Two types of auditory neglect

Auditory neglect, defined as inattention to stimuli within the left hemispa ce, is mostly reported in association with left ear extinction in dichotic listening. However, it remains disputed as to how far dichotic extinction r eflects a primary attentional deficit and is thus appropriate for the diagn osis of auditory neglect. We report here on four patients who presented lef t ear extinction in dichotic listening following right unilateral hemispher ic lesions. Auditory spatial attention was assessed with two additional tas ks: (i) diotic test by means of interaural time differences (ITDs), simulat ing bilateral simultaneous spatial presentation of the dichotic tasks witho ut the inconvenience of interaural intensity or content difference; and (ii ) sound localization. A hemispatial asymmetry on the ITD diotic test or a s patial bias on sound localization were found to be part of auditory neglect . Two patients (J.C.N. and M.B.) presented a marked hemispatial asymmetry f avouring the ipsilesional hemispace in the ITD diotic test, but did not sho w any spatial bias in sound localization. Two other patients (A.J. and E.S. ) had the reverse profile: no hemispatial asymmetry in the ITD diotic test, but a severe spatial bias directed to the ipsilesional side in sound local ization. J.C.N. and M.B. had mainly subcortical lesions affecting the basal ganglia, A.J. and E.S. had cortical lesions in the prefrontal, superior te mporal and inferior parietal areas. Thus, there are two behaviourally and a natomically distinct types of auditory neglect characterized by: (i) defici t in allocation of auditory spatial attention following lesions centred on basal ganglia; or (ii) distortion of auditory spatial representation follow ing frontotemporo-parietal lesions.