Cross-Sectional Analysis of Longitudinal Mediation Processes

Statistical mediation analysis can help to identify and explain the mechanisms behind psychological processes. Examining a set of variables for mediation effects is a ubiquitous process in the social sciences literature; however, despite evidence suggesting that cross-sectional data can misrepresent the mediation of longitudinal processes, cross-sectional analyses continue to be used in this manner. Alternative longitudinal mediation models, including those rooted in a structural equation modeling framework (cross-lagged panel, latent growth curve, and latent difference score models) are currently available and may provide a better representation of mediation processes for longitudinal data. The purpose of this paper is twofold: first, we provide a comparison of cross-sectional and longitudinal mediation models; second, we advocate using models to evaluate mediation effects that capture the temporal sequence of the process under study. Two separate empirical examples are presented to illustrate differences in the conclusions drawn from cross-sectional and longitudinal mediation analyses. Findings from these examples yielded substantial differences in interpretations between the cross-sectional and longitudinal mediation models considered here. Based on these observations, researchers should use caution when attempting to use cross-sectional data in place of longitudinal data for mediation analyses.     

Gender dimorphic effects of voluntary running in laboratory rats depends on maturational status

This study examined the effect of 24?hr per day wheel access on running, body weight, and food intake for 30- or 50-day-old male and female rats under ad lib feeding conditions. Food intake and body weight were also monitored in a control group housed without access to running wheels. A dimorphic effect was observed after wheel introduction in 50-day-old but not 30-day-old rats: A temporary decline in food intake and a lasting decrease in body weight occurred for active male rats in comparison to their sedentary controls, and wheel access facilitated food intake and preserved body weight gain in female rats in comparison to their sedentary counterparts. Hyperphagia in adult females is interpreted in terms of the evolutionary acquired advantage linked to their reproductive function.     

Multidimensional processing of dynamic sounds: more than meets the ear

Strong cross-modal interactions exist between visual and auditory processing. The relative contributions of perceptual versus decision-related processes to such interactions are only beginning to be understood. We used methodological and statistical approaches to control for potential decision-related contributions such as response interference, decisional criterion shift, and strategy selection. Participants were presented with rising-, falling-, and constant-amplitude sounds and were asked to detect change (increase or decrease) in sound amplitude while ignoring an irrelevant visual cue of a disk that grew, shrank, or stayed constant in size. Across two experiments, testing context was manipulated by varying the grouping of visual cues during testing, and cross-modal congruency showed independent perceptual and decision-related effects. Whereas a change in testing context greatly affected criterion shifts, cross-modal effects on perceptual sensitivity remained relatively consistent. In general, participants were more sensitive to increases in sound amplitude and less sensitive to sounds paired with dynamic visual cues. As compared with incongruent visual cues, congruent cues enhanced detection of amplitude decreases, but not increases. These findings suggest that the relative contributions of perceptual and decisional processing and the impacts of these processes on cross-modal interactions can vary significantly depending on asymmetries in within-modal processing, as well as consistencies in cross-modal dynamics.     

Exploring task-set reconfiguration with random task sequences

Switching between two different tasks normally results in an impairment in people's performance known as a switch cost, typically measured as an increase in reaction time (RT) and errors compared to a situation in which no task switch is required. Researchers in task switching have suggested that this switch cost is the behavioural manifestation of the task set reconfiguration processes that are necessary to perform the upcoming task. However, an examination of the literature in task switching reveals apparently contradictory results about the nature of task set reconfiguration processes. In Experiment 1, we addressed this issue by comparing participants' performance in two different experimental conditions: predictable task switching and random task switching. In the predictable switch condition the switch cost completely vanished after the first repetition of the new task. However, in the random switch condition, while the difference between switch and repetition trials was not significant, we observed a significant reduction in RT between the first and second repetition of the new task. In Experiment 2, we further investigated the pattern of task set reconfiguration in the random switch situation. The results showed a progressive reduction of participants' response latencies across repetitions of the same task. The present study demonstrates that, whereas the results in predictable switching conditions are compatible with an exogenous-reconfiguration hypothesis, random task switching produces a more gradual, decay-like switch cost reduction with task repetition.     

What needs to be explained to account for age-related effects on multiple cognitive variables?

Structural equation methodology was used to investigate age-related influences across a number of cognitive variables in 204 adults ranging from 18 to 91 years of age with a hierarchical structure that contained 4 1st-order factors and 1 2nd-order common factor. Direct age relations were found to the common factor as well as to 1st-order speed and memory factors. Replicability of the findings was explored by investigating the same structure of age relations, using 2 different data sets, and a similar patten was found in each. These results suggest that at least 3 statistically distinct types of age-related influences are operating on a wide variety of cognitive variables and presumably require separate explanatory mechanisms.     

Modeling affective processes in dyadic relations via dynamic factor analysis

An intraindividual variability design, including application of dynamic factor models, was used to examine the affective processes of a husband-wife dyad over 182 consecutive days. Structural equation analyses indicated differences in the affective structure between the husband and the wife, and these differences were characterized in terms of their factorial configuration and temporal organization. Examination of the dyad's affective dynamics revealed unidirectional (i.e., from the husband to the wife) interpersonal influences with a defined structure over time.