Anna Soveri

Effects of Working-Memory Training on Striatal Dopamine Release

A cognitive training program that improves working memory is associated with increased dopamine release during task performance. Updating of working memory has been associated with striato-frontal brain regions and phasic dopaminergic neurotransmission. We assessed raclopride binding to striatal dopamine (DA) D2 receptors during a letter-updating task and a control condition before and after 5 weeks of updating training. Results showed that updating affected DA activity before training and that training further increased striatal DA release during updating. These findings highlight the pivotal role of transient neural processes associated with D2 receptor activity in working memory.

Is there a relationship between language switching and executive functions in bilingualism? Introducing a within-group analysis approach

Several studies have suggested a bilingual advantage in executive functions, presumably due to bilinguals’ massive practice with language switching that requires executive resources, but the results are still somewhat controversial. Previous studies are also plagued by the inherent limitations of a natural groups design where the participant groups are bound to differ in many ways in addition to the variable used to classify them. In an attempt to introduce a complementary analysis approach, we employed multiple regression to study whether the performance of 30- to 75-year-old Finnish–Swedish bilinguals (N = 38) on tasks measuring different executive functions (inhibition, updating, and set shifting) could be predicted by the frequency of language switches in everyday life (as measured by a language switching questionnaire), L2 age of acquisition, or by the self-estimated degree of use of both languages in everyday life. Most consistent effects were found for the set shifting task where a higher rate of everyday language switches was related to a smaller mixing cost in errors. Mixing cost is thought to reflect top-down management of competing task sets, thus resembling the bilingual situation where decisions of which language to use has to be made in each conversation. These findings provide additional support to the idea that some executive functions in bilinguals are affected by a lifelong experience in language switching and, perhaps even more importantly, suggest a complementary approach to the study of this issue.

Working memory training revisited: A multi-level meta-analysis of n-back training studies

The efficacy of working memory (WM) training has been a controversial and hotly debated issue during the past years. Despite a large number of training studies and several meta-analyses, the matter has not yet been solved. We conducted a multi-level meta-analysis on the cognitive transfer effects in healthy adults who have been administered WM updating training with n-back tasks, the most common experimental WM training paradigm. Thanks to this methodological approach that has not been employed in previous meta-analyses in this field, we were able to include effect sizes from all relevant tasks used in the original studies. Altogether 203 effect sizes were derived from 33 published, randomized, controlled trials. In contrast to earlier meta-analyses, we separated task-specific transfer (here untrained n-back tasks) from other WM transfer tasks. Two additional cognitive domains of transfer that we analyzed consisted of fluid intelligence (Gf) and cognitive control tasks. A medium-sized transfer effect was observed to untrained n-back tasks. For other WM tasks, Gf, and cognitive control, the effect sizes were of similar size and very small. Moderator analyses showed no effects of age, training dose, training type (single vs. dual), or WM and Gf transfer task contents (verbal vs. visuospatial). We conclude that a substantial part of transfer following WM training with the n-back task is task-specific and discuss the implications of the results to WM training research.

Bilingual advantage in attentional control: Evidence from the forced-attention dichotic listening paradigm

It has been claimed that due to their experience in controlling two languages, bilinguals exceed monolinguals in certain executive functions, especially inhibition of task-irrelevant stimuli. Here we investigated the effects of bilingualism on an executive phonological task, namely the forced-attention dichotic listening task with syllabic stimuli. In the standard non-forced (NF) condition, the participants reported all syllables they heard, be it from the right or the left ear. In the forced-right (FR) and forced-left (FL) attention conditions, they had to direct their attention to either the right- or the left-ear stimulus and inhibit information coming to the other ear. We tested Finnish monolinguals and early simultaneous Finnish–Swedish bilinguals from two age groups: (30–50-year-olds and 60–74-year-olds). The results showed that the bilinguals performed better than the monolinguals in the FR and FL conditions. This supports the idea of a bilingual advantage in directing attention and inhibiting task-irrelevant stimuli.

Language-specific activations in the brain: Evidence from inflectional processing in bilinguals

Abstract We investigated the neural correlates of morphological processing in two structurally different languages within the same individuals. An interesting contrast is provided by Finnish and Swedish where most inflected Finnish nouns tend to show a processing cost (i.e., longer reaction times and higher error rates) compared to monomorphemic nouns, while most inflected Swedish nouns do not show such a cost. This has been taken as evidence for morphological decomposition in Finnish and full-form recognition of inflected nouns in Swedish. While most previous imaging studies had studied the two morphological processing routes (decomposition and storage) within the same language and often by comparing regular vs. irregular forms, we employed a cross-language setting and a direct contrast between morphologically complex vs. simple words. We subjected high-proficient Finnish–Swedish early bilinguals to a visual lexical decision task with inflected vs. monomorphemic Finnish and Swedish nouns while measuring their brain activation by fMRI. The participants showed an inflectional processing cost and related left fronto-temporal activation increases in Finnish but not in Swedish. This suggests a language-specific processing difference in the brain, possibly reflecting the structural difference between these two languages. In addition, the activations appeared in regions related to lexical-semantic and syntactic processing rather than visual word form processing. This is in line with previous studies in Finnish, suggesting that the morphological processing cost stems primarily from the later, semantic-syntactic stage.

