Psychological Refractory Period Paradigm Research Articles

Age-Differential Effects of Proactive Control in Dual Tasking: The Moderating Effect of Task Difficulty

AbstractDual tasking refers to the ability to perform two concurrent tasks. Using the psychological refractory period (PRP) paradigm, two experiments examined whether providing a prompt that facilitated proactive control could benefit dual-task performance among younger and older adults. In Experiment 1, difficulty-related prompt words (“difficult,” “easy,” or null) were presented before easier dual tasks with a longer stimulus onset asynchrony (SOA) of 800 ms or harder tasks with a shorter SOA of 100 ms. Experiment 2 extended the investigation by presenting these prompts (“difficult” or “easy”) before dual tasks with a fixed SOA of 150 ms. It also examined the moderating effects of actual task difficulty by manipulating task congruency. Both experiments suggested that proactive control triggered by difficulty-related prompts facilitated dual-task performance in both age groups. Notably, prompts benefited younger adults’ dual-task performance only when the actual task difficulty was relatively higher, but they benefited older adults’ dual-task performance regardless of the actual task difficulty. These findings contribute to our understanding of proactive control and the different effects of prompts on cognitive performance among younger and older adults.

Fate of the second task in dual-task interference is associated with sensory system interactions with default-mode network

Psychological refractory period (PRP) effect refers to the delay in responding to the second of two tasks occurring in rapid succession. While all the major models of PRP highlight the importance of the frontoparietal control network (FPCN) in prioritizing the neural processing of the first task, the fate of the second task remains poorly understood. Here, we provide novel neural evidence on how the functional connectivity between sensory systems and the default-mode network (DMN) suspends the neural processing of the second task to ensure the efficient completion of the first task in dual-task situation. In a cross-modal PRP paradigm, a visual task could either precede or follow an auditory task. The DMN was generally deactivated during task performance and selectively coupled with the sensory system underlying the second task subjected to the PRP effect. Specifically, the DMN showed neural coupling with the auditory system when the auditory task came after the visual task, and with the visual system vice versa. More critically, the strength of the DMN-Sensory coupling correlated negatively with the size of the PRP effect: the stronger the coupling, the shorter the PRP. Therefore, rather than being detrimental to the dual-task performance, temporary suspension of the second task, via the DMN-Sensory coupling, surprisingly guaranteed the efficient completion of the first task by reducing the interference from the second task. Accordingly, the entry and processing of the second stimuli in the central executive system were speeded up as well.

Prolonged Processing Time for Manual and Vocal Responses in Parkinson Disease: A Psychological Refractory Period Paradigm Study

The purpose of this study was to examine a potential increased cognitive processing bottleneck within Parkinson disease (PD) by extending a previous overlapping task methodology. Additionally, this study extends previous overlapping task methodology in PD to examine the influence of modality (vocal vs. manual) on response delays in overlapping tasks in PD. This study used the psychological refractory period (PRP) paradigm (overlapping-task paradigm) to study processing limitations as participants complete two tasks that increasingly overlap in time. Three levels of temporal overlap of tasks were utilized to vary cognitive demands on manual and vocal response time tasks. Ten participants with PD (PwPD) and 12 participants without PD were included in this study. Participants with PD demonstrated response time delays across temporal overlap conditions (likely indicating motor deficits) along with a larger increase in response delays in the most overlapped, cognitively taxing condition (likely indicating longer central processing bottleneck). Additionally, modality did not influence response times differently in overlapping task conditions or within participant groups. An extension of previous overlapping task methodologies within a complex task was successful in demonstrating an increased central processing deficit across manual and vocal response delays in PD, regardless of modality of response.

Executive function abilities in cognitively healthy young and older adults-A cross-sectional study.

