Relation between auditory resolution capacity (click fusion threshold : CFT) and severity of verbal comprehension disturbance in aphasic patients

The auditory resolution performance of 31 aphasic patients was measured using the click fusion test, and compared with severity of verbal comprehension disturbance (auditory retention span : ARS). The controls were 15 cases with right hemisphere lesion (RHL) and 13 normals. The CFT of the aphasic patients was significantly worse than that of the normals (p=0.0018) , but was not different from the RHL cases with no verbal comprehension disturbance (p=0.0779). In the aphasic patients, there was no correlation between severity of verbal comprehension (ARS) and CFT (r=—0.135, p=0.4737). Lesions of the medial geniculate body or of the medial part of the auditory radiations, as well as lesions of the extensive regions of the transverse temporal gyrus or of the superior temporal gyrus of the left hemisphere produced disturbance of CFT in both bilateral simultaneous stimulation and right unilateral stimulation. Lesions of the lateral part of the auditory radiations, as well as partial lesions of the upper part of the transverse temporal gyrus or of the superior temporal gyrus of the left hemisphere seemed to yield disturbance of CFT only in the right ear presentation condition. From these findings, it was concluded that 1) disturbance of auditory resolution of bilateral ears results from extensive unilateral damage to the auditory systems, and that 2) verbal comprehension performance of aphasic patients is dependent upon both auditory resolution capacity and phonemic recognition performance, although the effect of the latter seems to be significantly stronger. For another measurement procedure of auditory resolution performance, click counting test (CCT) was used in some reports. However, our data suggested that the score of the test was decreased by the lesion of the frontal lobe.