Syntactic And Auditory Spatial Processing In The Human .

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NeuroImage 57 (2011) 624–633Contents lists available at ScienceDirectNeuroImagej o u r n a l h o m e p a g e : w w w. e l s e v i e r. c o m / l o c a t e / y n i m gSyntactic and auditory spatial processing in the human temporal cortex:An MEG studyBjörn Herrmann a,⁎, Burkhard Maess a, Anja Hahne a, Erich Schröger b, Angela D. Friederici aabMax Planck Institute for Human Cognitive and Brain Sciences, Leipzig, GermanyInstitute for Psychology, University of Leipzig, Leipzig, Germanya r t i c l ei n f oArticle history:Received 5 January 2011Revised 12 April 2011Accepted 18 April 2011Available online 29 April 2011Keywords:Interaural time differenceMagnetoencephalographyPerceptual processingSuperior temporal cortexSyntactic processinga b s t r a c tProcessing syntax is believed to be a higher cognitive function involving cortical regions outside sensorycortices. In particular, previous studies revealed that early syntactic processes at around 100–200 ms affectbrain activations in anterior regions of the superior temporal gyrus (STG), while independent studies showedthat pure auditory perceptual processing is related to sensory cortex activations. However, syntax-relatedmodulations of sensory cortices were reported recently, thereby adding diverging findings to the previousstudies. The goal of the present magnetoencephalography study was to localize the cortical regionsunderlying early syntactic processes and those underlying perceptual processes using a within-subject design.Sentences varying the factors syntax (correct vs. incorrect) and auditory space (standard vs. change ofinteraural time difference (ITD)) were auditorily presented. Both syntactic and auditory spatial anomalies ledto very early activations (40–90 ms) in the STG. Around 135 ms after violation onset, differential effects wereobserved for syntax and auditory space, with syntactically incorrect sentences leading to activations in theanterior STG, whereas ITD changes elicited activations more posterior in the STG. Furthermore, ourobservations strongly indicate that the anterior and the posterior STG are activated simultaneously when adouble violation is encountered. Thus, the present findings provide evidence of a dissociation of speechrelated processes in the anterior STG and the processing of auditory spatial information in the posterior STG,compatible with the view of different processing streams in the temporal cortex. 2011 Elsevier Inc. All rights reserved.IntroductionPrevious studies investigating early syntactic processes in auditorysentence comprehension reported an enhanced negativity around100–200 ms, labeled early left anterior negativity (ELAN), that waselicited by sentences containing a syntactic word category violation(Friederici et al., 1993; Hahne and Friederici, 1999, 2002). It has been apoint of discussion whether prosodic effects contribute to such earlysyntax-related responses. However, a recent finding provides contradicting evidence by showing that a change in the prosodic contourcannot account for the ELAN effect, thereby highlighting theinterpretation of the ELAN as a marker for initial syntactic processes(B. Herrmann et al., 2011).Another question that has been raised in the context of theinterpretation of the ELAN is whether this component belongs to thefamily of the mismatch negativity (MMN), an early negativity associatedwith rule violations in auditory perception (Näätänen et al., 1978). TheMMN is elicited by an infrequently presented auditory event among aseries of frequently repeated auditory events reflecting a memory⁎ Corresponding author at: Max Planck Institute for Human Cognitive and BrainSciences, Postbox 500355, 04303 Leipzig, Germany.E-mail address: bherrmann@cbs.mpg.de (B. Herrmann).1053-8119/ – see front matter 2011 Elsevier Inc. All rights rison process (Schröger, 2005). The MMN has its maximum ataround 100–200 ms following the onset of the infrequent event and hasbeen reported for frequency (Näätänen et al., 1978; Shalgi and Deouell,2007), duration (Jemel et al., 2002) or spatial deviations (Schröger,1996; Nager et al., 2003), for example.The relation between processing syntactic and auditory perceptualinformation was first investigated by Hahne et al. (2002) who studiedearly syntactic and auditory spatial processing in combination usingelectroencephalography (EEG). In this study, infrequent spatialdeviations within a spoken sentence elicited a MMN, whereassentences containing a syntactic word category violation elicited anELAN. Sentences including an infrequent spatial deviation as well as asyntactic violation led to a larger negativity around 125–175 ms thanthe single violations, although the amplitude was less than a completeaddition of the two single violations. The results were taken as anindicator that early syntactic and physical acoustic information can beprocessed in parallel within the first 200 ms (Hahne et al., 2002).However, it remains an open question what parallel processing inthis context means as only slight differences in the EEG scalpdistribution of the syntactic and auditory spatial violation effectswere reported in the study of Hahne et al. (2002). The presentmagnetoencephalography (MEG) study aims to shed more light onthis issue. It might be the case that both types of single deviations

