Event Abstract

A diffusion model approach to analyzing bilingual older adults’ performance on the Flanker task: The role of left DLPFC

  • 1 University of Melbourne, Australia
  • 2 University of Hong Kong, Hong Kong, SAR China
  • 3 University Vita-Salute San Raffaele, Italy
  • 4 University of Queensland, Australia

Ong et al. (2016) reported diffusion model analyses to test the bilingual advantage in Hong Kong seniors. Diffusion Modelling (Ratcliff, 1978) explains decision-making in terms of a stochastic evidence accumulation process whereby the task decision is driven by sequentially sampling stimuli that provides a quantity of evidence favoring a target response. Information accumulates until threshold. Different parameters will manifest as performance in validated psychological processes that are related to decision-making (Voss, Rothermund, & Voss, 2004). At least four decision parameters called starting point, boundary, separation drift rate and non-decision time can be mapped to cognitive mechanisms to infer underlying processes. The starting parameter is the time that evidence accumulation begins; boundary separation refers to the amount of evidence accumulated before initiating a response; drift rate indicates speed of evidence accumulation toward the decision boundary, which is affected by strength of information on providing evidence towards a response. Finally, non-decision time is the time required by for any cognitive process that is not involved in evidence accumulation, such as perceptual encoding of stimulus and execution of motor response (Voss et al., 2004). Ong et al (2016) found an advantage in non-decision time on incongruent trials in the Flanker task (Fan et al., 2002). Faster non-decision time was observed in the incongruent condition by bilinguals, with no significant difference observed on any other parameters (Ong et al., 2016). Study aims and hypotheses Greater inhibition is required in the incongruent compared to congruent condition on Flanker. We predicted GMV would be correlated more with performance in the incongruent condition than the congruent condition, specifically in brain regions involved in executive control such as anterior cingulate gyrus (ACC), dorsolateral prefrontal cortex (DLPFC), inferior frontal gyrus (IFG), supplementary motor area (SMA), caudate nucleus and sub-thalamic nucleus, putamen and supramarginal gyrus. Furthermore, given that bilingual seniors from Hong Kong have more GMV in some of these regions (Abutalebi et al. 2014), the correlation is expected to be statistically different in bilingual than monolingual speakers. Method Twenty-nine healthy bilinguals (13 males mean age = 63.4; standard deviation [SD] = 5.8) and twenty-seven healthy monolinguals (13 males mean age = 61.9; SD = 6.4) participated. Monolingual controls were recruited from Milan due to the low prevalence of, and difficulty recruiting, monolingual speakers in Hong Kong. Monolinguals in Hong Kong tend to possess lower SES and education. In contrast, monolinguals in Milan were matched on MMSE score, socio-economic status (SES) and level of education (Abutalebi et al., 2015). Milan and Hong Kong are similar cities in that they are both densely populated global economic hubs located in a network defined by a common ethnic and historical identity (Hong Kong in China and Milan in Italy). Culturally, both of these cities have distinct identities in their respective states with clearly defined epistemological, linguistic and pedagogical roots. The Human Research Ethics Committee at the University of Hong Kong approved the study, which formed a larger neurobiological study in Hong Kong and all participants provided informed consent. Flanker stimuli were presented via a computer monitor. Each trial began with a fixation point at the centre of a screen presented for 400 ms, followed by a row of five arrows pointing either left or right for 1700 ms (after this point, the stimulus disappeared; trials longer than 1700 ms were not analysed). Participants were required to identify arrow orientation (left or right) of the central target by pressing a dedicated response button. The flanking arrows (two on the left, and two on the right) could be congruent (same orientation as target), incongruent (opposite orientation to target) or neutral (no arrowhead). The fMRI experiment was carried out with a 3-T Trio MRI scanner in the Department of Diagnostic Radiology, University of Hong Kong. Diffusion model parameters (drift rate, non-decision time, boundary separation and starting point) were estimated by individually fitting each participant's RT distribution data. Three RT distributions (congruent, incongruent and neutral trials) were simultaneously fit per participant. Unique drift rate and non-decision time parameters were estimated for each of the flanker conditions. As there was no manipulation of reward for different response types we assumed an unbiased decision process and set z 1⁄4 a/2 (cf. Voss et al., 2004). Similarly, because the different trial types occurred in a random order and thus prevented systematic trial-by-trial differences in decision criterion, boundary separation was held constant across all flanker trial types. In addition to the standard diffusion model parameters, between-trial drift and non-decision time variability were also estimated (see Ratcliff & Tuerlinckx, 2002). Results and Conclusions For monolinguals, there was a significant correlation between GMV and non-decision time (Ter) in the left DLPFC for the congruent condition (r=-.538 p<0.01 uncorrected), incongruent condition (r=-.54 p<0.01 uncorrected) and the neutral condition (r=-.479 p=0.011 uncorrected). There were no significant correlations for bilinguals (see Figure 1). Better inhibition correlates with DLPFC in a range of studies (Menon et al. 2001). Therefore, greater GMV in this brain region decreases Ter in all conditions for monolinguals. Results from bilinguals are more surprising. Ong et al. (2016) reported an advantage in the incongruent condition for Ter with (the same) bilingual seniors and located effects at the level of attention control and inhibition. The dissociation between an advantage for Ter together with the lack of any relationship with GMV in predicted areas on both congruent and incongruent trials suggests that the DLPFC is redundant in explaining the bilingual advantage at least on the non-decision time parameter. One possibility is that the DLFPC is usurped by deeper structures. This may be due to greater synaptic pruning of excitatory neurons (Bourgeois, et al. 1994) in the DLPFC in bilinguals or more efficient use of LDPFC for alternative processes e.g. for multiple and often competing articulatory plans (Menon et al. 2001).

