Abstract
The brain site of perceptual learning has been constantly debated. Recent evidence showing complete learning transfer to an untrained retinal location or orthogonal orientation suggests that perceptual learning occurs in high-level brain areas (Xiao et al., 2008; Zhang et al., 2010). Contradictorily, ERP C1 changes after learning are used as evidence for V1 plasticity because of C1’s early onset (Pourtois et al., 2008; Bao et al., 2010). However, C1 can be top-down modulated (Rauss et al., 2011), which is especially likely after an observer practices/learns the same stimuli/task for several sessions. Here we measured C1 changes associated with learning transfer at a completely untrained location, with the assumption that any C1 changes observed here would indicate top-down modulation, rather than V1 plasticity. Twelve subjects were trained to discriminate grating orientation (ref_ori=36°) for five days. Two locations at 5-deg eccentricity in diagonal quadrants where obvious C1 components were evoked were used as training and transfer locations, respectively. EEGs responding to suprathreshold orientation judgment (36° or 36°±15°) were acquired pre- and post-training in separate sessions. Training improved orientation thresholds significantly (46.3%, p<0.001). Performance at the untrained location (using pretest threshold at the trained location as baseline) was also significantly improved, although by a less amount (28.3%, p<0.001). Importantly, ERP C1 increased significantly after training at not only the trained location (p=0.009), but also the untrained location (p=0.001)! These results support our hypothesis that ERP C1 is top-down modulated in perceptual learning, and that C1 changes do not necessarily indicate V1 plasticity. Bao et al. (2010) and Pourtois et al. (2008) also show no significant C1 changes if learning does not transfer to the untrained location. These associations between C1 changes and learning-induced performance improvement together suggest that C1 is likely top-down modulated by high-level perceptual learning.
Meeting abstract presented at VSS 2013