Top-down processes during auditory phoneme categorization in dyslexia: A PET study

O. Dufor, W. Serniclaes, L. Sprenger-Charolles, J.-F. Démonet
2007 NeuroImage  
While persistence of subtle phonological deficits in dyslexic adults is 10 well documented, deficit of categorical perception of phonemes has 11 received little attention so far. We studied learning of phoneme 12 categorization during an activation H 2 O 15 PET experiment in 14 13 dyslexic adults and 16 normal readers with similar age, handedness 14 and performance IQ. Dyslexic subjects exhibited typical, marked 15 impairments in reading and phoneme awareness tasks. During the 16 PET
more » ... e 16 PET experiment, subjects performed a discrimination task involving 17 sine wave analogues of speech first presented as pairs of electronic 18 sounds and, after debriefing, as syllables /ba/ and /da/. Discrimination 19 performance and brain activation were compared between the acoustic 20 mode and the speech mode of the task which involved physically 21 identical stimuli; signal changes in the speech mode relative to the 22 acoustic mode revealed the neural counterparts of phonological top-23 down processes that are engaged after debriefing. Although dyslexic 24 subjects showed good abilities to learn discriminating speech sounds, 25 their performance remained lower than those of normal readers on the 26 discrimination task over the whole experiment. Activation observed in 27 the speech mode in normal readers showed a strongly left-lateralized 28 pattern involving the superior temporal, inferior parietal and inferior 29 lateral frontal cortex. Frontal and parietal subparts of these left-sided 30 regions were significantly more activated in the control group than in 31 the dyslexic group. Activations in the right frontal cortex were larger 32 in the dyslexic group than in the control group for both speech and 33 acoustic modes relative to rest. Dyslexic subjects showed an unexpected 34 large deactivation in the medial occipital cortex for the acoustic mode 35 that may reflect increased effortful attention to auditory stimuli. 36
doi:10.1016/j.neuroimage.2006.10.034 pmid:17196834 fatcat:gjrsowi7znhqpmepox4mjtnh2a