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PubMed1994

Tracking of small objects in front of a textured background by insects and vertebrates: phenomena and neuronal basis.

To follow visually a small object moving in front of a textured background, insects and vertebrates can employ a similar strategy: saccadic tracking. In the case of vertebrates, the neural components that generate this behavior are not known in detail. The neural substrate of optomotor behavior in Diptera is relatively well understood. Here a model developed from the dipteran data is found to be capable of saccadic tracking. It is characterized by the following components and functions: (1) Two subsystems contribute to the response, a small-field tracking system and a large-field compensatory optomotor system, as suggested previously (Egelhaaf et al. 1988). (2) Both systems need to be suppressed during saccadic rotation. In the small-field system, the suppression, close to the visual input, is mediated by the activity of the large-field system. In the large-field system, suppression, close to the motor output, is due to efferent signals from the saccade generator. A similar model could also apply to vertebrates. Two implications of the present model are that saccadic tracking does not require object identification, and under saccadic tracking it is the background rather than the object that is stabilized on the retina. If objects are identified under these conditions, this must occur even though their image is not stabilized on the retina.

Animals↗
PubMed1991

Self-monitored exercise at three different RPE intensities in treadmill vs field running.

The aims of the present study were a) to compare the outcome of running exercise performed on a treadmill (laboratory) and an outdoor track (field) using an RPE production protocol and b) to study this kind of protocol used over time (3-5 wk). A group of 11 healthy male subjects participated, with ages varying from 33 to 65 yr (mean = 42.9 +/- 11.0 yr). Two test sessions consisting of both treadmill and track exercise were performed in a rotated order to control for sequential effects. All subjects exercised according to an identical protocol: two successive trials (3 min each) at RPE 11 (light exertion), followed by a RPE 13 (somewhat hard) trial (11 min) and, finally, a RPE 15 (hard) trial (5 min). Results show significantly different levels of heart rate (HR), blood lactate, and velocity at the three RPE levels. Large differences were also observed in all measured variables between field and laboratory. These differences were consistent over time. A high internal consistency, measured by test-retest reliability (alpha greater than 0.9), was obtained for both velocity and HR between the first two trials at RPE 11. In conclusion, the RPE method functioned well as a means of monitoring and regulating exercise intensity.

Adult↗
PubMedDate not supplied

Automatic eye tracker for excimer laser photorefractive keratectomy.

Acute overlapping of successive laser pulses onto the cornea during photorefractive keratectomy (PRK) is important to avoid refractive distortions. Most excimer laser systems performing corneal ablation lack control of the patient's eye movements and they cannot track the target corneal zone. We developed an eye-tracker based on television monitoring of the pupil and on automatic electro-mechanical deflection of the laser turning mirror, and we applied it to the ExciMed UV200 ArF work station (Summit Technology, Inc., Waltham, Mass.). Basic components are a black and white CCD camera and two fast stepping motors. The circuitry for target discrimination and tracking, and the optical imaging system are designed specifically. The tracker assembly does not interfere with the laser beam path nor with the operator's observation. Tracking of the pupil has been successfully achieved on different color irides, with an accuracy better than 0.1 mm in a 6 x 6 mm2 tracking field. Response time is less than 100 ms. Recordings of eye movements during PRK are presented. Tracking ablations have been performed on moving test eye-balls with plastic corneas. The proposed automatic system appears to be a reliable and effective method for the compensation of patient eye movements appears to be a reliable and effective method during PRK procedures.

Cornea↗
PubMed1991

The interaction of hand vibration with oculomanual coordination in pursuit tracking.

The effects of high frequency hand vibration (150 Hz) on simultaneous ocular and manual tracking performances were investigated in trained human subjects. First, a zero-order pursuit tracking task was performed with and without direct visual control of the hand. Second, eye tracking of an imaginary target linked to the hand was also performed. The results show that hand vibration significantly alters eye and hand tracking performances when the hand is out of sight. However, when the hand is placed in the visual field, tracking performances are less affected by vibration. Visual cues on limb segments may compensate to some extent for the vibration-induced alteration of proprioceptive information otherwise used to control movements. Eye movements are altered during vibration while the subject is tracking or fixating an imaginary target attached to the hand. These findings explicitly show that hand vibration can perturb oculo-manual coordination control. The present results imply that vibration-induced activity of somesthetic mechanoreceptors is likely to contribute to oculomanual coordination alteration and tracking decrement in vibratory environments. Furthermore, direct visual control of the hand and/or arm may be of particular interest in manipulation tasks executed under vibration.

Adult↗
PubMed1994

Manipulating the shape of distance effects in visual curve tracing: further evidence for the zoom lens model.

