Lucy J. MacGregor

It's the way that you, er, say it: hesitations in speech affect language comprehension.

Everyday speech is littered with disfluency, often correlated with the production of less predictable words (e.g., Beattie & Butterworth [Beattie, G., & Butterworth, B. (1979). Contextual probability and word frequency as determinants of pauses in spontaneous speech. Language and Speech, 22, 201-211.]). But what are the effects of disfluency on listeners? In an ERP experiment which compared fluent to disfluent utterances, we established an N400 effect for unpredictable compared to predictable words. This effect, reflecting the difference in ease of integrating words into their contexts, was reduced in cases where the target words were preceded by a hesitation marked by the word er. Moreover, a subsequent recognition memory test showed that words preceded by disfluency were more likely to be remembered. The study demonstrates that hesitation affects the way in which listeners process spoken language, and that these changes are associated with longer-term consequences for the representation of the message.

Ultra-rapid access to words in the brain

Rapid information processing in the human brain is vital to survival in a highly dynamic environment. The key tool humans use to exchange information is spoken language, but the exact speed of the neuronal mechanisms underpinning speech comprehension is still unknown. Here we investigate the time course of neuro-lexical processing by analysing neuromagnetic brain activity elicited in response to psycholinguistically and acoustically matched groups of words and pseudowords. We show an ultra-early dissociation in cortical activation elicited by these stimulus types, emerging ~50 ms after acoustic information required for word identification first becomes available. This dissociation is the earliest brain signature of lexical processing of words so far reported, and may help explain the evolutionary advantage of human spoken language.

Listening to the sound of silence: disfluent silent pauses in speech have consequences for listeners

Silent pauses are a common form of disfluency in speech yet little attention has been paid to them in the psycholinguistic literature. The present paper investigates the consequences of such silences for listeners, using an Event-Related Potential (ERP) paradigm. Participants heard utterances ending in predictable or unpredictable words, some of which included a disfluent silence before the target. In common with previous findings using er disfluencies, the N400 difference between predictable and unpredictable words was attenuated for the utterances that included silent pauses, suggesting a reduction in the relative processing benefit for predictable words. An earlier relative negativity, topographically distinct from the N400 effect and identifiable as a Phonological Mismatch Negativity (PMN), was found for fluent utterances only. This suggests that only in the fluent condition did participants perceive the phonology of unpredictable words to mismatch with their expectations. By contrast, for disfluent utterances only, unpredictable words gave rise to a late left frontal positivity, an effect previously observed following ers and disfluent repetitions. We suggest that this effect reflects the engagement of working memory processes that occurs when fluent speech is resumed. Using a surprise recognition memory test, we also show that listeners were more likely to recognise words which had been encountered after silent pauses, demonstrating that silence affects not only the process of language comprehension but also its eventual outcome. We argue that, from a listeners perspective, one critical feature of disfluency is the temporal delay which it adds to the speech signal.

Multiple routes for compound word processing in the brain: Evidence from EEG

Highlights • MMN response dissociates lexical access and combinatorial processing of compounds.• Compound lexical frequency and meaning transparency affect the MMN.• Larger MMN for high vs. low-frequency opaque compounds.• No MMN frequency effects for transparent compounds or differences to pseudo-compounds.• Results support a parallel dual-route account of compound word processing.

Semantics, Syntax or Neither? A Case for Resolution in the Interpretation of N500 and P600 Responses to Harmonic Incongruities

The processing of notes and chords which are harmonically incongruous with their context has been shown to elicit two distinct late ERP effects. These effects strongly resemble two effects associated with the processing of linguistic incongruities: a P600, resembling a typical response to syntactic incongruities in language, and an N500, evocative of the N400, which is typically elicited in response to semantic incongruities in language. Despite the robustness of these two patterns in the musical incongruity literature, no consensus has yet been reached as to the reasons for the existence of two distinct responses to harmonic incongruities. This study was the first to use behavioural and ERP data to test two possible explanations for the existence of these two patterns: the musicianship of listeners, and the resolved or unresolved nature of the harmonic incongruities. Results showed that harmonically incongruous notes and chords elicited a late positivity similar to the P600 when they were embedded within sequences which started and ended in the same key (harmonically resolved). The notes and chords which indicated that there would be no return to the original key (leaving the piece harmonically unresolved) were associated with a further P600 in musicians, but with a negativity resembling the N500 in non-musicians. We suggest that the late positivity reflects the conscious perception of a specific element as being incongruous with its context and the efforts of musicians to integrate the harmonic incongruity into its local context as a result of their analytic listening style, while the late negativity reflects the detection of the absence of resolution in non-musicians as a result of their holistic listening style.

Near-instant automatic access to visually presented words in the human neocortex: neuromagnetic evidence.

Rapid and efficient processing of external information by the brain is vital to survival in a highly dynamic environment. The key channel humans use to exchange information is language, but the neural underpinnings of its processing are still not fully understood. We investigated the spatio-temporal dynamics of neural access to word representations in the brain by scrutinising the brain’s activity elicited in response to psycholinguistically, visually and phonologically matched groups of familiar words and meaningless pseudowords. Stimuli were briefly presented on the visual-field periphery to experimental participants whose attention was occupied with a non-linguistic visual feature-detection task. The neural activation elicited by these unattended orthographic stimuli was recorded using multi-channel whole-head magnetoencephalography, and the timecourse of lexically-specific neuromagnetic responses was assessed in sensor space as well as at the level of cortical sources, estimated using individual MR-based distributed source reconstruction. Our results demonstrate a neocortical signature of automatic near-instant access to word representations in the brain: activity in the perisylvian language network characterised by specific activation enhancement for familiar words, starting as early as ~70 ms after the onset of unattended word stimuli and underpinned by temporal and inferior-frontal cortices.

Concreteness effects in single-meaning, multi-meaning and newly acquired words

This study examined the extent to which concreteness influences the acquisition and subsequent processing of novel (low frequency) concepts. Participants were trained on 70 rare English words (35 concrete, 35 abstract) paired with definitions. ERPs were then recorded while participants performed a semantic categorisation (concrete vs. abstract) and a lexical decision task on single-meaning, multi-meaning and the newly acquired words. During training there was a significant effect of concreteness, in that participants were more successful at acquiring concrete concepts. In both the semantic categorisation and the lexical decision task, concreteness effects were evident in the behavioural and in the ERP data for all word types, with concrete words eliciting more negative waveforms than abstract words in the N400 time window. Behaviourally, participants experienced greater difficulty in judging the concreteness of multi-meaning words, yet concreteness effects in the N400 were equally strong for all three word types across both tasks. These findings indicate that concreteness represents a fundamental distinction in the way that items are represented in memory, which is independent of the participants perceived judgement. They further demonstrate that novel concepts can be acquired rapidly after minimal training, and that the neurophysiological correlates associated with processing novel words are modulated by the specific nature of the conceptual characteristics assigned to the word.