Feature Blindness: A Case Study

This article provides evidence that supports the hypothesis that developmental dysphasia results from a deficit in marking a specific class of linguistic features. The data show that this deficit is not the result of a perceptual problem or any general cognitive problem in representing hierarchical relationships, but rather appears to be a specifically linguistic problem. Moreover, it is not a deficit that affects all parts of language equally. Syntacficosemantic features are affected, whereas some other language processes, like thematic relations in simple sentences, are unimpaired. Because these features are absent, morphophonemic rules and rules that match features in the syntax are also absent. The fact that the same errors are found in all manifestations of language-spontaneous speech, grammatical judgment, repetition, and writing-supports the hypothesis that the deficit is in the underlying grammar rather than merely a problem of performance. Data from a wide range of features (including number, person, tense, aspect, and gender) confirm specific predictions that follow from the feature-deficit hypothesis but that cannot be accounted for by a perceptual or cognitive deficit hypothesis. This explanation is supported by data from a detailed case study as well as by data reported in the literature to be typical of dysphasia. There is also evidence that suggests that the form of dysphasia described in this article may be genetic in origin.