SEARCH · PubMed Health

Results for “visual feedback”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,027 records · Page 57Linked to original sources

PubMed2002

Virtual-reality techniques resolve the visual cues used by fruit flies to evaluate object distances.

Insects can estimate distance or time-to-contact of surrounding objects from locomotion-induced changes in their retinal position and/or size. Freely walking fruit flies (Drosophila melanogaster) use the received mixture of different distance cues to select the nearest objects for subsequent visits. Conventional methods of behavioral analysis fail to elucidate the underlying data extraction. Here we demonstrate first comprehensive solutions of this problem by substituting virtual for real objects; a tracker-controlled 360 degrees panorama converts a fruit fly's changing coordinates into object illusions that require the perception of specific cues to appear at preselected distances up to infinity. An application reveals the following: (1) en-route sampling of retinal-image changes accounts for distance discrimination within a surprising range of at least 8-80 body lengths (20-200 mm). Stereopsis and peering are not involved. (2) Distance from image translation in the expected direction (motion parallax) outweighs distance from image expansion, which accounts for impact-avoiding flight reactions to looming objects. (3) The ability to discriminate distances is robust to artificially delayed updating of image translation. Fruit flies appear to interrelate self-motion and its visual feedback within a surprisingly long time window of about 2 s. The comparative distance inspection practiced in the small fruit fly deserves utilization in self-moving robots.

Animals↗

PubMed2001

Median frequency of the electromyographic signal: effect of time-window location on brief step contractions.

The purpose of this study was to determine, for different back muscles, if the median frequency (MF) of the electromyographic (EMG) power spectrum changes according to the position of the time window during a 5 s step contraction. Twenty males with no known back problems were standing upright in a dynamometer allowing lower limb and pelvis stabilization. Trunk extension efforts were performed by pushing on a force platform positioned at the T4 level while the extension moment at L5/S1 was displayed as visual feedback. The EMG signals from four homologous back muscles (multifidus at L5, ilicostalis lumborum at L3, and longissimus at L1 and T10) were collected using active surface electrodes during two 5 s static step contractions performed at five force levels (10, 20, 40, 60 and 80% of the maximal voluntary contraction). The root mean square (RMS) and MF values of the EMG signals corresponding to three 250 ms time windows (beginning, middle and end of each step contraction) were computed. The RMS values of several back muscles increased from the first to the third time window for contractions performed at high force levels only. However, a concomitant decrease in the MF values was observed only for the left multifidus muscle. It was concluded that muscle fatigue does not generally manifest itself during 5 s step contractions through the EMG signal. However, it is recommended to use step contractions lasting less than 5 s and to choose a time window located in the first 1-3 s to completely eliminate the possible effects of fatigue.

Adult↗

PubMed2001

Spectral profile of superficial cervical muscles.

The objective of the study was to determine the median frequency (MF) and mean power frequency (MPF) of the stermodeidomastorial, splenius capitis and trapezius in progressively and linearly increasing isometric cervical flexion and extension. There is a dearth of data on spectral parameters of cervical muscles. Such data have been generated from 40 young adult subjects (21 male and 19 female). The subjects were seated upright in an individually adjusted chair and stabilized with a 4-point Velcro restraint system to stabilize the torso. These subjects exerted isometric flexor and extensor forces in a random sequence on an instrumented resistance device (specifically designed for the study) in a gradual and linearly increasing manner with a visual feedback to their maximal voluntary contraction (MVC) within a 5 s period. Surface EMG was sampled from the sternocleidomastoid, the splenius capitis and the trapezius muscles bilaterally at 1 kHz. The EMG signals were subjected to Fast Fourier Transform (FFT) analysis. Spectral profiles of all muscles in the dimensions of frequency, power, and grade of contraction were plotted. The mean median frequency (MF), mean power frequency (MPF), peak power and total power were analyzed. In the sternocleidomastoid, and the splenius the MF increased with the grade of contraction, widening its bandwidth at higher grades. The trapezius maintained a narrow bandwidth and its MF declined with the grade of contraction.

