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PubMed1997

Transient visual attention is dominated by the magnocellular stream.

Robust visual attentional responses are produced by the sudden onset of a visual cue, but the properties of cues that best elicit an attentional response are not fully known. We used the line-motion illusion (Hikosaka et al., 1991) to investigate the optimal cue properties that evoke visual attention. We found that visual attention is driven primarily by the luminance contrast of the cue. Furthermore, by manipulating the spatial, chromatic, and contrast properties of cues, we found that magnocellular (M) stream biased cues always override the response to parvocellular (P) stream biased cues, even when the P stream biased cues are presented first. Our data suggest that cues that preferentially excite the M pathway predominantly capture visual attention.

Color Perception↗
PubMed1997

The perception of motion and structure in structure-from-motion: comparisons of affine and Euclidean formulations.

I investigated the discrimination of rigid from nonrigid structure and the perception of affine stretches along the line of sight [Norman & Todd (1993). Perception and Psychophysics, 53, pp. 279-291]. Investigations of performance at discriminating rigid from nonrigid structure showed that performance improved when number of views and amount of simulated three-dimensional nonrigidity increased. Investigations of rotations about the vertical which include affine stretches along the line of sight compared Euclidean interpretations of affine-stretching stimuli to human perception. These Euclidean interpretations were obtained from a simple algorithm which recovered structure and motion from this limited class of stimuli under the assumption that distances to the axis of rotation did not change. The algorithm predicted that stretches along the line of sight would be perceived as nearly rigid and have variable angular velocity. These predictions were supported by subjects' reports of occurrences of nonrigidity and minima of angular velocity. The Euclidean algorithm also provided measures of nonrigidity and motion coherence, and experimental results were consistent with a prediction of when perception of nonrigidity would be independent of perception of coherence. The results are discussed relative to the advantages and shortcomings of both the affine and Euclidean approaches to structure-from-motion.

Algorithms↗
PubMed1998

Feature asymmetries in visual search: effects of display duration, target eccentricity, orientation and spatial frequency.

In Experiments 1-3, we monitored search performance as a function of target eccentricity under display durations that either allowed or precluded eye movements. The display was present either until observers responded, for 104 msec, or for 62 msec. In all three experiments an orientation asymmetry emerged: observers detected a tilted target among vertical distracters more efficiently than a vertical target among vertical distracters. As target eccentricity increased, reaction times and errors augmented, and the set size effect became more pronounced, more so for vertical than tilted targets. In Experiments 4-7, the stimulus spatial properties were manipulated: spatial frequency; size; and orientation. The eccentricity effect was more pronounced for vertical than tilted targets and for high- than low-spatial frequency targets. This effect was eliminated when either the size, the size and orientation, or the size and spatial frequency were magnified (M-cortical factor). By increasing the signal-to-noise ratio, magnification reduced the extent of both asymmetries; it aided more the detection of tilted than vertical and of high- than low-spatial frequency targets. Experiments 4-7 indicate that performance improvement in the magnified conditions was due to the specific pairing of stimulus size with retinal eccentricity and not to the larger stimulus size of the magnified conditions. We conclude that stimulus size, orientation and spatial frequency influence the extent of the eccentricity effect and the efficiency of search performance.

Eye Movements↗
PubMed1998

Temporal modulation enhances the efficiency of spatial offset discriminations by 6-month-olds.

Fourteen- and 24-week-old infants were tested for sensitivity to small position differences under two conditions: (a) the Vernier stimulus was flashed on and off at 1.2 or 4.8 Hz (flash condition); and (b) the Vernier breaks were presented in apparent motion at 1.2 or 4.8 Hz (motion condition). The latter stimulus also contained local flicker cues. Each infant was tested at one temporal frequency with both stimuli. No benefit was shown by 14-week-olds at either temporal frequency from the additional motion and flicker cues. However, 24-week-olds required spatial offsets only one third as large in the motion condition as they required in the flash condition at 4.8 Hz. Ideal observer methodology was used to ensure that the spatial information for both of these discriminations was held strictly equivalent. Increasing sensitivity to flicker and/or motion or uncertainty reduction may underlie the enhancement in discrimination shown by 24-week-olds at 4.8 Hz.

