Sound symbolism in synesthesia: evidence from a lexical-gustatory synesthete

Synesthesia is a condition in which perceptual or cognitive stimuli (e.g., a written letter) trigger atypical additional percepts (e.g., the color yellow). Although these cross-modal pairings appear idiosyncratic in that they superficially differ from synesthete to synesthete, underlying patterns do exist and these can, in some circumstances, reflect the cross-modal intuitions of nonsynesthetes (e.g., higher pitch sounds tend to be "seen" in lighter colors by synesthetes and are also paired to lighter colors by nonsynesthetes in cross-modal matching tasks). We recently showed that grapheme-color synesthetes are more sensitive to sound symbolism (i.e., cross-modal sound-meaning correspondences) in natural language compared to nonsynesthetes. Accordingly, we hypothesize that sound symbolism may be a guiding force in synesthesia to dictate what types of synesthetic experiences are triggered by words. We tested this hypothesis by examining the cross-modal mappings of lexical-gustatory synesthete, JIW, for whom words trigger flavor experiences. We show that certain phonological features (e.g., front vowels) systematically trigger particular categories of taste (e.g., bitter) in his synesthesia. Some of these associations agree with sound symbolic patterns in natural language. This supports the view that synesthesia may be an exaggeration of cross-modal associations found in the general population and that sound symbolic properties of language may arise from similar mechanisms as those found in synesthesia

Neural mechanisms of foreign language phoneme acquisition in early adulthood : MEG study

