Electroencephalographic and reaction time asymmetries to musical chord stimuli

The AEP T-complex to synthesised musical tones: left-right asymmetry in relation to handedness and hemisphere dominance

Auditory evoked potentials were recorded to onset and offset of synthesised instrumental tones in 40 normal subjects, 20 right-handed for writing and 20 left-handed. The majority of both groups showed a T-complex which was larger at the right temporal electrode (T4) than the left (T3). In the T4-T3 difference waveforms, the mean potential between latencies of 130 and 165 ms was negative in all right-handed subjects except two for whom the waveforms were marginally positive-going. Amongst the left-handers, however, this converse asymmetry was seen in 7 subjects, 5 of them more than 2 standard deviations from the mean of the right-handed group. The degree of asymmetry was not significantly correlated with the degree of left-handedness according to the Edinburgh Handedness Inventory. Asymmetry of the T-complex to instrumental tones appears to reflect the lateralisation of auditory 'musical' processing in the temporal cortex, confirming evidence from other sources including PET that this is predominantly right-sided in the majority of individuals. The proportion of left-handers showing the converse laterality is roughly in accordance with those likely to be right-hemisphere-dominant for language. If linguistic and 'musical' processes are consistently located in opposite hemispheres, AEPs to complex tones may prove a useful tool in establishing functional lateralisation.

Auditory evoked potentials to abrupt pitch and timbre change of complex tones: electrophysiological evidence of 'streaming'?

Examination of the cortical auditory evoked potentials to complex tones changing in pitch and timbre suggests a useful new method for investigating higher auditory processes, in particular those concerned with 'streaming' and auditory object formation. The main conclusions were: (i) the N1 evoked by a sudden change in pitch or timbre was more posteriorly distributed than the N1 at the onset of the tone, indicating at least partial segregation of the neuronal populations responsive to sound onset and spectral change; (ii) the T-complex was consistently larger over the right hemisphere, consistent with clinical and PET evidence for particular involvement of the right temporal lobe in the processing of timbral and musical material; (iii) responses to timbral change were relatively unaffected by increasing the rate of interspersed changes in pitch, suggesting a mechanism for detecting the onset of a new voice in a constantly modulated sound stream; (iv) responses to onset, offset and pitch change of complex tones were relatively unaffected by interfering tones when the latter were of a different timbre, suggesting these responses must be generated subsequent to auditory stream segregation.

Individual variations in awakening times, daytime alertness and somnograms as a function of ad libitum extended sleep

Individual variations in timing of polysomnograms, vigilance, alertness ratings, and wakeful electrocorticograms were investigated after being potentiated by extended sleep. The entire (N = 16) constituency of healthy young adults was dichotomized into subgroups (Ns = 8) whose delayed awakenings occurred before 1045 (0930-1036) and at 1105 (1105-1430) or later. Statistical analyses were applied to determine whether selected dependent variables during ad libitum delayed sleep covaried as a function of the substantial (5-hr) range observed for awakening times. Relative to the rigidly scheduled 8-hr control condition, statistically significant average increases occurred in stage 2, REM sleep and REM cycle length as a function of delayed afternoon awakening times, whereas this proved true for stage 3 during the morning. For all indexes of sleep physiology, there were statistically significant interactions of the ad-libitum extended treatment with arising times. Average elevations in stage 2, REM sleep and REM cycle length were associated with ad libitum sleep which terminated at 1105 or later. By contrast, increases of stage 3 coincided with extended sleep wherein awakenings occurred between 0930 and 1036 in the morning. The average integrated amplitude (microV) of 8-13 Hz alpha rhythm was greater (less cortical alertness), whereas psychometric alertness ratings were significantly less in conjunction with ad libitum delayed morning sleep and among individuals whose awakenings occurred greater than 1100. Finally, sublingual temperature was significantly more elevated within the vicinity of 1105-1430, and this proved true with respect to d', the signal detection index, from 0930 until 1036. Accumulated evidence does indicate that acute variations in sleep patterns contribute to a disturbance in the diurnal cycle most conspicuously during either: (1) morning or (2) when postdormital evaluations of alertness are initially completed. The clinical relevance of these findings for neuropsychiatric states such as idiopathic hypersomnias, bipolar affective illness and depression is explicated.

Reaction-times of normal subjects to monaurally presented verbal and tonal stimuli

Sixteen right-handed subjects responded to monaurally presented verbal and tonal stimuli with their right and left hands at separate times. Subjects' reaction-times to speech were significantly faster when they heard words in their right ears, while their reaction-times to tones proved significantly faster after left-ear stimulations. Reaction-times to speech were significantly faster when subjects responded with their right hands, but after tonal stimulation. Left-handed responses were significantly faster. These results were interpreted as demonstrating consistent laterality effects--the faster response occurring after intrahemispheric processing. Furthermore, the interactions between ear stimulated and hand of response were suggestive of minor hemisphere processing.