Child Development↗
PubMed1999

Non-veridical size perception of expanding and contracting objects.

Observers were presented with various types of stimulus expansion and contraction which resulted in marked misperceptions of size. Firstly, the perceived size of an object which is changing in size is shown to be biased in the direction of the size change. Secondly, expansion or contraction of the internal texture of objects is found to influence their perceived size. Finally, an illusory texture manipulation in the form of a movement after-effect is shown to produce the same type of size misperception as a real expansion or contraction of internal texture. The spatio-temporal characteristics of these illusory size changes are investigated.

Humans↗
PubMed1998

Kinematic analysis of prehension movements in children.

The kinematics of the reach-to-grasp movement were analyzed in ten healthy children (age 6-7 years) under different experimental conditions: distance and size of the target objects, and visual feedback during the reach were varied in a within-subjects design. To assess age-related differences, the same experiments were performed in ten healthy adults. The experimental set-up was scaled according to body proportions to obtain equivalent conditions for both age groups. The temporal coupling between the transport and grasp components of prehension was very similar in children and adults. Peak transport velocity increased by the same factor in both age groups when the object distance was doubled. However, the decelerating approach phase was shorter in the children, who opened their hands relatively wider than adults. Unlike the adults, children failed to scale their grip aperture according to object size when visual feedback during the movement was lacking. The grip aperture increased with object distance in adults, but not in the children. The intrasubject variability of kinematic parameters was distinctly higher in the children. The results suggest that grip formation is not yet mature at an age of 6-7 years, depending more on visual feedback than in adult prehension.

Adult↗
PubMed2003

Object temporal connotation.

Recent studies show that what connotes an object is first of all a certain spatio-temporal structure. In this paper we describe some of the temporal features characterizing the temporal structure of objects: pre-existence, persistence, conservation of identity in spite of perceptive discontinuity, surviving changes in colour, size, and shape. We argue that time is an indispensable attribute for every type of object and briefly discuss the implication of this view with respect to a specific neuropsychological syndrome: unilateral spatial neglect.

Adult↗
PubMed2003

The processing of emotional facial expression is gated by spatial attention: evidence from event-related brain potentials.

To investigate whether the processing of faces and emotional facial expression can be modulated by spatial attention, ERPs were recorded in response to stimulus arrays containing two faces and two non-face stimuli (houses). In separate trials, attention was focused on the face pair or on the house pair, and facial expression was either fearful or neutral. When faces were attended, a greater frontal positivity in response to arrays containing fearful faces was obtained, starting about 100 ms after stimulus onset. In contrast, with faces located outside the attentional focus, this emotional expression effect was completely eliminated. This differential result demonstrates for the first time a strong attentional gating of brain processes involved in the analysis of emotional facial expression. It is argued that while an initial detection of emotionally relevant events mediated by the amygdala may occur pre-attentively, subsequent stages of emotional processing require focal spatial attention. The face-sensitive N170 component was unaffected by emotional facial expression, but N170 amplitudes were enhanced when faces were attended, suggesting that spatial attention can modulate the structural encoding of faces.

Adolescent↗
PubMed2003

Spatiotemporal brain activity related to intelligence: a low resolution brain electromagnetic tomography study.

Differences in current density between high intelligent (IQ=124), and average intelligent individuals (IQ=110), while solving two complex cognitive tasks (analytical-figural, and identification of emotions) were analyzed with low resolution brain electromagnetic tomography (LORETA). High intelligent individuals, as compared with average ones in both tasks displayed a lesser full width at half maximum (FWHM) volume-indicating the amount of spatial dispersion of the source. High and average intelligent individuals also differed in their source location. The source location of high intelligent individuals was in the inferior right hemispheric brain areas, whereas the source location of average intelligent individuals was in the superior left hemispheric brain areas. The findings were explained in the light of the neural efficiency model.

Adult↗
PubMed1998

Temporal dynamics of early perceptual processing.

