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PubMed1984

Alterations in auditory processing of speech stimuli during aging in healthy subjects.

Studies of auditory processing during aging in man have not provided a consensus on whether aging affects the ability to process speech stimuli. To evaluate the relationship between speech recognition tasks and age, we examined 36 male subjects between the ages of 21 and 83 years, who were screened for the absence of disease, particularly in the cardiovascular and neurologic systems. Measures were obtained on the following tests: pure tone thresholds, speech reception threshold, speech discrimination, low-pass filtered speech, and binaural fusion. A statistically significant correlation was found between pure tone thresholds and age for all frequencies. When the effect of peripheral hearing loss was taken into account, speech measures did not correlate with age, with the exception of low-pass filtered speech in the left ear. Our findings suggest that the aging process in healthy man is not necessarily accompanied by deficits in the processing of speech stimuli beyond those which are due to peripheral hearing loss.

Adult↗
PubMed1984

Body perception and somatic discomfort in relation to right- versus left-handedness.

Multiple studies analyzed differences in body perception and body complaints between right- and left-handed subjects. Both male and female samples were included. The findings indicated that the left-handed exceeded the right-handed in feelings of body security and degree of body boundary differentiation. In addition, handedness was shown to be linked with different modes of distributing attention to the major sectors of one's body. An adequate explanation of the link between handedness and body perception is not at present available.

Adolescent↗
PubMedDate not supplied

Body perception index: benefits, pitfalls, ideas.

Estimates of body size are often expressed as a ratio of actual size [body perception index or BPI = (estimated size/actual size) x 100%]. In this article, we examine the possibility that overestimation of body size in patients with anorexia nervosa, as measured by the BPI, is due to their smaller body size rather than to their being anorexic. Using 50 mean body sizes derived from seven studies we investigated whether the error of estimation is a constant proportion of the body size to be estimated, as the use of the BPI assumes. A negative linear relation between BPI and actual body size was found, confirming that smaller size is associated with greater overestimation. However, although both groups showed a strong tendency to overestimate smaller sizes, anorexic subjects showed even greater overestimation than controls. Hence, overestimation of body size in AN can only partially be accounted for by the smaller body size of anorexic patients. Recommendations for future use of the BPI are put forward.

Adolescent↗
PubMed1999

Body size perception in anorexia nervosa: a signal detection approach.

This study investigated whether individuals with anorexia nervosa (AN) visualize themselves as fatter than they are because they perceive themselves as fatter. Females with AN who overestimated their own body size judged size differences between pictures of their own body, and then again of someone else's body. Signal detection analysis of the results showed no differences in perceptual sensitivity between the AN and normal and thin control groups. No significant correlations were found between body size estimates and perceptual sensitivity. The anorexic group did, however, show a bias to report seeing "thin" differences, which was opposite to that of thin controls. Because bias differences between the groups were significant while sensitivity differences were not, it was concluded that abnormalities of body image most probably arise during reconstruction of the visual body image, rather than during perception of the body.

Adult↗
PubMed2000

Weighing the evidence for cross over in neglect.

When patients with left-sided neglect are asked to bisect horizontal lines, they tend to place their marks to the right of the line's objective mid-point. However, when asked to bisect short lines they are either more accurate or paradoxically cross over and place their marks to the left of the objective mid-point. Previous explanations of the cross over phenomenon have considered specific aberrations of spatial attention. However, these explanations make no predictions about judgments of non-spatial stimuli. Two patients with right brain damage were asked to judge weights placed on both hands simultaneously. They were biased in reporting weights on the right as being heavier than those on the left. This rightward bias changed with lighter pairs of weights presented in the context of equal reference weights. In one patient the directional bias was eliminated and in the other the bias was reversed so that she was more likely to report the left weight as heavier than the right. These data suggest that a phenomenon analogous to cross over in line bisections also occurs with judgments of non-spatial stimuli. Representations of stimuli appear to be influenced by features of the stimuli encountered on-line and by memory traces of similar stimuli encountered previously. With an attentional deficit, memory traces influence the magnitude of the representation derived on-line disproportionately.

Aged↗
PubMed2001

Disruption of estimation of body-scaled aperture width in Hemiparkinson's disease.

