Gordon D. Logan

Toward an instance theory of automatization.

This article presents a theory in which automatization is construed as the acquisition of a domainspeciSc knowledge base, formed of separate representations, instances, of each exposure to the task. Processing is considered automatic if it relies on retrieval of stored instances, which will occur only after practice in a consistent environment. Practice is important because it increases the amount retrieved and the speed of retrieval; consistency is important because it ensures that the retrieved instances will be useful. The theory accounts quantitatively for the power-function speed-up and predicts a power-function reduction in the standard deviation that is constrained to have the same exponent as the power function for the speed-up. The theory accounts for qualitative properties as well, explaining how some may disappear and others appear with practice. More generally, it provides an alternative to the modal view of automaticity, arguing that novice performance is limited by a lack of knowledge rather than a scarcity of resources. The focus on learning avoids many problems with the modal view that stem from its focus on resource limitations.

On the ability to inhibit thought and action: A theory of an act of control

Many situations require people to stop or change their current thoughts and actions. We present a theory of the inhibition of thought and action to account for peoples performance in such situations. The theory proposes that a control signal, such as an external stop signal or an error during performance, starts a stopping process that races against the processes underlying ongoing thought and action. If the stopping process wins, thought and action are inhibited; if the ongoing process wins, thought and action run on to completion. We develop the theory formally to account for many aspects of performance in situations with explicit stop signals, and we apply it to several sets of data. We discuss the relation between response inhibition and other acts of control in motor performance and in cognition, and we consider how our theory relates to current thinking about attentional control and automaticity.

Impulsivity and Inhibitory Control

We report an experiment testing the hypothesis that impulsive behavior reflects a deficit in the ability to inhibit prepotent responses Specifically, we examined whether impulsive people respond more slowly to signals to inhibit (stop signals) than non-impulsive people In this experiment, 136 undergraduate students completed an impulsivity questionnaire and then participated in a stop-signal experiment, in which they performed a choice reaction time (go) task and were asked to inhibit their responses to the go task when they heard a stop signal The delay between the go signal and the stop signal was determined by a tracking procedure designed to allow subjects to inhibit on 50% of the stop-signal trials Reaction time to the go signal did not vary with impulsivity, but estimated stop-signal reaction time was longer in more impulsive subjects, consistent with the hypothesis and consistent with results from populations with pathological problems with impulse control

On the ability to inhibit simple and choice reaction time responses: a model and a method.

This article reports four experiments on the ability to inhibit responses in simple and choice reaction time (RT) tasks. Subjects responding to visually presented letters were occasionally presented with a stop signal (a tone) that told them not to respond on that trial. The major dependent variables were (a) the probability of inhibiting a response when the signal occurred, (b) mean and standard deviation (SD) of RT on no-signal trials, (c) mean RT on trials on which the signal occurred but subjects failed to inhibit, and (d) estimated RT to the stop signal. A model was proposed to estimated RT to the stop signal and to account for the relations among the variables. Its main assumption is that the RT process and the stopping process race, and response inhibition depends on which process finishes first. The model allows us to account for differences in response inhibition between tasks in terms of transformations of stop-signal delay that represent the relative finishing times of the RT process and the stopping process. The transformations specified by the model were successful in group data and in data from individual subjects, regardless of how delays were selected. The experiments also compared different methods of selecting stop-signal delays to equate the probability of inhibition in the two tasks.

Response inhibition in AD/HD, CD, comorbid AD/HD + CD, anxious, and control children : A meta-analysis of studies with the stop task

The aim of this study was to investigate whether impaired response inhibition is uniquely related to AD/HD or whether deficits in response inhibition are also evident in other psychopathological disorders. Furthermore, the suggestion was examined that anxiety disorders are associated with abnormally high levels of response inhibition. This paper presents the results of a meta-analysis of eight studies in which response inhibition was assessed with the so-called stop task in five groups of children: children with attention deficit/hyperactivity disorder (AD/HD), children with conduct disorder (CD), children with AD/HD + CD, children with anxiety disorders, and control children. A total of 456 children participated in the 8 studies. All children were in the age range 6-12 years. Consistent and robust evidence was found for a response inhibition deficit in AD/HD. However, response inhibition deficits did not distinguish children with AD/HD from children with CD, nor from children with comorbid AD/HD + CD. Contrary to predictions, anxious children did not demonstrate enhanced levels of response inhibition.

