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At least 721 records · Page 40Linked to original sources
PubMed2005

Vector navigation in desert ants, Cataglyphis fortis: celestial compass cues are essential for the proper use of distance information.

Foraging desert ants navigate primarily by path integration. They continually update homing direction and distance by employing a celestial compass and an odometer. Here we address the question of whether information about travel distance is correctly used in the absence of directional information. By using linear channels that were partly covered to exclude celestial compass cues, we were able to test the distance component of the path-integration process while suppressing the directional information. Our results suggest that the path integrator cannot process the distance information accumulated by the odometer while ants are deprived of celestial compass information. Hence, during path integration directional cues are a prerequisite for the proper use of travel-distance information by ants.

Adaptation, Physiological↗
PubMed2004

Influence of viewing distance on vertical strabismus.

BACKGROUND: Vertical strabismus can be modulated by the viewing distance. We report on 19 patients with this disorder. METHODS: The following squint angles were measured by the alternate prism and cover test at a viewing distance of 5 m. At 0.3 m, measurements were taken with and without an addition of 3.0 D to the corrected refraction. Cases of a dissociated vertical deviation were excluded. Fifteen patients underwent surgery. They were reexamined 3 months later. RESULTS: At a viewing distance of 5 m, the vertical deviation ranged from 0 degrees to 16 degrees (median 7 degrees ). At 0.3 m, the deviation increased by 2 degrees -15 degrees (median 7 degrees ) in 15 patients and decreased by 3.5 degrees -8 degrees (median 4.5 degrees ) in 4 patients. Eleven patients had a strabismus sursoadductorius and one had a strabismus deorsoadductorius. Eye muscle surgery reduced both the vertical deviation for distance fixation to 0 degrees -14 degrees (median 2 degrees ) and the difference between the deviations for distance and proximal fixation to 1 degrees -6 degrees (median 3 degrees ). CONCLUSIONS: In certain cases, vertical strabismus can be modulated by convergence and accommodation. This condition is frequently associated with an incomitance of the vertical deviation in side gaze. The baseline deviation can be reduced by appropriate eye muscle surgery. In cases of vertical accommodative vergence, bifocal glasses can be helpful.

Accommodation, Ocular↗
PubMed1982

The effects of viewing distance on fear of snakes.

Phobic subjects made magnitude estimations of the intensity of fear felt when viewing a snake at distances from 2.5 to 15.0 ft. Heart rate, skin conductance, and respiration were also measured throughout each 20 sec viewing period. A control group of nonphobic subjects made magnitude estimates of perceived nearness for the empty Plexiglas snake box at the same test distances. Judged fear was inversely proportional to distance. Thus, the fear-distance relation obeys Stevens' psychophysical power law with an exponent of -1.0. Examination of previous studies reporting such a finding revealed systematic departures from a power relation similar in form to the results of the perceived nearness control group, and to the expected outcome when category judgements of fear are made instead of magnitude estimates. The physiological measures varied in outcome. Measures of respiration showed no reliable effects. But heart rate and skin conductance decreased significantly for phobics as viewing distance increased.

Adolescent↗
PubMed1992

Contrast sensitivity as a function of spatial frequency, viewing distance and eccentricity with and without spatial noise.

Using computer graphics and a two-alternative forced-choice method we measured threshold contrast as a function of viewing distance, spatial frequency, and eccentricity for gratings with and without added, white two-dimensional spatial noise. Our experiments showed that in spatial noise contrast sensitivity was independent of viewing distance as long as contrast sensitivity was lower with noise than without. With increasing spatial frequency (f) the grating area (A) was reduced in order to keep the relative grating size (Af2) constant. At all spatial frequencies the test gratings thus had the same amount of detail and contour. Noise spectral density was reduced in direct proportion to grating area in order to keep the physical signal-to-noise ratio constant. An increase in spatial frequency was thus accompanied with reductions in grating area and noise spectral density similar to those produced by a corresponding increase in viewing distance. In agreement, contrast detection in spatial noise was found to be independent of spatial frequency as long as contrast sensitivity was lower with noise than without. The effect of increasing eccentricity on visual performance can be compensated for by reducing the viewing distance (M-scaling). Hence, without M-scaling the effect of increasing eccentricity is similar to that of increasing viewing distance. In agreement, we found that contrast sensitivity in spatial noise was independent of eccentricity as long as contrast sensitivity was lower with noise than without.

