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Biomedical subjects

R W Christina

Publications and source records attributed to R W Christina.

At least 19 recordsLinked to original sources
PubMed1990

Time needed to change the isometric force production of a response.

This study investigated the time needed to change a motor program that specified the elbow flexor muscles to gradually increase the isometric force production from 15% to 75% of one's maximum voluntary contraction (MVC). A double-stimulation paradigm was used with the restriction that subjects (N = 12) be at 15% of their MVC before the presentation of the first stimulus. Subjects reacted to the first stimulus (randomly presented) by gradually increasing their isometric force from 15% to 75% of their MVC and then reacted to the second stimulus by altering the force production in one of four ways: (a) increasing the force to the 75% level rapidly instead of gradually, (b) discontinuing the increase and maintaining the level of force attained, (c) discontinuing all force production, or (d) reversing the direction of force so that it is produced by the elbow extensors. The data revealed that more time was needed to increase the force rapidly than to perform any of the other three conditions.

Adult↗
PubMed1989

Psychomotor decline can be described by discontinuities in response trajectories: comments on Vrtunski and Patterson (1985).

Five methodological and experimental design concerns are identified in Vrtunski and Patterson's (1985) article. The discussed concerns involved: (a) the use of misleading premotor segment terminology, (b) the uncertain status of the repeated measures sphericity assumptions, (c) mean calculations across unequal trials of the four levels of stimulus conditions, (d) improper selection of a main effect for post hoc analysis and discussion of these results when a significant interaction was present, and (e) conflicting text and table values. These concerns have prompted us to question their psychomotor decline conclusions. And unless Vrtunski and Patterson can convince us that these concerns are unjustified, we have no choice but to doubt seriously the validity of their conclusions.

Animals↗
PubMed1984

Organization in children's recall of information about movement.

Children's recall of five randomly presented movement distances was studied as a function of three organization groups. The group given subjective organization was free to recall the movements in any order. The group given experimenter-presented order had to recall the movements from shortest to longest. The forced-random group was required to recall the movements in the same order in which they were randomly presented. 60 boys and girls, 7 to 8 and 11 to 12 yr. old, volunteered. No appreciable difference in mean absolute error was found between the first two groups, but they did recall the movement distances with less error than the forced-random group. It was concluded that the organization of movement information is important for effective recall by children, but subjective organization was not superior to an organization imposed by the experimenter.

Child↗
PubMed1983

Target location and visual feedback as variables determining accuracy of aiming movements.

The accuracy of a long aiming movement was studied as a function of whether it was performed toward or away from the midline of the subject's body in the presence or absence of visual feedback. 30 right-handed, male university students (19-26 yr.) served as subjects. With movement distance and duration controlled, the mean percentage of error was 6.34% less for movements made toward the body's midline than for those performed away from the midline. The mean percentage of error was also 48% less in the presence of visual feedback than in its absence. However, contrary to our expectation, movements executed toward the body's midline were not appreciably less disrupted in the absence of visual feedback than movements performed away from the midline.

Adult↗
PubMed1982

Hand position as a variable determining the accuracy of aiming movements.

Two experiments investigated the effect of hand position on the accuracy of short- and long-duration aiming movements in the presence and absence of visual feedback. In Experiment 1 (N = 16) short aiming movements were executed rapidly, which would require them to be predominantly programmed, whereas in Experiment 2(N = 8) these movements were performed slowly enough so that visual feedback, which implies that they were predominantly programmed. However, the long-duration, short-length movements of Experiment 2 were disrupted when visual feedback was removed, which suggests that these movements were being guided by visual feedback. Having the heel of the responding hand in contact with the target platform during the response resulted in greater accuracy than no hand contact for the short-length movements of both experiments. Taken together, these results indicated that hand contact produced greater aiming accuracy than no hand contact for both programmed- and feedback-based movements.

Adolescent↗
PubMed1982

Simple reaction time as a function of response complexity: memory drum theory revisited.

The prediction emanating from memory drum theory (Henry & Rogers, 1960') that simple reaction time (SRT) increases as a response becomes more complex (i.e., increases in number of movement parts) was investigated. Experiments 1 (N = 20) and 3 (N = 16) indicated that SRT was longer for responses consisting of two and three parts than it was for a one-part response and this may be interpreted as support for the prediction. Failing to support the prediction, however, was the finding that SRT was essentially the same for responses consisting of two and three parts. This may not be too damaging to the theory because it could simply be reflecting an upper limit in terms of numbers of parts or response duration for causing an increase in SRT. Experiments 2 (N = 20) and 3 revealed an SRT effect between two responses that were supposed to be equal in complexity. At first, this finding appeared to be contrary to the prediction, but it may be interpreted as support for it because one of the responses defined as having one movement part could actually have had two

Journal Article↗
PubMed1981

The learning of programmed- and feedback- based processes controlling the production of a positioning response in two dimensions.

Two experiments were conducted to investigate the learning of the programmed- and feedback-based processes controlling the production of a slow, self-paced positioning response in two dimensions (direction and extent) in the horizontal plane. Both experiments had two phases: an acquisition phase of 60 trials with KR, followed by a KR withdrawal phase of 20 trials. In Experiment 1, one group (N=15) had visual feedback about the ongoing movement and the other group (N=15) did not. In Experiment 2, one group (N=15) practiced initiating the response in the criterion direction and moving the criterion extent, whereas, the other group (N=15) practiced initiating the response in the criterion direction and moving randomly varied extents. The results of Experiment 1 indicated that the learning of a programmed-based process is a gradually acquired freedom from visual feedback. Experiment 2 revealed that a programmed-based process can be learned independent of a feedback-based process.

Journal Article↗
PubMed1979

The effect of movement amplitude and target diameter on reaction time: comments on Siegel (1977).

Siegel's (1977) interpretation that his reaction time results were solely a function of response factors (movement amplitude and target diameter) was discussed and criticized. It was argued that Siegel's interpretation was inappropriate because stimulus factors (eccentric and visual angle) and response factors were confounded. It was also argued that the surprising U-shaped relation between reaction time and movement amplitude was probably the result of the confounding between stimulus and response factors.

Journal Article↗
PubMed1978

Proprioceptive feedback as a mediator in interlimb timing.

Prior findings regarded as evidence for proprioceptive feedback as a mediator in interlimb timing can also be interpreted as evidence for motor outflow because they came from research that had subjects make voluntary movements, and such movements allow for both feedback and outflow to operate. The present study was designed to resolve this controversy by determining if these findings could be replicated with passive movements which allow for feedback, but not outflow, to operate. The interlimb timing task studied was one where subjects made the timing response with their right hand while moving their left arm during the 1.5-sec interval to be timed. Three groups of 16 male college students performed 50 trials of the right-hand response with knowledge of results, under one of three left-arm conditions: (a) passive movement, (b) voluntary movement, and (c) no movement. The results indicated that the findings were replicated with passive movements and this was interpreted as support for the involvement of proprioceptive feedback in interlimb timing.

Journal Article↗