What the neurocognitive study of inner language reveals

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What the neurocognitive study of inner language revealsabout our inner space

Hélène Loevenbruck

To cite this version:Hélène Loevenbruck. What the neurocognitive study of inner language reveals about our inner space.Epistémocritique, épistémocritique : littérature et savoirs, 2018, Langage intérieur - Espaces intérieurs/ Inner Speech - Inner Space, 18. �hal-02039667�

https://hal.archives-ouvertes.fr/hal-02039667

https://hal.archives-ouvertes.fr

Preliminary version produced by the author. In Lœvenbruck H. (2008). Épistémocritique, n° 18 : Langage intérieur - Espaces intérieurs / Inner Speech - Inner Space, Stéphanie Smadja, Pierre-Louis Patoine (eds.) [http://epistemocritique.org/what-the-neurocognitive-study-of-inner-language-reveals-about-our-inner-space/] - hal-02039667

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Whattheneurocognitivestudyofinnerlanguage

revealsaboutourinnerspace

HélèneLœvenbruck

UniversitéGrenobleAlpes,CNRS,LaboratoiredePsychologieetNeuroCognition(LPNC),

UMR5105,38000,GrenobleFrance

Abstract

Ourinnerspaceisfurnished,andsometimesevenstuffed,withverbalmaterial. The

natureofinnerlanguagehaslongbeenunderthecarefulscrutinyofscholars,philosophers

andwriters,throughthepracticeofintrospection.Theuseofrecentexperimentalmethods

in the field of cognitive neuroscience provides a newwindow of insight into the format,

properties, qualities and mechanisms of inner language. Gathering findings from

introspectionandempiricalworks,thisarticlefirstassessestheproportionoflanguagein

ourinnerspace.Severalvariantsof innerlanguagearethendescribed, includingwilfulvs

spontaneousinstances,condensedvsexpandedforms,silentvocalisationduringreadingor

writing,containedvsruminativeoccurrences,andself-controlledvshallucinatorycases.The

natureofthesevariantsandtheirembodiedmultisensoryqualitiesareexamined.Finally,a

neurocognitivemodelof the production of inner language is drawn, in the framework of

predictive control, speculating on the neuralmechanisms that underlie one of the most

significantcomponentsofourinnerspace.

Keywords: Inner language, Verbal mind wandering, Rumination, Hallucination,

Sensorimotorrepresentation,Embodiment,PredictiveControl


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Introduction

Ourinnerspaceisfurnishedwithverbalmaterialwhichcontributestoenrichingour

innerlife.Ourinternalvoiceplaysacentralroleinself-awareness,helpingustoremember

ourpast,toimagineandplanourfuture,tointerpretourpresentenvironment,togetabetter

control of situations, to solve problems, to encourage, comfort or regulate ourselves.

Engaging in mental verbalisation shapes our inner existence and is instrumental in the

maintenanceofacoherentself-narrative.

The claim that ourmental space contains inner verbalisation can be traced back to

Ancient Egyptian sages and Ancient Greek philosophers. Early Medieval scholars were

inspired from these ancient views on inner experience. Augustine’s Confessions, which

appearedin397-398,areconsideredasthefirstbookusingasubjectivetoneandfocusing

oninnerexperience.IntheConfessionsandinmanyofAugustine’slaterworks,itseemsthat

languageinvadestheauthor’sinnerspace.

Sincethen,innerlanguagehasbeenunderthescrutinyofphilosophers,writers,poets,

filmmakers,artists, literaryscholars,psychoanalysts,andlinguists,throughthepracticeof

careful introspection and reflection. Their investigations suggest that silent self-talk and

innerdialoguesorconversationstakeanimportantpartofourinnerspace.Innerlanguage

isoftenreportedaspervasiveorevenubiquitous.TheFrenchphilosopher,psychologistand

epistemologistVictorEggerforinstanceclaimed:

Atoutinstant,l’âmeparleintérieurementsapensée.Cefait,méconnuparlaplupartdes

psychologues,estundesélémentslesplusimportantsdenotreexistence.Ilaccompagnela

presque totalitédenosactes ; la sériedesmots intérieurs formeunesuccessionpresque

continue,parallèleàlasuccessiondesautresfaitspsychiques;àelleseuleelleretientdonc

unepartieconsidérabledelaconsciencedechacundenous.1(Egger,1881,p.1).

John Locke (1970) similarly asserted: “it is in constant use, accompanying many

language-relatedactivitiessuchaswriting,silentreading,learning,thinking,listeningand,

1 At every moment, the soul is speaking its thought internally. This fact, ill-recognized by manypsychologists,isoneofthemostimportantelementsofourexistence.Itaccompaniesnearlyallofouracts;theseriesofinteriorwordsformsanearlycontinuoussuccession,inparallelwiththesuccessionofotherpsychicfacts;itthusretains,initself,aconsiderablepartofourconsciousness.


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possibly,dreaming.”(Locke,1970,p.7).SuchastanceisalsotakenbythelinguistGabriel

Bergounioux(2001,p.107):

Pasd'activitévigilequinesoitaccompagnéed'unesonorisation intériorisée, fût-elle

réduite aux inepties de l'avant-sommeil, aux remembrances du vieillard idiot, à un

ressassementouuneritournelle,etpasnonplusd'activitéonirique.2

AsimilarlyextremepositionistakenbyBaars(2003)whoclaimedthat“Overtspeech

takesupperhapsa tenthof thewakingday;but innerspeechgoesonall the time”.Even

Chomskyaffirmed:“Nowletustakelanguage.Whatisitscharacteristicuse?Well,probably

99.9%ofitsuseisinternaltothemind.Youcan’tgoaminutewithouttalkingtoyourself.It

takesanincredibleactofwillnottotalktoyourself”.(Chomsky,2012,p.11).

Someoftheseintrospectiveaccountscanbeexamined,testedandcomplementedusing

recent experimental methods and technology developed in psychology and cognitive

neuroscience.Findingsfromtheselatterfieldsmayprovideanewwindowofinsightintothe

format,properties,qualitiesandmechanismsofinnerlanguageandmayallowustobetter

describewhatourinnerspaceconsistsof.

Inthisarticle,introspectiveviewsofinnerlanguagearejuxtaposedwithempiricaldata,

manyofwhicharereviewedelsewhere,e.g.inPerrone-Bertolottietal.(2014),Alderson-Day

&Fernyhough(2015)orLœvenbrucketal.(2018).

This article first assesses the significance of language in our inner space and the

proportionittakes.Severalvariantsofinnerlanguagearethendescribed,includingwilfulvs

spontaneousinstances,condensedvsexpandedforms,silentvocalisationduringreadingor

writing,containedvsruminativeoccurrences,andself-controlledvshallucinatorycases.Itis

then shown that some variants of inner language have multisensory qualities, with the

presenceofauditory,somatosensoryandvisualelements.Itisarguedthatwilfulversionsof

inner languagemay recruit alsomotor processes. Finally, a neurocognitivemodel of the

productionofinnerlanguageisdrawn,intheframeworkofpredictivecontrol,speculating

ontheneuralmechanismsthatunderlieoneofthemostsignificantcomponentsofourinner

2 Nowakefulactivityisunaccompaniedbysomeinteriorisedsound,beitpre-sleepnonsense,afoolisholdman’sreminiscing,broodingoramusicearworm,andnooneiricactivityeither.


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space.

1. Theimportanceofinnerlanguageinourinnerspace

1.1 Evidencefortheoccurrenceofinnerlanguage

Innerlanguageisclaimedtobeanessentialpartofourinnerspace.Butisourinner

spacefilledwithlanguage,withallofitsclothes,orratherbymeaning?Canwefindevidence

thatthismentalactivitythatwerefertoasinnerlanguageisindeedspelledoutinalinguistic

form, that it does use ordinarywords and syntax? Augustine himselfmade a distinction

betweentheverbumincorde,theinteriorverbalisation,andthelocutio,theexteriorisedoral

form(Cary,2011;Panaccio,2014).Ifthelatterobviouslyuseswordsandisexpressedina

givenlanguage,theformer,accordingtoAugustine(inDeTrinitate)isuniversal,itprecedes

overtlanguageproduction,anditisnotassociatedwithanyparticularlanguage.Aswewill

seebelow(in1.2)severalintrospectiveworksandlanguageimpairmentcasereportssuggest

indeedthatcognitiveactivitycanoccurwithoutusingnaturallanguage.Yet,introspectively,

we can sometimes hear a little voice in our head. Is these instances, is our little voice

expressedinagivenlanguage,isitshapedbythelanguage(s)weuse?

Examining innerexperience inbilingualandmultilingualspeakerscancontributeto

betterqualifyingourinnerspace.Inherbookentitled“TheBilingualMind”,Pavlenko(2014)

dedicatedachaptertobilingualismandinnerspeech,inwhichshereviewsseveralstudiesof

innerlanguageuseinbilingualandmultilingualspeakers.AnothersurveybyDewaele(2015)

provides further interesting data. These reviews show that the age of acquisition of the

secondlanguage(L2)(orofthethird,fourth,fifth,ormorelanguages,LX)isastrongfactor

in determiningwhich language is dominant in the inner speech of participants. Another

factor is the linguistic context of the cognitive event entertained in the inner speech.

