How do bi/multilinguals switch between languages so effectively that there is no obvious intrusion from the alternatives? One can examine this by comparing language selection with task selection, or language switching with task switching. This is the approach adopted in the first of two strands of research presented in this thesis. In task switching, providing advance warning of the task typically leads to a reduction in the performance ‘switch cost’, suggesting top-down biasing of task selection. It is not clear whether the language switch cost also reduces with preparation, partly because there have been very few attempts to examine preparation for a language switch, and partly because these attempts suffered from non-trivial methodological drawbacks. In Experiments 1-3 I used an optimised picture naming paradigm in which language changed unpredictably and was specified by a language cue presented at different intervals before the picture. Experiment 1, conducted on ‘unbalanced’ bilinguals, revealed some evidence of reduction in the language switch cost for naming times with preparation, but only when cue duration was short. In an attempt to further optimise the paradigm, in Experiment 2 the cue-stimulus interval (which was varied from trial to trial in Experiment 1), was varied over blocks instead. Visual cues were replaced with auditory cues – the latter also enabled a comparison between semantically transparent word cues (the spoken names of the languages) and less transparent cues (fragments of national anthems). Experiment 2 revealed a reduction in switch cost with preparation for naming latencies, but only in the second language; the first language showed the reverse. To examine whether the increase in switch cost with preparation in the first language could be due to unbalanced bilinguals biasing processing towards L2, balanced bilinguals were tested in Experiment 3. This revealed a robust reduction in switch cost in naming latencies for both languages, which was driven primarily by the trials with the anthem cues. However, in the error rates the switch cost increased with preparation interval, thus complicating the interpretation of the reduction observed for response times. Experiment 4 investigated whether preparation for a language switch elicits the electrophysiological patterns commonly found during preparation for a task switch – a switch-induced positive polarity Event-Related Potential (ERP) with a posterior scalp distribution. Contrary to a recent report of the absence of the posterior positivity in language switching, it was clearly present in the present EEG data. As in task switching, the amplitude of the posterior positivity predicted performance. The electrophysiological data suggest that preparation for a language switch and preparation for a task switch rely on highly overlapping control mechanisms. The behavioural data suggest that advance control can be effective in language switching, but perhaps not as effective as in task switching. Experiments 1-3 also examined the effect of stimulus associative history – whether the language used on the previous encounter with a given stimulus influenced performance on the current trial). Having previously named a given picture in the same language benefited overall performance, but did not do so more for switches than repeats. Thus, stimulus associative history does not seem to contribute to the language switch cost. The second strand of my research asked whether bilinguals can set themselves independently for speech vs. comprehension. Previous research has examined the cost of switching the language in output tasks and in input tasks. But, it is not clear whether one can apply separate control settings for input and output selection. To investigate this, I used a paradigm that combined switching languages for speech production and comprehension. My reasoning was that, if there is cross-talk between the control settings for input vs. output, performance in one pathway should benefit if the language selected for the other pathway is the same relative to when it is different: a ‘language match effect’. Conversely, if there is no cross-talk, there should not be a language match effect. In Experiment 5 bilinguals alternated predictably between naming numbers in their first and second language (in runs of 3 trials), whilst also having to semantically categorise spoken words which occasionally (and unpredictably) replaced the numbers. The language of the categorisation ‘probes’ varied over blocks of ~17 naming runs, but was constant within a block. The results showed a clear match effect in the input task (categorisation), but not the output task (naming). To examine the potential role of proficiency, Experiment 6 used the same paradigm to test unbalanced and balanced bilinguals. The pattern of results was qualitatively similar in both groups to that observed in Experiment 5: a language match effect confined to the input task. These results suggest ‘leakage’ from the output control settings into the input control settings.

This review has examined the spatial and temporal neural activation of speech comprehension. Six theories on speech comprehension were selected and reviewed. The most fundamental structures for speech comprehension are the superior temporal gyrus, the fusiform gyrus, the temporal pole, the temporoparietal junction, and the inferior frontal gyrus. Considering temporal aspects of processes, the N400 ERP effect indicates semantic violations, and the P600 indicates re-evaluation of a word due to ambiguity or syntax error. The dual-route processing model provides the most accurate account of neural correlates and streams of activation necessary for speech comprehension, while also being compatible with both the reviewed studies and the reviewed theories. The integrated theory of language production and comprehension provides a contemporary theory of speech production and comprehension with roots in computational neuroscience, which in conjunction with the dual-route processing model could drive the fields of language and neuroscience even further forward.

Cette thèse s’est intéressée aux interférences linguistiques intervenant dans la situation de la parole dans la parole, en comparant l’effet de masque de masqueurs paroliers générés dans une langue intelligible pour les participants (français) à celui de masqueurs paroliers générés dans des langues non connues (gaélique irlandais et italien), sur l’identification de mots cibles français. Une tâche de décision lexicale à -5 dB nous a permis d’observer des résultats significativement différents entre les masqueurs paroliers générés dans les langues inconnues (irlandais et italien), avec les masqueurs paroliers italiens qui ont réduit l’intelligibilité des mots cibles français avec la même efficacité que les masqueurs paroliers français, alors que les masqueurs paroliers irlandais ont conduit aux performances les plus élevées. L’utilisation de masqueurs de bruit fluctuant générés à partir de chacun des masqueurs paroliers, a montré que seuls les masqueurs paroliers générés dans une langue intelligible ont produit des interférences linguistiques de haut niveau en plus d’interférences acoustiques et linguistiques de bas niveau. Ainsi, la différence de performances observée entre les masqueurs paroliers irlandais et italiens serait expliquée au niveau acoustique et non à un niveau linguistique. De plus, bien que les masqueurs paroliers italiens et français aient eu des effets de masque équivalents, leurs interférences étaient de natures différentes. Lorsque l’italien devient intelligible pour les participants, les masqueurs paroliers italiens, comme ceux générés en français, produisent des interférences linguistiques de haut niveau, et ce, que les mots cibles soient produits dans la langue native des participants ou dans leur langue seconde. / This research aimed to explore the linguistic interference that occurs during the speech-in-speech situation, by comparing the masking effects of speech backgrounds that were produced in an intelligible language for the participants (i.e., French), to the masking effects of speech backgrounds that were produced in unknown foreign languages (i.e., Irish and Italian), on the identification of French target words. At -5 dB SNR, a lexical decision task revealed significantly divergent results with the unknown languages (i.e., Irish and Italian), with Italian and French speech backgrounds hindering French target word identification to a similar extent, whereas Irish speech backgrounds led to significantly better performances. Using fluctuating noise backgrounds derived from each speech background signals, showed that only the speech backgrounds generated in an intelligible language (i.e., French) produced linguistic interference of high level in addition to acoustic interference and linguistic interference of low level. Thus, the difference observed between the speech backgrounds in Irish and Italian can be explained at an acoustic level but not at a linguistic level. Moreover, although the speech backgrounds in French and in Italian had equivalent masking effects on French word identification, the nature of their interference was different. When Italian became intelligible to the participants, the speech backgrounds in Italian produced linguistic interference of high level like those generated in French, with the target words produced in the native language to the participants or in their second language.

