Biomedical subjects

D E Parker

Publications and source records attributed to D E Parker.

At least 19 recordsLinked to original sources

PubMed2001

Self-motion perception: assessment by real-time computer-generated animations.

We report a new procedure for assessing complex self-motion perception. In three experiments, subjects manipulated a 6 degree-of-freedom magnetic-field tracker which controlled the motion of a virtual avatar so that its motion corresponded to the subjects' perceived self-motion. The real-time animation created by this procedure was stored using a virtual video recorder for subsequent analysis. Combined real and illusory self-motion and vestibulo-ocular reflex eye movements were evoked by cross-coupled angular accelerations produced by roll and pitch head movements during passive yaw rotation in a chair. Contrary to previous reports, illusory self-motion did not correspond to expectations based on semicircular canal stimulation. Illusory pitch head-motion directions were as predicted for only 37% of trials; whereas, slow-phase eye movements were in the predicted direction for 98% of the trials. The real-time computer-generated animations procedure permits use of naive, untrained subjects who lack a vocabulary for reporting motion perception and is applicable to basic self-motion perception studies, evaluation of motion simulators, assessment of balance disorders and so on.

Adult↗

PubMed2001

Stereotypy and motor control: differences in the postural stability dynamics of persons with stereotyped and dyskinetic movement disorders.

We examined whether dynamic measures of postural stability differentiated persons with stereotyped movement disorder from persons with dyskinetic movement disorder. Participants from three groups (stereotypy, dyskinesia, control) were given a goal-oriented postural stability task, and performance was measured using a force platform and computerized posturographic techniques. The results showed that both movement disorder groups differed from the control group in the posture task. Further, the stereotypy and dyskinesia groups demonstrated markedly different postural movement profiles. The postural motion of the stereotypy group was characterized by greater amplitude and variability but lower complexity than the dyskinesia group. These results provide support for a motor control model of stereotypy.

Adult↗

PubMed2000

Varieties of repetitive behavior in autism: comparisons to mental retardation.

Systematic study of abnormal repetitive behaviors in autism has been lacking despite the diagnostic significance of such behavior. The occurrence of specific topographies of repetitive behaviors as well as their severity was assessed in individuals with mental retardation with and without autism. The occurrence of each behavior category, except dyskinesias, was higher in the autism group and autistic subjects exhibited a significantly greater number of topographies of stereotypy and compulsions. Both groups had significant patterns of repetitive behavior co-occurrence. Autistic subjects had significantly greater severity ratings for compulsions, stereotypy, and self-injury. Repetitive behavior severity also predicted severity of autism. Although abnormal repetition is not specific to autism, an elevated pattern of occurrence and severity appears to characterize the disorder.

Adult↗

PubMed2000

A randomized trial of the effect of single-vision vs. bifocal lenses on myopia progression in children with esophoria.

BACKGROUND: Bifocals have long been thought to reduce progression of childhood myopia. However, this hypothesis has not been definitively evaluated. METHODS: We conducted a randomized clinical trial to test the hypothesis that bifocals slow myopia progression in children with near-point esophoria. Eighty-two myopic children were randomized to single-vision glasses (n = 40) or to bifocals with a +1.50 D add (n = 42) and were followed for 30 months. Refraction was measured by an automated refractor after cycloplegia. The primary outcome was myopia progression defined as the difference between the spherical equivalent at baseline and at the 30-month examination, averaged over both eyes. RESULTS: Follow-up was incomplete for six children in the bifocal group and one child in the single-vision group. Among the children completing the 30 months of follow up, myopia progression (mean spherical equivalent of the two eyes) averaged 0.99 D for bifocals and 1.24 D for single vision (unadjusted, p = 0.106; adjusted for age, p = 0.046). Treatment groups differed in their cumulative distributions (Kolmogorov-Smirnov procedure, p = 0.031). Evidence for a treatment effect on growth in vitreous chamber depth was similar (p = 0.046 by K.S.). CONCLUSION: Use of bifocals, instead of single-vision glasses, by children with near-point esophoria seemed to slow myopia progression to a slight degree.

