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PubMed2000

Perception of two-dimensional, simulated ego-motion trajectories from optic flow.

A veridical percept of ego-motion is normally derived from a combination of visual, vestibular, and proprioceptive signals. A previous study showed that blindfolded subjects can accurately perceive passively travelled straight or curved trajectories provided that the orientation of the head remained constant along the trajectory. When they were turned (whole-body, head-fixed) relative to the trajectory, errors occurred. We ask whether vision allows for better path perception in that situation, to correct or complement vestibular perception. Seated, stationary subjects wore a head mounted display showing optic flow stimuli which simulated linear or curvilinear 2D trajectories over a horizontal ground plane. The observer's orientation was either fixed in space, fixed relative to the path, or changed relative to both. After presentation, subjects reproduced the perceived movement with a model vehicle, of which position and orientation were recorded. They tended to correctly perceive ego-rotation (yaw), but they perceive orientation as fixed relative to trajectory or (unlike in the vestibular study) to space. This caused trajectory misperception when body rotation was wrongly attributed to a rotation of the path. Visual perception was very similar to vestibular perception.

Head Movements↗

PubMed1997

Contrast affects flicker and speed perception differently.

We have previously shown that contrast affects speed perception, with lower-contrast, drifting gratings perceived as moving slower. In a recent study, we examined the implications of this result on models of speed perception that use the amplitude of the response of linear spatio-temporal filters to determine speed. In this study, we investigate whether the contrast dependence of speed can be understood within the context of models in which speed estimation is made using the temporal frequency of the response of linear spatio-temporal filters. We measured the effect of contrast on flicker perception and found that contrast manipulations produce opposite effects on perceived drift rate and perceived flicker rate, i.e., reducing contrast increases the apparent temporal frequency of counterphase modulated gratings. This finding argues that, if a temporal frequency-based algorithm underlies speed perception, either flicker and speed perception must not be based on the output of the same mechanism or contrast effects on perceived spatial frequency reconcile the disparate effects observed for perceived temporal frequency and speed.

Contrast Sensitivity↗

PubMed2004

The fragile nature of the speech-perception deficit in dyslexia: natural vs synthetic speech.

A number of studies reported that developmental dyslexics are impaired in speech perception, especially for speech signals consisting of rapid auditory transitions. These studies mostly made use of a categorical-perception task with synthetic-speech samples. In this study, we show that deficits in the perception of synthetic speech do not generalise to the perception of more naturally sounding speech, even if the same experimental paradigm is used. This contrasts with the assumption that dyslexics are impaired in the perception of rapid auditory transitions.

Auditory Perceptual Disorders↗

PubMed2003

Speech perception of Mandarin Chinese speaking young children after cochlear implant use: effect of age at implantation.

OBJECTIVE: The purposes of this study were to examine (1). whether the benefit of cochlear implants in Mandarin-speaking congenitally deaf children persists over a 2-year follow-up period, and (2). whether the age of the child at implantation affects the acquisition of speech perception by young deafened children. METHOD: Sixteen congenitally deaf children received implants of Nucleus CI24M devices. Speech perception tests were conducted using the Mandarin Auditory Perception Test Battery at 6-month intervals after connection of the device. We determined the benefit of cochlear implants by monitoring percent correct scores between 12 and 24 months after implantation. Regression analysis was used to correlate the measures of progress and the age at implantation. RESULTS: In the comparison of performance at 12 and 24 months post-connection, subjects performed significantly better at 24 than at 12 months in spondee, vowel, and consonant tests (P<0.05). In phrase and sentence tests, the mean score improved over time with device use, but the difference was not significant (P=0.066 and 0.067, respectively). However, no obvious improvement in average score was found in tone tests (P=0.386). Progress (improvement in speech perception) at 12 and 24 months had moderate negative correlations with age at implantation in spondee, vowel, phrase and sentence tests (P<0.05), but no correlation with age in consonant (P=0.20) and tone tests (P=0.26). CONCLUSION: The result, in accordance with the reports on Western language-speaking children, showed cochlear implants increasingly benefit Mandarin-speaking congenitally deaf children over a 2-year post-implantation period. Because age at implantation negatively correlates with improved speech perception after implantation, congenitally affected children with profound deafness (if they cannot obtain enough benefit from hearing aids) should receive implants as early as possible.

Age Factors↗

PubMed2002

Shifts in blood volume alter the perception of posture: further evidence for somatic graviception.