Adult↗
PubMed1995

The effect of perceived distance on accommodation under binocular steady-state conditions.

Spatiotopic cues, such as perceived distance, have little effect on accommodation unless blur has been reduced or eliminated. We investigated the effect of perceived distance on accommodation under binocular steady-state conditions, about which little is known. Blur was reduced but not eliminated by using a stimulus with a moderately low luminance. Accommodation was measured under two conditions: (1) when cues from perceived distance, blur, and convergence were aligned; and (2) when perceived distance was opposed by both blur and convergence. We found a significant difference in accommodation between the two conditions, which we attribute to perceived distance.

Accommodation, Ocular↗
PubMed1982

Comparing frontal and lateral viewing in the pigeon. I. Tachistoscopic visual acuity as a function of distance.

Pigeon's visual acuity has mainly been tested in free viewing conditions so that the direction of gaze could not be controlled. In order to be able to compare the resolving power of the two retinal areas of higher cellular density--the area dorsalis in the red field with frontal binocular projection and the fovea centralis with lateral monocular projection--a method of behavioural fixation was used. This method consists in a forced pecking schedule and a tachistocopic presentation of the stimulus. The pigeon has to discriminate the orientation (vertical, positive; horizontal, negative) of square gratings of increasing spatial frequency. Tests were done with the stimuli appearing 25 degrees below the beak for frontal and 80 degrees back from the beak for lateral viewing, at distances of 10, 20, 40 and 80 cm for each direction. Results show that while frontal acuity decreases with distance, lateral acuity increases with distance. These psychophysical data confirm previous dioptric measurements done on frozen eyes, showing that the pigeon is myopic in the frontal field and hyperopic in the lateral field. Pigeons seem to be well adapted for visually guided frontal tasks at near distances (feeding, landing) and for visually guided lateral tasks at far distances (warning).

Animals↗
PubMed1984

Distance estimation in the Mongolian gerbil: the role of dynamic depth cues.

The role of dynamic depth cues in distance estimation was investigated in the Mongolian gerbil. Animals were trained to jump randomly varied distances on a jumping stand under both binocular and monocular conditions. Videotape analysis revealed that prior to jumping, the gerbils executed a series of vertical head movements, the amplitude and velocity of which were related to the gap distance and to each animal's accuracy. This suggested that the gerbils were employing motion parallax cues to judge distance. An inverse relation between the magnitude of forward movement and the frequency of vertical head movements suggested that loom cues were also being used to judge distance. This hypothesis received support from a second experiment in which forward movements were constrained by a short take-off platform. In this condition, frequency of vertical head movements increased, suggesting that a compensation had occurred for the loss of information from loom.

Animals↗
PubMed1982

Social distance from the stigmatized. A test of two theories.

Attribution of responsibility and disruption of social interaction are two explanations proposed in previous literature for the existence of differential social distance from individuals with various types of stigmas. This paper tests the relative merits of the theories in explaining perceived social distance that individuals in the study expressed from a wide range of stigmatized conditions representing two general stigma types: the disabled and deviants. The research is based on a sample of professionals and managers in key decision making positions. Perceived social distance was measured by a modified Bogardus Scale. Respondents expressed greater social distance from deviants such as alcoholics and drug addicts than from the disabled such as paraplegics and the blind. Little support was found for the contention that attribution of responsibility determines variations in social distance across or within the two major stigma types of disability and deviance. Rather, results suggest that differential rejection stems from the disruption a stigma causes in social interaction.

