Selective influence of working memory load on exceptionally slow reaction times.

Abstract

The rate of exceptionally slow reaction times (RTs), described by the long tail of the RT distribution, was found to be amplified in a variety of special populations with cognitive deficits (e.g., early-stage Alzheimer's disease, attention-deficit/hyperactivity disorder, low intelligence, elderly). Previous individual differences studies found high correlations between working memory (WM) and parameters that characterize the magnitude of the long-RT tail. However, the causal direction remains unknown. In 3 choice-reaction task experiments, we examined this relationship by directly manipulating WM availability. In Experiment 1, the stimulus-response rules were either arbitrary (WM demanding) or nonarbitrary. In Experiment 2, the arbitrary rules were either novel (demanding) or practiced. In Experiment 3, WM was loaded with either declarative (stimulus-stimulus) or procedural (stimulus-response) arbitrary rules. Using an ex-Gaussian model fitting, we found across all experiments that WM demands uniquely influenced the τ parameter, mostly responsible for the long-RT distribution tail. Evidence accumulation modeling of the choice process indicated that WM load had little influence on the decision process itself and primarily affected the duration of an exponentially distributed nondecision component, assumed to reflect the process of rule retrieval. Theoretical interpretations and implications are discussed.

The Role of Speed in ADHD-Related Working Memory Deficits

“…Thus, though most commonly conceptualized as indexing stimulus encoding and motor preparatory time, Ter should also represent the portion of the RT that is spent refreshing memory items, particularly in a situation in which no additional time is allotted for refreshing (i.e., when there are no explicit gaps left between stimuli; Figure 1). This assumption is not without precedent, as previous studies utilizing evidence accumulation models have similarly proposed and demonstrated that Ter can capture WM operations, including task rule retrieval (Shahar Teodorescu, Usher, Pereg & Meiran, 2014; Schmitz & Voss, 2012). In a complex span task where no time is explicitly left open for refreshing between stimuli (as in the current experiment), this assumption allows cognitive load in each condition and for each individual to be estimated by subtracting the proportion of the mean RT taken up by nondecision processes from 1 (cognitive load = 1 - Ter /RT).…”

Formation of abstract task representations: Exploring dosage and mechanisms of working memory training effects

“…For reaction-times analyses, error and post-error trials, ten first trials in each condition and the first trial after each recess were discarded. Reaction-times below 200ms or above 3.5 SDs from the participant's mean in the respective condition were considered as outliers and thus omitted [PROCEDURAL WORKING MEMORY TRAINING] 15 (Schmiedek et al, 2007;Shahar et al, 2014). For the mean-RT, we found strong evidence for lack of transfer effects (see Figure 3).…”

“…A battery of 6-choice-RT tasks was used. In each task, participants were asked to follow a set of six stimulus-response rules, and identify a target using a manual response (Shahar, Teodorescu, Usher, Pereg, & Meiran, 2014) . Three tasks were used:…”

“…To explore for the mechanism underlying the effect of training on accuracy and RTs, we fitted the two-stage-decision model to choice-RT data (Shahar, Teodorescu, Anholt, Karmon-Presser, & Meiran, 2017;Shahar et al, 2016Shahar et al, , 2014. The two-stage-decision model is an evidence accumulation model describing the decision as involving two processing stages.…”

“…The second stage involves the retrieval of the action rule (i.e., knowing what response is associated with the target that was identified in the previous step). The second decision stage is extrinsic to the evidence accumulation mechanism and involves action-rule retrieval (Shahar et al, 2014). We hypothesized that given the very short duration, a reasonable approximation is that this process is characterized by a constant rate, i.e., a constant hazard function.…”