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At least 595 records · Page 33Linked to original sources
PubMed2003

Sonification of range information for 3-D space perception.

We present a device that allows three-dimensional (3-D) space perception by sonification of range information obtained via a point laser range sensor. The laser range sensor is worn by a blindfolded user, who scans space by pointing the laser beam in different directions. The resulting stream of range measurements is then converted to an auditory signal whose frequency or amplitude varies with the range. Our device differs from existing navigation aids for the visually impaired. Such devices use sonar ranging whose primary purpose is to detect obstacles for navigation, a task to which sonar is well suited due to its wide beam width. In contrast, the purpose of our device is to allow users to perceive the details of 3-D space that surrounds them, a task to which sonar is ill suited, due to artifacts generated by multiple reflections and due to its limited range. Preliminary trials demonstrate that the user is able to easily and accurately detect corners and depth discontinuities and to perceive the size of the surrounding space.

Acoustics↗
PubMed2003

Cognitive styles: errors in directional judgments.

Previous studies on spatial memory have shown that, in judging direction, participants are more accurate and faster when a map is aligned with the perspective of the spatial layout they had learned (alignment effect). Rossano and Warren (1989 Perception 18 215-229) have shown that when participants have to do a contra-aligned judgment they can either answer correctly, or make alignment or mirror-image errors. We think that the kind of response depends on the different way in which people acquire environmental knowledge: landmark, route, and survey. We hypothesise that landmark and route participants show alignment effects and make, respectively, alignment errors and mirror-image errors, whereas survey participants do not show an alignment effect. An experiment is reported in which participants performed three tasks in order to distinguish their cognitive style. We selected thirty landmark, thirty route, and twenty-eight survey participants. They were then submitted to directional judgment tasks to verify whether the alignment effect was present and to observe the kind of responses. The results revealed that survey participants did not show an alignment effect, and that the kind of errors could depend on the directional judgment task participants had to do, and not only on the cognitive style.

Adult↗
PubMed2004

Visual illusion in virtual world alters women's target-directed walking.

In this study we investigated whether a visual illusion located in far space alters a person's open-loop, target-directed walking path in the same manner as it alters the perception of the target's position. Through the use of immersive VR the subject was able to walk physically to the location of a target embedded in a scene that was manipulated to create a visual illusion, known as the induced Roelofs effect. This illusion has been shown to alter the perception of a target's position. The experiment consisted of two tasks: a perception task and an action task. In the perception task, subjects viewed the scene for 1 s, it disappeared, and they were to report the target's location verbally. The results showed that the visual illusion altered the reported positions in all but one subject. In the action task, subjects viewed the scene for 1 s, it disappeared, and the subjects were asked to walk to the target's location. The results showed that the illusion significantly altered the walking paths of most of the women and less than half of the men. A significant gender effect was observed; women's walking paths deviated, on average, by 7.1 degrees and men's, by only 2.0 degrees . These results indicate that action tasks in far space are susceptible to the effects of visual illusions, unlike the action tasks in near space that reportedly have been resistant to them. Furthermore, the significant gender effect suggests that men and women either have different strategies and/or employ different mechanisms when executing a visually guided task in far space.

Adolescent↗
PubMed2004

Action-specific extrapolation of target motion in human visual system.

Neuropsychological studies have indicated two distinct visual pathways in our brain, one dedicated to conscious perception and one to visuomotor control. Some psychophysical results support this idea with normal subjects, but they are still controversial. This study provides new psychophysical evidence for the dissociation by showing action-specific extrapolation of the visual target trajectory. When a moving target disappears, the perceived final position is liable to be shifted forward (representational momentum). In experiment 1, larger and more robust forward shifts were found when the position was directly touched without seeing the screen (open-loop pointing) than when the position was judged perceptually. The most striking dissociation was that fixation did not affect the forward shift in open-loop pointing while it almost abolished the shifts in perceptual judgements. In experiment 2, this action-specific result was found to disappear after a response delay of 4000 ms. Experiments 3 and 4 confirmed that the results were not affected by the external reference frames. The specific forward shifts found in open-loop pointing suggest that the visuomotor system compensates for the neural delays by extrapolating the target motion. The results, together with earlier findings, lead to a psychophysical double dissociation of the two visual pathways.

