The influence of neurostimulation on stimulus discrimination: tDCS at Fp3 can modulate old / new recognition and target detection for faces and chequerboards.

Abstract

This paper reports the results of three experiments investigating the effect of transcranial Direct Current Stimulation (tDCS), a form of neurostimulation, on stimulus discrimination in an ‘old/new recognition’ and a target detection task. Experiment 1 presents regular faces alongside a set of manipulated faces, Thatcherised faces, or familiar chequerboards; showing that anodal stimulation can selectively increase or reduce the face inversion effect for regular faces simply by changing the accompanying stimuli. That tDCS can reliably disrupt or enhance performance on an index of facial recognition as robust as the face inversion effect is a significant finding. Experiment 1 also provides the first direct evidence that a set of manipulated faces generalise onto regular faces and do so sufficiently to reduce the inversion effect in the latter. The results are interpreted, using a theory of representational development known as the McLaren, Kaye and Mackintosh (MKM) model, as tDCS altering error-based salience modulation with the effect of enhancing generalisation between within-category stimuli. Experiment 2 extends the analysis offered to a detection task with ‘realistic’ and standardised faces while Experiment 3 presents familiar chequerboards in the same task. The results show that anodal stimulation has a different effect to that in the ‘old/new recognition’ task, having no significant effect on sensitivity but an unexpected effect on response bias.