subject and each experi-ent. Listeners were unaware of the background of this experiment and were blind

s to the model stimulus triggering a response. The model-stimuli were also includedn these ratings, with each stimulus being rated by 30 listeners. Model-stimuli ofhe category “reduced” ranged between .07 and .93, with an average score of .45,hereas the model-stimuli of the category “explicit” received a mean score of 2.33

range: 1.57–2.79).

.5. Acoustic analyses

F0-traces were calculated for each of the 48 three-syllabic model-stimuli, andhe distance between the average F0 of the stressed, second syllable relative to thewo unstressed syllables was determined. This parameter will in the following beeferred to as pitch elevation magnitude (PEM). The PEM-values of the model-stimuliaried naturally between 0 and 47 Hz (mean 17.4 Hz). No negative differences werebtained. To account for the non-linearity of perceived vocal pitch, PEM-values werexpressed in semitones.

The F0-contours of the responses given by the participants were processedccordingly, resulting in PEM-values (in semitones) for each participant and eachtem. All acoustic analyses were done using Praat software (Boersma & Weenink,008).

.6. Lesion analysis

MRI scans were available in all subjects. Scans had been obtainedt least 2 weeks after the vascular accident. Lesion mapping was per-ormed using the MRIcro software (Rorden & Brett, 2000; Rorden & Karnath,004, www.sph.sc.edu/comd/rorden/mricro.html), which provides a T1-weightedRI scan template from the Montreal Neurological Institute (www.bic.mni.cgill.ca/cgi/icbm view). Individual lesions were mapped on a fixed set of tem-

lates with an interslice distance of 8 mm by using the closest matching transversallice of each patient. Individual lesion size was calculated from the resulting regionsf interest (ROI) using MRIcro software.

To allow for voxel-wise statistical analyses, ROIs were transformed into volumesf interest (VOIs) of 8 mm thickness. Further analyses were performed by usingRIcron software (www.sph.sc.edu/comd/rorden/mricron.index.html). To increase

tatistical power, only voxels affected in at least two individuals per patient groupere considered for analysis.

. Results

.1. Phonemic accuracy

To start with, a major indicator for the integrity of auditory-to-otor mapping processes is phonemic accuracy. As expected, the

ealthy participants and RHD subjects had low overall errors rates.cross experiments and subjects, .04 errors per item (min: 0, max:) occurred in the group of healthy subjects. For the RHD group,n average error rate of .09 per item was obtained. A substantiallyigher overall error rate of .5 was observed in the LHD group.

Subjects’ mean error rates were entered into a one-way ANOVAith the factor GROUP. The analysis revealed a significant main

ffect of GROUP (F(1, 28) = 24, p < .001). Post hoc comparisons of

roups showed significantly higher error rates in the LHD grouphan in both the NC and the RHD group (p < .001). Error rates didot differ between the NC and the RHD group.

A comparison of error rates in repetition and transformationas only performed for the LHD group, since only the LHD patients

able 2ehavioral patterns of imitation (SSE, PEM) in repetition and transformation among subje

Group Subjects Phonemic errors inrepetition (mean)

SSE-imitationin repetition

1 L10 0 +L7 0.13 +L9 0.17 +L5 0.26 +

2 L1 0.3 −L6 0.55 −L4 0.61 −

3 L3 0.89 −L2 0.89 −L8 0.96

gia 48 (2010) 1115–1124

made substantial numbers of phoneme errors. In repetition, meanerror rates per stimulus were .48 (±.35), ranging from 0 to .96.

Error rates in repetition correlated negatively (r = −.72, p < .05)with the percentile values, which had been obtained in the subtest“repetition” (AAT; Huber et al., 1983).

In transformation, mean error rates were .52 (±.24), rangingbetween .14 and .88. Error rates did not differ between the twoexperiments (Wilcoxon Signed Ranks Test, Z = −.76, p > .1). Table 2lists the phoneme error rates together with further variables to bereported later.

