Uncorking the central bottleneck: Even novel tasks can be performed automatically.

Can people perform two novel tasks in parallel? Available evidence and prevailing theories overwhelmingly indicate that the answer is no, due to stubborn capacity limitations in central stages (e.g., a central bottleneck). Here we propose a new hypothesis, which suggests otherwise: people are capable of fully parallel central processing (i.e., bypassing the central bottleneck), yet often fail to do so, mainly due to preparation neglect. This preparation-neglect hypothesis was evaluated in four dual-task experiments pairing novel tasks (Task 1 and Task 2) using arbitrary stimulus-response mappings. Experiment 1, using a classic psychological refractory period (PRP) procedure, replicated the finding of dozens of previous PRP studies: none of the participants bypassed the bottleneck, instead exhibiting large dual-task interference on Task 2 (445 ms). In Experiment 2, the same dual-task PRP trials were randomly intermixed with single-task trials on Task 2, to boost preparation on that task. Here, nearly half the sample of participants bypassed the central bottleneck, exhibiting small dual-task interference on Task 2 (48 ms). Two additional experiments showed that initial practice does not by itself enable bottleneck bypassing, but boosting preparation of Task 2 (via intermixing single-task trials of Task 2) does. We conclude that, when properly prepared, people are capable of far more dual-task automaticity than was previously believed. (PsycInfo Database Record (c) 2024 APA, all rights reserved).

Survival processing occupies the central bottleneck of cognitive processing: A psychological refractory period analysis.

Words judged for relevance in a survival situation are remembered better than words judged for relevance in a nonsurvival context. This survival processing effect has been explained by selective tuning of human memory during evolution to process and retain information specifically relevant for survival. According to the richness-of-encoding hypothesis the survival processing effect arises from a domain-general mechanism-namely, a particularly rich and distinct form of encoding. This form of information processing is effortful and requires limited cognitive capacities. In our experiment, we used the well-established psychological refractory period framework in conjunction with the effect propagation logic to assess the role of central cognitive resources for the survival processing effect. Our data demonstrate that the survival memory advantage indeed relies on the capacity-limited central stage of cognitive processing. Thus, rating words in the context of a survival scenario involves central processing resources to a greater amount than rating words in a nonsurvival control condition. We discuss implications for theories of the survival processing effect.

Serial attention to serial memory: The psychological refractory period in forward and backward cued recall.

Guided by the conjecture that memory retrieval is attention turned inward, we examined serial attention in serial memory, combining the psychological refractory period (PRP) procedure from attention research with cued recall of two items from brief six-item lists. We report six experiments showing robust PRP effects in cued recall from memory (1-4) and cued report from perceptual displays (5-6), which suggest that memory retrieval requires the same attentional bottleneck as "retrieval" from perception. There were strong direction effects in each memory experiment. Response time (RT) was shorter and accuracy was higher when the cues occurred in the forward direction (left-to-right, top-to-bottom, first-to-last), replicating differences between forward and backward serial recall. Cue positions had strong effects on RT and accuracy in the memory experiments (1-4). The pattern suggested that subjects find cued items in memory by stepping through the list from the beginning or the end, with a preference for starting at the beginning. The perceptual experiments (5-6) showed weak effects of position that were more consistent with direct access. In all experiments, the distance between the cues in the list (lag) had weak effects, suggesting that subjects searched for each cue from the beginning or end of the list more often than they moved through the list from the first cue to the second. Direction, distance, and lag effects on RT and inter-response interval changed with SOA in a manner that suggested they affect bottleneck or pre-bottleneck processes that create and execute a plan for successive retrievals. We conclude that sequential retrieval from memory and sequential attention to perception engage the same computations and we show how computational models of memory can be interpreted as models of attention focused on memory.

Time expectancies in dual tasking: Evidence for proactive resource sharing?

The present study explored whether dual-task performance is affected by deviations from the expected time point of a secondary task. In two psychological refractory period experiments, participants responded to two tasks, separated by either a short or long delay. In contrast to traditional dual-tasking studies, however, the identity of Task 1 probabilistically predicted the delay after which Task 2 would occur. Violations of these expectations impaired performance in both Task 2 and Task 1. For Task 2, this effect was more pronounced when Task 2 occurred unexpectedly early, while for Task 1, it was more pronounced when Task 2 occurred unexpectedly late. The results are consistent with the notion that processing resources can be shared, and that even in the absence of Task 2, some resources are withheld from Task 1, based on early available Task 1 features. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

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

PURPOSE: 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. METHOD: 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. RESULTS: 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. CONCLUSION: 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.

