Same-hand and different-hand finger pairings in two-choice reaction time: presence or absence of response competition?

The impact of anatomical and spatial distance between responses on response conflict

Different features of objects can be associated with different responses, so that their concurrent presence results in conflict. The Simon effect is a prominent example of this type of response conflict. In two experiments, we ask whether it is modulated by the anatomical or spatial relation between responses. Predictions were derived from an extended variant of the leaky, competing accumulator (LCA) model proposed by Usher and McClelland (Psychological Review, 108, 550-592, 2001). The relation between responses was represented by the lateral-inhibition parameter of the model. For the anatomical distance between responses the expectations were largely confirmed, but not for spatial distance. First, the Simon effect was stronger when responses were performed with two fingers of the same hand than with different hands. Second, the Simon effect was larger only for responses with different hands at short reaction times and disappeared at long ones, whereas for responses with fingers of the same hand, the Simon effect was essentially the same for shorter and longer reaction times. This difference resulted in smaller variability of reaction times in noncorresponding than in corresponding conditions. The dependence of decision processes, as modelled by the LCA model, on the anatomical relation between responses supports the broad hypothesis that the accumulation of evidence on the state of the world is intricately linked with the activation of response codes, that is, the selection of the appropriate actions.

On Sequence Learning Models: Open-loop Control Not Strictly Guided by Hick's Law

According to the Hick’s law, reaction times increase linearly with the uncertainty of target stimuli. We tested the generality of this law by measuring reaction times in a human sequence learning protocol involving serial target locations which differed in transition probability and global entropy. Our results showed that sigmoid functions better describe the relationship between reaction times and uncertainty when compared to linear functions. Sequence predictability was estimated by distinct statistical predictors: conditional probability, conditional entropy, joint probability and joint entropy measures. Conditional predictors relate to closed-loop control models describing that performance is guided by on-line access to past sequence structure to predict next location. Differently, joint predictors relate to open-loop control models assuming global access of sequence structure, requiring no constant monitoring. We tested which of these predictors better describe performance on the sequence learning protocol. Results suggest that joint predictors are more accurate than conditional predictors to track performance. In conclusion, sequence learning is better described as an open-loop process which is not precisely predicted by Hick’s law.

Preparing for perception and action (I): the role of grouping in the response-cuing paradigm

Human skilled behavior requires preparatory processes that selectively make sensory and motor systems more efficient for perceiving the upcoming stimulus and performing the correct action. We review the literature concerning these preparatory processes as studied by response-cuing paradigm, and propose a model that accounts for the major findings. According to the Grouping Model, advance or precue information directs a dynamic process of subgroup making-that is, a process of stimulus- and response-set reconfiguration-whereby the internal representation of the task is simplified. The Grouping Model assigns a critical role to the unit of selection, with Gestalt factors and interresponse dependencies mediating the formation and strength of stimulus and response subgroups. In a series of five experiments, we manipulated perceptual and motoric grouping factors, and studied their independent and interactive effects on the pattern of precuing benefits. Generally, the results were consistent with the Grouping Model's account of response-cuing effects.

Influence of practice on response-selection and response-implementation processes involved in the response-interference effect

In a choice reaction-time task, the response-interference effect is an increase in reaction times when the two possible responses are from the same hand compared to when the two possible responses are from different hands [Psychonomic Science 2 (1965) 55-56; Human Motor Control, Academic Press, San Diego, CA, 1991]. Although the influence of practice on other reaction-time effects (i.e., the complexity effect and precuing) has been examined, research evaluating the influence of practice on the response-interference effect is limited. Therefore, two experiments were conducted to determine the influence of practice on the response-interference effect. In Experiment 1, a bilateral transfer task was used to assess the influence of practice on the response-selection processes associated with the response-interference effect. The practice results indicated decreased reaction times, but did not influence the response-interference effect. In Experiment 2, a priming task was used to assess the influence of practice on response-implementation processes associated with the response-interference effect. The reaction time results indicated a change in the response-interference effect. The results of these two experiments suggest that with only two fingers on response keys, practice alters the mechanical constraints affecting the response-implementation processes and thereby decreases the response-interference effect.

Finger Pairings in Two-Choice Reaction Time Taskscolon: Does the Between-Hands Advantage Reflect Response Preparation?

Two fractionated RT experiments tested whether the response-preparation or response-implementation hypothesis better accounts for the observation that two-choice reaction time (RT) usually takes longer when the responses are performed by the fingers of the same hand (within-hand repertoire) than by the fingers of the two hands (between-hands repertoire). In Experiment I (n equals 8), the effect of repertoire on the premotor time and the motor time were studied. RT was divided into the two periods with respect to the onset of change in electromyographic (EMG) activity of the flexor digitorum profundus. Type of repertoire affected both time periods. In Experiment 2 (n = 16), the effects of repertoire and foreperiod duration on the premotor and motor times of the flexor digitorum profundus and flexor digitorum sublimis were studied. The results of Experiment I were confirmed, and the effects of repertoire and foreperiod duration were found to be additive on premotor time but interactive on motor time. These findings led to rejection of the response-preparation hypothesis and instead supported the view that the central command for the flexion of the right middle finger differs according to the type of repertoire. The command appears to specify a lower rate of recruitment of the prime movers in the within-hand repertoire than in the between-hands repertoire. The execution of the central commands may depend on the state of excitability of the spinal neurons. Analysis of the EMG signals revealed that speed of contraction of the prime movers depends on repertoire when the foreperiod is long but not when it is short. The additivity of the effects of repertoire and of foreperiod duration on premotor time support the view that regardless of the state of preparation of the subject the pattern of EMG activity required for flexion of the right middle finger in each repertoire is specified during the premotor time.