Autobiographicalmemoryretrievalstendtobementallyutteredinthelanguageusedwhen

theevent tookplace.Contextofacquisitionandsocialisationare factors that facilitate the

shiftfromL1toLXininnerspeech.AcquiringtheLXinanaturalisticenvironment(rather

thananinstructedsetting)willincreaseitsuseininnerspeech.Self-perceivedproficiency

alsoinfluencesthelanguagechoiceininnerspeechandmentalactivities(mentalcalculation,

reasoning).HigherfrequencyofsocialspeechintheLXalsoincreasesthelikelihoodofitsuse


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forinnerspeech.InnerLXuseisalsoproportionaltothesizeofthespeaker’ssocialnetwork

inLX.Thedominantlanguageininnerspeechisalsopredictedbylengthofresidenceinthe

newcountryandthelanguagepredominantlyusedinovertspeech.Inaveryrecentstudy,

Resnik (2018) has found that in addition to these factors (high frequency of L2 use,

naturalisticexposuretoL2,highself-reportedproficiencyinL2),ahighbilingualismindex

andtheoverallnumberoflanguagesknownallcontributedtoboostL2useininnerspeech.

Asshowninthegrowingnumberofstudiesoninnerspeechinmultilingualspeakers,

ourinnerspacedoesseemtocontainverbalmaterialthatisnotabstract,orpurelysemantic,

butexpressedingivennaturallanguages,withfullsyntacticandlexicalclothing.Ourinner

spaceincorporatesourcultural,socialandlinguisticenvironment.

1.2 Othercomponentsofinnerspace:images,emotions,sensations,unsymbolisedelements

Itseemssafetoconcludethatourinnerspaceisfurnishedwithanimportantamount

ofverbalmaterial.Buthowmuch?Althoughthecontentionthatinnerlanguageispervasive

iswidelyheld,quantitativedescriptionsofitsoccurrenceinthegeneralpopulationaremore

nuanced.Inathoughtsamplingstudy,Klinger&Cox(1987)hadstudentscarryabeeperfor

up tosevendaysanddescribepropertiesof theirmental contentat each randombeeper

signal.Theyfoundthat51%ofthoughtsamplescontainedsomeinteriormonologue.Even

loweroccurrencesarefoundwhenusingmorecarefulinnerexperiencesampling.Hurlburt

has created amethod, called Descriptive Experience Sampling (DES), designed to obtain

more accurate accounts of inner experience (Hurlburt, 1993; 2011). Traditional

questionnairesoninnerexperiencearebiased,sinceparticipantsuselanguagetodescribe

their experience, which places them in a verbal thinking mode and leads them to

overestimate theamountof innerspeech. Inaddition,questionnaires containpre-defined

questions,whichcanorienttheparticipants’descriptions.Instead,DESdoesnotspecifyin

advancewhatcharacteristicstoexplore.Afterhavingcarriedthebeeperforadayandhaving

jotteddownnotesabouttheirinnerexperiencebeforeeachbeep,subjectsparticipateinan

“expositional interview”with the investigators,duringwhich theyareguided todescribe

theirinnerexperiencewiththehighestpossiblefidelity.Thissequenceofbeepedreportsand

detailedinterviewingisrepeated,leadingtoincreasingskillinthereporting.UsingDESwith


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hundredsofpeopleformorethanthirtyyears,Hurlburtandcolleagueshaveroutinelymet

participants who reported nomoments of inner speaking at all. They conclude that the

frequencyofinnerspeakingdisplaysalargeinter-individualvariability,rangingfromabout

zerotonearly100%,withameanofabout26%ofsampledmoments(Heavey&Hurlburt,

2008).Theysuggestthattherestofourinnerexperienceconsistsoffourothercomponents:

innerseeing,feeling,sensoryawarenessandunsymbolisedthinking.Innerseeingisvisually

imaginingsomethingthatisnotpresent.Feelingcorrespondsto“affectiveexperiences,such

assadness,happiness,humor,anxiety, fear, joy,nervousness,anger,embarrassment,etc”.

Sensoryawarenessispayingattentiontoasensoryaspectoftheenvironment(cold,wind,

hunger). Unsymbolised thinking is “thinking a particular definite thought without the

awareness of that thought being conveyed inwords, images or any other symbols”. It is

arguedtobeadistinctphenomenon,notaprecursortoanyotherphenomenon,andtobe

clearlyarticulatedandspecific.Evenifthisclassificationcanbedebatedandifsomeauthors

rejecttheexistenceofunsymbolisedthinking(Carruthers,2009),ithasbeenacknowledged

thatnon-verbalthinkingmayexist.Hurlburt’snotionofunsymbolisedthinkingisforinstance

reminiscentofPaivio’s(1990)DualCodingTheory,accordingtowhichstimulicanbecoded

andmentallymanipulatedinaverbalorvisualmode.

Hurlburt is not alone in defending that our inner space is not entirely filled with

language.Other authorshave estimated that approximately one quarter of our conscious

waking life consists of inner language (e.g. Uttl, Morin, Faulds, Hall & Wilson, 2012).

Furthermore, inner language, when it occurs, can be intertwined with non-linguistic

fragments. According to Wiley (2014), words can be combined with “sounds, numbers,

visuals,colors,tastesandodors,tactilefeelings,kinestheticsandemotions.”Theseelements

canbeplacedintosyntacticalslots,producinginnerutterancesthatareonlypartiallyverbal

(e.g.thewords“I’dlike”followedbytheimageofahamburger).

Ourinnerspaceisthereforenotfullyoccupiedbylanguage:onaverage,approximately

aquarterofourinnerspaceconsistsofinnerverbalisation,therestismadeupofimages,

emotions,sensationsandunsymbolisedelements.


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2. Variousinstancesofinnerlanguage

2.1 Wilfulinnerlanguagevsverbalmindwandering

Inner language manifests in various ways. We often deliberately engage in short

instancesofinnerspeech,forinstancewhenwecount,makealist,orscheduleourweekly

objectives.Wecanengage in longersophisticated innertalk,carriedout in fullsentences,

when we prepare a lecture, think hard about an argument, or imagine possible future

conversations.Theseshortandlonginstancesofinnerlanguagecanbereferredtoas“wilful”

or “deliberate” inner language. But sometimes our internalmonologue is lesswilful, less

activeand“morepassive”(Bonald,cited inEgger,1881).Themorepassive formof inner

languagewasseizedbyPlatowhodrewadistinctionbetweenopinionandfancy:“[thought]

isasilentinnerconversationofthesoulwithitself.[…]whenthisarisesinthesoulsilently

byway of thought, can you give it any other name than opinion? […] Andwhen such a

condition is brought about in anyone, not independently, but through sensation, can it

properlybecalledanythingbutseeming,orfancy?"(Plato,Sophist,263e-264a).Thisfanciful

innerlanguagehasbeenreferredtoas“verbalmindwandering”(Perrone-Bertolottietal.,

2014),andoftenoccursduring“restingstates”(mindwanderingcanalsotakeanon-verbal

form,suchasvisualimagery,hencetheadjective“verbal”).Verbalmindwanderingconsists

of flowing, spontaneous, unconstrained, external-stimulus-independent verbal thoughts.

Mind wandering (MW) has been the focus of several recent neurocognitive studies.

Smallwood and Schooler (2015) have recognized several beneficial outcomes of mind

wandering(seealsoMooneyhamandSchooler,2013,Schooleretal.,2014,Smallwoodand

Andrews-Hanna, 2013). According to them, the first benefit of MW is prospection. The

thoughts thatoccurduringMWareoften future-oriented,helping to improvedaily life.A

second beneficial outcome is creativity.MW seems to be associatedwith the capacity to

generatenovel,creativethoughts.Athirdvalueistoaddmeaningtopersonalexperience.By

engaginginmentaltimetravel,MWenablespeopletointegratepastandfutureeventsintoa

meaningful life narrative. Other beneficial outcomes include mental breaks to relieve

boredomfrommonotonousactivities,andday-dreamingtoprepareforpotentialobstacles

orthreats.ItcanbespeculatedthatamongthemanyformsofVM,theverbalone(unwilful

innerlanguage)isthemostlikelytoplaythefirstthreeoftheseroles:prospection,creativity


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andmeaning.

2.2 Condensedvsexpandedinnerlanguage

In addition to the various intentionaldegreesof inner language, various degrees of

unfoldinghavebeenidentified.Somevariantsarecondensedrelativetootherfullyformed,

orexpanded,versions(e.g.Fernyhough,2004;Alderson-DayandFernyhough,2015orGeva,

Jones,Crinion,Price,Baron&Warburton,2011b).Condensationseemstooperateatdifferent

levels:articulation,phonology,lexiconandsyntax. Introspectiveaccountsofcondensation

are abundant. It has been argued for instance that because inner language is directed to

oneself, it isshortenedcomparedtoovertspeechaddressedtoanexternal listener.Egger

(1881,p.69-71)wasthefirsttoclearlylistphysiologicalandsocialconstraintsforwhyinner

languagemaybeshorter.First,hearguedthatwecannotovertlyarticulateasquickly;the

speedofourtonguemovementsbeingphysiologicallylimited(“àparlertropvitelalangue

s’embarrasse”3).Moreover,whenwespeakaloud,weneedtotakebreathbetweenfragments

ofspeech,asspeechonlyoccursduringexpiratoryphases.Becauseitisnotsubjectedtothese

physiologicalconstraints,innerspeechisacceleratedcomparedwithovertspeech.Secondly,

Eggernotedsocialconstraints.Whenwespeaktosomeone,weneedtoarticulateclearlyand

slowly,inordertobeunderstood.Whenweuseinnerspeech,thissocialconstraintcanbe

abandoned and our articulation can bemore “sketchy”. Furthermore, according to Egger

(1881,p.71),someexpressionsthatweusementallybearmeaningsthatareexplicitonlyto

ourselves. In order for them to be understood, we would need to provide contextual

informationandtoreplacetheseexpressionsbyadetailedandexplicitdiscourse.

