Inhibition of return in aging and Alzheimer's disease: Performance as a function of task demands and stimulus timing

Inhibition of return (IOR) is a phenomenon of spatial attention that biases attention toward novel events in the environment. Recent evidence suggests that the magnitude and timing of IOR varies as a function of task conditio ns (e.g., detection vs. discrimination tasks, short vs. long cue-tar.-et in tervals, intrinsic vs. extrinsic cues). Although IOR appears relatively pre served with both normal aging and Alzheimer's disease (AD), it has been tes ted under relatively simple task conditions. To test whether IOR is resista nt to age and/or AD when cognitive demands are increased, we employed a dou ble-cue IOR paradigm that required categorization as well as detection resp onses. The stimulus onset asynchrony (SOA) between the cue and target event s was varied to determine whether group differences existed in IOR effects over time. Younger normal adults and older normal adults exhibited signific ant IOR effects on both the detection task and the categorization task at a short cue-target SOA (950 ms). In contrast, AD patients exhibited signific ant IOR effects at the short SOA on the detection task but not on the categ orization task. From the short to the long SOA (3500 ms), IOR effects exhib ited by younger normal adults declined significantly during both the detect ion and the categorization tasks, suggesting that inhibition resolved over time. In contrast, neither older normal adults nor AD patients exhibited SO A-related IOR reductions on the detection task. These results suggest that IOR may show differential age- and AD-related vulnerabilities depending on task conditions and timing characteristics.