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Robert Patterson

Publications and source records attributed to Robert Patterson.

13 recordsLinked to original sources
PubMed2006

Perceptual issues in the use of head-mounted visual displays.

OBJECTIVE: We provide a review and analysis of much of the published literature on visual perception issues that impact the design and use of head-mounted displays (HMDs). BACKGROUND: Unlike the previous literature on HMDs, this review draws heavily from the basic vision literature in order to help provide insight for future design solutions for HMDs. METHOD: Included in this review are articles and books found cited in other works as well as articles and books obtained from an Internet search. RESULTS: Issues discussed include the effect of brightness and contrast on depth of field, dark focus, dark vergence, and perceptual constancy; the effect of accommodation-vergence synergy on perceptual constancy, eyestrain, and discomfort; the relationship of field of view to the functioning of different visual pathways and the types of visual-motor tasks mediated by them; the relationship of binocular input to visual suppression; and the importance of head movements, head tracking, and display update lag. CONCLUSION: This paper offers a set of recommendations for the design and use of HMDs. APPLICATION: Consideration of the basic vision literature will provide insight for future design solutions for HMDs.

Computer Terminals↗
PubMed2006

Active heading control in simulated flight based on vertically extended contours.

In two experiments, we manipulated the properties of 3-D objects and terrain texture in order to investigate their effects on active heading control during simulated flight. Simulated crosswinds were used to introduce a rotational component into the retinal flow field that presumably provided the visual cues used for heading control An active control task was used so that the results could be generalized to real-world applications such as flight simulation. In Experiment 1, we examined the effects of three types of terrain, each of which was presented with and without 3-D objects (trees), and found that the presence of 3-D objects was more important than terrain texture for precise heading control In Experiment 2, we investigated the effects of varying the height and density of 3-D objects and found that increasing 3-D object density improved heading control, but that 3-D object height had only a small effect. On the basis of these results, we conclude that the vertical contours improved active heading control by enhancing the motion parallax information contained in the retinal flow.

Adult↗
PubMed2005

Selective attention and cyclopean motion processing.

The effect of diverted selective attention on the induction of the cyclopean motion aftereffect (aftereffect induced from dynamic disparity information) was investigated. The luminance motion aftereffect was examined for comparison. During diverted-attention trials, observers ignored background adapting motion and performed a low-load or high-load rapid serial visual presentation (RSVP) task presented in the center of the motion display. Baseline motion aftereffects were obtained with no diverted attention. The results showed that the cyclopean motion aftereffect, similar to the luminance motion aftereffect, declined only modestly under diverted-attention conditions. Selective attention appears to play a modest role in the visual processing of cyclopean motion.

Adaptation, Ocular↗
PubMed2005

Monitoring lung edema using the pacemaker pulse and skin electrodes.

Previous clinical studies have shown that impedance measurements using right ventricular (RV) leads can monitor congestion due to heart failure. We previously reported on a three-fold advantage of bipolar left ventricular (LV) leads, which are near the lung, over RV leads in detecting pulmonary edema with impedance. A combined system of internal and external electrodes is now investigated using computer models, for use with conventional cardiac resynchronization (CRT) systems with unipolar LV leads. The system uses the normal LV pacing pulse as current source, and the resultant voltage at two skin electrodes to obtain a lung edema impedance (Z) measurement. Using gated MRIs, thoracic computer models of 3.8 million control volumes were constructed. Changes of Z with edema were simulated with a conventional totally implanted system, as well as with combined implanted-external systems. Right atrial (RA), RV, RV defibrillator coil and LV leads were used. Per cent Z responses to edema were compared. The all implanted responses were RA: 11.8%, RV: 8.6%, RVcoil: 11.3%, LV: 23.8%. The combined system responses were LV-ext: 21.45%, RA-ext: 10.13%, LV-arm leg: 26.08%. The computer models suggest that combined internal-external systems can be as sensitive as the totally implanted ones. Lung edema may be monitored at follow up or home for LV paced patients with only two external electrodes. Using very low impedance configurations optimized by computer can greatly maximize the response, with a cost of poor stability.