Aging and Inhibition: Beyond a Unitary View of Inhibitory Processing in Attention

The authors examined the question of whether a decrease in the efficiency of inhibitory processing with aging is a general phenomenon. Thirty elderly and 32 young adults performed a series of tasks from which the authors could extract measures of inhibitory function. The tasks and task components included response compatibility, negative priming, stopping, spatial precuing, Wisconsin Card Sorting Test (WCST), and the Cognitive Failures Questionnaire (CFQ). Only limited evidence for age-related differences in inhibitory function was obtained. Old adults had more difficulty than young adults in stopping an overt response and adopting new rules in a categorization task. However, elderly and young adults produced equivalent negative priming effects, response compatibility effects, spatial precuing effects, and self-reported cognitive failures. The findings are discussed in terms of the relationship between aging, inhibitory processes, and neuroanatomical and physiological function.

Development of inhibitory control across the life span.

The stop-signal procedure was used to examine the development of inhibitory control. A group of 275 participants, 6 to 81 years of age, performed a visual choice reaction time (go) task and attempted to inhibit their responses to the go task when they heard a stop signal. Reaction times to the stop and go signals were used to assess performance in inhibition and response execution, respectively. Results indicated the speed of stopping becomes faster with increasing age throughout childhood, with limited evidence of slowing across adulthood. By contrast, strong evidence was obtained for age-related speeding of go-signal reaction time throughout childhood, followed by marked slowing throughout adulthood. Hierarchical regression confirmed that the age-related change in inhibitory control could not be explained by general speeding or slowing of responses. Findings are discussed in regard to the contrast between the development of inhibition and response execution and the utility of the stop-signal procedure.

Response inhibition in the stop-signal paradigm

Response inhibition is a hallmark of executive control. The concept refers to the suppression of actions that are no longer required or that are inappropriate, which supports flexible and goal-directed behavior in ever-changing environments. The stop-signal paradigm is most suitable for the study of response inhibition in a laboratory setting. The paradigm has become increasingly popular in cognitive psychology, cognitive neuroscience and psychopathology. We review recent findings in the stop-signal literature with the specific aim of demonstrating how each of these different fields contributes to a better understanding of the processes involved in inhibiting a response and monitoring stopping performance, and more generally, discovering how behavior is controlled.

The ecological validity of delay aversion and response inhibition as measures of impulsivity in AD/HD: a supplement to the NIMH multimodal treatment study of AD/HD

Impulsivity is a primary symptom of the combined type of Attention Deficit/Hyperactivity Disorder (AD/HD). The Stop Signal Paradigm is premised upon a primary deficit in inhibitory control in AD/HD, whereas the Delay Aversion Hypothesis, by contrast, conceptualizes impulsivity in AD/HD, not as an inability to inhibit a response, but rather as a choice to avoid delay. This study compared the ecological validity of the Stop Signal Task (SST) and Choice-Delay Task (C-DT) measure of delay aversion, with respect to their relative utility in discriminating AD/HD children from normal control participants, and their correlations with classroom observations and with ratings of impulsivity and other core AD/HD symptoms on the Conners and SNAP-IV checklists. The tasks exhibited modest discriminant validity when used individually and excellent discriminant validity when used in combination. The C-DT correlated with teacher ratings of impulsivity, hyperactivity, and conduct problems, and with observations of gross motor activity, physical aggression, and an AD/HD composite score. The SST correlated with the observations only. These results suggest that delay aversion is associated with a broad range of AD/HD characteristics whereas inhibitory failure seems to tap a more discrete dimension of executive control

Horse-race model simulations of the stop-signal procedure

In the stop-signal paradigm, subjects perform a standard two-choice reaction task in which, occasionally and unpredictably, a stop-signal is presented requiring the inhibition of the response to the choice signal. The stop-signal paradigm has been successfully applied to assess the ability to inhibit under a wide range of experimental conditions and in various populations. The current study presents a set of evidence-based guidelines for using the stop-signal paradigm. The evidence was derived from a series of simulations aimed at (a) examining the effects of experimental design features on inhibition indices, and (b) testing the assumptions of the horse-race model that underlies the stop-signal paradigm. The simulations indicate that, under most conditions, the latency, but not variability, of response inhibition can be reliably estimated.