Cerebral blood flow velocity changes during dichotic listening with directed or divided attention: a transcranial Doppler ultrasonography study

Simultaneous bilateral transcranial Doppler ultrasonography (TCD) monitorin g of blood flow velocity (BFV) in the middle cerebral arteries was performe d in 28 normal right-handed volunteers during linguistic dichotic listening tasks to investigate the effect of hemispheric specialisation and allocati on of attention. A control task that required the repetition of monaurally presented words was followed by three randomised dichotic listening tasks i n which the subjects were instructed to direct their attention to the word stimuli of the right ear, the left ear, or to divide their attention betwee n both ears. Behavioural data indicated that the subjects used the required attentional strategies. A significant right ear advantage was not obtained in the divided attention condition due to a ceiling effect. Each task resu lted in a significant bilateral increase in BFV. We found no significant la teralisation of BFV change for any of the tasks. We noted marked difference s in BFV change between the different conditions that were significant in t he right hemisphere, showed a borderline significance in the left hemispher e and appeared to be related with the difficulty of the task. We conclude t hat the hemodynamic changes caused by attentional strategies or hemispheric specialisation in processing dichotic stimuli over and above the effect of bilateral auditory stimulation, are too subtle to be detected as lateralis ed changes in BFV. Functional TCD could be used for the evaluation of a tas k's workload relative to other tasks, and may contribute to elucidate the r ole of the right hemisphere in attention and arousal. (C) 2001 Elsevier Sci ence Ltd. All rights reserved.