This article examines the relation between the perception of one's own body position and the distribution of fluid along the subject's spinal (z-) axis. Two experiments are reported. The first one is a replication of the Vaitl et al. study [J. Psychophysiol. 27 (1997) 99] which has shown that changes in shifts of blood volume into or out of the thoracic cavity induced by lower body positive pressure (LBPP: +30 mmHg) or lower body negative pressure (LBNP: -30 mmHg) exerted on the lower body led subjects to feel tilted head-up or head-down, respectively. The second experiment was designed to differentiate between the influence of the otoliths and of the changes in fluid distribution on the perception of body position by means of a sled centrifuge in combination with LBPP and LBNP. In both experiments, changes in blood distribution within the thoracic cavity were measured by impedance plethysmography. Forty healthy volunteers (17 females) participated in experiment 1. They were positioned on the side (right-ear-down head position) on a tiltable board which the subject and the experimenter could tilt via remote control around the subjects' z-axis. Subjects were asked to rotate the board until they felt they were in a horizontal posture. The results clearly show that the perception of posture is influenced by the shift in blood distribution. During LBNP subjects perceived being tilted head-up, whereas LBPP led them feel tilted head-down. Thus, the results obtained in the 1997 study were replicated. Fourteen males volunteered in experiment 2. They were positioned on the sled on a centrifuge in the same manner as in experiment 1. The sled could be moved via remote control by both the subject and the experimenter. While the centrifuge rotated (omega=2 pi times 0.6 rotations per second) the subjects were asked to move the sled until they felt they were in a horizontal position. As in experiment 1, shifts in blood volume were induced by LBPP and LBNP. The distance between the binaural axis (position of the otoliths) and the centrifuge axis served as dependent measure indicating the subjective horizontal position. Due to the additional centrifugal forces exerted on the body the shifts in blood volume were more pronounced than in experiment 1 where only gravitational forces were produced. The changes in the perception of posture were influenced by both the otoliths and the fluid distribution in such a way that both interact in a compensatory manner. These results again corroborate the evidence that afferent inputs from the cardiovascular system play a major role in the perception of the body posture. This phenomenon of graviception needs to be further elucidated with respect to the origins of the afferent inputs and the site and type of graviceptors (mechanoreceptors) involved.

Adult↗

PubMed2003

Circadian fluctuation of time perception in healthy human subjects.

Previous studies suggested that various psychophysiological factors have influences on human time perception. In particular, working memory loads, time of day, body temperature, and mood were known as important modifiers of time perception. The purpose of this study is to elucidate factors affecting the short-term time perception under controlled condition. Fourteen healthy young male adults participated in this study. Time perception sessions (TPS) were conducted 4 times at 0900, 1300, 1700 and 2100 h. The TPS consisted of five 10-s time production trials under five different conditions (control trial, those with reward, and 3 different dual-load working memory tasks). Subjective status was assessed using visual analogue scales (VAS). To verify a participant's vigilance state, an alpha attenuation coefficient (AAC) was calculated. Two-way repeated measures ANOVA for produced time revealed a significant main effect of session, but no effect of task or interaction. Although produced time was not correlated with AACs or VAS scores, there was a significant negative correlation between produced time and core body temperature. These results suggest that human short-term time perception may be more influenced by circadian rhythm than working memory load or psychophysiological status.

Adult↗

PubMed1997

Speech perception by prelingually deaf children using cochlear implants.

In this investigation we measured the performance of 50 prelingually deaf children on several speech perception tests. Children were from 2 to 15 years of age, and some children were tested with as much as 5 years of cochlear implant use. Speech perception tests included the recognition of stress pattern, consonants, vowels, words, and sentences. The audiovisual perception of consonants was also measured. Average results indicated that gains were being made in the perception of stress and words in a closed-set context within 1 year from implantation. The perception of words in an open-set context demonstrated much slower increases over time. Large individual differences were observed. Some preliminary data suggest that children who receive implants before the age of 4 years obtain higher scores, on average, than children who receive implants after the age of 5 years. Some children become part-time users or nonusers of their cochlear implants. The average results from 18 congenitally deaf children were significantly higher than the average results from 12 children with prelingually acquired deafness after 3 years of implant use. Information on vowel and consonant features shows increases in performance after 2 years of cochlear implant use, with the exception of the place feature. For this feature, no changes were observed. Vision-alone testing indicated that lipreading performance increased over time. An audiovisual enhancement provided by the cochlear implant was observed for all features.

Adolescent↗

PubMed1998

Effects of an ELF (50 Hz, 1 mT) electromagnetic field (EMF) on concentration in visual attention, perception and memory including effects of EMF sensitivity.

