The interaction between stop signal inhibition and distractor interference in the flanker and Stroop task

In the present study, two experiments were conducted to investigate the interaction between the behavioral inhibition, measured by the stop signal task, and distractor interference, measured by the flanker task and the Stroop task. In the first experiment, the stop signal task was combined with a flanker task. Analysis revealed that participants responded faster when the distractors were congruent to the target. Also, the data suggest that it is more difficult to suppress a reaction when the distractors were incongruent. Whether the incongruent distractor was part of the response set (i.e. the distractor could also be a target) or not, had no influence on stopping reactions. In the second experiment, the stop signal task was combined with a manual version of the Stroop task and the degree of compatibility was varied. Even though in the second experiment of the present study interference control is differently operationalized, similar results as in the first experiment were found, indicating that inhibition of motor responses is influenced by the presentation of distracting information that is not part of the response set.     

From models to rules: mechanization of reasoning as a way to cope with cognitive overloading in combinatorial problems

It is hypothesized that the transition from unfamiliar problems to familiar, well-learned problems coincides with the transition from a model-based style of reasoning to a rule-based style of reasoning; model-based style of reasoning helps understanding the problem structure, but can overload working memory when the number of models required increases; rule-based style of reasoning avoids cognitive overloading, at the cost of making individuals liable to mechanization errors. In Experiment 1, the number of models required to respond to a verification task affected response latencies with unfamiliar problems, but not with familiar problems, supporting the initial hypothesis. In Experiment 2, participants were prone to mechanization errors when confronted with slightly modified problems in the late stages of the experiment, supporting the hypothesis that they had developed a reasoning rule in the early stages and were blindly applying it. The findings suggest that model-based reasoning and rule-based reasoning serve different purposes and have different costs and benefits, are both available to human reasoners, and familiarization with a problem may induce the transition from the former to the latter. The findings also suggest that mechanization of reasoning may be the first step along a gradient of decreasing cognitive load, whose end-point is automatization, as discussed in theories of automatization of information processing.     

Resistance to the impact of interruptions during multitasking by healthy adults and dysexecutive patients

Two experiments (one with healthy adult volunteers and the other with controls and dysexecutive patients) assessed the impact of interruptions on a novel test of multitasking. The test involved switching repeatedly between four tasks (block construction, bead threading, paper folding, alphabetical searching) over a 10 min period. In Experiment 1, there were four groups of 20 healthy participants. One group attempted multitasking with no interruption, a second group was interrupted early in the test, a third group late in the test and a fourth group was interrupted both early and late. Interruption involved carrying out a fifth, unexpected task for a period of 1 min before returning to the four main tasks. There was no difference in multitasking performance between the groups. In Experiment 2 the participants were seven dysexecutive patients and 14 age-matched controls. A repeated measures approach was employed to assess the impact of two interruptions (early and late) for both groups. Contrary to predictions, the patients as well as controls were resistant to the effects of interruptions, despite their clearly impaired multitasking performance. These results suggest that the ability to deal with interruptions may be separable from the ability to organise and execute multiple tasks within a limited time frame.     

Measuring automatic retrieval: a comparison of implicit memory, process dissociation, and speeded response procedures

Using the stem completion task, we compared estimates of automatic retrieval from an implicit memory task, the process dissociation procedure, and the speeded response procedure. Two standard manipulations were employed. In Experiment 1, a depth of processing effect was found on automatic retrieval using the speeded response procedure although this effect was substantially reduced in Experiment 2 when lexical processing was required of all words. In Experiment 3, the speeded response procedure showed an advantage of full versus divided attention at study on automatic retrieval. An implicit condition showed parallel effects in each study, suggesting that implicit stem completion may normally provide a good estimate of automatic retrieval. Also, we replicated earlier findings from the process dissociation procedure, but estimates of automatic retrieval from this procedure were consistently lower than those from the speeded response procedure, except when conscious retrieval was relatively low. We discuss several factors that may contribute to the conflicting outcomes, including the evidence for theoretical assumptions and criterial task differences between implicit and explicit tests.     

An evaluation of the minimal constraining information during observation for movement reproduction

An important question in the field of imitation is what information is used for movement reproduction. While it is argued that relative motion information is perceived and minimised, direct evidence is lacking. In this experiment relative motion was manipulated to convey a novel kicking action. Twenty-four adults were assigned to one of the three impoverished relative motion display groups showing only the TOE, FOOT or LEG. After practise with partial information, participants watched a full-body display and in a final condition performed the action with an additional context constraint (i.e., a ball). Movement kinematics were collected and difference scores between participants and the model were analysed. The groups did not differ in terms of knee-ankle coordination. For hip-knee, the TOE group performed more like the model than the FOOT and LEG group. When transferred to the full-body display, there were no significant improvements. End-point trajectory information can provide sufficient information to reproduce key characteristics of the movement form.     