A prominent feature of cognitive aging is the decline of executive function (EF) abilities. Numerous studies have reported that older adults perform poorer than younger adults in such tasks. In this cross-sectional study, the effect of age on four EFs, inhibition, shifting, updating, and dual-tasking, was examined in 26 young adults (mean 21.18  years) and 25 older adults (mean 71.56  years) with the utilization of a pair of tasks for each EF. The tasks employed for DT were the Psychological Refractory Period paradigm (PRP) and a modified test for everyday attention, for inhibition the Stroop and Hayling sentence completion test (HSCT), for shifting a task switching paradigm and the trail making test (TMT), and for updating the backward digit span (BDS) task and a n-back paradigm. As all participants performed all tasks, a further aim was to compare the size of the age-related cognitive decline among the four EFs. Age-related decline was observed in all four EFs in one or both of the tasks employed. The results revealed significantly poorer performance in the older adults in the response times (RTs) of the PRP effect, interference score of the Stroop, RT inhibition costs of the HSCT, RT and error-rate shifting costs of the task switching paradigm, and the error-rate updating costs of the n-back paradigm. A comparison between the rates of decline revealed numerical and statistically significant differences between the four EFs, with inhibition showing the greatest decline, followed by shifting, updating, and dual-tasking. Thus, we conclude that with age, these four EFs decline at different rates.

Subjective estimates of total processing time in dual-tasking: (some) good news for bad introspection

Previous studies have shown severe distortions of introspection about dual-task interference in the Psychological Refractory Period (PRP) paradigm. The present study investigated participants’ ability to introspect about the total trial time in this paradigm, as this temporal information may arguably be more relevant for strategic task scheduling than subjective estimates of each task within the dual task. To this end, participants provided estimates of their reaction times (IRTs) for the two subtasks in one half of the experiment, and estimates of the total trial time (ITTs) in the other half of the experiment. Although the IRT results showed the typical unawareness of the PRP effect, ITTs reflected the effects of SOA and Task 2 difficulty on objective total trial time. Additional analyses showed that IRTs were influenced by the introspective task order; that is, the ITT pattern carried over to IRTs when IRTs were assessed in the second half of the experiment. Overall, the present results show that people are able to accurately introspect about total trial time in the PRP paradigm and thus provide some good news for bad introspection in the PRP paradigm.

Evidence of resource sharing in the psychological refractory period (PRP) paradigm.

Performance is generally worse when performing multiple tasks than when performing a single task, but there is debate about whether this multitasking interference arises due to a structural bottleneck that requires serial central processing or due to resource limitations that slow processing of 2 tasks when they are carried out in parallel. The present study used a novel approach of comparing first- and second-task reaction times (RTs) within the psychological refractory period (PRP) paradigm to contrast these 2 possibilities. Counterbalancing task order across participants to control for differences in task difficulty, we found that second-task responses were faster than first-task responses at long stimulus onset asynchronies (SOAs). This second-task advantage is difficult to explain within bottleneck models, which allow the first task to be processed at full speed while the second task waits for access to the bottleneck process. Instead, the effect suggests that processing of the first task is slowed because some cognitive resources are held back in case they are needed for second-task processing. At long SOAs, all resources can be allocated to second-task processing because the first task is already completed. Thus, we propose that cognitive control processes flexibly coordinating the sharing of limited central resources may better explain dual-task performance in the PRP paradigm than bottleneck-based waiting due to structural limitations. (PsycInfo Database Record (c) 2022 APA, all rights reserved).

Equal Quality for Online and Lab Data: A Direct Comparison from Two Dual-Task Paradigms

Abstract Conducting behavioral experiments online has become more prevalent recently. Still, there is reluctance to embrace the possibilities this technology has to offer. So far, only simple tasks have been replicated in an online setting. In order to investigate whether collecting online also leads to high quality data in demanding tasks, we directly compared data collected in the lab with data collected online from a demanding dual-task paradigm and a psychological refractory period paradigm. In Experiment 1, we recruited from local pools, online and offline; in Experiment 2, we collected lab data from our local pool and online data from a remote commercial participant platform. We found that all relevant effects were replicated in the lab and online settings; effect sizes were similar. Additionally, most response time distributions were even statistically equivalent when comparing online and lab data. Thus, online effect sizes and variances can be comparable to lab-based data. Online studies are time-efficient and recruiting an online sample instead or on top of a laboratory sample should be considered for basic behavioral research. This can serve an important role in the generalizability and replicability of findings in the cognitive and behavioral sciences.

