Effect of tDCS on task relevant and irrelevant perceptual learning of complex objects

Abstract

During perceptual learning the visual representations in the brain are altered, but these changes' causal role has not yet been fully characterized. We used transcranial direct current stimulation (tDCS) to investigate the role of higher visual regions in lateral occipital cortex (LO) in perceptual learning with complex objects. We also investigated whether object learning is dependent on the relevance of the objects for the learning task. Participants were trained in two tasks: object recognition using a backward masking paradigm and an orientation judgment task. During both tasks, an object with a red line on top of it were presented in each trial. The crucial difference between both tasks was the relevance of the object: the object was relevant for the object recognition task, but not for the orientation judgment task. During training, half of the participants received anodal tDCS stimulation targeted at the lateral occipital cortex (LO). Afterwards, participants were tested on how well they recognized the trained objects, the irrelevant objects presented during the orientation judgment task and a set of completely new objects. Participants stimulated with tDCS during training showed larger improvements of performance compared to participants in the sham condition. No learning effect was found for the objects presented during the orientation judgment task. To conclude, this study suggests a causal role of LO in relevant object learning, but given the rather low spatial resolution of tDCS, more research on the specificity of this effect is needed. Further, mere exposure is not sufficient to train object recognition in our paradigm.

Effects of Transcranial Direct Current Stimulation on Visual Neuroplasticity in Schizophrenia

“…For instance, a study that administered multiple sessions of tDCS to the left lateral occipital cortex during an object recognition task found that anodal tDCS improved perceptual learning (over 4 days) in healthy individuals. 47 However, in another study that used repeated stimulations, anodal tDCS applied to Oz impaired the overnight consolidation of learning on a visual contrast detection task. 48…”

Perceptual Learning with Complex Objects: A Comparison between Full-Practice Training and Memory Reactivation

“…A substantial body of evidence demonstrates training-induced improvements in the perception of relatively simple visual aspects, such as frequency discrimination (Fiorentini and Berardi, 1981), orientation discrimination (Aberg et al, 2009;Jeter et al, 2010) and feature discrimination (Amar-Halpert et al, 2017;Censor et al, 2006;Censor and Sagi, 2008;Karni and Sagi, 1993). Interestingly, similar learning curves have been reported with more complex objects (Baeck et al, 2012(Baeck et al, , 2014(Baeck et al, , 2016Furmanski and Engel, 2000;Van Meel et al, 2016). This so-called object learning involves improved recognition of objects after multiple days of training.…”

“…Note that the procedure of shortening stimulus duration as the SOA gets smaller in could arguably result in a situation in which challenges in recognition performance are due to reductions in perceived stimulus contrast in low-level visual areas. We cannot rule out this possibility, yet it is assuring that the same manipulation was used in previous studies that found correlations with object recognition performance in object-selective cortex (Grill-Spector et al, 2000) and causal effects after stimulation in lateral occipital cortex (Van Meel et al, 2016).…”

“…This so-called object learning involves improved recognition of objects after multiple days of training. This improvement in object recognition under perceptually challenging conditions seems related to activity in high-level object-selective cortex (Grill-Spector et al, 2000;Van Meel et al, 2016).…”

“…In earlier work (Baeck et al, 2016(Baeck et al, , 2014(Baeck et al, , 2012Baeck and Op de Beeck, 2010;Furmanski and Engel, 2000;Van Meel et al, 2016), each session started with a preview of all stimuli presented in that session. A preview of the stimuli (2 seconds each) with their corresponding names was displayed to ensure that participants know the object images and their names.…”