Abstract
Visual perceptual learning, a manifestation of neural plasticity, refers to improvements in performance on a visual task achieved by training. Attention is known to play an important role in perceptual learning, given that the observer's discriminative ability improves only for those stimulus feature that are attended. However, the distribution of attention can be severely constrained by perceptual grouping, a process whereby the visual system organizes the initial retinal input into candidate objects. Taken together, these two pieces of evidence suggest the interesting possibility that perceptual grouping might also affect perceptual learning, either directly or via attentional mechanisms. To address this issue, we conducted two experiments. During the training phase, participants attended to the contrast of the task-relevant stimulus (oriented grating), while two similar task-irrelevant stimuli were presented in the adjacent positions. One of the two flanking stimuli was perceptually grouped with the attended stimulus as a consequence of its similar orientation (Experiment 1) or because it was part of the same perceptual object (Experiment 2). A test phase followed the training phase at each location. Compared to the task-irrelevant no-grouping stimulus, orientation discrimination improved at the attended location. Critically, a perceptual learning effect equivalent to the one observed for the attended location also emerged for the task-irrelevant grouping stimulus, indicating that perceptual grouping induced a transfer of learning to the stimulus (or feature) being perceptually grouped with the task-relevant one. Our findings indicate that no voluntary effort to direct attention to the grouping stimulus or feature is necessary to enhance visual plasticity.
Highlights
One of the more remarkable properties of the human brain is plasticity, the ability of the brain to change through experience [1]
The results (Fig. 2A, B) showed that sensitivity (d’) in orientation discrimination was modulated by attention [33] and more importantly, by perceptual grouping
Pairwise comparisons (Bonferroni corrected) confirmed that in the last session performance was higher, compared to the no-grouping condition, in both the attended (P = 0.001) and grouping condition (P = 0.038). These results support the hypothesis that perceptual grouping can modulate perceptual learning, inducing a higher degree of plasticity for an unattended stimulus perceptually grouped with the attended one
Summary
One of the more remarkable properties of the human brain is plasticity, the ability of the brain to change through experience [1]. Grouping is obtained by means of a set of ‘‘Gestalt principles’’ – such as for example similarity, proximity, closure – that organize fragments of the retinal image into candidate objects by bundling together those parts that are likely to belong to the same object in the real world [30] The results of these grouping processes are segmented perceptual units, or ‘‘proto objects’’. This raises the interesting possibility that perceptual grouping might affect perceptual learning, either directly or by means of attention To address this issue we adapted a recently proposed paradigm showing that attention alters the degree of visual plasticity during exposure-based perceptual learning [33]. This paradigm appears to be suited to isolate the role of attention on perceptual learning, without the possible contribution of rewarding mechanisms
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