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2.
Sourcesofspeechsignalvariability
2.1.
Linguisticandnon-linguisticlevels
Thecomplexityofdifficultiesrelatedtospeechproduction,perceptionand
processingresults,regardlessofwhethertherecognitionsystemisthehuman
brainorthecomputer,fromspecificsignalproperties.Thesoundunitscreatedin
theprocessofarticulationarecarriersofvariouslinguistic,paralinguisticand
non-linguisticinformation.Linguisticinformationisdeterminedbygrammar
rulesaccordingtowhichacorrectlyformulatedwrittenutterancehasan
appropriatesyntactic,semanticandpragmaticstructure(ibid).Althoughthereare
numerouscontroversiesonhowtointerpret:1)linguistic,2)paralinguisticand
3)non-linguisticinformation,themostreadabledefinitionsareprovidedby
Roach(Roach,Barratt,Miller,&Leavitt,1998),whichdefinesparalinguisticas
addedtolinguisticcontentforpurposefulmodificationofthemeaningof
utterances(e.g.throughchangesinvoicequality,phonationmethod,emotional
colouring)andnon-linguistic,suchasthosethatcannotbeusedintentionally,
i.e.age,gender,healthcondition,unconditionalreflexes,noisesproducedby
speakersoftenassociatedwiththephysicalenvironment,e.g.coughing,throat
clearing,anduncontrolledreactionstoemotionalstateslikestress.
Comparedtothewrittentext,thespokentextisusuallyunprepared,thetime
toformulateandverbalizethoughtsisrelativelyshort,whichforcesthespeaker
topaymoreattentiontothecommunicativenessofthemessagethantoitsform.
Strongemotionalarousalmayresultinaninaccurateandnotverysmooth
presentationofwhatwewanttosay.Speechcanoftenbeutteredcontrarytothe
rulesofgrammar,insuchawayastobestexpressthespeaker'sintentions,style,
attitudetothecontentoftheutterance,attitudetothesituationorinterlocutor.
Paralinguisticinformationisnotcontainedinwrittentext,butistransmitted
duringtheperformanceofspeech,addedbythespeakerinordertomodifythe
meaningofthetransmittedcontent.Non-linguisticfactorsaremainlyassociated
withphysicalfactorsdescribingthespeaker.Relationsbetweenthesetypesof
informationarenotdirectlycodedinthespeechsignal.
Paralinguisticfeaturestransmittedmainlybyprosodyareassociatedwith
partiallycontrolledpsycholinguisticandneuropsychologicalconditions.Certain
emotionalstates,whichcanbecontrolledtoacertainextentbythespeaker,are
oftencorrelatedwithphysiologicalstates,whichhavequitemechanical,andthus
predictableeffectsintheacousticimageofspeech,andespeciallyinitsprosodic
structures.Forexample,whenaspeakerisinastateofanger,fearorjoy,the
sympatheticnervoussystemisstimulated,speechbecomesloud,fastandwith
strongenergyinhighfrequencyranges.Whensomeoneisboredandsad,the
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