Flexible Mediation Analysis in the Presence of Nonlinear Relations: Beyond the Mediation Formula

In the social sciences, mediation analysis has typically been formulated in the context of linear models using the Baron &; Kenny (1986) Baron, R. M. and Kenny, D. A. 1986. The moderator-mediator variable distinction in social psychological research: Conceptual, strategic and statistical considerations. Journal of Personality and Social Psychology, 51: 1173–1182. [Crossref], [PubMed], [Web of Science ®] , [Google Scholar] approach. Extensions to nonlinear models have been considered but lack formal justification. By placing mediation analysis within the counterfactual framework of causal inference one can define causal mediation effects in a way that is not tied to a specific statistical model and identify them under certain no unmeasured confounding assumptions. Corresponding estimation procedures using parametric or nonparametric models, based on the so-called mediation formula, have recently been proposed in the psychological literature and made accessible through the R-package mediation. A number of limitations of the latter approach are discussed and a more flexible approach using natural effects models is proposed as an alternative. The latter builds on the same counterfactual framework but enables interpretable and parsimonious modeling of direct and mediated effects and facilitates tests of hypotheses that would otherwise be difficult or impossible to test. We illustrate the approach in a study of individuals who ended a romantic relationship and explore whether the effect of attachment anxiety during the relationship on unwanted pursuit behavior after the breakup is mediated by negative affect during the breakup.     

Alternative-based thresholding with application to presurgical fMRI

Functional magnetic reasonance imaging (fMRI) plays an important role in pre-surgical planning for patients with resectable brain lesions such as tumors. With appropriately designed tasks, the results of fMRI studies can guide resection, thereby preserving vital brain tissue. The mass univariate approach to fMRI data analysis consists of performing a statistical test in each voxel, which is used to classify voxels as either active or inactive—that is, related, or not, to the task of interest. In cognitive neuroscience, the focus is on controlling the rate of false positives while accounting for the severe multiple testing problem of searching the brain for activations. However, stringent control of false positives is accompanied by a risk of false negatives, which can be detrimental, particularly in clinical settings where false negatives may lead to surgical resection of vital brain tissue. Consequently, for clinical applications, we argue for a testing procedure with a stronger focus on preventing false negatives. We present a thresholding procedure that incorporates information on false positives and false negatives. We combine two measures of significance for each voxel: a classical p-value, which reflects evidence against the null hypothesis of no activation, and an alternative p-value, which reflects evidence against activation of a prespecified size. This results in a layered statistical map for the brain. One layer marks voxels exhibiting strong evidence against the traditional null hypothesis, while a second layer marks voxels where activation cannot be confidently excluded. The third layer marks voxels where the presence of activation can be rejected.     

Forgetting of prior remembering in persons reporting recovered memories of childhood sexual abuse

Case studies of individuals reporting recovered memories of childhood sexual abuse suggest that some overestimate their prior forgetting of the abuse. People reporting recovered or continuous memories of childhood sexual abuse and control subjects reporting no history of abuse participated in two experiments examining this "forgot it all along" phenomenon. Participants in Experiment 1 were more likely to forget that they had previously recalled a studied item if they were cued to think of it differently on two recall tests than if they were cued to think of it in the same way on the two tests. This effect was stronger for recovered-memory participants than for continuous-memory and control participants. In Experiment 2, participants recalled autobiographical events three times over a period of 4 months. Much as in Experiment 1, they underestimated prior remembering when the events had been recalled in a different emotional frame (positive vs. negative) on the previous occasion. This underestimation was more pronounced for recovered-memory participants than for continuous-memory and control participants.     

Effects of repeated retrieval of central and peripheral details in complex emotional slides

Research has demonstrated that repeated retrieval enhances memory for practised verbal information, but undermines correct recall of unpractised related verbal information, a phenomenon known as retrieval-induced forgetting (RIF). This paper addresses the question of what happens with memory for unrehearsed aspects of an emotional picture when retrieval of other aspects of that picture is practised. In two experiments we investigated whether repeated retrieval of certain details of negative emotional slides undermines recall of unrehearsed details of such slides. In Experiment 1 retrieval of peripheral details was practised. The results demonstrated that recall for peripheral details was enhanced. However, correct recall of unpractised central details remained unaffected. Furthermore, retrieval practice did not alter the number of commission errors. Experiment 2 revealed that repeated retrieval of central details enhanced memory for these details. Although more commission errors were produced, again correct recall was not impaired for the unrehearsed central and peripheral details. This failure to find retrieval-induced forgetting effects for complex visual material is at odds with the RIF literature, and potential reasons for this are discussed. The data also extend previous studies in demonstrating that extensive retrieval can increase the number of commission errors.     

The analysis of zero-inflated count data: beyond zero-inflated Poisson regression

Infrequent count data in psychological research are commonly modelled using zero-inflated Poisson regression. This model can be viewed as a latent mixture of an "always-zero" component and a Poisson component. Hurdle models are an alternative class of two-component models that are seldom used in psychological research, but clearly separate the zero counts and the non-zero counts by using a left-truncated count model for the latter. In this tutorial we revisit both classes of models, and discuss model comparisons and the interpretation of their parameters. As illustrated with an example from relational psychology, both types of models can easily be fitted using the R-package pscl.     

