Neural Correlates of Letter Reversal in Children and Adults

Children often make letter reversal errors when first learning to read and write, even for letters whose reversed forms do not appear in normal print. However, the brain basis of such letter reversal in children learning to read is unknown. The present study compared the neuroanatomical correlates (via functional magnetic resonance imaging) and the electrophysiological correlates (via event-related potentials or ERPs) of this phenomenon in children, ages 5–12, relative to young adults. When viewing reversed letters relative to typically oriented letters, adults exhibited widespread occipital, parietal, and temporal lobe activations, including activation in the functionally localized visual word form area (VWFA) in left occipito-temporal cortex. Adults exhibited significantly greater activation than children in all of these regions; children only exhibited such activation in a limited frontal region. Similarly, on the P1 and N170 ERP components, adults exhibited significantly greater differences between typical and reversed letters than children, who failed to exhibit significant differences between typical and reversed letters. These findings indicate that adults distinguish typical and reversed letters in the early stages of specialized brain processing of print, but that children do not recognize this distinction during the early stages of processing. Specialized brain processes responsible for early stages of letter perception that distinguish between typical and reversed letters may develop slowly and remain immature even in older children who no longer produce letter reversals in their writing

Reversed Letters > Typical Letters.

<p>Activation from the whole-brain analysis for the reversed letters > typical letters contrast. Direct comparison of children and adults showed that adults exhibited significantly greater activation for the reversed > typical letters contrast than children did in multiple regions, including the left ventral visual stream and bilateral parietal cortices.</p

Localizer Accuracy and Reaction Time.

<p>Values listed are means, with standard deviation in parentheses.</p

VWFA Region of Interest Analysis.

<p>Average beta values for independently defined VWFA region of interest. Adults had greater activation for reversed letters than letters, while children showed no difference. There was a significant interaction between group and letter type.</p

Letter Reversal In-Scanner and ERP Behavioral Data.

<p>Values listed are means, with standard deviation in parentheses.</p

ERP Results.

<p>ERP Waveforms and Voltage Maps. Grand average waveforms for the adults (A) and for the Children (D) showing the P1 and N170 differences present in adults, but not children. The distribution of these effects is depicted in voltage maps (B and E) showing the difference between normally-oriented letters and mirror-reversed letters (reversed – normal). Black dots on the voltage maps indicate electrode sites included in the mean amplitude analysis. Note the scale difference between the P1 and N170 epoch. C shows the peak latency difference between reversed and normally-orientated letters in adults where the latency is increased for mirror reversed letters. In F, children show a delayed peak latency that does not differ between the two conditions.</p

Letter reversal task.

<p>Participants were presented with a stimulus (letter, reversed letter, or chair) for 200 ms followed by 800 ms of a blank screen. Stimuli were presented in a block design in the fMRI portion, and an event related design in the ERP portion of the experiment.</p

Behavioral Scores for Participants in fMRI Experiment.

<p>This table is reporting standard scores, except of the CTOPP where we report scaled scores, therefore they do not have the typical mean of 100 like standard scores, instead they have mean of 10 and a standard deviation of 3. KBIT  =  Kaufman Brief Intelligence Test; WRMT  =  Woodcock Reading Mastery Tests, CTOPP  =  Comprehensive Test of Phonological Processing; SWE  =  Sight Word Extraction; PDE  =  Phonemic Decoding Efficiency; ns  =  not significant. P values indicate significance level of t-test between the two groups on the measure.</p

Stimuli for the Visual Word Form Area (VWFA) Localizer.

<p>Localizer stimuli consisted of four categories: objects, faces, words, and squiggles. Images were redrawn as dots to control for contour structure and spatial frequency.</p

Whole Brain Activation.

<p>Whole Brain Activation.</p