Therefore,innerspeechisnotonlyphysicallyshortenedwithrespecttoovertspeech,

it can also be syntactically condensed, or left elliptical. Vygotsky further developed this

notion(Vygotsky,1934/1986).Histheoryisbasedonintrospection,andonexaminationof

children’sprivatespeech(oregocentricspeech),inwhichchildrentalktothemselvesaloud,

andwhichheclaimedtobeaprecursorofadultinnerspeech.Heassertedthatimportant

wordsorgrammaticalaffixesmaybedropped.Accordingtohim,thesyntaxofinnerspeech

is“predicated,” in thesensethatonlynecessary information issupplied.Thesubject, and

3“whenspeakingtooquicklythetonguegetstangledup”


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even the verb, might be omitted. Bergounioux follows this notion of abbreviation,

condensationandpredication,providingdetailedlinguisticdescriptionsofthephenomenon.

According to Bergounioux (2001, p. 120), “l’endophasie ne semble différer de la parole

explicite ni par sa grammaire ni par son lexique, à la réserve d’un emploi généralisé de

l’asyndèteetdel’anaphore,etd’unesurreprésentationdelaprédicativité.”4

Examples of such linguistic operations can be found in literary or artistic works,

typicallythoseassociatedwiththe“monologueintérieur”(Dujardin,1887,1931)or“stream

of consciousness”movement, initiated byDujardin (Smadja, in press). AlthoughDujardin

depicted internal monologue as swarming with syntactically expanded sentences, later

renditions–suchasMollyBloom’smonologueinJoyce’sUlysses,thedisjointedmonologuein

Samuel Beckett’sTheUnnamable or thehumanmonologuesoverheard by angels inWim

Wender’sWingsofDesire–areclosertotheintrospectivedescriptionsofEgger,Vygotskyor

Bergounioux,inthattheyaremorefragmentary,abbreviated,predicatedandcondensed,at

boththesyntacticandlexicallevels.

Empirical grounding for the condensed quality of inner speech at the syntactic and

lexical levels can be found in an astute study of the rate of spontaneous covert speech

production(Korba,1990).Participantswereaskedtomentallysolveaseriesofshortverbal

problems.Theyreportedtheellipticalinnerspeechusedtosolveeachproblem,whichgave

an estimation of the number of words used in this type of mentation. They were then

instructed to expand the same volume of words into a full ostensive statement of their

internalproblem-solvingstrategies,whichprovidedanextendedwordcount.Theextended

wordcountrepresentedanequivalentrateofspeechinexcessof4000wordsperminute,

which cannot possibly be reached in overt mode. These findings are in favour of the

introspectiveclaimthatinnerverbalisationiscondensedwithrespecttoovertpublicspeech,

atleastatthesyntacticandlexicallevels.

In line with Egger’s claim that inner speech is less articulated, it has further been

suggestedthatthephonologicalformofinnerwordsmayitselfbeabbreviated.Severalsoviet

psychologistssuggestedthatinnerspeechisphonologicallyreduced,withmanyphonemes

4“endophasiadoesnotseemtodifferfromexplicitspeech,neitherbyitsgrammar,noritslexicon,exceptperhapsinageneraliseduseofasyndeton,anaphoraandanover-representationofpredication”


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beingdropped,typicallyvowels,andonlytheword-initialsoundsbeingclearlyproduced(e.g.

Vygotsky,1934/1986,p.237,244;Anan’evcitedinSokolov,1972,p.50).Thisclaimreceives

supportfromstudiesthatshowthatwordproductionisfasterininnerthanovertmode,even

when lexical content is controlled (Marshall and Cartwright, 1978; Anderson, 1982).

Marshall and Cartwright (1980) examined both word and sentence productions in a

recitationtask.Theyfoundthatsilentrecitationwasfasterthanovertrecitationforlistsof

one-andthree-syllablewordsaswellaslistsofgrammaticalandungrammaticalsentences.

MacKay (1981) also examined sentence production. Participantswere asked to produce

identicalsentencesasrapidlyaspossible,eitherovertlyorcovertly.Resultsindicatedthat

bothinternalandovertspeechimprovedwithpracticeandthatovertsentenceproduction

tooklonger.Thesecontrolledstudiesimplythatinnerspeechisabbreviatedwithrespectto

overt speech, even at the phonological level, in linewith introspective views. This could

suggestthatsomeofthephonologicalorarticulatoryprocessesinvolvedinovertspeechare

absentincovertmode.Analternativeinterpretation,describedinSection3.4,isthatinner

speech involvesthesameoperationsasovertspeechbut that theexecutionofarticulator

movementstakeslongerthantheirsimulation.

Anothersourceofinformationonthelowerlevels(phonologicalandarticulatory)of

covertproductionareerrorpatterns.AsexplainedbyOppenheimandDell(2008),speech

errorsdisplayalexicalbias,abiastowardscreatingwords(e.g.REEFLEECHleadingtoLEAF

REACH)ratherthannonwords(e.g.WREATHLEAGUEleadingtoLEATHREEG),inbothovert

andcovertspeechmodes.Thisbiashasbeeninterpretedbytheseauthorsasevidenceforthe

spreading-activationmodel of Dell (1986), which posits an interactive flowof activation

betweenphonologicalandlexicallevels.Thelexicalbiassuggeststhatinnerspeechactivates

notonlyconceptualbutalsolexicalaswellasphonologicalrepresentations.

Asecondbiashasbeenreported,calledthe“phonemicsimilarityeffect,”atendencyto

exchangephonemeswithcommonsubphonemicarticulatoryfeatures(e.g.REEFslipsmore

oftentoLEAF,with/r/and/l/sharingmanyfeaturessuchasvoicingandapproximant,than

REEFtoBEEF,with/r/and/b/onlysharingvoicing).ThiseffectisexplainedbyOppenheim

and Dell with reference to reciprocal activations between articulatory and phonological

levels.OppenheimandDell(2008,2010)haveonlyfoundthiseffectinovertmodeorwith


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innerspeechaccompaniedwithmouthing.Thishasledthemtoclaimthatinnerspeechis

fullyspecifiedatthelexicalandphonologicallevels,butthatitisimpoverishedatthelower

subphonemic(orarticulatory)level.AswewillseeinSection3.4,thereareseveralempirical

argumentsagainstthisclaim,however,sotheconclusiononthearticulatorypovertyofinner

speechshouldbeconsideredwithcaution.

Tosummarise,somevariantsofinnerlanguagehavebeenclaimedtobesketchyand

impoverishedatmanylevels,includingsyntactic,lexical,phonologicalandarticulatory.This

abbreviationbestows innerlanguageanabstractquality thathas ledsomeresearchersto

consider it as an amodal phenomenon. MacKay (1992) stated that inner speech is

nonarticulatoryandnonauditory.Accordingtohim,articulatorymovements“areirrelevant

toinnerspeech.Eventhelowestlevelunitsforinnerspeecharehighlyabstract.”ForMacKay,

“[t]heseeminglyauditoryqualityofourinternalspeechcannotbeautomaticallyattributed

toeventswithinanauditoryoracousticsystem,oreven,aswewillsee,toanystrictlysensory

system.” This strong stance is in line with Bergounioux’ (2001) claim that “endophasia,

phenomenologicallyspeaking,isspeechwithoutasignal”,i.e.withouta“dépensed'énergie

quantifiableetcapturable”(“quantifiableandcapturableenergyexpenditure”).Thiswould

impliethatinnerlanguageisdivorcedfrombodilyexperienceandincludes,atmost,faded

auditoryrepresentations.

Aswewillseeinthefollowingsections,innerlanguageisnotalwayscondensedand

some variants of inner language are in fact fully expanded. Neurocognitive data do not

corroboratethestrongclaimthatinnerlanguageisimpoverishedandlacksarticulatoryor

auditoryspecification(see3).Someinstancesofinnerlanguage,includingmentalsentence

repetition, instructedmentalsentencegeneration, silent reading, verbalworkingmemory

aredependentonperceptuo-motorprocessesandtheiroperationaldetails.Theseinstances

may be considered as embodied, involving physical processes that unfold over time and

leadingtothecreationofarticulatoryandauditorypercepts.Theypresumablyintegratea

varietyofrepresentations,fromsemanticconceptstoarticulatoryfeatures,vialexicalitems

andphonologicalrepresentations.

These seemingly opposite views on the condensed and expanded quality of inner

languagearenotmutuallyexclusive,however.Fernyhough(2004)hassuggestedthatinner


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speech varies with cognitive and emotional conditions between these two forms. The

expandedformcanevenbeconsideredasanoutcomeofthecondensedform,whichitself

canbeconstruedastheconceptualmessagecastinapre-verbalform,thatinvolveslemmas5,

linearly ordered, but that does not yet have the full phonological (articulatory, acoustic)

specificationthatexpandedinnerlanguagehas(seee.g.Levelt,1989).Asimilarpositionis

defendedinVicente&Martínez-Manrique(2016).Innerlanguagecanbedefinedastruncated

overtverbalisation,but the levelatwhichtheproductionprocess is interrupted(abstract

linguistic representationvs. articulatory specification)dependsonwhichvariantof inner

languageisatplay.Thelesswilfulvariantsofinnerlanguage,suchasverbalmindwandering,

mighttakeonamorecondensedformat,whereaswilfulformsmightbemoreexpanded.

