Auditory extinction and spatio-temporal order judgment in patients with left- and right-hemisphere lesions

Auditory extinction and spatio-temporal order judgment (STOJ) were assessed in patients with acquired brain damage by systematically manipulating onset times in bilateral stimulation under free-field conditions. We tested the hypothesis that extinction will be reduced by increasing stimulus onset asynchrony. Two groups of patients with right-hemisphere (RH, n=17) or left-hemisphere (LH, n=17) damage were investigated in comparison to a healthy control group (n=12). The patients were recruited based on previously diagnosed impairments: auditory discrimination deficits with (RH(E)/LH(E)) or without extinction (RH(0)/LH(0)) due to cortical and/or subcortical temporo-parietally centred lesions. Stimuli were presented bilaterally in the acoustic free-field, with an onset asynchrony of ± 30 to ± 150 ms, or unilaterally, from speakers located ± 60°. Low frequency (LF) and high frequency (HF) stimuli were used to address spatial auditory processing in the horizontal plane based on the two main cues of interaural time and interaural intensity differences, respectively. The subjects' task was to indicate whether they perceived one (left or right) or two stimuli (left and right), and in the case of two make an STOJ (left or right first). Temporal asynchrony significantly reduced extinction in those patients that previously exhibited extinction for bilateral-simultaneous stimulation (RH(E)/LH(E)). In addition, their error rates in STOJ were higher than the controls'. A number of patients with no previous signs of extinction in bilateral-simultaneous stimulation (RH(0)/LH(0)) also showed impaired STOJ: in RH(0) patients this was specific to ipsilesional-leading stimuli, whilst in LH(0) patients no side-specific effect was observed. The data support the notion of differential roles for the two hemispheres in spatio-temporal auditory perception and are discussed with respect to prevalent models of extinction and its possible long-term reduction.