The time required to determine that two dots occur on the same curve in a visual display increases with increasing interdot curve distance. McCormick and Jolicoeur (1991) presented a model of visual curve tracing in which a local operator with a variable size receptive field tracks the curve segment intervening the two dots. In this model, human response time can be predicted by counting the number of shifts of the receptive field needed to trace the curve segment. The present study re-examined the predictive power of the zoom lens curve tracing model by selectively manipulating distractor proximity in four conditions and regressing the predictions of the model on human response time. The model was compared with two other curve tracing models, pixel by pixel tracing, and Jolicoeur, Ullman and MacKay's (1991) bipartite receptive field operator. The results provided strong support for McCormick and Jolicoeur's (1991) visual attention based zoom lens operator.

Adult↗
PubMedDate not supplied

A comparison of in situ methods for measuring net nitrogen mineralization rates of organic soil amendments.

In situ incubation methods may help provide site-specific estimates of N mineralization from land-applied wastes. However, there are concerns about the reliability of the data generated by the various methods due to containment artifacts. We amended a sandy soil with either poultry manure, biosolids, or yard-waste compost and incubated the mixtures using four in situ methods (buried bags, covered cylinders, standard resin traps, and "new" soil-resin traps) and a conventional laboratory technique in plastic bags. Each incubation device was destructively sampled at 45-d intervals for 180 d and net N mineralization was determined by measuring the amount of inorganic N that accumulated in the soil or soil plus resin traps. Containment effects were evaluated by comparing water content of the containerized soil to a field-reference soil column. In situ incubation methods provided reasonable estimates of short-term (< 45 d) N mineralization, but long-term (> 45 d) mineralization data were not accurate due to a variety of problems specific to each technique. Buried bags and covered cylinders did not retain mineralized N due to water movement into and out of the containers. Neither resin method captured all of the mineralized N that leached through the soil columns, but the new soil-resin trap method tracked field soil water content better than all other in situ methods evaluated. With further refinement and validation, the new soil-resin trap method may be a useful in situ incubation technique for measuring net N mineralization rates of organic soil amendments.

Animals↗
PubMed2001

Myocardial tracking, a new method to calculate ejection fraction with gated SPECT: validation with (201)Tl versus planar angiography.

UNLABELLED: Left ventricular ejection fraction (LVEF) and viability are essential variables for the prognosis of myocardial infarction and can be measured simultaneously by (201)Tl gated SPECT; however, most algorithms tend to underestimate LVEF. This study aimed to evaluate a new myocardial tracking algorithm, MyoTrack (MTK), for automatic LVEF calculation. METHODS: A rest/redistribution (20 min/4 h) (201)Tl gated SPECT protocol followed immediately by a (99m)Tc equilibrium radionuclide angiography (ERNA) was performed in 75 patients with history of myocardial infarction. Quality of myocardial uptake was evaluated from count statistics and automatic quantification of defect sizes and severities (CardioMatch). LVEFs were calculated both with Germano's quantitative gated SPECT (QGS) algorithm and with MTK. Briefly, the originality of this algorithm resides in the unique end-diastole segmentation, matching to a template and motion field tracking throughout the cardiac cycle. RESULTS: ERNA LVEF averaged 33% +/- 14%. QGS significantly underestimated this value at 20 min (30% +/- 13%, P < 0.001) and at 4 h (30% +/- 13%, P < 0.0001). By contrast, MTK did not miscalculate LVEF at 20 min (34% +/- 14%, probability value was not significant) though a similar underestimation occurred at 4 h (31% +/- 13%, P < 0.02). Individual differences between early and late gated SPECT values and differences between gated SPECT and ERNA values did not correlate with the extension of perfusion defects, count statistics, or heart rate. CONCLUSION: MTK algorithm accurately calculates LVEF on early/high-count images compared with ERNA [corrected], even in patients with severe perfusion defects, but tends to underestimate LVEF on delayed/low-contrast images, as other algorithms do.

Adult↗
PubMed2006

Feasibility of tracking within-field movements of Homalodisca coagulata (Hemiptera: Cicadellidae) and estimating its densities using fluorescent dusts in mark-release-recapture experiments.

