It is often remarked that natural language, used naturally, is unnaturally ungrammatical. *Spontaneous speech contains all manner of false starts, hesitations, and self-corrections that disrupt the well-formedness of strings. It is a mystery then, that despite this apparent wide deviation from grammatical norms, people have little difficulty understanding the non-fluent speech that is the essential medium of everyday life. And it is a still greater mystery that children can succeed in acquiring the grammar of a language on the basis of evidence provided by a mixed set of apparently grammatical and ungrammatical strings.
Donald Hindle (Sat,) studied this question.
Synapse has enriched 5 closely related papers on similar clinical questions. Consider them for comparative context: