Queuing or Sharing? A Critical Evaluation of the Single-Bottleneck Notion

Abstract

The model of a single central bottleneck for human information processing is critically examined. Most evidence cited in support of the model has been observed within the overlapping tasks paradigm. It is shown here that most findings obtained within that paradigm and that were used to support the model are also consistent with a simple resource model. The most prominent findings are the millisecondfor-millisecond slope at the left of the RT2-SOA curve, the high RT1-RT2 correlation, the additivity of the effects on RT2 of SOA and of the difficulty of selecting R2, and the washout of the effect of S2 discriminability on RT2 in a dual-task condition. In addition, the asymmetry of the effects of the dual-task requirement on RT1 and RT2 can be accounted for by the resource model provided that it assumes uneven allocation of resources, which is quite reasonable in view of the task asymmetry inherent in the demand characteristics of the paradigm. The same is true for two other findings that appear to support the single-bottleneck model-that in the dual-task condition, the demand of the first task affects equally RT1 and RT2 and that its effect on RT1 is the same as the corresponding effect in the singletask condition. Furthermore, the single-bottleneck model is hard to reconcile with a negative slope at the left of the RT1-SOA curve or a positive slope at the left of the IRI-SOA curve, unless augmented by ancillary assumptions that are yet to be substantiated. Representative data were fit by each of the models using its optimal set of parameters. Both models achieved quite good degrees of fit. It is further argued that since the overlapping tasks paradigm is heavily biased in favor of a speedy reaction to the stimulus that appears first, it is nonoptimal for testing the central bottleneck model. Finally, the bottleneck model is examined in terms of other scientific criteria.

Capacity demands of phoneme selection in word production: New evidence from dual-task experiments.

“…Many of the key findings obtained in the dual-task paradigm can be explained within both frameworks (Navon & Miller, 2002;Tombu & Jolicoeur, 2003). For the present purposes it is important to note that the shared capacity framework also predicts that at short SOAs variations in the time required for Task 1 processing components that are high in capacity demands will carry forward to Task 2 latencies.…”

“…A theoretical alternative to the central bottleneck model is that central processing capacity need not be allocated to only one task at a time but can be distributed over two tasks (Kahneman, 1973;McLeod, 1977;Navon & Gopher, 1980;Navon & Miller, 2002;Tombu & Jolicoeur, 2003; see also D. E. Meyer & Kieras, 1997a, 1997b, for a related theory). When two tasks are carried out simultaneously, they compete for limited resources.…”

Locus of semantic interference in picture naming: Evidence from dual-task performance.

“…For example, the effect of practice on the magnitude of the dual-task interference is also different across studies (e.g., Karlin & Kestenbaum, 1968;Ruthruff, Johnston, Van Selst, Whitsell, & Remington, 2003;Schumacher et al, 2001;Van Selst & Jolicoeur, 1997;Van Selst, Ruthruff, & Johnston, 1999). These and other findings challenge the assumption of a structural response-selection bottleneck in dualtask performance (e.g., Hübner & Lehle, 2007;Israel & Cohen, 2011;Karlin & Kestenbaum, 1968;Lehle & Hübner, 2009;Leonhard & Ulrich, 2011;Meyer & Kieras, 1997;Miller et al, 2009;Navon & Miller, 2002;Pannebakker et al, 2011;Schumacher et al, 1999Schumacher et al, , 2001Schvaneveldt, 1969;Szameitat, Schubert, Müller, & Von Cramon, 2002;Szameitat, Lepsien, von Cramon, Sterr, & Schubert, 2006;Tombu & Jolicoeur, 2003). Although under the strategic bottleneck account (Meyer & Kieras, 1997;Piai et al, 2011;Roelofs, 2007Roelofs, , 2008a, a responseselection bottleneck is optional rather than obligatory (i.e., response selection in Tasks 1 and 2 may, in principle, occur in parallel), the present findings suggest that participants seem to have a very strong preference for not overlapping responseselection processes in dual-task performance.…”

Testing the Predictions of the Central Capacity Sharing Model.

“…Like the central bottleneck model, the central capacity sharing model can account for all of the Task 2 effects observed in the PRP paradigm (for more detail, see Navon & Miller, 2002;Tombu & Jolicoeur, 2003). Specifically, for both models,…”

“…where SP refers to the proportion of capacity allocated to Task 1 (a full derivation of the predictions for the central capacity sharing model is included elsewhere; see Navon & Miller, 2002, or Tombu & Jolicoeur, 2003 When SP is set to 1, Equation 5 simplifies to Equation 3, and the central capacity sharing model becomes the central bottleneck model. When SP is not set to 1 and the SOA is sufficiently short, decreasing the SOA or decreasing precentral Task 2 processing is predicted to increase RT1.…”