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At least 1,351 records · Page 75Linked to original sources
PubMed2000

Vestibular perception of self-rotation in different postures: a comparison between sitting and standing subjects.

We investigated whether posture - either seated (S) or upright standing (O, orthostatic) - affects the vestibular perceptions of angular velocity (V) and displacement (D) in the horizontal plane. We also examined whether the two perceptions are equivalent, that is, whether perceived displacement can be viewed as the time integral of perceived velocity. Sinusoidal stimuli were delivered to subjects sitting on a Barany chair or standing on a turning platform. Frequencies ranged from 0.028 Hz to 0.45 Hz, peak-to-peak amplitudes from 11.3 degrees to 180 degrees, and peak velocities from 4 degrees/s to 64 degrees/s. Perceptions were measured by retrospective magnitude estimation in relation to a standard stimulus (STD) of 0.11 Hz, 45 degrees, 16 degrees/s. For D-estimates, two different moduli were assigned to the STD: Either "45 degrees" (allowing subjects to use the familiar degree scale, which can easily be related to the body scheme) or "10" (which bears no relation to an accustomed scale). For V-estimations the modulus was always "10" (there is no "natural" velocity scale). D-estimates exhibited only a marginal, non-significant dependence on posture (S larger than O); they were highly veridical (linear function of stimulus amplitude, gain close to 1) when subjects used the degree scale but had a reduced gain (approximately 0.76) with a modulus of 10. V-estimates, on the other hand, varied with posture (S significantly larger than O), particularly upon presentation of large stimuli; also, they deviated increasingly from veracity as stimulus magnitude increased (saturating function). Finally, posture had no effect upon the vestibular detection threshold. The frequency response of D-estimates, tested with stimuli of constant amplitude and varying frequency, was bimodal at low frequencies: stimuli were either not detected at all or were veridically estimated, on average (with a large scatter, though). The frequency response of V-estimates, tested with stimuli of constant peak velocity, exhibited a continuous increase with stimulation frequency. We conclude that published quantifications of vestibular self-motion perception, collected mostly with sitting subjects, are likely to be applicable also to the more natural situation of standing subjects provided they are based on displacement indications; in contrast, velocity indications appear to be modulated by posture. The different susceptibility of displacement and velocity estimates to posture and their incongruent frequency characteristics suggest that perceived displacement does not, or does not always, equal the time integral of perceived velocity. The persistence of nearly veridical displacement estimates at low frequencies suggests the intervention of cognitive processes.

Acceleration↗
PubMed2001

Comparison of perceptional nasal obstruction with rhinomanometric and acoustic rhinometric assessment.

Perception of nasal stuffiness, together with rhinomanometric and acoustic rhinometric assessments were evaluated before and after nasal and/or sinus surgery in 50 Japanese adult patients. Nasal resistance on both expiration and inspiration correlated well with the patients' perceptions (P<0.05). Nasal volumes (0-4 cm and 0-7 cm) obtained from acoustic rhinometry measurements also correlated well with perception (P<0.05). No significant relationships were found between rhinomanometric and acoustic rhinometric results. Perceptional nasal obstruction, rhinomanometric and acoustic rhinometric results (except for the sectional areas at the I-notch) improved significantly after the operations. Rhinomanometry and acoustic rhinometry are valuable methods for assessing nasal stuffiness, but we must take account of the differences between the two methods.

Adult↗
PubMed1999

Understanding the origin of visual percepts elicited by electrical stimulation of the human retina.

BACKGROUND: The success of a retinal prosthesis for patients with outer retinal degeneration (ORD) depends on the ability to electrically stimulate retinal cells other than photoreceptors. Experiments were undertaken in human volunteers to ascertain whether electrical stimulation of cells other than photoreceptors will result in the perception of light. METHODS: In two subjects, two areas of laser damage (argon green and krypton red) were created in an eye scheduled for exenteration due to recurrent cancer near the eye. In the operating room prior to exenteration, under local anesthesia, a hand-held stimulating device was inserted via the pars plana and positioned over the damaged areas and normal retina. Subjects' psychophysical responses to electrical stimulation were recorded. RESULTS: In both subjects, electrical stimulation produced the following perceptions. Normal retina: dark oval (subject 1), dark half-moon (subject 2); krypton red laser-treated retina: small, white light (both subjects); argon green laser treated retina: thin thread (subject 1), thin hook (subject 2). Histologic evaluation of the krypton red-treated retina showed damage confined to the outer retinal layers, while the argon green-treated area evinced damage to both the outer and the inner nuclear layers. CONCLUSION: The perception produced by electrical stimulation was dependent on the retinal cells present. Electrical stimulation of the krypton red-ablated area best simulated the electrically elicited visual perceptions of our blind, ORD patients, suggesting that the site of stimulation in blind patients is the inner retinal neurons.

Aged↗
PubMed2005

False consensus and adolescent peer contagion: examining discrepancies between perceptions and actual reported levels of friends' deviant and health risk behaviors.

Adolescents' perceptions of their friends' behavior strongly predict adolescents' own behavior, however, these perceptions often are erroneous. This study examined correlates of discrepancies between adolescents' perceptions and friends' reports of behavior. A total of 120 11th-grade adolescents provided data regarding their engagement in deviant and health risk behaviors, as well as their perceptions of the behavior of their best friend, as identified through sociometric assessment. Data from friends' own report were used to calculate discrepancy measures of adolescents' overestimations and estimation errors (absolute value of discrepancies) of friends' behavior. Adolescents also completed a measure of friendship quality, and a sociometric assessment yielding measures of peer acceptance/rejection and aggression. Findings revealed that adolescents' peer rejection and aggression were associated with greater overestimations of friends' behavior. This effect was partially mediated by adolescents' own behavior, consistent with a false consensus effect. Low levels of positive friendship quality were significantly associated with estimation errors, but not overestimations specifically.

Adolescent↗
PubMed2005

Perception and production of prosody by speakers with autism spectrum disorders.

Speakers with autism spectrum disorders (ASD) show difficulties in suprasegmental aspects of speech production, or prosody, those aspects of speech that accompany words and sentences and create what is commonly called "tone of voice." However, little is known about the perception of prosody, or about the specific aspects of prosodic production that result in the perception of "oddness." The present study examined the perception and production of a range of specific prosodic elements in an experimental protocol involving natural speech among speakers with ASD between 14 and 21 years of age, in comparison with a typical control group. Results revealed ceiling effects limiting interpretation of findings for some aspects of prosody. However, there were significant between-group differences in aspects of stress perception and production. The implications of these findings for understanding prosodic deficits is speakers with autism spectrum disorders, and for future research in this area, are discussed.

Adolescent↗
PubMed2006

Enhanced perceptual functioning in autism: an update, and eight principles of autistic perception.

We propose an "Enhanced Perceptual Functioning" model encompassing the main differences between autistic and non-autistic social and non-social perceptual processing: locally oriented visual and auditory perception, enhanced low-level discrimination, use of a more posterior network in "complex" visual tasks, enhanced perception of first order static stimuli, diminished perception of complex movement, autonomy of low-level information processing toward higher-order operations, and differential relation between perception and general intelligence. Increased perceptual expertise may be implicated in the choice of special ability in savant autistics, and in the variability of apparent presentations within PDD (autism with and without typical speech, Asperger syndrome) in non-savant autistics. The overfunctioning of brain regions typically involved in primary perceptual functions may explain the autistic perceptual endophenotype.

Asperger Syndrome↗
PubMed2007

Emotion perception in Asperger's syndrome and high-functioning autism: the importance of diagnostic criteria and cue intensity.

This study compared emotion perception accuracy between children with Asperger's syndrome (AS) and high-functioning autism (HFA). Thirty children were diagnosed with AS or HFA based on empirically supported diagnostic criteria and administered an emotion perception test consisting of facial expressions and tone of voice cues that varied in intensity. Participants with AS and the typically developing standardization sample of the emotion perception instrument had the same mean emotion perception accuracy, whereas participants with HFA performed significantly worse. Results also provided preliminary evidence for a difference in accuracy perceiving low-intensity tone of voice cues between participants with HFA and AS. Future research to build on these initial findings should include attention to tone of voice, underlying processing, and cue intensity.

Adolescent↗
PubMed2005

Sickness and satiety: physiological mechanisms underlying perceptions of nausea and stomach fullness.

The pathophysiology of nausea and the physiological mechanisms underlying perceptions of stomach emptiness and fullness are not clearly understood, but several potentially important factors have been identified. Gastric dysrhythmias are believed to contribute to the subjective experience of nausea and may also be involved with perceptions of stomach emptiness, hunger, and even dyspepsia symptoms like bloating and early satiety. Normal gastric neuromuscular function is more evident in the absence of nausea and is also thought to be related to feelings of satiety or comfortable stomach fullness. Autonomic and endocrine influences may also play a critical role in the pathophysiology of nausea and abnormal perceptions of stomach emptiness or fullness. Achieving a better understanding of the gastric neuromuscular and neurohormonal influences on perceptions arising from the viscera may prove invaluable in the development of novel treatments for such conditions as unexplained nausea, functional dyspepsia, and obesity.

Autonomic Nervous System↗
PubMed1995

Heartbeat perception and panic disorder: possible explanations for discrepant findings.

Results on cardiac awareness in panic disorder are inconsistent. The present study attempted to clarify whether differences in instructions or the inclusion of patients taking antidepressant medication could account for these inconsistencies. 112 patients with panic disorder with agoraphobia were compared to 40 normal controls on the heartbeat perception task developed by Schandry (1981) [Schandry, R., Psychophysiology, 18, 483-488] using a standard instruction ("count all heartbeats you feel in your body") and a strict instruction ("count only those heartbeats about which you are sure"). Superior heartbeat perception for patients was only found with the standard instruction. Similarly, only with the standard instruction, patients taking medication affecting the cardiovascular system performed worse than patients without medication, as expected based on the relationship between stroke volume and heartbeat perception. The pattern of group differences indicates that agoraphobic patients have a better feeling for how fast their heart is beating than controls although these differences may be due to a tendency to interpret weak sensations as heartbeats. Furthermore, we tested in a subgroup of 40 patients whether cardiac awareness changes with exposure treatment. No changes in heartbeat perception were observed.

Adrenergic beta-Antagonists↗
PubMed1995

Hyperglycemia alters perception of rectal distention and blunts the rectoanal inhibitory reflex in healthy volunteers.

BACKGROUND/AIMS: Acute hyperglycemia has been shown to alter gastrointestinal motility. The effects of hyperglycemia on rectal afferent neural and anal sphincter function were studied. METHODS: Perception of rectal balloon distention, pressure-volume relationships, volumes necessary to induce reflex internal anal sphincter relaxation, resting anal sphincter pressure, and maximal anal sphincter squeeze pressure were measured under basal, hyperglycemic clamp, and euglycemic, hyperinsulinemic clamp conditions in 9 healthy volunteers. RESULTS: Hyperglycemic clamping (258 +/- 14 mg/dL) significantly blunted threshold perception and the urge to defecate in response to rectal distention without altering perception of maximally tolerated distention. In contrast, euglycemic, hyperinsulinemic clamping had no effect on perception of rectal distention. Rectal pressure-volume relationships after hyperglycemic clamping were unchanged compared with basal conditions. Hyperglycemic clamping caused a significant increase in the distention necessary to induce the rectoanal inhibitory reflex. This effect was not observed under euglycemic, hyperinsulinemic clamp conditions. Hyperglycemia did not significantly affect resting internal anal sphincter pressure or maximal external anal sphincter squeeze pressure. CONCLUSIONS: Acute hyperglycemia but not secondary hyperinsulinemia reduces sensation of rectal distention and blunts the onset of the rectoanal inhibitory reflex, suggesting effects both on visceral afferents projecting to the cortex and intrinsic afferents mediating local reflex activity.

Adult↗
PubMed1984

Maternal perception, tocodynamometric findings and real-time ultrasound assessment of total fetal activity.

"Total" fetal motor activity was determined in 111 healthy patients between 25 weeks of pregnancy and term using two real-time ultrasound devices simultaneously. Furthermore tocographic findings and also maternal perception of fetal movements of the same patients were stored synchronously on magnetic tape. A comparison was drawn between these three methods, i.e. real-time ultrasonography, maternal perception and tocographic tracings ("spikes" indicating fetal movements). Of all fetal movements, as assessed by real-time ultrasonography, the mothers perceived a total of 38% whereas "spikes" in tocographic tracings corresponded with fetal motor activity (excluding "breathing") in only 25% of the cases (P less than 0.001). Also major statistically significant differences could be found between maternal perception of fetal body movements with or without fetal limb movements in 56% and routine- tocography in 37% (P less than 0.001). Also isolated limb movements were most often detected by mothers (23%) than were revealed by tocographic findings (14%; P less than 0.001). Maternal signals were truly positive in 74% compared to tocography in only 56% of the cases (P less than 0.001). It is concluded that maternal perception of fetal movements is a more reliable method of monitoring fetal motor activity than analysis of tocographic tracings.