3.2. Imitation of phonetic and prosodic detail in repetition

3.2.1. Imitation of schwa-syllable expression in repetitionIn order to investigate SSE-imitation within each group,

item-wise response-ratings (n = 24) were averaged over subjectsand were correlated with the model-stimulus ratings. Signifi-cant positive correlations between model- and response-ratingswere obtained for the NC (r = .83, p < .001), the LHD (r = .73,p < .001) and the RHD group (r = .79, p < .001). Accordingly, allgroups accommodated their degree of schwa-syllable expres-sion to the model speaker’s SSE-value on the 24 items in therepetition task (see Fig. 1A). To compare correlation strengthsbetween groups the coefficients were transformed into Fisher’sZ-scores (Bortz, 1993, p. 203). Although the LHD group hadthe lowest correlation coefficient, there was no significant dif-ference in correlation strengths between groups (p > .05 for allcomparisons).

To examine if SSE-imitation in repetition would likewise haveoccurred on a single subject level, we performed correlation anal-yses between model-ratings and response-ratings individually.Significant positive correlation coefficients between .56 and .92were revealed in all healthy subjects (p < .01). In the RHD subjects, rranged between .13 and .79, reaching significance in 8/11 subjects(p < .01), whereas in the LHD group r varied from −.09 to .76 andreached significance in only four subjects (p < .05). Although thenumber of subjects who imitated SSE was lower in the LHD thanin the RHD group (4/10 vs. 8/11), this difference failed to reachsignificance (Fisher’s Exact Test, df = 1, p > .05).

Correlations between the degree of SSE-imitation and errorrates were computed only for the LHD group, which was theonly group with a substantial number of phoneme errors. Again,the degree of SSE-imitation was measured by Z-transformed indi-vidual correlation coefficients from correlations of model- withresponse-SSE (see above). There was a significant negative cor-relation between individual phoneme error rates and the degree

of SSE-imitation (r = −.67, p < .05). Higher phonemic error rateswere associated with lower degrees of SSE-imitation. On the otherhand, SSE-imitation was not correlated with auditory nonword dis-crimination scores from the LeMo-battery (De Bleser et al., 2004)(r = −.31, p > .1; cf. Table 1, column 7).

cts with left hemisphere lesions, ordered by mean phonemic errors.

PEM-imitation inrepetition

PEM-imitation intransformation

Lesion sizein cc

+ − 64.2+ − 46.6+ + 29.2+ − 31.6

+ − 115.3− + 45+ − 100.9

− − 104.2− − 292.3− − 58.3

J. Kappes et al. / Neuropsychologia 48 (2010) 1115–1124 1119

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ig. 1. (A) Scatter plots of averaged rating scores for model schwa-syllable exprescompletely reduced SSE) to 3 (completely explicit SSE). (B) Scatter plots of model pontrol group, n = 10; LHD = participants with left hemisphere lesions, n = 10; RHD =

.2.2. Imitation of pitch elevation magnitude in repetitionTo examine imitation of word stress level in repetition we first

alculated group correlations between pitch elevation magnitudesf model-stimuli and their corresponding responses, averagedtem-wise across subjects. Again, significant positive correlationoefficients signalled imitation. All three groups imitated PEMNC: r = .84, p < .001; LHD: r = .72, p < .001; RHD: r = .88, p < .001,ee Fig. 1B). Comparisons of correlation strengths failed to revealignificant between-group differences (p > .05). Next, correlationsere calculated subject-wise across items. Correlation coefficients

anged between .24 and .80 in the NC group, between −.15 and .87n the RHD group, and between −.22 and .72 in the LHD group. Cor-elations were significant in 10/10 (NC), 9/11 (RHD), and 6/10 (LHD)ubjects, respectively. Although the number of subjects who imi-ated PEM was higher in the RHD group than in the LHD group (9/11s. 6/10), this difference missed statistical significance (Fisher’sxact Test, df = 1, p > .05).

Correlating individual phonemic error rates with the degree ofEM-imitation (expressed in Z-scores) for the LHD group failed toeach significance (p > .1). Similarly, there was no significant cor-elation of PEM-imitation with auditory nonword discriminationcores (r = −.49, p > .1).

