Chantel S. Prat

Working memory and Stroop interference: An individual differences investigation

We investigated the claim that individual differences in working-memory capacity reflect limitations on the ability to inhibit task-irrelevant information and/or to maintain activation in the face of distracting or interfering events. Specifically, we investigated whether high- and low-capacity individuals differed in their susceptibility to interference on the Stroop task and whether high-capacity individuals employed a strategy for minimizing Stroop interference. In Experiment 1, we found that high-capacity participants showed substantial interference when conflict trials were infrequent, but almost no interference when conflict trials were frequent. In contrast, low-capacity participants showed substantial interference irrespective of the proportion of conflict trials. In Experiment 2, we found that high-capacity participants experienced substantial negative priming, slow responses when the to-be-named color was the irrelevant word on the previous trial. We discuss these results and their implications for highcapacity individuals’ ability to reduce Stroop interference in light of both inhibitory and noninhibitory accounts of negative priming.

Language Experience and the Organization of Brain Activity to Phonetically Similar Words: ERP Evidence from 14- and 20-Month-Olds

The ability to discriminate phonetically similar speech sounds is evident quite early in development. However, inexperienced word learners do not always use this information in processing word meanings Stager & Werker (1997). Nature, 388, 381382. The present study used event-related potentials (ERPs) to examine developmental changes from 14 to 20 months in brain activity important in processing phonetic detail in the context of meaningful words. ERPs were compared to three types of words: words whose meanings were known by the child (e.g., bear), nonsense words that differed by an initial phoneme (e.g., gare), and nonsense words that differed from the known words by more than one phoneme (e.g., kobe). These results supported the behavioral findings suggesting that inexperienced word learners do not use information about phonetic detail when processing word meanings. For the 14-month-olds, ERPs to known words (e.g., bear) differed from ERPs to phonetically dissimilar nonsense words (e.g., kobe), but did not differ from ERPs to phonetically similar nonsense words (e.g., gare), suggesting that known words and similar mispronunciations were processed as the same word. In contrast, for experienced word learners (i.e., 20-month-olds), ERPs to known words (e.g., bear) differed from those to both types of nonsense words (gare and kobe). Changes in the lateral distribution of ERP differences to known and unknown (nonce) words between 14 and 20 months replicated previous findings. The findings suggested that vocabulary development is an important factor in the organization of neural systems linked to processing phonetic detail within the context of word comprehension.

Individual differences in sentence comprehension: A functional magnetic resonance imaging investigation of syntactic and lexical processing demands

Language comprehension is neurally underpinned by a network of collaborating cortical processing centers; individual differences in comprehension must be related to some set of this networks properties. This study investigated the neural bases of individual differences during sentence comprehension by examining the networks response to two variations in processing demands: reading sentences containing words of high versus low lexical frequency and having simpler versus more complex syntax. In a functional magnetic resonance imaging study, readers who were independently identified as having high or low working memory capacity for language exhibited three differentiating properties of their language network, namely, neural efficiency, adaptability, and synchronization. First, greater efficiency (defined as a reduction in activation associated with improved performance) was manifested as less activation in the bilateral middle frontal and right lingual gyri in high-capacity readers. Second, increased adaptability was indexed by larger lexical frequency effects in high-capacity readers across bilateral middle frontal, bilateral inferior occipital, and right temporal regions. Third, greater synchronization was observed in high-capacity readers between left temporal and left inferior frontal, left parietal, and right occipital regions. Synchronization interacted with adaptability, such that functional connectivity remained constant or increased with increasing lexical and syntactic demands in high-capacity readers, whereas low-capacity readers either showed no reliable differentiation or a decrease in functional connectivity with increasing demands. These results are among the first to relate multiple cortical network properties to individual differences in reading capacity and suggest a more general framework for understanding the relation between neural function and individual differences in cognitive performance.

Exploring the Neural Dynamics Underpinning Individual Differences in Sentence Comprehension

This study used functional magnetic resonance imaging to investigate individual differences in the neural underpinnings of sentence comprehension, with a focus on neural adaptability (dynamic configuration of neural networks with changing task demands). Twenty-seven undergraduates, with varying working memory capacities and vocabularies, read sentences that were either syntactically simple or complex under conditions of varying extrinsic working memory demands (sentences alone or preceded by to-be-remembered words or nonwords). All readers showed greater neural adaptability when extrinsic working memory demands were low, suggesting that adaptability is related to resource availability. Higher capacity readers showed greater neural adaptability (greater increase in activation with increasing syntactic complexity) across conditions than did lower capacity readers. Higher capacity readers also showed better maintenance of or increase in synchronization of activation between brain regions as tasks became more demanding. Larger vocabulary was associated with more efficient use of cortical resources (reduced activation in frontal regions) in all conditions but was not associated with greater neural adaptability or synchronization. The distinct characterizations of verbal working memory capacity and vocabulary suggest that dynamic facets of brain function such as adaptability and synchronization may underlie individual differences in more general information processing abilities, whereas neural efficiency may more specifically reflect individual differences in language experience.

