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.

Congruency Encoding Effects on Recognition Memory: A Stage-Specific Account of Desirable Difficulty.

Recent research suggests that selectively attending to relevant stimuli while having to ignore or resist conflicting stimuli can lead to improvements in learning. While mostly discussed within a broader "desirable difficulty" framework in the memory and education literatures, some recent work has focused on more mechanistic questions of how processing conflict (e.g., from incongruent primes) might elicit increased attention and control, producing enhanced incidental encoding of high-conflict stimuli. This encoding benefit for high-control-demand or high-difficulty situations has been broadly conceptualized as a task-general property, with no strong prediction of what particular task elements should produce this effect. From stage processing models of single- and dual-task performance, we propose that memory-enhancing difficulty manipulations should strongly depend on inducing additional cognitive control at particular processing stages. Over six experiments, we show that a memory benefit is produced when increased cognitive control (via incongruency priming) focuses additional processing on the core meaning of to-be-tested stimuli at the semantic categorization stage. In contrast, incongruency priming targeted at response selection within the same task produces similar effects on initial task performance, but gives no memory benefit for high-conflict trials. We suggest that a simple model of limited-capacity and stage-specific cognitive control allocation can account for and predict where and when conflict/difficulty encoding benefits will occur, and may serve as a model for desirable difficulty effects more broadly.

Dual-task backward compatibility effects are episodically mediated.

In dual-task performance, the backward compatibility effect (BCE; faster Task 1 reaction time when Task 1 and Task 2 responses are compatible) is thought to represent automatic activation of Task 2 response information in parallel with attended Task 1 performance. Work by Hommel and Eglau (Psychological Research, 66, 260-273, 2002) has suggested the BCE relies on stimulus-response learning in long-term memory. Subsequent work by Ellenbogen and Meiran (Memory and Cognition, 36, 968-978, 2008), however, proposed that the BCE is mediated by Task 2 rules held in working memory (WM) during Task 1 performance. The present study aimed to dissociate these two theoretical claims. In Experiment 1, we assessed the effects of prior single-task practice with Task 1 or Task 2 of a subsequent dual-task paradigm. Where the WM-mediated model predicts both BCE and overall reaction time improvement relative to prior task practice, an episodic learning model makes divergent predictions for BCE based on the context specificity of prior Task 2 learning. Results showed a close fit with episodic predictions and contradicted WM model predictions. Experiment 2 examined the finer grained timecourse of BCE over initial development, subsequent interference of this initial learning on BCE development with new conflicting Task 2 response mappings, and finally reestablishment of BCE in the original dual task. Data again showed close agreement with long-term learning predictions. We argue in favor of an episodic account of the BCE, and consider implications of WM and episodic mechanisms of automatic response activation on other aspects of dual-task performance.

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.

Information continuity across the response selection bottleneck: early parallel Task 2 response activation contributes to overt Task 2 performance.

Several studies of dual-task performance have demonstrated Task 2 to Task 1 response priming (backward compatibility effects), indicating some degree of parallel response computation for concurrent tasks and suggesting that the well-established response selection bottleneck (RSB) model may be incomplete. However, the RSB might be considered to remain informationally intact if this early parallel Task 2 response information does not persist across the attentional shift between tasks to contribute to overt Task 2 performance. We used an adapted psychological refractory period paradigm with an additional early transient Task 2 stimulus to examine whether response information generated for Task 2 in parallel with overt Task 1 response selection could persist across the bottleneck to influence eventual overt Task 2 performance. After controlling for potential indirect effects of Task 1 processing stage variability propagating onto Task 2 reaction time via locus of slack effects, we observed reliable and consistent effects of early Task 2 response information facilitating Task 2 reaction times. These effects were observed only when the responses to both tasks of the dual-task pair were compatible, under both univalent and bivalent response mappings across tasks. These findings may represent evidence of a variably sensitive response gating or suppression mechanism in dual-task performance and support the idea that backward response compatibility effects represent transient informational influences on central response codes, rather than later postbottleneck response execution processes.

Parallel response selection in dual-task situations via automatic category-to-response translation.

In contrast to the response selection bottleneck theory of dual-task performance, recent studies have demonstrated compatibility effects between secondary and primary responses on Task 1, suggesting that response information for two tasks may be generated in parallel. In two experiments, we examined the nature of Task 2 response activation in parallel with Task 1, using a psychological refractory period paradigm. Evidence of Task 2 to Task 1 response priming when each Task 2 stimulus was unique indicated that automatic parallel generation of response information occurred for Task 2 via abstract semantic category-to-response translation processes, independent of any direct stimulus-response influences. These findings are discussed in terms of their implications for the traditional response selection bottleneck theory of dual-task performance.