Interestingly, the variant of inner language that is most studied in experimental

psychology and cognitive neuroscience is thewilful form, because it can be examined in

controlledsettings,inareplicablefashion.Butthevariantthathasbeenthefocusofmost

introspective works by literary scholars, philosophers, artists, is unbidden interior

monologue,asubsetofverbalmindwandering(whichalsoincludesinteriorconversations).

Thisvariantisthemostdifficulttoexamineexperimentally,asitisspontaneous.Thiscould

explainwhy introspective and empirical accounts sometimes differ. A few neuroimaging

studieshaveendeavouredtocomparewilfulandspontaneousinnerlanguage,buttheyare

fartoorareforanyconclusiontobedrawn(Hurlburt,Alderson-Day,Kühn&Fernyhough,

2016;Grandchampandcolleagues,inpreparation).

2.3 Innerlanguageduringreading

Anothervariantofinnerlanguageisthesilentvocalisationthataccompaniesreading.

AccordingtoEgger(1881),innerspeechisinfacteasiesttonoticewhenonereads.Egger

(1881) and Ballet (1886) suggested that during reading, one does not only mentally

articulate the words that are read, but one can experience hearing them too. Several

experimentalpsychologystudieshaveexaminedthisclaimandhaveshownthatreadingdoes

involvean innervoice. Ithasbeenshownfor instancethatsilentreading is influencedby

5 The term lemma in Levelt and colleagues’ terminology refers to the word’s syntax, see Levelt et al. (1999). It is different from the lexeme which denotes the word’s phonological features and from the lexical concept which refers to the word’s semantics.


13

pronunciationcharacteristics.Alexander&Nygaard(2008)haveshownthatsilentreading

ofatextisinfluencedbytheknowledgewehaveofitsauthor’sspeakingrate.Participants

takelongertosilentlyreadatextwhentheyaretoldthatitwaswrittenbyaslowtalkerrather

thana fast talker.Silentreading isalsomodulatedbythereader’sregionalaccent.Filik&

Barber(2011)comparedtheeyemovementsofEnglishparticipantswithdifferentregional

accentswhowere reading limericks. Limericks are short poems inwhich the final word

rhymeswiththeendwordsofthefirsttwolines.Theauthorscreatedlimericksinwhichthe

finalwordwouldrhymeornot,dependingontheregionalaccent.Whenthefinalworddid

notrhymeinthereader’saccent,adisruptionintheeyemovementrecordwasobserved,

comparedtowhenitrhymed.Thisfindingsuggestthatsilentreadingincludespropertiesof

thereader’sownpronunciationhabits.

Theoccurrenceofinnerspeechduringsilentreadinghasalsobeenconfirmedbyrecent

intracranial electroencephalography recordings. Perrone-Bertolotti and her colleagues

(2012)measuredactivityinthetemporalvoicearea(TVA)ofepilepticpatients.Thisregion

in auditory cortex is selectively activated during human voice perception (Belin, Zatorre,

Lafaille,Ahad,&Pike,2000).Thepatientswereinstructedtosilentlyreadwords.Theresults

show thatsilentreadingactivates theTVA.Moreover,TVAactivitywas found tostrongly

increasewhenparticipantswerereadingattentively.Thissuggestthattheinnervoiceheard

duringsilentreadingisnotanautomaticprocess,whichwouldbetriggeredinresponseto

anywrittenword,butthatitismodulatedbyattention.

Itshouldbenoted,however,thatsilentreadingisnotsystematicallyassociatedwith

innerspeechproduction,evenwhenattentionishigh.Levine,Calvanio&Popovics(1982)

havereportedthecaseofapatient,whoasaresultofastroke,becamemuteandwasunable

tospeakcovertly.Hecouldnottellwhethertwowordsrhymed,whichsuggestshecouldnot

evoketheauditoryrepresentationsassociatedwithwords.Yethisreadingabilitiesremained

intact.Hisvisualimagerywasstronglydeveloped(hecouldmakehighlyaccuratedrawings

frommemory).Thiscasereportthereforesuggeststhatwhenvisualimageryisproficient,

thenreadingprocessesmaysometimesbypassphonologicalmediation(covertpronouncing

andinnervoicehearing),directlylinkingtheword’swrittenformtoitssemanticcontent.


14

2.4 Innerlanguageduringwriting

Writing is generally considered to involve an inner voice. In the filmPaterson, Jim

Jarmusch letsus followPaterson, a bus driverwhowrites poetry. The film suggests that

Patersonelaborateshispoemsmentallybeforewritingthemdown.Wecanhearhisinner

voiceashecomposeseachpoem,andthenashewritesthelinesinhisnotebook.Studiesin

experimentalpsychologyhaveshownthatwritinginvolvesmanyprocesses,includingidea

generation, concept and word retrieval from semantic and lexical memory, syntactic

processing and access to graphemic forms (letters in the words). A debated question is

whetherthetransformationfromlexicaltographemicformsrecruitsinnerspeech.According

to the “phonologicalmediation hypothesis,” spoken forms ofwords are retrieved before

graphemicformscanbeaccessed.Thishypothesisissupportedbystudiesofbrain-lesioned

patients,whichshowthatdeficits inspoken languageareassociatedwith impairments in

writtenlanguageproduction(e.g.Luria,1966).

Analternativeviewis thatorthographic formscanbeaccessedfromabstract lexical

knowledge without phonological mediation. A few brain-lesioned patient studies have

reporteddissociationsbetweenwritingandspeakingimpairments.Thepatientinthestudy

byLevineetal.(1982)discussedabovewasdeprivedofinnerspeechbutcouldstillreadand

write.Rappetal.(1997)presentedthecaseofastrokepatientwhosufferedfromspeech

deficits.Hewasoftenunabletoprovidethecorrectspokennameofanobject,althoughhe

could write it. These cases therefore seem to argue against the phonological mediation

hypothesis,inthatwritingcanbeachievedwithoutspokenlanguagemediation,whenword

productionisimpaired,duetoastroke.Itcannotberuledout,however,thattheseemingly

direct linkbetweengraphemeandmeaning,was initially(beforethestroke)mediatedby

covertspeechandthatthedirectconnectionwasgraduallylearned.Therecentstudyofa

childwithcongenitaloralapraxiaismorecompelling(Cossu,2003).Despitehisinabilityto

produceanyarticulation,thischildhadnormalreadingandwritingskills.Hepresumablydid

notrelyonacovertversionofhisownarticulationtoreadandwrite.Therefore,articulatory

mediation is not always necessary during writing. Nevertheless, since this child had

preservedauditorycapacities,wecouldarguethatwritingisstillassociatedwithauditory

representations,andthatthelexicon-graphemetransformationmaywellrelyonauditory-

phonological representations. Therefore, this study does not fully contradict the


15

phonologicalmediationhypothesis,eventhoughitmakesitweaker.Therepresentationsat

playinthischildareauditoryatbest,andnotarticulatory.

2.5 Containedvsruminativeinnerlanguage

Innerspeechplaysacentralroleinhumanconsciousnessattheinterplayoflanguage

andthought(Morin,2005)andisbeneficialtomanycognitiveoperations.Itinteractswith

working memory to encode new material (Baddeley & Hitch, 1974). It is involved in

rememberingpersonalpastepisodes,includingconversations,situationsandemotions,i.e.

itplaysaroleinautobiographicalmemories(Morin,2012).Itisusedinfutureplanning,in

reasoning, in problem solving (Sokolov, 1972; Baldo et al., 2015), in cognitive control,

executive function, cognitive flexibility (Emerson&Miyake,2003), in consciousness, self-

awareness, self-regulation, self-motivation (Morin, 2009), in self-encouraging and self-

comforting(Pavlenko,2014).

Inner language can sometimes play a detrimental role, however, when it becomes

repetitive and negative. Dostoyevsky’s Crime and Punishment provides illustrative

descriptionsofhowruminativeformsofinnerlanguagemaybecomeintrusive,suchaswhen

the ex-student and future murderer Raskolnikov, sitting in a tavern, reflects upon the

mysteriesofchanceanddestiny:"Astrangeideawaspeckingathisbrainlikeachickeninthe

egg,andvery,verymuchabsorbedhim"(part1,chapter6).

Self-reflection,ponderingaboutourselves,ourfeelings,thoughtsandbehaviours,can

contribute to clarifying the meaning of past and present experiences (Nolen-Hoeksema,

Wisco,&Lyubomirsky,2008).However, itcan leadtounconstructiveconsequenceswhen

self-referentthoughtstransformintoverbalrumination,i.e.repetitiveandself-criticalinner

speech(Watkins,2008;Nalborczyketal.,2017).Ithasbeenshownthatruminationalters

cognitive performance in depressed or dysphoric patients and that it can predict and

exacerbate themaintenanceofdysphoricordepressive states (Davis&Nolen-Hoeksema,

2000).

It still remains to be understood why excessive, negative inner speech impairs

performance whereas more contained and positive inner speech improves cognitive

performance.