Adolescent↗
PubMed1993

A dissociation of shape discrimination and figure-ground perception in a patient with normal acuity.

We report the case of a 21-year-old man who sustained brain damage due to anoxia. His visual acuity was normal and his colour perception was adequate if not completely normal. However, his shape discrimination was so impaired that he had great difficulty distinguishing a square from an oblong or a large square from a smaller square. At the same time, other aspects of his shape perception were remarkably intact. His performance on a shape detection task was good. He had no difficulty on tests of figure-ground (boundary) segmentation and his perception of subjective and illusory contours appeared to be normal. S.M.K.'s performance on a number of tasks is compared with that of a patient (F.G.P.) previously reported who showed the opposite pattern of deficit (Kartsounis and Warrington, Neuropsychologia 29, 969-980, 1991). This evidence of a double dissociation between two components of shape perception is discussed in the context of a neurophysiological model of the organization of the visual system.

Adult↗
PubMed1990

Conditions for versatile learning, Helmholtz's unconscious inference, and the task of perception.

It is a mistake to consider perception and learning separately because what one learns is strongly constrained by what one perceives, and what one perceives depends on what one has experienced. I shall propose the hypothesis that perception is the computation of a representation that enables us to make reliable and versatile inferences about associations occurring in the world around us--that is, perception prepares the ground for learning. The statistical problem in learning is to determine whether a compound event such as "C followed by U" is a random co-occurrence or a significant association, for if it is the former it would be a mistake to pay any particular attention to C, whereas if it is the latter C is a conditional stimulus for U and a useful predictor for it. Now you cannot decide whether the association is random or not without knowledge of the prior probabilities of C and U: hence on my hypothesis when you perceive an object or event the representation must not only signal "it's there" or "it's happened", but must also make evident (or rapidly accessible) the prior probability of what has been signalled. Furthermore it must do this for all the objects or events that can act as conditional stimuli, and this implies that the representative elements should be statistically independent (or approximately so) in the normal environment. Forms of coding that would do this, and the relationship with Helmholtz's unconscious inference, will be discussed. These considerations imply that the task performed in perception has been overlooked both by learning theorists and by connectionists working on associative and adaptive networks. Coding for independence may be particularly important in understanding the developmental processes during the sensitive period: it may be the operation that leads ontogenetically-timed, activity-dependent, connections to imprint appropriate codes if the animal has experience, but inappropriate codes without experience.

Adaptation, Physiological↗
PubMed1993

Nonlinear combination rules and the perception of visual motion transparency.

Experiments were performed to elucidate the decomposition performed by the human visual system in the segregation of complex motion stimuli into distinct moving surfaces. Subjects were presented with achromatic patterns consisting of four types of elements, generated from two random binary luminance patterns (random-dot checkerboards). The luminance of each of the four region classes was under program control. Animated sequences of such images were produced by displacing each of the two generating patterns in opposite directions on a frame by frame basis. These displays evoke a wide variety of percepts, depending on the programmed luminance values, including motion in a single direction, simultaneous motions of transparent sheets in opposite directions, dynamic noise with no directional component, or any combination of the above percepts. A theory is presented which relates the strengths of these percepts to the amplitudes of the components in the perceptual decomposition. The experiments described measured thresholds for seeing noise or "twinkling" in addition to the multiple motions, with the goal of determining the particular signal transformations preceding motion analysis. The results are consistent with a motion extraction mechanism which operates on a linear representation of the input imagery. These results extend a similar finding due to Anstis and Mather [(1985) Perception, 14, 167-179] and call into question the interpretation of a recent study by Stoner, Allbright and Ramachandran [(1990) Nature (London), 344, 153-155].

Contrast Sensitivity↗
PubMed1994

Interaction between primary and secondary mechanisms in human motion perception.