.3. Imitation of prosodic detail in transformation

A second question of this study was whether imitation of the

agnitude of stress-related pitch elevation would “survive” in a

ransformation condition, in which the phonetic correspondenceetween model-stimuli and responses was destroyed, or whether

mitation of PEM would be bound to a one-to-one input–outputorrespondence, as in repetition. To answer this question, we first

SSE) vs. response-SSE in repetition. Rating scores were obtained on a scale from 0evation magnitude (PEM) vs. averaged PEM of responses in repetition. NC = healthyipants with right hemisphere lesions, n = 11.

analyzed – on group- and on individual levels – if the requiredtransformation was actually performed. Only items which had beentransformed correctly were then included in the subsequent anal-yses of PEM-imitation.

3.3.1. Transformation of schwa-syllable expressionAs described in Section 2.4, our model-stimuli were rated by 30

experienced listeners on a four-point rating scale from 0 to 3. Toensure that the model-stimuli to be transformed were unequiv-ocally “reduced” or “explicit”, we excluded stimuli which hadreceived average scores between 1 and 2 (5 out of 48 stimuli).

To examine SSE-transformation performance in the three sub-ject groups we tested for correlations between model-SSE andresponse-SSE (see Section 2.4). Item-wise response-ratings (n = 43)were averaged across the subjects of each group and were corre-lated with the rating scores of the corresponding model-stimuli.We expected significant negative correlations as an indication ofSSE-transformation from explicit to reduced schwa-syllables andvice versa.

Fig. 2A presents scatter plots of averaged rating scores formodel-SSE vs. response-SSE for each group. Correlations reachedsignificance in all groups (NC: r = −.85, p < .001; LHD: r = −.48,p < .01; RHD: r = −.72, p < .001). Correlation coefficients were trans-formed into Fisher’s Z-scores to compare group correlations. Therewas a significant difference in correlation strengths between theNC and the RHD group (p < .05), with stronger correlation in the NC

group. The correlation observed in the LHD group was significantlyweaker than in NC (p < .01) and in RHD (p < .05).

To examine whether group effects could be confirmed on anindividual level, correlations between model-SSE and response-SSE were performed for single subjects. Again, negative correlation

1120 J. Kappes et al. / Neuropsychologia 48 (2010) 1115–1124

F on (SS0 del piN n = 10

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ig. 2. (A) Scatter plots of averaged rating scores for model schwa-syllable expressi(completely reduced SSE) to 3 (completely explicit SSE). (B) Scatter plots of moC = healthy control group, n = 10; LHD = participants with left hemisphere lesions,

oefficients signalled correct transformation. Significant negativeorrelations were obtained in all healthy participants (r between.43 and −.81, p < .01). Similarly, correlations of subjects with rightemisphere lesions ranged between −.41 and −.71, and were sig-ificant in all cases (p < .01). In the LHD group r ranged between .1nd −.6, and was significant (p < .05) in only three subjects.

Hence, with the exception of seven subjects with LH-lesions allubjects were able to phonetically transform schwa-syllables ineard nonwords into their explicit or reduced form, respectively.

.3.2. Imitation of pitch elevation magnitude in transformationItems which had not been transformed correctly were excluded

rom the analyses of PEM-imitation. For explicit model-stimuli (rat-ngs between 2 and 3), responses had to be rated lower than 1.5o be valid. For reduced model-stimuli (ratings between 0 and 1)esponses had to have a rating score higher than 1.5 to be consid-red correct. In the healthy control group 89% of responses werencluded, in the LHD group 60%, in the RHD group 83%.

In order to investigate PEM-imitation on the remaining items,EM-values (in semitones) were calculated for all valid transforma-ion responses and were averaged item-wise across the subjects ofach group. Response-PEM was then correlated with model-PEM.nly items which were valid in at least half of the subjects in aroup were used for group correlations.

Significant imitation of PEM was obtained for the NC (r = .63,< .001), and the RHD (r = .61, p < .001) group. In contrast, no signif-

cant imitation of PEM was present in the LHD group (r = .25, p > .1).

n Fig. 2B scatter plots of group correlations are depicted.

Comparison of correlations revealed no significant differenceetween the NC and the RHD group (p > .05). In contrast, the corre-

ation observed in the LHD group was significantly weaker than inoth, NC and RHD group (p < .05 in both comparisons).

E) vs. response-SSE in transformation. Rating scores were obtained on a scale fromtch elevation magnitude (PEM) vs. averaged PEM of responses in transformation.; RHD = participants with right hemisphere lesions, n = 11.

