Neural compensation through dorsal stream involvement in visual word recognition under perceptual degradation in a transparent language: evidence from fMRI.

backgroundVisual word recognition relies on a finely tuned interplay between the ventral and dorsal visual pathways. While the ventral stream is classically regarded as the primary substrate for orthographic processing, converging evidence suggests that the dorsal stream may provide compensatory support under increased perceptual demands. In particular, the degree of orthographic transparency influences the relative involvement of these pathways. We conducted a functional MRI study in Italian, a transparent orthography, to investigate supportive neural recruitment during reading under perceptual degradation. Participants performed a word recognition task in which visual real words were degraded through four types of visual manipulation (rotation, mirroring, reduced contrast, increased letter spacing) to increase processing difficulty. Both whole-brain and region-of-interest analyses were performed.

resultsAnalyses revealed robust engagement of canonical ventral reading regions across conditions, alongside increased recruitment of dorsal stream areas during degraded word processing, and this dorsal involvement scaled with increasing level of visual degradation. This dorsal involvement was most prominent in the superior parietal and temporo-parietal cortices, consistent with their role in visuo-spatial attention

conclusionThese findings suggest that, even in transparent languages where phonological decoding is relatively straightforward, the dorsal pathway can be part of a flexible reorganisation of the reading system. By demonstrating stimulus-driven adaptation of the reading network, our results provide novel insights into the neural flexibility underlying visual word recognition and highlight the importance of dorsal-ventral interactions in sustaining reading performance under suboptimal perceptual conditions.