Body Constitution↗
PubMed2005

Assessing compliance with 60-hertz magnetic-field exposure guidelines.

Exposure limits for magnetic fields in the extremely low frequency range (3 to 3000 hertz) have been established by a number of organizations. The limits are generally intended to prevent overstimulation of electrically sensitive tissue and are expressed as ceiling values-levels not to be exceeded even momentarily. Exposures near or above the limits occur around high-current equipment and often have large spatial and temporal variability. The combination of variable exposures and ceiling-value exposure limits means that a practical exposure assessment must be statistically based. Practical guidance for assessing compliance for these exposures is limited. To fill this gap, this work develops a statistically based sampling and analysis methodology for evaluating compliance with magnetic-field exposure guidelines, using 60-hertz exposures in the electric utility industry as a model. The resulting methodology relies on (1) defining a scenario that includes tasks with similar high-field exposures for a group of workers, (2) having appropriate protocols for performing magnetic-field personal exposure measurements or having an exposure data set corresponding to that scenario, (3) assuming that the measured peak field is consistent with the exposure limit, (4) assuming that the peak exposure values follow a lognormal distribution, and (5) collecting sufficient measurements to determine the probability of compliance with a desired degree of statistical confidence. As examples, specific compliance probabilities and their confidence intervals are estimated for electric utility scenarios from available personal exposure measurements. This specific application demonstrates the general methodology and indicates that compliance with existing exposure limits may become an issue for certain tasks.

Electric Power Supplies↗
PubMed2004

Determinants of radial artery pulse wave analysis in asymptomatic individuals.

BACKGROUND: Noninvasive techniques to evaluate arterial stiffness include noninvasive radial artery pulse contour analysis. Diastolic pulse contour analysis provides a separate assessment of large (C1) and small artery (C2) elasticity. Analysis of the systolic pulse contour identifies two pressure peaks (P1 and P2) that relate to incident and reflected waves. This study aimed to compare indices from systolic and diastolic pulse contour analysis from the radial pressure waveform and to correlate these indices with traditional risk factors in asymptomatic individuals screened for cardiovascular disease. METHODS: In 298 consecutive subjects (206 male and 92 female healthy subjects with a mean age of 50 +/- 12 years), noninvasive radial artery pressure waveforms were acquired with a piezoelectric transducer and analyzed for 1) diastolic indices of C1 and C2 from the CR-2000 CVProfiler, and 2) systolic indices of augmentation as defined by augmentation pressure (AP), augmentation index (AIx), and systolic reflective index (SRI = P2/P1). These indices were then correlated to each other as well as to individual traditional risk factors and the Framingham Risk Score. RESULTS: Diastolic indices were significantly and inversely correlated to systolic indices with C2 showing a stronger inverse association than C1. C2 and Alx were significantly correlated with height, weight, and body mass index in men but not in women. All indices correlated better to blood pressure in women than men. In women, only systolic indices were significantly correlated to HDL cholesterol and only diastolic indices were significantly correlated to LDL cholesterol. All indices were significantly correlated to the Framingham Risk Score, which was stronger in women then men, but when adjusted for age only diastolic indices remained significant in women. CONCLUSIONS: Diastolic and systolic indices of pulse contour analysis correlate differently with traditional risk factors in men and women.

Adult↗
PubMed2004

The effect of a computerized reminder system on the prevention of postoperative venous thromboembolism.

