Psychological Refractory Period Paradigm Research Articles

Is semantic activation from print capacity limited? Evidence from the psychological refractory period paradigm.

A widely accepted belief across a range of subfields in psychology is that print activates semantics "automatically" in some sense. One such sense is that activating semantics does not require capacity. This view is assessed here in the context of the Psychological Refractory Period (PRP) paradigm because it provides a way of determining whether semantic activation requires a form of capacity. Task 1 was tone classification. Task 2 was Stroop color naming. The distractors consisted of color words on some trials (e.g., BLUE), and semantic associates on others (e.g., TOMATO). Both types of distractors yielded a pattern of data inconsistent with the widespread view that semantic activation is capacity free.

Attentional constraints on semantic activation: Evidence from Stroop's paradigm

It is widely believed that semantic activation from print is automatic in the sense that it is capacity free. Two experiments addressed this issue in the context of the Psychological Refractory Period (PRP) paradigm. Participants identified whether a tone was high or low in pitch in Task 1, and named the color carried by an irrelevant word in Task 2. Tasks 1 and 2 were separated by a short or long SOA. In Experiment 1 incongruent color words and neutral words served as irrelevant distractors, whereas in Experiment 2 the distractors consisted of incongruent color associates (e.g., tomato) and the same set of neutral items. Additionally, the proportion of short and long SOAs between Task 1 and Task 2 varied across blocks, within subjects (e.g., 80:20), so as to determine whether the bottlenecking of semantic activation and response competition reported previously is best construed as structural, or subject to performance optimization. Replicating Miller, Ulrich, and Rolke (2009), SOA Proportion interacted with SOA in both experiments, consistent with performance optimization. In contrast, replicating Besner and Reynolds (2014), SOA and Congruency had additive effects on RT in both experiments, consistent with an account in which both response competition and semantic activation are bottlenecked. The best account to date is that (i) semantic processing and response competition are structurally bottlenecked (require some form of capacity), whereas (ii) other anonymous processes are subject to performance optimization.

EP 124. Dual-task processing in young and older adults

Introduction A substantial body of research has indicated impairments in dual-task performance with advanced age. Aim To corroborate previously reported age effects on dual-task performance and to examine potential moderating factors. In particular, we examined associations between dual-tasking and visuomotor coordination, cognitive flexibility, divided attention and task-switching. Methods The sample consisted of 20 young (mean age: 25.7 yrs.) and 20 elderly (mean age: 57.4 yrs.) adults. Dual-task performance was assessed using the well-established psychological refractory period (PRP) paradigm, in which two speeded choice-reaction tasks need to be performed either simultaneously or successively. Task 1 required a discrimination of high and low tones; Task 2 required a discrimination of letters “a” and “e”. A variable stimulus onset asynchrony (SOA; 50, 100, 350 or 800 ms) separated the two tasks. In addition, several tests were conducted to assess potential influencing factors including the Trail-Making Test (TMT) for visuomotor coordination and cognitive flexibility, a cross-modal divided-attention test, and an alternating-runs task-switching paradigm producing global and local switch costs. Results We observed typical dual-task costs for response speed (i.e., a significant PRP effect on reaction time, RT) but neither found a significant main effect of age on RT, nor a significant interaction between age and dual-task costs for RT in either Task. In the letter discrimination, however, there was a significant interaction between age and dual-task costs for accuracy driven by a more steeply increasing error rate with increasing task overlap in the older (vs. young) group. Neither visuomotor coordination nor cognitive flexibility co-varied with dual-task costs in RT and accuracy, but divided-attention and task-switching performance did. Difficulties in dividing attention and larger local switch costs were associated with a larger PRP effect on RT but not on accuracy. Conclusion When two speeded reaction tasks need to be performed in parallel, healthy aging may lead to deterioration in accuracy, rather than speed, relative to serial task processing. With regard to speed, however, both the ability to efficiently divide attention across sensory modalities and the ability to shift to a given task right after performing another one significantly predict low dual-tasking costs. As to accuracy, the pattern appears to be reversed, with age, rather than divided-attention or task-switching abilities, compounding dual-tasking costs. This suggests that doing two things at once is not per se compromised in old age but may depend more strongly on the integrity of other executive functions such as attentional control and task-set activation. Also, differential speed-accuracy tradeoffs need to be considered when studying age effects on performance.