A mark-release-recapture technique was developed and tested for use in tracking the field movements of adult glassy-winged sharpshooters, Homalodisca coagulata (Say) (Hemiptera: Cicadellidae), in various agricultural and urban plantings. Greenhouse experiments in which adult H. coagulata were marked with one of five colored fluorescent dusts (Aurora Pink-All, Horizon Blue-A19, Blaze Orange-A15N, Saturn Yellow-A17, and Corona Magenta-A21) and released into cages with citrus seedlings showed that their mortality rates during a 30-d period were statistically similar to that of the undusted controls. Adults marked with a sixth dust color (Signal Green-A18N) suffered higher rates of mortality than did the undusted controls and thus were eliminated from further consideration. Adult H. coagulata marked with one of the five accepted colors of fluorescent dust were able to fly beyond 100 m in a field devoid of vegetation within minutes of their release, and the marking did not affect overall flight behavior significantly compared with that of the undusted controls. However, at wind speeds above 5 m/s, percentage recapture was significantly reduced, which indicates that both dusted and undusted adults were unable to orient their flight. In total, 41,124 marked and unmarked adults were released in the three field experiments in southern California (Riverside and Kern counties) during 2000 and 2001 to evaluate flight dispersal and estimate densities of H. coagulata. The mark-release-recapture and feral data obtained during the June, July, and August 2001 studies, when coupled with the Lincoln index, yielded estimates of adult H. coagulata of 1.2 and 2.2 million per ha, respectively, at a San Joaquin Valley (Kern Co.) and a southern California (Riverside Co.) citrus grove. The use of colored dusts to mark H. coagulata proved to be reliable, cost-effective, and time-efficient for mark-release-recapture studies with this insect within a citrus grove, but they are less likely to be useful for studies of adult H. coagulata movements among plantings.

Animals↗
PubMed1991

Magnetic field changes associated with caloric stimulation of the human vestibular organ.

Caloric stimulation of the ear produces a shift of the vestibular resting potential. The current produced by the change in this potential produces a corresponding change in the associated magnetic field. A sensitive magnetic detector (second-derivative gradiometer) was used to detect a large shift in the magnetic field close to the ears of two normal subjects who underwent cold thermic ear stimulation. The shift in the magnetic field tracked the reflex responses in both individuals. This technique could offer a noninvasive direct measure of end-organ function.

Caloric Tests↗
PubMed2006

Physical and psychological functioning of daily living in relation to physical activity. A longitudinal study among former elite male athletes and controls.

BACKGROUND AND AIMS: Physical exercise plays an important role in the prevention and reduction of disabilities in elderly people. The aim of this study was to determine the role of physical activity in the physical and psychological functioning of daily living in a cohort of former elite male athletes representing different sports, and controls of middle and old age. METHODS: Subjects were 664 former elite male athletes (mean age 64.4 years) and 500 controls (62.0 years) in middle and old age. Subjects were mailed "Physical activity and health survey" questionnaires in 1985 and 1995. The primary outcomes the physical and psychological functioning of daily living--were assessed in 1995 using items from the Mini-Finland Health Survey. Logistic regression was used for longitudinal as well as cross-sectional analyses to estimate odds ratios (OR) for poor physical and psychological functioning of daily living in relation to recreational physical activity adjusted for age, sport group, life-style, BMI, mood, chronic diseases, personality characteristics, life-events and socio-economic status. RESULTS: In the longitudinal analysis, low levels of physical activity (lowest MET quintile vs highest quintile) in 1985 (OR 4.91, 95% confidence interval (CI) 2.02-11.9), older age (> or =70 yrs vs under 60 yrs OR 9.93, 95% CI 4.90-20.2), depression (OR 2.03, 95% CI 1.01-4.09) and anxiety in 1995 (OR 2.67, 95% CI 1.34-5.32) increased the risk of poor physical functioning of daily living in 1995, whereas an increase in a physical activity between 1985-1995 (OR 0.89, 95% CI 0.83-0.95) protected against poor physical functioning of daily living. A history of participating in specific types of sports, especially among certain power sports (weight-lifting and track & field throwers) (OR 0.19, 95% CI 0.06-0.60) and team sports (OR 0.34, 95% CI 0.15-0.81) did reveal a significant protective effect against poor psychological functioning of daily living in the longitudinal analysis. CONCLUSIONS: This study suggests that an increase in physical exercise supports physical daily functionality. A specific history of sports participation promotes psychological well-being at an older age.

Activities of Daily Living↗
PubMed1998

Forming independent components via temporal locking of reconstruction architectures: a functional model of the hippocampus.

The assumption is made that the formulation of relations as independent components (IC) is a main feature of computations accomplished by the brain. Further, it is assumed that memory traces made of non-orthonormal ICs make use of feedback architectures to form internal representations. Feedback then leads to delays, and delays in cortical processing form an obstacle to this relational processing. The problem of delay compensation is formulated as a speed-field tracking task and is solved by a novel control architecture. It is shown that in addition to delay compensation the control architecture can also shape long-term memories to hold independent components if a two-phase operation mode is assumed. Features such as a trisynaptic loop and a recurrent collateral structure at the second stage of that loop emerge in a natural fashion. Based on these properties a functional model of the hippocampal loop is constructed.