Adult↗

PubMed1998

Consequences of trapezius relaxation on the distribution of shoulder muscle forces: an electromyographic study.

This study was focused on the ability to reduce voluntarily the muscle activity in the descending part of the trapezius muscle without changing the arm position or hand load, and its consequences on the distribution of shoulder muscle forces. Visual feedback techniques were used. Six different arm positions were investigated in 11 subjects. Electromyography was used for monitoring the muscle involvement. The selection of relevant muscles was performed by a model simulation of the shoulder using a newly developed biomechanical model of the human shoulder. The ability to reduce the muscle activity of the descending part of the trapezius was confirmed and the reduction ranged from 60 to 76% depending on the arm position. Among the muscles studied the rhomboid major and minor and the transverse part of the trapezius were affected the most, increasing their activity on the average to 232, 175 and 201% respectively, compared to the initial activity. The anterior part of the deltoid and the medial part of the serratus anterior also intensified their activity. The influence on the levator scapulae was, contrary to simulation results and to empirical knowledge, a decrease of the muscle activity. It is suggested that attention is given to the rhomboids and the transverse part of the trapezius when muscle activity is reduced in the descending part of the trapezius, for instance in biofeedback-based therapy. In conclusion, the study showed that reducing the trapezius activity caused a redistribution of muscle forces in the shoulder.

Adult↗

PubMed1999

Optical measurement of hematocrit and other biological constituents in renal therapy.

Optical sensors have advanced significantly over the past 2 decades leading to today's noninvasive optical measurement capabilities and their widespread applications in renal therapy. These measurements provide significant advantages to the clinician. For example, a given blood constituent can be monitored in real time (continuously, nondestructively), which facilitates the ability to optimally "titrate" the therapy with immediate visual feedback. Optical methods have another intrinsic advantage in that each biologic constituent has its own unique spectral "signature" allowing for simultaneous, multiple, and specific measurements of biologic analytes. Use of this budding spectral technology in renal therapy today provides for increased patient safety (by measuring plasma-free hemoglobin, microemboli, clots, oxygen saturation, blood leaks, and hematocrit), measurements of dialysis dose (dialysate urea levels), dry weight (tissue water monitoring), access viability (recirculation, access blood flow), cardiac status (absolute blood volume, cardiac output), and enhanced continuous fluid management (fluid overload, critical blood volume). As microelectronics and signal processing capabilities continue to advance, so will the future of optical diagnosis and treatment. These capabilities translate directly to improved patient quality of life.

Hematocrit↗

PubMed2000

Electropalatography and the Linguagraph system.

This paper describes the technique of electropalatography and the development of Linguagraph, which is a user-friendly, clinical instrument, for measurement of tongue/palate contact, during speech. Linguagraph allows objective assessment of tongue function; appropriate targeting of therapy is therefore possible. Visual feedback is also provided, for therapy, and an objective measurement of outcome is easily obtained. Linguagraph was used, for both therapy and assessment, in a clinical trial. Technical aspects of Linguagraph and of the trial results are presented here. These suggest that the instrument will prove useful in the assessment and management of many speech disorders. Full clinical details of the trial are reported elsewhere.

Adult↗

PubMed2000

Development of a lightweight and adaptable multiple-axis hand prosthesis.

The last few decades have produced significant improvements in the design of upper limb prostheses through the increasing use of technology. However the limited function exhibited by these devices remains rooted in their single degree of freedom format. Commercial myoelectric hand prostheses warrant high grip forces to ensure stable prehension due to a planar pincer movement. Hence precise and conscious effort is required on the part of the user to ensure optimum grip. Consumers have shown dissatisfaction with the status quo due to the excessive weight and poor function of existing artificial hands. Increasing the number of grasping patterns and improving the visual feedback from an object in the hand are cited as key objectives. This paper outlines the development of the six-axis Southampton-Remedi hand prosthesis that addresses these design issues by maintaining stable prehension with minimal grip force. Constraints such as modularity, anthropomorphism, and low weight and power consumption are factors that have been adhered to throughout the design process.