Temporal discrimination of one's own reaction times in dual-task performance: Context effects and methodological constraints.

In this study we used the method of constant stimuli to investigate introspective reaction times in the psychological refractory period (PRP) paradigm under different temporal contexts. Previous introspective PRP studies have mostly used visual analogue scales to assess introspective reaction times and found that participants were largely unaware of the typical dual-task costs that arise in this paradigm (PRP effect). This apparent limitation of introspection has been taken as evidence for a serial processing bottleneck that encompasses response selection as well as conscious perception. In our study, in each trial participants first performed the PRP task and were then presented with a comparison interval that they had to compare with their reaction time to the second task (RT2). Across three experiments, we observed that the subjective estimates of RT2 (i.e., the points of subjective equality) did not reflect the objective pattern but were almost completely biased toward the center of the comparison intervals (asymmetry effect). In a control experiment in which participants discriminated RT2s of other participants without performing the PRP task, this bias was largely reduced. We interpret these results as indicating that in dual-task performance participants acquire only poor temporal representations of their own reaction times, and the apparent unawareness of the PRP effect may reflect disturbed timing abilities rather than a conscious perception bottleneck.

Do Arabic numerals activate magnitude automatically? Evidence from the psychological refractory period paradigm.

A single experiment (N = 30) tested the claim that Arabic numerals automatically activate their magnitude representations by assessing whether central attention is required in order to activate magnitude within the psychological refractory period (PRP) paradigm. Subjects performed a color discrimination task as Task 1 and a parity judgment task as Task 2. Task overlap was controlled by varying stimulus onset asynchrony (SOA). A spatial-numerical association of response codes (SNARC) effect arose in Task 2 and yielded under-additive effects with decreasing SOA. This result suggests that magnitude is activated prior to central attention, and is therefore consistent with the claim that numerals activate magnitude automatically.

Eliminating dual-task costs by minimizing crosstalk between tasks: The role of modality and feature pairings

We tested the independent influences of two content-based factors on dual-task costs, and on the parallel processing ability: The pairing of S–R modalities and the pairing of relevant features between stimuli and responses of two tasks. The two pairing factors were realized across four dual-task groups. Within each group the two tasks comprised two different stimulus modalities (visual and auditory), two different relevant stimulus features (spatial and verbal) and two response modalities (manual and vocal). Pairings of S–R modalities (standard: visual–manual and auditory–vocal, non-standard: visual–vocal and auditory–manual) and feature pairings (standard: spatial–manual and verbal–vocal, non-standard: spatial–vocal and verbal–manual) varied across groups. All participants practiced their respective dual-task combination in a paradigm with simultaneous stimulus onset before being transferred to a psychological refractory period paradigm varying stimulus-onset asynchrony. A comparison at the end of practice revealed similar dual-task costs and similar pairing effects in both paradigms. Dual-task costs depended on modality and feature pairings. Groups training with non-standard feature pairings (i.e., verbal stimulus features mapped to spatially separated response keys, or spatial stimulus features mapped to verbal responses) and non-standard modality pairings (i.e., auditory stimulus mapped to manual response, or visual stimulus mapped to vocal responses) had higher dual-task costs than respective standard pairings. In contrast, irrespective of modality pairing dual-task costs virtually disappeared with standard feature pairings after practice in both paradigms. The results can be explained by crosstalk between feature-binding processes for the two tasks. Crosstalk was present for non-standard but absent for standard feature pairings. Therefore, standard feature pairings enabled parallel processing at the end of practice.

Age-related emotional bias in processing two emotionally valenced tasks.

