Publications

Abstract

Different frequency bands in the electroencephalogram are postulated to support distinct language functions. Studies have suggested
that alpha–beta power decreases may index word-retrieval processes. In context-driven word retrieval, participants hear
lead-in sentences that either constrain the final word (‘He locked the door with the’) or not (‘She walked in here with the’). The last
word is shown as a picture to be named. Previous studies have consistently found alpha–beta power decreases prior to picture
onset for constrained relative to unconstrained sentences, localised to the left lateral-temporal and lateral-frontal lobes. However,
the relative contribution of temporal versus frontal areas to alpha–beta power decreases is unknown. We recorded the electroencephalogram
from patients with stroke lesions encompassing the left lateral-temporal and inferior-parietal regions or left-lateral
frontal lobe and from matched controls. Individual participant analyses revealed a behavioural sentence context facilitation effect
in all participants, except for in the two patients with extensive lesions to temporal and inferior parietal lobes. We replicated the
alpha–beta power decreases prior to picture onset in all participants, except for in the two same patients with extensive posterior
lesions. Thus, whereas posterior lesions eliminated the behavioural and oscillatory context effect, frontal lesions did not. Hierarchical
clustering analyses of all patients’ lesion profiles, and behavioural and electrophysiological effects identified those two
patients as having a unique combination of lesion distribution and context effects. These results indicate a critical role for the left
lateral-temporal and inferior parietal lobes, but not frontal cortex, in generating the alpha–beta power decreases underlying context-
driven word production.

Abstract

According to a prominent theory of language production, concepts activate multiple associated words in memory, which enter into competition for selection. However, only a few electrophysiological studies have identified brain responses reflecting competition. Here, we report a magnetoencephalography study in which the activation of competing words was manipulated by presenting pictures (e.g., dog) with distractor words. The distractor and picture name were semantically related (cat), unrelated (pin), or identical (dog). Related distractors are stronger competitors to the picture name because they receive additional activation from the picture relative to other distractors. Picture naming times were longer with related than unrelated and identical distractors. Phase-locked and non-phase-locked activity were distinct but temporally related. Phase-locked activity in left temporal cortex, peaking at 400 ms, was larger on unrelated than related and identical trials, suggesting differential activation of alternative words by the picture-word stimuli. Non-phase-locked activity between roughly 350–650 ms (4–10 Hz) in left superior frontal gyrus was larger on related than unrelated and identical trials, suggesting differential resolution of the competition among the alternatives, as reflected in the naming times. These findings characterise distinct patterns of activity associated with lexical activation and competition, supporting the theory that words are selected by competition.

Abstract

Disagreement exists regarding the functional locus of semantic interference of distractor words in picture naming. This effect is a cornerstone of modern psycholinguistic models of word production, which assume that it arises in lexical response-selection. However, recent evidence from studies of dual-task performance suggests a locus in perceptual or conceptual processing, prior to lexical response-selection. In these studies, participants manually responded to a tone and named a picture while ignoring a written distractor word. The stimulus onset asynchrony (SOA) between tone and picture–word stimulus was manipulated. Semantic interference in naming latencies was present at long tone pre-exposure SOAs, but reduced or absent at short SOAs. Under the prevailing structural or strategic response-selection bottleneck and central capacity sharing models of dual-task performance, the underadditivity of the effects of SOA and stimulus type suggests that semantic interference emerges before lexical response-selection. However, in more recent studies, additive effects of SOA and stimulus type were obtained. Here, we examined the discrepancy in results between these studies in 6 experiments in which we systematically manipulated various dimensions on which these earlier studies differed, including tasks, materials, stimulus types, and SOAs. In all our experiments, additive effects of SOA and stimulus type on naming latencies were obtained. These results strongly suggest that the semantic interference effect arises after perceptual and conceptual processing, during lexical response-selection or later. We discuss several theoretical alternatives with respect to their potential to account for the discrepancy between the present results and other studies showing underadditivity.

Abstract

Two fundamental factors affecting the speed of spoken word production are lexical frequency and sentential constraint, but little is known about their timing and electrophysiological basis. In the present study, we investigated event-related potentials (ERPs) and oscillatory brain responses induced by these factors, using a task in which participants named pictures after reading sentences. Sentence contexts were either constraining or nonconstraining towards the final word, which was presented as a picture. Picture names varied in their frequency of occurrence in the language. Naming latencies and electrophysiological responses were examined as a function of context and lexical frequency. Lexical frequency is an index of our cumulative learning experience with words, so lexical-frequency effects most likely reflect access to memory representations for words. Pictures were named faster with constraining than nonconstraining contexts. Associated with this effect, starting around 400 ms pre-picture presentation, oscillatory power between 8 and 30 Hz was lower for constraining relative to nonconstraining contexts. Furthermore, pictures were named faster with high-frequency than low-frequency names, but only for nonconstraining contexts, suggesting differential ease of memory access as a function of sentential context. Associated with the lexical-frequency effect, starting around 500 ms pre-picture presentation, oscillatory power between 4 and 10 Hz was higher for high-frequency than for low-frequency names, but only for constraining contexts. Our results characterise electrophysiological responses associated with lexical frequency and sentential constraint in spoken word production, and point to new avenues for studying these fundamental factors in language production.