Motor limitation in dual-task processing under ballistic movement conditions

The standard bottleneck model of the psychological refractory period (PRP) assumes that the selection of the second response is postponed until the first response has been selected. Accordingly, dual-task interference is attributed to a single central-processing bottleneck involving decision and response selection, but not the execution of the response itself. In order to critically examine the assumption that response execution is not part of this bottleneck, we systematically manipulated the temporal demand for executing the first response in a classical PRP paradigm. Contrary to the assumption of the standard bottleneck model, this manipulation affected the reaction time for Task 2. Specifically, reaction time for Task 2 increased with execution time for Task 1. This carryover effect from Task 1 to Task 2 provides evidence for the notion that response execution can be part of the processing bottleneck.     

Aging and input processing in dual-task situations

The psychological refractory period (PRP) paradigm was used to test whether older participants suffer from input interference in dual-task situations. Young (24 years) and older (57 years) adults gave speeded responses to 2 successively presented stimuli. The results showed increased susceptibility of older participants to input interference. Further experiments revealed that this input interference is related to the salience of the 2nd stimulus and that it is specific to older participants. Our findings indicate that parallel processing at the input stages of dual-task performance requires cognitive control. An age-related decline in the control of input processes should be considered as one source of age effects in dual-task performance.     

Dorsal and ventral processing under dual-task conditions

It is widely acknowledged that visual input is processed along two anatomically and functionally distinct pathways--a ventral pathway for conscious perception and a dorsal pathway for action control. The present study investigated whether the apparent direct and unmediated processing in the dorsal stream is subject to capacity limitations. Specifically, we tested whether a simple dorsal task of grasping an object is affected by the psychological refractory period (PRP), a well-known indication of capacity limitations. Subjects performed an auditory choice reaction task and then, following varying delays, had to judge an object's width (ventral task) or grasp an object across its width (dorsal task). Although these tasks were differentially affected by irrelevant variation of the objects' length, they were subject to comparable dual-task interference. These results show that despite important differences between ventral and dorsal information processing, both modes of processing are constrained by limited capacities.     

A dual-task investigation of automaticity in visual word processing

An analysis of activation models of visual word processing suggests that frequency-sensitive forms of lexical processing should proceed normally while unattended. This hypothesis was tested by having participants perform a speeded pitch discrimination task followed by lexical decisions or word naming. As the stimulus onset asynchrony between the tasks was reduced, lexical-decision and naming latencies increased dramatically. Word-frequency effects were additive with the increase, indicating that frequency-sensitive processing was subject to postponement while attention was devoted to the other task. Either (a) the same neural hardware shares responsibility for lexical processing and central stages of choice reaction time task processing and cannot perform both computations simultaneously, or (b) lexical processing is blocked in order to optimize performance on the pitch discrimination task. Either way, word processing is not as automatic as activation models suggest.     

Evidence for processing stages in skill acquisition: a dual-task study

We investigated the changes of resource demand during the acquisition of a sensorimotor skill, namely the tracking of a visual target under reversed visual feedback. This acquisition task was performed alone or concurrently with one of four manual reaction-time tasks as loading tasks, designed to tap different computational resources. As expected, we found tracking performance to deteriorate upon vision reversal and then to gradually improve with practice. We further found that acquisition task and loading task interfered little before vision reversal but substantially afterwards. Most importantly, we observed a different time-course of interference for each of our four loading tasks. The particular pattern led us to conclude that resources related to spatial attention and sensory transformations are in highest demand early during skill acquisition and those pertinent to movement preparation somewhat later. Our findings thus provide experimental support for the theory that motor learning progresses in stages characterized by different resource requirements.     