Artificial Limbs↗

PubMed1999

An instrument for the multiparameter assessment of speech.

This paper describes the development of SNORS+, a clinical, user-friendly instrument for measurement of the articulators during speech. The design criteria for the instrument were based upon a wide-ranging review of current practice and available techniques. SNORS+ allows objective assessment of the function and co-ordination of key articulators. Appropriate targeting of therapy is therefore possible. Visual feedback is provided, for therapy, and an objective measurement of outcome is easily obtained. Preliminary results are presented. These suggest that the instrument will prove extremely useful in the assessment and management of many speech disorders.

Adult↗

PubMed1998

Volumetric object modeling for surgical simulation.

Surgical simulation has many applications in medical education, surgical training, surgical planning and intra-operative assistance. However, extending current surface-based computer graphics methods to model phenomena such as the deformation, cutting, tearing or repairing of soft tissues poses significant challenges for real-time interactions. This paper discusses the use of volumetric methods for modeling complex anatomy and tissue interactions. New techniques are introduced that use volumetric methods for modeling soft-tissue deformation and tissue cutting at interactive rates. An initial prototype for simulating arthroscopic knee surgery is described which uses volumetric models of the knee derived from 3-D magnetic resonance imaging, visual feedback via real-time volume and polygon rendering, and haptic feedback provided by a force-feedback device.

Arthroscopy↗

PubMed2002

Time-dependent structure in the discharge rate of human motor units.

OBJECTIVES: The aim of this study was to examine the influence of visual and motor processes on the deterministic and stochastic structure of force output and motor unit discharge variability. METHODS: Young adult subjects produced continuous, isometric force at 3, 6, 12, and 24% of their maximal voluntary contraction at low and high visual gain levels through abduction of the index finger. Force and fine-wire intramuscular electromyography were recorded. RESULTS: There was a linear increase in discharge irregularity with increases in the mean motor unit discharge rate (8-30 Hz). Recurrence analysis showed that the percentage of deterministic structure in discharge variability remained high, but decreased linearly with increased motor unit discharge rate. Surrogate analyses confirmed that the motor unit discharge variability was inconsistent with an uncorrelated and linearly correlated Gaussian noise process. Spectral analysis revealed that both the force output and the mean time-varying motor unit discharge time series had a dominant frequency of 0-2 Hz. Visual feedback gain did not affect the individual motor unit discharge patterns. CONCLUSIONS: The motor unit discharge rate has deterministic time-dependent structure. The motor unit discharge rate is modulated at multiple time scales likely by pre- and post-synaptic induced fluctuations from spinal level pathways impinging on the motor neuron.

Action Potentials↗

PubMedDate not supplied

Power spectra of sternocleidomastoids, splenius capitis, and upper trapezius in oblique exertions.

BACKGROUND CONTEXT: There is relatively little known concerning the spectral profile of the cervical muscles, despite the fact that neck injury and pain are quite prevalent. PURPOSE: The objective of the study was to calculate and study the power spectral characteristics of the sternocleidomastoids, splenii capitis and upper trapezii in anterolateral flexion and posterolateral extension in a ramp contraction. STUDY DESIGN/SETTING: In a laboratory setting experiments were conducted to record surface electromyographic (EMG) data from six cervical muscles and power spectral variables obtained. PATIENT SAMPLE: Forty normal and healthy young adults (21 men, 19 women). OUTCOME MEASURES: Power spectral of EMG signals. METHODS: EMG data for the left and right isometric anterolateral flexion and posterolateral extension were acquired from the sternocleidomastoids, splenii capitis and upper trapezius bilaterally. The subjects were seated in an upright posture and exerted left and right anterolateral flexor and posterolateral extensor efforts from rest to their maximal voluntary contraction in a gradual linear ramp fashion using visual feedback as a guide. The force exerted and the surface EMG data were sampled at 1 kHz at every 10th percentile grade of contraction and the EMG data were subjected to the Fast-Fourier transform analysis. The median frequency (MF), mean power frequency (MPF), peak power and total power of all six cervical muscles were analyzed. RESULTS: In the anterolateral flexion the ipsilateral sternocleidomastoid and splenius capitis had a wider band of frequency, which further widened with increasing grade of contraction. The trapezius did not engage in the same manner or to the same magnitude. The MF of the sternocleidomastoid in the anterolateral flexion in both genders progressively increased, the splenius capitis remained relatively unchanged, and the upper trapezius declined with the increasing grades of contraction. CONCLUSIONS: There is no significant difference between the genders in spectral profile. There is a bilateral symmetry in spectral profile with reference to activity; however, they are significantly different in different activities for the same muscles. With increasing magnitude of contraction power, spectral density distribution increases and the median frequency decreases. These results can serve as a useful reference for painful necks. Restoration of power spectral characteristics may indicate normalcy, which cannot be gleaned by other EMG or force variables.