The attentional boost effect overcomes dual-task interference in choice-response tasks.

Dual-task interference often arises when people respond to an incoming stimulus according to an arbitrary rule, such as choosing between the gas pedal and the brake when driving. Severe interference from response selection yields a brief "Psychological Refractory Period," during which a concurrent task is put on hold. Here, we show that response selection in one task does not always hamper the processing of a secondary task. Responding to a target may paradoxically enhance the processing of secondary tasks, even when the target requires complex response selection. In three experiments, participants encoded pictures of common objects to memory while simultaneously monitoring a rapid serial visual presentation (RSVP) of characters or colours. Some of the RSVP stimuli were targets, requiring participants to press one of the two buttons to report their identity; others were distractors that participants ignored. Despite the increased response selection demands on target trials, pictures encoded with the RSVP targets were better remembered than those encoded with the RSVP distractors. Contrary to previous reports and predictions from dual-task interference, the attentional boost from target detection overcomes increased interference from response selection.

Information interference and loss in a dual task situation: Task 1, choice reaction time; Task 2, unspeeded recall.

The extraction and maintenance of second task information was explored in four dual task experiments. A variant of the psychological refractory period procedure was used with the first task, a speeded choice reaction to a tone and the second task, the unspeeded recall of letter triplets. Prior research had shown that recall accuracy dropped as the stimulus-onset asynchrony (SOA) decreased and task overlap increased. This could be due to interference with extracting perceptual information or to loss of the information while awaiting central resources. All four experiments showed evidence of interference, with the accuracy of recall for the first letter recalled relatively unaffected by SOA but with accuracy for later letters dropping as SOA decreased. Two of the experiments showed evidence for loss of second task information, with accuracy lower on trials with longer first task reaction times. The two other experiments showed loss of information when either the response complexity of Task 1 or the perceptual encoding difficulty was increased, increasing the processing time. The observed interference was attributed to slowed extraction of perceptual information. The observed loss was consistent with the encoded information being held in a fragile temporary store, susceptible to loss until consolidated into short-term memory. The evidence showed that the interference and the loss were independent processes.

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).

Dual-task interference in simulated car driving: The psychological refractory period effect when not only the second, but also the first task is ecologically relevant.

The psychological refractory period (PRP) effect denotes the finding that shortening the temporal interval between two tasks leads to increased reaction time in the second task. Earlier work in driving simulators confirmed the emergence of a PRP effect even if the second task (T2) was ecologically relevant, such as in a car-braking task. Here we evaluate the PRP effect if the first task (T1) is ecologically relevant as well. In a driving simulator, participants had to warn pedestrians against crossing the street (T1), and had to brake when the lead car braked (T2). As the temporal interval between tasks decreased, reaction time in T2 increased, confirming once more the emergence of a PRP effect. The PRP effect in our study was larger than in previous studies where T1 was artificial rather than ecologically relevant. This suggests that an ecologically relevant T1 is processed more elaborately, resulting in stronger interference with T2.

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.

The surprising role of stimulus modality in the dual-task introspective blind spot: a memory account.

Being able to accumulate accurate information about one's own performance is important in everyday contexts, and arguably particularly so in complex multitasking contexts. Thus, the observation of a glaring gap in participants' introspection regarding their own reaction time costs in a concurrent dual-task context is deserving of closer examination. This so-called introspective blind spot has been explained by a 'consciousness bottleneck' which states that while attention is occupied by one task, participants cannot consciously perceive another stimulus presented in that time. In the current study, a series of introspective Psychological Refractory Period (PRP) experiments were conducted to identify the determinants of an introspective blind spot; to our surprise, in half of the experiments participants appeared to be aware of their dual-task costs. A single trial analysis highlighted the sensory modality of the two stimuli within the trial as an important predictor of introspective accuracy, along with temporal gaps in the trial. The current findings call into question the claim that attention is required for conscious awareness. We propose a memory-based account of introspective processes in this context, whereby introspective accuracy is determined by the memory systems involved in encoding and rehearsing memory traces. This model of the conditions required to build up accurate representations of our performance may have far-reaching consequences for monitoring and introspection across a range of tasks.