A Direct Brain-to-Brain Interface in Humans

We describe the first direct brain-to-brain interface in humans and present results from experiments involving six different subjects. Our non-invasive interface, demonstrated originally in August 2013, combines electroencephalography (EEG) for recording brain signals with transcranial magnetic stimulation (TMS) for delivering information to the brain. We illustrate our method using a visuomotor task in which two humans must cooperate through direct brain-to-brain communication to achieve a desired goal in a computer game. The brain-to-brain interface detects motor imagery in EEG signals recorded from one subject (the “sender”) and transmits this information over the internet to the motor cortex region of a second subject (the “receiver”). This allows the sender to cause a desired motor response in the receiver (a press on a touchpad) via TMS. We quantify the performance of the brain-to-brain interface in terms of the amount of information transmitted as well as the accuracies attained in (1) decoding the sender’s signals, (2) generating a motor response from the receiver upon stimulation, and (3) achieving the overall goal in the cooperative visuomotor task. Our results provide evidence for a rudimentary form of direct information transmission from one human brain to another using non-invasive means.

Bilingual brain training: A neurobiological framework of how bilingual experience improves executive function

Individuals who develop bilingually typically outperform monolinguals on tests of executive functions. This advantage likely reflects enhanced prefrontal function, but the mechanisms that underlie this improvement are still poorly understood. This article describes a theory on the nature of the neural underpinnings of improved executive function in bilinguals. Specifically, we propose that growing up in a bilingual environment trains a gating system in the striatum that flexibly routes information to the prefrontal cortex. This article is divided into three sections. Firstly, literature establishing a three-way connection between bilingualism, executive function, and fronto-striatal loops is summarized. Secondly, a computational model of information processing in the basal ganglia is described, illustrating how the striatal nuclei function to transfer information between cortical regions under prerequisite conditions. Finally, this model is extended to describe how bilingualism may “train the brain,” enabling improved performance under conditions of competitive information selection during information transfer. Theoretical implications and predictions of this theory are discussed.

The bilingual brain: Flexibility and control in the human cortex

The goal of the present review is to discuss recent cognitive neuroscientific findings concerning bilingualism. Three interrelated questions about the bilingual brain are addressed: How are multiple languages represented in the brain? how are languages controlled in the brain? and what are the real-world implications of experience with multiple languages? The review is based on neuroimaging research findings about the nature of bilingual processing, namely, how the brain adapts to accommodate multiple languages in the bilingual brain and to control which language should be used, and when. We also address how this adaptation results in differences observed in the general cognition of bilingual individuals. General implications for models of human learning, plasticity, and cognitive control are discussed.

The importance of knowledge in vivid text memory: An individual-differences investigation of recollection and familiarity

The goal of this study was to examine how individual variation in readers’ skills and, in particular, their background knowledge about a text are related to text memory. Recollection and familiarity estimates were obtained from remember and know judgments to text ideas. Recollection estimates to old items were predicted by readers’ background knowledge, but not by other comprehension-related factors, such as word-decoding skill and working memory capacity. False alarms involving recollection of new items (inferences) were diminished as a function of verbal ability, working memory capacity, and reasoning but increased as a function of background knowledge. The results suggest that recollection indexes the reader’s ability to construct a text representation in which text ideas are integrated with relevant domain knowledge. Moreover, these results highlight the importance of background knowledge in explaining individual variation in comprehension and memory for text.

Bilingualism trains specific brain circuits involved in flexible rule selection and application

Bilingual individuals have been shown to outperform monolinguals on a variety of tasks that measure non-linguistic executive functioning, suggesting that some facets of the bilingual experience give rise to generalized improvements in cognitive performance. The current study investigated the hypothesis that such advantage in executive functioning arises from the need to flexibly select and apply rules when speaking multiple languages. Such flexible behavior may strengthen the functioning of the fronto-striatal loops that direct signals to the prefrontal cortex. To test this hypothesis, we compared behavioral and brain data from proficient bilinguals and monolinguals who performed a Rapid Instructed Task Learning paradigm, which requires behaving according to ever-changing rules. Consistent with our hypothesis, bilinguals were faster than monolinguals when executing novel rules, and this improvement was associated with greater modulation of activity in the basal ganglia. The implications of these findings for language and executive function research are discussed herein.

Individual differences in syntactic ambiguity resolution: readers vary in their use of plausibility information.

Two experiments investigated the relation between individual differences in working memory capacity and differences in the efficiency of syntactic processing. In one experiment, readers comprehended sentences containing main-verb/reduced-relative ambiguities that all resolved to the reduced-relative interpretation. High-span (but not low-span) readers processed sentences more slowly when the sentences were biased to the preferred, main-verb interpretation than when they were biased to the reduced-relative interpretation. Moreover, high-span (but not lowspan) readers used information about the plausibility of the different interpretations even though low-span readers appeared to possess the requisite knowledge. In Experiment 2, readers received intensive exposure to sentences with main-verb/reduced-relative ambiguities. Exposure enhanced low-span readers’ use of plausibility information. Moreover, the effect of exposure generalized to sentences that were not included in the training materials.