Abstract
We have previously shown that transcranial direct current stimulation (tDCS) improved performance of a complex visual perceptual learning task (Clark et al. 2012). However, it is not known whether tDCS can enhance perceptual sensitivity independently of non-specific, arousal-linked changes in response bias, nor whether any such sensitivity benefit can be retained over time. We examined the influence of stimulation of the right inferior frontal cortex using tDCS on perceptual learning and retention in 37 healthy participants, using signal detection theory to distinguish effects on perceptual sensitivity (d′) from response bias (ß). Anodal stimulation with 2 mA increased d′, compared to a 0.1 mA sham stimulation control, with no effect on ß. On completion of training, participants in the active stimulation group had more than double the perceptual sensitivity of the control group. Furthermore, the performance enhancement was maintained for 24 hours. The results show that tDCS augments both skill acquisition and retention in a complex detection task and that the benefits are rooted in an improvement in sensitivity (d′), rather than changes in response bias (ß). Stimulation-driven acceleration of learning and its retention over 24 hours may result from increased activation of prefrontal cortical regions that provide top-down attentional control signals to object recognition areas.
Highlights
Perceptual sensitivity, as measured by the signal detection theory metric d9 [1] and related indexes [2], is a basic measure of perceptual capability
This study examined whether stimulation of the right inferior frontal cortex using transcranial direct current stimulation (tDCS) enhances learning and/or retention of a
Complex threat detection task, and if so, whether enhancement is based on increased perceptual sensitivity or an alteration in response bias
Summary
Perceptual sensitivity, as measured by the signal detection theory metric d9 [1] and related indexes [2], is a basic measure of perceptual capability. Neuroimaging studies can help identify the key brain networks that are associated with the performance of a perceptual detection task and thereby help locate the scalp targets for anodal tDCS application We used this approach in a functional magnetic resonance imaging (fMRI) study of a complex perceptual learning task requiring participants to identify concealed and camouflaged objects representing threats in a simulation of naturalistic warzone environments [23]. One issue that needs further examination in tDCS studies, especially those involving perceptual detection tasks, is whether brain stimulation enhances perceptual sensitivity as opposed to making participants more liberal or conservative in responding The latter could result from non-specific changes in arousal, which can influence response bias [25]. We hypothesized that participants receiving 2.0 mA tDCS would show an increase in d9 but not in b, relative to participants receiving 0.1 mA, and that this effect would be significant immediately after training and again 24 hours later
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