Tämän tutkimuksen tavoitteena on selvittää omaan äidinkieleen kuulumattomien foneemikontrastien oppimisen mekanismeja nuorilla aikuisilla neurofysiologisten ja behavioraalisten menetelmien avulla. Perinteisesti kielen foneettisen avaruuden omaksumisen on ajateltu tapahtuvan ensisijaisesti varhaislapsuuden kielellisten herkkyyskausien aikana, jonka jälkeen uusien foneemien oppiminen on haastavaa. Myöhemmät tutkimukset ovat kuitenkin osoittaneet, että vieraiden foneemien omaksuminen on mahdollista myös aikuisiällä. Uusien foneemikategorioiden muodostuminen vaatii aivoissa solutason plastisia muutoksia. Aivojen kykyä erotella läheisesti toisiaan muistuttavia foneemikategorioita kielenprosessoinnin varhaisella tasolla on tutkittu neurofysiologisin menetelmin esimerkiksi tapahtumasidonnaisen poikkeavuusnegatiivisuusvasteen (eng. mismatch negativity, MMN) avulla. MMN-vaste, tai sen magneettinen vastine MMNm, syntyy seurauksena muutoksiin sensorisessa havaintoympäristössä. Tutkimuksissa lyhyenkin auditiivisen harjoittelujakson on havaittu vahvistavan aivojen kykyä erotella läheisesti toisiaan muistuttavia vieraita foneemeja ja voimistavan MMN- ja MMNm-vasteita. Tässä tutkimuksessa vieraan kielen foneettisen oppimisen neuraalista perustaa ja oppimisen aiheuttamia plastisia muutoksia aivoissa tutkittiin magnetoenkefalografialla (MEG) neuromagneettisten tapahtumasidonnaisten vasteiden (erityisesti MMNm) avulla. Tutkimuksessa mitattiin 20 suomalaista koehenkilöä, joiden tehtävänä oli oppia erottelemaan akustisesti toisiaan läheisesti muistuttavia venäjän kielen frikatiiveja Ш /ʂ/ ja Щ /ɕ(ː)/. Erottelukykyä mitattiin ensin behavioraalisella tehtävällä, jossa koehenkilöille toistettiin nauhoitettuja venäjänkielisiä epäsanaminimipareja, jossa sanan ensimmäistä foneemia varioitiin. Koehenkilöiden tehtävänä oli vastata, kuulivatko he sanoissa eroa. Samoja kuuloärsykkeitä toistettiin koehenkilöille sen jälkeen passiivisessa MEG-tehtävässä, jossa testattiin aivojen kykyä havaita ero ärsykkeissä ilman, että niihin kiinnitetään huomiota (koehenkilöt katselivat samalla äänetöntä elokuvaa). Mittauksen jälkeen koehenkilöt harjoittelivat foneemien erottelua kotona noin viikon ajan tietokoneavusteisen oppimispelin avulla, jonka jälkeen heidät mitattiin uudelleen. MEG-signaalien lähdemallinnusta varten koehenkilöiden aivoista otettiin myös rakenteelliset magneettikuvat. Tutkittavien foneemien behavioraalinen erottelukyky oli selvästi tuttuja kontrollifoneemeita heikompaa. Erottelukyky vaikutti paranevan harjoittelun seurauksena hieman, mutta ero ei ollut tilastollisesti merkitsevä. Hypoteesien vastaisesti tilastollisesti merkitseviä MMNm-vasteita ei löydetty ennen eikä jälkeen harjoittelun, eikä muissakaan auditorisissa MEG-vasteissa tai niiden neuraalisten lähdevirtojen voimakkuuksissa tai jakaumassa ollut tilastollisesti merkitsevää eroa mittauskertojen välillä. Yksilölliset erot oppimisessa olivat kuitenkin suuria. Koehenkilöillä, joilla behavioraalinen erottelukyky parani harjoittelun myötä, oli silmämääräisesti havaittavissa hypoteesien mukaista vahvistumista auditorisissa vasteissa. Vaikka efekti oli erittäin pieni eikä tilastollisesti merkitsevä, vastaavaa ei havaittu epäoppijoilla eikä kontrollitilanteessa. Tässä tutkimuksessa ei kyetty replikoimaan aiempien tutkimusten tuloksia foneemien omaksumisesta aikuisiällä. Vaikka on todennäköistä, että tietyt metodologiset heikkoudet (mm. vähäinen ärsykkeiden määrä MEG-tehtävässä, haastavat ärsykkeet) vaikuttivat tulosten merkitsevyyteen, voidaan tämän tutkimuksen valossa aiempien tutkimustulosten yleistettävyyttä kyseenalaistaa.The aim of this study is to examine the learning mechanisms and acquisition of non-native phoneme contrasts in young adults using neurophysiological and behavioral methods. According to the traditional view, acquiring novel phonemes after the sensitive periods in the early childhood is very difficult. However, later findings have shown that foreign phoneme contrasts can be learned at a later age, too. Acquiring new phonemic categories requires neuroplastic changes in the brain. Neurophysiological studies have examined the brain’s ability to differentiate between closely related phonemic categories at the early stage of spoken language processing by measuring, for example, event-related mismatch negativity responses (MMN). MMN, or its magnetic equivalent MMNm, is elicited when the brain registers a difference in a repetitive sensory stimulus. Studies have shown that even a moderate amount of auditory training with closely related foreign phonemes improves the brain’s ability to discriminate between them resulting in enhanced MMN or MMNm responses. In this experiment the neural mechanisms of foreign language phoneme acquisition and the learning-related neuroplastic changes were studied using magnetoencephalography (MEG) and neuromagnetic evoked responses (MMNm in particular). 20 Finnish subjects were measured in the experiment. Their task was to learn to differentiate between acoustically closely related Russian fricatives Ш /ʂ/ and Щ /ɕ(ː)/. The subjects’ differentiation skills were first tested in a behavioral task where Russian pseudoword minimal pairs were presented to them auditorily. The first phoneme in the word pairs was varied and the subjects had to report whether they heard a difference between the words or not. The same stimuli were then presented in a passive MEG task where the brain’s change detection responses were tested in an unattended situation as the subjects were watching a silent film. After the measurement the subjects practiced the phonemes at home for approximately one week by playing a learning game by computer. After training they were measured again. Structural magnetic resonance images of the subjects’ brain were also measured for MEG source localization purposes. Behavioral discrimination ability of the experimental phonemes was considerably worse than with familiar control phonemes. The discrimination skills seemed to improve by training, but the difference was not statistically significant. Contrary to the hypotheses, statistically significant MMNm responses were not found before or after training. No significant differences were found in other auditory MEG responses or their neural source current distributions between the measurements either. However, individual differences in learning were sizeable. For the subjects who improved their performance in the behavioral task a modest training-related boost in the auditory responses supporting the hypotheses could be observed. Although very small and statistically insignificant, the effect was opposite for control stimuli and did not exist in the non-learner group suggesting some sort of change in neural processing in the learner group. This study was not able to replicate the findings from various previous studies on phoneme acquisition in adulthood. Although it is likely that certain methodological limitations (e.g. small number of stimulus repetitions, challenging stimuli) affected the significance of the results, based on this study the generalizability of some of the previous findings can be called into question