STUDY OBJECTIVE: To measure the effect of an altered process of care, directed by a computerized reminder system, on rates of symptomatic postoperative venous thromboembolism. DESIGN: Comparisons of preintervention and postintervention measurements. SETTING: A university-affiliated community hospital in Utah. PATIENTS: Two-thousand seventy-seven consecutive patients who underwent major operations in four surgical divisions between January 1, 1997, and October 31, 1997 (preintervention), and 2,093 consecutive patients who underwent the same procedures between January 1, 1998, and October 31,1998 (postintervention). INTERVENTION: A program to prevent venous thromboembolism developed from American College of Chest Physicians guidelines, and an altered work process directed by a computerized reminder system. MEASUREMENTS: Rates of symptomatic, objectively confirmed deep vein thrombosis (DVT), pulmonary embolism (PE), and death attributable to venous thromboembolism occurring within 90 days of the date of surgery. RESULTS: The preintervention and postintervention cohorts did not differ with respect to age, severity of illness, number of risk factors for venous thromboembolism, or individual risk factors for venous thromboembolism. The overall prophylaxis rate increased from 89.9% before implementation of the computerized reminder system to 95.0% after implementation (p < 0.0001). The combined 90-day rate of symptomatic DVT, PE, and death attributable to PE remained the same (preintervention, 1.0%; postintervention, 1.2%; odds ratio, 1.21; 95% confidence interval, 0.67 to 2.20). Forty of 46 venous thromboembolic complications (87%) occurred despite the delivery of American College of Chest Physicians-recommended measures to prevent venous thromboembolism. CONCLUSIONS: Computerized reminder systems combined with altered care procedures increase the rate of prophylaxis against venous thromboembolism without decreasing the rate of symptomatic venous thromboembolism when the baseline rate of prophylaxis is high. A population of surgical patients exists who are resistant to American College of Chest Physicians-recommended prophylactic measures against venous thromboembolism. New strategies are needed to address prophylaxis-resistant venous thromboembolism.

Aged↗
PubMed2003

Feasibility and effects of transcutaneous phrenic nerve stimulation combined with an inspiratory impedance threshold in a pig model of hemorrhagic shock.

OBJECTIVE: Intrathoracic pressure changes are of particular importance under hypovolemic conditions, especially when central venous blood pressure is critically low. Accordingly, the purpose of this study was to assess the feasibility of transcutaneous phrenic nerve stimulation, used in conjunction with an inspiratory impedance threshold, on hemodynamic variables during hemorrhagic shock. DESIGN: Prospective, randomized laboratory investigation using a porcine model for measurement of hemodynamic variables, left and right ventricular diameter, and transmitral, transpulmonary, and transaortic blood flow employing transesophageal echo-Doppler technique. SETTING: University hospital laboratory. SUBJECTS: Thirteen female pigs weighing 28-36 kg. INTERVENTIONS: The anesthetized pigs were subjected to profound hemorrhagic shock by withdrawal of 55% of estimated blood volume over 20 mins. After a 10-min recovery period, the diaphragm was stimulated with a prototype transcutaneous phrenic nerve stimulator at a rate of ten per minute while the airway was intermittently occluded with an inspiratory threshold valve between positive pressure ventilations. Hemodynamic variables were monitored for 30 mins. MEASUREMENTS AND MAIN RESULTS: Phrenic nerve stimulation in combination with the inspiratory threshold valve significantly (p <.001) improved right and left ventricular diameter compared with hypovolemic shock values by 34 +/- 2.5% and 20 +/- 2.5%, respectively. Moreover, phrenic nerve stimulation together with the inspiratory threshold valve also increased transaortic, transpulmonary, and transmitral valve blood flow by 48 +/- 6.6%, 67 +/- 13.3, and 43 +/- 8.2%, respectively (p <.001 for comparisons within group). Mean +/- sem coronary perfusion and systolic aortic blood pressures were also significantly (p <.001) higher compared with values before stimulation (30 +/- 2 vs. 20 +/- 2 mm Hg, and 37 +/- 2 vs. 32 +/- 3 mm Hg, respectively). CONCLUSIONS: This feasibility study suggests that phrenic nerve stimulation with the inspiratory threshold valve may improve cardiac preload and, subsequently, key hemodynamic variables in porcine model of severe hemorrhagic shock.

Animals↗
PubMed2002

Three-systems theory of human visual motion perception: review and update: comment.

This comment addresses two issues raised by Lu and Sperling [J. Opt. Soc. Am. A 18, 2331 (2001)]. These authors stated that stereomotion (movement of binocular disparity) is processed exclusively by a third-order motion system that involves feature tracking. This comment discusses evidence that clearly shows that stereomotion is processed by a low-level mechanism that does not track features. Lu and Sperling also claimed that motion signals from binocular rivalry have confounded many stereomotion experiments in the past. This comment discusses how stimuli employed in most previous studies of stereomotion processing would not produce rivalry.

Depth Perception↗