EPV 17. Reduced tone detection contralateral to auditory cortex lesions in complex auditory scenes

Abstract

Objective Unilateral structural lesions of auditory cortex are considered to produce little neurological deficits and no elevation of contralateral detection thresholds. Extinction contralateral to the lesion has been shown with dichotic tests ( Blaettner et al., 1989 , Biedermann et al., 2008 , Gutschalk et al., 2012 ). Here we tested if auditory detection is more generally reduced in the presence of competing sounds using multi-tone informational masking ( Durlach et al., 2003 ). Methods We studied 14 patients with auditory cortex lesions (6 left-, 8 right-hemispheric) and 25 control listeners. Targets were six isochronous pure tones of 100 ms duration and a repetition interval of 400 ms. Target tones were presented monaurally and the frequency within a target sequence was fixed at 846 Hz, 950 Hz or 1066 Hz. Four difficulty levels of multi-tone maskers were used, comprising 2, 4, 6 or 12 tones within each 400-ms interval. Half of the masker tones were presented to the left ear and the other half to the right ear. Tone frequencies were randomly drawn from the range 100–5000 Hz. Half an octave around the target tones was kept as protected region to minimize energetic masking. Tone onsets were random within each 400 ms time interval. Participants indicated after each sequence, whether an isochronous target was present or not. There were 36 target trials and 18 catch trials without target for each masker level. Results Detection, as measured with the sensitivity index d ′ , decreased with increasing number of masker tones for controls and patients. Patients showed reduced target detection in the ear contralateral to the lesion. In comparison to the controls, patients also showed reduced absolute detection. Since this effect was stronger for right-hemisphere patients, we further explored if residual neglect could contribute to the effect. When neglect was modelled as additional factor, the effect of reduced overall detection depending on auditory cortex lesions was not significant any more. However, the contralateral deficit remained significant. Conclusion These results show that competing sounds reduce auditory detection in patients with auditory cortex lesion. Even though the effect was smaller than expected, it may potentially cause hearing difficulties of patients in crowded environments. Since the effect was only significant in the ear contralateral to the lesion, it has to be discussed how closely the effect is related to extinction in dichotic tests.