Recordings of electrical and magnetic brain responses to sensory stimulation provide high-resolution measures of the time course of early perceptual processing. Spatio-temporal analyses of brain activity patterns during the first 200 ms after stimulus presentation have characterized the timing of attentional selection processes and different stages of feature encoding and pattern analyses. Recent studies that incorporate blood flow neuroimaging techniques provide support for mechanisms of early selection of attended visual inputs in extrastriate cortical pathways. The spatial tuning properties of early auditory selection have also been delineated. Electrical and magnetic responses that index the encoding of higher-order pattern information have been identified in both visual and auditory modalities and localized to specific cortical areas.

Attention↗
PubMed2002

Vision: when the clock appears to stop.

Eye movements produce a temporary loss of visual sensitivity known as saccadic suppression, and a distortion of space perception known as saccadic compression. A new study has reported a seemingly related phenomenon --chronostasis---in which one's perception of time also undergoes an illusory distortion during rapid movements of the eyes.

Humans↗
PubMed2004

Control of prehension in hemiparetic cerebral palsy: similarities and differences between the ipsi- and contra-lesional sides of the body.

This study aimed at broadening our insight into ipsi- and contra-lesional control of prehension after unilateral brain damage. Six male adults with hemiparetic cerebral palsy (mean age 17 years 3 months, SD 15 months) performed unrestricted grasping of discs that differed in size (40, 60, and 80mm in diameter) and which were placed at different distances from the participants (150mm and 30mm). A precalibrated Optotrak 3020 system was used for recording motion. Kinematics of the transport and grasp component, and hand orientation at the moment of grasping, were determined. A marker on the wrist was used to calculate the kinematics of the transport component. The distance between the markers on the index finger and thumb was used for the calculation of the grasp component. Kinematic variables of the transport and grasp component were remarkably similar between both sides of the body. However, with the contra-lesional side, more time was spent in contact with the object before it was lifted, and movements were performed less fluently compared with the ipsi-lesional side. Maximum grasp aperture was attained very late during reaching. For final hand orientation, results showed a large standard deviation both within and between participants. These findings show that, despite the ostensible awkward prehension movements of the contra-lesional side (slowness and decreased fluency), similarities in the kinematics between both sides of the body are present, which may be indicative of intact central control of the movement. The results of variant final hand orientation, combined with the relative late occurrence of peak aperture, suggest that these participants encounter difficulties with forward planning and may use a step-by-step control strategy.

Adolescent↗
PubMed1999

Evidence of cognitive visual problems in children with hydrocephalus: a structured clinical history-taking strategy.

Damage to the occipital cortex in children can result in many complex disorders of cognitive visual function. A series of clinical questions, developed from the specific problems of a cohort of children with cortical visual impairment, was asked of the parents of 200 children with no history of cerebral pathology, aged 5 to 12 years. One hundred and ninety-two parents gave reliable consistent responses. The results show a progressive improvement in performance with age, culminating in few 11- and 12-year olds having frequent problems, apart from 8% having frequent difficulty with orientation in new surroundings and 2% having problems with simultaneous perception tasks. The parents of 52 children (aged 5 to 17 years) with shunted hydrocephalus were then asked the same set of questions. Evidence of cognitive visual problems was identified in 27 of these children of whom 16 manifested multiple difficulties. The disabilities identified by our study comprised problems with: shape recognition, simultaneous perception, perception of movement, colour perception, orientation, object recognition, and face recognition. The range, nature, and combinations of these disorders are presented in this paper.

Adolescent↗
PubMed2005

Neurocognitive and electrophysiological evidence of altered face processing in parents of children with autism: implications for a model of abnormal development of social brain circuitry in autism.