To investigate psychological effects of an extremely low frequency (ELF)-electromagnetic field (EMF), an experiment with three conditions was designed. EMF field of 50 Hz and 1 mT accompanied by 45 dB SPL noise (EMF + noise), noise, and control. A group of 66 subjects (Ss) participated in the control and in one of the experimental conditions. The sequence of conditions (expositions) was balanced. Expositions were double-blind (except for the obvious control), lasted 1 h and were separated by a 1 h pause. During exposition Ss (three by three) performed tests on attention, perception, memory and filled out a psychological questionnaire. Statistical analysis (one-tailed probability) showed less attention (P < 0.05), perception (P < 0.05) and memory performance (P < 0.1) in Ss exposed to EMF + noise compared with control, whereas for noise versus control no difference was found. Comparing EMF + noise versus noise related to control, reduced perception, less memory performance and more discomfort was observed (P < 0.1). Dividing Ss according to their self-rated sensitivity to EMF, all differences disappeared in the low sensitivity group (N = 30) and were pronounced in sensitive Ss (N = 36). Results indicate an immediate reduction of cognitive performance in attention, perception and memory performance by a 50 Hz EMF of 1 mT. These effects seem to be modulated by the self-perception of sensitivity to EMF.

Adult↗

PubMed2000

A comparison of substance abuse patients' and counselors' perceptions of relapse risk: relationship to actual relapse.

This study compared substance abuse patients' and their counselors' perceptions of relapse risk during treatment and evaluated whether these perceptions predict actual relapse 2 years later. Participants (N = 240) completed the Relapse Risk Index (RRI), which assesses confidence in abilities and need for services across four domains: coping skills, social support, resources, and leisure activities. Participants reported greater confidence and greater needs than counselors reported. Determinants of counselors' relapse risk perceptions included income, whereas participants' perceptions were related to polysubstance use. Counselors' ratings of coping skills predicted alcohol relapse; counselors' ratings did not predict drug relapse. Participants' ratings of coping skills and leisure activities predicted alcohol relapse; social support predicted drug relapse. When including background characteristics, counselors' ratings did not predict alcohol or drug relapse; participants' ratings predicted alcohol relapse but not drug relapse. Findings suggest the potential utility of considering patient perceptions to understand and possibly prevent relapse.

Adolescent↗

PubMed2004

Perception of prognostic risk in patients with multiple sclerosis: the relationship with anxiety, depression, and disease-related distress.

OBJECTIVE: The aim of the study was to investigate the impact of perception of prognostic risk on anxiety, depression, and disease-related distress in patients with multiple sclerosis (MS). STUDY DESIGN AND SETTING: Perceived risk and perceived seriousness of the 2-year, 10-year, and lifetime prognosis of wheelchair dependence, disability status, anxiety, depression, and disease-related distress were assessed in 101 patients. Distress was measured as the intrusion and avoidance of MS-related thoughts and feelings. RESULTS: Patients with higher perceptions of 2-year, 10-year, or lifetime risk were bothered by more intrusion of MS-related thoughts and feelings. Only higher perception of the 2-year risk of wheelchair dependence was significantly related with higher levels of anxiety, depression, and avoidance. Similarly, higher perception of the seriousness of wheelchair dependence was consistently associated with more intrusion and avoidance, but only perceived seriousness of the 2-year prospect of wheelchair dependence was significantly correlated with anxiety and depression. All relations were independent of clinically assessed disability status. CONCLUSION: Perceptions of the short-term risk and seriousness of wheelchair dependence were significantly related to anxiety, depression, and disease-related distress in patients with MS. These findings underscore the importance of informing patients with chronic disorders about the short-term prognosis of important long-term consequences of disease.

Adult↗

PubMed2003

Directional anisotropies reveal a functional segregation of visual motion processing for perception and action.

Human exhibits an anisotropy in direction perception: discrimination is superior when motion is around horizontal or vertical rather than diagonal axes. In contrast to the consistent directional anisotropy in perception, we found only small idiosyncratic anisotropies in smooth pursuit eye movements, a motor action requiring accurate discrimination of visual motion direction. Both pursuit and perceptual direction discrimination rely on signals from the middle temporal visual area (MT), yet analysis of multiple measures of MT neuronal responses in the macaque failed to provide evidence of a directional anisotropy. We conclude that MT represents different motion directions uniformly, and subsequent processing creates a directional anisotropy in pathways unique to perception. Our data support the hypothesis that, at least for visual motion, perception and action are guided by inputs from separate sensory streams. The directional anisotropy of perception appears to originate after the two streams have segregated and downstream from area MT.