The Resonant Dynamics of Speech Perception: Interword Integration and Duration-Dependent Backward Effects

How do listeners integrate temporally distributed phonemic information into coherent representations of syllables and words? During fluent speech perception, variations in the durations of speech sounds and silent pauses can produce different pereeived groupings. For exarnple, increasing the silence interval between the words "gray chip" may result in the percept "great chip", whereas increasing the duration of fricative noise in "chip" may alter the percept to "great ship" (Repp et al., 1978). The ARTWORD neural model quantitatively simulates such context-sensitive speech data. In AHTWORD, sequential activation and storage of phonemic items in working memory provides bottom-up input to unitized representations, or list chunks, that group together sequences of items of variable length. The list chunks compete with each other as they dynamically integrate this bottom-up information. The winning groupings feed back to provide top-down supportto their phonemic items. Feedback establishes a resonance which temporarily boosts the activation levels of selected items and chunks, thereby creating an emergent conscious percept. Because the resonance evolves more slowly than wotking memory activation, it can be influenced by information presented after relatively long intervening silence intervals. The same phonemic input can hereby yield different groupings depending on its arrival time. Processes of resonant transfer and competitive teaming help determine which groupings win the competition. Habituating levels of neurotransmitter along the pathways that sustain the resonant feedback lead to a resonant collapsee that permits the formation of subsequent. resonances.Air Force Office of Scientific Research (F49620-92-J-0225); Defense Advanced Research projects Agency and Office of Naval Research (N00014-95-1-0409); National Science Foundation (IRI-97-20333); Office of Naval Research (N00014-92-J-1309, NOOO14-95-1-0657

Central auditory processing and the acquisition of phonology in 2-year-old children with recurrent acute otitis media

