  In contrast with Williams syndrome, in which one sees comparatively  spared language in the face of mild to moderate mental retardation  and numerous physical defects, specific language impairment  (‘SLI’) is diagnosed when (i) non-verbal intelligence as  measured by standard IQ tests is normal; (ii) verbal IQ is well below normal; and (iii) obvious causes of language impairment (e.g.,  deafness, frank neurological damage) can be ruled out. As one might  expect given these diagnostic criteria, a diagnosis of SLI embraces a highly heterogeneous collection of language-related deficits, not all of which co-occur in every case of language impairment. (Bishop,  1994; Bishop et al,. 2000.) These include: