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Speech Perception, Production and Bilingualism
Cognitive Neuroscience of Auditory Perception and Attention
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Exploring Lexical Access in Speech Production

Project coordinator: Albert Costa.

Project members:  Marco Calabria, Mireia Hernández, Montserrat Juncadella, Clara Martin, Jasmin Sadat, Mikel Santesteban, Kristof Strijkers
       

GOALS OF THE PROJECT 

Speech production is a complex cognitive process entailing the orchestration of various mental operations over time (semantics, words, phonology, motor programming). In this project we explore the functional and temporal neuronal underpinnings related to these different processing stages. The end goal is to uncover the brain’s architecture underlying this fascinating human skill and to develop a biologically plausible cognitive model describing the temporal and spatial organization of speech production in monolingual and bilingual speakers.

 

SUBPROJECT 1: The time-course of word retrieval in speech production. Speakers are extremely fast and efficient in translating their ideas into words. How does this ability develop over time? How quickly do speakers access the lexicon? How does mastering two languages influence lexicon access? This research serves two main goals: First, to gather specific chronometric information of when and how long the brain needs to retrieve the words we want to say; second, to construct a temporal map of speech. These two goals are pursued in parallel in monolingual and bilingual speakers. We combined the fine temporal resolution of event-related brain potentials (ERPs) with overt picture naming. In the first study we investigated the electrophysiological response to word frequency and cognate status, two psycholinguistic variables known to produce their effects during lexical access. Both variables elicited ERP deflections as early as 185 ms after stimulus onset at the P2 component. The combined results provided the first direct time-course estimate of the speed with which the brain engages in word retrieval. In other words, we go from pictures to words in less than 200 ms! In a subsequent study we replicated these results with a different manipulation that allowed us to estimate how long the whole process of word retrieval takes. We explored the time course of the semantic cumulative effect. This effect refers to the observation that participants name pictures (e.g., snake) slower when they belong to the same semantic category as previously named pictures (e.g., turtle). Furthermore, this effect increases linearly as a function of the amount of previously named semantic members (thus, the higher the number of category members uttered previously, the slower subjects are to name a new member of that category). The ERP results mimicked the behavioural data exactly: we found a linear increase in the ERP responses with each new member of the same semantic category, starting again at the early P2 component (~ 200 ms) and extending up to 380 ms after picture onset (see Figure 1). These results confirm those of the first study, in that the brain engages in word retrieval during picture naming within 200 ms, and define a clear time-frame estimate of how long this retrieval lasts, namely around 180 ms.

           

 

 

Figure 1.  ERPs elicited by the five ordinal positions within the semantic categories. The dark gray area refers to the P2 peak and P3 peak showing a linear and cumulative increase in amplitude with each ordinal position. Above, the topographic maps of the averaged differences waves of the five ordinal positions for the P2 and P3 are shown. The light gray area refers to the time frame (208–388 ms) where ERP amplitudes correlated with ordinal position and RTs.

SUBPROJECT 2: Patient studies reveal the semantic and lexical organization of the monolingual and bilingual brain.  In this subproject we study several aspects of the semantic and lexical organization by exploring the performance of brain-damaged individuals. In the first study we observed that Alzheimer’s disease (AD) patients showed a differential impairment for different semantic categories. AD patients with moderate impairment of their semantic knowledge showed comparable priming effects to those of controls for the category of animals, but no priming effect for artefacts. Given the diffuse brain damage associated with AD, the dissociation observed suggests that the distribution of different types of semantic properties has a differential strength in overlap across categories. In another line of research, we explored the presence of dissociations between the two languages of bilingual speakers, by assessing the performance of bilingual patients suffering from category-specific deficits (either in grammar or semantics). Our results revealed that highly proficient brain-damaged bilingual speakers suffer impairment to the same extent in L1 as in L2. For example, in one single-case study a Catalan–Spanish bilingual woman (LPM) suffering from AD showed a disproportionate deficit for nouns in comparison to verbs. More recently, we reported similar findings for a Catalan-Spanish bilingual aphasic with a semantic deficit (JFF). Significantly, the patients’ deficits were present in both languages.  In sum, these single-case studies suggest that both L1 and L2 lexical representations are stored according to the same organizational principles (semantic category and grammatical class).  However, in another case-study with a bilingual patient (JPG) suffering from primary progressive aphasia (see Figure 2) we did observe differences between L1 and L2: that is, although JPG showed the same noun-verb dissociation in the two languages, his L2 seemed to be more affected than his L1. Two conclusions can be drawn from these findings: (a) As previously argued, the cortical organization of the two languages of a highly proficient bilingual follows similar principles, one of them being grammatical class; (b) The two languages of a bilingual can be damaged to different extents, but follow the same qualitative pattern.

           

OTHER SUBPROJECTS

  • Structural generalizations over consonants and vowels in 11-month-old infants (Pons & Toro)
  • How input interplays with initial biases: Asymmetries in vowel perception during the first year of life (Albareda-Castellot, Pons & Sebastian-Galles)
  • Early emergence of episodic memory in early infancy (Ressel & Sebastián-Gallés)
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    Figure 2.  (A) JPG’s performance on oral and written noun naming. (B) JPG’s performance on oral and written verb naming.