Verbal asymmetries and levels of processing in an interactive dual-task paradigm

This study examined how the dual-task laterality paradigm produces patterns of cerebral asymmetry different from those obtained in studies of comparable single-laterality tasks. We systematically examined at what level of processing a concurrent verbal memory-load influences accuracy of recognition of laterally presented nouns relative to that in a control condition. Four groups of 20 subjects each were tested in an interactive dual-task paradigm requiring them to compare lateralized nouns directly with one of three nouns concurrently held in memory prior to accuracy of recognition. The groups differed according to the types of comparisons being made: physical identity, phonetic orthographic similarity, phonetic similarity using non-orthographic words, and category membership. Subjects in each group carried out three tasks. They were required to determine if a specified match had occurred between a memory-load word and the lateralized word, identify the lateralized word, and report the memory-load words. Another 20 subjects were assigned to a control laterality condition in which no concurrent memory-load was used. Control subjects were required to respond to a laterally presented word by pressing a reaction-time key to indicate recognition of the word and then to report the word. No significant visual-field differences occurred in accuracy of recognition for either the control or matching-task groups. However, reaction-time latencies and errors increased as a function of the level of processing. The accuracy of recognition did not support the predictions of Kinsbourne's attentional model but the reaction times provided some support for the concept of selective left-hemisphere interference proposed by Hellige. A limited-capacity approach was suggested as a possible alternative explanation of laterality effects.     

Increased control demand results in serial processing: evidence from dual-task performance

Increased demands on cognitive control trigger changes in processing mode. One such modulation involves a shift from parallel to serial processing. This study assessed the role of control demand in determining whether dual-task processing is performed serially or in parallel. We used two critical indices, based on the response-selection bottleneck model, to show that response selection was serial when a task switch was involved, but partly parallel when the simultaneous performance of the tasks did not involve task switching.     

Effects of extensive dual-task practice on processing stages in simultaneous choice tasks

Schumacher et al. Psychological Science 12:101–108, (2001) demonstrated the elimination of most dual-task costs (“perfect time-sharing”) after extensive dual-task practice of a visual and an auditory task in combination. For the present research, we used a transfer methodology to examine this practice effect in more detail, asking what task-processing stages were sped up by this dual-task practice. Such research will be essential to specify mechanisms associated with the practice-related elimination of dual-task costs. In three experiments, we introduced postpractice transfer probes focusing on the perception, central response-selection, and final motor-response stages. The results indicated that the major change achieved by dual-task practice was a speed-up in the central response-selection stages of both tasks. Additionally, perceptual-stage shortening of the auditory task was found to contribute to the improvements in time-sharing. For a better understanding of such time-sharing, we discuss the contributions of the present findings in relation to models of practiced dual-task performance.     

Automatic-heuristic and executive-analytic processing during reasoning: Chronometric and dual-task considerations

Human reasoning has been shown to overly rely on intuitive, heuristic processing instead of a more demanding analytic inference process. Four experiments tested the central claim of current dual-process theories that analytic operations involve time-consuming executive processing whereas the heuristic system would operate automatically. Participants solved conjunction fallacy problems and indicative and deontic selection tasks. Experiment 1 established that making correct analytic inferences demanded more processing time than did making heuristic inferences. Experiment 2 showed that burdening the executive resources with an attention-demanding secondary task decreased correct, analytic responding and boosted the rate of conjunction fallacies and indicative matching card selections. Results were replicated in Experiments 3 and 4 with a different secondary-task procedure. Involvement of executive resources for the deontic selection task was less clear. Findings validate basic processing assumptions of the dual-process framework and complete the correlational research programme of K. E. Stanovich and R. F. West (2000).     

Motor processing modulates word comprehension

We evaluated whether movement modulates the semantic processing of words. To this end, we used homograph words with two meanings, one associated with hand movements (e.g., ‘abanico’, ‘fan’ in Spanish) or foot movements (‘bota’, ‘boot’ in Spanish), and the other not associated with movement (‘abanico’, ‘range’ in Spanish; ‘bota’, ‘wineskin’ in Spanish). After the homograph, three words were presented, and participants were asked to choose the word related to one of the two homograph meanings. The words could be either related to the motor meaning of the homograph (‘fan-heat’), to the non-motor meaning of the homograph (‘range-possibility’) or unrelated (‘fan-phone’). The task was performed without movement (simple condition) or by performing hand (Experiment 1) and foot (Experiment 2) movements. Compared with the simple condition, the performance of movement oriented the preference towards the motor meaning of the homograph. This pattern of results confirms that movement modulates word comprehension.     

