Response time as an index for selective auditory cognitive deficits

The full or partial recovery of cognitive functions following brain lesions is believed to rely on the recruitment of alternative neural networks. This has been shown anatomically for selective auditory cognitive functions (Adriani et al. 2003b). We investigate here behavioral correlates that may accompany the use of alternative processing networks and in particular the resulting increase in response times. The performance of 5 patients with right or left unilateral hemispheric infarction and 6 normal control subjects in sound identification, asemantic sound recognition, sound localization, and sound motion perception was evaluated by the number of correct replies and response times for correct and wrong replies. Performance and response times were compared across patients and normal control subjects. Two patients with left lesions were deficient in sound identification and sound motion perception and normal in sound localization and asemantic sound recognition; one patient with right lesion was deficient in sound localization and sound motion perception and normal in sound identification and asemantic sound recognition; deficient performance was associated with increased response times. The remaining 2 patients (1 with left, 1 with right lesion) had normal performance in all 4 tasks but had significantly longer response times in some (but not all) tasks. Patients with normal or deficient performance tended more often than normal subjects to give faster correct than wrong replies. We propose that increased response time is an indication of processing within an alternative network.