Multiple Processes Underlying Dimensional Change Card Sort Performance: A Developmental Electrophysiological Investigation

Cognitive flexibility follows a protracted developmental trajectory [Morton, J. B. Understanding genetic, neurophysiological, and experiential influences on the development of executive functioning: The need for developmental models. Wiley Interdisciplinary Reviews: Cognitive Science, 2010]. For example, performance and patterns of brain activity associated with the dimensional change card sort (DCCS) show continued age-related changes into early adolescence. According to many theoretical accounts, the DCCS places demands on a single underlying executive process. In the present study, we investigated the possibility that multiple processes unfold within the timeframe of a single DCCS trial through the use of ERPs. Children (n = 40), adolescents (n = 20), and adults (n = 20) performed a modified version of the DCCS with distinct instruction cue- and stimulus-related periods. On any particular trial, the sorting rule either changed (i.e., switch trials) or remained the same (i.e., repeat trials), and the imperative stimulus either embodied conflict (i.e., bivalent stimuli) or did not (i.e., univalent stimuli). Findings were consistent with the hypothesis that multiple distinct executive processes unfold within a single trial. First, for all age groups, rule switching and conflict processing made additive contributions to variability in RT. Second, ERPs time-locked to the instruction cue revealed a late frontal negativity whose amplitude was greater for switch trials relative to repeat trials and that was associated with the magnitude of the behavioral switch cost, whereas ERPs time-locked to the imperative stimulus revealed a fronto-central N2 whose amplitude was greater for bivalent than univalent stimuli and that was associated with the magnitude of the behavioral conflict cost. Finally, switch and conflict-related processes showed distinct developmental trajectories. Taken together, the findings suggest that multiple executive processes underlie DCCS performance and its development. Theoretical implications are discussed.

Smoking/Nicotine Affects the Magnitude and Onset of Lateralized Readiness Potentials

Smoking/nicotine improves cognitive performance for a variety of tasks. In most cases, reaction time (RT) is generally shorter after smoking/nicotine. While there may be some slight facilitation of stimulus-evaluation processing, most of the RT effects of nicotine appear to take place following the response-selection stage. This study investigated possible effects (in smokers) of smoking/nicotine on response preparation and execution processes using the lateralized readiness potential (LRP). On each trial, a warning stimulus preceded an imperative stimulus by 1.2s. The warning stimulus completely specified the correct response to the imperative stimulus. The study was completed in two morning sessions in which 4 cigarettes were smoked in each session. The nicotine yield of the cigarettes varied between sessions (0.05mg or 1.1mg). Maximum amplitudes of both the stimulus and response-locked LRPs were larger in the 1.1 mg session. For both stimulus- and response-locked LRPs, smoking the 1.1 mg cigarette (but not the 0.05 mg cigarette) shortened onset latency. However, the magnitude of the effect was much larger for the stimulus-locked LRPs, suggesting that response preparation is facilitated by smoking/nicotine to a greater degree than response execution.