Previous studies suggest that older adults process positive emotions more efficiently than negative emotions, whereas younger adults show the reverse effect. We examined whether this age-related difference in emotional bias still occurs when attention is engaged in two emotional tasks. We used a psychological refractory period paradigm and varied the emotional valence of Task 1 and Task 2. In both experiments, Task 1 was emotional face discrimination (happy vs. angry faces) and Task 2 was sound discrimination (laugh, punch, vs. cork pop in Experiment 1 and laugh vs. scream in Experiment 2). The backward emotional correspondence effect for positively and negatively valenced Task 2 on Task 1 was measured. In both experiments, younger adults showed a backward correspondence effect from a negatively valenced Task 2, suggesting parallel processing of negatively valenced stimuli. Older adults showed similar negativity bias in Experiment 2 with a more salient negative sound ("scream" relative to "punch"). These results are consistent with an arousal-bias competition model [Mather and Sutherland (Perspectives in Psychological Sciences 6:114-133, 2011)], suggesting that emotional arousal modulates top-down attentional control settings (emotional regulation) with age.

A startling acoustic stimulus interferes with upcoming motor preparation: Evidence for a startle refractory period

When a startling acoustic stimulus (SAS) is presented in a simple reaction time (RT) task, response latency is significantly shortened. The present study used a SAS in a psychological refractory period (PRP) paradigm to determine if a shortened RT1 latency would be propagated to RT2. Participants performed a simple RT task with an auditory stimulus (S1) requiring a vocal response (R1), followed by a visual stimulus (S2) requiring a key-lift response (R2). The two stimuli were separated by a variable stimulus onset asynchrony (SOA), and a typical PRP effect was found. When S1 was replaced with a 124dB SAS, R1 onset was decreased by 40–50ms; however, rather than the predicted propagation of a shortened RT, significantly longer responses were found for RT2 on startle trials at short SOAs. Furthermore, the 100ms SOA condition exhibited reduced peak EMG for R2 on startle trials, as compared to non-startle trials. These results are attributed to the startling stimulus temporarily interfering with cognitive processing, delaying and altering the execution of the second response. In addition to this “startle refractory period,” results also indicated that RT1 latencies were significantly lengthened for trials that immediately followed a startle trial, providing evidence for longer-term effects of the startling stimulus.

On the importance of Task 1 and error performance measures in PRP dual-task studies.

The psychological refractory period (PRP) paradigm is a dominant research tool in the literature on dual-task performance. In this paradigm a first and second component task (i.e., Task 1 and Task 2) are presented with variable stimulus onset asynchronies (SOAs) and priority to perform Task 1. The main indicator of dual-task impairment in PRP situations is an increasing Task 2-RT with decreasing SOAs. This impairment is typically explained with some task components being processed strictly sequentially in the context of the prominent central bottleneck theory. This assumption could implicitly suggest that processes of Task 1 are unaffected by Task 2 and bottleneck processing, i.e., decreasing SOAs do not increase reaction times (RTs) and error rates of the first task. The aim of the present review is to assess whether PRP dual-task studies included both RT and error data presentations and statistical analyses and whether studies including both data types (i.e., RTs and error rates) show data consistent with this assumption (i.e., decreasing SOAs and unaffected RTs and/or error rates in Task 1). This review demonstrates that, in contrast to RT presentations and analyses, error data is underrepresented in a substantial number of studies. Furthermore, a substantial number of studies with RT and error data showed a statistically significant impairment of Task 1 performance with decreasing SOA. Thus, these studies produced data that is not primarily consistent with the strong assumption that processes of Task 1 are unaffected by Task 2 and bottleneck processing in the context of PRP dual-task situations; this calls for a more careful report and analysis of Task 1 performance in PRP studies and for a more careful consideration of theories proposing additions to the bottleneck assumption, which are sufficiently general to explain Task 1 and Task 2 effects.

A cognitive framework for explaining serial processing and sequence execution strategies.

