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PubMed2002

Perception of aggression among psychiatric nurses in Switzerland.

OBJECTIVE: To identify principal components and patterns in the perception of aggression by psychiatric nurses and to explore relationships between the perception of aggression and personal and workplace characteristics. METHOD: Seven hundred and twenty-nine nurses working in psychiatric inpatient departments of German-speaking Switzerland completed the perception of aggression scale (POAS). Data analysis included factor analysis, group comparisons and multivariate analysis of covariance. RESULTS: Two plausible factors were identified, representing different dimensions in the perception of aggression and accounting for 35% of the variance. Firstly, aggression is perceived as dysfunctional/ undesirable and, secondly, aggression is perceived as a functional/ comprehensible phenomenon. Only minor differences were found in the perception of aggression with regard to personal characteristics or work environment of the nurses. CONCLUSION: Nurses perceive aggression not just as a negative phenomenon. The perception of aggression as measured by POAS is independent of many characteristics expected to be related to the perception of violence, such as grade of education, work experience, etc.

Aggression↗

PubMed1996

Influence of treatment with beclomethasone, cromoglycate and theophylline on perception of bronchoconstriction in patients with bronchial asthma.

1. Perception of asthma by patients can be assessed from the relationship between symptom scores and peak expiratory flows. This study was designed to investigate the possibility that medication can affect perception of the sensation of asthma independently of changes in lung function. 2. Twelve subjects whose asthma was inadequately controlled by inhaled bronchodilator alone were studied during four different drug treatments over 3 months. Subjective self-assessment of asthma was scored on a 10 cm visual analogue scale and followed by three consecutive measurements of peak expiratory flow, using a coded electronic peak flow meter. This was recorded not less than three times daily on diary cards. Observations were recorded during the second week of each of four treatments: (i) a run-in period using only inhaled salbutamol as required, (ii) inhaled beclomethasone, (iii) inhaled cromoglycate and (iv) oral theophylline at a dose adjusted to achieve blood levels of 10-20 mg/l. Inhaled salbutamol was permitted during the other treatments as required. Changes in the slope and position of the regression lines of asthma scores on PEF were used to measure changes in perception of asthma on each treatment. Dynamic lung volumes were measured in the clinic before the study and after each treatment period. 3. In the group as a whole, theophylline improved lung function (mean peak flow and dynamic lung volumes) without affecting mean visual analogue scores, beclomethasone improved mean visual analogue scores with much less effect on lung function, while cromoglycate had a small though consistent effect on both. 4. Perception of asthma, measured by the relationship between peak flow rate and visual analogue scores, was unaffected by cromoglycate. On theophylline, perception of asthma was heightened in five subjects despite a definite improvement in their peak flow. On beclomethasone, perception of asthma was reduced in most subjects, often with no discernible improvement in mean peak flow or dynamic spirometry. 5. Perception of bronchoconstriction in asthma can be affected by drugs independently of control of the condition. Theophylline may produce a paradoxical increase in awareness of asthma in some individuals. With beclomethasone therapy a reduction in symptoms of asthma may occur without any improvement in tests of air flow.

Adult↗

PubMed1998

Improvements in speech perception by children with profound prelingual hearing loss: effects of device, communication mode, and chronological age.

The present investigation expanded on an earlier study by Miyamoto, Osberger, Todd, Robbins, Karasek, et al. (1994) who compared the speech perception skills of two groups of children with profound prelingual hearing loss. The first group had received the Nucleus multichannel cochlear implant and was tested longitudinally. The second group, who were not implanted and used conventional hearing aids, was tested at a single point in time. In the present study, speech perception scores were examined over time for both groups of children as a function of communication mode of the child. Separate linear regressions of speech perception scores as a function of age were computed to estimate the rate of improvement in speech perception abilities that might be expected due to maturation for the hearing aid users (n=58) within each communication mode. The resulting regression lines were used to compare the estimated rate of speech perception growth for each hearing aid group to the observed gains in speech perception made by the children with multichannel cochlear implants. A large number of children using cochlear implants (n=74) were tested over a long period of implant use (m=3.5 years) that ranged from zero to 8.5 years. In general, speech perception scores for the children using cochlear implants were higher than those predicted for a group of children with 101-110 dB HL of hearing loss using hearing aids, and they approached the scores predicted for a group of children with 90-100 dB HL of hearing loss using hearing aids.