B. Herrmann et al. / NeuroImage 57 (2011) 624–633recruit the same brain regions and that the double deviation thusleads to stronger activation in these very same regions. On the otherhand, different brain regions might be involved in processingsyntactic versus spatial deviations and that these regions are activatedsimultaneously when a combined violation is encountered. Accordingto dual stream auditory processing models (Rauschecker and Scott,2009) spatial information is processed in the dorsal stream involvingthe posterior portion of the superior temporal cortex, while speech(intelligibility of speech) processes recruit regions anterior to Heschl'sgyrus in the ventral stream. It could, therefore, be hypothesized thatpartly different regions are activated when speech-related andauditory spatial features are processed in parallel.Previous studies on the localizations of the neural mechanisms thatunderlie early syntactic processes, have localized the sources of themagnetic ELAN (ELANm) to the superior temporal cortex (Groß et al.,1998; Knösche et al., 1999), and more specifically to the anterior partsof the superior temporal gyrus (aSTG) and the inferior frontal cortex(IFC; Friederici et al., 2000). More recently, a so called “sensoryhypothesis” for early syntactic effects has been introduced in the visualdomain (Dikker et al., 2009). This hypothesis is based on theobservation that early sensory cortex activations were affected ataround 100–200 ms when participants encountered a syntactic wordcategory violation (Dikker et al., 2009, 2010; B. Herrmann et al., 2009).It has been suggested that these early sensory effects rely on formproperties associated with the syntactic category, e.g. overt categorymarking by an affix (Dikker et al., 2010). For the processing of syntacticviolations in an auditory oddball paradigm, B. Herrmann et al. (2009)observed modulations of the primary auditory cortex (AC) and thesuperior temporal sulcus, thus, suggesting activations in regionsdifferent from previous localizations showing aSTG and IFC activationsin processing word category violations (Friederici et al., 2000). Oneexplanation for these diverging findings that has been proposedrelates to the methodological approaches applied (Dikker et al., 2009).In the study conducted by Friederici et al. (2000), for instance, dipolemodeling was constrained by functional magnetic resonance imaging(fMRI) results from a previous sentence processing study (Meyer et al.,2000). Dikker et al. (2009) argued that this constraint might not bevalid, as fMRI lacks the temporal resolution to derive solid assumptionsabout an early stage in sentence processing. In the study by B.Herrmann et al. (2009), on the other hand, two-word utterances werepresented in an auditory oddball paradigm in which syntacticprocessing is accompanied by an acoustic change (Shtyrov andPulvermüller, 2007), thus, possibly biasing the source localizationtowards primary regions.The underlying neural sources of the MMN have mainly beenlocalized to auditory sensory cortex regions (Giard et al., 1990; Alhoet al., 1998; Maess et al., 2007). Particularly relevant for the currentstudy, the MMN and its magnetic counterpart (MMF, mismatch field)has been found sensitive to infrequent changes of interaural time andinteraural level differences (ITD, ILD; Schröger, 1996; Schröger andWolff, 1996; Kaiser et al., 2000; Nager et al., 2003). The ITD and ILD aretwo important auditory cues which allow spatial sound localization(Middlebrooks and Green, 1991). The MMN to changes in ITD/ILD hasbeen shown to modulate brain activations in the posterior STG/AC(Kaiser et al., 2000; Tata and Ward, 2005; Sonnadara et al., 2006;Deouell et al., 2006). Sometimes, an additional neural generatorlocalized to the right IFC has been reported to underlie the MMNmechanism (Giard et al., 1990; Jemel et al., 2002; Shalgi and Deouell,2007).In addition to the ELAN effect in the 100–200 ms time window,previous studies were able to disentangle the “early syntax effect” intodifferent sub-stages, observing an additional very early syntax-relatedeffect that modulated the M50 component (C. S. Herrmann et al.,2000; B. Herrmann et al., 2009, 2011). Furthermore, the detection ofsimple rule violations in an auditory oddball paradigm has not onlybeen shown to elicit the MMN, but also to modulate the brain's625activity very early, starting at around 30 ms (Boutros and Belger,1999; Ermutlu et al., 2005; Slabu et al., 2010; Grimm et al., 2011).In the present study, anatomically constrained magnetoencephalography (MEG) was used to further investigate the early syntacticand auditory perceptual parallel processing effect in the brain. On thisaccount, auditory sentence materials were presented that varied insyntax (syntactically correct vs. syntactically incorrect) and auditoryspace (standard vs. infrequent ITD change). For the source analysis, adistributed source model was used without any priors regarding thelocation of the underlying cortical regions modulated by syntax andauditory space. Our main goals were to examine the neuralmechanisms that underlie the processing of (1) syntactic violations,(2) auditory spatial violations (ITD change), and (3) double violations,i.e. in syntax and auditory space.