Publications

Abstract

Speakers sometimes produce lexical errors, such as saying “salt” instead of “pepper.” This study aimed to better understand the origin of lexical errors by assessing whether they arise from a hasty selection and premature decision to speak (premature selection hypothesis) or from momentary attentional disengagement from the task (attentional lapse hypothesis). We analyzed data from a speeded picture naming task (Lampe et al., 2023) and investigated whether lexical errors are produced as fast as target (i.e., correct) responses, thus arising from premature selection, or whether they are produced more slowly than target responses, thus arising from lapses of attention. Using ex-Gaussian analyses, we found that lexical errors were slower than targets in the tail, but not in the normal part of the response time distribution, with the tail effect primarily resulting from errors that were not coordinates, that is, members of the target’s semantic category. Moreover, we compared the coordinate errors and target responses in terms of their word-intrinsic properties and found that they were overall more frequent, shorter, and acquired earlier than targets. Given the present findings, we conclude that coordinate errors occur due to a premature selection but in the context of intact attentional control, following the same lexical constraints as targets, while other errors, given the variability in their nature, may vary in their origin, with one potential source being lapses of attention.

Abstract

Decreases in oscillatory alpha- and beta-band power have been consistently found in spoken-word production. These have been linked to both motor preparation and conceptual-lexical retrieval processes. However, the observed power decreases have a broad frequency range that spans two “classic” (sensorimotor) bands: alpha and beta. It remains unclear whether alpha- and beta-band power decreases contribute independently when a spoken word is planned. Using a re-analysis of existing magnetoencephalography data, we probed whether the effects in alpha and beta bands are spatially distinct. Participants read a sentence that was either constraining or non-constraining toward the final word, which was presented as a picture. In separate blocks participants had to name the picture or score its predictability via button press. Irregular-resampling auto-spectral analysis (IRASA) was used to isolate the oscillatory activity in the alpha and beta bands from the background 1-over-f spectrum. The sources of alpha- and beta-band oscillations were localized based on the participants’ individualized peak frequencies. For both tasks, alpha- and beta-power decreases overlapped in left posterior temporal and inferior parietal cortex, regions that have previously been associated with conceptual and lexical processes. The spatial distributions of the alpha and beta power effects were spatially similar in these regions to the extent we could assess it. By contrast, for left frontal regions, the spatial distributions differed between alpha and beta effects. Our results suggest that for conceptual-lexical retrieval, alpha and beta oscillations do not dissociate spatially and, thus, are distinct from the classical sensorimotor alpha and beta oscillations.

Abstract

In conversation, speech planning can overlap with listening to the interlocutor. It has been
postulated that once there is enough information to formulate a response, planning is initiated
and the response is maintained in working memory. Concurrently, the auditory input is
monitored for the turn end such that responses can be launched promptly. In three EEG
experiments, we aimed to identify the neural signature of phonological planning and monitoring
by comparing delayed responding to not responding (reading aloud, repetition and lexical
decision). These comparisons consistently resulted in a sustained positivity and beta power
reduction over posterior regions. We argue that these effects reflect attention to the sequence
end. Phonological planning and maintenance were not detected in the neural signature even
though it is highly likely these were taking place. This suggests that EEG must be used cautiously
to identify response planning when the neural signal is overridden by attention effects

Abstract

Changes in brain organization following damage are commonly observed, but they remain poorly understood. These changes are often studied with imaging techniques that overlook the temporal granularity at which language processes occur. By contrast, electrophysiological measures provide excellent temporal resolution. To test the suitability of magnetoencephalography (MEG) to track language-related neuroplasticity, the present study aimed at establishing the spectro-temporo-spatial across-session consistency of context-driven picture naming in healthy individuals, using MEG in two test–retest sessions. Spectro-temporo-spatial test–retest consistency in a healthy population is a prerequisite for studying neuronal changes in clinical populations over time. For this purpose, 15 healthy speakers were tested with MEG while performing a context-driven picture-naming task at two time points. Participants read a sentence missing the final word and named a picture completing the sentence. Sentences were constrained or unconstrained toward the picture, such that participants could either retrieve the picture name through sentence context (constrained sentences), or could only name it after the picture appeared (unconstrained sentences). The context effect (constrained versus unconstrained) in picture-naming times had a strong effect size and high across-session consistency. The context MEG results revealed alpha–beta power decreases (10–20 Hz) in the left temporal and inferior parietal lobule that were consistent across both sessions. As robust spectro-temporo-spatial findings in a healthy population are required for working toward longitudinal patient studies, we conclude that using context-driven language production and MEG is a suitable way to examine language-related neuroplasticity after brain damage.

Abstract

Flexible language use requires coordinated functioning of two systems: conceptual representations and control. The interaction between the two systems can be observed when people are asked to match a word to a picture. Participants are slower and less accurate for related word-picture pairs (word: banana, picture: apple) relative to unrelated pairs (word: banjo, picture: apple). The mechanism underlying interference however is still unclear. We analyzed word-picture matching (WPM) performance of patients with stroke-induced lesions to the left-temporal (N = 5) or left-frontal cortex (N = 5) and matched controls (N = 12) using the drift diffusion model (DDM). In DDM, the process of making a decision is described as the stochastic accumulation of evidence towards a response. The parameters of the DDM model that characterize this process are decision threshold, drift rate, starting point and non-decision time, each of which bears cognitive interpretability. We compared the estimated model parameters from controls and patients to investigate the mechanisms of WPM interference. WPM performance in controls was explained by the amount of information needed to make a decision (decision threshold): a higher threshold was associated with related word-picture pairs relative to unrelated ones. No difference was found in the quality of the evidence (drift rate). This suggests an executive rather than semantic mechanism underlying WPM interference. Both patients with temporal and frontal lesions exhibited both increased drift rate and decision threshold for unrelated pairs relative to related ones. Left-frontal and temporal damage affected the computations required by WPM similarly, resulting in systematic deficits across lexical-semantic memory and executive functions. These results support a diverse but interactive role of lexical-semantic memory and semantic control mechanisms.