Degraded written words engage the dorsal visual pathway in an fMRI study of Italian readers
In an fMRI study with Italian readers, dorsal visual areas became more active as written words were degraded, while ventral reading regions stayed engaged, the authors report.
A functional MRI study published in Behavioral and Brain Functions examined how the brain reads words that are visually degraded. It was conducted in Italian, a language with transparent orthography. According to the authors, dorsal visual areas were recruited more strongly as the degradation increased, while the classical ventral reading regions remained active. biomedcentral.com
Behavioral and Brain Functionsbiomedcentral.comOpen source ↗
Dorsal and ventral pathways in reading
Visual word recognition relies on an interplay between the ventral and dorsal visual pathways. The ventral stream, anchored by the visual word form area along the fusiform gyrus, is classically regarded as the main substrate of orthographic processing. The dorsal stream has historically been linked to letter-by-letter decoding and to the allocation of visuo-spatial attention.
The authors tested whether degrading the printed signal makes the reading system of mature readers lean on dorsal mechanisms. Italian was chosen because its letters map onto speech sounds in a consistent way, so phonological decoding is relatively straightforward. Participants performed a word recognition task with real words presented in isolation, without sentence context. Each word could be degraded in one of four ways: rotation, mirroring, reduced contrast or increased letter spacing. Participants read the words silently, and catch trials with animal names, which required a button press, were used to monitor attention. Both whole-brain and region-of-interest analyses were performed.
Results: dorsal recruitment scaled with degradation
The analyses showed robust engagement of the canonical ventral reading regions across all conditions. Dorsal stream areas were additionally recruited during the processing of degraded words, and this recruitment scaled with the level of visual degradation. It was most prominent in the superior parietal and temporo-parietal cortices, which the authors link to their role in visuo-spatial attention. biomedcentral.com
Behavioral and Brain Functionsbiomedcentral.comOpen source ↗
The authors conclude that even in a transparent language, where phonological decoding is relatively straightforward, the dorsal pathway can be part of a flexible reorganisation of the reading system. They describe this as a stimulus-driven adaptation of the reading network and point to the importance of dorsal-ventral interactions in sustaining reading performance under suboptimal perceptual conditions.
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