Memory for serial order in Alzheimer's disease and vascular dementia: A competitive queuing analysis

Objective: Competitive Queuing (CQ) models of memory for serial order comprise two layers: Parallel planning where target items are activated and competitive choice where serial order is specified. The application of CQ models regarding healthy and pathological aging has received little attention. Method: Participants included patients with Alzheimer's disease (AD; n = 26), vascular dementia (VaD; n = 29), and healthy controls (HC; n = 35). Memory for serial order in the visual domain was assessed using the Object Span Task, where participants briefly viewed then drew a sequence of four figures. Percent correct and total errors (omissions, intrusions, repetitions, transpositions) were computed for each serial position. Results: Significant primacy effects were detected in each group. AD and VaD participants were less accurate and showed more omission and between-trial repetition errors than HC (HC < AD = VaD, p < .05). VaD participants produced more transposition and intrusion errors than the AD and HC groups (HC < AD < VaD, p < .05). A group × position interaction was significant for omissions (p < .05), with AD and VaD participants producing more omissions in later serial positions (SP1 < SP2 < SP3 < SP4, all p values < .05). Conclusions: Analysis of accuracy and errors by serial position identified unique patterns of performance across groups that suggest involvement of distinct layers of response activation and selection. Serial order difficulties in AD may be due to weakened activation of task items affecting later serial positions, whereas poor performance in VaD may be due to weakened activation plus interference from extraneous stimuli at all serial positions.