Some confounding factors in the study preparatory set in reaction time

In Experiment I. the effects of the range of the distribution of preparatory intervals (Pls) on the effect of PI on RT was demonstrated, and disparate conclusions about the development of preparatory set were thereby accounted for to some degree. In Experiment II. both range of the PIs and their average value were examined in a factorial design for their effects on RT. and it was concluded that, for any average value, greater range will result in greater PI effects; and for any range, greater average values will result in smaller PI effects on RT.     

Brain regions activated by endogenous preparatory set shifting as revealed by fMRI

An ongoing controversy concerns whether executive control mechanisms can actively reconfigure the cognitive system in preparation for switching to a new task set. To address this question, we recorded brain activity from 14 healthy participants, using event-related functional magnetic resonance imaging, while they performed a cued attention task. Critically, in any particular trial, the cued task set was either the same as that in the previous trial or switched. As was hypothesized, cue-related, switch-specific preparatory activity was observed in a network of dorsal frontal and parietal brain areas that are typically associated with cognitive control processes. Moreover, the magnitude of switch-specific preparatory activity varied with the number of possible task sets that could be presented in a given trial block. These findings provide compelling support for the existence of top-down, preparatory control processes that enable set switching. Furthermore, they demonstrate that global task structure is a critical determinant of whether switch-specific preparatory activity is observed.     

Effects of force output and preparatory set on premotor time of simultaneous bilateral responses

Premotor times in simultaneous bilateral elbow-flexion movements were measured for 20 subjects when loads (light or heavy) were applied to both elbow joints. Premotor times for the heavy load were longer than those for the light load on both sides. The difference in premotor time between the two loads was larger for bilateral response than for unilateral response, suggesting that exertion of strength combines with response modality to increase the difference between the two loads. Preparatory set did not affect premotor time under the heavy load but affected premotor time under the light load. Possible mechanisms subserving these findings are discussed.     

Evaluation of informational control and preparatory response factors in classical aversive conditioning

Subjects performed in a differential eyelid conditioning paradigm with either airpuff or infraorbital shock as the UCS. The trial series included interpolated UCS-alone presentations, and subjects rated UCS aversiveness on all trials. Ratings of the airpuff, but not the shock UCS, were negatively correlated with the magnitude of anticipatory eyelid CRs, as predicted by preparatory response or law-of-effect models of classical conditioning. However, subjects showed no tendency to rate signaled (CS-UCS) trials as less aversive than unsignaled (UCS-alone) trials, and showed no significant preference for the signaled ucs. These results suggest that the operation of informational control and preparatory response factors is more complex than is assumed by available theories. Also, instrumental shaping and preparatory response mechanisms may not be involved in the acquisition of CRs.     

A method for detailed movement pattern analysis of tadpole startle response

Prolonged space flight, specifically microgravity, presents a problem for space exploration. Animal models with altered connections of the vestibular ear, and thus altered gravity sensation, would allow the examination of the effects of microgravity and how various countermeasures can establish normal function. We describe an experimental apparatus to monitor the effects of ear manipulations to generate asymmetric gravity input on the tadpole escape response. To perform the movement pattern analysis, an imaging apparatus was developed that uses a high‐speed camera to obtain time‐resolved, high‐resolution images of tadpole movements. Movements were recorded in a temperature‐controlled test chamber following mechanical stimulation with a solenoid actuator, to elicit a C‐start response. Temperature within the test cell was controlled with a recirculating water bath. Xenopus laevis embryos were obtained using a standard fertilization technique. Tadpole response to a controlled perturbation was recorded in unprecedented detail and the approach was validated by describing the distinct differences in response between normal and one‐eared tadpoles. The experimental apparatus and methods form an important element of a rigorous investigation into the response of the tadpole vestibular system to mechanical and biochemical manipulations, and can ultimately contribute to improved understanding of the effects of altered gravity perception on humans.     