To examine individual results, we tested subject-wise for cor-relations between model- and response-PEM. Significant positivecorrelation coefficients were obtained in all healthy participantsbut one (r between −.1 and .71, p < .05). In RHD subjects, r rangedbetween −.21 and .63, reaching significance in 7 out of 11 cases(p < .05). By contrast, only two LHD subjects obtained significantcorrelations (r between −.23 and .74, p < .01).

The number of subjects who imitated PEM in transformationwas not significantly higher in the group with right hemispherelesions (7/11) than in the group with left hemisphere lesions (2/10;Fisher’s Exact Test, df 1, two-sided, p > .05).

Taken together the results for PEM-imitation in repetition andtransformation, all healthy subjects imitated word stress magni-tude in at least one of two experiments. In the RHD group, 10 outof 11 subjects imitated in repetition or transformation. Among theLHD subjects, 7 out of 10 subjects imitated PEM in at least onetask, repetition or transformation, whereas three patients failed toimitate (see Table 2).

The relationship between phonemic abilities and PEM-imitationin transformation was assessed by correlating the individual Z-scores of stimulus-response correlations with numbers of phonemeerrors. Again, this analysis was confined to the LHD group. The cor-relation was not significant (r = −.46, p > .1). There was, however,a significant relationship of PEM-imitation with the auditory non-word discrimination scores from the LeMo-battery (De Bleser et al.,2004) (r = −.70, p < .05; cf. Table 1, column 7).

3.4. Relationships between imitation parameters

Table 2 lists the ten LHD-participants in the order of their phone-mic repetition abilities (column 3), from mild to severe. The tablealso specifies, for the two imitation parameters and the two tasks,

J. Kappes et al. / Neuropsychologia 48 (2010) 1115–1124 1121

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ig. 3. Lesion mappings on transversal MRicro-scan-templates (MRIcro software; Ro1–L10: participants with left hemisphere lesions, R1–R11: participants with right

hether or not a participant imitated, as inferred from the signifi-ance of the corresponding stimulus-response correlations. The listeveals a consistent patterning of these data: Four LHD-patients,esignated as group 1, imitated SSE and PEM in the repetitionask. These were the patients with the mildest phonemic impair-

ent. Three further patients consistently failed to imitate SSE, buttill imitated the prosodic parameter, PEM, in either the repetitionr the transformation task (group 2). These patients had moder-te repetition impairments. A third group, designated as group 3,howed no imitative behavior at all. These patients also had theost severe phonemic impairment. Hence, the table reveals that

one of the LHD patients imitated SSE but not PEM, suggestinghat PEM-imitation was more robust than SSE-imitation in the LHDroup. It also reveals that the tendency to imitate diminished withncreasing nonword repetition impairment.

.5. Lesion analysis

A further objective of this study was to identify neural structureshat play a role in mediating imitation of phonetic and prosodic

etail in nonword repetition (see Fig. 3 for lesion mappings ofach patient). Influences of lesion side on imitation have alreadyeen reported in the group comparisons of the preceding sections.e furthermore analyzed lesion size and intra-hemispheric lesion

ocation as possible predictors of imitation behavior and phonemicccuracy.

Brett, 2000; Rorden & Karnath, 2004, www.sph.sc.edu/comd/rorden/mricro.html);phere lesions.

3.5.1. Lesion sizeCorrelations between lesion size, on the one hand, and the

degree of SSE- and PEM-imitation and phonemic accuracy, onthe other, were calculated. For the LHD group, significant nega-tive correlations between lesion size and SSE-imitation (r = −.83,p < .01), and between lesion size and PEM-imitation in transfor-mation (r = −.83. p < .01) were obtained. No significant correlationswere present between lesion size and phonemic errors or betweenlesion size and PEM-imitation in repetition (p > .1; cf. Table 2, right-most column).

For the RHD group no significant correlations were obtainedbetween lesion size and any of the imitation parameters.

3.5.2. Intra-hemispheric lesion locationWe used the Brunner and Munzel test for voxel-wise analyses

of the influence of lesion location on patients’ phonemic accuracyand/or imitation patterns. Mean repetition error rate per subjectserved as a phonemic accuracy index in the LHD group. Individ-ual correlation coefficients for prosodic and segmental imitation inrepetition were transformed into Z-scores and used as continuousvariables indicating the degree of imitation in the LHD and the RHD

group, respectively.

