Contrasting spatial hearing deficits in hemianopia and spatial neglect

SPATIAL hearing deficits have been described in widely differing pathologie s, including bilateral temporal or unilateral parietal lesions, hemispherec tomy, spatial neglect and right-sided cortical lesions without neglect. How ever, the topography of spatial hearing deficits after cortical lesions is only poorly understood, unlike that of vision and touch. We investigated th e auditory subjective straight ahead (SSA) with a new technique of binaural sound source simulation using broad-band single pulses which were filtered with head-related transfer functions and delivered with a 5 degrees resolu tion over headphones in front space. Normal subjects showed quite accurate judgments of the SSA, with a small but significant shift to the left of cen tre (-1.7 degrees) in the horizontal plane. Hemineglect without a scotoma, produced a large ipsilesional deviation of the auditory SSA (+22 degrees), while two hemianopic subjects, both without neglect, showed the opposite de viation of their perceived auditory SSA towards their contralesional, blind hemifield (+10 vs -28 degrees). TWO control patients with unilateral lesio ns, both without neglect and without hemianopia, produced normal judgments of their auditory SSA (-3.0 degrees, +3.8 degrees). These results suggest a t least two contrasting influences on directional spatial hearing after uni lateral cortical lesions: hemianopia vs hemispatial neglect. The results ar e interpreted in favour of multisensory convergence of visual and auditory information in directional spatial hearing. (C) 1999 Lippincott Williams & Wilkins.