Pattern of localisation error in patients with stroke to sound processed by a binaural sound space processor

The ability of 46 patients with supratentorial stroke and 15 healthy subjects to localise sounds was tested using an apparatus with headphone and sound space processor.

With a binaural sound space processor, sounds were randomly presented from seven directions in the 180 degree frontal area of the subject at intervals of 30 degrees. The subject was asked to imagine a clock face through the horizontal plane passing through the subject's ears with 12 o'clock denoting a sound from directly in front of the subject. After each sound, the subject indicated the direction from which he or she thought the sound came by mentioning the corresponding hour hand on the clock face; therefore, the answer directions were also separated by 30 degrees. A total of 21 sounds with three sounds from each direction, were presented in random order. The error between the presented direction and the answered direction of each sound was calculated.

The mean absolute error which does not distinguish whether an error was in the counterclockwise or clockwise direction, was larger in the patients with stroke than in the healthy subjects. Overall, the patients with stroke who had right brain damage (n=29) had a larger mean absolute error than those who had left brain damage (n=17). The patients with right brain damage did not show any systematic deviation such as a rightward error or leftward error.

A right brain lesion or left brain lesion can cause a patient to have error in sound localisation, and patients with right brain damage generally have a larger mean absolute error of sound localisation. The difference in the mean absolute error of sound localisation between patients with stroke with right brain damage and those with stroke with left brain damage may be explained by the inattention theory of hemispatial neglect.