Georgina Rippon

Auditory event-related potentials, dichotic listening performance and handedness as indices of lateralisation in dyslexic and normal readers

Evidence suggests that children with developmental dyslexia have poor phonological processing skills, are less likely to show lateralised activation during the processing of verbal information than children with normal reading ability and tend towards the left of the handedness continuum. The present study investigated this relationship between cerebral lateralisation and reading ability in children with and without dyslexia, directly using a dichotic listening paradigm with contemporaneous recording of auditory evoked potentials and indirectly using measures of hand preference and hand skill. The two groups were significantly different on a phonemic awareness task, particularly with reference to rime rather than phoneme onset. The two groups performed equally well on the dichotic listening task. However, normal readers produced significantly greater N100 amplitudes in the left temporal region during dichotic listening than the dyslexics who displayed approximately equivalent levels of amplitude bilaterally. In terms of hand preference the dyslexics were significantly less right-hand preferent than the controls, although the groups did not differ on a measure of right/left hand skill. The AEP lateralisation indices and the hand preference scores were significantly related to phonemic awareness performance. The different patterns of AEP activity produced by the two groups of children during the dichotic listening task and the differences in hand preference may be related to abnormal cerebral lateralisation of language functions. The failure of the dichotic listening task to discriminate between the two groups in spite of evidence of differences in cortical activation suggests that the processing difficulties which may be indexed by these differences in cortical activation affect the reading process at a later stage than that tapped by dichotic listening.

Trait and state EEG indices of information processing in developmental dyslexia

L asymmetry in beta activity in the dyslexic group, again in both tasks. Theta activity did discriminate between the two tasks in the dyslexic group. In the phonological task, task-related frontal theta in the dyslexic group was significantly different from the control group, with the former showing an increase in amplitude and the latter a decrease. In the visual task, there was no significant difference between the dyslexic and the control group, with both showing a task-related decrease in amplitude. The inter-task variations in EEG response in the dyslexic group paralleling variations in task performance are interpreted in terms of the varying engagement of a frontally-based attentional system. Inter-task consistencies of EEG response despite variations in performance are interpreted in terms of the continued application of a specific cognitive strategy.

Hemispheric Differences and Electrodermal Asymmetry - Task and Subject Effects

As with most areas, bilateral electrodermal activity research raises both empirical and theoretical issues. With respect to the former, a basic assumption of such research is that the tasks used reliably result in differential activation of the cerebral hemispheres, and that resulting responses can be interpreted accordingly. One aspect of this paper will be a challenge to this assumption and presentation of data that illustrates particular difficulties. Further, in the selection of subjects, although some attention is paid to individual differences, by taking note of sex and handedness, it may be that researchers are doing themselves a disservice by ignoring more subtle measures of functional lateralisation. Data will be presented to illustrate this point. Finally, the interpretation of data from such studies has led to the generation of particular models concerning the cortical control of electrodermal activity; the significance of the studies reported here for the formulation of such models will be discussed.

Paranoid-nonparanoid differences--psychophysiological parallels.

It was predicted that the psychological differences between paranoids and nonparanoids would be parallelled by differences in psychophysiological responses to stimuli varying along both informational and motivational dimensions. Skin conductance and heart rate responses to stimuli in a guessing task were measured in a group of paranoid patients and compared with those from non-paranoid and non-patient controls. A group of nonschizophrenic patients on phenothiazine medication served as drug-matched controls. Skin conductance level, response frequency and amplitude data are reported; heart rate response changes were examined by means of times series analysis and reported as first and second deceleration and first and second acceleration components. It was predicted that paranoid patients would show a greater increase in skin conductance measures with cognitive demand, and an increase in acceleratory components of the heart rate to increases in motivational variables. The normal pattern of greater electrodermal responding to the negative stimuli than the positive, and greater heart rate acceleration to the positive stimuli but not the negative (Fowles, 1980) was predicted to be reversed in schizophrenic patients, and possibly more marked in paranoids. Cognitive manipulations showed the predicted increase in electrodermal and heart rate responding in normal controls. The paranoid subjects showed a similar increase as a function of task demands, but there was no significant difference between the other groups. Motivational manipulations produced increased skin conductance responding and increases in heart rate acceleration components in normal controls, this was not parallelled in the patient groups. All subject groups failed to show greater electrodermal activity to negative than to positive stimuli. Normal controls showed significant heart rate acceleration to positive as compared to negative stimuli, this pattern was reversed in paranoid patients.

Paranoid/nonparanoid differences—Psychophysiological parallels

It was predicted that the psychological differences between paranoids and nonparanoids would be parallelled by differences in psychophysiological responses to stimuli varying along both informational and motivational dimensions. Skin conductance and heart rate responses to stimuli in a guessing task were measured in a group of paranoid patients and compared with those from non-paranoid and non-patient controls. A group of nonschizophrenic patients on phenothiazine medication served as drug-matched controls. Skin conductance level, response frequency and amplitude data are reported; heart rate response changes were examined by means of times series analysis and reported as first and second deceleration and first and second acceleration components. It was predicted that paranoid patients would show a greater increase in skin conductance measures with cognitive demand, and an increase in acceleratory components of the heart rate to increases in motivational variables. The normal pattern of greater electrodermal responding to the negative stimuli than the positive, and greater heart rate acceleration to the positive stimuli but not the negative (Fowles, 1980) was predicted to be reversed in schizophrenic patients, and possibly more marked in paranoids. Cognitive manipulations showed the predicted increase in electrodermal and heart rate responding in normal controls. The paranoid subjects showed a similar increase as a function of task demands, but there was no significant difference between the other groups. Motivational manipulations produced increased skin conductance responding and increases in heart rate acceleration components in normal controls, this was not parallelled in the patient groups. All subject groups failed to show greater electrodermal activity to negative than to positive stimuli. Normal controls showed significant heart rate acceleration to positive as compared to negative stimuli, this pattern was reversed in paranoid patients.