Figure 1

References

Abutalebi, J., Guidi, L., Borsa, V., Canini, M., Della Rosa, P. A., Parris, B. A., & Weekes, B. S. (2015). Bilingualism provides a neural reserve for aging populations. Neuropsychologia, 69, 201-210.

Bourgeois, J-P., Goldman-Rakic P.S., & Rakic, P. (1994). Synaptogenesis in the prefrontal cortex of Rhesus Monkeys. Cerebral Cortex, 4(1), 78-96.

Fan, J., McCandliss, B. D., Sommer, T., Raz, A., & Posner, M. I. (2002). Testing the efficiency and independence of attentional networks. Journal of Cognitive Neuroscience, 14(3), 340-347.

Menon, V., Adleman, N.E., White, C.D., Glover, G.H., & Reiss, A.L. (2001). Error-related brain activation during a Go/NoGo response inhibition task. Human Brain Mapping, 12(3), 131-43.

Ong, G., Sewell, D. K., Weekes, B., McKague, M., & Abutalebi, J. (2016). A diffusion model approach to analysing the bilingual advantage for the Flanker task: The role of attentional control processes. Journal of Neurolinguistics.

Ratcliff, R. (1978). A theory of memory retrieval. Psychological Review, 85(2), 59-108.

Ratcliff, R., & Smith, P. L. (2004). A comparison of sequential sampling models for two-choice reaction time. Psychological Review, 111(2), 333-367.

Ratcliff, R., & Tuerlinickx, F. (2002). . Psychonomic Bulletin & Review, 9(3), 438-481.

Voss, A., Rothermund, K., & Voss, J. (2004). Interpreting the parameters of the diffusion model: An empirical validation. Memory & Cognition, 32(7), 1206-1220.

Keywords: Diffusion analysis, fMRI, Bilingualism and Brain, Flanker conflict, IC model

Conference: Academy of Aphasia 55th Annual Meeting , Baltimore, United States, 5 Nov - 7 Nov, 2017.

Presentation Type: poster or oral

Topic: Consider for student award

Citation: Ong G, Abutalebi J, McKague M, Sewell D and Weekes B (2019). A diffusion model approach to analyzing bilingual older adults’ performance on the Flanker task: The role of left DLPFC. Conference Abstract: Academy of Aphasia 55th Annual Meeting . doi: 10.3389/conf.fnhum.2017.223.00041

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Received: 03 May 2017; Published Online: 25 Jan 2019.

* Correspondence: Prof. Brendan Stuart Weekes, University of Hong Kong, Hong Kong, Hong Kong, SAR China, 481709@frontiersin.org