Age Factors↗

PubMed2000

Professional nurses' perception of nursing mentally ill people in a general hospital setting.

The aim of this study was to explore professional nurses' perception of nursing mentally ill patients in a tertiary hospital in Durban. An explorative, qualitative, descriptive and contextual design was followed as the basis for conducting the study. The above-mentioned research design was achieved through field work conducted in an urban-based general hospital. A sample of 12 professional nurses was selected from a population of 800 professional nurses employed in this setting using a purposive sampling technique. This sample size was determined by saturation of data as reflected in repeating themes. Both individual phenomenological semistructured interviews and field notes in the form of observations were used as methods of data collection. The field work was conducted without any preset theoretical framework of reference by using bracketing and intuiting. During interviews, participants were asked only one research question, namely: 'How do you perceive nursing mentally ill patients in your unit or ward?' Communication skills were employed to encourage participants to verbalize their perception of nursing mentally ill patients in a general hospital setting. A tape recorder was used to collect data and the data was transcribed verbatim. Data collected was analysed following the descriptive method of Giorgi (1986). Coding was carried out by the researcher and an independent expert who is a psychiatric nursing specialist and a qualitative research expert. After data analysis, the results were reflected within universal categories of the Nursing for the Whole Person Theory in order to give them structure. The four themes that emerged from the findings are: perception of self, perception of a patient, perception of feelings that hinder nursing the mentally ill, and perception of the environment. The measures for ensuring trustworthiness proposed by Guba (Lincoln Y.S. & Guba E.G. (1985) Naturalistic Inquiry. Sage, Beverly Hills) were used as the basis for ensuring reliable and valid findings. The perception of nursing mentally ill people within a general hospital setting was negative and affected the intellectual and the affective component of the nurses' psychological functioning within their internal environment. It was recommended that nurses' knowledge and skills should be increased and that they should be given emotional support in terms of counselling.

Adult↗

PubMed2001

Sex differences in weight perception and nutritional behaviour in adults with cystic fibrosis.

INTRODUCTION: Good nutritional status in cystic fibrosis (CF) is associated with improved clinical status and survival. In some conditions where dietary and pharmacological treatment are important (e.g. diabetes), a combination of eating disorders and failure of treatment compliance has been reported. Cases of eating disorders have been reported in CF. Societal pressures on young women to remain slim may compromise optimum clinical management as women are content to remain underweight. OBJECTIVE: To determine whether women have different perception of their weight than men with CF and whether this manifests in different nutritional behaviour. METHODS: Confidential postal questionnaire to 1870 adults with CF in 1994 known to the Association of Cystic Fibrosis Adults (UK). Participants were asked their own weight and height, and their perception of their weight. Very underweight was defined as < 85% ideal body weight, underweight as 85-94%, normal weight as 95-104%, overweight as 105-114% and very overweight as 115% and over. RESULTS: A significantly higher proportion of women than men who are very underweight (29% vs. 11%) or underweight (41% vs. 15%) saw themselves as being of normal weight or overweight. Conversely, a significantly higher proportion of men than women who were normal weight (42% vs. 19%) saw themselves as underweight. All P-values < 0.01. A significantly higher proportion of people who perceived themselves to be underweight were taking oral or enteral food supplements compared with those who did not (77% vs. 30%, P < 0.05). Multiple logistic regression showed that perception of self as underweight was the strongest predictor of taking oral or enteral food supplements (adjusted odds ratio 2.42), even after adjustment for age, sex, overall severity score, body mass index, and seeing a dietitian in the last year. CONCLUSION: Young women with CF tend to overestimate their weight, and young men with CF underestimate their weight when compared with their actual body weight. Perception of self as underweight is reflected in nutritional behaviour, being a significantpredictor of taking oral and enteral food supplements. People working with young patients with CF should be aware of these sex differences in weight perception, and work with young women and young men with CF to achieve a realistic perception of body weight and realistic nutritional goals. There is a need for further research into body image, weight perception, eating behaviour and adherence to pancreatic enzyme supplementation and oral and enteral food supplementation in young patients with CF.