Aging↗

PubMed1999

The use of an independent visual background to reduce simulator side-effects.

BACKGROUND: Simulator sickness (SS) is a major problem which potentially limits interface applications that feature simulated motion. While display imperfections play a role, a large part of SS is motion sickness (MS). Sensory rearrangement theory holds that MS is related to conflicting motion cues; in the case of simulators, mainly a conflict between inertial cues (usually indicating no self-motion) and visual stimuli from the display (indicating self-motion). It is suggested that MS does not arise from conflicting motion cues per se, but rather from conflicting rest frames selected from those motion cues. There is strong evidence that the visual rest frame is heavily influenced by the visual background. Providing an independent visual background (IVB) consistent with the inertial rest frame may reduce SS, even when the simulator's content-of-interest (CI) is not consistent with the inertial rest frame. METHODS: In two experiments, a circular vection stimulus was shown for 3-4.5 min in a head-mounted display, comparing see-through (i.e., IVB) to occluded (i.e., no IVB) modes. Measures included a standard SS questionnaire and a pre-exposure ataxia measure. Experiment 2 added a visual task which forced attention into the CI and a post-exposure ataxia measure. In both experiments, subjects rated the CI as significantly more visible than the IVB. RESULTS: A large effect was found for the reduction of SS and ataxia in the first experiment, and for pre-exposure ataxia in the second. CONCLUSIONS: Future research will further test the IVB idea and examine applications to high-end simulators.

Adolescent↗

PubMed1998

Relationship between selected orientation rest frame, circular vection and space motion sickness.

Space motion sickness (SMS) and spatial orientation and motion perception disturbances occur in 70-80% of astronauts. People select "rest frames" to create the subjective sense of spatial orientation. In microgravity, the astronaut's rest frame may be based on visual scene polarity cues and on the internal head and body z axis (vertical body axis). The data reported here address the following question: Can an astronaut's orientation rest frame be related and described by other variables including circular vection response latencies and space motion sickness? The astronaut's microgravity spatial orientation rest frames were determined from inflight and postflight verbal reports. Circular vection responses were elicited by rotating a virtual room continuously at 35 degrees/s in pitch, roll and yaw with respect to the astronaut. Latency to the onset of vection was recorded from the time the crew member opened their eyes to the onset of vection. The astronauts who used visual cues exhibited significantly shorter vection latencies than those who used internal z axis cues. A negative binomial regression model was used to represent the observed total SMS symptom scores for each subject for each flight day. Orientation reference type had a significant effect, resulting in an estimated three-fold increase in the expected motion sickness score on flight day 1 for astronauts who used visual cues. The results demonstrate meaningful classification of astronauts' rest frames and their relationships to sensitivity to circular vection and SMS. Thus, it may be possible to use vection latencies to predict SMS severity and duration.

Adult↗

PubMed1998

Prenatal survival of mouse embryos irradiated in utero with fission neutrons or 250 kV X-rays during the two-cell stage of development.

PURPOSE: To investigate the relationship between radiation dose at the two-cell stage and prenatal survival. MATERIALS AND METHODS: Pregnant mice were irradiated with fast neutrons (0.53-1.94 Gy) or X-rays (1.50-5.00 Gy), or sham irradiated. At selected times up to gestation day 16, the mice were killed and the uterine contents examined. RESULTS: At doses up to 0.82 Gy of neutrons and 2.50 Gy of X-rays, all or virtually all the radiation-induced deaths occurred during the period from the time of implantation to gestation day 10. At higher doses an appreciable proportion of the deaths occurred after day 10. Many neutron-induced deaths in the period from implantation to day 10 occurred before day 7. A mathematical model was developed for estimating survival to gestation day 16 as a function of neutron dose. CONCLUSIONS: The mortality pattern, in which low radiation doses led to early deaths and high doses to both late and early deaths, suggests the existence of two lethal processes. The relationship between neutron dose and survival to gestation day 7 has been interpreted as indicating that the early deaths involved predominantly a two-event inactivation mechanism. An individual cell of a two-cell embryo was found to be less sensitive to lethal radiation injury than a pronuclear zygote.