A role for set in the control of automatic spatial response activation

Spatial stimulus-response (S-R) compatibility effects are widely assumed to reflect the automatic activation of a spatial response by the spatial attributes of a stimulus. The experiments reported here investigate the role of the participant's set in enabling or interacting with this putatively automatic spatial response activation. Participants performed a color discrimination task (Experiment 1) or a localization task (Experiment 2). In each experiment, two different S-R mappings were used and a task-cue indicated the appropriate mapping on each trial. S-R compatibility and the time between the task-cue and target were manipulated, and compatibility effects were assessed as a function of (a) the time between the task-cue and the stimulus, and (b) whether the S-R mapping repeated or switched on consecutive trials. Critically, whether response mappings repeated or switched on consecutive trials determined the relation between compatibility effects and the time between task-cue and stimulus. These results are discussed in terms of an interaction between automatic spatial response activation and the participant's set.     

The interaction of response complexity and instructional set

This study investigated the interaction of experimental instructions and response complexity in an attempt to provide a possible explanation for some of the equivocalness in the programming time literature. Response complexity was manipulated by varying the accuracy required of subjects striking circular targets in a simple reaction time paradigm. Subjects were tested on two days, one week apart, during which experimental instructions emphasized either leaving the start position as soon as possible (initiation emphasis) or completing the response with a rapid but smooth movement (form emphasis). Subjects had shorter reaction times but longer movement times when they performed under initiation-emphasis instructions rather than under form-emphasis instructions. Furthermore, in contrast to form-emphasis conditions, there was no effect of response complexity on reaction time in conditions of initiation emphasis. It appears that subtle changes in experimental instructions can lead to very different patterns of reaction time and movement time data. These findings highlight the need for caution in preparing subject instructions in response programming experiments.     

Timing of movement phases of a repeated response

How can one determine the nature of timing control that exists among various distinct phases of movement in a repetitive activity? A statistical approach is suggested and is exemplified by reference to data on the timing of two phases of movement, arrival at and departure from the response plate, in repetitive finger tapping. Two contrasting models are presented, and the predictions for the covariation of the various intervals between the two movement phases are compared. Data on finger tapping support the model that assumes the initiation of each phase is centrally determined without reference to the time of occurrence of the immediately preceding phase.     

Frequency response characteristics for sinusoidal movement in the fovea and periphery

Threshold sensitivity was measured for sinusoidal movement of bright 1-deg lines against a dark background as a function of oscillation frequency and retinal location. Sensitivity was greatest in the fovea and at a frequency of 1–2 Hz. Peripheral sensitivity was more narrowly tuned than foveal sensitivity. The presence of a stationary reference line affected mainly the foveal sensitivity. The results are interpreted as evidence for both position- and velocity-sensitive mechanisms in the movement detection system.     

Effects of anticipation certainty on preparatory brain activity and anticipatory postural adjustments associated with voluntary unilateral arm movement while standing

We examined the effects of anticipation certainty concerning which voluntary movement is required in response to a stimulus while standing on preparatory brain activity and anticipatory postural adjustments (APAs). Ten right-handed adults abducted their left or right arm rapidly in response to a visual imperative stimulus, based on the type of stimulus. A warning cue, which did or did not contain information about the side of arm abduction, was presented 2000ms before the imperative stimulus. Preparatory brain activity before arm abduction was quantified by the mean amplitude of the contingent negative variation 100ms before the imperative stimulus (late CNV amplitude). Compared with the low anticipation condition, in the high anticipation condition the following results were obtained only in the case of right arm abduction: (1) larger late CNV amplitude, (2) earlier postural muscle activities with respect to the focal muscle of arm abduction, and (3) smaller peak displacement of center of pressure during the abduction. These findings suggest that high anticipation of voluntary movement of dominant arm to a stimulus while standing influences preparatory brain activity before the movement, resulting in earlier APAs and thus smaller disturbance of postural equilibrium during the movement.     

Manipulating response set in a choice reaction task: evidence for anatomical coding in response selection

Accurate motor performance requires a process of response selection that chooses the correct response out of a set of possible ones. Most theories of response selection assume that this selection process operates on spatial codes, which define the location of stimuli and responses in environmental coordinates, with little or no role for the anatomical codes of the effectors involved. In this study, I systematically manipulated the anatomical identities of the response fingers in a four-choice reaction task, while keeping the stimulus and response locations constant. Results showed that homologous fingers on different hands modulated the reaction time profiles and error patterns in a mirror-symmetrical way. This finding indicates that anatomical factors may play a more substantial role in response selection than often assumed.