Biomedical subjects

James C Johnston

Publications and source records attributed to James C Johnston.

5 recordsLinked to original sources

PubMed2006

On the locus of dual-task interference: Is there a bottleneck at the stimulus classification stage?

Recent studies have provided evidence that dual-task interference is typically caused by a single-channel bottleneck, but the processing locus of the bottleneck has yet to be pinned down. A bottleneck locus at the response-selection stage is widely advocated, but an earlier locus would be consistent with most previous evidence. Four new experiments used the "locus of slack" method to investigate whether the stages postponed by the central bottleneck include stimulus classification, a very late stage of perceptual processing. The experiments varied stimulus classification difficulty for two different analogueue perceptual judgements. Experiment 1 found only modest absorption into slack for the difficulty of a spatial position judgement. Experiments 2-4 found virtually no absorption into slack for the difficulty of a box-width judgement. These results support a bottleneck locus beginning at or before the stage of stimulus classification and hence prior to the stage of response selection. Other evidence, however, leaves no doubt that response selection is also subject to bottleneck postponement. Two architectures are discussed that can account parsimoniously for both old and new results. One posits a single bottleneck resulting from a unified CPU-like central processor; the other posits multiple bottlenecks resulting from multiple processors accomplishing different substages of central processing.

Acoustic Stimulation↗

PubMed2005

On the limits of advance preparation for a task switch: do people prepare all the task some of the time or some of the task all the time?

This study investigated the nature of advance preparation for a task switch, testing 2 key assumptions of R. De Jong's (2000) failure-to-engage theory: (a) Task-switch preparation is all-or-none, and (b) preparation failures stem from nonutilization of available control capabilities. In 3 experiments, switch costs varied dramatically across individual stimulus-response (S-R) pairs of the tasks-virtually absent for 1 pair but large for others. These findings indicate that, across trials, task preparation was not all-or-none but, rather, consistently partial (full preparation for some S-R pairs but not others). In other words, people do not prepare all of the task some of the time, they prepare some of the task all of the time. Experiments 2 and 3 produced substantial switch costs even though time deadlines provided strong incentives for optimal advance preparation. Thus, there was no evidence that people have a latent capability to fully prepare for a task switch.

Analysis of Variance↗

PubMed2004

How does practice reduce dual-task interference: integration, automatization, or just stage-shortening?

The present study assessed three hypotheses of how practice reduces dual-task interference: Practice teaches participants to efficiently integrate performance of a task pair; practice promotes automatization of individual tasks, allowing the central bottleneck to be bypassed; practice leaves the bottleneck intact but shorter in duration. These hypotheses were tested in two transfer-of-training experiments. Participants received one of three training types (Task 1 only, or Task 2 only, or dual-task), followed by dual-task test sessions. Practice effects in Experiment 1 (Task 1: auditory-vocal; Task 2: visual-manual) were fully explained by the intact bottleneck hypothesis, without task integration or automatization. This hypothesis also accounted well for the majority of participants when the task order was reversed (Experiment 2). In this case, however, there were multiple indicators that several participants had succeeded in eliminating the bottleneck by automatizing one or both tasks. Neither experiment provided any evidence that practice promotes efficient task integration.

Automatism↗

PubMed2003

Vanishing dual-task interference after practice: has the bottleneck been eliminated or is it merely latent?

Practice can, in some cases, largely eliminate measured dual-task interference. Does this absence of interference indicate the absence of a processing bottleneck (defined as an inability to carry out certain stages in parallel)? The authors show that a bottleneck need not produce any observable interference, provided that there is no temporal overlap in the demand for bottleneck stages on the 2 tasks. Such a "latent" bottleneck is especially likely after practice, when central stages are short. The authors provide new evidence that a latent bottleneck occurred for a participant who produced no interference in M. Van Selst, E. Ruthruff, and J. C. Johnston (1999). These findings demonstrate that the absence of dual-task interference does not necessarily indicate the absence of a processing bottleneck.

Attention↗

PubMed2002

Repetition blindness has a perceptual locus: evidence from online processing of targets in RSVP streams.

Four experiments tested whether repetition blindness (RB; reduced accuracy reporting repetitions of briefly displayed items) is a perceptual or a memory-recall phenomenon. RB was measured in rapid serial visual presentation (RSVP) streams, with the task altered to reduce memory demands. In Experiment 1 only the number of targets (1 vs. 2) was reported, eliminating the need to remember target identities. Experiment 2 segregated repeated and nonrepeated targets into separate blocks to reduce bias against repeated targets. Experiments 3 and 4 required immediate "online" buttonpress responses to targets as they occurred. All 4 experiments showed very strong RB. Furthermore, the online response data showed clearly that the 2nd of the repeated targets is the one missed. The present results show that in the RSVP paradigm, RB occurs online during initial stimulus encoding and decision making. The authors argue that RB is indeed a perceptual phenomenon.

Blindness↗