Adult↗

PubMed1988

Clinical application of electrolaryngograph for speech rehabilitation in near-total laryngectomy with myo-mucosal valved neoglottis.

Near-total laryngectomy with myomucosal valved neoglottis is the most recent of the various surgical procedures for speech rehabilitation. The electrolaryngographic wave form (Lx), which was recorded initially to explore the site and mechanism of phonatory function of the neoglottis, has been successfully used in speech rehabilitation of these patients. In a pilot study it was tried as a visual feedback. The results confirm its utility for speech rehabilitation of these laryngectomees.

Electrodiagnosis↗

PubMed1994

Central monitoring deficiency and schizophrenic symptoms.

Twenty-five schizophrenic patients currently experiencing Schneiderian symptoms performed a series of tasks in which drawings had to be made in the absence of immediate visual feedback. In comparison to 10 normal controls and to 30 patients not experiencing Schneiderian symptoms, the target group had great difficulty in keeping track of their performance and remembering what actions they had made. These results are consistent with the hypothesis that Schneiderian symptoms (such as delusions of alien control) are associated with impairments in the central monitoring of action.

Adolescent↗

PubMed1995

Myoclonic-like finger microdisplacements in patients with cerebellar deficits.

BACKGROUND: Here we assess the ability of patients with cerebellar disease to execute a simple visually-guided movement task involving tracking of a target with the index finger. METHODS: Spontaneous microdisplacements in index finger position are compared in patients with cerebellar deficits (ischemia [n = 3], multiple sclerosis [n = 3], degenerative cerebellar disease [n = 3]) and age-matched healthy subjects. Subjects were required to maintain a constant finger position relative to a stationary baseline displayed on an oscilloscope. RESULTS: Unusual transient abrupt movements (saccadic or myoclonic-like) directed with or against gravity were seen in patients whose neurological deficits were the most severe (7/9 patients). These abrupt myoclonic-like movements occurred independently of visual input, were not associated with clinically observable myoclonus, and were not detected previously in patients with Parkinson's disease. These abrupt myoclonic-like movements were not associated with abnormalities in either physiological tremor, or oscillations in finger microdisplacements induced by insertion of a delay (300-1400 ms) into the visual feedback of this finger "holding" experiment. An unexpected finding is that the results obtained for patients with cerebellar deficits by insertion of an experimental delay are not significantly different from those obtained with their age-matched controls. CONCLUSIONS: These observations suggest that abrupt myoclonic-like movements are a characteristic abnormality of patients with a variety of cerebellar deficits and emphasize the value of this simple motor tracking task for characterizing movement disorders.

Adolescent↗

PubMed2004

Characteristics of tremor in normal subjects and in the diagnosis and treatment of Parkinsonism.

