The locus of redundant-targets and nontargets effects: evidence from the psychological refractory period paradigm

In target detection tasks, responses are faster when displays have 2 targets (redundant-targets effect; RTE) and slower when they have no targets (nontargets effect; NTE) relative to displays with a single target. The psychological refractory period paradigm was used to localize these effects. In Experiment 1, participants classified tones as high or low and then classified letters as targets or nontargets after a short or long stimulus onset asynchrony (SOA). The magnitudes of the RTE and NTE did not depend on SOA. In Experiment 2, the order of the tasks was reversed, and at short SOAs the RTE and NTE had similar magnitudes for both tone discrimination and target detection responses. These findings suggest that the RTE and NTE arise during response selection. Interactive effects of tone pitch with the number and type of target features were also observed, and these were tentatively interpreted as synesthetic effects.     

Bypassing the central bottleneck after single-task practice in the psychological refractory period paradigm: Evidence for task automatization and greedy resource recruitment

In this research, the controversial issue of whether the central bottleneck can be bypassed through task automatization was investigated. To examine this issue, participants received six single-task practice sessions with an auditory-vocal task (low vs. high pitch). We then assessed dual-task performance using the analytically tractable psychological refractory period (PRP) paradigm, in which the highly practiced auditory-vocal task was presented as Task 2, along with an unpracticed visual-manual Task 1. The results provide evidence of bottleneck bypass for virtually all the participants (17 out of 20). Several converging tests suggest that the bottleneck reemerged, however, in a follow-up experiment with tasks presented in the opposite order (auditory-vocal Task 1 and visual-manual Task 2). One possible explanation is that tasks greedily recruit central resources when available, even though they can operate without central resources when unavailable.     

Backward response-level crosstalk in the psychological refractory period paradigm

Bottleneck models of psychological refractory period (PRP) tasks suggest that a Task 1 response should be unaffected by the Task 2 response in the same trial, because selection of the former finishes before selection of the latter begins. Contrary to this conception, the authors found backward response-level crosstalk effects in which Task 2 response force requirements influenced the force-time dynamics of Task 1 responses. Specifically, Task 2 required a hard or soft keypress response. Task 1 responses were harder when the upcoming Task 2 response was to press hard rather than soft, suggesting some activation of Task 2 response parameters before Task 1 processing reached the final ballistic motor output stage. A 3rd experiment using a flankers paradigm showed that this effect did not arise from automatic activation of responses by the stimuli associated with hard and soft responses. This backward response-level crosstalk extends previous findings of backward crosstalk in the PRP paradigm by showing that crosstalk can affect motor output as well as response time and can arise even when the 2 tasks being performed are not semantically related.     

Online order control in the psychological refractory period paradigm

The authors examined the role of online order control in the psychological refractory period (PRP) paradigm. In the first 2 experiments, participants switched between color-letter and letter-color orders so that subtask order was isolated as the only element being switched. The results indicated that order switching impaired the 2 PRP responses and modulated the PRP effect. Importantly, these effects were reduced by advance preparation, demonstrating that order representation was activated before the subtasks themselves. Preparation for subtask order did not reflect preparation for hand order, as shown in Experiment 3. In addition, there was no evidence that subtask order information dissipated between trials. The relevance of the results to theories of the PRP paradigm and task switching is discussed.     

Blindness to response-compatible stimuli in the psychological refractory period paradigm

This study investigated the conditions under which the processing in a speeded response task interferes with concurrent processing in a visual encoding task. Three experiments used a dual-task paradigm, in which a speeded left or right response to at one was combined with the identification of a masked left-or right pointing arrow following the tone with variable SOA. Two additional experiments tested the impact of the presentation of pure tone on visual encoding.There were four major findings. First, an unspecific decrease in identification accuracy was observed with decreasing SOA. Second, a blindness to response-compatible stimuli was observed with speeded responses. Third, a specific interference was found between low- and high-pitched tones and left- or right-pointing arrows. Fourth, the specific tone-arrow interference modulated the specific responsearrow interference when the task allowed both to occur simultaneously. The present findings, which suggest both procedural and structural interference between response preparation and stimulus encoding, are discussed in terms of a two-stage model of action planning.     