16

2.6 Self-controlledvshallucinatoryforms

Another dysfunctional case of inner languageare auditory verbal hallucinations. As

argued by Fernyhough (1996, 2004) and Alderson-Day and colleagues (2016), inner

languageisoftendialogic,mirroringtheexternalexperienceofcommunication.Wecanhave

imaginaryconversationsandwecanthenheartheothers’voices,theirtimbre,theirpitch.

Whenwedoso,weusuallyknowthatthesevoicesareself-generatedandwedonotmistake

these imaginary voices for external voices. This is becausewe are endowedwith a self-

monitoring mechanism. It has been suggested that when this mechanism is defective,

auditoryverbalhallucinationmayoccur.

Auditoryverbalhallucination(AVH)or“hearingvoices”canbeconsideredasspeech

perceptionsintheabsenceofanyrelevantexternalacousticinput.Itaffects50-80%ofthe

patientswho suffer from schizophrenia (Nayani & David, 1996). Patients report hearing

voices,whichareoftendistressingandengendersufferingandfunctionaldisabilityaswell

as social marginalisation (Franck, 2006). Auditory verbal hallucination is, however, a

complexphenomenonwithmultiple formsandcauses (Larøi&Woodward,2007). It also

occurs in non-psychiatric populations, and it is estimated that 4-10 % of the healthy

populationexperienceit(Lindenetal.,2011).

ManytheoreticalmodelshavebeenproposedtoexplainAVHsinschizophrenia(see,

David, 2004, for a review). An influentialmodel formulates AVHs as dysfunctions of the

monitoringof innerspeech(Feinberg,1978;Frith,1992).Themodelclaimsthatduetoa

failureoftheself-monitoringmechanism,theinnerspeechofthepatientisnotidentifiedas

self-generatedandisexperiencedascomingfromanexternalsource.

However,voicehearers(patientswithschizophreniaaswellashealthyindividuals)can

alsouse inner languagedeliberately,withoutexperiencingvoices. Inner language invoice

hearers is not always dysfunctional. Some researchers have focused on the distinction

betweenAVHandinnerspeechinnon-clinicalhallucinators.Lindenandcolleagues(2011)

havearguedthatthedistinctionisrelatedtosubjectivecontrol:AVHoccursspontaneously,

whilewilfulinnerspeechoccursundervolitionalcontrol.Thisclaimisinlinewithstudiesby

Rapinetal.(2012)andLavigneetal.(2015)whosuggestthatthesupervisoryprocessesthat

areatplayduringwillfulinnerspeechcanservetonormalisetheactivityinsensorycortex.


17

Theabsenceofsuchprocessescouldexplainwhyhyperactivityinsensorycortexisobserved

inhallucinatoryexperience.Itcanthereforebespeculatedthatwilfulinnerspeechengages

supervisory control thatmodulatessensoryactivity,whereasmore spontaneous formsof

inner language,deprivedofsupervisoryandself-monitoringprocesses,mayendupbeing

attributedtoexternalsources.

3. Variousformatsofinnerlanguage

3.1 Auditorysensations

Earlyintrospectiveworks(Egger,1881,Ballet,1886)haveclaimedthatinnerspeechis

endowed with auditory qualities. Egger (1881) wrote that “[l]a parole intérieure a

l’apparence d’un son”6 and that “[l]es caractères de la parole [rythme, hauteur, intensité,

timbre][…]seretrouventtousdanslaparoleintérieure”7.

The concept of a mind’s ear finds support in psycholinguistic data. The "Verbal

TransformationEffect"(VTE)referstotheperceptualphenomenoninwhichlistenersreport

hearing a newperceptwhen an ambiguous stimulus is repeated rapidly (Warren, 1961).

Rapidrepetitionsof theword“life”, forexample,produceasoundstreamfullycompatible

withsegmentationsinto“life”or“fly”.Smith,Wilson,andReisberg(1995)furtherexamined

theVTE,andfoundthatitalsooccursinacovertmode.Inaddition,theyobservedareduction

of theeffectduringauditory interference.These findingssuggest thatsubjectsrelyonthe

mind’seartodetecttransformations.TheneuralcorrelatesoftheVTEhavebeenexamined

by Sato and colleagues (2004). Participantswere asked to silently repeat pseudo-words.

Activesearchforverbaltransformationincreasedactivityinseveralbrainregions,including

auditorycortex.

Findingsoferrordetectionduringcoverttongue-twisterrepetitionalsoindicatethat

inner speech has auditory qualities that can be attended to. Several studies (see Dell &

Oppenheim, 2015 for a review) have investigated error slips reports. They show that

participantsareabletoattendtoandreportthe“errorsthattheyhear,”liketheydowithslips

produced inaudible speech.This canbe interpretedasa role for themind’s ear in inner

6“Innerspeechhastheappearanceofasound.”7“Thecharacteristicsofspeech[rhythm,pitch,intensity,timbre](…)areallfoundininnerspeech.”


18

speechmonitoring.

Further empirical arguments for the auditory nature of inner speech come from

neuroimaging studies. Several fMRI (functional Magnetic Resonance Imaging) studies of

covert speech production reveal auditory cortex, specifically superior temporal gyrus,

activation(Perrone-Bertolottietal.,2014forareview).Althoughthisactivationislesserthan

theoneobservedinovertspeech,itimpliesthatanauditoryexperienceaccompaniesinner

speech. In that line, an fMRI study by Lœvenbruck, Baciu, Segebarth and Abry (2005)

suggested that covertly produced speech can include prosodic characteristics, with

distinctiveauditoryfeaturesthatcorrespondtoobjectivelymeasurablecerebralcorrelates.

Tosumup,behaviouralandneuroimagingdatasuggestthatauditorysensationsare

presentduringseveralvariantsofinnerlanguage.

3.2 Somatosensorysensations

Thephenomenologicalintuitionthatinnerlanguageinvolvesavoicethatcanbeheard

inthemind’searisnotcontroversialandmeetswithempiricalfindings.Butothersensory

qualitiesmaybeattributedtoinnerlanguage,typicallyimaginaryproprioceptiveandtactile

sensations.Taine(1870)himselfwasaprecursorofthatideawhenhewrote:“Al'étatnormal

nouspensonstoutbaspardesmotsmentalemententendus,oulus,ouprononcés,etcequi

estennousc'estl'imagedetelssons,detelleslettres,oudetellessensationsmusculaireset

tactilesdugosier,delalangueetdeslèvres.(jesouligne)”8.Paulhan(1886)wrotethatlengthy

verbal thinkingcancause fatigue inarticulatorymuscles,which implies that innerspeech

involvessomatosensorysensations.AccordingtoLacknerandTuller(1979),overtspeech

errors can be detected by means of proprioceptive information on articulatory

configurations aswell as tactile information about labial or lingual contacts. It has been

suggested that proprioceptive and tactile feedback play a role in speech motor control

(Levelt,1989;Postma,2000). Itcanthereforebespeculatedthat imaginedproprioceptive

andtactilefeedbackcouldbepartofinnerspeech,justasimaginedvoiceis.Inadditiontothe

mind’sear,the“mind’stouch"shouldalsobeconsidered.Neuroimagingstudiescorroborate

8Inthenormalstate,wesilentlythinkwithwordsthatarementallyheard,readoruttered,andwhatisinsideofusistheimageofcertainsounds,ofcertainletters,orofcertainmuscularandtactilesensationsinthethroat,tongueandlips.(emphasisismine)


19

thisassumption.SeveralstudiesreviewedbyPerrone-Bertolottiandcolleagues(2014)show

somatosensorycortexactivationduringtasksthatinvolveinnerspeech.

3.3 Visualimages

Introspectionsuggestthatthe"mind’seye"alsoplaysaroleininnerlanguage.Paulhan

(1886)claimedthatinnerspeechmaysometimesincludevisualimages.Byvisualimageshe

meanttheform,shapeandcolourofthelettersthatcomposewrittenwords.Butothervisual

elementsmayalsobeincluded.

Recentworkson inner verbalisation indeaf individuals suggest that itmay contain

visualelementsrelatedtoarticulationorsign.Bellugi,Klima,andSiple(1975)comparedthe

propertiesofshorttermmemoryinnormalhearingparticipantsanddeafparticipantswhose

native languagewasAmericanSignLanguage(ASL).Listsofwordswerepresentedtothe

deaf participants in the visual modality as signs on a videotape. The same words were

presentedintheauditorymodalityonanaudiotapetothehearingcontrols.Thetaskwasto

recallthesignedorspokenwordsandtowritetheminEnglishorthography.Theerrorsmade

by hearing subjects were mainly sound-based (e.g. “vote" misrecalled as “boat”). This

suggeststhathearingsubjectshadbeenencodingandrememberingthewordsintermsof

theirphonologicalproperties.Insigningsubjects,manysubstitutionerrorscoincidedwith

words thatwere visually (not auditorily) close to the target, such as "noon” replaced by

“tree,” which corresponds to a similar arm position in ASL. Other behavioural studies of

verbalworkingmemoryindeafsignerssimilarlyreflectatransferfromtheauditorytothe

visualmodality.WilsonandEmmorey(1998)observedasignlengtheffectindeafusersof

ASL, analogous to the auditory word length effect in spoken language. Poorer memory

performancewasfoundforlongsignscomparedtoshortsigns,independentlyoftheauditory

wordlength.Manualsuppression(repetitivemovementsofthehands)producedadropin

performance, just like articulatory suppression (repetitive syllable production) disrupts

verbalworkingmemory in hearing subjects. These studies suggest that sign language is

stored in memory in terms of its gestural properties. Therefore, inner language in deaf

signerspresumablyinvolvesvisualrepresentations.