3.5.2.1. Left hemisphere lesions. The results of voxel-wise analysesare shown in Fig. 4A–C. All voxels receiving Z-values above 2.3,corresponding to an uncorrected probability below .01, are dis-

1122 J. Kappes et al. / Neuropsychologia 48 (2010) 1115–1124

F ic erre

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ig. 4. Voxel-wise analyses of lesions in the LHD group associated with (A) phonemlevation magnitude (PEM) in repetition.

layed. Mean error rates in repetition ranged from 0 to .96 in theHD-participants. The analysis revealed a cortical region centeredn Heschl’s gyrus, extending through posterior STG to the supra-

arginal gyrus. Lesions in these regions were associated with aigher number of phoneme errors (see Fig. 4A).

Individual correlation coefficients indicating SSE-imitationanged between −.09 and .76, corresponding to Z-scores between.09 and .99. These Z-scores were entered into a voxel-wise analy-

is. The analyses revealed a small area at the medial end of Heschl’syrus where lesions were associated with a weakening of SSE-mitation. Notably, this region was part of the larger region foundo be associated with higher phonemic error rates (see Fig. 4B).

The same analysis was performed for imitation of prosodic

etail (PEM). Correlation coefficients ranged between −.22 and

72, corresponding to Z-scores between −.22 and .92. Voxel-ise analyses revealed two small areas within the lateralortion of Heschl’s gyrus whose lesion influenced the degreef PEM-imitation in LHD. Again, this location was part of the

or rates, (B) imitation of schwa-syllable expression (SSE), and (C) imitation of pitch

larger area associated with higher rates of phonemic errors, but didnot overlap with the region where lesions affected SSE-imitation(see Fig. 4C).

Lesions to anterior language areas did not influence imitationbehavior, as can be inferred from the fact that three of the fourpatients of subgroup 1 in Table 2, i.e., patients L7, L9, and L10, hadsubstantial lesions encroaching on anterior insular cortex, inferiorfrontal gyrus (pars triangularis and pars opercularis), and putamenof the left hemisphere, and still imitated consistently. Patient L8,on the contrary, who had an infarction of comparable size but didnot imitate in any one of the experiments (see Table 2), had a lesionin middle and posterior STG, Heschl’s gyrus, and inferior-parietalcortex, sparing frontal lobe areas and the anterior part of the insula.

3.5.2.2. Right hemisphere lesions. In the RHD patients, the sameanalyses failed to reveal any anatomical region within the righthemisphere whose lesion had influenced the degree of imitation inindividuals with right hemisphere damage.

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. Discussion

The present study aimed at investigating the imitation of fineegmental and prosodic detail in speech repetition, especially of theegree of schwa-syllable expression and of the magnitude of stress-elated pitch elevation. Since both of these parameters within theimits of variation used here, are phonologically irrelevant, theirmitation would not a-priory be expected to occur in repetitionasks, because verbal repetition is commonly understood to sim-ly require correct reproduction of the phonological content of theuditory verbal stimulus. A second aim of this study was to exam-ne if such imitation also occurs when the task requires more than

ere repetition of a heard verbal stimulus, i.e., when it includeshonetic transformation prior to motor production. In the trans-ormation task administered here, the explicitness or reduction ofchwa-syllables in the verbal stimuli had to be altered intentionallyefore responding, with the question if this transformation wouldamper the imitation of prosodic details of the stimuli.

In both experiments we investigated three groups of par-icipants, i.e., healthy controls and patients with right and leftemisphere lesions, respectively. Regarding the LHD-participants,ll of whom were aphasic, our question was whether imitation ofhonetic detail occurs, and if yes, whether it would be related withheir phonemic accuracy in nonword repetition. As for the RHDroup, we specifically asked if patients with lesions in the rightCA-territory would imitate the prosodic variation that occurred

n the stimuli to be repeated.In the normal subjects we obtained strong imitation effects for

oth parameters, SSE and PEM, in the repetition task, replicatingarlier findings of unintentional reproduction of phonologicallyrrelevant acoustic details (Delvaux & Soquet, 2007; Gentilucci &ernadis, 2007; Shockley et al., 2004). More specifically, for the SSE-arameter, – an index related to speaking style and to the formalr informal attitude of a speaker – we corroborated our findingsrom an earlier study, which had shown that neurologically healthyubjects consistently tend to imitate the extent to which a schwa-yllable is reduced in the model stimulus (Kappes et al., 2009). Liken this earlier study, all normal subjects examined here, withoutxception, imitated SSE.2