Bypassing the central bottleneck with easy tasks: Beyond ideomotor compatibility.

Maquestiaux, Lyphout-Spitz, Ruthruff, and Arexis (2020) demonstrated that ideomotor-compatible (IM) tasks (e.g., pressing the left key when an arrow points left) can operate automatically, entirely bypassing the central bottleneck that constrains dual-task performance. But is bottleneck bypassing a specific consequence of IM compatibility or is it due to task ease? To answer this question, we tested the automaticity of a task that was easy but not IM. The task was easy due to the high semantic compatibility between the stimulus and the response: saying "ping" when hearing "pong" and "pong" to "ping" in Experiment 1, saying "low" when hearing "high" and "high" to "low" in Experiment 2. We presented it as Task 2, along with a Task 1 that was not easy, due to the use of an arbitrary stimulus-response mapping. Single-task trials were randomly intermixed with dual-task trials and then used as baselines to assess dual-task costs and to simulate distributions of inter-response intervals (IRIs) predictive of bottleneck bypassing vs. bottlenecking. The results of both experiments provided converging evidence that the entire Task 2 bypassed the bottleneck on virtually all trials: very small dual-task costs, high percentages of response reversals, and a close match between the observed IRI distributions and that predicted by bottleneck bypassing. Neither ideomotor compatibility nor task speed (the semantic task was not particularly fast) explain these findings. We therefore propose that the key to bypassing the central bottleneck is the ease with which people can fully load the stimulus-response mapping into working memory.

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.

Multitasking costs on metacognition in a triple-task paradigm.

Multitasking situations, such as using one's phone while driving, are increasingly common in everyday life. Experimental psychology has long documented the costs of multitasking on task performance; however, little is known of the effects it has on the metacognitive processes that monitor such performance. The present study is a step toward filling this void by combining psychophysical procedures with complex multitasking. We devised a multimodal paradigm in which participants performed a sensorimotor tracking task, a visual discrimination task, and an auditory 2-back working memory task, either separately or concurrently, while also evaluating their task performance every ~15 s. Our main finding is that multitasking decreased participants' awareness of their performance (metacognitive sensitivity) for all three tasks. Importantly, this result was independent of the multitasking cost on task performance, and could not be attributed to confidence leak, psychological refractory period, or recency effects on self-evaluations. We discuss the implications of this finding for both metacognition and multitasking research.

Testing the over-reliance on central attention (ORCA) hypothesis: Do older adults have difficulty automatizing especially easy tasks?

Does aging increase the reliance on central attention to carry out tasks, even when those tasks do not need it? To test the hypothesis of over-reliance on central attention (ORCA), we examined the ability of older adults to entirely bypass ideomotor-compatible (IM) tasks. IM tasks operate automatically for younger adults: The perception of an IM stimulus (e.g., a left-pointing arrow) directly activates the associated response code (e.g., pressing the left key). In a psychological refractory period (PRP) procedure, younger and older adults performed a slow auditory-vocal Task 1 paired with a fast visual-manual Task 2 that was either IM or non-IM. Task-2 compatibility (IM vs. non-IM) was manipulated as a between-subjects factor (Experiment 1) and as a within-subjects factor (Experiment 2). Both experiments yielded the counterintuitive finding of larger age differences in dual-task performance when Task 2 was easy (i.e., IM) than when it was difficult (i.e., non-IM), as evidenced by old/young ratio analyses and Brinley plots. Relatedly, whereas younger adults routinely bypassed the bottleneck with an IM Task 2 (as evidenced by a small PRP effect and a high rate of response reversals), older adults did not. The present findings cannot easily be explained by the hypotheses of generalized cognitive slowing and of specific processing deficits but support the ORCA hypothesis. As cognitive decline sets in, older adults begin to try harder: This extra application of central attention compensates for cognitive decline but can result in applying attention when it is not needed. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Introspection about backward crosstalk in dual-task performance.

