Evidence taken from patients who have lesions in specific brain regions & specific impairments (which leave other modalities relatively unharmed); Studies first done on adults; later done in children. Caused by deletion of 28 genes on one copy of chromosome 7. Proficient with language & face-processing; mean iq of 58 & severely impaired spatial & numerical cognition. Similar claims made with specific language impairment (sli), and prosopagnosia (inability to recognize familiar faces) Suggests that there are no interactions in the brain. Must take into account ontogenetic development; claimed. Rely more on perception than language when identifying objects. Normal asymmetry between comprehension & production is absent in ws. Karmiloff-smith: modularity of the mind, atypical eye movement planning; these deficits outside the language domain could, through development, lead to the deficits seen in ws, genetic underpinnings of cognitive modules. Believed that mutations/problems with genes have direct effects on behaviour.