Animals↗

PubMed1999

Poor perception of nonverbal social-emotional cues in relatives of schizophrenic patients.

The present study compared nonverbal social perception in relatives of schizophrenic patients (n = 21) with that of normal controls (n= 19). We hypothesized that relatives would display deficits in social perception and we sought to determine the skills that are associated with this deficit. Relatives performed significantly worse than controls on the Profile of Nonverbal Sensitivity Test (PONS), despite comparable performance on skills hypothesized to be related to nonverbal social perception: visual perception, nonverbal problem solving, facial recognition, facial affect recognition, naming, social judgment, and vigilance. To further explore the relationships among these skills, we calculated correlations between the PONS score and associated skills separately within both the relative and control groups and assessed whether the values of these correlations differed between groups. Correlations that differed significantly indicated a greater association, within relatives, between slower reaction times on vigilance tasks and poor PONS performance. Further research is needed to clarify the nature of this relationship, to better characterize social perception deficits in relatives, and to determine whether these perceptual deficits are part of the genetic diathesis to schizophrenia.

Adult↗

PubMed1998

Investigation of facial recognition memory and happy and sad facial expression perception: an fMRI study.

We investigated facial recognition memory (for previously unfamiliar faces) and facial expression perception with functional magnetic resonance imaging (fMRI). Eight healthy, right-handed volunteers participated. For the facial recognition task, subjects made a decision as to the familiarity of each of 50 faces (25 previously viewed; 25 novel). We detected signal increase in the right middle temporal gyrus and left prefrontal cortex during presentation of familiar faces, and in several brain regions, including bilateral posterior cingulate gyri, bilateral insulae and right middle occipital cortex during presentation of unfamiliar faces. Standard facial expressions of emotion were used as stimuli in two further tasks of facial expression perception. In the first task, subjects were presented with alternating happy and neutral faces; in the second task, subjects were presented with alternating sad and neutral faces. During presentation of happy facial expressions, we detected a signal increase predominantly in the left anterior cingulate gyrus, bilateral posterior cingulate gyri, medial frontal cortex and right supramarginal gyrus, brain regions previously implicated in visuospatial and emotion processing tasks. No brain regions showed increased signal intensity during presentation of sad facial expressions. These results provide evidence for a distinction between the neural correlates of facial recognition memory and perception of facial expression but, whilst highlighting the role of limbic structures in perception of happy facial expressions, do not allow the mapping of a distinct neural substrate for perception of sad facial expressions.

Adult↗

PubMed2002

Visual motion stimulation, but not visually induced perception of self-motion, biases the perceived direction of verticality.

Large-field torsional optokinetic stimulation is known to affect the perceived direction of gravity with verticality judgements deviating towards the direction of visual stimulus rotation. The present study aimed to replicate this effect and to examine it further by subjecting participants to optokinetic stimulation in roll, resulting in spontaneous alternations between the perception of object-motion and that of contradirectional self-motion (vection), as reported by the subjects. Simultaneously, subjects were oscillated laterally in a flight simulator and indicated their perception of postural verticality. Results confirmed that rotation of the visual environment in the frontal plane biases the perceived orientation of gravity towards the direction of visual stimulus motion. However, no differential effect of perceptual state on postural verticality was obtained when contrasting verticality judgements made during the perception of object-motion with those obtained during reported self-motion perception. This finding is likely to reflect a functional segregation of central nervous visual-vestibular subsystems that process the perception of self-tilt and that of self-rotation to some degree independently.

Adult↗

PubMed1998

Changes in lung volumes and poor perception of bronchoconstriction-induced respiratory symptoms.

BACKGROUND: Changes in lung volumes may contribute to the perception of bronchoconstriction-induced breathlessness. AIM: To verify whether histamine-induced increases in lung volumes are more marked in asthmatic subjects with normal compared with low symptom perception scores and whether changes in lung volumes are detected similarly in both groups of subjects. METHODS: A group of 16 asthmatic subjects with low (< or =1) breathlessness score (scale: 0 to 10) at 20% fall in FEV1 (PS20B) on at least one of 2 histamine inhalation tests (HIT) performed on separate days (hypoperceivers) were studied. They were compared with a group of 12 asthmatic patients with a PS20B >1 on the 2 tests (normoperceivers). Lung volumes were measured before and after the second HIT and changes correlated with PS20B and PS20 for the sensation of chest tightness PS20CT) and with the slopes of these perception scores/% fall in FEV1 (PS B or CT/deltaFEV1). RESULTS: Hypoperceivers had a mean (+/-sem) PS20B of 1.03+/-0.20 on HIT1 and 0.66+/-0.12 on HIT2 (P>.05) and normoperceivers 2.59+/-0.14 on HIT1 and 2.38+/-0.18 on HIT2 (P>.05). Subjects' age, gender, duration of asthma, medication needs, and baseline and post-HIT pulmonary function (FEV1, FVC, FRC) were not significantly different between the two groups. Contrary to PS20B (P<.0001), PS20 for chest tightness (PS20CT) was similar in the two groups (HIT 1/2; hypoperceivers: 1.41/1.07, normoperceivers: 1.57/1.99, both P>.05). Perception of bronchoconstriction-induced breathlessness was not correlated with the degree of reduction in FVC at 20% fall in FEV1. In normoperceivers, (PS B/deltaFEV1) was significantly correlated with the postchallenge increase in FRC (rs = 0.63, P=.036) although there was no significant correlation in hypoperceivers (rs = -0.041, P>.05). CONCLUSION: Changes in lung volumes were similar in hypoperceivers and hyperperceivers of bronchoconstriction. Perception of breathlessness, however, was positively correlated with changes in lung volumes in normoperceivers but not in hypoperceivers suggesting that normoperceivers have an ability to detect these changes, presumably through proprioception, ability that is lacking or lost in hypoperceivers. More subjects should be studied to confirm this finding.

Adult↗

PubMed2001

Effects of whole body cooling on sensory perception and manual performance in subjects with Raynaud's phenomenon.

Patients with Raynaud's phenomenon (RP) have abnormal digital vasoconstriction in response to cold. The aim of the study was to investigate the effects of cooling on sensory perception and manual performance in healthy male subjects and subjects with RP. There were two groups of subjects with primary RP: 12 subjects fulfilled the criteria of Lewis (L) and the other 12 the more critical criteria of Maricq (M). Control group (C) consisted of 19 healthy men. Subjects were exposed to 5 degrees C for 60 min. Skin temperatures were measured. Finger dexterity, pinch strength, abduction/adduction of fingers, pressure perception threshold and vibration perception threshold were tested during the exposure every 15 min. At the beginning of the exposure the mean (S.E.) finger temperature was 2.5 (1.2) degrees C (P<0.05) lower in M than in C. Manual performance and sensory perception were impaired due to the cooling, the impairment being significantly greater in M than in C. Responses of L were between those of M and C. In a given finger temperature vibration and pressure sensibility and manual performance were lower in M and L than in C. In conclusion, cold exposure decreased sensory perception and manual performance in the subjects with RP to a lower level than in the healthy subjects. Non-thermal factors may also decrease performance in RP.

Adult↗

PubMed1997

The relationship between smooth pursuit performance, motion perception and sustained visual attention in patients with schizophrenia and normal controls.

BACKGROUND: In this study, we tested the hypothesis that low smooth pursuit gain in schizophrenia is related to an abnormality in motion perception. METHODS: The subjects were 19 schizophrenics treated with clozapine and 19 controls. In addition to smooth pursuit and motion perception paradigms, sustained attention was also assessed using a continuous performance task (CPT). RESULTS: In the patient group, there was a statistically significant negative correlation between smooth pursuit gain and motion perception threshold (r = -0.60, P < 0.01). This relationship was not secondary to attention deficits as assessed by the CPT. CONCLUSIONS: Our results are consistent with the notion that the smooth pursuit gain deficit is related to a deficit in motion perception rather than in attention. Brain area V5 (also referred to as "MT' in macaque), located in the parieto-occipital region, is known to be critically important both for motion perception and gain. Thus, our results point to an abnormality in this area in schizophrenia.

Adult↗

PubMed2000

Do positive self-perceptions have a "dark side"? Examination of the link between perceptual bias and aggression.

The hypothesis that positive self-perceptions may have a "dark side" was investigated in the present study by examining the relationship between positively biased self-perceptions and aggression. Ratings of actual and perceived social acceptance of third-grade (n = 278), fourth-grade (n = 260), and fifth-grade (n = 321) students were compared to form a measure of perceptual bias. Peers provided nominations for overt and relational aggression. Gender differences were found for aggression (males were more overtly and relationally aggressive than females) but not perceptual bias. African-American children held more positive perceptions of their social acceptance and were perceived by peers as more aggressive than Caucasian children. Even after controlling for the effects of gender and ethnicity, more positively biased perceptions were associated with more peer nominations for overt and relational aggression. Contrary to an optimal range of bias hypothesis, even moderately positive self-perceptions were associated with elevated levels of aggression.

Aggression↗