As for PEM, our finding of a consistent imitation of the degreef pitch elevation on stressed syllables is novel, but it extendsarlier reports of an imitation of parameters related to fundamen-al frequency (Bailly, 2003; Kappes et al., 2009; Peschke et al.,009). In this paradigm we exploited the natural variation of theagnitude of F0-elevation on the stressed syllable of each of the

tems produced by the model speaker, which ranged across severalemitones without altering the weak–strong–weak category of theccent patterns of the stimuli. The healthy subjects as a group, andll subjects but one individually, imitated this gradual variation,ithout being required to do so.

Based on these results we claim that (unintentional) imitationf phonetic detail is a frequent phenomenon in speech repetition.ur findings corroborate and extend earlier reports of stimulus-

esponse accommodation in verbal repetition (Fowler, Brown,abadini, & Weihing, 2003; Gentilucci & Bernadis, 2007; Namy,ygaard, & Sauerteig, 2002; Shockley et al., 2004). On the whole,

hey are inconsistent with a purely abstractionist view of ver-al repetition. In abstractionist theories, the acoustic incidentals

f a stimulus to repeat would be assumed to be stripped-off“talker-normalisation”) and only phonologically relevant informa-ion gains access to the output system. Episodic theories, to theontrary, are more consistent with the observations made here,

2 Since there was no overlap of the normal groups examined here and in Kappest al. (2009), the data presented here are strongly validated by these earlier findings.

ia 48 (2010) 1115–1124 1123

since they predict that any acoustic information contained in astimulus can affect speech output in verbal repetition (Goldinger,1998).

Interestingly, imitation behavior in the normal controls was notbound to a one-to-one correspondence of input and output, butwas still present when speakers transformed the input stimulusand produced a phonetically different nonword. In the transforma-tion experiment there was still a strong tendency, – on the groupaverage and in all participants except one –, to reproduce the grad-ing of stress-related pitch modulation in the model-stimuli. Hence,in accordance with earlier results (Kappes et al., 2009) our datademonstrate that para-phonological information contained in aspoken model may survive the transfer from speech perception into(motor) speech production, even if the heard stimulus undergoessome phonetic accommodation before reproduction. This findingis in line with the results reported by Delvaux and Soquet (2007),who found ambient dialectal speech characteristics to influence thespeech of listeners, although the participants were not engaged ina repetition task.

On the whole, the RHD group was not much different fromthe normal controls, to the extent that the patients with righthemisphere lesions, as a group, showed similarly high correlationsof stimulus-SSE with (averaged) response-SSE or of stimulus-PEM with (averaged) response-PEM. Analyses based on individualresults revealed slightly smaller numbers of participants who imi-tated, but there was no remarkable difference between the SSEand the PEM paradigm in this regard. To the contrary, imitation ofprosodic detail in repetition seemed to be even somewhat strongerthan imitation of schwa-articulation (group correlation: .88 vs. .79,numbers of imitating participants: 9/11 vs. 8/11). We would there-fore reject the hypothesis that lesions to right peri-sylvian areasspecifically interfere with the unintended imitation of F0-patterns,such as word stress.

The LHD-patients, as a group, demonstrated imitation in non-word repetition as well, although they had the weakest groupcorrelations, and substantial numbers of non-imitating participantsoccurred in this group. More specifically, SSE-imitation, whichseemed to be particularly robust in the normal population, provedto be particularly vulnerable since it occurred in only four out of tenpatients. The assumption that lesions in the left MCA-territory mayinterfere with unintended imitation was also bolstered by the find-ing that the degree of imitation was linked to phonemic accuracy:patients who made many phoneme errors in repetition also failedto imitate both types of sub-phonemic variation in the stimuli, andwith decreasing error rates there was, first, imitation of prosodic(i.e., PEM), and in still milder cases, also of segmental phoneticdetails (i.e., SSE).

