Investigation of the development of neural and behavioural auditory rhythmic sensitivity and of its contribution to reading acquisition

241 p.The main goal of the current doctoral dissertation was to examine the contribution of brain and behavioural rhythmic sensitivity during pre-reading stages to the development of future reading. To achieve this goal, we conducted a longitudinal study in which typically developing children were tested three times: twice before they had received formal reading instruction (T1: 4-5 y.o.; T2: 5-6 y.o.) and once after reading instruction was introduced in the school curriculum (T3: 6-7 y.o.). Along these three testing times, we used EEG to measure the children¿s brain rhythmic (oscillatory) activity in response to natural speech and to auditory signals modulated at rates relevant for speech perception (at the stress, syllabic and phonemic rates). The children also ran a battery of behavioural tasks that included a measure of rhythmic skills (tapping to a beat in synchrony) and several classical reading predictors (e.g. phonological awareness, phonological short-term memory). The longitudinal nature of this work allowed us testing for the first time the trajectory of brain coherence to auditory signals during early childhood. Furthermore, this is the first study finding a long-hypothesized relation between brain oscillatory activity at low frequency bands (0.5 Hz) in pre-reading stages and later reading achievement, such that right-lateralized brain responses to speech at T2 correlated significantly with children¿s reading achievement at T3. Regarding behavioural rhythm sensitivity, whereas rhythmic skills were tightly related to other reading predictors before reading was acquired (T1 and T2), we found no evidence that it contributed significantly to final reading outcome. Differences among measures of brain vs. behavioural rhythmic sensitivity are discussed, especially in the context of early detection and intervention of children at risk of developing reading disorders.bcbl: basque center on cognition, brain and languag

Hearing aids do not alter cortical entrainment to speech at audible levels in mild-to-moderately hearing-impaired subjects

Background: Cortical entrainment to speech correlates with speech intelligibility and attention to a speech stream in noisy environments. However, there is a lack of data on whether cortical entrainment can help in evaluating hearing aid fittings for subjects with mild to moderate hearing loss. One particular problem that may arise is that hearing aids may alter the speech stimulus during (pre-)processing steps, which might alter cortical entrainment to the speech. Here, the effect of hearing aid processing on cortical entrainment to running speech in hearing impaired subjects was investigated. Methodology: Seventeen native English-speaking subjects with mild-to-moderate hearing loss participated in the study. Hearing function and hearing aid fitting were evaluated using standard clinical procedures. Participants then listened to a 25-minute audiobook under aided and unaided conditions at 70 dB A sound pressure level (SPL) in quiet conditions. EEG data were collected using a 32-channel system. Cortical entrainment to speech was evaluated using decoders reconstructing the speech envelope from the EEG data. Null decoders, obtained from EEG and the time-reversed speech envelope, were used to assess the chance level reconstructions. Entrainment in the delta- (1-4 Hz) and theta- (4-8 Hz) band, as well as wideband (1-20 Hz) EEG data was investigated. Results: Significant cortical responses could be detected for all but one subject in all three frequency bands under both aided and unaided conditions. However, no significant differences could be found between the two conditions in the number of responses detected, nor in the strength of cortical entrainment. The results show that the relatively small change in speech input provided by the hearing aid was not sufficient to elicit a detectable change in cortical entrainment. Conclusion: For subjects with mild to moderate hearing loss, cortical entrainment to speech in quiet at an audible level is not affected by hearing aids. These results clear the pathway for exploring the potential to use cortical entrainment to running speech for evaluating hearing aid fitting at lower speech intensities (which could be inaudible when unaided), or using speech in noise conditions