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The role of the posterior fusiform gyrus in reading - PubMed

Comparative Study

The role of the posterior fusiform gyrus in reading

Joseph T Devlin et al. J Cogn Neurosci. 2006 Jun.

Abstract

Studies of skilled reading [Price, C. J., & Mechelli, A. Reading and reading disturbance. Current Opinion in Neurobiology, 15, 231-238, 2005], its acquisition in children [Shaywitz, B. A., Shaywitz, S. E., Pugh, K. R., Mencl, W. E., Fulbright, R. K., Skudlarski, P., et al. Disruption of posterior brain systems for reading in children with developmental dyslexia. Biological Psychiatry, 52, 101-110, 2002; Turkeltaub, P. E., Gareau, L., Flowers, D. L., Zeffiro, T. A., & Eden, G. F. Development of neural mechanisms for reading. Nature Neuroscience, 6, 767-773, 2003], and its impairment in patients with pure alexia [Leff, A. P., Crewes, H., Plant, G. T., Scott, S. K., Kennard, C., & Wise, R. J. The functional anatomy of single word reading in patients with hemianopic and pure alexia. Brain, 124, 510-521, 2001] all highlight the importance of the left posterior fusiform cortex in visual word recognition. We used visual masked priming and functional magnetic resonance imaging to elucidate the specific functional contribution of this region to reading and found that (1) unlike words, repetition of pseudowords ("solst-solst") did not produce a neural priming effect in this region, (2) orthographically related words such as "corner-corn" did produce a neural priming effect, but (3) this orthographic priming effect was reduced when prime-target pairs were semantically related ("teacher-teach"). These findings conflict with the notion of stored visual word forms and instead suggest that this region acts as an interface between visual form information and higher order stimulus properties such as its associated sound and meaning. More importantly, this function is not specific to reading but is also engaged when processing any meaningful visual stimulus.

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Figures

Figure 1
Figure 1

Subtle visual form differences in written words are often critical for correctly identifying the word, independent of the writing system. Here we illustrated this with examples each from alphabetic (Arabic), syllabic (Hindi), and logographic (Mandarin) orthographies. Literacy in a language makes recognising these visual differences quick and effortless. In contrast, identifying these differences in an unfamiliar script typically involves conscious serial comparisons.

Figure 2
Figure 2

The two behavioural pre-tests are schematized in the top row and the group results in the bottom row. In the first task, participants read words aloud that were presented for either 33 or 200 msec between visual masks while in the second, they performed a forced choice matching task under similar conditions. The dotted line in the bottom right plot indicates chance (50%) performance. Masked words presented for 33 msec were not consciously perceived in either task.

Figure 3
Figure 3

A) A schematic diagram of the visual masked priming paradigm. The prime was forward masked by a visual noise pattern and backward masked by the uppercase target. A bar plot of B) accuracy and C) reactions times from the main lexical decision experiment with error bars indicating standard error of the mean. Repetition (upward diagonals) led to a significant facilitation effect for words but not pseudowords (top row), although the improved accuracy for repeated pseudowords may indicate a condition-specific speed-accuracy trade-off. In addition, relative to unrelated word pairs (Unrel), orthographically related pairs that were unrelated in meaning (Orth) or related in meaning (O+S) led to significant priming effects. Light colored bar indicate orthographic relatedness and downward diagonals indicate semantic relatedness. * indicates a significant difference at p<0.05; ** indicates p<0.01.

Figure 4
Figure 4

A) Both words (red) and pseudowords (orange, overlap in yellow) activated the left posterior fusiform gyrus relative to consonant letter strings. Activations are displayed on slices through the participants’ mean structural scan in standard space. B) The mean percent BOLD signal change per condition is shown for the region relative to consonant strings. The top bar plot illustrates words in red and pseudowords in orange with repeated trials (e.g. “cabin-CABIN” & “solst-SOLST”) marked with upwards sloping lines. C) The lower plot shows word pairs related in form (darker bars) and meaning (downward sloping lines). The same labelling is used as in the previous figure.

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