We have hypothesized that the language and learning impairments that distinguish lower functioning autism (LFA) from higher-functioning forms of autism (HFA) result partly from an impairment of semantic memory additional to the impairment of episodic memory known to occur across the spectrum. More specifically, we hypothesize that whereas recollection (which plays a critical role in episodic memory) is impaired across the spectrum, familiarity (which plays a critical role in semantic memory) is impaired only in individuals with LFA.
The main objective of the research is to assess recollection and familiarity in LFA relative to comparison groups including an HFA group. If, as predicted, familiarity is impaired in the LFA group, but not the HFA group, a subsidiary objective is to assess the predicted associations in LFA between impaired familiarity, language (in particular, lexical-semantic knowledge), and learning (as manifested in crystallized intelligence).
Participants. Four groups of c. 25 participants are being assessed: adolescents (11-17 years) with LFA (VQ ≤75; adolescents (11-17 years) with intellectual disability without autism (ID) (VQ≤75; children (6-10 years) with HFA (VIQ≥90); and typically developing (TD) children (6-10 years) with VQ in the average range.
Baseline tests. Participant groups will be equated for verbal MA on the Similarities and Vocabulary subtests from the Wechsler scales. Additional baseline tests are: Ravens Matrices (to assess nonverbal IQ); The Children’s Embedded Figures Test (to assess field dependence-independence); and the Pyramids and Palm Trees test (to assess lexical-semantic knowledge).
Experimental studies (ongoing). Two methods of assessing familiarity and recollection independently of each other are being used. In Study 1, ‘Shape recognition, action recall’ tests are used. This pair of tests was developed and used with the predicted result in children with HFA, as reported in Bigham, Boucher, Mayes, and Anns (2010). In Study 2 two forced choice recognition tests are used. This pair of tests was developed and successfully used to discriminate between familiarity and recollection in patients with acquired amnesia associated with selective hippocampal lesions, as reported by Migo, Mayes et al. (2009).
Statistical analyses. Between group differences on the tests of recollection and familiarity will be assessed using analyses of variance, covarying the effects of nonverbal IQ (fluid intelligence) and field dependence-independence (central coherence). Within-group associations between familiarity and lexical-semantic knowledge, and between familiarity and crystallized intelligence, will be assessed using correlation tests.
Results: and Conclusions:
These will be available in time to be reported.
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