Investigation of reward effects in overlapping dual-task situations

In dual-task (DT) situations, performance in reaction time and error rates decrease compared with single-task situations. These performance decrements are usually explained with the serial processing at the response selection stage constituting a bottleneck. Evidence for this assumption stems from the observation that response times for the second task (task 2; RT 2) increase with decreasing stimulus-onset asynchrony (SOA). In this study, we investigated the effect of reward on bottleneck processing in DTs. In Experiment 1, we addressed two questions. First, does reward provided for task 2 performance affect task 2 performance, or does it affect task 1 performance? To conclude whether reward affected task 2 or task 1 performance, we relied on the psychological refractory period paradigm (PRP) as a chronometric tool. Second, we asked for the locus of the reward effect within the DT stream. We demonstrated shorter RTs in task 1 in a rewarded compared with an un-rewarded condition indicating reward affected task 1 processing. Furthermore, this reward effect is propagated onto task 2 at short SOA suggesting that the locus of the reward effect can be pinpointed before or at the bottleneck of task 1. In Experiment 2, we tested for the locus of the effect propagation onto task 2. To this end, we implemented an additional difficulty manipulation of the response selection of task 2 and found that the reward effect is propagated from task 1 onto the response selection stage of task 2.

Usability enhancement based on usability heuristics: An examination of the underlying mechanism utilizing the psychological–refractory–period paradigm

User Interface (UI) design practices often abide by popular usability heuristics such as Nielsen’s (1994) “10 usability heuristics for user interface design” or Gerhardt–Powals' (1996) cognitive engineering principles. To examine the underlying mechanism of user performance enhancement by following some of these usability heuristics, we compared user performance between two device conditions: one representing design practices following two selected sets of usability heuristics (experimental condition) and the other without following them (control condition). As a research framework, we adopted the psychological–refractory–period (PRP) paradigm along with the locus–of–slack logic, a well–established dual–task paradigm for examining the nature of cognitive benefits caused by experimental manipulations. Results showed that the experimental–device condition that followed the usability heuristics yielded faster performance than the control condition, especially when the stimulus–onset–asynchrony between the two tasks was long than when it was short. According to the locus–of–slack logic, these results suggest that the nature of cognitive benefits caused by following the usability heuristics is more likely to be due to shortening of the response–activation stage (rather than the response–selection stage). These findings suggest that following the two usability heuristics tends to facilitate a specific stage of the information processes more than other stages.

The working memory costs of a central attentional bottleneck in multitasking

When two (or more) tasks, each requiring a rapid response, are performed at the same time then serial processing may occur at certain processing stages, such as the response selection. There is accumulating evidence that such serial processing involves additional control processes, such as inhibition, switching, and scheduling (termed the active scheduling account). The present study tested whether the existence of serial processing in multitasking leads to a requirement for processes that coordinate processing in this way (active scheduling account) and, furthermore, whether such control processes are linked to the executive functions (EF) of working memory (WM). To test this question, we merged the psychological refractory period (PRP) paradigm with a WM task, creating a complex WM span task. Participants were presented with a sequence of letters to remember, followed by a processing block in which they had to perform either a single task or a dual task, and finally were asked to recall the letters. Results showed that WM performance, i.e. the amount of letters recalled in the correct order, decreased when performing a dual task as compared to performing a single task during the retention interval. Two further experiments supported this finding using manipulations of the dual task difficulty. We conclude that the existence of serial processing in multitasking demands additional control processes (active scheduling) and that these processes are strongly linked to the executive functions of working memory.

Neural Correlates of Aging-Related Differences in Pro-active Control in a Dual Task.

Background: Multi-tasking is usually impaired in older people. In multi-tasking, a fixed order of sub-tasks can improve performance by promoting a time-structured preparation of sub-tasks. How proactive control prioritizes the pre-activation or inhibition of complex tasks in older people has received no sufficient clarification so far.Objective: To explore the effects of aging on neural proactive control mechanisms in a dual task.Methodology: To address this question, the psychological refractory period (PRP) paradigm was used. Two 2-alternative-forced-choice reaction tasks with a predefined order (T1 and T2) signaled by a cue had to be executed simultaneously or consecutively by young (mean age 25.1 years, n = 36) and old subjects (mean age 70.4 years, n = 118). Performance indices of dual-task preparation were used to assess the focused preparation of T1 and T2. To compare preparatory mechanisms at the neurophysiologic level, multi-channel electroencephalogram (EEG) was recorded and negative slow cortical potentials (SCPs) were analyzed as objective markers of the amount and localization of cortical pre-activation before sub-task presentation.Results: Dual-task performance was significantly slower in old adults. T1 performance was facilitated in both age groups, but T2 processing in old adults was not optimized by the temporal structure as efficiently as in young adults. Also, only young adults manifested a stable pattern of focused of negative slow-wave activity increase at medial frontal and right-hemisphere posterior regions, which was associated with a coordinated preparatory T1 pre-activation and T2 deferment, while old adults manifested a broad topographic distribution of negative SCPs associated with a pre-activation of sensory and motor processes.Conclusions: These observations demonstrate that the proactive preparation for dual tasking is altered with aging. It is suggested that in young adults, attention-based pre-activation of working memory and inhibitory networks in the right hemisphere synchronizes the simultaneous preparation of the two sub-tasks, whereas in old adults, sensory and motor networks appear to be non-specifically pre-activated for subsequent deferred mode of processing.

