The effects of tDCS on object perception: A systematic review and meta-analysis.

Transcranial direct current stimulation (tDCS) is a novel, non-invasive method of modulating brain activity by applying electrical current directly to the scalp. While the effects of tDCS are more established in the clinical setting, its influence on cognition, specifically object perception, is less clear. The goal of this systematic review was to investigate whether object perception can be improved by tDCS, and if so, under what conditions. A literature search was conducted on the following databases: PubMed, ScienceDirect, Google Scholar and PsycInfo. To be included, studies must have employed tDCS on healthy adult populations and included a measure of object perception. A total of 18 articles met inclusion criteria. The results showed that 58% of studies that applied anodal tDCS to the target region observed enhanced object perception. This was particularly the case with frontal stimulation for object detection tasks. A quantitative meta-analysis further confirmed that anodal tDCS improved object perception overall, and specifically, tDCS to frontal sites increased accuracy scores by an average of 8.8%. Although the qualitative synthesis suggested that anodal tDCS to occipital sites, such as the lateral occipital complex, may enhance object recognition, the meta-analysis showed that this effect was not significant within the occipital subgroup. This is the first systematic review and meta-analysis investigating the effects of tDCS on object perception. Although there are inconsistencies in the behavioral and tDCS methodologies employed by these studies, our analysis revealed that tDCS can enhance object perception when targeting frontal brain regions involved in top-down attention.

Cross-modal masked priming of the tritone paradox.

The tritone paradox is a musical illusion consisting of pairs of octave-ambiguous tones that could be heard as ascending or descending in pitch. This study investigated whether perception of the tritone paradox can be unconsciously influenced by a masked visual prime - specifically, a musical notation. In Experiment 1, participants were first given a "neutral" masked prime (an image of an empty music staff) to assess baseline perception. Then, they were presented with a "meaningful" masked prime consisting of two music notes arranged in either an ascending or a descending configuration, depending on their baseline perception. The results showed that the meaningful prime shifted participants' perception of the tritone paradox in the direction indicated by the musical notation. This effect was stronger for musicians than non-musicians. Experiment 2 replicated Experiment 1 and further ascertained that this effect occurred unconsciously and was not due to regression to the mean. Together, the results of this study demonstrate that relevant visual images can unconsciously influence auditory perception under conditions of ambiguity.