Ruth de Diego Balaguer

Different neurophysiological mechanisms underlying word and rule extraction from speech.

The initial process of identifying words from spoken language and the detection of more subtle regularities underlying their structure are mandatory processes for language acquisition. Little is known about the cognitive mechanisms that allow us to extract these two types of information and their specific time-course of acquisition following initial contact with a new language. We report time-related electrophysiological changes that occurred while participants learned an artificial language. These changes strongly correlated with the discovery of the structural rules embedded in the words. These changes were clearly different from those related to word learning and occurred during the first minutes of exposition. There is a functional distinction in the nature of the electrophysiological signals during acquisition: an increase in negativity (N400) in the central electrodes is related to word-learning and development of a frontal positivity (P2) is related to rule-learning. In addition, the results of an online implicit and a post-learning test indicate that, once the rules of the language have been acquired, new words following the rule are processed as words of the language. By contrast, new words violating the rule induce syntax-related electrophysiological responses when inserted online in the stream (an early frontal negativity followed by a late posterior positivity) and clear lexical effects when presented in isolation (N400 modulation). The present study provides direct evidence suggesting that the mechanisms to extract words and structural dependencies from continuous speech are functionally segregated. When these mechanisms are engaged, the electrophysiological marker associated with rule-learning appears very quickly, during the earliest phases of exposition to a new language.

Regular and irregular morphology and its relationship with agrammatism: evidence from two Spanish-Catalan bilinguals.

We report the performance of two aphasic patients in a morphological transformation task. Both patients are Spanish-Catalan bilingual speakers who were diagnosed with agrammatic Brocas aphasia. In the morphological transformation task, the two patients were asked to produce regular and irregular verb forms. The patients showed poorer performance with irregular than regular morphological transformations in both of their languages. These results are at odds with the proposal that agrammatic speech is always or even preponderantly associated with poorer performance in processing regular versus irregular verb form. Instead, these results support the view that a major component of agrammatic production is a deficit in morphosyntactic processing, independently of whether this processing ultimately involves regular or irregular forms.

Neural Circuits Subserving the Retrieval of Stems and Grammatical Features in Regular and Irregular Verbs

Many languages, including English and Spanish, feature regular (dance → danced) and irregular (catch → caught) inflectional systems. According to psycholinguistic theories, regular and irregular inflections are instantiated either by a single or by two specialized mechanisms. Those theories differ in their assumptions concerning the underlying information necessary for the processing of regular verbs. Whereas single mechanism accounts have stated an increased involvement of phonological processing for regular verbs, dual accounts emphasize the prominence of grammatical information. Using event‐related functional magnetic resonance imaging, we sought to delineate the brain areas involved in the generation of complex verb forms in Spanish. This language has the advantage of isolating specific differences in the regular–irregular contrasts in terms of the number of stems associated with a verb while controlling for compositionality (regular and irregular verbs apply suffixes to be inflected). The present study showed that areas related to grammatical processing are active for both types of verbs (left opercular inferior frontal gyrus). In addition, major differences between regular and irregular verbs were also observed. Several areas of the prefrontal cortex were selectively active for irregular production, presumably reflecting their role in lexical retrieval (bilateral inferior frontal area and dorsolateral prefrontal cortex). Regular verbs, however, showed increased activation in areas related to grammatical processing (anterior superior temporal gyrus/insular cortex) and in the left hippocampus, the latter possibly related to a greater implication of the phonological loop necessary for the reutilization of the same stem shared across all forms in regular verbs. Hum Brain Mapp, 2006.

Huntington's disease impairs recognition of angry and instrumental body language

Patients with Huntingtons disease (HD) exhibit motor impairments as well as cognitive and emotional deficits. So far impairments in the ability to recognize emotional stimuli have mostly been investigated by using facial expressions and emotional voices. Other important emotional signals are provided by the whole body. To investigate the impact of motor deficits on body recognition and the relation between motor disorders and emotion perception deficits, we tested recognition of emotional body language (instrumental, angry, fearful and sad) in 19 HD patients and their matched controls with a nonverbal whole body expression matching task. Results indicate that HD patients are impaired in recognizing both instrumental and angry whole body postures. Furthermore, the body language perception deficits are correlated with measures of motor deficit. Taken together the results suggest a close relationship between emotion recognition (specifically anger) and motor abilities.

Speaker's hand gestures modulate speech perception through phase resetting of ongoing neural oscillations

Speakers often accompany speech with spontaneous beat gestures in natural spoken communication. These gestures are usually aligned with lexical stress and can modulate the saliency of their affiliate words. Here we addressed the consequences of beat gestures on the neural correlates of speech perception. Previous studies have highlighted the role played by theta oscillations in temporal prediction of speech. We hypothesized that the sight of beat gestures may influence ongoing low-frequency neural oscillations around the onset of the corresponding words. Electroencephalographic (EEG) recordings were acquired while participants watched a continuous, naturally recorded discourse. The phase-locking value (PLV) at word onset was calculated from the EEG from pairs of identical words that had been pronounced with and without a concurrent beat gesture in the discourse. We observed an increase in PLV in the 5-6 Hz theta range as well as a desynchronization in the 8-10 Hz alpha band around the onset of words preceded by a beat gesture. These findings suggest that beats help tune low-frequency oscillatory activity at relevant moments during natural speech perception, providing a new insight of how speech and paralinguistic information are integrated.

Electrical stimulation mapping of nouns and verbs in Broca's area

Electric stimulation mapping (ESM) is frequently used during brain surgery to localise higher cognitive functions to avoid post-chirurgical disabilities. Experiments with brain imaging techniques and neuropsychological studies showed differences in the cortical representation and processing of nouns and verbs. The goal of the present study was to investigate whether electric stimulation in specific sites in the frontal cortex disrupted noun and verb production selectively. We found that most of the stimulated areas showed disruption of both verbs and nouns at the inferior frontal gyrus. However, when selective effects were obtained, verbs were more prone to disruption than nouns with important individual differences. The overall results indicate that selective impairments can be observed at inferior and middle frontal regions and the action naming task seems to be more suitable to avoid post-chirurgical language disabilities, as it shows a greater sensitivity to disruption with ESM than the classical object naming task.

Spontaneous gestures modulate speech processing through phase resetting of delta–theta neural oscillations

In everyday life conversations, speakers often accompany verbal utterances with spontaneous gestures (beats) to emphasize certain parts of the utterance. Such affect is thought to be driven by the temporal alignment between visual (gestures) and auditory (speech) inputs. However, the brain mechanisms sustaining this ability remain unknown. We hypothesize that beats, usually preceding word onset by 200 ms, drive the auditory system into an ‘optimal state’, enhancing its integration of ensuing acoustic information. In this study, we tested whether beat gestures reset the phase of ongoing neural oscillations and align neural activity into the high excitability phase at the arrival of the relevant auditory input. Electroencephalographic (EEG) recordings were acquired while participants watched a continuous, naturally recorded political discourse. The phase-locking index (PLI) was calculated from the EEG time locked to the onset of equivalent words appearing naturally in the discourse, sometimes preceded by beat gestures and sometimes not. We observed an increase in phase-locking at the delta–theta frequency range (2–6 Hz) from around 200 ms before word-onset to 200 ms post word-onset, when words were accompanied with a beat gesture compared to audio alone. Furthermore, this increase in phase-locking, most noticeable at fronto-central electrodes, was not accompanied by an increase in power in the same frequency range, confirming the oscillatory-based nature of this effect. These results suggest that beat gestures are used as robust predictive information capable to tune neural oscillations to the optimal phase for auditory integration of relevant parts of the discourse during natural speech processing.