Adult↗
PubMed2004

Multifactorial interactions involved in linear self-transport distance estimate: a place for time.

As the vestibular system is the only sensory organ whose primary function is self-motion detection, we examined the conditions under which the otoliths, which detect the linear acceleration of the head, could be used to estimate traveled distance. In order to isolate the contribution of the otoliths (with the somatosensory system) from contributions of the visual and motor systems subjects were transported in darkness. We initially hypothesized that self-transport with continuously varying linear velocity should facilitate distance computation by continuously stimulating the otoliths, and that active control of self-motion should also help subjects estimate the distance traveled. However, it was found that the distance covered during self-motion is actually better estimated when transport velocity is quasi-constant. Nevertheless, such estimates strongly depend upon velocity magnitude; subjects show an idiosyncratic preferred self-motion velocity for which distance measurements are most accurate. Furthermore, the active control of self-transport improves estimates of self-motion mainly because the subjects can then adopt a constant velocity, and more precisely their preferred one. It was finally found that subjects mentally count in order to assess their displacement length, and that time perception is indeed disturbed by varying self-motion velocity.

Acceleration↗
PubMed2005

Timing and distance characteristics of interpersonal coordination during locomotion.

Most studies about human locomotion only tend to consider single subjects walking alone in a stationary environment. Nevertheless, human subjects have often to plan and generate their locomotor trajectories according to one another's displacements. Therefore, in the present study we address the question of the interpersonal coordination when pairs of subjects walk simultaneously. Six pairs of subjects walking face to face, backwards and forwards on a 8 m x 2 m track were involved in our experiment. Within each pair, the leader (L) was required to break the initial interpersonal distance whereas the follower (F) had to maintain this distance constant (1, 2 or 3 m). We measured their position and analyzed their travelled distance, the time course of their linear displacement, and the kinematics parameters of their steps. Our results show that F travels smaller distances than L and that even if they are highly correlated, some temporal delays exist between displacements of L and F with greater values when the interpersonal distance increases (from 1 to 3 m). These results are discussed in terms of high level imitation, i.e. bidirectional interactions with mutual influences of each subject on one another.

Distance Perception↗
PubMed2006

Depth scaling in phantom and monocular gap stereograms using absolute distance information.

The present study aimed to investigate whether the visual system scales apparent depth from binocularly unmatched features by using absolute distance information. In Experiment 1 we examined the effect of convergence on perceived depth in phantom stereograms [Gillam, B., & Nakayama, K. (1999). Quantitative depth for a phantom surface can be based on cyclopean occlusion cues alone. Vision Research, 39, 109-112.], monocular gap stereograms [Pianta, M. J., & Gillam, B. J. (2003a). Monocular gap stereopsis: manipulation of the outer edge disparity and the shape of the gap. Vision Research, 43, 1937-1950.] and random dot stereograms. In Experiments 2 and 3 we examined the effective range of viewing distances for scaling the apparent depths in these stereograms. The results showed that: (a) the magnitudes of perceived depths increased in all stereograms as the estimate of the viewing distance increased while keeping proximal and/or distal sizes of the stimuli constant, and (b) the effective range of viewing distances was significantly shorter in monocular gap stereograms. The first result indicates that the visual system scales apparent depth from unmatched features as well as that from horizontal disparity, while the second suggests that, at far distances, the strength of the depth signal from an unmatched feature in monocular gap stereograms is relatively weaker than that from horizontal disparity.

Convergence, Ocular↗
PubMed2002

Student and faculty issues in distance education occupational safety and health graduate programs.