Animals↗

PubMed1998

Baseline characteristics in the Myopia Progression Study, a clinical trial of bifocals to slow myopia progression.

BACKGROUND: Retrospective studies have indicated that myopic children with nearpoint esophoria experienced slower myopia progression if they wore bifocal glasses rather than single-vision glasses. A small, 18-month clinical trial also supported that finding, but the results were not statistically significant. The Myopia Progression Study was funded by the National Eye Institute to test more rigorously the efficacy of bifocals, compared with single-vision glasses, in slowing myopia progression in children with nearpoint esophoria. A secondary objective of the study was to identify other variables that might influence the rate of myopia progression. This report describes the design and methods of the Myopia Progression Study and the baseline characteristics of the subjects. METHODS: A 3-year, randomized clinical trial was initiated. Subjects were children between 6 and 12 years of age who were myopic (at least -0.50 D in each eye) and who demonstrated nearpoint esophoria by the von Graefe technique. RESULTS: Eighty-two children were enrolled. After blocking by gender and clinical site (two sites), subjects were randomly assigned to one of the two treatments: correction with single-vision spectacle lenses or correction with bifocal lenses having a +1.50 D add in a flattop segment. The average degree of myopia at baseline was -2.31 D (SD = 1.31 D). CONCLUSION: This clinical trial can be expected to determine the effectiveness of bifocal glasses in slowing the progression of myopia in children with nearpoint esophoria.

Child↗

PubMed1997

Introducing case management to a general medicine ward team of a teaching hospital.

PURPOSE: To introduce case management to a general medicine ward team of a teaching hospital to improve patient care and ensure comprehensive longitudinal care. METHOD: The Department of Veterans Affairs Medical Center is one of four hospitals used by University of Oklahoma School of Medicine residents. There are five medicine teams, each comprising a second- or third-year resident, one or two interns, two medical students, and a faculty physician. The case-management program was initiated in November 1994. No attempt was made to limit the residents assigned to the case-managed team (i.e., many residents who worked with the case-managed team subsequently rotated through the other teams). Patients were assigned to the teams by rotation, and no attempt was made to adjust for the severity of illness among admissions. The teams were separated as follows: pre-case-management teams (all five teams prior to the case-management program), non-case-management teams (the four teams without case managers after the program's initiation), and the case-management team. The study periods were January-July 1994 (pre-case management) and January-July 1995 (after case management). RESULTS: The numbers of patients treated by the three groups were 1,305, 1,139, and 289, respectively. The median length of stay for pre-case-management patients was 5 days (interquartile range, 3-9 days); for non-case-management patients, 5 days (range, 3-8 days); and for case-management patients, 5 days (range, 3-7 days). The cumulative distribution of lengths of stay for case-management patients was significantly different from those of the other study groups by the Kolmogorov-Smirnov test (p = .02). More case-management patients were discharged by day 7. Rates of readmission were not significantly different between the teams. CONCLUSION: In this study a case-management program was effectively implemented in a teaching hospital, resulting in reduced lengths of stay for patients. As academic health centers become more concerned with efficiency and cost, case management should be seriously considered as a way to deal with such issues.

Academic Medical Centers↗

PubMed1997

Volumetric changes following barrier regeneration procedures for the surgical management of grade II molar furcation defects in baboons: I. Overall defect fill.

A computer imaging technique has been advocated for measuring the volumetric fill in furcation defects. Histologic material for this investigation was obtained from an animal study using five adult baboons (Papio anubis). The photographed histology was converted into digitized electronic information, and a computer calculated the overall volume of defect fill for the treated and the untreated control sites. All volumetric measurements were expressed as a percentage of the original surgically created defect size, with 100% indicating complete healing of the defect. The results indicate that none of the defects achieved complete healing. Teeth that had received flap debridement had the most overall defect fill (79.50%). Teeth that received a biodegradable barrier (Epi-Guide) showed a mean overall defect fill of 74.98%, while sites treated with an exclusion barrier (Gore-Tex) showed 70.75% overall fill. The untreated control teeth showed a mean overall fill of 78.70%. A variety of statistical tests revealed no significant differences among teeth within the same animal and between treatments and controls. The following conclusions were drawn: (1) digital imaging technology is a useful research tool for determining the volume of defect fill in surgically created grade II molar periodontal furcation defects in the baboon model; and (2) no significant differences were found among the treatment modalities and the untreated control sites.