Animals↗
PubMed1999

Field exercise testing for assessing fitness in French standardbred trotters.

This review considers standardized exercise testing which is, routinely used for French Trotters in the field. Track testing provides a more limited range of measurements than treadmill testing, but has the advantage of being performed in the horse's natural environment. Various measurements such as heart rate during exercise and blood lactate concentration after exercise may be measured on the track and lead to the calculation of physiological variables such as V200 (velocity corresponding to a 200 bpm heart rate) and V4 (velocity corresponding to a 4 mmol/L blood lactate concentration). V4 is related to the onset of blood lactate accumulation and relates to the aerobic capacity of the horse, as horses with high values for V4 have higher aerobic capacities. Although V4 is calculated during submaximal intensity exercise, it is related to racing performance and seems to be the most important measurement to assess changes in fitness. V200 represents the cardiac capacity of the horse during exercise and is close to V4 in mature horses. To explain further the clinical usefulness of track testing, and to help interpret both V4 and V200 variables, examples of exercise tests in 3-year-old French Trotters are presented here. These results show that changes may occur in V4 and V200 according to different factors such as the horse's physical ability and either training or disease states. It underlines the importance of exercise tests for both trainers and veterinarians and how they may help in the evaluation of a horse's performance ability; in defining the intensity of a training program, and also in the early detection of underlying diseases.

Animals↗
PubMed2003

Antiretroviral therapy and declining AIDS mortality in New York City.

OBJECTIVE: This study estimates the impact of Highly Active Antiretroviral Therapy (HAART) and other antiretroviral therapy combinations on reducing mortality risk for a cohort of HIV-infected persons living in New York City. MATERIALS AND METHODS: Data for this study come from the CHAIN project, an ongoing multiwave longitudinal study of HIV-infected persons is living in New York City (n = 700) initiated in 1994. The study sample is drawn from the clients of 43 medical and social service agencies and is broadly representative of New York City residents, who were aware of their positive serostatus at time of enrollment. Occurrences of deaths were obtained through routine field tracking and searches of death certificates and an online death registry. Information on other study variables was obtained through in-person interviews. A Cox proportional hazard model was applied to estimate the effects of medication on mortality risk. RESULTS: Mortality rates for the CHAIN cohort dropped steadily from a high of 131 deaths per 1000 persons/year in 1995 to 31 deaths per 1000 persons/year in 1999, with the historically low mortality rates continuing through 2000. Current use of HAART was associated with a 50% reduction in mortality risk (hazard ratio = 0.51, P <0.01). CONCLUSIONS: These results demonstrate that in the case of HAART, the therapeutic benefits of an innovative but costly medical treatment are reaching populations that traditionally have poor access to quality health care.

Acquired Immunodeficiency Syndrome↗
PubMed2001

Ockham's razor modeling of the matrisome channels of the basal ganglia thalamocortical loops.

A functional model of the basal ganglia-thalamocortical (BTC) loops is described. In our modeling effort, we try to minimize the complexity of our starting hypotheses. For that reason, we call this type of modeling Ockham's razor modeling. We have the additional constraint that the starting assumptions should not contradict experimental findings about the brain. First assumption: The brain lacks direct representation of paths but represents directions (called speed fields in control theory). Then control should be concerned with speed-field tracking (SFT). Second assumption: Control signals are delivered upon differencing in competing parallel channels of the BTC loops. This is modeled by extending SFT with differencing that gives rise to the robust Static and Dynamic State (SDS) feedback-controlling scheme. Third assumption: Control signals are expressed in terms of a gelatinous medium surrounding the limbs. This is modeled by expressing parameters of motion in parameters of the external space. We show that corollaries of the model fit properties of the BTC loops. The SDS provides proper identification of motion related neuronal groups of the putamen. Local minima arise during the controlling process that works in external space. The model explains the presence of parallel channels as the means to avoiding such local minima. Stability conditions of the SDS predict that the initial phase of learning is mostly concerned with selection of sign for the inverse dynamics. The model provides a scalable controller. State description in external space instead of configurational space reduces the dimensionality problem. Falsifying experiment is suggested. Computer experiments demonstrate the feasibility of the approach. We argue that the resulting scheme has a straightforward connectionist representation exhibiting population coding and Hebbian learning properties.

Basal Ganglia↗
PubMed1997

Static and dynamic state feedback control model of basal ganglia-thalamocortical loops.