Behavioral research has produced many task-specific cognitive models that do not say much about the underlying information-processing architecture. Such an architecture is badly needed to better understand how cognitive neuroscience can benefit from existing cognitive models. This problem is especially pertinent in the domain of sequential behavior where behavioral research suggests a diversity of cognitive processes, processing modes and representations. Inspired by decades of reaction time (RT) research with the Additive Factors Method, the Psychological Refractory Period paradigm, and the Discrete Sequence Production task, we propose the Cognitive framework for Sequential Motor Behavior (C-SMB). We argue that C-SMB accounts for cognitive models developed for a range of sequential motor tasks (like those proposed by Keele et al., Psychological Review, 110(2), 316-339, 2003; Rosenbaum et al., Journal of Experimental Psychology: Human Perception and Performance, 9(1), 86-102, 1983, Journal of Memory and Language, 25, 710-725, 1986, Psychological Review, 102, 28-67, 1995; Schmidt, Psychological Review, 82(4), 225-260, 1975; Sternberg et al., 1978, Phonetica, 45, 177-197, 1988). C-SMB postulates that sequence execution can be controlled by a central processor using central-symbolic representations, and also by a motor processor using sequence-specific motor representations. On the basis of this framework, we present a classification of the sequence execution strategies that helps researchers to better understand the cognitive and neural underpinnings of serial movement behavior.

Parallel and serial processing in dual-tasking differentially involves mechanisms in the striatum and the lateral prefrontal cortex.

The lateral prefrontal cortex and the basal ganglia are known to be important for response selection processes, also in dual-task situations. However, response selection in dual-task situations can be achieved using different modes ranging from a parallel selection to a more serial selection of responses. Nothing is known whether differences in these processing modes during dual-tasking have distinct functional neuroanatomical correlates. In this fMRI study we analyzed performance in a psychological refractory period paradigm. In this paradigm we design a PRP task where we vary the frequency of short and long stimulus onset asynchronies between the two tasks. Using mathematical constraints we interpret the effects of this manipulation with respect to processing modes ranging from more serial to more parallel response selection. Contrastingly these blocks showed that response selection in dual-tasking under the constraint of more parallel processing is mediated by mechanisms operating at the striatal level, while response selection under the constraint of more serial processing is mediated via mechanisms operating in the lateral prefrontal cortex. The results suggest that lateral prefrontal and striatal regions are 'optimized' for a certain processing modes in dual tasking.

The locus of the emotional Stroop effect: A study with the PRP paradigm

Stimuli that are clearly positive or negative (hence valence-laden stimuli) have the potential to interrupt unrelated task processing. A typical example is the emotional Stroop effect (ESE) in which responding to a certain task feature (e.g., color) is delayed by the presentation of task-irrelevant valent stimuli (e.g., negative pictures) compared to valence-neutral stimuli. Here we scrutinize which processes are slowed down by irrelevant but valent stimulation. In Experiment 1, participants performed in a Psychological Refractory Period (PRP) experiment with tone discrimination as Task 1 and color discrimination as Task 2. Importantly, colors in Task 2 were accompanied by valent or neutral pictures. Valent pictures delayed responding in Task 2 (thus an ESE) and this delay was additive to the time interval between tasks. In Experiment 2, task order was reversed and the ESE in Task 1 fully propagated to the Task 2 tone discrimination. These results imply that irrelevant valence-laden stimulation delays capacity-limited processes, and we suggest that this is a late perceptual process acting on stimulus categorization.

PRP training shows Task1 response selection is the locus of the backward response compatibility effect.

The present study investigates the effect of practice in a psychological refractory period (PRP) paradigm on the backward compatibility effect (BCE), in order to determine the locus of this response priming effect on Task1 performance. In two experiments, we show that the size of the BCE is closely associated with the duration of the response selection stage in Task1. When this stage is shortened through PRP practice, the magnitude of the BCE decreases. Subsequently increasing the duration of Task1 response selection results in a larger BCE, but manipulating the same stage in Task2 does not. Our results suggest that the BCE reflects crosstalk of unattended response information for Task2 acting on the response selection stage in Task1, and that response information for two tasks may be activated simultaneously.