Gesturesarenotonlyusedinthedeafpopulation.Theyaccompanyspeechinnormal


20

hearersandplayafundamentalroleinthoughtandspeech(DeRuiter,2007).Gestureand

speech are coordinated to form coherent multimodal messages. Moreover, speech is

audiovisual: lip reading enhances speech comprehension when the acoustic signal is

degraded by noise (Sumby& Pollack, 1954). Lip reading occurs evenwith nondegraded

acousticsignals,suchasintheMcGurkeffect(McGurk&MacDonald,1976).Thisillusionary

effectoccurswhenanauditorysyllable(suchas/ba/)issynchronouslypresentedwiththe

videoofafaceutteringadiscrepantvisualsyllable(suchas/ga/).Mostparticipantsreport

hearingasyllablecorrespondingtothefusionoftheauditoryandvisualchannels(/da/or

/ða/).Basedonthisaudiovisualintegrationeffectandotherstudies,ithasbeenarguedthat

auditory and visual speech information include common stages of processing (Nahorna,

Berthommier,&Schwartz,2015).Itcanthereforebeassumedthatvisualinformation(facial

andmanual)maybeinvolvedininnerspeech,eveninhearingsubjects.Apreliminarywork

byArnaud,Schwartz,Lœvenbruck,andSavariaux(2008)providestentativesuggestionsthat

speakers can have visual representations of their own lipmovements. More research is

needed to confirm that inner language involves visual (labial, facial, manual, written)

representations,eveninthehearingpopulation.

To sumup, innerverbalisingappears to involve the receptionof imaginary sensory

signals,includingauditory,somatosensoryandvisualelements,handledbythemind’sear,

touchandeye.Theformatofinnerlanguagecanthereforebedescribedasmultisensory.

3.4 Motorrepresentation

Inparallelwiththesensoryaccounts,ithasbeensuggestedthatinnerspeechrequires

motorprocesses.Theearliestclaimsconcerningthemotorqualityofinnerspeechprobably

date back to Erdmann (1851) and Geiger (1868), who, as cited by Stricker (1885),

introspectively observed that inner speech is accompanied by feelings of tension in the

speechmusculature.Bainhimselfwrotein1855:“Whenwerecalltheimpressionofaword

orasentence,ifwedonotspeakitout,wefeelthetwitteroftheorgansjustabouttocometo

thatpoint.Thearticulatingparts,—thelarynx,thetongue,thelips,—areallsensiblyexcited;

asuppressedarticulationisinfactthematerialofourrecollection.”

Stricker(1885,chapterII)designedacleverintrospectiveexercisetoexperiencethis


21

orofacial activity.Hehinted that,whenone’smouth ispositioned into theroundedshape

requiredtopronouncethesoundofan"o,"ifonetriestoimagineutteringthatofan"m,"a

slightcontractionisfeltinthelipmuscles,asifonewaspressinglipstopronouncethelabial

sound. Stricker (1885) claimed from several introspective exercises that inner speech is

accompanied by sensations in the oral musculature similar to those driving the actual

pronunciation of articulated sounds. He introduced the notion of motor representations

associated with inner speech and speculated that word representations consist in the

awarenessofimpulsionsdrivenfromcerebralspeechcentrestospeechmuscles.

In the same vein, Watson (1919) described inner speech (which he referred to as

“implicit language”) as a weakened form of overt speech. He explicitly considered inner

speech (whichheequatedwith thought)asa “highly integratedbodilyactivity" (Watson,

1919, 325). According to him, inner speech involves “abbreviated, short-circuited and

economisedprocesses”(323),butitisnotclearwhetherheactuallypostulatedthatinner

speech systematically involvesovertmovement,or rathermotorprograms, i.e. simulated

actions.Theextremeviewthatinnerspeechrequiresactualmovementhasbeenrefutedby

Smithandcolleagues (1947).Curarewasadministered toahealthyvolunteer, inducinga

temporaryskeletalmuscularparalysis.Althoughthevolunteerbecameincapableofmouth

movementandofovertspeech,hewasstillawareof thequestionsaskedandwasable to

correctly report them after recovery. This experiment suggests that some form of inner

speech must have been present during muscular paralysis. Therefore, verbal thinking,

memory storage and presumably inner speech can take place even when articulation is

completelyprevented.Thus,theextremeversionofWatson’sviewcannotbeupheld.Amore

nuancedview,referredtoastheMotorSimulationhypothesis,isthatinnerspeechisamental

simulationofarticulation,withoutactualmovement.Assuch, itmayfeaturephysiological

correlates with recordable physical signals. In this physicalist or embodied view, inner

speechproductionisdescribedassimilartoovertspeechproduction,exceptthatthemotor

executionprocessisblockedandnosoundisproduced(Grèzes&Decety,2001;Postma&

Noordanus, 1996). Under the Motor Simulation hypothesis, a continuum exists between

overtandcovertspeech, in linewiththecontinuumbetween imaginedandactualactions

proposedbyDecetyandJeannerod(1996).Thishypothesishasledsomeauthorstoclaim

that inner speechbyessence shouldshare featureswith speechmotoractions (Feinberg,


22

1978; Jones & Fernyhough, 2007). The Motor Simulation hypothesis is supported by

empirical findings, including physiological measurements, neural evidence and

psycholinguisticdata.

Physiologicalandneuralevidence

Objective measurements of respiratory rate, speaking rate, muscular activity and

cerebralpatternsallsuggestthatinnerspeechinvolvesmotorprocesses.

As concerns respiratory rate, Conrad and Schönle (1979) have shown that the

respiratory cycle varies along a continuum, from rest to overt speech, via inner speech.

During rest, the breathing cycle is symmetrical, with inspiration and expiration phases

displayingsimilardurations.Inovertspeech,thecycleisstronglyasymmetricalwithashort

inspiration and a long expiration during which speech is emitted. Inner speech is also

characterisedbyaprolongedexpiratoryphase.Theyconcludedthatthismodificationofthe

respiratorycyclefromresttoinnerspeechsuggeststhatmotorprocessesareatplayduring

innerspeech(seeChapell,1994,forsimilarfindings).

Speakingratefindingsaremoredebated.AsmentionedinSection2.2,silentrecitation

hasbeen found tobe faster thanovert recitationbymany researchers. (Anderson,1982;

Korba,1990;MacKay,1981;MarshallandCartwright,1978,1980).Somestudiesof inner

speech ratehave foundsimilar results for recitation in covert andovertmodes,however

(Landauer,1962;Weber&Bach,1969;Weber&Castleman,1970).Thiswouldsuggestthat

innerandaloudspeechmayinvolvecommoncentralprocesses,atleastduringrecitationof

storedwords,sentencesordiscourses(alphabet,numbers,pledges).Netsellandcolleagues

have examinedmore spontaneous sentence production in both covert and overt modes

(Netsell,Kleinsasser,&Daniel,2016).Participantsgeneratedfullsentencesbysayingthefirst

thing that came to their mind. Spontaneous sentence generation involves conceptual

preparation and formulation (including morphological, phonological, and phonetic

encoding)beforearticulationcantakeplace(e.g.Levelt,1989).Ininnerspeech,articulation

isinhibited,butconceptualpreparationandformulationinvolveprocessesthatunfoldover

time.Usingspontaneoussentencegeneration,Netsellandcolleaguesfoundthattherateof

innerspeech(5.8syllablespersecond)wassignificantlyfaster(5.2syllablespersecond)than

thatofovertspeech.Butthefactthatthedifferenceisrelativelysmallimpliesthatspeaking


23

aloudmayonlydifferfrominnerspeechbytheadditionaltimeneededtoovertlyarticulate,

oncethespeechmotorplanisfullydesigned.AsadvocatedbyNetsellandcolleagues,more

research isneeded toprovideprecisemeasuresof speaking rateduring covert andovert

speech,andtoallowforinformativeconclusionsonthetimecourseofthetwoprocesses.