Middle ear infections (acute otitis media, AOM) are among the most common infectious diseases in childhood, their incidence being greatest at the age of 6–12 months. Approximately 10–30% of children undergo repetitive periods of AOM, referred to as recurrent acute otitis media (RAOM). Middle ear fluid during an AOM episode causes, on average, 20–30 dB of hearing loss lasting from a few days to as much as a couple of months. It is well known that even a mild permanent hearing loss has an effect on language development but so far there is no consensus regarding the consequences of RAOM on childhood language acquisition. The results of studies on middle ear infections and language development have been partly discrepant and the exact effects of RAOM on the developing central auditory nervous system are as yet unknown. This thesis aims to examine central auditory processing and speech production among 2-year-old children with RAOM. Event-related potentials (ERPs) extracted from electroencephalography can be used to objectively investigate the functioning of the central auditory nervous system. For the first time this thesis has utilized auditory ERPs to study sound encoding and preattentive auditory discrimination of speech stimuli, and neural mechanisms of involuntary auditory attention in children with RAOM. Furthermore, the level of phonological development was studied by investigating the number and the quality of consonants produced by these children. Acquisition of consonant phonemes, which are harder to hear than vowels, is a good indicator of the ability to form accurate memory representations of ambient language and has not been studied previously in Finnish-speaking children with RAOM. The results showed that the cortical sound encoding was intact but the preattentive auditory discrimination of multiple speech sound features was atypical in those children with RAOM. Furthermore, their neural mechanisms of auditory attention differed from those of their peers, thus indicating that children with RAOM are atypically sensitive to novel but meaningless sounds. The children with RAOM also produced fewer consonants than their controls. Noticeably, they had a delay in the acquisition of word-medial consonants and the Finnish phoneme /s/, which is acoustically challenging to perceive compared to the other Finnish phonemes. The findings indicate the immaturity of central auditory processing in the children with RAOM, and this might also emerge in speech production. This thesis also showed that the effects of RAOM on central auditory processing are long-lasting because the children had healthy ears at the time of the study. An effective neural network for speech sound processing is a basic requisite of language acquisition, and RAOM in early childhood should be considered as a risk factor for language development.Välikorvatulehdukset ovat lapsuuden yleisimpiä infektiosairauksia, ja niiden esiintyvyys on suurimmillaan 6–12 kuukauden iässä. Noin 10–30 % lapsista sairastaa toistuvia välikorvatulehduksia. Akuutissa välikorvatulehduksessa välikorvaontelon tulehduserite alentaa kuulokynnystä keskimäärin 20–30 dB, ja eritteen poistuminen tulehduksen parantuessa kestää muutamasta päivästä jopa pariin kuukauteen. Pysyvän, lievänkin kuulovian tiedetään vaikuttavan lapsen kielenkehitykseen. Sen sijaan välikorvatulehdusten aiheuttamien vaihtelevien kuulohavaintojen vaikutuksiakeskushermostolliseen kuulojärjestelmään ja kielenkehitykseen ei täysin tunneta. Tässä väitöskirjassa tutkittiin 2-vuotiaiden, toistuvia välikorvatulehduksia sairastaneiden lasten kuulotiedon käsittelyä sekä puheen tuottoa. Kuuloherätevasteita (englanniksi event-related potential, ERP) aivosähkökäyrästä rekisteröimällä saadaan luotettavasti tarkkaa tietoa keskushermostollisen kuulojärjestelmän toiminnasta. Tutkimuksessa hyödynnettiin ensimmäistä kertaa puheäänille ja yllättäville ääniärsykkeille syntyviä kuuloherätevasteita, kun pyrittiin selvittämään välikorvatulehduksia sairastaneiden lasten aivokuorella tapahtuvaa äänitiedon peruskäsittelyä, esitietoista kuuloerottelua ja automaattisen tarkkaavuuden kääntymisen mekanismeja. Lisäksi tarkasteltiin lasten tuottamien konsonanttien määrää ja laatua,koska akustisesti vokaaliäänteitä vaikeammin kuultavien konsonanttien omaksuminen heijastaa kykyä muodostaa tarkkoja muistiedustumia äidinkielen äänteistä. Myöskään konsonanttien tuottoa ei ole aiemmin suomen kieltä omaksuvilla, välikorvatulehduksia sairastaneilla lapsilla tutkittu. Tulokset osoittivat, että toistuvia välikorvatulehduksia sairastaneiden lasten äänitiedon peruskäsittely oli vastaavaa kuin vertailuryhmän lapsilla, mutta heidän esitietoinen kuuloerottelunsa oli poikkeavaa useiden puheäänenpiirteiden osalta. Lisäksi automaattisen tarkkaavuuden suuntautuminen yllättäviin ääniärsykkeisiin oli välikorvatulehduksia sairastaneilla lapsilla poikkeavaa ja viittasi siihen, että nämä lapset häiriintyivät verrokkejaan enemmän yllättävistä mutta merkityksettömistä äänistä. Välikorvatulehduksia sairastaneet lapset myös tuottivat vähemmän konsonantteja kuin vertailuryhmän 2-vuotiaat. Erityisesti viive ilmeni sanan keskellä tuotettujen konsonanttien määrässä sekä akustisilta ominaisuuksiltaan vaikeasti havaittavissa olevan /s/-äänteen omaksumisessa. Väitöstutkimus osoitti, että varhaislapsuudessa toistuvia välikorvatulehduksia sairastaneiden lasten kuulotiedon käsittelyssä on kypsymättömyyttä, mikä saattoi ilmetämyös puheen tuotossa. Välikorvatulehdusten vaikutukset kuulotiedon käsittelyyn säilyvät myös tulehduseritteen poistuttua, sillä lasten korvat olivat tutkimushetkellä terveet. Koska varhaislapsuuden aikainen tehokkaan hermosoluverkoston kehittyminen puheäänten käsittelylle luo pohjan myös myöhemmälle kielen oppimiselle, toistuvat välikorvatulehdukset on syytä huomioida yhtenä riskitekijänä lapsen kielenkehitykselle.Siirretty Doriast