Neuroimaging and behavioral studies have shown that children and adults with autism have impaired face recognition. Individuals with autism also exhibit atypical event-related brain potentials to faces, characterized by a failure to show a negative component (N170) latency advantage to face compared to nonface stimuli and a bilateral, rather than right lateralized, pattern of N170 distribution. In this report, performance by 143 parents of children with autism on standardized verbal, visual-spatial, and face recognition tasks was examined. It was found that parents of children with autism exhibited a significant decrement in face recognition ability relative to their verbal and visual spatial abilities. Event-related brain potentials to face and nonface stimuli were examined in 21 parents of children with autism and 21 control adults. Parents of children with autism showed an atypical event-related potential response to faces, which mirrored the pattern shown by children and adults with autism. These results raise the possibility that face processing might be a functional trait marker of genetic susceptibility to autism. Discussion focuses on hypotheses regarding the neurodevelopmental and genetic basis of altered face processing in autism. A general model of the normal emergence of social brain circuitry in the first year of life is proposed, followed by a discussion of how the trajectory of normal development of social brain circuitry, including cortical specialization for face processing, is altered in individuals with autism. The hypothesis that genetic-mediated dysfunction of the dopamine reward system, especially its functioning in social contexts, might account for altered face processing in individuals with autism and their relatives is discussed.

Autistic Disorder↗
PubMed2002

Three dimensional spatial memory and learning in real and virtual environments.

Human orientation and spatial cognition partly depends on our ability to remember sets of visual landmarks and imagine their relationship to us from a different viewpoint. We normally make large body rotations only about a single axis which is aligned with gravity. However, astronauts who try to recognize environments rotated in 3 dimensions report that their terrestrial ability to imagine the relative orientation of remembered landmarks does not easily generalize. The ability of human subjects to learn to mentally rotate a simple array of six objects around them was studied in 1-G laboratory experiments. Subjects were tested in a cubic chamber (n = 73) and a equivalent virtual environment (n = 24), analogous to the interior of a space station node module. A picture of an object was presented at the center of each wall. Subjects had to memorize the spatial relationships among the six objects and learn to predict the direction to a specific object if their body were in a specified 3D orientation. Percent correct learning curves and response times were measured. Most subjects achieved high accuracy from a given viewpoint within 20 trials, regardless of roll orientation, and learned a second view direction with equal or greater ease. Performance of the subject group that used a head mounted display/head tracker was qualitatively similar to that of the second group tested in a physical node simulator. Body position with respect to gravity had a significant but minor effect on performance of each group, suggesting that results may also apply to weightless situations. A correlation was found between task performance measures and conventional paper-and-pencil tests of field independence and 2&3 dimensional figure rotation ability.

Adolescent↗
PubMed1976

The Honi phenomenon revisited: factors underlying the resistance to perceptual distortion of one's partner.

An individual being viewed in an Ames room usually appears considerably altered in physical size to an observer. However, some married persons perceive less size distortion of their spouses than a stranger. This instance of selective perceptual distortion, known as the Honi phenomenon, could perhaps reflect differential familiarity and/or emotional involvement toward these stimulus persons. Using heterosexual couples as subjects, we investigated familiarity (i.e., length of the relationship), type of relationship (i.e., dating, engaged, or married), and positive cathexis (i.e., love, liking, and trust of one's partner) as possible mediators of this effect and also explored the impact of some judgemental variations. Neither familiarity nor type of relationship influenced relative perceptual distortion of partner versus stranger. Rather, selective perceptual distortion was directly related to the strength of positive cathexis, principally among females. Only women high in positive cathexis exhibited the Honi phenomenon and perceived a stranger as being more distorted than their partners. In contrast, size judgements by men were affected only by the sequence in which stimulus persons were observed. Implications and interpretations of these findings are discussed.

Awareness↗
PubMed1975

Perception and extrapolation of velocity and acceleration.

A moving target disappeared behind a screen and subjects predicted when the target passed behind a marker on the screen. When the target moved with constant velocity, predictions were extremely accurate, regardless of the spatial and temporal exposure and concealment of the target and regardless of its rate of velocity. When the target accelerated, accuracy of prediction decreased with increasing acceleration and with increasing target concealment. Analyses of the results suggest that the perception of velocity and acceleration is direct and accurate and that extrapolation of velocity and acceleration incorporates concrete and abstract characteristics of the motion that was seen. It is proposed that the motion perception system is tuned to accelerated rather than to constant velocity movement.

Acceleration↗