Tobias Stevens

Proactive and reactive stopping when distracted: An attentional account

Performance in response inhibition paradigms is typically attributed to inhibitory control. Here we examined the idea that stopping may largely depend on the outcome of a sensory detection process. Subjects performed a speeded go task, but they were instructed to withhold their response when a visual stop signal was presented. The stop signal could occur in the center of the screen or in the periphery. On half of the trials, perceptual distractors were presented throughout the trial. We found that these perceptual distractors impaired stopping, especially when stop signals could occur in the periphery. Furthermore, the effect of the distractors on going was smallest in the central stop-signal condition, medium in a condition in which no signals could occur, and largest in the condition in which stop signals could occur in the periphery. The results show that an important component of stopping is finding a balance between ignoring irrelevant information in the environment and monitoring for the occurrence of occasional stop signals. These findings highlight the importance of sensory detection processes when stopping and could shed new light on a range of phenomena and findings in the response inhibition literature.

Are the effects of response inhibition on gambling long-lasting?

A recent study has shown that short-term training in response inhibition can make people more cautious for up to two hours when making decisions. However, the longevity of such training effects is unclear. In this study we tested whether training in the stop-signal paradigm reduces risky gambling when the training and gambling task are separated by 24 hours. Two independent experiments revealed that the aftereffects of stop-signal training are negligible after 24 hours. This was supported by Bayes factors that provided strong support for the null hypothesis. These findings indicate the need to better optimise the parameters of inhibition training to achieve clinical efficacy, potentially by strengthening automatic associations between specific stimuli and stopping.

How Does Response Inhibition Influence Decision Making When Gambling

Recent research suggests that response inhibition training can alter impulsive and compulsive behavior. When stop signals are introduced in a gambling task, people not only become more cautious when executing their choice responses, they also prefer lower bets when gambling. Here, we examined how stopping motor responses influences gambling. Experiment 1 showed that the reduced betting in stop-signal blocks was not caused by changes in information sampling styles or changes in arousal. In Experiments 2a and 2b, people preferred lower bets when they occasionally had to stop their response in a secondary decision-making task but not when they were instructed to respond as accurately as possible. Experiment 3 showed that merely introducing trials on which subjects could not gamble did not influence gambling preferences. Experiment 4 demonstrated that the effect of stopping on gambling generalized to different populations. Further, 2 combined analyses suggested that the effect of stopping on gambling preferences was reliable but small. Finally, Experiment 5 showed that the effect of stopping on gambling generalized to a different task. On the basis of our findings and earlier research, we propose that the presence of stop signals influences gambling by reducing approach behavior and altering the motivational value of the gambling outcome.

Limits of Executive Control Sequential Effects in Predictable Environments

Cognitive-control theories attribute action control to executive processes that modulate behavior on the basis of expectancy or task rules. In the current study, we examined corticospinal excitability and behavioral performance in a go/no-go task. Go and no-go trials were presented in runs of five, and go and no-go runs alternated predictably. At the beginning of each trial, subjects indicated whether they expected a go trial or a no-go trial. Analyses revealed that subjects immediately adjusted their expectancy ratings when a new run started. However, motor excitability was primarily associated with the properties of the previous trial, rather than the predicted properties of the current trial. We also observed a large latency cost at the beginning of a go run (i.e., reaction times were longer for the first trial in a go run than for the second trial). These findings indicate that actions in predictable environments are substantially influenced by previous events, even if this influence conflicts with conscious expectancies about upcoming events.

Comment on: Effects of static magnetic fields on cognition, vital signs, and sensory perception: A meta-analysis

Heinrich et al recently published a meta-analysis on effects of static magnetic fields on cognition, vital signs, and sensory perception in this journal (1). Having been involved in the majority of studies on neurobehavioral effects considered in this meta-analysis, we would like to address a few issues. An important basis for conducting a meta-analysis is that the individual studies included share an underlying common risk factor and endpoint, and that variations that result from clinical or methodological differences among studies are due to chance (2). However, Heinrich et al attempt to combine effects from exposure to (ultra)high, but spatially homogeneous static magnetic fields (SMFs) encountered inside the magnet bore with an order of magnitude lower, but spatially heterogeneous SMF surrounding magnetic resonance imaging (MRI) systems (stray fields); or with time-varying (electro)magnetic fields induced by movements in these stray fields. This issue has been discussed specifically for these studies previously (3). They have also included a nonexperimental study that assessed exposure during normal work practices of MR engineers (4). This study investigated whether neurobehavioral performance differed after a work shift compared to the start of the work shift to evaluate whether any measurable effects remained after exposure to the MRI-generated (electro)magnetic fields had ended. This is a distinctly different study design and hypothesis than for the other studies included by Heinrich et al, in which the effect of these fields were tested while the individuals were present in these fields. In other words, in this meta-analysis different exposures have been combined, while also effects experienced in the bore (by patients) are taken together with those that may be experienced by personnel working around MRI scanners. By combining these studies without taking into account the different types, levels, and patterns of exposure, Heinrich et al assume that the magnitude of any effect is independent of type and level of exposure; a hypothesis that directly contradicts the conclusion from one of the studies also included in this meta-analysis (5), but also from a pooled analysis published in this journal in 2007 (6). This analysis pooled data from three case-crossover studies with comparable positioning of test subjects in the stray fields, but with MRI systems of different strengths. These analyses indicated exposure-effect associations for visuomotor speed and visual contrast sensitivity during exposure, with data from other sources indicating that these effects disappear quickly after exposure has ended (4,7,8). Heinrich et al further present a list of recommendations that will be a useful framework for future studies in this area. However, to our surprise two important shortcomings identified in our work: 1) the use of a single-blind study design in which test administrators could not be blinded to the magnet status, and 2) the absence of personal exposure measurements during the studies to improve exposure assessment in such a heterogeneous SMF, were not mentioned and translated into recommendations for future studies. Furthermore, in contrast to their assessment which rightly suggests that exposure to SMF consistently affects tests of visual contrast sensitivity, they do not recommend a more thorough investigation of these visual impairments using appropriately sensitive, non-introspective, visual tests. Instead, they suggest new unguided explorations of more cognitive functions (even though they conclude data do not indicate consistent effects on such functions) and use of questionnaires on sensory perception, which is not likely to provide new information on neurobehavioral mechanisms not already known. In conclusion, we do not believe these studies should have been combined in one meta-analysis, while in addition we recommend that Heinrich et al update their list of recommendations to incorporate the issues discussed here.

Improved memory for information learnt before alcohol use in social drinkers tested in a naturalistic setting

Alcohol is known to facilitate memory if given after learning information in the laboratory; we aimed to investigate whether this effect can be found when alcohol is consumed in a naturalistic setting. Eighty-eight social drinkers were randomly allocated to either an alcohol self-dosing or a sober condition. The study assessed both retrograde facilitation and alcohol induced memory impairment using two independent tasks. In the retrograde task, participants learnt information in their own homes, and then consumed alcohol ad libitum. Participants then undertook an anterograde memory task of alcohol impairment when intoxicated. Both memory tasks were completed again the following day. Mean amount of alcohol consumed was 82.59 grams over the evening. For the retrograde task, as predicted, both conditions exhibited similar performance on the memory task immediately following learning (before intoxication) yet performance was better when tested the morning after encoding in the alcohol condition only. The anterograde task did not reveal significant differences in memory performance post-drinking. Units of alcohol drunk were positively correlated with the amount of retrograde facilitation the following morning. These findings demonstrate the retrograde facilitation effect in a naturalistic setting, and found it to be related to the self-administered grams of alcohol.