Phonological Processing in Human Auditory Cortical Fields

We used population-based cortical-surface analysis of functional magnetic imaging data to characterize the processing of consonant–vowel–consonant syllables (CVCs) and spectrally matched amplitude-modulated noise bursts (AMNBs) in human auditory cortex as subjects attended to auditory or visual stimuli in an intermodal selective attention paradigm. Average auditory cortical field (ACF) locations were defined using tonotopic mapping in a previous study. Activations in auditory cortex were defined by two stimulus-preference gradients: (1) Medial belt ACFs preferred AMNBs and lateral belt and parabelt fields preferred CVCs. This preference extended into core ACFs with medial regions of primary auditory cortex (A1) and the rostral field preferring AMNBs and lateral regions preferring CVCs. (2) Anterior ACFs showed smaller activations but more clearly defined stimulus preferences than did posterior ACFs. Stimulus preference gradients were unaffected by auditory attention suggesting that ACF preferences reflect the automatic processing of different spectrotemporal sound features

The influence of music in the development of phonetics, phonology and phonological awareness in 3-year-olds with typical development and 3- to 6-year-olds with speech or language disorder

The relation between music and language has been intensively studied in recent years. Research has revealed that both domains engage similar processing mechanisms, including auditory processing and higher cognitive functions, and recruite partially overlapping brain structures. Furthemore, different authors have shown that linguistic functions can be positively influenced by music training above 4 years old. Music has also been shown to be associated with the promotion of linguistics skills in children with specific pathologies related to language, such as dyslexia, in 7- to 10-year-olds. In this thesis, we conducted four studies on the effect of music training on different aspects of language development. We studied this influence on phonological awareness in children with typical development and speech or language disorder (Studies 1 and 2) and on phonetic and phonological development in the same populations (Studies 3 and 4). In this randomized control study, with a test-training-retest methodology, 49 typically developing children, aged between 3 and 4, were assessed with a phonological awareness test (Study 1) and a phonetic and phonological test (Study 3). These tests were applied before and after a school year with weekly Music Classes (experimental group) or Visual Arts Classes (control group) in kindergarten. Two additional studies with the same methodology were conducted with 16 atypically developing children, aged between 3 and 6. This group included children with phonologically based Speech Sound Disorder (SSD) and / or Developmental Language Disorder (DLD). The goal of investigating this topic in this group of atypical children was to understand music relation with phonological awareness development (Study 2) and phonetic and phonological development (Study 4), and this at stages earlier than those where the beneficial effect of music in language-related skills has already been found. When comparing pre- and post-assessment and irrespective of type of lessons’ exposure (music or visual arts), results always showed significant differences in each group, as expected due to general developmental reasons. In Study 1, Music Classes’ students outperformed the control group, showing significantly larger differences between the beginning and the end of the lessosns period, indicating that music lessons have influenced phonological awareness, and pointing to a causal relation between music training and phonological awareness as soon as 3 years of age. In Studies 2, 3 and 4 no significant differences were found between groups in the post-assessment moment. This fact may suggest the need of more intensive music training or, in what concerns atypically developing children, a specific music curriculum designed to bridge their linguistic rhythm (and possibly pitch) processing deficits. Globally, this thesis supports the hypothesis that music training may promote language abilities, in particular phonological awareness, in 3-year-olds with typical development, that is prior to the ages that have been previously studied.A relação entre música e linguagem tem sido alvo de diversos estudos ao longo dos últimos anos. Estes estudos têm demonstrado que as duas áreas estão relacionadas, utilizando mecanismos de processamento comuns (incluindo o processamento auditivo e o processamento de funções cognitivas) e recorrendo a estruturas neuronais comuns. Vários autores referem a influência da música em diferentes áreas do desenvolvimento linguístico em crianças com idades superiores a 4 anos, nomeadamente no que diz respeito a competências de consciência