Publications

Abstract

There is a range of variability in the speed with which a single speaker will produce the same word from one instance to another. Individual differences studies have shown that the speed of production and the ability to maintain attention are related. This study investigated whether fluctuations in production latencies can be explained by spontaneous fluctuations in speakers' attention just prior to initiating speech planning. A relationship between individuals' incidental attentional state and response performance is well attested in visual perception, with lower prestimulus alpha power associated with faster manual responses. Alpha is thought to have an inhibitory function: Low alpha power suggests less inhibition of a specific brain region, whereas high alpha power suggests more inhibition. Does the same relationship hold for cognitively demanding tasks such as word production? In this study, participants named pictures while EEG was recorded, with alpha power taken to index an individual's momentary attentional state. Participants' level of alpha power just prior to picture presentation and just prior to speech onset predicted subsequent naming latencies. Specifically, higher alpha power in the motor system resulted in faster speech initiation. Our results suggest that one index of a lapse of attention during speaking is reduced inhibition of motor-cortical regions: Decreased motor-cortical alpha power indicates reduced inhibition of this area while early stages of production planning unfold, which leads to increased interference from motor-cortical signals and longer naming latencies. This study shows that the language production system is not impermeable to the influence of attention.

Abstract

Bilinguals usually select the right language to speak for the particular context they are in, but sometimes the nontarget language intrudes. Despite a large body of research into language selection and language control, it remains unclear where intrusion errors originate from. These errors may be due to incorrect selection of the nontarget language at the conceptual level, or be a consequence of erroneous word selection (despite correct language selection) at the lexical level. We examined the former possibility in two language switching experiments using a manipulation that supposedly affects language selection on the conceptual level, namely whether the conversational language context was associated with the target language (congruent) or with the alternative language (incongruent) on a trial. Both experiments showed that language intrusion errors occurred more often in incongruent than in congruent contexts, providing converging evidence that language selection during concept preparation is one driving force behind language intrusion.

Abstract

Bilingual speakers have to control their languages to avoid interference, which may be achieved by enhancing the target language and/or inhibiting the nontarget language. Previous research suggests that bilinguals use inhibition (e.g., Jackson et al., 2001), which should be reflected in the N2 component of the event-related potential (ERP) in the EEG. In the current study, we investigated the dynamics of inhibitory control by measuring the N2 during language switching and repetition in bilingual picture naming. Participants had to name pictures in Dutch or English depending on the cue. A run of same-language trials could be short (two or three trials) or long (five or six trials). We assessed whether RTs and N2 changed over the course of same-language runs, and at a switch between languages. Results showed that speakers named pictures more quickly late as compared to early in a run of same-language trials. Moreover, they made a language switch more quickly after a long run than after a short run. This run-length effect was only present in the first language (L1), not in the second language (L2). In ERPs, we observed a widely distributed switch effect in the N2, which was larger after a short run than after a long run. This effect was only present in the L2, not in the L1, although the difference was not significant between languages. In contrast, the N2 was not modulated during a same-language run. Our results suggest that the nontarget language is inhibited at a switch, but not during the repeated use of the target language.

Abstract

Whereas it has long been assumed that most linguistic processes underlying language production happen automatically, accumulating evidence suggests that some form of attention is required. Here, we investigated the contribution of sustained attention, which is the ability to maintain alertness over time. First, the sustained attention ability of participants was measured using auditory and visual continuous performance tasks. Next, the participants described pictures using simple noun phrases while their response times (RTs) and gaze durations were measured. Earlier research has suggested that gaze duration reflects language planning processes up to and including phonological encoding. Individual differences in sustained attention ability correlated with individual differences in the magnitude of the tail of the RT distribution, reflecting the proportion of very slow responses, but not with individual differences in gaze duration. These results suggest that language production requires sustained attention, especially after phonological encoding.

Abstract

It has previously been shown that language production, performed simultaneously with a nonlinguistic task, involves sustained attention. Sustained attention concerns the ability to maintain alertness over time. Here, we aimed to replicate the previous finding by showing that individuals call upon sustained attention when they plan single noun phrases (e.g., "the carrot") and perform a manual arrow categorization task. In addition, we investigated whether speakers also recruit sustained attention when they produce conjoined noun phrases (e.g., "the carrot and the bucket") describing two pictures, that is, when both the first and second task are linguistic. We found that sustained attention correlated with the proportion of abnormally slow phrase-production responses. Individuals with poor sustained attention displayed a greater number of very slow responses than individuals with better sustained attention. Importantly, this relationship was obtained both for the production of single phrases while performing a nonlinguistic manual task, and the production of noun phrase conjunctions in referring to two spatially separated objects. Inhibition and updating abilities were also measured. These scores did not correlate with our measure of sustained attention, suggesting that sustained attention and executive control are distinct. Overall, the results suggest that planning conjoined noun phrases involves sustained attention, and that language production happens less automatically than has often been assumed.