Visuomotor and audiomotor processing in continuous force production of oral and manual effectors

The authors examined force control in oral and manual effectors as a function of sensory feedback (i.e., visual and auditory). Participants produced constant isometric force via index finger flexion and lower lip elevation to 2 force levels (10% and 20% maximal voluntary contraction) and received either online visual or online auditory feedback. Mean, standard deviation, and coefficient of variation of force output were used to quantify the magnitude of force variability. Power spectral measures and approximate entropy of force output were calculated to quantify the structure of force variability. Overall, it was found that the oral effector conditions were more variable (e.g., coefficient of variation) than the manual effector conditions regardless of sensory feedback. No effector differences were found for the structure of force variability with visual or auditory feedback. Oral and manual force control appears to involve different control mechanisms regulating continuous force production in the presence of visual or auditory feedback.     

On the degree of attention and capacity limitation in tactile processing

Two conditions were used to evaluate Os’ ability to detect near-threshold vibrotactile stimuli. In both conditions, a signal was presented at one of three skin loci, the O stating which locus received the stimulus. In the simultaneous condition, there was a single observation interval during which a signal occurred at one of the three loci. In the sequential condition, there were three observation intervals presented successively at 800-msec intervals, with a signal presented at one of the three loci during one of the three observation intervals. Each observation interval was associated with a particular locus. Theories postulating attentional control and limitations of capacity during this type of vibrotactile information processing predict performance to be inferior in the simultaneous condition, since that condition requires sharing of attention among the three possible sources of tactile stimulation. The data showed performance to be identical in the two conditions. This result not only disconfirms the single-channel model proposed by Franzen, Markowitz, and Swets (1970), but also argues for an unlimited-capacity nonattention model of tactile perceptual processing. The results are in accord with similar findings for visual processing by Shiffrin and Gardner (1972).     

Specific effect of a cognitive-motor dual-task training on sport performance and brain processing associated with decision-making in semi-elite basketball players

ObjectivesIn this study, we aimed at evaluating the effects of cognitive-motor dual-task training (CMDT) on sport-specific athletic performance and cognitive functions of semi-elite basketball players. Further, we investigated the CMDT effects on reactive brain processing by employing event-related potential (ERP) analysis. Design: A randomized controlled trial was conducted including 52 young semi-elite basketball players (28 females mean age 16.3 ± 1.1 years) who were randomly assigned into an experimental (Exp) group executing the CMDT and a control (Con) group performing standard motor training. Method: Athletes’ sport-specific performance was evaluated with dribbling tests before and after a five-week training. Cognitive performance was assessed by measuring speed and accuracy in a discrimination response task. Brain activity associated with sensory processing, selective attention, and decision-making was measured through the P1, N1, and P3 components. The CMDT consisted of simultaneous execution of dribbling exercises and cognitive tasks which were realized using interactive devices located around the athlete on the basket court. Data were submitted to a mixed analysis of variance. Results: Both groups showed some improvements from pre-to post-tests, but the Exp group improved basket-specific performance by 13% more than the Con group; in addition, the cognitive performance also improved more in the Exp group (25.8% in accuracy and 5.4% response speed). According to the EEG results, training did not affect sensory processing and attentional processing which were equally increased after both kinds of training; however, decision-making processes were specifically affected by the experimental training. Conclusions: This study confirmed the effectiveness of the proposed CMDT protocol on both sport-specific and cognitive performance of basketball players and showed that the neural basis of these benefits may be mediated by more intense decisional processing allowing faster connection between sensory encoding and response execution.     