Although the between-group differences reported here wereremarkable, they failed to become significant in most compar-isons, both regarding group correlation strengths and regardingnumbers of imitators. This is, in the first instance, probably dueto the restricted numbers of participants in the three groups.On the other hand, it also reflects that we did find imitationin all three groups, i.e., even in the aphasic patients, despitetheir sometimes large lesions in the left peri-sylvian region.The presence of imitation effects in an aphasic patient demon-strates that she/he is still sensitive to graded acoustic variationand even able to translate this variation into her/his own motoroutput.

The transformation task introduced here proved to be particu-larly sensitive to left hemisphere involvement, since the correlation

coefficient signalling transformation was significantly lower inthe LHD as compared to the two other groups and only threeout of ten patients showed the expected inverse relationshipbetween stimulus- and response-SSE. Remarkably, the transfor-mation requirement also disrupted PEM-imitation in the LHD

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124 J. Kappes et al. / Neuropsy

roup,3 suggesting that the auditory-to-motor translation of pho-etic information was more vulnerable to interfering phonologicalrocessing in these patients.

Regarding lesion analyses, the imitation behavior of the RHDatients showed no relationship with lesion size, and the voxel-ased analysis failed to reveal any region whose lesion was relatedith reduced imitation strength, although lesion size varied con-

iderably in this group (and even more than in the LHD group). Thisesult seems to provide another reason for assuming that the rightemisphere was not involved in the speech imitation paradigms

ncluded here, even not in the prosodic paradigm.In the LHD subjects, on the contrary, there was a significant

orrelation between lesion size and two of the imitation param-ters, and we also found, in the voxel-based analysis, a remarkablyonsistent patterning of lesion–symptom relationships. Voxels pre-icting phonemic accuracy in repetition were found in a ratherircumscribed area extending from Heschl’s gyrus along the pos-erior part of the STG to the supramarginal gyrus. This is not annexpected finding, since it conforms with the standard view ofhe posterior temporal and inferior-parietal region as a phonolog-cal processing network (Jacquemot, Pallier, LeBihan, Dehaene, &upoux, 2003; Scott & Wise, 2004). The regions whose lesion wasssociated with an absence of imitation of prosodic and segmen-al phonetic properties were part of this area, centering in smallocations at the medial (SSE) and the lateral (PEM) end of Heschl’syrus in the left hemisphere. Although these results, due to themall sample size, need to be interpreted with the outmost cau-ion, it seems remarkable that the region found to be responsibleor speech imitation immediately neighbours the area that Warrent al. (2005) had suggested to convey a matching of auditory inputignals onto templates representing traces from earlier auditoryxperiences, i.e., the posterior temporal plane. In their model of anauditory do-system” this area is considered to play a key role inhe translation of auditory input signals into speech motor events.he implication of Heschl’s gyrus found here should also not beiewed as a trivial source of imitation failure due to a basic percep-ual impairment, since imitation in the LHD group observed hereas not correlated with auditory-perceptual abilities as measured

y a nonword discrimination task.Still more important than this might be the result that lesions to

nterior portions of the presumed dorsal stream, even when theyre extensive, do not necessarily interfere with imitation. This isn line with the result of our preliminary study of two aphasicatients, in which we applied similar paradigms to demonstrate,mong other things, that one of the patients, who had a large ante-ior lesion sparing the temporal-parietal zone, imitated perfectlyne acoustic details in word repetition.

The finding that an aphasic patient absorbs the phonetic prop-rties of acoustic input stimuli to reproduce them in her/his speechutput may provide an important indication that she/he is still sen-itive to information in the auditory domain, and is even able toranslate such information into articulation. This knowledge coulde of great importance in the framing of therapeutic approaches tohe remediation of phonological and motor impairments of speak-ng.

cknowledgments

This study was part of a joint project supported by the Ger-an Ministry of Education and Research (BMBF). We are grateful toeHa-Hilfe e.V. for their constant support. Marco Mebus is acknowl-dged for his excellence in producing naturally sounding nonword

3 Recall that only correctly transformed items had been used for further analysisf PEM-imitation.

gia 48 (2010) 1115–1124

stimuli. We thank two anonymous reviewers for constructive com-ments on an earlier version of the manuscript.

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