Neil Brewer's research while affiliated with Flinders University and other places

Monitoring accuracy during choice RT allows subjects to maintain fast, safe RT bands and avoid overly fast, unsafe RT bands. 5 retarded adults received trial-by-trial feedback on accuracy over a number of sessions to train monitoring of accuracy and to improve RT performance. Training was introduced according to a multiple-baseline-across-subjects (with reversal) design. Training had no significant effect on subsequent RT performance, suggesting that inefficient monitoring of accuracy may be a structural characteristic of mental retardation.

Young and older adults' mechanisms of trial-by-trial control of accuracy and choice reaction times (RTs) were compared in 2,000 trials. With equal mean error rates, the older group's correct and error RT were longer, and their within-subject distribution was a linear function of the younger group's. Conditional accuracy functions (CAFs) were very similar in location and shape, with both groups achieving 95% accuracy at the same RT. Combining RT distributions with CAFs showed that the older group did not track their limits as often as the younger group, and they were more careful, having fewer very fast (near random) responses, more average speed responses in long error-free runs, and more slowing following an error. All participants were faster before an error and slower immediately after, but the older participants had coarser RT control. To compensate for this, the older participants produced slower responding to avoid the very fast, high-error part of the CAF.

Young and older adults' mechanisms of trial-by-trial control of accuracy and choice reaction times (RTs) were compared in 2,000 trials. With equal mean error rates, the older group's correct and error RT were longer, and their within-subject distribution was a linear function of the younger group's. Conditional accuracy functions (CAFs) were very similar in location and shape, with both groups achieving 95% accuracy at the same RT. Combining RT distributions with CAFs showed that the older group did not track their limits as often as the younger group, and they were more careful, having fewer very fast (near random) responses, more average speed responses in long error-free runs, and more slowing following an error. All participants were faster before an error and slower immediately after, but the older participants had coarser RT control. To compensate for this, the older participants produced slower responding to avoid the very fast, high-error part of the CAF.

Brewer and Smith (1984) showed that control mechanisms mediating speed-accuracy regulation contribute to retarded-nonretarded differences in processing speed, with poorly controlled trial-to-trial RT adjustments underlying the greater RT variability of retarded individuals. In Experiment 1, response deadlines controlled processing time, thus minimizing the influence of such control mechanisms. The obtained speed-accuracy relations showed that retarded subjects were unable to match nonretarded subjects' accuracy when responding as rapidly, thus indicating structural limitations on processing speed. The results of Experiment 2 showed, however, that significant adjustments to retarded subjects' processing speed--exceeding those produced by practice--are achievable. Extended training at a short deadline led to tighter control of RT adjustments, with substantial improvements in mean RT when subjects transferred to a self-paced RT task.

We investigated the possibility that marked improvements in speed of information processing from early childhood to adulthood reflect improved speed–accuracy monitoring and regulation. Trial-by-trial examination of reaction time (RT) and accuracy transitions during serial choice RT performance revealed developmental changes in accuracy monitoring and speed regulation; these changes corresponded to the most pronounced age-related changes in average RT. For 5-year-olds, poor control over speed of responding, coupled with inconsistent accuracy monitoring, resulted in less orderly trial-to-trial RT transitions and a consequent failure to constrain responses within fast RT bands just safely above overly fast error RT levels. Control over speed of responding was improved by age 7, but inconsistent accuracy monitoring was still a factor. From age 9 up to adulthood, subjects monitored accuracy consistently and showed quite precise control over speed of responding. These developments were associated with a marked improvement in RT constraint within narrow, fast RT bands. (PsycINFO Database Record (c) 2012 APA, all rights reserved)

Rabbitt (1979, 1981) has argued that the slowing of choice RT performance with old age reflects less sensitive control over speed of responding. Based on the finding that old subjects' errors were as fast as young subjects', whereas their correct responses were much slower, Rabbitt suggested that old subjects often overshoot when trying to increase or reduce response speed. Data collected from a different serial, four-choice RT task in this experiment were not, however, consistent with Rabbitt's account. Error as well as correct RTs were longer in old than in young adults, with both showing similar increases with age. A post hoc examination of the aged subjects' data also indicated important individual differences within aged samples. Some subjects' RTs and error rates were no different from those of the young; other subjects' longer RTs and lower error rates were consistent with an increased emphasis on accuracy.

Brewer and Smith in 1984 reported pre- and posterror RT data indicating that fast, accurate responding on a visual, four-choice RT task is mediated by a trial-by-trial tracking mechanism such as outlined by Rabbitt recently. In this study the generality of this account was examined by testing subjects on visual or vibrotactile choice-RT tasks (two-, four-, and eight-choice). The pre- and posterror RT patterns in all tasks and stimulus conditions were consistent with trial-by-trial RT tracking.

Two experiments, with 34 mentally retarded (MR) 16-33 yr olds (WAIS IQs 43-76) and 34 CA-matched normal controls, investigated whether differences in the way that MR and non-MR monitor and regulate speed and accuracy of responding contribute to the slower and more variable performance of MR Ss on choice RT tasks. In Exp I, most MR Ss detected their errors as efficiently as controls, a finding that excludes the possibility that MR Ss do not monitor accuracy efficiently but achieve comparable levels of accuracy by consistently responding within slow RT bands that minimize likelihood of errors. Exp II showed that while a qualitatively similar trial-by-trial tracking mechanism mediated the performance of both groups, MR Ss were less efficient at constraining RTs within fast but safe bands. Increasing error probabilities at longer RTs suggested that momentary fluctuations in stimulus discriminability and/or attention affected RT variability in MR Ss. The RT patterns for various sequences of correct responses initiated and terminated by errors suggested that the effective past experience guiding trial-by-trial RT adjustments of MR Ss was short and inadequate and that this accounted for much of the remaining RT variability contributing to differences between MR and non-MR Ss. (53 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved).

Previous research suggests that slower responding by mentally retarded individuals reflects impairments in those executive cognitive processes mediating rapid information-processing. We suggest that one approach to the clarification of the nature and extent of such impairments and, specifically, the involvement of structural and control process parameters is via an examination of those processes underlying the speed-accuracy operating characteristics of retarded subjects. To respond as quickly as possible while maintaining virtually error-free performance, subjects must sensitively monitor and regulate both accuracy and speed of responding from trial to trial. Suggested procedures for investigating the efficiency of such processes in retarded subjects involve examinations of error detection performance, and of speed-accuracy tradeoff functions generated using time bands, reaction-time partitioning, and response signals.