Animals↗

PubMed1996

Growth differences associated with compulsive and stereotyped behavior disorders in adults with mental retardation.

We have recently observed that compulsive behaviors in mentally retarded patients appear to be quite prevalent, can be reliably assessed, and have a high rate of co-occurrence with stereotyped and self-injurious behaviors in this population. As abnormal growth rate has been observed in obsessive-compulsive disorder (OCD) patients, we examined physical stature in adults with mental retardation who display repetitive movement disorders. Identification of cases with stereotypic movement disorder, and cases with compulsive behaviors was done using a symptom checklist and direct observation. Subjects with repetitive movement disorders were smaller in stature than control subjects, with gender differences observed across repetitive behavior disorders. Specifically, female subjects with compulsive behavior disorder, but not stereotypic movement disorder, were significantly shorter and weighted significantly less than same sex-matched controls. Conversely, male subjects with stereotypic movement disorder, but not compulsive disorder, were significantly shorter and weighed significantly less than same sex controls. These findings may point to a neuroendocrine abnormality associated with repetitive movement disorders.

Adolescent↗

PubMed1996

Clomipramine treatment for self-injurious behavior of individuals with mental retardation: a double-blind comparison with placebo.

The efficacy of the serotonin (5-HT) uptake inhibitor clomipramine in the treatment of self-injurious behavior (SIB) was tested in individuals with severe and profound mental retardation. Six of the 8 subjects who completed a double-blind, placebo-controlled crossover trial exhibited a clinically significant improvement (50% or greater reduction from placebo) in the frequency of SIB. Clomipramine treatment was also associated with improvement in SIB intensity, frequency of stereotypy and compulsions, teacher ratings of stereotypy and social withdrawal, and frequency of staff intervention required for problem behaviors. Adverse effects (seizure and tachycardia/agitation) occurred in 2 of the 8 subjects. These results represent the first controlled trial of a 5-HT uptake inhibitor in the treatment of SIB in mental retardation.

Adult↗

PubMed1995

Middle latency auditory responses in males who stutter.

Little research exists that explores subcortical function in people who stutter. One study suggested that auditory middle latency response Wave Pb was prolonged in subjects who stutter as compared to controls. Other studies have suggested that Pb was generated within the thalamic portion of the reticular system. MLRs were recorded from 10 males who stutter and 10 controls using a variety of filter passbands in response to clicks presented binaurally at various rates. The latency of Pb was found to be significantly shorter in the group of subjects who stutter.

Acoustic Stimulation↗

PubMed1995

Inertial acceleration as a measure of linear vection: an alternative to magnitude estimation.

The present study focused on the development of a procedure to assess perceived self-motion induced by visual surround motion--vection. Using an apparatus that permitted independent control of visual and inertial stimuli, prone observers were translated along their head x-axis (fore/aft). The observers' task was to report the direction of self-motion during passive forward and backward translations of their bodies coupled with exposure to various visual surround conditions. The proportion of "forward" responses was used to calculate each observer's point of subjective equality (PSE) for each surround condition. The results showed that the moving visual stimulus produced a significant shift in the PSE when data from the moving surround condition were compared with the stationary surround and no-vision condition. Further, the results indicated that vection increased monotonically with surround velocities between 4 and 40 degrees/sec. It was concluded that linear vection can be measured in terms of changes in the amplitude of whole-body inertial acceleration required to elicit equivalent numbers of "forward" and "backward" self-motion reports.

Acceleration↗

PubMed1995

Compulsions in adults with mental retardation: prevalence, phenomenology, and comorbidity with stereotypy and self-injury.