fonológica, consciência fonémica, precursores da leitura e capacidade de leitura (em crianças com desenvolvimento típico e com dislexia). De forma a compreender a influência do treino musical no desenvolvimento da consciência fonológica (Estudos 1 e 2) bem como das capacidades fonéticas e fonológicas da criança (Estudos 3 e 4), foi desenhado um estudo com metologia teste-treino-reteste, com randomização de uma amostra e constituição de um grupo com Aulas de Música (grupo experimental) e outro grupo com Aulas de Artes Visuais (grupo de controlo). Esta metodologia incidiu sobre uma população de crianças com desenvolvimento típico (N=49), com 3 anos de idade (Estudos 1 e 3) e sobre uma população com Perturbação de Sons de Fala de base fonológica e / ou Perturbação do Desenvolvimento da Linguagem (N=16), entre os 3 e os 6 anos de idade (Estudos 2 e 4). Todas as crianças foram avaliadas antes e depois do período de intervenção, que decorreu durante um ano escolar, em contexto de Jardim de Infância, com a frequência de uma aula semanal de 45 minutos (Música VS Artes Visuais). A comparação realizada entre os momentos de avaliação inicial e final revelou diferenças significativas no desenvolvimento das diversas competências, em todos os grupos – melhoria expectável devido ao desenvolvimento da criança resultante apenas do tempo decorrido. No Estudo 1, sobre a influência da música no desenvolvimento da Consciência Fonológica, os alunos de Música obtiveram melhores resultados do que os alunos de Artes Visuais, mostrando uma evolução significativamente maior do que o grupo de controlo no momento da pós-avaliação. Este facto indica que o treino musical influenciou positivamente o desenvolvimento das competências de consciência fonológica, apontando para uma relação de causa-efeito, aos 3 anos de idade. Nos Estudos 2 (influência da música no desenvolvimento da consciência fonológica em crianças com desenvolvimento atípico), 3 (influência da música no desenvolvimento fonético-fonológico em crianças com desenvolvimento típico) e 4 (influência da música no desenvolvimento fonético-fonológico em crianças com desenvolvimento atípico) não foram encontradas diferenças significativas entre os grupos experimentais e de controlo no momento de avaliação final. Este facto pode indicar a necessidade de um treino musical mais intensivo ou, no caso das crianças com desenvolvimento atípico, que compreenda um currículo especificamente desenhado para colmatar as dificuldades ao nível do processamento linguístico e musical. Esta tese suporta a hipótese de que o treino musical promove o desenvolvimento de capacidades linguísticas, nomeadamente de consciência fonológica, aos 3 anos de idade, numa faixa etária anterior às até aqui estudadas. Este facto poderá ter impacto na criação de programas de promoção da consciência fonológica em contexto de Jardim de Infância, ou na potenciação de estratégias utilizadas pelo educador de infância, no seu dia-a-dia, no sentido de promover o desenvolvimento de competências fundamentais nas aprendizagens subsequentes da leitura e da escrita

Acoustic-phonetic and auditory mechanisms of adaptation in the perception of sibilant fricatives

Listeners are highly proficient at adapting to contextual variation when perceiving speech. In the present study, we examined the effects of brief speech and nonspeech contexts on the perception of sibilant fricatives. We explored three theoretically motivated accounts of contextual adaptation, based on phonetic cue calibration, phonetic covariation, and auditory contrast. Under the cue calibration account, listeners adapt by estimating a talker-specific average for each phonetic cue or dimension; under the cue covariation account, listeners adapt by exploiting consistencies in how the realization of speech sounds varies across talkers; under the auditory contrast account, adaptation results from (partial) masking of spectral components that are shared by adjacent stimuli. The spectral center of gravity, a phonetic cue to fricative identity, was manipulated for several types of context sound: /z/-initial syllables, /v/-initial syllables, and white noise matched in long-term average spectrum (LTAS) to the /z/-initial stimuli. Listeners’ perception of the /s/–/ʃ/ contrast was significantly influenced by /z/-initial syllables and LTAS-matched white noise stimuli, but not by /v/-initial syllables. No significant difference in adaptation was observed between exposure to /z/-initial syllables and matched white noise stimuli, and speech did not have a considerable advantage over noise when the two were presented consecutively within a context. The pattern of findings is most consistent with the auditory contrast account of short-term perceptual adaptation. The cue covariation account makes accurate predictions for speech contexts, but not for nonspeech contexts or for the absence of a speech-versus-nonspeech difference