Concerningmuscularactivity,Stricker’sintrospectiveobservationthatinnerspeechis

accompaniedwithmuscularcontractionfindssupportfromafewelectromyographic(EMG)

studies during controlled tasks involving inner speech. Using electrodes inserted in the

tonguetipor lipsofparticipants, Jacobson(1931)wasable todetectEMGactivityduring

severalinnerspeechtasks.Sokolov(1972)carriedoutsurfaceEMGmeasurementsoflipand

tongue muscles. He recorded more intense muscle activation when participants had to

perform complex tasks, such as problem solving, which, according to him, necessitated

substantialinnerspeechproduction.SurfaceEMGrecordingscarriedoutbyMcGuiganand

Dollins(1989)indicatedthatthelipsweresignificantlyactivewhensilentlyreadingtheletter

“P” (bilabial articulation), but notwhen reading the letter “T” (alveolar articulation) or a

nonlinguisticcontrolstimulus.Thereversepatternwasobservedforthetongue.Theauthors

concludedthat thespeechmusculatureusedforovertproductionofspecificphonemes is

selectively active in covert production of these phonemes. Livesay, Liebke, Samaras, and

Stanley (1996)measuredEMG activity in the lipsof participants during rest and several

mental tasks. They found a significant increase in EMG activity during silent recitation

comparedtorest,butnoincreaseduringnon-verbalvisualisation.Astudyonspeechmuscle

activity during dreamed speech using inserted electrodes suggests that the silent (non-

phonated)speechthatoccursindreamisassociatedwithEMGactivityinorbicularisorisand

mentalismuscles(Shimizu&Inoue,1986).SurfaceEMGactivityhasalsobeendetectedin

orbicularis oris during auditory verbal hallucination (which has been described as inner

speech attributed to an external source, see Section 2.6) in patients with schizophrenia

(Rapin,Dohen,Polosan,Perrier,&Lœvenbruck,2013).AstudybyNalborczykandcolleagues

(2017)oninducedmentalrumination,whichcanbeviewedasaformofexcessivenegative

inner speech (see Section 2.5), has also found an increase in labial EMG activity during

rumination compared with a relaxed state. In addition, after rumination induction, an

orofacial relaxation session reduced labialEMGactivityandhadabeneficial (decreasing)

effectonmentalruminations.Althoughmoreworkneedstobecarriedouttodisentanglethe


24

factors thatmodulate lipactivityduringrumination(negativeaffectsmay influence labial

activity),thisstudysuggeststhatthemotorsystemisinvolvedduringmentalrumination.

A further argument for the motor nature of inner language comes from cerebral

patterns.AsreviewedinPerrone-Bertolottiandcolleagues(2014,seealsoPerrone-Bertolotti

etal.,2016andLœvenbrucketal.,2018),covertandovertspeechproductionbothrecruit

essentiallanguageareasinthelefthemisphere.Theseincludemotorandpremotorcortexin

thefrontallobeincludingBroca'sarea(leftinferiorfrontalgyrus),sensoryareas(bilateral

auditoryareasandWernicke'sareainsuperiortemporalgyrus),andanassociativeregion,

theleftinferiorparietallobule,includingtheleftsupramarginalgyrus.However,thereare

differences.ConsistentwiththeMotorSimulationhypothesisandthenotionofacontinuum

betweencovertandovertspeech,overtspeechisassociatedwithmoreactivityinmotorand

premotorcorticesthaninnerspeech(e.g.Palmeretal.,2001).Moreover,overtspeechmore

stronglyactivates sensoryareas, and typicallyauditoryareas (Shuster&Lemieux,2005).

Thissuggeststhatovertspeechincludessensoryactivationassociatedwiththeprocessingof

one’sownutteredspeech.Reciprocally, innerspeech involves cerebral areas that arenot

activatedduringovertspeech(Basho,Palmer,Rubio,Wulfeck,&Müller,2007).Someofthese

activations(cingulategyrus,leftmiddlefrontalgyrus)canbeattributedtotheinhibitionof

overt response. Overall, these findings support the claim that inner speech is a motor

simulationofspeech,andthat,assuch, itsharesmostof theprocessesdedicatedtoovert

speechproduction,includingmotorplanningbutexcludingmotorexecution.Theprocesses

involved in overt speech therefore include those required for inner speech (except for

inhibition).Somebrainlesionstudiessupportthisview:whenovertspeechisimpaired,inner

speech is either intact (Baddeley &Wilson, 1985; Vallar & Cappa, 1987) or altered (e.g.

Levine,Calvanio&Popovics,1982;Martin&Caramazza,1982),dependingontheprocesses

impacted.

Afewstudieshavereportedadissociationthatgoesagainstthisview,however(e.g.

Geva,Bennett,Warburton,andPatterson,2011a;Langland-Hassan,Faries,Richardson,and

Dietz,2015).Theyfoundthatthepatients’performanceincovertspeechtaskswaspoorer

thaninovertspeechtasks.AsexplainedinLœvenbrucketal.(2018),thisdissociationcanbe

explained by limitations in the tasks used. Covert speech was only tested using rhyme


25

judgment,whichdoesnotreflectgenuinespeechproductionandwhichmaywellbeeasier

overtly(eveninhealthypatients).

Psycholinguisticdata

Psycholinguistic data further indicate that motor processes and articulatory

representationsarepartofinnerspeechproduction.

As explained in Section 2.2, some researchers have suggested that inner speech is

impoverishedatthearticulatorylevel.Thisclaimisstilldebatedhowever,sinceaphonemic

similarity effect has in fact been found by Corley, Brocklehurst andMoat (2011) during

tongue-twister production, even in a covert mode. Furthermore, a study by Smith,

Hillenbrand, Wasowicz, & Preston (1986) shows that articulatory content influences

speakingrateinbothovertandcovertmodes.Certainrepeatedstimulirequiredmoretime

toproducebecausetheyincludedarticulatorilycomplexsequences,typicallyalternationsof

similarphonemesinthesamesyllableposition(e.g.“wristwatch”longerthan“wristband”,

becauseinvolvingtwogestureswiththesamearticulator/r/-/w/insteadoftwogestures

withtwodifferentarticulators/r/-/b/,whichareeasiertoanticipateandcoordinate).The

findingthatarticulatorilycomplexstimulialsotooklongertoproducecovertlysuggeststhat

subphonemiccoordinationandanticipationprinciplesareatplayduringinnerspeech.

Moreover, Scott, Yeung, Gick and Werker (2013) have examined the influence of

concurrentinnerspeechproductiononspeechperception.Scottandcolleaguesshowedthat

the content of inner speech orients the perception of ambiguous syllables. In a first

experiment,theyfoundthatambiguous/ɑ’bɑ/-/ɑ’vɑ/sequenceswereperceiveddifferently

depending on the concurrent inner production (more perception of /ɑ’bɑ/ when inner

producing/ɑ’bɑ/andtheoppositepullwhenproducing/ɑ’vɑ/).Inasecondexperimenton

the same ambiguous syllables, they tested subphonemic effects. They found that inner

production of /ɑ’fɑ/ biased perception towards /ɑ’vɑ/, and imagining /ɑ’pɑ/ biased

perceptiontowards/ɑ’bɑ/.Thissuggeststhatsubphonemiccontentisstillpresentininner

speech. Overall, these findings suggest that, contrary to Oppenheim and Dell’s (2010)

findingsandinlinewithCorleyandcolleagues’s(2011),innerspeechcanbespecifiedatthe

articulatorylevel.ArecentfMRIstudysuggeststhatinnerspeechduringreadingcodesdetail

asfineasvoicing(Kell,Darquea,Behrens,Cordani,Keller&Fuchs,2017).Inthisstudy,the


26

numberofvoicelessandvoicedconsonantsinthesilentlyreadsentenceswassystematically

varied.Increasedvoicingmodulatedvoice-selectiveregionsinauditorycortex.Overall,these

datasuggestthatinnerspeechmaybespecifiedatthearticulatorylevel.

TowrapuptheargumentspresentedinSection3,theformatofsomevariantsofinner

language(atleasttheexpandeddeliberateform,seeSection2)isbothmotorandsensory.It

can be construed that imaginary acts give rise to multisensory percepts. But these acts

themselves could stem fromprior sensorygoals, asPaulhanhinted in1886,which could

themselvesbederivedfrommoreabstractrepresentations(condensedinnerspeech).

4. Neuralmechanismsofinnerspeech:simulation,predictionandthefeelingofagency

Thesemanyfacetsof inner language,oneof themostsignificantcomponentsofour

innerspace,canbeaccountedforwhenapredictivecontrolperspectiveistaken.Inpredictive

controlaccounts,anyactionisaccompaniedwithapredictionofitssensoryconsequences.

Motorandsensoryaspectsarethustightlylinked.The“Action”view(Jones&Fernyhough,

2007)andthe“Activity”view(Martinez-Manrique&Vicente,2015)holdthatinnerlanguage

is itself anaction. In linewiththeseviews, and inthe frameworkofFrithandcolleagues’

predictiveaccountofactioncontrol(Frith,1992;Frith,Blakemore&Wolpert,2000),wehave

designedaneurocognitivepredictivemodelofthelaststageofinnerspeechproduction(i.e.

articulatoryprogramming:fromphoneticgoalstothemotorprogram),whichaccountsfor

thesensoryaswellasmotorqualitiesofinnerspeech(Lœvenbrucketal.,2018).

Itcanbespeculatedthatpredictivecontrolalsooperatesattheearlierstagesofinner

language production. Hierarchical predictive control has been applied to overt speech

controlbyPickeringandGarrod(2013,2014).PickeringandGarrod’smodelincludespairs

ofcontrollersandpredictorsthatuseefferencecopymechanismstoimplementmonitoring

at each level of speech production (semantics, syntax, phonology). Vicente & Martínez-

Manrique (2016) suggest that this type of modelling can be applied to inner language

production.InLœvenbruck(inpreparation),IelaborateonthesesuggestionsandIpropose

a hierarchical predictive control model of language production, from communicative

intention to articulatory program, that includes a detailed account of inner speech

production(seealsoGrandchampetal.,inpreparation).Thismodel,illustratedinFigure1,


27

includessemantic,syntacticandarticulatorylevels.

At the lowesthierarchical level, i.e.articulatoryprogramming,wilful innerspeech is

consideredasderivingfromdesiredphoneticgoals,inaheteromodalformatthatintegrates

multiplesensoryrepresentations.AsexplainedinLœvenbrucketal.(2018),thesedesired

goalsaretransformedintomotorcommandsbyacontroller(or“internalinversemodel”).