A group of patients with left-sided symptoms of Parkinson's disease (LPD) was compared with a group of patients with right-sided symptoms (RPD) and with a group of healthy age-matched controls on body-scaled judgements of aperture width. Participants judged whether or not they would fit through a life-sized schematic doorway shown on a large screen. A staircase technique was used to find the door width for which 50% of the judgements were positive. The ratio between this measure and the width of the participant's body at the shoulders (the aperture to shoulder - A/S ratio) was calculated. The A/S ratio was approximately 1.5 in the LPD group, approximately 0.9 in the RPD group, and approximately 1.1 in the control group, suggesting that the visual representation of the doorway (or that of its relationship to perceived body-size) is compressed in LPD (and perhaps expanded in RPD). The A/S ratios were invariant with viewing distance (0.6 or 1.5 m), the contrast polarity of the display (white on dark, or vice versa) and the doorway surround (blank, or vertical or horizontal stripes). The findings are discussed with reference to the neural representation of external space and of the body, and to the motor problems of Parkinson's disease.

Aged↗
PubMed2002

Abnormal line bisection judgements in children with Tourette's syndrome.

Tourette's syndrome (TS) has been associated with loss of normal basal ganglia asymmetry, as well as loss of normal functional asymmetry, including the leftward bias on traditional visuospatial tasks such as line bisection and turning bias tests. The aim of the present study was to examine the lateralisation of visuospatial attention in TS. We examined the effect of an irrelevant moving-dot background on line bisection judgements. Nine children with a DSM IV diagnosis of TS participated, in addition to 9 healthy controls, individually matched for age, sex and IQ. Horizontal lines of varying length were presented on a computer screen with either a blank background, or a moving, random-dot field. The dots moved either leftward or rightward across the screen at 40 or 80 mm/s, and participants were instructed to ignore these distracting stimuli when judging the lines. TS children were found to be abnormally right-biased in line bisection in a similar fashion to unmedicated ADHD children who, in a previous study, showed a similar small, yet significant, right-bias in line bisection. Matched controls showed a small, nonsignificant left bias, consistent with past research. Unlike previous findings with hemineglect patients, the irrelevant moving background had no effect on bisection performance for TS children or healthy controls. The present findings suggest a deficit in visuospatial attention consistent with the emerging picture of a lateralised dysfunction of frontostriatal circuitry in TS.

Adolescent↗
PubMed1999

Motor and perceptual factors in pseudoneglect.

An important variant of the traditional line bisection task has involved a mechanical device invented by Bisiach and his colleagues (Bisiach et al. Perceptual and premotor factors of unilateral neglect. Neurology 1990;40:1278-81 [3]). This tool was devised to dissociate motor from perceptual factors in hemi-spatial neglect, by means of a mid-line indicator which moved 'congruently' or 'non-congruently' with the direction of hand movement. In the non-congruent condition, Bisiach was able to demonstrate a reduction, or reversal, of the direction of bisection error in a number of patients with neglect. These errors were interpreted as instances of 'motor' neglect. Bisiach et al. [3] also tested 10 normal subjects, who did not differ on the two conditions of the task. However, the original experiment [3] required the use of the right hand only, and it has since become clear that bisection errors in normal subjects (i.e. pseudoneglect) are more substantial when dextral subjects use their left hands. By using a modified version of the Bisiach Tool we show that there is an effect of the motor versus perceptual condition on this task, but only when subjects use their non-dominant (left) hand.

Adult↗
PubMed1998

Visual discrimination in pigeons impaired by glutamatergic blockade of nucleus accumbens.

The nucleus accumbens septi (Acc) is thought to be involved in the control of cognitive processes and to be implicated in the pathophysiology of schizophrenia. Because perceptual-cognitive distortions are a core symptom in schizophrenia, any evidence that the Acc intervenes in a sensory recognition task in an animal species would be of interest. Pigeons were instrumentally trained to discriminate visual shapes. The acute effects of drug microinjections into the Acc on the discrimination of the training shapes, on the correction responding after errors, and on the generalisation to different shapes were examined. The effects of conduction blockade with lidocaine, glutamatergic blockade with 7-aminophosphonoheptanoic acid, and dopaminergic stimulation with apomorphine on behavioural performance were tested. No effects were observed with lidocaine and apomorphine. A significant and reversible performance disruption to near chance levels was obtained after aminophosphonoheptanoic acid injections into the Acc. It appears that a glutamatergic blockade of the Acc interferes with the visual discrimination processes of pigeons.

2-Amino-5-phosphonovalerate↗
PubMed1996

Perception of breast cancer risk among women in breast center and primary care settings: correlation with age and family history of breast cancer.

