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A meta-analysis on the effectiveness of transcranial direct current stimulation (tDCS) on the processing of implicit associations (IATs) in men and women
Poster Session A, Friday, September 12, 11:00 am - 12:30 pm, Field House
The Implicit Association Test (IAT) is a widely used language-based paradigm that measures implicit social biases by assessing the speed of participants categorizing word-based stimuli representing social stereotypes (Greenwald et al. 1998). For example, reflecting common gender biases or stereotypes, participants taking a gender-based IAT are generally faster at associating “men” with “boxing” than “Pilates,” and similarly, generally faster at associating “women” with “Pilates” than “boxing” (Proverbio et al. 2017). The difference in response times (RTs) during IATs is more extreme for participants with stronger biases and reflected in more extreme difference (D) scores. The IAT measures implicit rather than explicit social cognition in the sense that social biases or stereotypes are measured with implicit response times rather than explicit verbal reports, which can be useful in cases where people may not accurately report (or even be aware of) their own social biases. The IAT is frequently used in social psychology to measure implicit social biases as well as in cognitive neuroscience to measure the neural networks involved in semantic processing and social categorization. Since the IAT is widely used to measure implicit social biases, recent research has investigated whether brain stimulation techniques, such as transcranial direct current stimulation (tDCS), can be used as an effective intervention for reducing implicit social biases as measured with IAT scores. To determine the general effectiveness of tDCS on implicit bias across studies, a meta-analysis of all relevant studies involving tDCS and IATs was therefore conducted. Using a random-effects model, this meta-analysis found no significant effect for tDCS versus sham on implicit bias scores among all participants (k = 39, SMD = -0.063, p = 0.311). Further subgroup analyses also found no significant effect for tDCS versus sham on implicit bias scores in men (k = 14, SMD = -0.236, p = 0.107) or women (k = 14, SMD = 0.054, p = 0.470). Results also showed no significant effect for tDCS versus sham on response times among all participants (k = 78, SMD = -0.043, p = 0.472). However, further subgroup analyses revealed a small yet significant effect for tDCS versus sham on increasing response times in men (k = 28, SMD = 0.252, p = 0.012) and a very small yet significant effect for tDCS versus sham on decreasing response times in women (k = 28, SMD = -0.140, p = 0.026). A between-group heterogeneity test further indicated that sex significantly moderated the effect of tDCS on response times across groups (Q-between = 14.828, df = 2, p < 0.001). The results from this meta-analysis therefore reveals that tDCS significantly modulates IAT response times, degrading processing speed in men but improving processing speed in women, without affecting implicit bias scores, highlighting sex-specific effects on the general neurobiological mechanisms of language-mediated cognitive processing. Potential factors for sex differences in the response times of men and women discussed here include differences in anatomy (skull thickness), hormone regulation (testosterone and estrogen), neurotransmitter dynamics (GABA modulation), and neural network organization (baseline connectivity and flexibility).
Topic Areas: Methods, Meaning: Lexical Semantics