Biomedical subjects

B J Pollock

Publications and source records attributed to B J Pollock.

11 recordsLinked to original sources

PubMed1997

Dissociated contextual interference effects in children and adults.

24 7-yr.-old children and 24 university-age adults practiced a ballistic aiming task under either low contextual interference (blocked practice) or high contextual interference (random practice). All subjects performed 90 acquisition trials, followed by 20 transfer trials and 15 retention trials. Similar to previous findings, the adults performed the acquisition trials better under blocked than under random conditions, yet performed the retention and transfer tests better after random than blocked practice. No differences in acquisition were found between blocked and random practice conditions for the children; nevertheless, the random group performed the retention and transfer tests better than the blocked group. The results are discussed in relation to applied and theoretical issues of contextual interference.

Adult↗

PubMed1995

Optimizing the use of vision in manual aiming: the role of practice.

The purpose of this study was to determine how subjects learn to adjust the characteristics of their manual aiming movements in order to make optimal use of the visual information and reduce movement error. Subjects practised aiming (120 trials) with visual information available for either 400 msec or 600 msec. Following acquisition, they were transferred to conditions in which visual information was available for either more or less time. Over acquisition, subjects appeared to reduce target-aiming error by moving to the target area more quickly in order to make greater use of vision when in the vicinity of the target. With practice, there was also a reduction in the number of modifications in the movement. After transfer, both performance and kinematic data indicated that the time for which visual information was available was a more important predictor of aiming error than the similarity between training and transfer conditions. These findings are not consistent with a strong "specificity of learning" position. They also suggest that, if some sort of general representation or motor programme develops with practice, that representation includes rules or procedures for the utilization of visual feedback to allow for the on-line adjustment of the goal-directed movement.

Adult↗

PubMed1995

Intermittent vision and discrete manual aiming.

This study was designed to assess how the precision requirements of discrete aiming movements affect the utility of brief visual samples provided during execution of movement. Subjects pointed with a hand-held stylus to targets with indices of difficulty of 3, 4, 5, and 6 bits with full vision, no vision, and in conditions in which 20-msec. visual samples were provided every 80, 140, or 200 msec. While intermittent vision required slightly longer movement times for targets with a high index of difficulty, subjects' accuracy was similar to the full-vision situation. Moreover, with intermittent vision, the movement trajectories resembled the full-vision and not the no-vision situation. It would appear that brief visual samples of the movement environment are sufficient for reasonably precise closed-loop control.

Adult↗

PubMed1995

Cerebral specialization for spatial processing in adults with Down syndrome.

Cerebral specialization for spatial processing in adults with Down syndrome was examined. In the first experiment, both control and right-handed subjects with Down syndrome exhibited no lateral advantage in a dihaptic shape-matching task, whereas left-handed subjects with Down syndrome displayed an expected left-hand advantage. In a visual field dot enumeration task in the second experiment, all groups exhibited left-field superiority. Thus, atypical cerebral organization of function in adults with Down syndrome appears to be confined to speech perception (Elliott & Weeks, 1993).

Brain↗

PubMed1994

The influence of intermittent vision on manual aiming.

Two experiments were conducted to examine the influence of intermittent vision on right and left hand aiming. In Experiment 1, increased visual occlusion times led to a steady deterioration in performance that was most pronounced for high index of difficulty targets. Longer visual sample times only partially compensated for this effect (Experiment 2). It is suggested that a short-lived visual representation of the movement environment may in some cases provide a reasonable, although not perfect, substitute for direct visual pickup. In Experiment 2, there was some indication that the right hand system may be faster at using visual information than the left hand system.

Female↗

PubMed1993

Variance and invariance in expert and novice triple jumpers.

The purpose of this study was to examine relative timing, relative distance, and effector independence characteristics of the triple jump. We videotaped expert and novice triple jumpers using standing and running starts. On some trials, the triple jumpers were required to take off from their nondominant leg. Gentner's (1987) interaction test was used to assess the proportional duration model in describing the timing of the component submovements. For both experts and novices, the proportional durations varied with the type of start. For experts, the relative timing of the jump components was independent of the take-off leg. The findings were mixed for the novices. Similar results were obtained when relative distance was examined. These results are discussed with respect to constructs related to variability in skilled performance.