Task switching and response correspondence in the psychological refractory period paradigm

Three experiments examined the effects of task switching and response correspondence in a psychological refractory period paradigm. A letter task (vowel-consonant) and a digit task (odd-even) were combined to form 4 possible dual-task pairs in each trial: letter-letter, letter-digit, digit-digit, and digit-letter. Foreknowledge of task transition (repeat or switch) and task identity (letter or digit) was varied across experiments: no foreknowledge in Experiment 1, partial foreknowledge (task transition only) in Experiment 2, and full foreknowledge in Experiment 3. For all experiments, the switch cost for Task 2 was additive with stimulus onset asynchrony, and the response-correspondence effect for Task 2 was numerically smaller in the switch condition than in the repeat condition. These outcomes suggest that reconfiguration for Task 2 takes place after the central processing of Task 1 and that the crosstalk correspondence effect is due to response activation by way of stimulus-response associations.     

The locus of temporal preparation effects: Evidence from the psychological refractory period paradigm

In reaction time (RT) tasks, responses are especially fast when participants can anticipate the onset of an imperative response signal. Although this RT facilitation is commonly attributed to temporal preparation, it is unclear whether this preparation shortens the duration of early or late processes. We used the effect propagation property of the psychological refractory period paradigm to localize the effect of temporal preparation. Manipulation of temporal uncertainty affected the RT of Task 1, regardless of the level of stimulus onset asynchrony (SOA). Consistent with the prediction of an early locus of temporal preparation, this effect propagated completely to the RT of Task 2 at short SOAs, but propagation diminished virtually to zero at long SOAs.     

All-or-none bottleneck versus capacity sharing accounts of the psychological refractory period phenomenon

The goal of the present experiment was to test the predictions of Central Bottleneck and Central Capacity Sharing models. According to the Central Bottleneck model, dual task interference, as observed in the PRP paradigm, is caused by an all-or-none bottleneck in information processing. The Central Capacity Sharing model postulates that dual task interference is caused by a capacity limited process that can allocate capacity in a graded fashion. The Central Bottleneck model predicts no change in RT1 with decreasing SOA, whereas the Central Capacity Sharing model predicts that RT1 will increase with decreasing SOA and that the slope of the RT1 SOA effect will depend upon the difficulty of task 2. Subjects were required to perform a tone pitch judgement and shape-matching task in rapid succession. Task order was randomized and the SOA between the first and second stimulus varied from 50 to 1250 ms. Results from this experiment favour the Central Capacity Sharing model. The results were then run through simulations of both the Central Bottleneck and Central Capacity Sharing models. Results from the simulations also favoured the Central Capacity Sharing model. As the difficulty of the second task increased, more capacity was allocated to it, confirming the prediction that as task 2 difficulty increases, the RT1 SOA slope increases. The proportion of capacity allocated to the first task varied from.78 to.91 indicating that capacity can be allocated in a graded fashion.     

Phonological codes are assembled before word fixation: evidence from boundary paradigm in sentence reading

This experiment employed the boundary paradigm during sentence reading to explore the nature of early phonological coding in reading. Fixation durations were shorter when the parafoveal preview was the correct word than when it was a spelling control pseudoword. In contrast, there was no significant difference between correct word and pseudohomophone previews. These results suggest that the phonological codes are assembled before word fixation and are used for lexical access. Moreover, there was evidence that orthographic codes influence the activation of word meaning. We found that fixation durations were shorter for orthographically similar parafoveal previews, and this orthographic priming effect is limited to pseudohomophones. Thus, it seems that both the orthographic and the phonological similarities of the parafoveal preview to the target play a part in the facilitative effects of the preview.     

Response grouping in the psychological refractory period (PRP) paradigm: models and contamination effects

Response grouping is a ubiquitous phenomenon in psychological refractory period (PRP) tasks, yet it hampers the analysis of dual-task performance. To account for response grouping, we developed several extended versions of the standard bottleneck model, each of which incorporates a possible grouping mechanism into this model. Computer simulations were used to assess how the predictions of the standard model would change with each grouping mechanism. One set of simulations investigated the basic effects of grouping on the means and intercorrelation of the reaction times in the two tasks, as well as the percentage of trials with short interresponse times (IRTs). A second set of simulations examined whether response grouping would invalidate the use of PRP paradigms for localizing experimental effects. Finally, we investigated whether the post-hoc elimination of trials with short IRTs removes the contaminating effects of response grouping.     

Dual route for subtask order control: Evidence from the psychological refractory paradigm

A change in subtask order in the psychological refractory period (PRP) paradigm increases the effect of stimulus onset asynchrony (SOA) on the second response. We used a paradigm with cued, randomly determined subtask order to test the hypothesis that this SOA by order switch overadditivity reflects order control, via “copying” stimulus order. In Experiments 1a and 1b, overadditivity was evident only with insufficient opportunity for cue-based order control. In Experiment 2, overadditivity was decreased by using the same set of stimuli in the two subtasks, presumably by removing the opportunity to rely on stimulus order. In Experiment 3, removing the order cue increased the overadditivity, presumably because control was based solely upon copying stimulus order. The results indicate interactive top-down and bottom-up order control. Implications to theories of the PRP paradigm are discussed.     

