Word comprehension - The distinction between refractory and storage impairments

We report a series of experiments in which we compare the residual word comprehension skills of patients with cortical degenerative conditions and those with an 'access' dysphasia. Using word-picture matching tasks it was shown that (i) the presentation rate (the response-stimulus interval) affected the word comprehension performance of the patients with an access dysphasia but not of the patients with degenerative conditions; (ii) the semantic relatedness of the stimulus arrays had a greater influence in the performance of the access dysphasic patients than with a degenerative condition; (iii) word frequency was a strong determinant of the performance of patients with degenerative conditions but not those with an access dysphasia; and (iv) response inconsistency was a characteristic of the patients with an access dysphasia, whereas this was not observed in those with a degenerative condition. These four effects clearly differentiate the word comprehension performance of these two types of patients. Thus, two types of word comprehension impairment have been identified A unitary account of the pattern of performance in the access patients in terms of refractoriness has previously been proposed and it is reiterated here. Similarly a unitary account of the patients with degenerative conditions in terms of storage deficit is advanced. it is speculated that these two types of deficit, refractoriness and storage, reflect two sources of damage to the stored representations underpinning a word, rather than a dichotomy between deficits affecting the procedures of accessing semantic representations and the stored representations themselves. The implications for neurological diagnosis and therapeutic intervention are discussed.