(1) The localization of the neural responses elicited by syntacticviolations allowed us to test previous localizations of the ELANm(Friederici et al., 2000), and to examine whether auditory sensorycortices are sensitive to syntactic manipulations (Dikker et al.,2009). The former study predicts activations in the anterior STGwith additional weaker frontal activations, whereas the latterview predicts the ELANm to be localized in auditory sensorycortices.(2) We sought to localize the neural sources of the MMF elicited byinfrequent ITD changes within naturally spoken sentences inorder to have a condition which reflects auditory perceptualrule processing (Schröger, 1996, 2005). We expected theposterior STG/AC to be sensitive to auditory spatial deviations(Kaiser et al., 2000; Deouell et al., 2006). Based on the dualpathways in the auditory system (Rauschecker and Scott,2009), the neural sources of the ELANm and MMF wereexpected to differ in location.(3) By localizing the neural responses to sentences including adouble violation, we aimed to investigate how processing asyntactic violation and an auditory spatial violation in parallelis accomplished by different regions in the temporal cortex(Rauschecker and Scott, 2009). We expected the brain regionsinvolved in processing the single syntactic and those involvedin processing the auditory spatial violations to be activatedsimultaneously for sentences containing both violations.Apart from the effects in the 100–200 ms time window (i.e., theELANm and MMF), we intended to further elucidate on the very earlysyntax and simple rule violation effects that precede the ELANm andMMF, and ask whether parallel processing can be observed already atthis processing stage.Methods and materialsParticipantsTwenty-four healthy, native German-speaking adults (11 female,mean age 25.3 years, standard error of the mean (SEM) 1)participated in the MEG study. They were all right-handed as measuredby the Edinburgh Handedness Inventory (Oldfield, 1971). The 20thpercentile of the laterality quotient was 100 (range: 83–100). Allparticipants gave written consent prior to testing and were paid sevenEuros per hour. They had no known hearing deficit or neurologicaldiseases in their history.Stimulus materialThe material comprised 192 syntactically correct sentences and192 sentences which included a syntactic word category violation.Stimuli were taken from a previous EEG experiment (Hahne et al.,2002). They were spoken by a trained female native speaker ofGerman and digitized at 44.1 kHz (16 bit, stereo). The factor syntax

626B. Herrmann et al. / NeuroImage 57 (2011) 624–633was tested by introducing syntactically correct sentences consistingeither of a “determiner–noun–auxiliary–past participle” sequence(e.g., “Das Obst wurde geerntet.”, Engl. “The fruit was harvested.”) or ofa oun–past participle” sequence (e.g., “ Das Gemüse wurde im Herbst geerntet.”, Engl. “Thevegetable was in-the autumn harvested.”). Syntactically incorrectsentences consisted of a ast participle” sequence (e.g., “Die Gerste wurde im geerntet.”, Engl.“The barley was in-the harvested.”). In these sentences, the prepositionwas directly followed by the past participle, causing a word categoryviolation. The participle of each sentence was overtly marked byclosed class morphology (i.e., by the prefix “ge-” and a suffix, e.g., “-t”).Incorrect sentences were created following the procedure describedby Hahne and Friederici (1999), and have been evaluated to avoidunwanted acoustic and/or prosodic effects (Hahne and Friederici,1999; B. Herrmann et al., 2011).In order to test for the factor auditory space, a standard and adeviant condition were created for each of the 384 sentences. Thedeviant condition included an infrequent ITD change of 0.2 ms (theleft channel was delayed) starting at the onset of the participle, thusgiving a right-lateralized impression. No such ITD change wasincluded in the standard condition. Based on the number of words,an ITD change occurred in only 10% of the words, while 90% of thewords did not include a lateralization effect. Correct sentenceswithout an ITD change are henceforth called “correct standardcondition”, syntactically incorrect sentences without an ITD change“incorrect standard condition”, correct sentences including an ITDchange “correct deviant condition” and syntactically incorrect sentencescontaining an ITD change “incorrect deviant condition” (see Table 1).incorrect. The positions (left vs. right) of the happy and sad smileywere randomized uniformly within each block