Dual route for subtask order control: Evidence from the psychological refractory paradigm

A change in subtask order in the psychological refractory period (PRP) paradigm increases the effect of stimulus onset asynchrony (SOA) on the second response. We used a paradigm with cued, randomly determined subtask order to test the hypothesis that this SOA by order switch overadditivity reflects order control, via “copying” stimulus order. In Experiments 1a and 1b, overadditivity was evident only with insufficient opportunity for cue-based order control. In Experiment 2, overadditivity was decreased by using the same set of stimuli in the two subtasks, presumably by removing the opportunity to rely on stimulus order. In Experiment 3, removing the order cue increased the overadditivity, presumably because control was based solely upon copying stimulus order. The results indicate interactive top-down and bottom-up order control. Implications to theories of the PRP paradigm are discussed.     

Intersensory effects in the psychological refractory period

Two experiments examined reaction time (RT) to each of two stimulus events separated by short interstimulus intervals (1SI). The essential contrast was RT to the second visual signal, RT₂, in auditory-visual (A-V) vs visual-visual (V-V) sequences. With response, certain pairings in Experiment 1, an effect apparently demonstrating a single-channel process (Welford, 1952), was noted. RT₂ was generally faster for A-V as opposed to V-V sequences especially when Ss were uncertain as to the sequence that would occur. At 0-msec ISI, the RT₂ difference between sequences approached the RT! difference. More rapid RT₂ to A-V sequences was also observed with go vs no-go pairings in Experiment 2 when the initial event was a go signal. However, the RT difference disappeared upon error correction, making the RT₂ sequence difference of questionable relevance to the hypothetical single-channel process. RT₂ was more rapid following a null no-go signal when the no-go signal was contrasted with a visual as opposed to auditory go signal. The latter effect was independent of error and is consistent with channel-switching theory (Kristofferson, 1967).     

Parallel processing and the psychological refractory period

The serial processor theory proposed by Welford is the traditional explanation of the delay in responding to the second stimulus presented in psychological refractory period paradigm experiments. This paper reviews results which do not accord either with that theory or with later modifications of it by Smith and Tolkmitt. To explain these results a model is proposed which contains three propositions: (a) parallel processing of concurrent stimuli, (b) fixed total processing capacity, (c) capacity allocation either dependent on the relative difficulty of the stimuli or set by the subject according to experimental instructions. The predictions of this model for the effects of stimulus difficulty and interstimulus interval on reaction time and interresponse interval are computed. These predictions are compared with those of other parallel processing models of the psychological refractory period which have been proposed by Herman and Kantowitz, by Kahneman and by Keele.     

The bottleneck of the psychological refractory period effect involves timing of response initiation rather than response selection

Psychonomic Bulletin & Review - The Psychological Refractory Period (PRP) effect is a delay in responding that is assumed to be caused by a bottleneck that prevents preparation of a second...     

Sensitivity and decisional factors in the psychological refractory period

Three trained Ss responded to a pair of events presented at fixed interstimulus intervals (ISIs) of 33, 67, and 100 msec. Each event was the independent presence of a visual stimulus (S-P) or its absence (S-A), to which Ss were to respond or not, with a set for speed over accuracy. The probabilities of Sop occurrence [P(S)] to each of the events were varied. Pretrial verbal reports or behavioral hypotheses (BHs) werealso obtained. P(S), ISI, BH, and order (first vs second event) were all generally determinants of both RT to Sop and inhibition probability to S-A. However, when the RT data were corrected for inhibition probability, order was the only systematic effect that remained. The results were discussed in terms of approaches to the psychological refractory period derived from signal detection theory involving differential sensitivity as opposed to criterion.     

A revision of the psychological refractory period

A brief review of the major psychological refractory period (PRP) theories reveals that they have lost their original objective, i.e., to explain human information processing under rapid sequential stimulation. Conventional data interpretation has restricted attention to delay of reaction times as a result of interstimulus interval (ISI) variation. This form of data interpretation fails to capture important performance aspects under double-stimulation, e.g., the phenomenon that stimulus complexity affects the processing rate. Effects of stimulus rate and complexity are better analyzed in terms of reaction times as well as interresponse intervals (IRI). If this is done, behavioral phenomena emerge that cannot be explained within the frame of any of the existing PRP theories. To account for these newly revealed phenomena a processing interrupt model is introduced which is based on three major hypotheses: single-channel processor, additive stages, and perceptual interrupt facility.