[2 kinds of perception. Close up or at a distance?].
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Spectral content as a cue to perceived auditory distance.
Changes in the spectral content of wide-band auditory stimuli have been repeatedly implicated as a possible cue to the distance of a sound source. Few of the previous studies of this factor, however, have considered whether the cue provided by spectral content serves as an absolute or a relative cue. That is, can differences in spectral content indicate systematic differences in distance even on their first presentation to a listener, or must the listener be able to compare sounds with one another in order to perceive some change in their distances? An attempt to answer this question and simultaneously to evaluate the possibly confounding influence of changes in the sound level and/or the loudness of the stimuli are described in this paper. The results indicate that a decrease in high-frequency content (as might physically be produced by passage through a greater amount of air) can lead to increases in perceived auditory distance, but only when compared with similar sounds having a somewhat different high-frequency content, ie spectral information can serve as a relative cue for auditory distance, independent of changes in overall sound level.
Acoustic Stimulation↗
Is space representation distorted in neglect?
It has been argued that neglect of contralateral stimuli following brain damage might be associated with either a compressed or an anisometric neural representation of space along the earth-horizontal axis. Two different models have been put forward. One model proposes a uniform compression of subjective space, while the other envisages an expansion on one side of space and a compression on the other. We tested these models by determining neglect patients' perception of spatial distances in the horizontal plane. The models differ concerning the expected degree of under- vs overestimation of distances in the left and right hemispace. In the first experiment, patients were asked to position ten red LEDs equidistantly along a semicircle, which was located horizontally in front of them at eye level. A second experiment compared the patients' subjective perception of short, medium and long distances extending into left and right hemispace. We found no evidence for any compression or expansion, nor for anisometry along the earth-horizontal axis. These findings argue against a distortion of subjective space along the horizontal axis in patients with neglect which could account for their failure to orient towards and to explore the contralesional parts of space.
Aged↗
Lighting position and judgments of distance of shadow-casting objects.
Participants recruited on the web performed in two experiments in which they viewed eight pictures of the same two rods in the exact same positions with shadows generated by a light source located at eight positions around the rods. In Exp. 1, participants judged how much shadows projected to the front, back, and sides of the rods facilitated the correct perception of the actual distance of the rods relative to each other. In Exp. 1 (n: 52), frontal lighting facilitated judgments more than lighting from the rear, but frontal and side lighting did not differ in facilitative effects. In Exp. 2 (n: 72), judgments of rods depicted with shadows were relative to a judgment of the rods depicted without shadows (raw scores were the value of the judgment of the shadowless rods subtracted from the value of the judgment of each of the eight sets of rods). Again, frontal lighting was more facilitative than rear lighting and frontal lighting did not differ from side lighting. However, when the average of each participant's backlighting judgments was compared with his judgment of the shadowless rods, shadows generated by backlighting were more facilitative than none.
Distance Perception↗
Accommodation, occlusion, and disparity matching are used to guide reaching: a comparison of actual versus virtual environments.
The authors used a virtual environment to investigate visual control of reaching and monocular and binocular perception of egocentric distance, size, and shape. With binocular vision, the results suggested use of disparity matching. This was tested and confirmed in the virtual environment by eliminating other information about contact of hand and target. Elimination of occlusion of hand by target destabilized monocular but not binocular performance. Because the virtual environment entails accommodation of an image beyond reach, the authors predicted overestimation of egocentric distances in the virtual relative to actual environment. This was confirmed. The authors used -2 diopter glasses to reduce the focal distance in the virtual environment. Overestimates were reduced by half. The authors conclude that calibration of perception is required for accurate feedforward reaching and that disparity matching is optimal visual information for calibration.
Accommodation, Ocular↗
An apparatus for indirect measurement of perceived distance.
Two methods of measuring perceived distance are contrasted. One of these, called a direct method, accepts the observer's direct response to perceived distance as a valid measure of the distance perceived. The other, called an indirect measure, uses the observer's direct response to a perception that is not perceived distance but which has a known relation to perceived distance in order to calculate the distance perceived. There are indications that the direct measure of perceived distance provided by the verbal report sometimes will be modified by cognitive factors. A procedure and apparatus for an indirect measure is suggested which is likely to be free of the cognitive effects found in verbal reports of distance. This apparatus adjusts the distance around which the line-of-sight to the object pivots as the head is moved laterally. The pivot distance at which no apparent motion of the object occurs with head motion is a measure of the perceived distance of the object.
Cognition↗
Sudden onset of subjective dimensionality: a case study.
For 45 years, Bob had no subjective sense of depth; the world appeared two-dimensional to him. Then, when he was viewing mountain vistas while using marijuana, he suddenly was able to see three dimensions. This case, apparently unique in the literature, suggests that subjective dimensionality may be functionally separate from use of distance cues.
Awareness↗
Explaining the moon illusion.
An old explanation of the moon illusion holds that various cues place the horizon moon at an effectively greater distance than the elevated moon. Although both moons have the same angular size, the horizon moon must be perceived as larger. More recent explanations hold that differences in accommodation or other factors cause the elevated moon to appear smaller. As a result of this illusory difference in size, the elevated moon appears to be more distant than the horizon moon. These two explanations, both based on the geometry of stereopsis, lead to two diametrically opposed hypotheses. That is, a depth interval at a long distance is associated with a smaller binocular disparity, whereas an equal depth interval at a smaller distance is associated with a larger disparity. We conducted experiments involving artificial moons and confirmed the hypothesis that the horizon moon is at a greater perceptual distance. Moreover, when a moon of constant angular size was moved closer it was also perceived as growing smaller, which is consistent with the older explanation. Although Emmert's law does not predict the size-distance relationship over long distances, we conclude that the horizon moon is perceived as larger because the perceptual system treats it as though it is much farther away. Finally, we observe that recent explanations substitute perceived size for angular size as a cue to distance. Thus, they imply that perceptions cause perceptions.
Accommodation, Ocular↗
Timing sight and sound.
It has been proposed that there is a perceptual compensation for the difference between the speeds of light and sound. We examined this possibility using a range of auditory-visual tasks, in which performance depends on the relative timing of auditory and visual information, and manipulated viewing distance to test for perceptual compensation. We explored auditory-visual integration, cross modal causal attributions, and auditory-visual temporal order judgments. We observed timing shifts with viewing distance following loudspeaker, but not headphone, presentations. We were unable to find reliable evidence of perceptual compensation. Our findings suggest that auditory and visual signals of an event that reach an observer at the same point in time tend to become perceptually bound, even when the sources of those signals could not have occurred together.
Acoustic Stimulation↗
Multiple reference frames in neglect? An investigation of the object-centred frame and the dissociation between "near" and "far" from the body by use of a mirror.
In this single case study of a man (AE) who suffered a right hemisphere stroke we showed the co-existence of neglect within different spatial frames: (a) In left hemispace and (b) in 'far' versus 'near' space, both as defined from the patient's viewpoint, as well as (c) for the left side of an object (as defined from an object-centred view). In the experiment, AE's latencies to name the colour of two cubes, each located in one hemispace, were measured. In some conditions, the cubes were placed on a table but in other conditions each cube was held in one hand of an experimenter who could either face the patient or show the cubes while her back was turned towards him. One prediction was that AE would show longer latencies for cubes in left hemispace; however, if object-centred neglect also occurred, then latencies should be even longer for cubes held in the experimenter's left hand. In order to reveal the presence of neglect for 'far' versus 'near' space, the cubes could also be positioned either near to (i.e. reaching distance) or far from the patient (i.e., several metres out of reach), by moving the table or the experimenter. Finally, in some conditions, AE looked at the cubes into a mirror that was positioned far away from his body. Because external objects seen in a mirror can be 'near' the patient's body, the patient actually looked at a 'far' location (i.e. the surface of the mirror) to see an object that is 'near'. The experiment confirmed the presence of all forms of neglect, since AE not only named the colour of a cube seen in his left hemispace more slowly than in right hemispace, but latencies increased for a cube held by the experimenter in her left hand and in left hemispace (both when the left hand was seen directly or as a mirror reflection). Finally, AE's performance was worse for 'far' than 'near' locations, when the cubes were physically located near his body (i.e., within "grasping" space) but seen in the mirror.
