Abstract
A basic human visual function is to identify objects from different viewpoints. Typically, the ability to discriminate face views based on in-depth orientation is necessary in daily life. Early neuroimaging studies have identified the involvement of the left fusiform face area (FFA) and the left superior temporal sulcus (STS) in face view discrimination. However, many studies have documented the important role of the right FFA in face processing. Thus, there remains controversy over whether one specific region or all of them are involved in discriminating face views. Thus, this research examined the influence of high-definition transcranial direct current stimulation (HD-tDCS) over the left FFA, left STS or right FFA on face view discrimination in three experiments. In experiment 1, eighteen subjects performed a face view discrimination task before and immediately, 10 min and 20 min after anodal, cathodal and sham HD-tDCS (20 min, 1.5 mA) over the left FFA in three sessions. Compared with sham stimulation, anodal and cathodal stimulation had no effects that were detected at the group level. However, the analyses at the individual level showed that the baseline performance negatively correlated with the degree of change after anodal tDCS, suggesting a dependence of the change amount on the initial performance. Specifically, tDCS decreased performance in the subjects with better baseline performance but increased performance in those with poorer baseline performance. In experiments 2 and 3, the same experimental protocol was used except that the stimulation site was the left STS or right FFA, respectively. Neither anodal nor cathodal tDCS over the left STS or right FFA influenced face view discrimination in group- or individual-level analyses. These results not only indicated the importance of the left FFA in face view discrimination but also demonstrated that individual initial performance should be taken into consideration in future research and practical applications.
Highlights
As a kind of visual stimulus or complex object, the face is important to the survival and social communication of various species, including humans
The slope differences between the cathodal and sham linear models were not significant, F < 1. These results demonstrated that anodal transcranial direct current stimulation (tDCS) over the left fusiform face area (FFA) can modulate the threshold of face view discrimination in comparison with sham tDCS
The current study used high-definition transcranial direct current stimulation (HD-tDCS) over the left FFA, left superior temporal sulcus (STS) or right FFA to modulate cortical excitability of these three brain regions and explored whether they were causally related to face view discrimination. Both anodal and cathodal tDCS over the left FFA had no effects at the group level
Summary
As a kind of visual stimulus or complex object, the face is important to the survival and social communication of various species, including humans It is a remarkable property for the primate visual system to recognize faces across different viewpoints in invariant views (Axelrod and Yovel, 2012). Studies have confirmed that face perception can be improved through perception learning (Hussain et al, 2009; Bi et al, 2010; Mcmahon and Leopold, 2012) This method is time consuming because it generally needs hundreds or thousands of practice trials over days to weeks to improve. TDCS contributes to exploring the causality between a certain cortical area and its corresponding functions
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