Abstract

Two major components form the basis of spoken word production: the access of conceptual and lexical/phonological information in long-term memory, and motor preparation and execution of an articulatory program. Whereas the motor aspects of word production have been well characterized as reflected in alpha-beta desynchronization, the memory aspects have remained poorly understood. Using magnetoencephalography, we investigated the neurophysiological signature of not only motor but also memory aspects of spoken-word production. Participants named or judged pictures after reading sentences. To probe the involvement of the memory component, we manipulated sentence context. Sentence contexts were either constraining or nonconstraining toward the final word, presented as a picture. In the judgment task, participants indicated with a left-hand button press whether the picture was expected given the sentence. In the naming task, they named the picture. Naming and judgment were faster with constraining than nonconstraining contexts. Alpha-beta desynchronization was found for constraining relative to nonconstraining contexts pre-picture presentation. For the judgment task, beta desynchronization was observed in left posterior brain areas associated with conceptual processing and in right motor cortex. For the naming task, in addition to the same left posterior brain areas, beta desynchronization was found in left anterior and posterior temporal cortex (associated with memory aspects), left inferior frontal cortex, and bilateral ventral premotor cortex (associated with motor aspects). These results suggest that memory and motor components of spoken word production are reflected in overlapping brain oscillations in the beta band.

Abstract

Previous dual-task studies examining the locus of semantic interference of distractor words in picture naming have obtained diverging results. In these studies, participants manually responded to tones and named pictures while ignoring distractor words (picture-word interference, PWI) with varying stimulus onset asynchrony (SOA) between tone and PWI stimulus. Whereas some studies observed no semantic interference at short SOAs, other studies observed effects of similar magnitude at short and long SOAs. The absence of semantic interference in some studies may perhaps be due to better reading skill of participants in these than in the other studies. According to such a reading-ability account, participants' reading skill should be predictive of the magnitude of their interference effect at short SOAs. To test this account, we conducted a dual-task study with tone discrimination and PWI tasks and measured participants' reading ability. The semantic interference effect was of similar magnitude at both short and long SOAs. Participants' reading ability was predictive of their naming speed but not of their semantic interference effect, contrary to the reading ability account. We conclude that the magnitude of semantic interference in picture naming during dual-task performance does not depend on reading skill.

Abstract

In two studies, we examined whether explicit distractors are necessary and sufficient toevoke selective inhibition in three naming tasks: the semantic blocking, picture-word interference, and color-word Stroop task. Delta plots were used to quantify the size of the interference effects as a function of reaction time (RT). Selective inhibition was operationalized as the decrease in the size of the interference effect as a function of naming RT. For all naming tasks, mean naming RTs were significantly longer in the interference condition than in a control condition. The slopes of the interference effects for the longest naming RTs correlated with the magnitude of the mean interference effect in both the semantic blocking task and the picture-word interference task, suggesting that selective inhibition was involved to reduce the interference from strong semantic competitors either invoked by a single explicit competitor or strong implicit competitors in picture naming. However, there was no correlation between the slopes and the mean interference effect in the Stroop task, suggesting less importance of selective inhibition in this task despite explicit distractors. Whereas the results of the semantic blocking task suggest that an explicit distractor is not necessary for triggering inhibition, the results of the Stroop task suggest that such a distractor is not sufficient for evoking inhibition either.

Abstract

Four experiments examined crossmodal versions of the Stroop task in order (1) to look for Stroop asymmetries in color naming, spoken-word naming, and written-word naming and to evaluate the time course of these asymmetries, and (2) to compare these findings to current models of the Stroop effect. Participants named color patches while ignoring spoken color words presented with an onset varying from 300 msec before to 300 msec after the onset of the color (Experiment 1), or they named the spoken words and ignored the colors (Experiment 2). A secondary visual detection task assured that the participants looked at the colors in both tasks. Spoken color words yielded Stroop effects in color naming, but colors did not yield an effect in spoken-word naming at any stimulus onset asynchrony. This asymmetry in effects was obtained with equivalent color- and spoken-word-naming latencies. Written color words yielded a Stroop effect in naming spoken words (Experiment 3), and spoken color words yielded an effect in naming written words (Experiment 4). These results were interpreted as most consistent with an architectural account of the color-word Stroop asymmetry, in contrast with discriminability and pathway strength accounts.