Adult↗

PubMed1993

Movement preparation in adults with and without Down syndrome.

This study was designed to determine whether adults with mental retardation, with and without Down syndrome, display flexibility in the preparation of limb movements. A four-alternative target-aiming task involving movements with either the right or left hand to near or far targets was employed. Prior information about the movement to be made was manipulated by precuing specific features. Although reaction times and movement times were longer for subjects with than for those without mental retardation, the pattern of results was similar. Specifically, both retarded groups were able to use advance information to reduce movement preparation time. Moreover, information about movement distance was useful to subjects whether or not hand was precued. This finding indicates that the individuals with mental retardation were not limited by a fixed-order movement preparation process.

Adult↗

PubMed1992

Effects of the model's skill level on observational motor learning.

Observation of a model prior to physical practice often facilitates the acquisition of motor skills. The majority of research studies on observational motor learning has used a skilled model for the demonstration. Recent research, however, suggests that observing an unskilled (learning) model may also be effective. The experiment reported here compared motor skill acquisition following observation of a learning model or a skilled model to the performance of subjects who lacked the benefit of observation. The task was to play a computer tracking game. Subjects were tested in pairs. Observers watched either a skilled or a learning model perform 3 trials. The observers then practiced the game for 3 trials. Observation of another 12 trials was followed by 12 more practice trials. Substantial observational learning was found, as both groups of observers performed better than the learning models after both the 3 initial trials of observation and after 12 more observation trials. However, there were no differences due to observing the skilled or the learning model. These findings are discussed in relation to theoretical issues of observational learning.

Analysis of Variance↗

PubMed1989

Human monoclonal antibodies to HIV-1: cross-reactions with gag and env products.

Human monoclonal antibodies were raised by in vitro immunization of normal human spleen cells with denatured HIV-1 and subsequent fusion to an Epstein-Barr virus (EBV) transformed cell line. Three monoclonals reacted with both gag-encoded p24 core protein and env-encoded gp41 transmembrane glycoprotein. The cross-reaction was confirmed by reactivity with p24- and gp41-derived recombinant peptides. The peptides share two amino acid sequences which may be the basis for the cross-reaction. Attempted epitope mapping using synthetic peptides was unsuccessful due to non-specific reactivity with the short linear peptides.

Antibodies, Monoclonal↗

PubMed1983

The pattern of expression of chick delta-crystallin genes in lens differentiation and in trans-differentiating cultured tissues.

During development of the vertebrate lens, the lens epithelium undergoes a final stage of differentiation into lens fibre cells. Lens fibre cells can also be produced by trans-differentiation from certain extralenticular structures, all of which are of different developmental origin from lens, including embryonic neural retina and retinal pigmented epithelium. Delta-crystallin is the major lens protein in the chick and appears first in development; it is the major product in trans-differentiated retina of younger embryos. In both normal differentiation and trans-differentiation an increase of delta-crystallin coding RNA is detectable in the nucleus of cells prior to their terminal differentiation into lens fibres. The increase in transcription of delta-crystallin genes accompanying final differentiation of lens fibres, appears to take place slightly in advance of an increase in the capacity to process and transport this mRNA to the cytoplasm.

Animals↗

PubMed1983

Partial retinal dysplasia and subsequent degeneration in a mutant strain of domestic fowl (rdd).

An inherited recessive form of retinopathy has been discovered in the domestic fowl (rdd) which is characterized by progressive deterioration of the retina, culminating in blindness by sexual maturity. Morphologically, the condition is recognizable by abnormalities in both the retinal pigment epithelium and the neural retina. Gaps in the pigment epithelium which are first detected macroscopically at nine days of incubation become larger and more numerous until the time of hatching, then disappear during the subsequent week. Undulations in the outer nuclear, outer plexiform, and inner nuclear layers are obvious by 11 days of incubation. There is a marked reduction of photoreceptors at 18 days of incubation as compared to normal controls. After hatching, the thickness of the retina decreases with age, primarily due to cell loss from the photoreceptor region and inner nuclear layer. Detachment of the atrophic retinas generally occurs in adults, and is followed in some adults by granulation and ossification of the vitreous. Problems concerning the site of the lesion are discussed.

Aging↗