Effects of working memory load on processing of sounds and meanings of words in aphasia

Background: Language performance in aphasia can vary depending on several variables such as stimulus characteristics and task demands. This study focuses on the degree of verbal working memory (WM) load inherent in the language task and how this variable affects language performance by individuals with aphasia. Aims: The first aim was to identify the effects of increased verbal WM load on the performance of judgements of semantic similarity (synonymy) and phonological similarity (rhyming). The second aim was to determine if any of the following abilities could modulate the verbal WM load effect: semantic or phonological access, semantic or phonological short-term memory (STM), and any of the following executive processing abilities: inhibition, verbal WM updating, and set shifting. Method & Procedures: A total of 31 individuals with aphasia and 11 controls participated in this study. They were administered a synonymy judgement task and a rhyming judgement task under high and low verbal WM load conditions that were compared to each other. In a second set of analyses multiple regression was used to identify which factors (as noted above) modulated the verbal WM load effect. Outcomes & Results: For participants with aphasia, increased verbal WM load significantly reduced accuracy of performance on synonymy and rhyming judgements. Better performance in the low verbal WM load conditions was evident even after correcting for chance. The synonymy task included concrete and abstract word triplets. When these were examined separately the verbal WM load effect was significant for the abstract words, but not the concrete words. The same pattern was observed in the performance of the control participants. Additionally, the second set of analyses revealed that semantic STM and one executive function, inhibition ability, emerged as the strongest predictors of the verbal WM load effect in these judgement tasks for individuals with aphasia. Conclusions: The results of this study have important implications for diagnosis and treatment of aphasia. As the roles of verbal STM capacity, executive functions and verbal WM load in language processing are better understood, measurements of these variables can be incorporated into our diagnostic protocols. Moreover, if cognitive abilities such as STM and executive functions support language processing and their impairment adversely affects language function, treating them directly in the context of language tasks should translate into improved language function.

Modulation of Auditory Attention by Training : Evidence From Dichotic Listening

We studied the effects of training on auditory attention in healthy adults with a speech perception task involving dichotically presented syllables. Training involved bottom-up manipulation (facilitating responses from the harder-to-report left ear through a decrease of right-ear stimulus intensity), top-down manipulation (focusing attention on the left-ear stimuli through instruction), or their combination. The results showed significant training-related effects for top-down training. These effects were evident as higher overall accuracy rates in the forced-left dichotic listening (DL) condition that sets demands on attentional control, as well as a response shift toward left-sided reports in the standard DL task. Moreover, a transfer effect was observed in an untrained auditory-spatial attention task involving bilateral stimulation where top-down training led to a relatively stronger focus on left-sided stimuli. Our results indicate that training of attentional control can modulate the allocation of attention in the auditory space in adults. Malleability of auditory attention in healthy adults raises the issue of potential training gains in individuals with attentional deficits.

Is Bilingualism Associated With Enhanced Executive Functioning in Adults? A Meta-Analytic Review

Because of enduring experience of managing two languages, bilinguals have been argued to develop superior executive functioning compared with monolinguals. Despite extensive investigation, there is, however, no consensus regarding the existence of such a bilingual advantage. Here we synthesized comparisons of bilinguals’ and monolinguals’ performance in six executive domains using 891 effect sizes from 152 studies on adults. We also included unpublished data, and considered the potential influence of a number of study-, task-, and participant-related variables. Before correcting estimates for observed publication bias, our analyses revealed a very small bilingual advantage for inhibition, shifting, and working memory, but not for monitoring or attention. No evidence for a bilingual advantage remained after correcting for bias. For verbal fluency, our analyses indicated a small bilingual disadvantage, possibly reflecting less exposure for each individual language when using two languages in a balanced manner. Moreover, moderator analyses did not support theoretical presuppositions concerning the bilingual advantage. We conclude that the available evidence does not provide systematic support for the widely held notion that bilingualism is associated with benefits in cognitive control functions in adults.

Transfer after Working Memory Updating Training.

During the past decade, working memory training has attracted much interest. However, the training outcomes have varied between studies and methodological problems have hampered the interpretation of results. The current study examined transfer after working memory updating training by employing an extensive battery of pre-post cognitive measures with a focus on near transfer. Thirty-one healthy Finnish young adults were randomized into either a working memory training group or an active control group. The working memory training group practiced with three working memory tasks, while the control group trained with three commercial computer games with a low working memory load. The participants trained thrice a week for five weeks, with one training session lasting about 45 minutes. Compared to the control group, the working memory training group showed strongest transfer to an n-back task, followed by working memory updating, which in turn was followed by active working memory capacity. Our results support the view that working memory training produces near transfer effects, and that the degree of transfer depends on the cognitive overlap between the training and transfer measures.

Effects of Auditory Attention Training with the Dichotic Listening Task: Behavioural and Neurophysiological Evidence

Facilitation of general cognitive capacities such as executive functions through training has stirred considerable research interest during the last decade. Recently we demonstrated that training of auditory attention with forced attention dichotic listening not only facilitated that performance but also generalized to an untrained attentional task. In the present study, 13 participants underwent a 4-week dichotic listening training programme with instructions to report syllables presented to the left ear (FL training group). Another group (n = 13) was trained using the non-forced instruction, asked to report whichever syllable they heard the best (NF training group). The study aimed to replicate our previous behavioural results, and to explore the neurophysiological correlates of training through event-related brain potentials (ERPs). We partially replicated our previous behavioural training effects, as the FL training group tended to show more allocation of auditory spatial attention to the left ear in a standard dichotic listening task. ERP measures showed diminished N1 and enhanced P2 responses to dichotic stimuli after training in both groups, interpreted as improvement in early perceptual processing of the stimuli. Additionally, enhanced anterior N2 amplitudes were found after training, with relatively larger changes in the FL training group in the forced-left condition, suggesting improved top-down control on the trained task. These results show that top-down cognitive training can modulate the left-right allocation of auditory spatial attention, accompanied by a change in an evoked brain potential related to cognitive control.