Individual differences in causal learning and decision making

In judgment and decision making tasks, people tend to neglect the overall frequency of base-rates when they estimate the probability of an event; this is known as the base-rate fallacy. In causal learning, despite people's accuracy at judging causal strength according to one or other normative model (i.e., Power PC, DeltaP), they tend to misperceive base-rate information (e.g., the cause density effect). The present study investigates the relationship between causal learning and decision making by asking whether people weight base-rate information in the same way when estimating causal strength and when making judgments or inferences about the likelihood of an event. The results suggest that people differ according to the weight they place on base-rate information, but the way individuals do this is consistent across causal and decision making tasks. We interpret the results as reflecting a tendency to differentially weight base-rate information which generalizes to a variety of tasks. Additionally, this study provides evidence that causal learning and decision making share some component processes.     

Programming of expected and unexpected movements: effects on the onset of the lateralized readiness potential

When participants utilize prime information to prepare some or all aspects of the forthcoming movement, reaction time (RT) costs are obtained when the imperative response signal demands an unexpected rather than an expected movement. Longer RT in trials for which primes are invalid rather than valid, i.e., the response validity effect, are taken to reflect prolonged motoric processing time. The present study was designed to test this assumption by using the lateralized readiness potential (LRP) in order to reveal influences of response validity at motoric processes, pre-motoric processes, or both. In two response priming experiments LRP onset latency was examined when valid and invalid advance information about direction (Experiment 1) or about direction and hand (Experiment 2) was provided. RT revealed large response validity effects in both experiments. Analysis of LRP onsets provided strong evidence against the common assumption of a motoric locus of the RT increase in invalid trials. Rather, the present results suggest a pre-motoric locus of the response validity effect within information processing.     

Detectability of the negative event: effect on the acceptance of pre- or post-event risk-defusing actions

In risky decision situations, many decision makers search for risk-defusing operators (RDOs). An RDO is an action intended by the decision maker to be performed additionally to a specific alternative and is expected to decrease the risk. Pre-event RDOs (e.g., vaccination) have to be applied before a negative event (e.g., infection) occurs. Post-event RDOs do not need to be initiated before and unless the event happens (e.g., medical treatment). For the successful application of Post-event RDOs, the negative event must be detected in time. Two experiments investigated the effect of uncertainty in the detection of the negative event. In Experiment 1, only a small minority of subjects noted this uncertainty without a cue, and even with cue, only a minority actively searched for probability information. In Experiment 2, the probability for correctly detecting the negative event was varied. When detection was certain, most subjects chose the alternative with a Post-event RDO, whereas this percentage decreased significantly with decreasing probability of correct detection. Also, in the conditions with a more extreme negative outcome, less decision makers chose the alternative with the Post-event RDO.     

Reducing bias in frequency judgment by improving source monitoring

A common finding in judgment and decision making is that people's frequency judgments often fail to map onto objective frequencies. The present research examined the possibility that one source of bias in frequency judgment is attributable to people's inability to screen out irrelevant memory traces. We used a two-list source-monitoring paradigm to investigate whether frequency judgments are influenced by "extra-experimental" experiences and whether enhancing source monitoring improves judgment accuracy. Across four experiments we found: (1) frequency judgments regarding one list were biased by the second, (2) manipulating encoding between lists improved source monitoring and resulted in more accurate judgments, (3) manipulating item context between lists improved source monitoring and resulted in more accurate judgments, but only when the context was item specific, and (4) manipulating simple-background context between lists was ineffective at improving source monitoring.     

Stochastic cascade processes as a model of multi-stage concurrent information processing

McClelland's (Psychol. Rev. 86 (1979) 287) influential cascade model of reaction time (RT) is often seen as an important explicitly formulated alternative to strictly serial models because some of its basic notions fit in with known characteristics of neural activation processes. A disadvantage is that it is an essentially deterministic model to which noise is added by across-trials parameter variability that is unrelated to the concept of cascaded activation propagation per se. We propose and analyze a general stochastic cascade model based on neural counting processes; within this framework we present a new process-oriented interpretation of McClelland's cascade activation equation. We then theoretically explain and numerically explore conditions under which the stochastic cascade model predicts additive vs. interactive mean RT effects, and compare them to known properties of McClelland's model. Some of these properties remain valid even within a stochastic neural counting formulation, while others reflect assumptions which are essentially unrelated to the concept of cascaded activation.