Adult↗
PubMed2006

Kinematic features of movement tunes perception and action coupling.

How do we extrapolate the final position of hand trajectory that suddenly vanishes behind a wall? Studies showing maintenance of cortical activity after objects in motion disappear suggest that internal model of action may be recalled to reconstruct the missing part of the trajectory. Although supported by neurophysiological and brain imaging studies, behavioural evidence for this hypothesis is sparse. Further, in humans, it is unknown if the recall of internal model of action at motion observation can be tuned with kinematic features of movement. Here, we propose a novel experiment to address this question. Each stimulus consisted of a dot moving either upwards or downwards, and corresponding to vertical arm movements that were masked in the last part of the trajectory. The stimulus could either move according to biological and or non-biological kinematic laws of pointing tasks. We compared subjects' estimations of the stimulus vanishing or final positions after biological and after non-biological motion displays. Subjects systematically overestimated the vanishing and final position for the two directions (up and down) and the two kinematics displayed (biological and non-biological). However, estimation of the final position decreased in precision and increased in variability for movements that violated the kinematic laws of arm pointing task. The results suggest that motion inference does not rely only upon visual extrapolating mechanisms based on past visual trajectory information. We propose that motion estimation relies on internal models that contain specific kinematic details of vertical arm movement, which can be rapidly recalled during motion observation.

Adult↗
PubMed1991

[Invariance in relation to transformations: a comparison of space perception and imagined space].

The present paper is based on the assumption of a functional equivalence between the processes of perception and imagination and a functional isomorphism between physical and phenomenal relations. The intention is to look for systematic deviations between 'measured', 'perceived' and 'imagined' space. Therefore a room was equipped with 32 pieces of furniture, giving it the appearance of a combined library and study room. A miniature model (1:10) of the room was constructed. In a two-factorial design with 10 experimental conditions, subjects performed model-reconstructions. The first factor refers to cognitive modality and represents different amounts of information of the physical layout, the endpoints of the continuum being 'complete insight' and 'no insight'. The second factor is a rotation of the model during the reconstruction (0 degrees vs. 180 degrees). Data analysis is based on location and orientation measures of the objects and distinguishes between 'semantic' and 'geometric' errors. The main results are: Even under conditions of only partial insight the spatial relations of the missing objects can be consensually reconstructed. While the absolute amount of the reconstruction errors largely depends on the two factors (modality and rotation), substantial relations of the original room are preserved under the different experimental conditions. The results are in good accordance with the assumption of functional equivalence and are critically discussed with respect to the concept of functional isomorphism.

Adult↗
PubMed2006

Factors influencing the radial-tangential illusion in haptic perception.

According to the radial-tangential illusion, in the horizontal plane, arm movements executed in directions radial to the trunk are sensed to be longer than movements of the same length in the orthogonal direction. It has been suggested that the illusion arises from the fact that radially directed movements are executed more slowly and require more effort. These suggestions were tested in a series of experiments, using a robotically controlled manipulandum. In all of the experiments subjects grasped the handle of the manipulandum, in some cases exploring the virtual boundary of a rectangle, while in others being guided along a rectangular contour by the robot. In a two-alternative forced choice design, subjects reported whether the rectangle was wide or narrow. In a control experiment, subjects manifested the radial-tangential illusion. Contrary to the hypothesis, the magnitude of this illusion was not altered when a resistive force was added in the tangential direction or when the ratio of movement times in the tangential and radial directions was changed. However, when the contour was explored in the counterclockwise direction, the illusion was much smaller than when it was explored in the clockwise direction. A second series of experiments, in which subjects only explored two sides (i.e., an L-shape), demonstrated that this effect arose from distortions induced by the serial ordering of the exploratory movements. The illusion was much smaller when the radial segment was explored first. We suggest that this distortion arises from the serial nature of haptic exploration, in which the length of the initial segment decreases as it is stored in working memory for subsequent comparison.

