Meta-analysis indicated sustained activation during ongoing task processing
Meta-analysis studies have shown an exciting mix of findings with some studies showing age-related decrements in prospective memory 11 and others showing no age differences1819. An understanding of this pattern in the study can be attributed to the reasoning that age differences may be less prominent with prospective memory paradigms that stimulate dependence on spontaneous retrieval processes. Supporting the hypothesis, there was a series of experiments conducted by20, with the young, middle age, and old participants indicating no age differences when spontaneous retrieval was encouraged. These outcomes supportforthepossibilitythatspontaneousretrievaliswell-maintainedinolderadulthoodandthatprospectivememorycanattenuate with age differences under certain conditions. There are not much neuroimaging studies that have focused on isolating the spontaneous retrieval processes21. There is still some evidence supporting the claim that different neural routes support monitoring and spontaneous retrieval which are based on fewer studies where monitoring processes were disengaged. An example study by2122 indicated sustained activation during ongoing task processing in prefrontal areas associated with attentional control during a nonfocal prospective memory task but not during a focal prospective memory task. In another study 23, it was found that hippocampal volume was signi cantly correlated with focal prospective memory performance but lacked correlation with nonfocal task performance. Combining the findings of these studies indicates that different prospective memory processes rely on different brain structures; namely, it appears that the frontal regions such as the aPFC are involved in attentionally demanding monitoring processes, but hippocampal regions support spontaneous retrieval. 5.3DelayTheory Fundamentaltothistheoryisthehypothesisthatmonitoringisacognitivelyisacognitivelydemandingprocess,andthatprospective memory task must compete for resources with the ongoing task. As more and more resources are devoted to the prospective memory task, it results in delayed response time for the ongoing task. Under this theory, information relevant to the ongoing task and the prospective memory task are accumulated in parallel (but at different rates), and both types of information compete in a horse-race fashion to determine the response selection. There is a congregating indication for this conceptualization in studies of aging (Kliegel et al., 2008), working memory (Smith, 2003), and neuroimaging (McDaniel et al., 2013). The delay theory proposed by Heathcote et al.(2015) consisted of an evidence linear ballistic accumulation model that characterizes a fast, two-option decision. It determines the rate at which information for the decision accumulates and the decision boundary when the accumulated information is suf cient to make a decision. The assumption is that the prospective memory re ects a more conservative boundary setting for the ongoing-task decision (allowing the time necessary to fetch information relevant to the prospective memory task). Thus, the change in ongoing task performance when a prospective memory task is present relative to when it is not present should be captured just by the parameter estimates (acquired from the evidence accumulator) for the decision boundary. Also, the theory predicts no change in the rate of information accumulation parameter. Heathcote et al. (2015) observation in the changes to decision boundary parameter using the parameter estimate approach suggested that the costs associated with having a nonfocal prospective memory task were due to participants “relaxing” their decision boundaries. Heathcote and colleagues through an experiment also proposed that participants were raising their word/nonword decision threshold on the lexical decision task allowing more time for prospective memory information to be accumulated. Supported by the work of Lourenço et al. (2013) that showed when participants are told that nonfocal prospective memory targets will only occur on5word trials in a lexical decision task, there was less slowing on nonword trials. Implying that participants were successfully able to adjust their decision threshold based on the task demands (and the formal modeling of data supports this interpretation; Heathcote et al.,2015). However, delay theory has dif culty explaining for other behavioral evidence, and it is apparent that a complete reformulation of the interpretation of costs is required. Also, neuroimaging studies have provided complications in support of the theory. Participants engaging in nonfocal tasks have shown sustained aPFC activation, an area strongly associated with attentional control while for focal prospective memory tasks this sustained activation was absent (McDaniel et al.,2013). Therefore, the question here is why a single underlying process would leave different neural footprints depending on the type of cue given. More speci cally, the question here is why sustained aPFC activation is seen for the ongoing task when a nonfocal cue is present, but these same mechanisms do not require sustained aPFC with a focal cue.