Consistency, not speed: temporal regularity as a metacognitive cue.

We examined the hypothesis that skilled performance is monitored on the basis of fluency, where fluency is operationally defined as temporal regularity or rhythmicity rather than speed. Since error is often associated with variable timing, we tested the possibility that people use varied timing as a metacognitive cue. Using a sequential counting task, which may be representative of the broader class of skilled, multi-step tasks, we found that shifting between irregular and regular timing led to greater confidence ratings when the timing associated with the task was regular. We argue that regular, consistent timing, when compared directly to irregular timing, produced feelings of fluent task performance, leading to increased confidence. In the first experiment, we demonstrated that both accuracy and confidence were higher when participants completed a task presented with regular timing. In the second experiment, we found a dissociation between accuracy and confidence, strengthening the argument that individuals relied on monitoring of fluency to support their metacognitive judgments. In Study 3 and an assessment of naïve beliefs, we ruled out alternative explanations for these findings.

Temporal tuning in the acquisition of cognitive skill.

The temporal tuning hypothesis suggests that individuals adjust the timing of cognitive performances to achieve temporal coordination of mental processes and the data on which they operate, and that this adjustment becomes more precise with practice. Participants in two experiments performed self-paced multiple-step arithmetic tasks in which the information needed for each step was briefly displayed at the participants' request. Timing constraints were manipulated by varying between subjects the delay between requests and displays of information. In Experiment 1, both operators and operands appeared step by step, and participants achieved a modest degree of temporal adjustment that did not change with practice. In Experiment 2, participants could preview operators while operands appeared step by step. In that experiment, participants achieved more precise temporal adjustment, and the amount of adjustment increased with practice. These results demonstrate the phenomenon of temporal tuning in symbolic cognitive skills and suggest some constraints on the ability to anticipate the time course of one's mental processes.

Information acquisition strategies and the cognitive structure of arithmetic.

In three experiments, we examined the sensitivity of information acquisition strategies to the underlying cognitive structure of arithmetic tasks. Previous work has shown that individuals solve arithmetic problems more quickly when they consider operators before operands. The operators establish the goal, and the operands are then assimilated into that goal. In the present experiments, participants performed arithmetic tasks in which they controlled the display of operators and operands, using separate keystrokes. The participants chose to see the operator before the operands in most conditions. This ordering was more likely when task constraints made it easier to achieve, when feedback emphasized execution time, and in a more complex multiple-step task. These results extend previous research on strategy selection and information acquisition, supporting the idea that coordination between the environment and ongoing cognition is an important feature of cognitive skill.

Activation mechanism of CDK2: role of cyclin binding versus phosphorylation.

Activation of the cyclin-dependent kinases is a two-step process involving cyclin binding followed by phosphorylation at a conserved threonine residue within the kinase activation loop. In this study, we describe the separate roles of cyclin A binding versus phosphorylation in the overall activation mechanism of CDK2. Interaction of CDK2 with cyclin A results in a partially active complex that is moderately defective in the binding of the protein substrate, but not ATP, and severely defective in both phosphoryl group transfer and turnover. Alternatively, phosphorylation of the CDK2 monomer also results in a partially activated species, but one that is severely (> or = 480-fold) defective in substrate binding exclusively. Catalytic turnover in the phosphorylated CDK2 monomer is largely unimpaired (approximately 8-fold lower). Our data support a model for the activation of CDK2 in vivo, in which interaction of unphosphorylated CDK2 with cyclin A serves to configure the active site for ground-state binding of both ATP and the protein substrate, and further aligns ATP in the transition state for phosphoryl transfer. Optimizing the alignment of protein substrates in the phosphoryl transfer reaction is the principal role of phosphorylation at Thr(160).