It is argued that a novel control architecture, the Static and Dynamic State (SDS) feedback scheme, which utilizes speed-field tracking, exhibits global stability, and allows on-line tuning by any adaptation mechanism without canceling stability if certain structural conditions are met, can be viewed as a model of basal ganglia-thalamocortical loops since (1) the SDS scheme predicts the neuronal groups that fit neuronal classification in the supplementary motor area, the motor cortex and the putamen, (2) the structural stability conditions require parallel channels, a feature that these loops provide, and (3) the SDS scheme predicts two major disorders that can be identified as Parkinson's and Huntington's diseases. Simulations suggests that the basal ganglia work outside the realm of the stability condition allowed by the robustness of the scheme and required for increased computation speeds.

Basal Ganglia↗
PubMed1999

Results after cheilectomy in athletes with hallux rigidus.

From 1987 to 1993, 20 athletes (22 feet) underwent cheilectomy for Regnauld grade I, grade II hallux rigidus. Average age was 31 years (10 men and 12 women); mean follow-up was at 5.1 years. All patients performed high-level sports (judo, track & field, soccer, and skating). Indications for surgery included failure of nonsurgical treatment with persistent pain during sports activities, shoefitting problems, and recurrent bursitis. The aim of our study was to evaluate the results clinically, radiographically, and objectively, using dynamic and static pedodynographic measurements. After a mean follow-up of 5 years, cheilectomy was demonstrated to be a reliable treatment method in athletes with Regnauld grades 1 and 2 hallux rigidus. Functionally, 14 excellent, seven good, and one fair result were noted. Radiological progression was noted in 7 of 13 patients, with a follow-up of >4 years. Postoperative dynamic pedodynographic findings demonstrated moderate but significant changes in peak pressures under the first metatarsal head, the hallux, and in the center of pressure distribution under the forefoot.

Adult↗
PubMed1990

Glenohumeral elevation studied in three dimensions.

We studied the position and rotational changes associated with elevation of the glenohumeral joint, using a three-dimensional magnetic-field tracking system on nine fresh cadaveric shoulders. The plane of maximal arm elevation was shown to occur 23 degrees anterior to the plane of the scapula. Elevation in any plane anterior to the scapula required external humeral rotation, and maximal elevation was associated with approximately 35 degrees of external humeral rotation. Conversely, internal rotation was necessary for increased elevation posterior to the plane of the scapula. The observed effects of this rotation were to clear the humeral tuberosity from abutting beneath the acromion and to relax the inferior capsular ligamentous constraints. Measurement of the obligatory humeral rotation required for maximal elevation helps to explain the relationship of the limited elevation seen in adhesive capsulitis and after operations which limit external rotation.

Biomechanical Phenomena↗
PubMed1998

Cardiorespiratory adaptations induced by aerobic training in middle-aged men: the importance of a decrease in sympathetic stimulation for the contribution of dynamic exercise tachycardia.

We investigated the effects of aerobic training on the efferent autonomic control of heart rate (HR) during dynamic exercise in middle-aged men, eight of whom underwent exercise training (T) while the other seven continued their sedentary (S) life style. The training was conducted over 10 months (three 1-h/sessions/week on a field track at 70-85% of the peak HR). The contribution of sympathetic and para-sympathetic exercise tachycardia was determined in terms of differences in the time constant effects on the HR response obtained using a discontinuous protocol (4-min tests at 25, 50, 100 and 125 watts on a cycle ergometer), and a continuous protocol (25 watts/min until exhaustion) allowed the quantification of the parameters (anaerobic threshold, VO2 AT; peak O2 uptake, VO2 peak; power peak) that reflect oxygen transport. The results obtained for the S and the T groups were: 1) a smaller resting HR in T (66 beats/min) when compared to S (84 beats/min); 2) during exercise, a small increase in the fast tachycardia (delta 0-10 s) related to vagal withdrawal (P < 0.05, only at 25 watts) was observed in T at all powers; at middle and higher powers a significant decrease (P < 0.05 at 50, 100 and 125 watts) in the slow tachycardia (delta 1-4 min) related to a sympathetic-dependent mechanism was observed in T; 3) the VO2 AT (S = 1.06 and T = 1.33 l/min) and VO2 peak (S = 1.97 and T = 2.47 l/min) were higher in T (P < 0.05). These results demonstrate that aerobic training can induce significant physiological adaptations in middle-aged men, mainly expressed as a decrease in the sympathetic effects on heart rate associated with an increase in oxygen transport during dynamic exercise.

Adaptation, Physiological↗