Waiting impulsivity: a distinctive feature of ADHD neuropsychology?

Impulsivity is a core feature of attention-deficit hyperactivity disorder (ADHD). It has been conceptualized in a number of different ways. In the current article, we examine how the new concept of “waiting impulsivity”, which refers to premature responding before a scheduled target appears, adds to our understanding of impulsivity in ADHD. Sixty children (8–12 years old; 30 ADHD; 30 typically developing controls) completed the 4-choice serial reaction time task, a measure of waiting impulsivity, alongside tasks measuring inhibitory control and temporal discounting and questionnaires measuring behavioral disorder symptoms, delay aversion, and various aspects of impulsivity. A multiple logistic regression model was used to explore the contribution of the primary task outcomes to predict group membership. Children with ADHD displayed more waiting impulsivity and less inhibitory control; they did not differ in temporal discounting. There was no correlation between waiting impulsivity and inhibitory control. Waiting impulsivity was correlated with parent-reported ratings of hyperactivity/impulsivity, inattention, oppositional defiant disorder (ODD), and conduct disorder (CD) and with self-reported delay aversion ratings. Only waiting impulsivity was a significant predictor of ADHD status. In conclusion, waiting impulsivity is distinct from inhibitory control deficits and predicts ADHD status independently of it. Future research needs to examine the relationship with delay aversion and ODD/CD more thoroughly.     

The Mental Regulation of Autobiographical Recollection in the Aftermath of Trauma

ABSTRACT— Survivors of psychological trauma are frequently troubled by intrusive recollection of the traumatic event. We describe research showing that attempts to suppress such trauma memories can be associated with paradoxically enhanced remembering of the trauma, enhanced access to other negative personal material, and a lack of specificity in the recollection of the personal past. This suggests that attempted suppression is generally a counterproductive approach to the regulation of traumatic memories in distressed trauma survivors. Working with trauma memories, rather than suppressing them, is more adaptive.     

Retrieval‐induced forgetting of autobiographical memory details

Several studies suggest that intrusive and overgeneral autobiographical memory are correlated. Thus, paradoxically, in some patients a hyperaccessibility of memory for one (series of) event(s) goes hand‐in‐hand with a scarcity of memories for other personal experiences. This clinical observation is reminiscent of the laboratory phenomenon of retrieval‐induced forgetting (RIF). This refers to the finding that repeatedly recalling some experimental stimuli impairs subsequent recall of related (i.e., tied to the same retrieval cue) stimuli. RIF of emotional autobiographical memories might provide an experimental model for the clinical memory phenomena in question. The present paper reports two experiments that explored the merits of applying the retrieval practice paradigm to relatively broad categories of autobiographical memories. Both studies found a significant RIF effect in that practised memories were recalled better than unrelated unpractised (baseline) memories. In addition, unpractised memories that were related to the practised memories were recalled more poorly than baseline memories. Implications of these findings for modelling the co‐occurrence of intrusive and overgeneral memories are discussed.     

Autobiographical memory specificity after manipulating retrieval cues in adults reporting childhood sexual abuse

Traumatized samples have relative difficulty in generating specific autobiographical memories on a cue word task, compared to nonexposed controls. Simultaneously, trauma is associated with highly specific intrusive trauma memories in day-to-day life. Possibly, day-to-day intrusions and memories generated to cue words rely on different retrieval processes, with the former dependent on close associations between retrieval cues and specific memory representations (direct retrieval), and the latter on iterative retrieval cycles through a hierarchical memory system (generative retrieval). This study investigated this distinction using two versions of the cue word task, designed to promote generative and direct retrieval, respectively, in participants with or without a history of child sexual abuse (CSA). The data demonstrated that CSA participants were less specific than nonabused controls to generative retrieval cues, but this difference disappeared with direct retrieval cues. This interaction was stronger in CSA participants with relatively greater posttraumatic stress and remained significant when participants with past or current major depressive disorder were excluded and also when only those participants with corroborated CSA were included.     

Prepartum autobiographical memory specificity predicts post-traumatic stress symptoms following complicated pregnancy

Prior research has shown that reduced autobiographical memory specificity predicts an increase in post-traumatic stress severity in traumatised individuals. Studies have also demonstrated that reduced memory specificity predicts later symptoms of depression after pregnancy-related life stress. So far, no reported studies have tested the predictive value of memory specificity at the onset of a potentially traumatic situation. Therefore the aim of the present study was to investigate whether prenatal memory specificity would predict post-traumatic stress after complicated pregnancy. The results demonstrate that women who retrieved fewer specific memories with a pregnancy-related content to positive cues during pregnancy (i.e., directly after hospitalisation) reported more post-traumatic stress 6 weeks after giving birth. This relationship remained significant after controlling for variables that were related to both baseline autobiographical memory specificity and later post-traumatic stress. A similar pattern was found for depression symptomatology, even when somatic symptoms were excluded from the analyses. Taken together, these data suggest that the relationship of memory specificity with later depression can be generalised to post-traumatic stress symptoms.