Adolescents with learning disorders have atypical EEG correlation indices. I. Correlation indices during visual discrimination.

OBJECTIVE: To find out whether 14-16-year-old pupils with visual perception disabilities have atypical EEG activation patterns during visual discrimination. METHODS: EEG correlation indices (EEGCIs), based on the waveform characteristics of two EEG signals, were used as measures of slow joint activation of cortical regions during visual discrimination in pupils with visual perception disabilities. RESULTS: During visual discrimination low EEGCIs were seen between the left temporal and both parieto-occipital EEG channels in pupils with visual perception disabilities and in pupils with a poor occupational outcome. The pupils with low performance intelligence and those with difficulties in the visual discrimination task had low EEGCIs within the left hemisphere. The left hemispheric dominance of the findings is suggested to reflect the psychophysiology of the task since visual discrimination demands attention to details (local processing) and is thus supposed to be more strongly represented in the left hemisphere. CONCLUSIONS: During visual discrimination, low EEGCIs were seen in the posterior and left hemispheric regions of pupils with disabilities in visual perception and visual discrimination and with a poor occupational outcome. SIGNIFICANCE: Low EEGCIs in posterior and left hemispheric regions during visual discrimination can to some extent be seen as neurophysiological markers for visual perception disabilities and a poor occupational outcome and imply an increased need for adjustment of the educational curriculum and a need for occupational guidance.

Adolescents with learning disorders have atypical EEG correlation indices. II. Correlation indices during reading.

OBJECTIVE: To find out whether 14-16 year old reading and writing impaired pupils have atypical EEG activation patterns during reading. METHODS: EEG correlation indices (EEGCIs), based on the waveform characteristics of two EEG signals, were used as measurers of slow joint activation of cortical regions during reading in pupils with reading and writing impairment. RESULTS: Reading was associated with high EEGCIs within the right hemisphere in reading and writing impaired pupils. The finding is analogous to the results of an earlier study [Byring, Electroencephalogr. Clin. Neurophysiol. 63 (1986) 1] in boys with spelling disabilities. The activation in the right hemisphere might represent a compensation for a left hemisphere dysfunction in pupils with reading and writing impairment during reading, as suggested by a number of functional neuroimaging studies. This interpretation was corroborated by high EEGCIs especially in those impaired pupils who had a good occupational outcome. CONCLUSIONS: EEGCIs during reading are high within the right hemisphere in pupils with reading and writing impairment. SIGNIFICANCE: High EEGCIs within the right hemisphere during reading might be considered neurophysiological markers for reading and writing impairment.

Psycholphysical 'measurement' of cortical colour mechanisms: reply of Meyer.

In a paper recently published in this journal, Meyer criticised our study on relationships between channels for colour and spatial frequence for not being able to demonstrate a size aftereffect not specific to colour, a McCollough effect not specific to size, or the functions of cortical colour mechanisms. In fact, our study attempted none of these demonstrations in the sense suggested by Meyer because the first would have been impossible for empirical reasons, the second for conceptual reasons, and the third for methodological reasons. Instead, our study yielded evidence that at least three different types of perceptual channel underlie our capacity to perceive the size and colour of objects.