and across conditions.Participants were instructed to ignore lateralization effects in theauditory stimulation. All steps of randomization were conductedindividually.MEG data recording and processingParticipants sat in an electromagnetically shielded room(Vacuumschmelze, Hanau, Germany). MEG signals were recorded witha 306-channel MEG device (Vectorview, Elekta-Neuromag, Helsinki,Finland) at 500 Hz and online filtered with a band-pass of 0.1–160 Hz.Two pairs of electrodes recorded a bipolar electrooculogram (EOG).Triggers marked the onset of the sentences as well as the onset of theparticiple within all sentences. During blocks, the position of theparticipant's head was quasi-continuously measured by five HPI (headposition indicator) coils to correct the magnetic fields for headmovements. Head movement correction, bad channel interpolationand external interference suppression were obtained by applying theSignal Space Separation Method (Taulu et al., 2004). The MEG recordingswere filtered with a high-pass of 2 Hz to avoid baseline correction and alow-pass of 10 Hz to maximize the signal-to-noise-ratio. By leaving thebroad deflections untouched, this procedure has proven to be usefulwhen investigating language- or memory-related processes (Tervaniemiet al., 1999; Friederici et al., 2000; C. S. Herrmann et al., 2000; Maess et al.,2006). The data was divided into epochs of 700 ms ( 200 ms to 500 ms)that were time-locked to the onset of the participle and to the sentenceonset. Epochs were screened for blinks and other artifacts and excludedfrom averaging if they contained a signal change of more than 200 pT/m(gradiometer), 4 pT (magnetometer) or 100 μV (EOG).Design and procedureSource reconstructionThe present experiment used a within-subject design. All 384sentences were presented via in-ear headphones at an intensity of55 dB above a participant's individual hearing threshold. One half ofthe sentences was randomly selected as standards, while the otherhalf was selected as deviants. Sentences were randomly distributedover four blocks with equal probability for each condition. Sentenceswithin each block were randomized with the constraint that no morethan three stimuli of the same type were presented in a row. Duringauditory stimulation, participants looked at a small fixation square inthe middle of a screen to reduce eye movements. In order to avoidmotor preparation, a variable response key assignment was used. Onethousand five hundred milliseconds after the sentence ended, apicture was presented showing a happy and sad smiley next to eachother. Participants were instructed to press the button for the happysmiley whenever the sentence was syntactically correct and to pressthe button for the sad smiley whenever the sentence was syntacticallyTable 1Examples of the sentence materials. The asterisk marks syntactically incorrectsentences and the underlined participle highlights the interaural time differencechange of 0.2 ms within the sentence. The number of sentences presented to theparticipants is provided in parentheses.Sentence, e.g.:SyntaxAuditory spaceDas Obst wurde geerntet. (48) The fruit was harvested. Die Gerste wurde im Herbst geerntet. (48)The barley was in-the autumn harvested.*Die Gerste wurde im geerntet. (96)*The barley was in-the harvested.Das Obst wurde geerntet. (48) The fruit was harvested. Die Gerste wurde im Herbst geerntet. (48)The barley was in-the autumn harvested.*Die Gerste wurde im geerntet. (96)*The barley was in-the harvested.Correct0.0 ms/standardIncorrect0.0 ms/standardCorrect0.2 ms/deviantIncorrect0.2 ms/deviantIndividual T1-weighted MRI images were obtained with a 3 T MRIscanner (Magnetom Trio, Siemens AG, Germany). The software Freesurfer(http://surfer.nmr.mgh.harvard.edu/) was applied to construct individualtopological representations of the cortical surface for each hemisphereusing the individual MRI images.The MNE package provided by M. Hämäläinen, MGH, Boston, MA,USA data/)was used to compute forward and inverse solutions. On this basis,inner skull surfaces were extracted using the above-mentioned T1weighted MRI images in order to construct individual boundaryelement models (BEM) for the volume conductor. Such a singlecompartment volume conductor has been shown to be sufficient forsolving the MEG forward problem (Hämäläinen and Sarvas, 1989).The MRI coordinate system was transformed into the MEG coordinatesystem using the HPI coils and about 50 additional points on the headsurface estimated by a Polhemus FASTRAK 3D digitizer. As sourcespace, the individual white matter surface was adopted.For the inverse solution, the approximately 130,000 vertices needed todescr

and auditory perceptual parallel processing effect in the brain. On this account, auditory sentence materials were presented that varied in syntax (syntactically correct vs. syntactically incorrect) and auditory space (standard vs. infrequent ITD change). For the source analysis, a distributed source model was used without any priors regarding the

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