Adolescent↗

PubMed2000

Abnormal visceral perception in patients with functional dyspepsia: use of cerebral potentials evoked by electrical stimulation of the oesophagus.

Altered visceral perception is thought to be included in the pathogenesis of functional dyspepsia. However, in previous studies, the assessment of visceral perception has been based solely on patients self-reported symptoms. Cerebral evoked potential (EP), either by mechanical or electrical stimulation (ES) of the visceral organ, is used to evaluate visceral perception via afferent neural pathways. In this study, we investigated the visceral perception in patients with functional dyspepsia by EP to eliminate the possibility of self-reported bias. EP responses were recorded by oesophageal ES at 37 cm from the nostril in 14 patients with functional dyspepsia and 14 normal healthy control subjects. Threshold levels of perception, peak latencies and peak-to-peak amplitudes of EP were evaluated. There was no difference in the sensory threshold between the dyspeptic patients and the control subjects (median 6 mA, range 2-12 mA, vs. 8 mA, range 6-14 mA; P= 0.09). There was a strong trend towards a decreased discomfort threshold in the patients when compared to the control subjects (median 14 mA, range 6-24 mA vs. 20 mA, range 14-26 mA; P = 0.05). The latency of the later EP peak (N2) among the patients (154 ¿ 4 ms) was significantly shorter than that of the control subjects (171 ¿ 3 ms, P < 0.01) although there was no difference between the earlier peaks (Ni and P1). There was also no difference in the amplitudes (Ni/Pi and P1/N2) of EP between the patients and the control subjects. Half of the patients (seven out of 14) complained of nausea during ES but the control subjects were unaffected. The latency of the first EP peak (Ni) in the patients with nausea was significantly shorter (66 ¿ 3 ms) than that of the patients without nausea (79 ¿ 4 ms, P 0.05) or among the control subjects (80 ¿ 3 ms, P < 0.05). These results suggest that dyspeptic patients may recruit a greater number of fast conducting myelinated nerve fibres that convey visceral afferent impulses to the brain and/or that dyspeptic patients may have an altered central processing of the visceral perception. We conclude that EP recording by oesophageal ES provides an objective measurement of altered visceral perception in patients with functional dyspepsia.

Adolescent↗

PubMed1999

Neuronal correlates of real and illusory contour perception: functional anatomy with PET.

Illusory contours provide a striking example of the visual system's ability to extract a meaningful representation of the surroundings from fragmented visual stimuli. Psychophysical and neurophysiological data suggest that illusory contours are processed in early visual cortical areas, and neuroimaging studies in humans have shown that Kanizsa-type illusory contours activate early retinotopic visual areas that are also activated by real contours. It is not known whether other types of illusory contours are processed by the same mechanisms, nor is it clear to what extent attentional effects may have influenced these results, as no attempt was made to match the salience of real and illusory stimuli in previous imaging studies. It therefore remains an open question whether there are any brain regions specifically involved in the perception of illusory contours. To address these questions, we have used 15O-butanol positron emission tomography (PET) and a novel kind of illusory contour stimulus that is induced only by aligned line ends. By employing a form discrimination task that was matched for attention and stimulus salience across conditions we were able to directly contrast perception of real and illusory contours. We found that the regions activated by illusory contour perception were the same as those activated by real contours. Only one region, located in the right fusiform gyrus, was significantly more strongly activated by perception of illusory contours than by real contours. In addition, a principal component analysis suggested that illusory contour perception is associated with a change in the correlation between V1 and V2. We conclude that different kinds of illusory contours are processed by the same cortical regions and that these regions overlap extensively with those involved in processing of real contours. At the regional level, perception of illusory contours thus appears to differ from perception of real contours by the degree of involvement of higher visual areas as well as by the nature of interaction between early visual areas.