Multitasking and Aging: Do Older Adults Benefit from Performing a Highly Practiced Task?

Background/Study Context: The present study examined the effect of training on age differences in performing a highly practiced task using the psychological refractory period (PRP) paradigm (Pashler, 1984, Journal of Experimental Psychology: Human Perception and Performance, 10, 358–377). Earlier training studies have concentrated on tasks that are not already overlearned. The present question of interest is whether task dual-task integration will be more efficient when single-task performance is approaching asymptotic levels.Methods: Task 1 was red/green signal discrimination (green = “go” and red = “wait”; analogous to pedestrian signals) and Task 2 was tone discrimination (white noise vs. a horn “honk”; analogous to traffic sound). The stimulus onset asynchrony (SOA) between Task 1 and Task 2 was varied (50, 150, 600, and 1000 ms). All individuals participated in eight sessions spread over 8 weeks (one session per week). Participants completed a dual-task pretest (Week 1), followed by 6 weeks of single-task testing (Weeks 2–7), followed by a dual-task posttest (Week 8).Results and Conclusion: Although older adults showed larger overall dual-task costs (i.e., PRP effects), they were able to reduce the costs with practice as much as younger adults. However, even when training on Task 1 results in asymptotic performance, this still did not lead to an appreciable reduction in dual-task costs. Also, older adults, but not younger adults, responded more rapidly to green stimuli than to red stimuli in the Task 1 training latency data. The authors confirmed this green/go bias using diffusion modeling, which takes into account response time and error rates at the same time. This green/go bias is potentially dangerous at crosswalks, especially when combined with large dual-task interference, and might contribute to the high rate of crosswalk accidents in the elderly.

Orienting attention in visual working memory requires central capacity: Decreased retro-cue effects under dual-task conditions

The retro-cue effect (RCE) describes superior working memory performance for validly cued stimulus locations long after encoding has ended. Importantly, this happens with delays beyond the range of iconic memory. In general, the RCE is a stable phenomenon that emerges under varied stimulus configurations and timing parameters. We investigated its susceptibility to dual-task interference to determine the attentional requirements at the time point of cue onset and encoding. In Experiment 1, we compared single- with dual-task conditions. In Experiment 2, we borrowed from the psychological refractory period paradigm and compared conditions with high and low (dual-) task overlap. The secondary task was always binary tone discrimination requiring a manual response. Across both experiments, an RCE was found, but it was diminished in magnitude in the critical dual-task conditions. A previous study did not find evidence that sustained attention is required in the interval between cue offset and test. Our results apparently contradict these findings and point to a critical time period around cue onset and briefly thereafter during which attention is required.

Locus of Backward Crosstalk Effects on Task 1 in a Psychological Refractory Period Task

Our performance on a task decreases when the task is in a dual-task situation than when it is in isolation. An important experimental setting for dual-task situation is the psychological refractory period (PRP) paradigm, and the dual-task performance decrements in the PRP paradigm are referred to as PRP interference. The standard response-selection bottleneck (RSB) models state that the response-selection stage of the second task (T2) cannot start until the response-selection stage of the first task (T1) finishes, resulting in the PRP interference. Contrary to the prediction of RSB models, several researchers have found T2's modulations on T1's performance, and have suggested that T1's selection-related processes are affected by T2's selection-related processes, referred to as backward crosstalk effects. The locus of backward crosstalk effects is not clear, however, because RTs were measured in most previous studies. By using semantically unrelated stimuli and responses and by measuring T1's lateralized readiness potential, we examined the locus of backward crosstalk effects. We found that the interval between T1's stimulus onset and the stimulus-locked LRP onset was affected, suggesting T2's response selection starts before T1's selection is complete. The present result provided electrophysiological evidence focusing on T1's changes in favor of the hypothesis of parallel response selection in the PRP paradigm.

Exceptions to the PRP effect? A comparison of prepared and unconditioned reflexes.