A variety of conceptual similarities between compulsions seen in individuals with obsessive compulsive disorder and stereotypy and self-injury seen in individuals with mental retardation led us to investigate the prevalence, phenomenology, and comorbidity of compulsions in adults with severe or profound mental retardation. We developed simple assessment screening instruments for stereotypy and self-injury and used Gedye's Compulsive Behavior Checklist and found acceptable levels of reliability, stability, and validity for each instrument. Prevalences were as follows: stereotypy: 60.9%; self-injury: 46.6%; and compulsion: 40%. The occurrence of compulsions was significantly positively associated with the occurrence of stereotypy, self-injury, and stereotypy plus self-injury.

Adolescent↗

PubMed1994

Preflight adaptation training for spatial orientation and space motion sickness.

Two part-task preflight adaptation trainers (PATs) are being developed at the NASA Johnson Space Center to preadapt astronauts to novel sensory stimulus conditions similar to those present in microgravity to facilitate adaptation to microgravity and readaptation to Earth. This activity is a major component of a general effort to develop countermeasures aimed at minimizing sensory and sensorimotor disturbances and Space Motion Sickness (SMS) associated with adaptation to microgravity and readaptation to Earth. Design principles for the development of the two trainers are discussed, along with a detailed description of both devices. In addition, a summary of four ground-based investigations using one of the trainers to determine the extent to which various novel sensory stimulus conditions produce changes in compensatory eye movement responses, postural equilibrium, motion sickness symptoms, and electrogastric responses are presented. Finally, a brief description of the general concept of dual-adapted states that underly the development of the PATs, and ongoing and future operational and basic research activities is presented.

Adaptation, Physiological↗

PubMed1994

Differences in otolith and abdominal viscera graviceptor dynamics: implications for motion sickness and perceived body position.

Human graviceptors, located in the trunk by Mittelstaedt, probably transduce acceleration by abdominal viscera motion. As demonstrated previously in biodynamic vibration and impact tolerance research, the thoraco-abdominal viscera exhibit a resonance at 4 to 6 Hz. Behavioral observations and mechanical models of otolith graviceptor response indicate a phase shift, increasing with frequency between 0.01 and 0.5 Hz. Consequently, the potential exists for intermodality sensory conflict between vestibular and visceral graviceptor signals, at least at the mechanical receptor level. The frequency range of this potential conflict corresponds with the primary frequency range for motion sickness incidence in transportation, in subjects rotated about Earth-horizontal axes (barbecue spit stimulation), and in periodic parabolic flight microgravity research, and also for erroneous perception of vertical oscillations in helicopters. We discuss the implications of this hypothesis for previous self-motion perception research and suggestions for various future studies.

Abdomen↗

PubMed1993

Screening for urethral infection in adolescent and young adult males.

We evaluated the urinary leukocyte esterase (LE) dipstick as a predictor of a positive urethral culture for Neisseria gonorrhoeae and/or Chlamydia trachomatis in adolescent and young adult males. Sexual and sexually transmitted disease (STD) histories were also analyzed to determine predictors of infection. Subjects were recruited from sexually active males attending an adolescent medicine clinic. Patients were interviewed regarding presence of symptoms of urethritis and a variety of clinical variables. First-voided urine for LE dipstick and urethral swabs for gonorrhea and C. trachomatis cultures were obtained. One hundred patients (mean age, 19.2 years) were asymptomatic; 50 patients (mean age, 19.0 years) had symptoms of urethritis. In asymptomatic patients, the sensitivity, specificity, predictive value positive (PVP), and predictive value negative (PVN) of the LE dipstick were 0.31, 0.92, 0.57, and 0.90, respectively. These values were 0.66, 0.71, 0.76, and 0.60, respectively, in symptomatic patients. In each patient group the dipstick was more sensitive in detecting, and a better predictor of, a positive culture for gonorrhea than Chlamydia. LE dipstick results and clinical variables were evaluated as correlates of infection using stepwise logistic regression. A positive LE dipstick and four additional variables increased the probability of obtaining a positive culture for one or both organisms from symptomatic patients. These variables were the following: sexual contact in the previous month with a partner diagnosed as having a sexually transmitted disease, having ever used a condom, five or more lifetime sexual partners, and more than one sexual partner in the past month. Only a positive LE dipstick entered the model as a predictor of infection in asymptomatic patients.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