Adult↗

PubMed2000

Perception of induced bronchoconstriction in a community sample of adolescents.

BACKGROUND: Poor perception of asthma symptoms has been cited as a risk factor for asthma death, yet there is no consensus as to the best way to characterize perception, and little is known about perception in normative samples. Hypoperceivers are of clinical interest because of risks of undertreatment; hyperperceivers are at risk for adverse iatrogenic effects caused by overtreatment. OBJECTIVE: This study investigates perception of methacholine-induced bronchoconstriction in 175 adolescents. METHODS: Breathlessness was rated after each inhalation by using the Borg scale. Perception groups were calculated on the basis of change from placebo Borg to high Borg scores (perception score at the highest methacholine dose). Subjects were called hypoperceivers if their Borg change score was greater than 1 SD below the mean for their FEV(1) group, hyperperceivers if their Borg change score was greater than 1 SD above the mean for their FEV(1) group, and accurate perceivers otherwise. RESULTS: For subjects with an FEV(1) drop of less than 10%, accurate perceivers had a change in Borg score of 1.4 or less, and hyperperceivers had a change of greater than 1.4. For a drop in FEV(1) between 10% and 19%, hypoperceivers had a change in Borg score of less than 0.2, accurate perceivers had a change between 0.2 and 2.1, and hyperperceivers had a change of greater than 2.1. For those with an FEV(1) drop of 20% or greater, hypoperceivers had a Borg change of less than 0.2, accurate perceivers had a change between 0.2 and 2.6, and hyperperceivers had a change of greater than 2.6. No differences in age, sex, placebo Borg ratings, baseline pulmonary functions, PC(20) values, or psychologic variables were found among perception groups. CONCLUSION: This study provides reference Borg values during methacholine challenge for 175 community adolescents.

Adolescent↗

PubMed1988

A mechanism for the direct perception of change: the example of bacterial chemotaxis.

The relationship between the behavior of single-celled organisms and cognition in higher animals is explored. Recent research and theory in bacterial chemotaxis are presented, together with a discussion of the implications of chemotaxis for perceptual theory. A number of parallels between chemotaxis and perception in higher organisms are drawn. It is suggested that Koshland's model of the chemical processes controlling chemotaxis is an example of a mechanism for direct perception of change and can help elucidate Runeson's work on 'smart mechanisms' of perception. It is argued, more generally, that the growing body of knowledge about the perceptual activities of lower organisms should be used to broaden the factual base on which theories of perception are constructed: eg explication of perceptual parallels between humans and lower organisms should help clarify the nature of these phenomena in humans and, perhaps, help in the development of theories of greater generality. Also, the debate between direct and indirect theories of perception may be advanced by analysis of the specific mechanisms used by lower organisms. Contrasts to mediated perception are pointed out and arguments for the relative simplicity and explanatory power of theories of direct perception are provided.

Animals↗

PubMed2006

Evidence for a role of action in colour perception.

Action is not usually considered to play a role in colour perception. However, sensorimotor theories of perception (eg O'Regan and Noë, 2001 Behavior and Brain Science 24 939-1011) suggest that, on the contrary, the transformations created by action in the sensory input are a necessary condition for all perception. In the case of colour vision, eye movements may explain how a retina with significant irregularities in resolution and cone arrangement (Roorda and Williams, 1999 Nature 397 520-522) could permit the perception of a richly coloured world (Clark and O'Regan, 2000 15th International Conference on Pattern Recognition volume 2: Pattern Recognition and Neural Networks pp 503-506; Skaff et al, 2002 16th International Conference on Pattern Recognition volume 2, pp 681-684). We provide evidence that perception of colour is modified when an artificial coupling is introduced linking eye movements and colour changes. After 40 min of wearing left-field-blue/right-field-yellow spectacles, observers' colour vision adapts so that, after removing the spectacles, white patches seem to become bluer when the eyes move rightwards and yellower when the eyes move leftwards. This induced dependence of colour perception on the direction of eye saccade is shown to be related to the amount of eye movements during exposure. This result, which cannot be explained either by retinal adaptation, or by a conditioned association between colour and side, constitutes first clear evidence for a role of eye movements in perceived colour and argues for the involvement in colour perception of neural mechanisms continuously tuned to sensorimotor contingencies.

