Objectives: The aim was to expand existing knowledge to determine if difficulties in explicit memory extend to spatial relational information whilst implicit memory for this information remains intact.
Methods: Sixteen participants with a confirmed clinical diagnosis of ASD and 16 age, gender and IQ matched TD individuals were tested. An object-location memory test was implemented using the process dissociation procedure developed by Jacoby (Jacoby, 1991; J Mem Lang, 30, 513-541) to test for explicit and implicit memory. In this task participants studied locations of objects in pictures of rooms presented on a computer screen. In the testing phase participants were shown an object and had to either choose its old location from a choice of three (‘inclusion trials’) or choose a new location (‘exclusion trials’). Eye-movements were also recorded during the test and following the primary ‘inclusion/exclusion’ test, recognition memory was tested for objects and locations separately using the ‘remember-know’ procedure.
Results: On inclusion trials ASD individuals chose the old location significantly less often (F(1,30) = 5.71, p < .05) but they did as well as the TD individuals on exclusion trials. This led to a significantly lower estimate of explicit memory for the ASD group (F(1,30) = 5.65, p < .05) but implicit memory was preserved. This is unlikely to be due to differences between groups in attending to the various response options during the test because both groups looked significantly longer at the old object location during inclusion trials (F(1,29) = 105.37, p < .001) and longer at another location during exclusion trials (F(1,29) = 105.37, p< .001). The object and location recognition tests indicated that the lower performance of the ASD group in explicit object-location memory was unlikely to be the result of poorer memory for the objects or locations separately.
Conclusions: This experiment extends findings of diminished explicit memory in ASD from the verbal to the spatial domain and indicates that these difficulties might not be due to differential attention or lower memory for items or locations but rather due to the relation between both. It gives further support for the theory that individuals with ASD seem to have a problem with relational binding and the hippocampus rather than other regions in the medial temporal lobes of the brain.
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