Investigating early changes in cognitive ability in the cognitively healthy and early‐stage cognitively impaired older adult populations

AbstractBackgroundDecline in cognitive ability is well understood to occur due to advanced age and pathological impairment. However, not all affected aspects of cognitive ability deteriorate at the same rate (Petersen, RC, et al., 1997; Craik, FI, and Salthouse TA, 2000, 2008, 2011; Salthouse, TA, 2009, 2012).In this study, we research how executive function abilities (mental processes that regulate and control our cognition) differ between cognitively healthy older adults and individuals living with Mild Cognitive Impairment (MCI) and early‐stage Alzheimer's disease (AD). Assessment was focused on four areas of executive functions dual‐tasking, inhibition, shifting and updating commonly utilised in everyday life (Miyake, A, et al., 2000; Alvarez, JA, and Emory, E, 2006; Suchy, Y, 2009; Baddeley, A., 2012). The aim is to better understand the nature and rate of deterioration as a means to aid in early detection and intervention for both conditions.MethodWe aim to assess approximately 30 cognitively healthy older adults, and a combination of 30 individuals living with MCI and early‐stage AD on four different aspects of executive functions, i.e. dual‐tasking, inhibition, shifting and updating. Two separate tasks will be utilised to measure each EF, dual‐tasking (the Test of Everyday Attention dual‐task telephone search subtest and Psychological Refractory Period paradigm task), inhibition (the Hayling Sentence Completion test and Stroop task), shifting (the Trail Making Test and a task switching test), and updating (the backward digit recall span test and a N‐back task).ResultData collection is ongoing.ConclusionWe predict better cognitive ability will be evident in the healthy older adult group, followed by the MCI and then the early‐stage AD groups. However, we expect dual‐tasking and updating ability to be most severely affected in individuals living with early‐stage AD and then shifting with inhibition showing most preservation.

Artificial Intelligence-Powered Smartphone App to Facilitate Medication Adherence: Protocol for a Human Factors Design Study.

BackgroundMedication Guides consisting of crucial interactions and side effects are extensive and complex. Due to the exhaustive information, patients do not retain the necessary medication information, which can result in hospitalizations and medication nonadherence. A gap exists in understanding patients’ cognition of managing complex medication information. However, advancements in technology and artificial intelligence (AI) allow us to understand patient cognitive processes to design an app to better provide important medication information to patients.ObjectiveOur objective is to improve the design of an innovative AI- and human factor–based interface that supports patients’ medication information comprehension that could potentially improve medication adherence.MethodsThis study has three aims. Aim 1 has three phases: (1) an observational study to understand patient perception of fear and biases regarding medication information, (2) an eye-tracking study to understand the attention locus for medication information, and (3) a psychological refractory period (PRP) paradigm study to understand functionalities. Observational data will be collected, such as audio and video recordings, gaze mapping, and time from PRP. A total of 50 patients, aged 18-65 years, who started at least one new medication, for which we developed visualization information, and who have a cognitive status of 34 during cognitive screening using the TICS-M test and health literacy level will be included in this aim of the study. In Aim 2, we will iteratively design and evaluate an AI-powered medication information visualization interface as a smartphone app with the knowledge gained from each component of Aim 1. The interface will be assessed through two usability surveys. A total of 300 patients, aged 18-65 years, with diabetes, cardiovascular diseases, or mental health disorders, will be recruited for the surveys. Data from the surveys will be analyzed through exploratory factor analysis. In Aim 3, in order to test the prototype, there will be a two-arm study design. This aim will include 900 patients, aged 18-65 years, with internet access, without any cognitive impairment, and with at least two medications. Patients will be sequentially randomized. Three surveys will be used to assess the primary outcome of medication information comprehension and the secondary outcome of medication adherence at 12 weeks.ResultsPreliminary data collection will be conducted in 2021, and results are expected to be published in 2022.ConclusionsThis study will lead the future of AI-based, innovative, digital interface design and aid in improving medication comprehension, which may improve medication adherence. The results from this study will also open up future research opportunities in understanding how patients manage complex medication information and will inform the format and design for innovative, AI-powered digital interfaces for Medication Guides.International Registered Report Identifier (IRRID)PRR1-10.2196/21659

The role of attentional slippage in Stroop dilution.

