Foreign Language Learning in Older Adults: Anatomical and Cognitive Markers of Vocabulary Learning Success.

In recent years, foreign language learning (FLL) has been proposed as a possible cognitive intervention for older adults. However, the brain network and cognitive functions underlying FLL has remained largely unconfirmed in older adults. In particular, older and younger adults have markedly different cognitive profile-while older adults tend to exhibit decline in most cognitive domains, their semantic memory usually remains intact. As such, older adults may engage the semantic functions to a larger extent than the other cognitive functions traditionally considered the most important (e.g., working memory capacity and phonological awareness). Using anatomical measurements and a cognitive test battery, the present study examined this hypothesis in twenty cognitively normal older adults (58-69 years old), who participated in a two-month Italian learning programme. Results showed that the immediate learning success and long-term retention of Italian vocabularies were most consistently predicted by the anatomical measures of the left pars orbitalis and left caudal middle frontal cortex, which are implicated in semantic and episodic memory functions. Convergent evidence was also found based on the pattern of cognitive associations. Our results are consistent with a prominent role of semantic and episodic memory functions in vocabulary learning in older learners.

Can inhibition deficit hypothesis account for age-related differences in semantic fluency? Converging evidence from Stroop color and word test and an ERP flanker task.

The inhibition deficit hypothesis (IDH) proposed that individual differences in inhibitory control is an underlying reason for age-related language decline. This study examined whether the hypothesis holds within the domain of lexico-semantic retrieval. Sixty-six older adults aged 60-79 were tested in a semantic fluency task comprising 16 categories; each response was classified as automatic or controlled. Also, Stroop color and word test and an ERP flanker task were employed to yield both behavioral and neural measures of inhibitory control. Mixed-effects modelling revealed that the number of controlled (but not automatic) responses was negatively associated with age. This interaction could be partially accounted for by the behavioral Stroop inhibition score and two neural measures from the ERP flanker task (P2 and Pc amplitudes). These results not only provide converging evidence supporting the IDH, but also demonstrate the involvement of specific inhibitory control components, including attentional control and performance monitoring.

Which cognitive functions subserve clustering and switching in category fluency? Generalisations from an extended set of semantic categories using linear mixed-effects modelling.

Clustering and switching are hypothesised to reflect the automatic and controlled components in category fluency, respectively, but how they are associated with cognitive functions has not been fully elucidated, due to several uncertainties. (1) The conventional scoring method that segregates responses by semantic categories could not optimally dissociate the automatic and controlled components. (2) The temporal structure of individual responses, as characterised by mean retrieval time (MRT) and mean switching time (MST), has seldom been analysed alongside the more well-studied variables, cluster size (CS) and number of switches (NS). (3) Most studies examined only one to a few semantic categories, raising concerns of generalisability. This study built upon a distance-based automatic clustering procedure, referred to as temporal-semantic distance procedure, to thoroughly characterise the category fluency performance. Linear mixed-effects (LME) modelling was applied to re-examine the differential associations of clustering and switching with cognitive functions with a sample of 80 university students. Our results revealed that although lexical retrieval speed (LRS) is clearly the determining factor for effective clustering and switching, matrix reasoning and processing speed also have significant roles to play, possibly in the processes of identifying and validating the semantic relationships. Interestingly, total fluency score was accurately predicted by the four clustering/switching indices alone; including the cognitive variables did not significantly improve the prediction. These findings underline the importance of the clustering and switching indices in explaining the category fluency performance and the cognitive demands in category fluency.

Conflict monitoring in multi-sensory flanker tasks: Effects of cross-modal distractors on the N2 component.

The N2 component is a well-known neural correlate of conflict monitoring (CM), being more negative in the presence of conflicting information in visual conflict tasks. However, whether to-be-ignored auditory distractors can introduce additional conflict remains unknown. In the present work, subjects performed a visual (V) and audiovisual (AV) version of a Go/NoGo flanker task, and responded only if the target arrow pointed toward a pre-specified direction (e.g., left). In the AV task, in which to-be-ignored auditory distractors that were semantically associated with the flankers were concurrently presented, the congruency effect on both RT and N2 amplitude was enhanced, confirming that additional conflict can be brought about by cross-modal distractors at both behavioural and neural levels. Consistent with the hypothesis that N2 amplitude reflects response conflict in visual conflict tasks, within-subject correlation between N2 amplitude and RT was significant in the Go conditions for the V task (congruent/incongruent). However, for the AV task, the correlation was significant only in the congruent condition. These findings suggest that while the cross-modal conflict is registered by the CM process, only part of this conflict could effectively induce response conflict.