Psychological research has documented again and again marked performance decrements whenever humans perform 2 or more tasks at the same time. In fact, the available evidence seems to suggest that any type of behavior is subject to such limitations. The present experiments employed the psychological refractory period (PRP) paradigm to identify a clear exception to this rule: Unconditioned reflexes do escape dual-task interference, whereas intended simple responses, so called "prepared reflexes," do not. Beyond this empirical novelty, we discuss the findings in broader terms of human action control. In particular, we suggest that the (non)susceptibility to dual-task interference may provide a clear empirical delineation between goal-directed behavior (i.e., actions) and other, not goal-directed behavior.

Processing order in dual-tasks when the duration of motor responses varies

Bajo el paradigma de periodo refractario psicológico (PRP), recientes estudios han hallado que la duración del procesamiento central influye en el orden en el que dos tareas son procesadas. En el presente trabajo se examinó si la duración de la respuesta también influye en el orden en el que dos tareas se ejecutan. Para este propósito, se utilizó una tarea de discriminación auditiva en combinación con una tarea de discriminación visual. En el experimento se varió el orden de presentación de las tareas de forma aleatoria así como se utilizaron diferentes intervalos entre estímulos (stimulus onset asynchrony; SOA) En una condición, los participantes respondieron a cada estímulo pulsando una tecla (condición de respuesta simple). En la otra condición, mientras que a la tarea auditiva se respondía de nuevo pulsando una tecla, la respuesta a la tarea visual requería pulsar una secuencia de teclas, aumentando la duración de la respuesta (condición de respuesta compleja). Los resultados mostraron que los participantes tienden a ejecutar más a menudo la tarea auditiva en primer lugar cuando la respuesta de la tarea visual es más compleja. Este resultado apoya la noción de que, en escenarios de doble tarea, los participantes pueden invertir sus respuestas si con ello optimizan su ejecución.

Evidence for a response preparation bottleneck during dual-task performance: Effect of a startling acoustic stimulus on the psychological refractory period

The present study was designed to investigate the mechanism associated with dual-task interference in a psychological refractory period (PRP) paradigm. We used a simple reaction time paradigm consisting of a vocal response (R1) and key-lift task (R2) with a stimulus onset asynchrony (SOA) between 100ms and 1500ms. On selected trials we implemented a startling acoustic stimulus concurrent with the second stimulus to determine if we could involuntarily trigger the second response. Our results indicated that the PRP delay in the second response was present for both control and startle trials at short SOAs, suggesting the second response was not prepared in advance. These results support a response preparation bottleneck and can be explained via a neural activation model of preparation. In addition, we found that the reflexive startle activation was reduced in the dual-task condition for all SOAs, a result we attribute to prepulse inhibition associated with dual-task processing.

Individual differences effects on the psychological refractory period

The goal of this study was to assess the impact of individual neuropsychological differences on the ability to share attention between concurrent tasks. Participants (n = 20) were trained on six single task practice sessions and dual-task was assessed with reaction time performance on a psychological refractory period (PRP) paradigm. Neuropsychological test scores were also acquired. Furthermore, one of the known variables that can influence performances on neuropsychological tests is gender, which was added as a potential predictor. Results show that the small PRP group was associated with better performances in processing speed, inhibition, flexibility and working memory on neuropsychological tests. Gender also had an impact on the PRP, males having a lower PRP than females. A multiple regression was performed to determine which variables explained the most PRP duration, which showed that 49.1% of the variance of the PRP length could be explained by gender, reaction times of the PRP practice trials at the sixth session, the denomination and flexibility conditions of the Modified Stroop Task as well as results on the Symbol Search Test. Gender was the variable that explained the PRP variance the most (23%). Processing speed also seemed to be a great determinant of the PRP as well as the ability to alternate between task-sets as assessed by the Flexibility condition of the Modified Stroop Task. Thus, this study reveals that good performances on certain neuropsychological tests could predict one’s ease to manage two tasks simultaneously with a higher chance for males to perform better.