Two layers of information processing can be distinguished as being involved in human motion perception. The primary motion detection stage processes displacements of the luminance distribution across space, such as experienced in natural scenes during the pursuit of moving targets. Primary motion detection is often investigated with artificial motion stimuli realized as random-dot kinematograms (RDKs). Such stimuli belong to the class of "Fourier motion", and their perception can be easily explained by means of elementary motion detectors (EMDs) of the correlation type. Other tasks require the comparison of motion signals from neighbouring areas in the visual field. The perception of the displacement of the motion distribution, for instance, has been accounted for by a secondary motion processing stage. In order to understand the principles of interaction between the motion in neighbouring areas of the visual field, we investigated the sensitivity of the human visual system for moving objects which are defined by moving dots in variable directions. These experiments lead to "secondary tuning curves" of direction discrimination for secondary motion as function of primary motion direction. A base level of sensitivity for all dot motion directions without a velocity component in the same direction of the object movement is enhanced when the object and the dots have a common velocity component. Thus primary motion in any direction can be exploited by the secondary stage, and primary and secondary system both feed into the object motion percept. Furthermore it is suggested from the shape of the secondary tuning curve that the outputs from the two layers of motion processing do not superimpose linearly, but are combined by some sort of veto-like mechanism which increases the directional sensitivity when the two processing layers experience movement along the same direction.

Adult↗
PubMed1990

Auditory perception of temporal and spectral events in patients with focal left and right cerebral lesions.

The auditory perception of temporal and spectral information was studied in subjects with lesions in the temporoparietal region of the left (LH group), or right (RH group) hemisphere (n = 5 in each group) and in five normal controls. The temporal tasks included gap detection and two complex pattern perception tasks in which subjects had to identify the placement of the two closest tones (separated by the shortest interval) within a sequence of six tones. The spectral tasks involved pitch matching and frequency discrimination. The results showed a "double dissociation": (1) the LH group was impaired in their ability to perceive temporal information, but the perception of spectral information was normal, and (2) the RH group was impaired in their ability to perceive spectral information, but the perception of temporal information was normal. The findings are consistent with the notion that temporal processing is a function of left-hemisphere structures and that spectral processing is a function of right-hemisphere structures.

Adult↗
PubMed1991

Adolescents' perceptions of risk for HIV infection: implications for future research.

Few studies have investigated adolescents' perceptions of their risk for HIV infection. Findings from two studies of adolescents in Massachusetts indicate that there are differences in the knowledge, beliefs, behaviors, and perceptions of risk among adolescents and suggest the need for understanding the differences among adolescents from different racial or ethnic backgrounds. In both studies, white students were the most knowledgeable about casual, sexual, and drug use transmission of HIV followed by black, Hispanic, and Asian students. In both studies more black adolescents than other racial or ethnic groups were sexually active, and black and Hispanic adolescents began having sexual intercourse at an earlier age than white or Asian adolescents. Asian and Hispanic adolescents were most worried about getting AIDS. Although more Hispanics than other groups reported changing their behavior because of AIDS, fewer of them who had changed their sexual or contraceptive behavior were using effective methods. Despite clear differences in the perceived risk of getting AIDS among these adolescents, the underlying reasons remain to be explicated, using, among other data collection methods, ethnographic techniques to probe adolescents' risk perceptions, their understandings of sickness, and their explanatory models of AIDS. Life events affect risk taking behaviors and also shape perceptions of risk. To understand what it is that adolescents consider 'risky' requires seeing their life options as they do in the larger context of their aspirations and worries about how 'to fit in'.

Acquired Immunodeficiency Syndrome↗
PubMed1978

Paradoxical sleep and depth perception.

It has been hypothesised that one possible function of paradoxical (REM) sleep is the maintenance of facilitation of co-ordinated eye movements. A prediction from this hypothesis is that binocular depth perception will be more accurate at the end of periods of paradoxical sleep than at the beginning. The results from previous studies are conflicting. Using two groups of eight healthy male volunteers in a two factor repeated measures design, it was found that for a period of paradoxical sleep in the second half of the night only, there was an improvement in binocular depth perception accuracy between the beginning and end of paradoxical sleep. The accuracy at the end of the paradoxical sleep was not significantly different to that on going to bed or on awakening in the morning; the effect was due to a large decrease in accuracy at the start of the REM period. There was no effect of paradoxical sleep on binocular depth perception in the early part of the night. Monocular depth perception accuracy was unaffected by paradoxical sleep.

Adolescent↗