Attention↗
PubMed1989

The consistency of element transformations affects the visibility but not the direction of illusory motion.

Two experiments tested whether the consistency of element transformations affected perceptions of long-range apparent motion. Vertical lines were used to generate apparent motion against one of two different backgrounds, control and depth. Consistency was manipulated by changing the size of the vertical lines. In some displays, the size of the vertical lines remained constant during movement. In other displays, the size of the vertical lines changed during movement. Consistent movement occurred when the size manipulation was in agreement with the type of background used. In Experiment I, points of subject equality for the quality of motion relative to a standard display were measured. These PSEs indicated that consistent movement (e.g., line sizes held constant for control background displays) was more visible than inconsistent movement (e.g., line sizes constant for depth background displays). In Experiment II, a motion competition display was used to measure thresholds for perceived direction of motion. The depth background was used to make motion in one direction more consistent than motion in the opposite direction. However, no significant differences were noted between thresholds obtained in this condition and those obtained in a control condition. Thus the consistency of element transformations affected the quality of motion, but did not affect the perceived direction of motion. These results are consistent with Ullman's (The Interpretation of Visual Motion, MIT Press, 1979) two-component theory of apparent motion.

Distance Perception↗
PubMed2001

Interactions among end-effectors and movement parameters influence reaction time in discrete, rapid aimed movements.

Two reliable findings in discrete, rapid aimed movements are that reaction time increases with decrease in target diameter (for the short-length movements), and reaction time is not affected by movement length [Journal of Experimental Psychology, Human Perception and Performance 104 (2) (1975) 147]. Participants normally use a short stylus (SS) to tap targets located on either side of a central (aligned with body midline) start-point with no restrictions imposed on the initial posture of the limb or segmental recruitment except as determined by movement conditions. Thus, the effects of movement parameters on reaction time in previous work are potentially confounded with the effect of initial posture of the limb at the start-point, along with order and amount of the contribution of segments recruited in response execution. Two experiments were performed to resolve the confounding between initial posture and recruitment of limb segments. In the first experiment a conventional stylus (pen-like) was employed and the starting position of the limb was aligned either with the body midline or with the participant's right shoulder. The effect of starting position on reaction time was not significant. In the second experiment the starting position was in line with the right shoulder. Two groups participated. One group used a conventional stylus. For the second group a modified (lengthened) stylus was used that permitted initial limb posture and number of limb segments recruited to be held constant across an extended range of movement lengths. When similar sets of limb segments were used, reaction time increased with decreasing movement length and diminishing target diameter. These findings suggest that uncontrolled initial limb posture, uncontrolled order of joint(s) recruitment, and the subsequent inclusion of reaction time values from incompatible sources may, in the final analysis, have confounded previous work investigating movement amplitude and target diameter effects on reaction time.

Adult↗
PubMed2002

Exploring the syndrome of spatial unilateral neglect through an illusion of length.