Adaptation, Psychological↗

PubMed2004

The role of attention in affect perception: an examination of Mirsky's four factor model of attention in chronic schizophrenia.

Attentional skills among people with schizophrenia may be related to deficits in affect perception. Such deficits can dramatically inhibit appropriate social functioning. We examined attention and affect perception in a sample of 65 people diagnosed with chronic schizophrenia. We used Mirsky's four factor model of attention to assess attentional functioning. To measure affect perception, we used two reliable measures of emotion recognition, the Bell-Lysaker Emotion Recognition Test and the Face Emotion Identification Test. Multiple regression analysis showed that all four attentional factors and a diagnosis of paranoid schizophrenia were significantly predictive of affect perception scores. In contrast, psychiatric symptoms, medication levels, demographic variables, verbal fluency, and face recognition scores were not predictive of affect perception scores. The four factors of attention accounted for 78 percent of the variance in affect perception scores. These results emphasize the role that attentional abilities play in affect perception for people with schizophrenia.

Adult↗

PubMed2002

Functional MRI of self-controlled stereoscopic depth perception.

Stereoscopic depth perception was studied in healthy young adults using fMRI imaging at 2.0 T. In a novel paradigm we compared the cortical activation elicited by single-image stereograms which create alternating 2D and 3D percepts (event-related analysis triggered on the self-controlled switches between the two percepts) with the activation caused by a more conventional approach contrasting pairs of stereoscopic images with pairs of identical images (block design). The data show a distributed network of cortical areas embedded within the visual pathways that included about one-quarter of the cortical surface activated by 2D visual stimulation and about one-half of the area activated by 3D percepts based on stereoscopic image pair. 3D perception recruited mostly neuronal populations in higher order visual areas: whereas about 40% of the visually activated locations along the intraparietal sulcus were also activated by 3D perception based on single-image stereograms (resp. 90% stereoscopic images), only 10% such overlap was found in striate cortex. The study revealed no sup-port for a right-hemispheric lateralization of depth perception.

Adult↗

PubMed2005

Mechanisms of face perception in humans: a magneto- and electro-encephalographic study.

We have been studying the underlying mechanisms of face perception in humans using magneto- (MEG) and electro-encephalography (EEG) including (1) perception by viewing the static face, (2) differences in perception by viewing the eyes and whole face, (3) the face inversion effect, (4) the effect of gaze direction, (5) perception of eye motion, (6) perception of mouth motion, and (7) the interaction between auditory and visual stimuli related to the vowel sounds. In this review article, we mainly summarize our results obtained on 3, 5, and 6 above. With the presentation of both upright and inverted unfamiliar faces, the inferior temporal cortex (IT) centered on the fusiform gyrus, and the lateral temporal cortex (LT) near the superior temporal sulcus were activated simultaneously, but independently, between 140 and 200 ms post-stimulus. The right hemisphere IT and LT were both active in all subjects, and those in the left hemisphere in half of the subjects. Latencies with inverted faces relative to those with upright faces were longer in the right hemisphere, and shorter in the left hemisphere. Since the activated regions under upright and those under inverted face stimuli did not show a significant difference, we consider that differences in processing upright versus inverted faces are attributable to temporal processing differences rather than to processing of information by different brain regions. When viewing the motion of the mouth and eyes, a large clear MEG component, 1M (mean peak latency of approximately 160 ms), was elicited to both mouth and eye movement, and was generated mainly in the occipito-temporal border, at human MT/V5. The 1M to mouth movement and the 1M to eye movement showed no significant difference in amplitude or generator location. Therefore, our results indicate that human MT/V5 is active in the perception of both mouth and eye motion, and that the perception of movement of facial parts is probably processed similarly.