The listening talker: A review of human and algorithmic context-induced modifications of speech

International audienceSpeech output technology is finding widespread application, including in scenarios where intelligibility might be compromised - at least for some listeners - by adverse conditions. Unlike most current algorithms, talkers continually adapt their speech patterns as a response to the immediate context of spoken communication, where the type of interlocutor and the environment are the dominant situational factors influencing speech production. Observations of talker behaviour can motivate the design of more robust speech output algorithms. Starting with a listener-oriented categorisation of possible goals for speech modification, this review article summarises the extensive set of behavioural findings related to human speech modification, identifies which factors appear to be beneficial, and goes on to examine previous computational attempts to improve intelligibility in noise. The review concludes by tabulating 46 speech modifications, many of which have yet to be perceptually or algorithmically evaluated. Consequently, the review provides a roadmap for future work in improving the robustness of speech output

The role of sound offsets in auditory temporal processing and perception

Sound-offset responses are distinct to sound onsets in their underlying neural mechanisms, temporal processing pathways and roles in auditory perception following recent neurobiological studies. In this work, I investigate the role of sound offsets and the effect of reduced sensitivity to offsets on auditory perception in humans. The implications of a 'sound-offset deficit' for speech-in-noise perception are investigated, based on a mathematical model with biological significance and independent channels for onset and offset detection. Sound offsets are important in recognising, distinguishing and grouping sounds. They are also likely to play a role in perceiving consonants that lie in the troughs of amplitude fluctuations in speech. The offset influence on the discriminability of model outputs for 48 non-sense vowel-consonant-vowel (VCV) speech stimuli in varying levels of multi-talker babble noise (-12, -6, 0, 6, 12 dB SNR) was assessed, and led to predictions that correspond to known phonetic categories. This work therefore suggests that variability in the offset salience alone can explain the rank order of consonants most affected in noisy situations. A novel psychophysical test battery for offset sensitivity was devised and assessed, followed by a study to find an electrophysiological correlate. The findings suggest that individual differences in sound-offset sensitivity may be a factor contributing to inter-subject variation in speech-in-noise discrimination ability. The promising measures from these results can be used to test between-population differences in offset sensitivity, with more support for objective than psychophysical measures. In the electrophysiological study, offset responses in a duration discrimination paradigm were found to be modulated by attention compared to onset responses. Overall, this thesis shows for the first time that the onset-offset dichotomy in the auditory system, previously explored in physiological studies, is also evident in human studies for both simple and complex speech sounds

Synaesthetes’ sensitivity to sound symbolism and the role of sound symbolism in lexical-gustatory synaesthesia

Sound symbolism is the phenomenon of cross-modal correspondences non-arbitrarily linking phonological components and semantic meanings in language (e.g., words meaning round contain a high proportion of rounded vowels such as /u/; Mathur, 2010). Our study suggests that this cross-modal phenomenon is related to synaesthesia, a cross-modal phenomenon wherein one sensory or cognitive stimulus (e.g., the written word jail) causes the experience of an additional percept in the same modality (e.g., the colour pink) or across modalities (e.g., the taste of chocolate). In Experiment 1, we found that grapheme-colour synaesthetes (synaesthetes that experience colours in association with letters and/or numbers) were better at determining the meanings of sound symbolic foreign words than nonsynaesthetes, suggesting that synaesthetes possess heightened skills in domains unrelated to their specific form of synaesthesia. In Experiment 2, we discovered that the word-taste associations of lexical-gustatory synaesthete JIW abide by sound symbolic rules, which nonsynaesthetes’ sound-taste associations also follow. Together, these experiments support a relationship between sound symbolism and synaesthesia likely arising from a common set of cross-modal mechanisms. Our paper discusses the implications of these results for the relationship between sound symbolism and synaesthesia as well as for each individual phenomenon