Abstract There are multiple factors simultaneously affecting speech perception in elderly people. These factors include hearing acuity, aging of the auditory system, and changes in both perception and cognitive processes, all of which can interfere with speech comprehension, especially in cognitively demanding situations. The aim of this study is to clarify which factors influence the use of an automatic phone service system designed for elderly (N = 36) people. More specifically, the aim is to investigate whether it is the factors connected to the system itself or the factors connected to the elderly users and their actions with the system that are the most crucial for using the system successfully. Both quantitative and qualitative methods are used in the study. There were four people who performed as speakers in the system. Analysis of the prosodic features of their speech was performed using acoustic analysis software. The variables connected to the elderly participants (n = 30) were investigated using interviews, pure-tone and speech audiometric tests, the Mini-Mental State Examination test (MMSE), and the Token Test for speech comprehension. Statistical analyses were used to explore whether there was a statistical connection between the acoustic measurements or the variables connected to participants themselves and their performance in usability test situation. In addition, the elderly participants’ actions in the test situation were observed using a material-based, qualitative video-analysis. The individuals who performed as speakers in the system were observed to use features of elderspeak in their speech. However, these speaker characteristics had little effect on the participants’ performance in the tasks. It was the voice-menu that contained the most semantically complex text structure that proved to be the most difficult for participants. Both low scores in the Token test and poor word recognition were connected to poor performance in the tasks. It was found based on the qualitative analysis that in addition to speech comprehension, there were other cognitive processes that were important for completing the tasks successfully, i.e. remembering the instructions given (memory), and the ability to direct, divide and maintain attention during the tasks. Poor performance in the tasks and in the Token Test, as well as problems in executive functions observed in the test situation, were found to be factors predicting dropping out of the next phase of the study the following year. Qualitative analysis of language use in cognitively demanding situations can be used in evaluation of high-level language performance. It may be useful for detecting mild changes in language skills that can be symptomatic of early stages of memory disorders. The results of this study can also be utilized when designing voice-based interfaces. In addition, it is important to consider both advantages and disadvantages of using elderspeak in the fields of nursing and speech therapy. / Tiivistelmä Ikääntyvien ihmisten puheen vastaanotossa vaikuttavat samanaikaisesti monet tekijät: kuulokyky, auditiivisen järjestelmän ikääntymismuutokset sekä havaintotoimintojen ja kognitiivisten toimintojen muutokset. Nämä voivat vaikeuttaa puheen ymmärtämistä erityisesti kognitiivisesti vaativassa tilanteessa. Tämän tutkimuksen tavoitteena on selvittää ikääntyneille osallistujille (N = 36) suunnitellun automaattisen puhelinpalvelujärjestelmän käyttöön liittyviä tekijöitä. Tavoitteena on selvittää se, missä määrin toisaalta kokeiltuun järjestelmään liittyvät tekijät ja toisaalta käyttäjien ominaisuudet sekä heidän toimintansa tutkimustilanteessa olivat yhteydessä järjestelmän menestykselliseen käyttöön. Tutkimuksessa käytetään kvantitatiivisia ja kvalitatiivisia menetelmiä. Järjestelmässä kokeiltiin neljän eri puhujan äänillä nauhoitettuja toimintaohjeita. Heidän puheensa prosodisia piirteitä analysoitiin äänen ja puheen analyysiohjelmilla. Ikääntyneisiin osallistujiin (n = 30) liittyviä muuttujia tutkittiin haastattelulla, kuulon tutkimuksilla (äänesaudiometria ja puheaudiometria), kognitiivisella seulontatestillä (Mini-mental state examination = MMSE) ja puheen ymmärtämistä mittaavalla Token-testillä. Mittaustulosten ja muuttujien yhteyttä tehtävistä suoriutumiseen tarkasteltiin tilastollisesti. Osallistujien toimintaa havainnoitiin järjestelmän käyttötilanteessa aineistolähtöisellä laadullisella videoanalyysillä. Järjestelmän puhujilla havaittiin ikääntyneille suunnatun puheen piirteitä. Tehtävistä suoriutuminen oli kuitenkin hyvin samanlaista puhujasta riippumatta. Semanttisesti monimutkaisin tekstivalikko oli osallistujille vaikein äänite. Matala Token-testin pistemäärä ja heikko puheen tunnistuskyky liittyivät heikkoon tehtävistä suoriutumiseen. Laadullisen analyysin perusteella puheen ymmärtämisen ohella keskeisiä kognitiivisia prosesseja tehtävissä menestymisen kannalta olivat seuraavat: ohjeiden muistaminen, huomion suuntaaminen, jakaminen ja ylläpito. Heikko suoriutuminen tehtävissä ja Token-testissä sekä tutkimustilanteessa havaitut toiminnan ohjauksen ongelmat ennustivat toisesta tutkimusvaiheesta poisjääntiä seuraavana vuonna. Kognitiivisesti vaativista kielen käyttötilanteista tehtävillä laadullisilla analyyseilla voidaan arvioida monimutkaisia kielellis-kognitiivisia toimintoja ja löytää mahdollisesti alkaviin muistisairauksiin liittyviä lieviä kielellisiä muutoksia. Tuloksia voidaan hyödyntää ääneen perustuvien käyttöliittymien suunnittelussa. Ikääntyneille suunnatun puheen etuja ja haittoja on tärkeää pohtia myös hoitotyön ja puheterapian näkökulmasta.