The present study investigated participants' ability to introspect about the effect of between-task crosstalk in dual tasks. In two experiments, participants performed a compatibility-based backward crosstalk dual task, and additionally provided estimates of their RTs (introspective reaction times, IRTs) after each trial (Experiment 1) or after each pair of prime and test trials (Experiment 2). In both experiments, the objective performance showed the typical backward crosstalk effect and its sequential modulation depending on compatibility in the previous trial. Very similar patterns were observed in IRTs, despite the typical unawareness of the PRP effect. In sum, these results demonstrate the reliability of between-task crosstalk in dual tasks and that people's introspection about the temporal processing demands in this complex dual-task situation is intriguingly accurate and severely limited at the same time.

Electrophysiological examination of response-related interference while dual-tasking: is it motoric or attentional?

The possibility that interference between motor responses contributes to dual-task costs has long been neglected, yet is supported by several recent studies. There are two competing hypotheses regarding this response-related interference. The motor-bottleneck hypothesis asserts that the motor stage of Task 1 triggers a refractory period that delays the motor stage of Task 2. The response-monitoring hypothesis asserts that monitoring of the Task-1 motor response delays the response-selection stage of Task 2. Both hypotheses predict lengthening of Task-2 response time (RT2) when Task 1 requires motor processing relative to when it does not. However, they assume different loci for the response-related bottleneck, and therefore make different predictions regarding (a) the interaction between Task-1 motor requirement and the Task-2 difficulty effect as measured by RT2 and (b) the premotoric durations and motoric durations of Task 2 as measured by lateralized readiness potentials (LRPs). To test these predictions, we conducted two experiments manipulating the Task-1 motor requirement (Go vs. NoGo) and Task-2 response-selection difficulty, as well as the stimulus-onset asynchrony (SOA). Task-1 motor processing significantly lengthened RT2, suggesting response-related interference. Importantly, the Task-1 motor response reduced the Task-2 difficulty effect at the short SOA, indicating postponement of the Task-2 motor stage, consistent with the motor-bottleneck hypothesis. Further consistent with the motor-bottleneck hypothesis, the Task-2 LRP indicated a consistent premotoric duration of Task 2 regardless of Task-1 motor requirement. These results are difficult to reconcile with the response-monitoring hypotheses, which places the response-related bottleneck before the response-selection stage of Task 2. The results also have important implications regarding use of locus-of-slack logic in PRP studies.

Dual-task interference and response strategies in simulated car driving: impact of first-task characteristics on the psychological refractory period effect.

Presentation of a task T1 typically delays the response to a subsequent task T2, more so with high temporal task overlap than with low temporal overlap. This so-called "psychological refractory period effect" (PRP effect) has been observed even if T1 required not a choice between distinct stimulus-response pairs, but rather between a given stimulus-response pair occurring once or twice. We explored which response strategy participants use for responding to such an unusual type of T1 and how such a T1 interacts with T2 performance. In a driving simulator, participants followed a lead car and had to honk when that car's rear window changed color (T1). In condition "pure", the color always changed once and required a single honk; in condition "mixed", the color changed once and required a single honk on some trials, but on other trials, it changed twice 200 ms apart and required a double honk. Participants also had to brake when the lead car braked (T2). On dual-task trials, T1 preceded T2 with a varying stimulus onset asynchrony (SOA) of 50-1200 ms. Reaction time to the first T1 stimulus was similar in "pure" and "mixed" and it was comparable with the reaction time to the second T1 stimulus. Reaction time to the T2 stimulus increased as SOA decreased from 350 to 50 ms, confirming the existence of a PRP effect. Furthermore, reaction time to the T2 stimulus was similar in "pure" and in "mixed" with one T1 stimulus, but was higher in "mixed" with two T1 stimuli. This pattern of findings is compatible with the view that presentation of the first T1 stimulus triggers a single response, which is amended into a double response, if a second T1 stimulus is displayed. The amendment does not need to wait until central processing of the original response is completed, and it therefore begins with no delay beyond the regular reaction time. Our findings further suggest that the mere possibility of a second T1 stimulus being presented does not increase the PRP effect on T2, probably because response amendments are not equivalent to classical response choices. However, the actual presentation of a second T1 stimulus indeed does increase the PRP effect on T2, probably because amendments start 200 ms later than the original response, and therefore prolong central processing of T1.

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.