Klinische Neurophysiologie 2010; 41 - ID13
DOI: 10.1055/s-0030-1250842

Success is left and control is right? Intercultural, TMS, and stimulus-varying experiments on the left-hemifield advantage in identifying targets among rapid series of letters

R Verleger 1, K Smigasiewicz 1
  • 1Universität Lübeck, Klinik für Neurologie, Lübeck, Deutschland

Introduction: In the dual-stream task, rapid sequences of stimuli (10/s) are presented left and right, including two target stimuli. In a number of studies, the second target was found to be identified much better in the left than in the right visual field. Thus, this might be a task that shows the presumed dominance of the right hemisphere for attention-requiring processing in healthy participants.

Material and Methods: Based on these preceding studies, here we tested generality and mechanisms of the effect

  • in an intercultural study: Hebrew letters (Israelis) vs. Chinese symbols (Taiwanese) vs. Latin letters (both groups and Germans)

  • in two TMS studies: rTMS at the right parietal cortex (5 pulses in 50ms intervals during the stimulus series) vs. rTMS left vs. sham-rTMS right or left

  • by varying the stimuli

  • by recording event-related EEG potentials during the task.

Results:

  • The advantage of the left hemifield was equal in all three cultures with Latin letters, and was somewhat reduced, though still distinct, with Hebrew and Chinese symbols.

  • The advantage of the left hemifield was not attenuated by rTMS at P3, but was further increased by rTMS at P4.

  • The advantage was also obtained with Tibetian letters (which were hard to verbalize), likewise in an environment of digits instead of letters.

  • N2pc and, consecutively, P3 had earlier latencies with left than with right targets.

Conclusion: The advantage of the left hemifield in the dual-stream-task might indeed be a stable indicator of the superiority of the right hemisphere for attention-requiring processing. Contributing mechanisms apparently are

  • greater resistance of the right hemisphere against interference (rTMS experiment) and

  • faster speed of processing in the right hemisphere (EEG results).

Supported by DFG (Ve110/15–1 in the package proposal Neuro-cognitive mechanisms of conscious and unconscious visual perception, Pak270).

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