Motor expertise modulates movement processing in working memory

A substantial amount of literature has demonstrated individuals' tendency to code verbally a series of movements for subsequent recall. However, the mechanisms underlying movement encoding remain unclear. In this paper, I argue that sensorimotor expertise influences the involvement of motor processes to store movements in working memory. Experts in motor activities and individuals with limited motor expertise were compared in three experimental conditions assessing movement recall: (a) without suppression task, (b) with verbal suppression, and (c) with motor suppression. Athletes outperformed controls in movement recall, but the suppression tasks affected the two groups differently. Verbal suppression affected controls more than athletes, whereas the effect was reversed with motor suppression. Together, these findings suggest that controls and athletes favor different mechanisms to encode movements, either based on verbal or on motor processes, providing further evidence for a tight relationship between sensorimotor and cognitive processes.     

Task shifting in dual-task settings

When a participant is asked to perform two tasks in alternation, their mean reaction times were slower than when they performed the same tasks repeatedly. This "shift cost" has been hypothesized to reflect the time course of a single central executive that exerts control over thought and actions in task shifting. This study attempted to test this hypothesis using dual-task methodology. Participants were asked to carry out both a subtracting task and a rule-shifting task simultaneously. The main interest is to examine the effect of dual task on the magnitude of shift cost. The results showed that performing a concurrent subtracting task significantly interfered with the shifting operation resulting in over-additive time cost for shifting of task set. We further suggest that such interference may arise from the competition between activations of various rules.     

Localizing practice effects in dual-task performance

Practice effects on dual-task processing are of interest in current research because they may reveal the scope and limits of parallel task processing. Here we used onsets of the lateralized readiness potential (LRP), a time marker for the termination of response selection, to assess processing changes after five consecutive dual-task sessions with three stimulus onset asynchronies (SOAs) and priority on Task 1. Practice reduced reaction times in both tasks and the interference between tasks. As indicated by the LRP, the reduction of dual-task costs can be explained most parsimoniously by a shortening of the temporal demands of central bottleneck stages, without assuming parallel processing. However, the LRP also revealed a hitherto unreported early activation over the parietal scalp after practice in the short SOA condition, possibly indicating the isolation of stimulus–response translation from other central processing stages. In addition, further evidence was obtained from the LRP for a late motoric bottleneck, which is robust against practice.     

Bimanual response grouping in dual-task paradigms

In three experiments we measured response time (RT) and peak force (PF) to investigate the grouping of left- and right-hand key press responses in a dual-task paradigm involving two independent go/no-go tasks. Within each task, a go stimulus within one of two modalities (i.e., visual versus auditory) required a response by one hand. In Experiment 1 with simultaneous go stimuli in the two tasks, responses appeared to be grouped in approximately 75-80% of trials, compared with nearly 100% grouping in a single-task condition requiring bimanual responses to the onset of any stimulus in either modality. In Experiment 2 with stimulus onset asynchronies (SOAs) of 0-400 ms between the two go stimuli, response grouping clearly declined as SOA increased, although some grouping was still evident even at the longest SOA. The same pattern was observed in Experiment 3 with the same range of SOAs but unpredictable stimulus order, suggesting that grouping is not strongly dependent on prior knowledge of the likely response order. These results emphasize the pervasiveness of response grouping in bimanual dual-task RT paradigms and provide useful clues as to its nature.     

Localizing practice effects in dual-task performance

Practice effects on dual-task processing are of interest in current research because they may reveal the scope and limits of parallel task processing. Here we used onsets of the lateralized readiness potential (LRP), a time marker for the termination of response selection, to assess processing changes after five consecutive dual-task sessions with three stimulus onset asynchronies (SOAs) and priority on Task 1. Practice reduced reaction times in both tasks and the interference between tasks. As indicated by the LRP, the reduction of dual-task costs can be explained most parsimoniously by a shortening of the temporal demands of central bottleneck stages, without assuming parallel processing. However, the LRP also revealed a hitherto unreported early activation over the parietal scalp after practice in the short SOA condition, possibly indicating the isolation of stimulus-response translation from other central processing stages. In addition, further evidence was obtained from the LRP for a late motoric bottleneck, which is robust against practice.