BACKGROUND: A great deal of information about breast cancer risk is available to the public. The accuracy of impressions formed from this information is unknown. METHODS: A total of 750 women attending a breast center and 112 women attending a primary care office completed written surveys of their perceptions of average population risk, personal lifetime risk, and personal 10-year risk of getting breast cancer. Data sufficient to apply the Gail model were obtained, and a calculated estimate of risk was generated. Ratios of perceived to calculated risk were correlated with the respondent's age, family history of breast cancer, and location in a breast center or primary care office. RESULTS: Women in both practice settings overestimated population risk by more than twofold. Eighty percent overestimated personal lifetime risk by more than 50% and 35% by more than fivefold. Only 7% significantly underestimated risk. Ten-year risk estimates were even more inaccurate, with 69% overestimating risk by more than fivefold, 46% by more than 10-fold, and 17% by more than 20-fold. Results from a primary care population were nearly identical. Women at the extremes of age were most inaccurate in estimating risk. It was surprising that family history had little impact on perception of personal risk. CONCLUSIONS: Women in both breast center and primary care settings have a fals:ly high perception of both short-term and long-term breast cancer risk. Health care providers should recognize these misconceptions and be aware that many women may benefit from risk counseling.

Adult↗
PubMed2000

Direction biasing by brief apparent motion stimuli.

The perceived direction of a motion step (probe stimulus) can be influenced by an earlier motion step or a brief motion sweep containing a series of steps (biasing stimulus). Depending upon experimental conditions, the biasing of the direction of the probe step (a phase shift of 180 degrees +/-Phi) by a biasing stimulus which precedes it by approximately 250 ms can either increase (positive filter biasing) or decrease (negative filter biasing) the tendency to see the probe move in the biasing direction as computed with a motion filter with a biphasic temporal impulse response. In a series of experiments it was found that biasing motions traversing 90 degrees of phase angle in fewer than six steps in less than 100 ms produced positive filter biasing. Also, biasing of the probe direction could be dissociated from the consciously reported direction of the biasing stimulus, and it did not occur when the probe preceded rather than followed the biasing stimulus. A biasing sweep containing more than six steps traversing 90 degrees or a sweep traversing 270 degrees produced negative filter biasing. Perceptual fusion of the steps of the sweep was not a necessary condition for obtaining negative filter biasing. In general, the negative filter biasing effects were found to be the most pervasive for the conditions investigated, and they are suggestive of a direction-specific, adaptation-like (gain-control) process in first-order motion filters. The exception to the negative biasing rule was found only with biasing stimuli which were short in duration or distance spanned.

Humans↗
PubMed2000

Accuracy of estimating time to collision using only monocular information in unilaterally enucleated observers and monocularly viewing normal controls.

Since individuals who have lost an eye in early life rely on monocular information, one asked if they would better estimate the time to collision (TTC) with an approaching object based on the monocular cue [(θ/(dθ/dt), i.e. tau] than a control group using only monocular information. Estimates of TTC were measured with a simulated approaching textured object using a staircase procedure. Seven adult observers who were unilaterally enucleated at an early age were compared with 18 normally sighted control observers who viewed the stimuli monocularly. Consistent with previous findings, the majority of the controls (13/18) underestimated TTC. Three enucleated observers had larger estimation errors than the 95% confidence interval of the mean of the control group. One enucleated observer was unable to give reliable results. These results suggest that unilaterally enucleated observers cannot estimate TTC more accurately (and may even be worse) than normal controls when estimates are based on monocular information alone. Further, the majority (83%) of enucleated observers were influenced by perceived distance information derived from the object's initial size when estimating TTC with an approaching object. The use of this other optical variable could account for their reduction in performance. It was suggested that in every day life enucleated individuals make use of as many optical variables as possible to partially compensate for the lack of binocularity.

Adaptation, Physiological↗
PubMed2000

Eye movements and visible persistence explain the mislocalization of the final position of a moving target.

When observers are asked to localize the final position of a moving target, the judged position is usually displaced from the actual position in the direction of motion. The short-term time course of the displacement was investigated to test theories that attribute the localization error to spatial and temporal properties of human perception or to representational momentum. It was found that briefly after target offset, the judged position is already displaced in the direction of motion. It is argued that the shift results from eye movements after target offset that move the target's persisting image in the direction of motion.

Analysis of Variance↗
PubMed2001

Smooth eye movements and spatial localisation.

We asked subjects to align a target that flashed as their eyes rotated to the right in pursuit of a moving ring, with a target that flashed as their eyes rotated to the left in pursuit of the ring. Subjects systematically mislocalised the targets in the direction of pursuit. When the ring and flashes were the only structures that were visible, the alignment error was about 4 cm, corresponding to a timing error of about 100 ms. The timing error was independent of the position along the ring's path, but did depend to some extent on pursuit velocity. Adding a textured background reduced the mislocalisation considerably, presumably because it enabled subjects to localise the targets relative to the surrounding. There was almost no mislocalisation if the subject was not pursuing the ring. It is suggested that the mislocalisation arises because incoming retinal signals are combined directly with outgoing oculo-motor commands, with no attempt to account for any of the involved neuronal and muscular delays.

