Knowledge Media Research Center _

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Schroeder P.A.,University of Tübingen | Nuerk H.-C.,University of Tübingen | Nuerk H.-C.,Knowledge Media Research Center _ | Plewnia C.,University of Tübingen | Plewnia C.,Werner Reichardt Center for Integrative Neuroscience
Biological Psychology | Year: 2017

Numerical and non-numerical sequence items interact with spatial responding, pointing towards mental representations that are grounded in space and referred to as SNARC effects (spatial-numerical association of response codes). An ongoing controversy pertains to the universal origin of different SNARC effects and whether their underpinning is a spatial arrangement of cardinal magnitude (mental number line) or a sequential arrangement of ordinal elements in working memory. Recent results from prefrontal neuromodulation with transcranial direct current stimulation (tDCS) were supportive of the unified working memory account. The current tDCS experiment was designed to empirically test the generalizability of the prefrontal modulation effects previously found for numbers in a non-numerical sequence (weekdays) and to examine predictions from the universal account. Participants performed a series of classification tasks with numerical and non-numerical sequences (1–5, Monday–Friday) before and concurrent to a prefrontal stimulation with either anodal (N = 24) or cathodal polarity (N = 24). Results show a dissociation of SNARC effects for numbers and weekdays by anodal tDCS: Spatial associations of weekdays were reversed by stimulation, when order was relevant for the task, but SNARC effects with number symbols were emphasized in the regular left-to-right direction, corroborating previous results. A control experiment showed that the polarity-dependent neuromodulation effects were absent in order-irrelevant font color classification, supporting the tDCS principle of activity-dependence. We discuss differences in linguistic markedness between temporal and magnitude-related classifications in an integrative account explaining the full pattern. We suggest that stimulation-enhanced psycholinguistic processing can evoke space-number associations whose direction is opposite to cultural visuospatial experience. © 2017 Elsevier B.V.


Schroeder P.A.,University of Tübingen | Pfister R.,University of Würzburg | Kunde W.,University of Würzburg | Nuerk H.-C.,University of Tübingen | And 3 more authors.
Journal of Cognitive Neuroscience | Year: 2016

Cognitive conflicts and distractions by task-irrelevant information often counteract effective and goal-directed behaviors. In some cases, conflicting information can even emerge implicitly, without an overt distractor, by the automatic activation of mental representations. For instance, during number processing, magnitude information automatically elicits spatial associations resembling a mental number line. This spatial-numerical association of response codes (SNARC) effect can modulate cognitive-behavioral performance but is also highly flexible and context-dependent, which points toward a critical involvement of working memory functions. Transcranial direct current stimulation to the PFC, in turn, has been effective in modulating working memory-related cognitive performance. In a series of experiments, we here demonstrate that decreasing activity of the left PFC by cathodal transcranial direct current stimulation consistently and specifically eliminates implicit cognitive conflicts based on the SNARC effect, but explicit conflicts based on visuospatial distraction remain unaffected. This dissociation is polarity-specific and appears unrelated to functional magnitude processing as classified by regular numerical distance effects. These data demonstrate a causal involvement of the left PFC in implicit cognitive conflicts based on the automatic activation of spatial-numerical processing. Corroborating the critical interaction of brain stimulation and neurocognitive functions, our findings suggest that distraction from goaldirected behavior by automatic activation of implicit, taskirrelevant information can be blocked by the inhibition of prefrontal activity. © 2016 Massachusetts Institute of Technology.

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