Adult↗

PubMed2004

Are switches in perception of the Necker cube related to eye position?

The issue of the relation of eye position to perceptual reversals of the ambiguous figure of the 'Necker cube' dates back to Necker's original article [L.A. Necker (1832) The London & Edinburgh Philosophical Magazine and Journal of Science, 1, 329-337]. Despite the investigations of many distinguished psychophysicists since then, the question of whether perceptual switching is a cause or a consequence of associated changes in eye position has remained a matter of debate. In the present study we overcame methodological problems that have bedevilled many previous studies. We avoided any instruction that could interfere with the human subjects' free viewing of the Necker cube, tracked the eye position precisely and used biased versions of the cube that produced unambiguous percepts to determine how each subject actually looked at the cube. We show that, under these free-viewing conditions, there is a close link between the perception of the Necker cube and eye position. The average eye position of most subjects is at an extreme value at about the time when the subject's perception switches. From the biased cube trials we can infer that the polarity of the extreme corresponds to the percept which the subject had before the switch. These data indicate a bidirectional coupling between eye position and perceptual switching so that, after a subject's perceptual state changes, their eye position shifts to view the newly established percept. When the eye position approaches the corresponding extreme, the percept, in turn, becomes more and more likely to switch. This result suggests that the changed eye position itself might provide a negative feedback signal that suppresses the percept.

Adult↗

PubMed2004

Acupuncture has a placebo effect on rectal perception but not on distensibility and spatial summation: a study in health and IBS.

BACKGROUND: Recent data suggest that acupuncture has effects on gut physiology and perception. Spatial summation is a central mechanism of perception and describes the phenomenon that thresholds for perception are lower if more receptors are stimulated. OBJECTIVES: We assessed perception thresholds for rectal distension and cutaneous referral of symptoms, while inflating one or two rectal balloons and the effect of both electro-acupuncture and placebo-acupuncture on rectal distensibility, perception, and spatial summation. METHODS: A tube with two barostat balloons was placed in the rectum of 12 healthy subjects and nine irritable bowel syndrome (IBS) patients with rectal symptoms. Volume-controlled stepwise distension of the distal balloon only or both balloons was performed first as a control, and thereafter with simultaneous placebo- or electro-acupuncture in dermatomes S3 and S4. A symptom questionnaire and anatomic questionnaire was completed during each distension. RESULTS: Rectal elastance increased from 42.0 +/- 19.6 log mmHg/ml during one-balloon distension to 59.6 +/- 33.1 log mmHg/ml during two-balloon distension (p < 0.05) in healthy subjects, and from 48.8 +/- 14.4 log mmHg/ml (one balloon) to 77.6 +/- 24.2 log mmHg/ml (p < 0.001) in patients with IBS. Electro-acupuncture had no effect on rectal sensation, elastance, and cutaneous referral when compared to placebo-acupuncture. However, acupuncture (both electro- and placebo-) increased volume thresholds for sensation compared to control experiments, while objective parameters like rectal tone and elastance were unaltered. CONCLUSION: Acupuncture has a placebo effect on rectal perception but has no effect on rectal distensibility and visceral referral. Spatial summation affected both rectum distensibility and perception, but was also not altered by acupuncture.

Acupuncture Therapy↗

PubMed2005

Perceptions of school toilets as a cause for irregular toilet habits among schoolchildren aged 6 to 16 years.

Irregular bladder and bowel habits can contribute to urinary and bowel problems. Schoolchildren undergoing treatment for these problems often do not follow the recommendation of regular toilet visits at school, claiming negative perceptions of school toilets. This study examined 6- to 16-year-old schoolchildren's perceptions of school toilets and whether the perceptions affect bladder and bowel habits at school Some 385 Swedish schoolchildren aged 6 to 16 years were surveyed using a semistructured questionnaire. Children aged 13 to 16 years had the most negative perceptions. Twenty-five percent (overall 16%) of older children reported never using the school toilet to urinate, and 80% (overall 63%) never used it to defecate. Perceptions of sight and smell and emotional constraints hindered children from using the school toilets. Children generally based their perceptions of school toilets on physical appearance, offensive smell, and feelings of insecurity. Children's perceptions affected their toilet habits and would rather endure physical discomfort than the psychological and social discomfort of using the school toilet. Children already suffering from urinary tract or intestinal problems face particular difficulties without regular toilet visits during the day.

