Intentional and unintentional contributions to nonspecific preparation during reaction time foreperiods.

The nonspecific preparation that follows a warning stimulus (WS) to speed responding to an impending imperative stimulus (IS) is generally viewed as a strategic, intentional process. An alternative view holds that WS acts as a conditioned stimulus that unintentionally elicits a tendency to respond at the moment of IS presentation as a result of a process of trace conditioning. These views were contrasted as explanatory frameworks for classical effects on reaction time of the duration and intertrial variability of the foreperiod, the interval between WS and IS. It is shown that the conditioning view accounts for the available data at least as well as the strategic view. In addition, the results of 3 experiments provide support for the conditioning view by showing that unintentional contributions to nonspecific preparation can be dissociated from intentional contributions.

Visuo-motor adaptation in smokeless tobacco users.

Ten smokeless tobacco (ST) users and 11 non-smokers participated in a visuo-motor adaptation experiment in which the visual feedback of point-to-point horizontal arm movements, displayed in real-time on a computer screen, was rotated by 45 degrees counterclockwise for some trials. Visuo-motor performance between smokers and non-smokers was compared on three occasions, once after at least 8 h of tobacco abstinence (Session 1), a second time following ST intake (Session 2), and a third time 45 min after the original ST intake (Session 3). Non-smokers were tested at the same relative times as the smokers in the absence of any tobacco. Both groups performed the three conditions during each session: baseline (normal visual feedback), rotated visual feedback (45 degrees visual feedback rotation), and post-adaptation (normal visual feedback immediately following feedback rotation). Compared with non-smokers, ST users had significantly larger normalized jerk scores (a measure of movement smoothness) after ST intake during the adaptation and post-adaptation conditions in Sessions 2 and 3, but not during the baseline conditions, implying a differential effect of ST use specific to rotated visual feedback. Movement duration was also longer for smokers than for non-smokers after ST intake, but only in the post-adaptation condition. Overall the results suggest that ST use, and hence nicotine, has a detrimental effect on visuo-motor performance, particularly on movement smoothness.

Axial pen force increases with processing demands in handwriting.

In two experiments, during handwriting movements, the on-line visual feedback of either slant (Experiment 1) or size (Experiment 2) was transformed to study the time course and biomechanics of the participants' compensations for these distortions. Fluency, movement time, and axial pen force were measured. According to our theory, changing the scaling factor of slant or size is equivalent to a processing demand that is reflected in deteriorated signal-to-noise ratios (SNRs) in the neuromotor system. At the behavioral level, deteriorated SNRs will result in less fluent writing, which can be compensated by applying a biomechanical noise-filtering strategy of increased limb stiffness. This strategy will lead to increased axial pen force, and, with higher degrees of difficulty, to a loss of movement speed. Results revealed decrements in writing fluency together with increments in axial pen force and increments in movement time when compensations to the feedback transformations coincided with the more difficult task conditions. These findings contrast with the traditional resource theory (Kahneman, 1973) in which chronometric measures alone indicate increased processing demands.