Tensotremorography was used to record voluntary forces and to study the characteristics of the involuntary and voluntary components of isometrically recorded hand strength. The frequency ranges for changes in the spectral density of oscillations recorded here supported the existence of two suprasegmental systems associated with voluntary control and continuous regulation of force maintaining or holding a posture. Cross-correlation analysis of hand force maintained in conditions of visual feedback in normal conditions and in conditions of central disorders of the movement control system is presented.

Basal Ganglia↗

PubMed2004

Characteristics of learning voluntary control of posture in lesions of the pyramidal and nigrostriatal systems.

The aim of the study reported here was to investigate impairments on the learning of voluntary control of the center of pressures using visual feedback in patients with lesions of the corticospinal and nigrostriatal systems. Participants were 33 patients with Parkinson's disease and 20 patients with hemipareses due to circulatory lesions in the basin of the middle cerebral artery. Subjects stood on a stabilometric platform and used two computer games over 10 days to learn to shift the body relative to the foot to move the centre of pressures, indicated by the position of a cursor on the screen, with the target and to move the target to a specified part of the screen. The games differed in terms of the postural tasks. In one, the direction of movement of the center of pressures was not known to the subjects, and subjects learned a general strategy for posture control; the other formed a strictly defined postural coordination. Both groups of patients were found to have impairments of voluntary control of the position of the center of pressures. There were no differences between groups of patients, in terms of the severity of the initial performance deficit in the task involving shifts of the center of pressures in different directions (the general strategy for controlling the center of pressures), while learning of this task was more difficult for patients with Parkinson's disease. The initial deficit in the fine postural coordination task was more marked in patients with Parkinsonism, though learning in these patients was significantly better than in patients with hemipareses. It is suggested that the mechanisms of involvement of the nigrostriatal and corticospinal systems in learning the voluntary control of posture have elements in common as well as unique elements.

Adult↗

PubMed2000

Nasal peak inspiratory flow through Turbuhaler in children with symptomatic rhinitis and in healthy children.

Topical treatment of allergic or vasomotor rhinitis is possible by means of pressurized metered dose inhalers, aqueous spray, or dry powder inhalers. In children, little is known about nasal drug delivery by dry powder inhalation. The airflow through the device is critical for the drug release and a sufficient nasal inspiratory flow is needed for intranasal drug delivery from a dry powder inhaler. In order to investigate from what age children with allergic or vasomotor rhinitis can reliably use such a device, device-dependent nasal peak inspiratory flow (DnPIF) was measured. The maximal DnPIF was measured in children aged 4-13 years making use of a dry powder inhaler (Turbuhaler) connected to a spirometer (Vitalograph). In the clinically relevant context, instructions from the doctor and one week's use of a Turbuhaler at home were found to be sufficient to obtain a good inhalation technique and were shown to improve DnPIF at least as effectively as visual feedback training at the clinic. Children with rhinitis, as well as healthy children from the age of 6 years, were able to generate a DnPIF sufficient to obtain a reliable nasal delivery of a dry powder drug dose. DnPIF values correlated with age. Consequently, a recommendation to use a nasal Turbuhaler from the age of 6 for topical drug delivery in the treatment of allergic or vasomotor rhinitis seems reasonable.

Administration, Inhalation↗

PubMed1990

Eye-hand coordination: oculomotor control in rapid aimed limb movements.

Three experiments are reported in which Ss produced rapid wrist rotations to a target while the position of their eyes was being monitored. In Experiment 1, Ss spontaneously executed a saccadic eye movement to the target around the same time as the wrist began to move. Experiment 2 revealed that wrist-rotation accuracy suffered if Ss were not allowed to move their eyes to the target, even when visual feedback about the moving wrist was unavailable. In Experiment 3, wrist rotations were equally accurate when Ss produced either a saccadic or a smooth-pursuit eye movement to the target. However, differences were observed in the initial-impulse and error-correction phases of the wrist rotations, depending on the type of eye movement involved. The results suggest that aimed limb movements use information from the oculomotor system about both the static position of the eyes and the dynamic characteristics of eye movements. Furthermore, the information that governs the initial impulse is different from that which guides final error corrections.

Adult↗