The motor commands are inhibited and their efference copy is assigned as input to a

predictor(or“simulator”, “forward internalmodelof thevocalapparatus”) thatgenerates

simulated acts, which themselves provide predicted multisensory percepts (voices,

somatosensorysensations,facialvisemes).Thesepredictedperceptsunfoldovertime.The

innervoice inwilful,expanded innerspeech,preciselyconsistsof thesepredictedsignals.

Thissimulatedexperienceoccursearlierthantheactualexperiencewould,whichexplains

whyinnerspeechmaytakeshortertobedeliveredthanovertspeech(seeSection2.2).An

integrator transforms these multisensory percepts into a heteromodal representation. A

compararisonbetweenpredictedheteromodalstatesanddesiredphoneticgoalsprovidesan

error signal which can be used to monitor inner speech. It has been claimed that the

comparison between desired goals and predicted states also contributes to the sense of

agency,offeelingincontrolofone’sinnerspeech(Rapinetal.,2013,2016,revisedfromFrith,

1992).Ifdesiredandpredictedstatesmatch,thentheperceivedstimuliareself-generated.A

defectinthismechanismcanexplainthephenomenonofauditoryverbalhallucination.Ifthe

prediction is faulty, there is no match between predicted and desired states, agency is

defectiveandtheinnervoice(predictedexperience)canfeelalien.

Atthehigherlevels,thepredictorsarenotsimulatorsofthevocalapparatus(contrary

toPickering&Garrod’saccount),becausethereisnophysicalapparatustosimulate.Instead,

Ispeculatethatpredictorsarecomputationalproceduresthattransformonetypeofmental

representationintoanother.Comparisonsbetweendesiredandpredictedstatesplayarole

inmonitoringateachlevelinthehierarchy.Theypresumablyalsoplayaroleinagency.

Attheformulatinglevel(syntax-phonologyencoding),thedesiredpre-verbalmessage

istransformedintoaphoneticplanbyacontroller.Apredictivetransformationconvertsthis

planintoapredictedpre-verbalmessage,whichcanbecomparedwiththedesiredpre-verbal

message.Ifthepredictiondoesnotmatchthegoal,thenthecontrollerreceivesanerrorsignal


28

andisadjusted,andthelower(articulatoryplanning)levelisaffected(i.e.beforearticulatory

programmingeventakesplace).

Similarly, at the conceptualising level, a predicted communicative intention is

generated by the highest controller-predictor pair in the hierarchy. This prediction is

comparedwiththeoriginaldesiredcommunicativeintention.Iftheydonotmatch,thenthe

controllercanbeadjustedandlowerlevelsinthehierarchyareaffected.


29

Figure1.Ahierarchicalpredictivemodelofspeechproduction,inspiredfromsuggestionsby

Harunoetal.(2003),Pacherie(2008),Pickering&Garrod(2013)andDuffauetal.(2014).

direct control

efferent predictive control

feedback control

temporal pole

controller

DLPF, orbito-frontal cortex

communicative intentiondesired predicted actual

associative cortex (IPL)

heteromodal phonetic plandesired predicted actual

SMA, vPM, M1

motor commands

sensorimotorapparatus

multisensory cortex (auditory, somatosensory, visual)

actual multisensory experience

post. TL, IFG

controller

cerebellum, thal.

predictor

post. middle temporal gyrus

pre-verbal messagedesired predicted actual

CONCEPTUALISATION

FORMULATION(prosody-syntax-phonology)

ARTICULATION

post. TL, IFG

predicted predictor actual

multisensory cortexpredicted sensory

experience

wilfulinner speech

spontaneousinner speech

AgencyAttenuation

∆t

MonitoringAgency

Monitoring∆t

MonitoringAgency

MonitoringAgency

MonitoringAgency

∆t

MonitoringAgency

∆t

IFG, insula

programmer

cerebellum, thal.

controller

TPJ

predicted integrator actual

temporal pole

predicted predictor actual


30

AsshowninFigure1,followingsuggestionsandmodelsbyIndefrey(2011),Guenther

andVladusich(2012),Hickok(2012)TianandPoeppel(2013),Duffauandcolleagues(2014),

I speculate that the articulation level engages the auditory cortex (posterior superior

temporal gyrus, superior temporal sulcus), aswell as the somatosensory cortex (anterior

supramarginal gyrus and primary sensory cortex, in parietal lobe), together with the

temporo-parietal junction, cerebellum, left inferior frontal gyrus, insula, supplementary

motorarea,ventralpremotorcortexandlowerprimarymotorcortex(seeLœvenbrucketal.,

2018). Similarly, I propose that the formulating level involves the arcuate fasciculus, left

inferior frontalgyrus,posteriorpartof thetemporal lobeandof thesuperior longitudinal

fasciculus and posterior middle temporal gyrus. Finally, the conceptualising level

presumablyengagesthedorsolateralprefrontalcortex,orbito-frontalcortexandtemporal

pole.

Thishierarchicalmodelaccounts for thedifferencebetweenwilfulandspontaneous

inner speech.Wilful inner speechconsistsofpredictedmultisensorypercepts thatunfold

overtimeandthatresultfromcomputationsofpairsofcontrollerandpredictormodels,all

through the hierarchy, down to the lowest articulatory level. Spontaneous inner speech

(unbidden thoughts) is subjectively more evanescent and tenuous. I speculate that it

correspondstomeredesiredheteromodalstates,phoneticgoals,derivingfromhigherlevels

(semanticandsyntactic).Inthatcase,innerspeechproductioniscutshortbeforearticulatory

programming. Therefore, the phonetic goals are not transformed into simulated acts and

their predicted sensory consequences, resulting in a more fleeting experience. I further

assume that during wilful inner speech, top-down executive signals may be issued in

prefrontalcortextolaunchthelastpredictionmechanismaswellaswellastoinhibitmotor

execution.Thesesignalsarehypothesizedtobeabsentinspontaneousinnerspeech,hence

theabsenceofsimulatedactsandtheirpredictions.Theabsenceofapredictionitselfmakes

fortheweakerfeelingofagencywhichcharacterizesspontaneousinnerspeech(Gallagher,

2004).Asthismodelshows,thepredictivecontrolmechanism,whenfunctional,therefore

contributestocreatingtherichsensoryqualitiesof innerspeech,aswellas the feelingof

agency, of awareness of our wilful verbal thoughts. Flaws in the prediction or in the

comparisonprocessescouldexplainthedisruption inagencyobserved inauditoryverbal

hallucination. Further researchneeds to be carried out to better describe how top-down


31

signalsandcomparatormechanismsatdifferenthierarchicallevelsallcontributetoagency.

Conclusion

Inner language takes a significant part of our inner space, with many beneficial

outcomes,whichspanfromimprovingcognitiveperformancetocontributingtoautonoetic

consciousness. It can become excessive (in verbal rumination), and even run amok (in

auditoryverbalhallucination) thusbecomingdetrimental, andengendering sufferingand

functionaldisability.The integrated approachpresented here, inwhich inner language is

conceivedofasamultimodalactwithmultisensorypercepts,offersinterestinginsightsinto

thevariousformsofbeneficialanddetrimentalinnerlanguage.Butmanyissuesstillneedto

beresolved.Adeeperunderstandingofhowtheoscillationsbetweenwilfulandspontaneous

formsof inner languagemayenhance cognitiveperformance couldhelppeoplewithhigh

concentrationneeds.Itcouldalsobebeneficialtotheunderstandingofverbalruminationas

wellasauditoryverbalhallucinations.Inaddition,althoughmanyofthesubcomponentsof

innerlanguageproductioncanbeassociatedwithspecificneuralnetworks(seeSection4),

several operations remain ill-described. It is still unclear which networks process the

outcomesofthecomparisonssupposedtooccurafterpredictionsaremadeateachleveland

howanefficientcognitivecontrolmechanismmightintegratetheseoutcomes.Moreresearch

isneededalsoontheprocessesbywhichwecangenerateinnerspeechwithsomeoneelse’s

voice.Dowehaveapredictorforeachofthevoicesweknow?

In summary, although an integrative neurocognitivemodel, gathering findings from

introspection and empiricalworks, can shed lighton the formatof inner language,many

issuesare far fromresolved. Ibelievethatendeavouringto furthercombine introspective

effortswith objective behavioural and neurophysiologicalmeasurements, should help to

betterportrayourinnerlinguisticspace.


32

Acknowledgements

ThisresearchwasfundedbytheANRprojectINNERSPEECH[grantnumberANR-13-

BSH2-0003-01], http://lpnc.univ-grenoble-alpes.fr/InnerSpeech. I sincerely thank my

colleagues Lucile Rapin, Marion Dohen, Pascal Perrier, Monica Baciu, Marcela Perrone-

Bertolotti,RomainGrandchamp,Jean-PhilippeLachaux,LadislasNalborczyk,MirceaPolosan,

Stéphanie Smadja, Ernst Koster, Elsa Spinelli who contributed to many of the ideas and

hypothesesdevelopedinthispaper.IalsothankAnneVilain,MaëvaGarnier,LucianoFadiga,

CédricPichat,YanicaKlein,LaurentLamalle,Jean-LucSchwartz,IrèneTroprès,Christopher

Moulin,AgustinVicente,PeterLangland-Hassan,CharlesFernyhoughandBenAlderson-Day

forhelpfulsuggestionsanddiscussions.

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