Analysis of Variance↗
Quality, accessibility, and contraceptive use in rural Tanzania.
We examine how informants' reports on community perceptions of the quality and accessibility of family planning facilities relate to the use of modern contraceptives by individuals in rural Tanzania. Using information on individual-level contraceptive use in conjunction with community-level information on the accessibility and quality of family planning facilities, we employ two distinct statistical procedures to illustrate the impacts of accessibility and quality on contraceptive use. Both procedures treat the community-level variables as imperfect indicators of characteristics of the facilities, and they yield nearly identical implications. We find that a community-level, subjective perception of a family planning facility's quality has a significant impact on community members' contraceptive use whereas other community measures such as time, distance, and subjective perception of accessibility have trivial and insignificant direct impacts, net of the control variables. Future research that uncovers the determinants of perceptions of both community-level and individual-level quality could provide key insights for developing effective and efficient family planning programs.
Adolescent↗
The role of eye accommodation in the depth perception of common toads.
Distance estimation in prey catching was as exact in monocular toads (Bufo bufo (L.)) as in binocular ones. Application of Atropine or Miotic had no significant effect on binocular animals, whereas in monocular toads it made accurate distance estimation impossible. The accommodative state of the eye is decisive for depth estimation of monocular, but not of binocular toads.
Accommodation, Ocular↗
The paradoxical moon illusions.
An adaptation theory of visual space is developed and applied to the data of a variety of studies of visual space perception. By distinguishing between the perceived distance of an object and that of the background or sky, the theory resolves the paradox of the moon illusions and relates both perceived size and perceived distance of the moon to the absolute level of spatial adaptation. The theory assumes that visual space expands or contracts in adjustment to changes in the sensory indicators of depth and provides a measure, A, of this adaptation-level. Changes in A have two effects--one on perceived size, one on perceived distance. Since A varies systematically as a function of angle of regard, availability of cues, and the total space-value, A is a measure of the moon illusions, and a practical index of individual differences by pilots and astronauts in the perception of the size and distance of objects on the ground and in the air.
Distance Perception↗
Intact spatial updating during locomotion after right posterior parietal lesions.
One function of the posterior parietal cortex (PPC) is to monitor and integrate sensory signals relating to the current pointing direction of the eyes. We investigated the possibility that the human PPC also contributes to spatial updating during larger-scale behaviors. Two groups of patients with brain injuries either including or excluding the right hemisphere PPC and a group of healthy subjects performed a visually-directed walking task, in which the subject views a target and then attempts to walk to it without vision. All groups walked without vision accurately and precisely to remembered targets up to 6 m away; the patient groups also performed similarly to the healthy controls when indicating egocentric distances using non-motoric responses. These results indicate that the right PPC is not critically involved in monitoring and integrating non-visual self-motion signals, at least along linear paths. In addition, visual perception of egocentric distance in multi-cue environments is immune to injury of a variety of brain areas.
Adult↗
Parallel-alleys and distance-alleys on horopter plane in the dark.
On each of three frontoparallel planes at distances of about 98, 186, and 276 cm from the subject, two series of light points running horizontally in the dark, one above the other, were constructed by six subjects: a P-alley in which the two series appear as two straight lines that are parallel, and a D-alley in which each pair of points appear equally separated in the vertical direction. Luneburg's mapping functions between visual space and physical space have been used to obtain estimates of K (curvature) and sigma (a constant related to depth perception). In addition, ratios of perceptual distances were assessed by four out of the six subjects with eleven triplets of points on the alleys and values of K were estimated (and the fits of theoretical equations were tested) without the use of the mapping functions. In contrast to experiments with P-alleys and D-alleys on the horizontal plane, K was not unequivocally negative in either of the two experiments.