The present study examined the cognitive locus of Stroop dilution using a psychological refractory period (PRP) paradigm. Participants were asked to perform a tone discrimination task via a bimanual keypress response and a modified Stroop task via a vocal response serially as Task 1 and Task 2, respectively. In Task 2, a neutral word was added on half of the trials and no neutral word on the other half of the trials to observe the Stroop dilution effect. The amount of Stroop dilution, as well as the Stroop effect, was relatively constant across different stimulus-onset asynchronies (SOAs), which implies that Stroop dilution occurs due to the competition between a neutral word and a color word after a target color bar is selected to be processed further. These results indicate that focused attention plays an important role in the modulation of Stroop interference by the presence of a neutral word.

Automaticity of facial attractiveness perception and sex-specific mating strategies

The current literature shows mixed results regarding whether the perception of facial attractiveness is automatic, i.e. that it operates independently from attentional resources. We argue that an evolutionary perspective on mating strategies provides a comprehensive account of the findings. In two studies, we used the locus-of-slack logic in a psychological refractory period paradigm. Task 1 was a speeded judgment of tone pitch (low vs. high), and Task 2 was a speeded judgment of whether a face was attractive or unattractive on two difficulty levels. Male and female participants judged the attractiveness of opposite-sex faces (Study 1, n = 73) or same-sex faces (Study 2, n = 94) in this paradigm. Results indicate that men do not need attentional resources when processing female faces (Study 1), but require attentional resources when processing same-sex faces (Study 2). In contrast, women need attentional resources to process the attractiveness of opposite as well as same-sex faces.

Two sources of task prioritization: The interplay of effector-based and task\xa0order-based capacity allocation in the PRP paradigm

When processing of two tasks overlaps, performance is known to suffer. In the well-established psychological refractory period (PRP) paradigm, tasks are triggered by two stimuli with a short temporal delay (stimulus onset asynchrony; SOA), thereby allowing control of the degree of task overlap. A decrease of the SOA reliably yields longer RTs of the task associated with the second stimulus (Task 2) while performance in the other task (Task 1) remains largely unaffected. This Task 2-specific SOA effect is usually interpreted in terms of central capacity limitations. Particularly, it has been assumed that response selection in Task 2 is delayed due to the allocation of less capacity until this process has been completed in Task 1. Recently, another important factor determining task prioritization has been proposed—namely, the particular effector systems associated with tasks. Here, we study both sources of task prioritization simultaneously by systematically combining three different effector systems (pairwise combinations of oculomotor, vocal, and manual responses) in the PRP paradigm. Specifically, we asked whether task order-based task prioritization (SOA effect) is modulated as a function of Task 2 effector system. The results indicate a modulation of SOA effects when the same (oculomotor) Task 1 is combined with a vocal versus a manual Task 2. This is incompatible with the assumption that SOA effects are solely determined by Task 1 response selection duration. Instead, they support the view that dual-task processing bottlenecks are resolved by establishing a capacity allocation scheme fed by multiple input factors, including attentional weights associated with particular effector systems.

Disentangling stimulus and response compatibility as potential sources of backward crosstalk

In two experiments (N= 60 each), we investigated the locus of backward crosstalk effects in dual tasking. Specifically, we embedded the typical flanker task within a dual-task paradigm by assigning stimulus-response (S-R) rules to the flankers. In Experiment 1, participants were instructed to first respond to the center letter and only respond to the flanker if the center was a no-go stimulus (i.e., prioritized processing paradigm). Mapping condition was varied between-subjects to be either matched (i.e., same S-R rule for flankers as for center letters), reversed (i.e., opposite S-R rule for flankers), or neutral (i.e., different letters for flankers with separate S-R rules). The results indicated that the backward crosstalk effect was mainly driven by a stimulus-based compatibility, as indicated by a significant S2−R1 compatibility effect in the matched and reversed conditions, with little change in this effect between the matched and reversed conditions. Experiment 2 replicated and extended these findings to a psychological refractory period paradigm. The present findings suggest that in the matched and reversed conditions, there was only one S-R rule active at a time.