Computer Graphics↗
PubMed2001

Lines and dots: characteristics of the motion integration process.

Local motion detectors can only provide the velocity component perpendicular to a moving line that crosses their receptive field, leading to an ambiguity known as the "aperture problem". This problem is solved exactly for rigid objects translating in the screen plane via the intersection of constraints (IOC). In natural scenes, however, object motions are not restricted to fronto-parallel translations, and several objects with distinct motions may be present in the visual space. Under these conditions the usual IOC construction is no longer valid, which raises questions as its use as a basis for spatial integration and selection of motion signals in uniform and non-uniform velocity fields. The influence of the motion of random dots on the perceived direction of a horizontal line grating was measured, when dots and lines are seen through different apertures. The random dots were mapped on a plane that translates in a fronto-parallel plane (uniform 2D translation) or in depth (3D, corresponding to a non-uniform projected velocity field, either expanding or contracting). The grating was either moving rigidly with the dots or in the opposite direction. Subjects' responses show that the direction of line grating movement was reliably influenced only in conditions consistent with rigid motion; where there was a reliable influence, the perceived direction was consistent with the dot motion pattern. This finding points to the existence of a motion-based selection mechanism that operates prior to the disambiguation of the line movement direction. Disambiguation could occur for both uniform and non-uniform velocity fields, even though in the last case none of the individual dots indicated the proper direction in 2D velocity space. Finally, the capture by non-uniform motion patterns was less robust than that by uniform 2D translations, and could be disrupted by manipulations of the shape and size of the apertures.

Adult↗
PubMed2003

Face recognition with perspective transformation.

The effect of perspective transformation on transfer of face training was investigated in a yes/no recognition task using face stimuli with 42 degrees, 10 degrees, or no perspective convergence. A strong dependence of recognition performance on the magnitude of perspective transformation was found, with large perspective changes such as from 42 degrees at learning to orthogonal at test producing the strongest impairment and small perspective changes such as from 10 degrees at learning to orthogonal at test the least. In a second experiment, the internal and external features of a face from different perspective convergence were artificially combined to produce identical local features between this composite image and the original but producing an impossible perspective transformation from either. The results of transfer between the composite and untouched images showed face recognition to be strongly affected by local featural similarities and relatively insensitive to global coherence of perspective transformation.

Adult↗
PubMed2003

Electrical activity in visual cortex associated with combined auditory and visual stimulation in temporal sequences known to be associated with a visual illusion.

When a subject views a visual stimulus paired with a brief click, a second click occurring approximately 80 ms later produces the hallucination of a second visual stimulus. We have used combinations of visual and sound stimuli to evoke cortical activity and have recorded the associated event-related potentials. We have recorded EPs in a conventional manner, and have calculated from multichannel recordings the Laplacian derivations to determine if the currents were generated in primary visual cortex. Clicks alone do not cause significant activity in V1, but if paired with pattern stimulation, modify the evoked potential. The timing of this extra activity almost certainly excludes "feed back" activation from higher centres, and can most simply be explained if sound-activated thalamo-cortical input can rapidly produce extra activity in 'primed' visual cortex. This finding has general implications for cortical function, for the generation of the hallucination and for 'blindsight'.

Auditory Perception↗
PubMed1997

Reversible dissociation of sensitivity to dynamic stimuli in Parkinson's disease: is magnocellular function essential to reading motion-defined letters?

A group of 20 control subjects carried out the following visual tests: Snellen acuity; contrast detection threshold for a temporally unmodulated grating and for a temporally modulated grating; speed threshold for recognising motion-defined dotted letters. Normal limits were defined as 2.5 standard deviations from the respective control means. A patient with Parkinson's disease carried out the tests 12 hr after medication was withheld at a time when symptoms were evident ("off" stage), and after administration of medication when it had taken full effect ("on" stage). Confirming previous reports, contrast detection threshold for the temporally modulated grating was much higher during the "off" stage than during the "on" stage, but contrast detection threshold for the temporally unmodulated grating showed little difference. Speed threshold for recognising motion-defined letters did not, however, fall during the "on" stage. We suggest that magnocellular function is not essential for the recognition of motion-defined form.

Contrast Sensitivity↗