Both a neuropsychological syndrome (unilateral spatial neglect) and a visual illusion of length (the Brentano version of the Müller-Lyer illusion) bring about a misjudgement of the subjective centre of a horizontal line, with a unilateral shift. In experiment 1 we investigated, in patients with left unilateral neglect, illusory effects of horizontal length, with the aim of exploring the functional and neural basis of horizontal space perception, and the role of visual processing in shaping the patients' bisection performance. Fourteen right-brain-damaged patients with left spatial unilateral neglect, seven with and seven without left visual half-field deficits (assessed by confrontation, perimetry, and visual event-related potentials), entered this study. Two conditions of manual line bisection were assessed: setting the mid-point of a horizontal line, and of the shaft of the Brentano-Müller-Lyer illusion, with either a left- or a right-sided expansion. Both groups of patients set the subjective midpoint to the right of the objective centre of the line, consistent with the presence of left neglect. Patients with neglect and left hemianopia showed no illusory effects and a greater bisection error. The effects of the illusion, by contrast, were fully present in neglect patients without hemianopia, in both illusory conditions, adding to, or subtracting from, the rightward bisection bias. Anatomoclinical correlations revealed an association of damage to the occipital regions with the lack of illusory effects. Conversely, more anterior damage, sparing these regions, did not disrupt the illusion, revealing a dissociation between visual and spatial processing of extension. These findings suggest that processing of the Müller-Lyer illusion of length is likely to occur in the occipital cortex, at a retinotopic level of representation. In neglect patients with left homonymous hemianopia the visual deficit adds to the spatial bias, yielding a greater error in line bisection, but not in other visual exploratory tasks, such as cancellation, where the contribution of retinotopic frames is likely to be comparatively minor. Experiment 2 showed preserved illusory effects in patients with homonymous visual field defects without spatial unilateral neglect, suggesting that preserved spatial processing may compensate for unilateral visual field defects.

Adult↗
PubMed2001

Expertise and the perception of kinematic and situational probability information.

Two experiments were conducted on the nature of expert perception in the sport of squash. In the first experiment, ten expert and fifteen novice players attempted to predict the direction and force of squash strokes from either a film display (occluded at variable time periods before and after the opposing player had struck the ball) or a matched point-light display (containing only the basic kinematic features of the opponent's movement pattern). Experts out-performed the novices under both display conditions, and the same basic time windows that characterised expert and novice pick-up of information in the film task also persisted in the point-light task. This suggests that the experts' perceptual advantage is directly related to their superior pick-up of essential kinematic information. In the second experiment, the vision of six expert and six less skilled players was occluded by remotely triggered liquid-crystal spectacles at quasi-random intervals during simulated match play. Players were required to complete their current stroke even when the display was occluded and their prediction performance was assessed with respect to whether they moved to the correct half of the court to match the direction and depth of the opponent's stroke. Consistent with experiment 1, experts were found to be superior in their advance pick-up of both directional and depth information when the display was occluded during the opponent's hitting action. However, experts also remained better than chance, and clearly superior to less skilled players, in their prediction performance under conditions where occlusion occurred before any significant pre-contact preparatory movement by the opposing player was visible. This additional source of expert superiority is attributable to their superior attunement to the information contained in the situational probabilities and sequential dependences within their opponent's pattern of play.

Adolescent↗
PubMed1979

Visual-motor adaptation. Quantitative demonstration in patients with posterior fossa involvement.

Short-term visual-motor adaptation to magnifying spectacle lenses was studied in normal subjects and in patients with nonacute posterior fossa lesions. When normal subjects, looking through magnifying lenses, pointed open loop to targets without viewing their hands, they initially underestimated the distance (magnification effect). After a 20-minute close-loop training or adaptation exposure period during which they viewed the performance of their hands, a modified visual-motor scheme evolved, compensating for about half of the lens-induced pointing error (adaptation effect). Removal of the lenses after adaptation caused open-loop, overshooting pointing errors (adaptation after-effect). Four patients with remission of cerebellar signs showed normal visual-motor adaptive performance, evidence of ability to recalibrate gain. One patient with persisting cerebellar ataxia was unable to recalibrate gain during close-loop visual-motor training. His history of transient palatal myoclonus implicates a role for the cerebellar-olivary system in calibration of visual-motor gain.

Adaptation, Ocular↗
PubMed1984

Clinical performance of a disability glare tester.

