Overinclusive thought and loosening of associations are not unique to schizophrenia and are produced in Alzheimer's dementia.
BACKGROUND
Bleuler's concept of loosening of associations which he believed epitomised psychotic thinking can manifest as overinclusion (merging of semantic categories) on semantic categorisation tasks. Overinclusion is explained by excessive activation within the semantic memory network to subordinate features with low associative strength. Therefore patients with degradation of subordinate semantic knowledge (e.g., with Alzheimer's Dementia-AD) should not produce overinclusion errors.


METHODS
22 people with schizophrenia and 26 people with AD (nonpsychotic, semantic memory impairment) were compared on a semantic categorisation test, the Category Generation Test (CGT). The CGT involves free-sorting 45 cards of pictured objects from five taxonomic groups (e.g., animals). Overinclusion and underinclusion (subdivision of categories) errors were recorded and the strategies used in generating these abnormal categories were explored qualitatively.


RESULTS
Two-thirds of both groups generated abnormal categories, including frequent overinclusions. Using a semantic probes test, abnormal categorisations could not be attributed to knowledge degradation as this appeared preserved. Qualitatively, the two groups differed in their sorting strategies.


CONCLUSIONS
Loosening of associations is found in nonpsychotic people, who have semantic memory impairments (e.g., AD), using semantic knowledge tasks. However there may be different explanations; atypical semantic categorisation in schizophrenia appears to result from attention to thematic rather than feature-based associations.
Doughty
Olivia J
OJ
University of Hertfordshire, School of Psychology, Hatfield AL10 9AB, UK. o.j.doughty@herts.ac.uk
Lawrence
Verity A
VA
Al-Mousawi
Adil
A
Ashaye
Kunle
K
Done
D John
DJ
D000328:Adult; D000544:Alzheimer Disease / Q000523:psychology*; D005260:Female; D006801:Humans; D008297:Male; D008568:Memory / Q000502:physiology; D008606:Mental Processes / Q000502:physiology*; D009483:Neuropsychological Tests; D011569:Psychiatric Status Rating Scales; D011597:Psychomotor Performance / Q000502:physiology; D012565:Schizophrenic Psychology