Item-specific proportion congruency (ISPC) modulates, but does not generate, the backward crosstalk effect.

When both tasks in a psychological refractory period (PRP) paradigm have compatible manual responses, a compatibility benefit in RT can often be observed on Task1 performance, in apparent violation of a strict traditional response selection bottleneck model. This compatibility-based backward crosstalk effect (BCE) has been generally attributed to automatic activation of Task2 response information, in parallel with attended Task1 performance. This paper tests a potential alternative mechanism of the BCE. Item-specific proportion congruency (ISPC) effects are previously well demonstrated, where learning of associations between stimuli and task conflict (e.g., that particular Stroop items are typically incongruent) allows rapidly and automatically elicited control adjustments in performance. Similar proportion manipulations have recently been shown to modulate the BCE in dual-task performance. If participants could similarly learn associations between particular pairs of stimuli and resulting response conflict in a PRP task, this kind of mechanism could produce relative speeding versus slowing of Task1 RT on response compatible versus incompatible trials. This pattern of data directly describes the BCE, and represents a potential alternative mechanism that does not require any response crosstalk, and would reinforce a stricter view of the response selection bottleneck model, if true. Over two experiments, we demonstrate that while the BCE is sensitive to ISPC-like effects based on Task1 conflict contingencies, the BCE is insensitive to relationships between particular pairs of stimuli and associated conflict. While ISPC effects can modulate the BCE, they do not generate the BCE. These findings reinforce the current Task2 parallel response activation account of the BCE.

Global-local processing and dispositional bias interact with emotion processing in the psychological refractory period paradigm.

The reciprocal link between scope of attention and emotional processing is an important aspect of the relationship between emotion and attention. Larger scope of attention or global processing has been linked to positive emotions and narrow scope of attention or local processing has been linked to negative emotions. The nature of this relationship in the context of central capacity limitations and individual differences in attentional processing has not been studied in detail so far. To investigate such a relationship, here we used the psychological refractory period (PRP) paradigm, in which we manipulated the stimulus onset asynchrony (SOA: 150ms, 300ms, 900ms) of stimuli corresponding to two tasks in a sequence. The first task was identifying a number at the global or local level; the second task was recognizing the emotional expression (happy or angry). Additionally, predisposition towards local or global perceptual dimension was measured with the global-local task. Results indicated that global precedence modulated PRP effect and that response accuracy was impaired by the combination of local-angry task modalities. Interestingly, interference between simultaneous tasks was modulated by the predisposition to different perceptual levels resulting in different cognitive strategies for performing simultaneous tasks: locally biased subjects tended more towards serial processing, meanwhile globally biased ones were performing tasks in a parallel manner. This result suggest that individual differences may play a role in the choice of dual-task performing strategies.

Investigating limits of task prioritization in dual-tasking: evidence from the prioritized processing and the psychological refractory period paradigms.

Dual-tasking often requires prioritizing one task over the other. For example, in the psychological refractory period (PRP) paradigm, participants are instructed to initially respond to Task 1 (T1) and only then to Task 2 (T2). Furthermore, in the prioritized processing paradigm (PP), participants are instructed to perform T2 only if T1 was a no-go trial-requiring even more prioritization. The present study investigated the limits of task prioritization. Two experiments compared performance in the PRP paradigm and the PP paradigm. To manipulate task prioritization, tasks were rewarded differently (e.g., high reward for T1, low reward for T2, and vice versa). We hypothesized (a) that performance will improve for the highly rewarded task (Experiments 1 and 2) and (b) that there are stronger reward effects for T1 in the PRP than in the PP paradigm (Experiment 2). Results showed an influence of reward on task prioritization: For T1, high reward (compared to low reward) caused a speed-up of responses that did not differ between the two paradigms. However, for T2, reward influenced response speed selectively in the PP paradigm, but not in the PRP paradigm. Based on paradigm-specific response demands, we propose that the coordination of two motor responses plays a crucial role in prioritizing tasks and might limit the flexibility of the allocation of preparatory capacity.