A glare tester was described previously and was found, in the presence of cataracts, to be almost twice as predictive as was Snellen measurement for determining visual acuity outdoors. The current study tests the reproducibility of glare test scores and the influence of refractive error and contrast sensitivity on such scores when used in a clinical environment. Although the effects of visual acuity and impaired contrast sensitivity were found to be statistically significant components of glare test scores, the magnitudes of their effects were found to be clinically insignificant. Sequential retesting of physiologically stable eyes or, in the case of progressive cataracts, within intervals short enough to preclude discernible lenticular changes indicated that, for the most part, reproducibility of glare testing was comparable to that of visual acuity testing.

Adult↗
PubMed1977

Single unit and lesion experiments on the sensory inputs to the hippocampal cognitive map.

The hippocampal cognitive map theory states that the hippocampus calculates the animal's location in an environment and also the locations of objects such as rewards and threats. In this paper we report single cell experiments which explored how sensory inputs are used by the hippocampus to calculate spatial information and behavioural experiments which tested the sensory capabilities of fornix-lesioned rats. Both sets of experiments were done in cue-controlled enclosures which contained only a few distant cues by which the rat could locate itself and the goal. Other cues were eliminated by rotating the constellation of cues and the goal from trial to trial. The results of the single cell experiment show that the place fields of hippocampal cells recorded in this environment are related to the controlled cues and, further, that some of these place cells maintain their fields after the removal of any two of four controlled cues. The lesion studies show that rats with damaged fornices can learn to approach distant cues behind and below the level of the goal but not ones behind and above the goal. A second study showed that the addition of redundant distant cues to the enclosure impairs the learning ability of the lesioned, but not the normal, animals.

Animals↗
PubMed1980

Spasms of the iris sphincter.

A patient is described who suffered from intermittent spasms of the pupillary sphincter and ciliary muscle. Both intraocular muscles contracted several times a minute, producing sporadic darkening of vision in the affected eye. The spasms continued for eleven days, so it was possible to document them pupillographically. This curious phenomenon seems to have been the result of a transient "irritability" of the ciliary ganglion.

Adult↗
PubMed2006

The planning of tool-to-object relations in young children.

This study investigated the way young children used a cane for displacing an object. In the experiment, 11 children with an average age of 32.3 months were asked to pick up a cane (hooked stick) that was located and orientated differently on each trial. With this cane they had to displace a target-object towards a free-to-choose goal location. The way the children used the cane for transporting the object was not determined by its starting location and orientation relative to the object. In fact, the children preferred enclosing the object in the hook, irrespective of the starting configuration. This contradicts a prediction that follows from an earlier study by Van Leeuwen et al. (1994). Final location of the target object and hand use was influenced by preferences as well as constraining task variables.

Child, Preschool↗
PubMed2006

Preferential reaching across regions of hemispace in adults and children.

The purpose of the current study was to examine hand selection during reaching in children utilizing a developmental version of the preferential reaching paradigm (Bryden, Pryde, & Roy, 2000). A cross-sectional sample of eighty right-handed participants (ranging in age from 3 to 20 years) were asked to reach to objects located in different regions of hemispace. Each participant was asked to carry out two different actions, varying in degree of complexity, on the objects while the experimenter observed, which hand was used to perform each of the tasks. A repeated-measures ANOVA revealed that reaching towards the midline and ipsilateral positions in hemispace resulted in significantly more preferred hand reaches than reaching towards contralateral hemispace, regardless of age and task. With respect to age group effects, it was found that the 6 and 7 year olds and the 9 and 10 year olds relied heavily on their preferred hand to perform the task, indicating that hand selection in these children was driven primarily by motor dominance. In comparison, the youngest children and adults used their nonpreferred hand more frequently in contralateral space, indicating that object proximity cues or a hemispheric bias was driving hand selection. The implications of these findings for understanding hand preference and skill were discussed in terms of motor dominance versus spatial reasoning theory of hand selection in unimanual reaching.

Adolescent↗