Depth Perception↗
Relationships between perceptions of performance expectations and mood among distance runners: the moderating effect of depressed mood.
Recent research has proposed that depressed mood is the most important mood dimension due to its de-motivating nature. Lane and Terry (2000a) proposed that depressed mood influences the intensity of other mood dimensions, and moderates the nature of anger and tension. Distance runners (N = 188) completed the 24-item Profile of Mood States-A (POMS-A: Terry, Lane, Lane, & Keohane, 1999) and a 7-item Pre-race Questionnaire to assess Perceived Readiness and Course Suitability 1 hr. before competition. On the basis of scores on the POMS-A Depression subscale, participants were dichotomized into a No-depression group (n = 137) or a Depressed mood group (n = 51). MANOVA results indicated that the Depressed mood group reported significantly higher scores on Anger, Confusion, Fatigue, Tension with lower Vigor and Perceived Readiness. In the No-depression group, Vigor correlated with Perceived Readiness, whereas in the Depressed mood group, Vigor was associated more closely with Course Suitability than Perceived Readiness. Anger showed a positive relationship with Perceived Readiness in the No-depression group, and an inverse relationship with Perceived Readiness in the Depressed mood group. Collectively, findings lend support to the notion that mood and thoughts about performance are significantly associated. Further, findings show that depressed mood fosters a negative psychological state and moderates the nature of anger but not tension.
Adolescent↗
Apparent distance of sounds recorded in echoic and anechoic chambers.
With miniature microphones inserted into the external ear canals of a model and the sound source 90 degrees to left of midline, low-pass, and broadband noise bursts were picked up and recorded on magnetic tape. The bursts were generated in two highly contrasting acoustic environments: an anechoic and an echoic chamber. The taped sounds were played back monaurally and binaurally via headphones to 16 listeners seated in an acoustically neutral setting. They were instructed to estimate the distance of the stimuli. Apparent distances of bursts recorded in the echoic or reverberant chamber far exceeded those recorded in the anechoic chamber. It mattered not whether the sounds were presented monaurally or binaurally. What did influence distance estimates dramatically was the frequency composition of the stimuli. Low-pass sounds recorded in either acoustic environment were consistently judged to be further removed than high-pass sounds recorded in the same setting. They were also more likely to appear from behind the listener. In our moment-to-moment transaction with the acoustic environment, distant sounds generally have less acoustic energy in the higher audio frequency. We suggest that this lifetime of auditory experience influenced our listeners' scale of relative distance.
Auditory Perception↗
Assessment of the quality of interaction in distance learning programmes utilizing the Internet or interactive television: perceptions of students and lecturers.
WebCT, a web-based virtual learning environment (VLE) and Interactive TV (ITV) are relatively new technologies that are used to deliver distance education at the Faculty of Health Sciences, Stellenbosch University. This study explores how effective current approaches to instructional design and interaction have been in utilizing these two technologies to support interaction and what lessons can be learnt. Five focus-group interviews were held with students and lecturers to assess the perceived quality of student-lecturer/student-student interactions. All students were invited to complete a questionnaire at the end of every module to assess their perceptions of interaction. Interaction was highly valued by students and lecturers participating in distance-learning programmes utilizing either VLE or ITV. Students rated courses using both technologies as moderately interactive. Significant differences between VLE and ITV were detected in student-lecturer and student-student interactions, use of additional modes of communication, instructional design, technological interactivity and social rapport activities. The groups did not differ across a number of likely barriers to interaction and both also reported the need for more flexible and better paced instructional designs.
Adult↗
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