Adolescent↗

PubMed1994

Proprioceptive, visual and vestibular thresholds for the perception of sway during standing in humans.

1. Thresholds for the perception of postural sway induced by gentle perturbations were determined for five normal standing subjects. In this context we understand 'perception' to mean 'able to give a subjective report'. The thresholds for the perception of movements that were equivalent to sway in velocity and amplitude were determined when the available sensory input was limited to only one, or a pair, of the vestibular, visual, and proprioceptive systems. To examine vestibular inputs alone, vision was excluded and the whole body was moved with the ankles in a fixed position. To examine visual inputs alone, the body was kept stationary and a 'room' was moved around the subjects to simulate the relative visual-field movement that occurs during standing. To limit the available sensory input to proprioception from the legs, subjects were held stationary and balanced a load that was equivalent to their own body using their ankles. In this situation, perturbations were applied to the 'equivalent body' and these could only be perceived from the resulting ankle movements. Thresholds for perceiving ankle movements were also determined in the same posture, but with the leg muscles bearing no load. 2. The thresholds for the perception of sway during standing were very small, typically 0.003 rad at a velocity of 0.001 rad s-1, and even smaller movements were perceived as the mean velocity of the sway increased up to 0.003 rad s-1. No difference was found between the thresholds for perceiving forward sway and backward sway. Eye closure during standing did not affect the threshold for perceiving sway. 3. When sensory input was limited to proprioception from the legs, the thresholds for the perception of passive ankle movements were equivalent to the thresholds for the perception of sway during standing with all sensory inputs available. When the leg muscles were relaxed, the thresholds for perceiving ankle movements increased approximately twofold. 4. The visual thresholds for perceiving movement were higher than the proprioceptive thresholds at slower velocities of movement, but there was no difference at higher velocities. 5. Both the proprioceptive and visual thresholds were sufficiently small to allow perception of the sway that was recorded when the subjects stood normally in a relaxed manner. In contrast, the vestibular thresholds were an order of magnitude greater than the visual or proprioceptive thresholds and above the largest sway movements that were recorded during normal standing.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1994

Perception of fluoroscopy last-image hold.

Last-image hold (LIH) is used in x-ray fluoroscopy systems as a convenience and dose savings feature. In the case of an image sequence, temporal filtering in the human visual system (HVS) reduces perceived noise. In the case of a constant, single image frame, this phenomenon is not present: the image looks noisier, and low-contrast objects disappear. Using low-contrast, stationary cylinder and disk phantoms in noise, perception of single frames are compared with that of conventional 30 acq/s continuous fluoroscopy (continuous). The dose of continuous is fixed at Q/acq, and the dose of single-frame presentations is varied in order to determine an "equivalent-perception dose" for a paired-comparison task. The equivalent-perception dose depends upon the shape and size of an object. As cylinder diameter increases from 1 to 21 pixels, the equivalent-perception dose decreases from 4.6 to 2.8 Q/acq. At equal equivalent-perception dose values, the relationship between cylinder and disk diameters are determined; a cylinder diameter of 10 pixels is roughly equivalent to a disk diameter of 20 pixels. For interventional angiography, an average equivalent-perception dose of approximately 3.5 Q/acq for a single-frame presentation is predicted. Thus processing by the HVS effectively reduces noise variance by a factor of 3.5, corresponding to an effective averaging time of 3.5 frames or 120 ms. Several variance reduction techniques are suggested to create an LIH frame having perception equal to the fluoroscopy sequence.

Biophysical Phenomena↗