PROBLEM: There is increasing interest in delivering degree programs without requiring students to attend traditional classroom-based classes. There are many differences between classroom and distance courses that must be addressed to have effective distance programs. METHOD: Occupational safety and health faculty and occupational safety and health professionals were surveyed to determine the need for graduate occupational safety and health programs, delivered by means of distance education, and the best means to deliver the program from the perspective of faculty and working occupational safety and health professionals. RESULTS: Adequate time is the largest problem issue for potential students and the distance student's needs must be considered when developing program policies and procedures. Faculty must be sufficiently trained in pedagogy, technology, and communications so that they have the same comfort level with this method of instruction as they do for the more familiar classroom, and technical and instructional support personnel need to be readily available to work with the faculty and support course development. IMPACT ON INDUSTRY: Findings indicate that there is interest in a distance education-based program and it is believed that industry will be positively impacted as educational opportunities expand for working professionals.

Adult↗
PubMedDate not supplied

A partnership model of distance education: students' perceptions of connectedness and professionalization.

This article describes a partnership model of distance education for a master's nursing program in a midwestern state and an evaluation that assessed students' perceptions of professionalization and connectedness in the program. Students at the originating and distance sites were asked to complete evaluations at the end of each course. Connectedness and professionalization were measured using rated satisfaction with three modes of contact for each item. Results indicated that students at the distance site had a significantly higher overall level of satisfaction with interactive television (ITV) and experienced high levels of connectedness and professionalization through the ITV courses. However, among the three modes of connectedness, students at the distance site rated satisfaction with contact with same-site students as the highest, followed by contact with the instructor. Students also perceived that their professional identity increased through the three modes, particularly for contact with same-site peers at the distance site and for contact with instructors at both sites. Recommendations for faculty and student responsibilities are provided to ensure a positive learning environment.

Adult↗
PubMed2006

One-dimensional and multi-dimensional studies of the exocentric distance estimates in frontoparallel plane, virtual space, and outdoor open field.

The aim of this study is twofold: on the one hand, to determine how visual space, as assessed by exocentric distance estimates, is related to physical space. On the other hand, to determine the structure of visual space as assessed by exocentric distance estimates. Visual space was measured in three environments: (a) points located in a 2-D frontoparallel plane, covering a range of distances of 20 cm; (b) stakes placed in a 3-D virtual space (range = 330 mm); and (c) stakes in a 3-D outdoors open field (range = 45 m). Observers made matching judgments of distances between all possible pairs of stimuli, obtained from 16 stimuli (in a regular squared 4 x 4 matrix). Two parameters from Stevens' power law informed us about the distortion of visual space: its exponent and its coefficient of determination (R2). The results showed a ranking of the magnitude of the distortions found in each experimental environment, and also provided information about the efficacy of available visual cues of spatial layout. Furthermore, our data are in agreement with previous findings showing systematic perceptual errors, such as the further the stimuli, the larger the distortion of the area subtended by perceived distances between stimuli. Additionally, we measured the magnitude of distortion of visual space relative to physical space by a parameter of multidimensional scaling analyses, the RMSE. From these results, the magnitude of such distortions can be ranked, and the utility or efficacy of the available visual cues informing about the space layout can also be inferred.

Adult↗
PubMed2006

Does energy expenditure affect the perception of egocentric distance? A failure to replicate experiment 1 of Proffitt, Stefanucci, Banton, and Epstein (2003).

In a series of recent studies, Proffitt and his colleagues have reported that the perceived distance to a target is influenced by the energy expenditure associated with any action, such as walking or throwing, for spanning the distance to the target. In particular, Proffitt, Stefanucci, Banton, and Epstein (2003) reported that wearing a heavy backpack caused verbal reports of distance to increase. We conducted a study to determine whether three responses dependent on perceived distance (verbal report of distance, blind walking, and estimates of object size) are influenced by the backpack manipulation. In two experiments, one involving a between-participants design and the other involving a within-participants design, we found that none of the three responses were influenced by the wearing of a heavy backpack.

Adolescent↗
PubMed2002

Cognitive and behavioral distancing from the poor.

The author argues that distancing is the dominant response to poor people on the part of those who are not poor and that distancing, separation, exclusion, and devaluing operationally define discrimination. Such responses, together with stereotypes and prejudice, define classism. The article focuses on classism in the United States. Classism is examined in the context of theoretical propositions about the moral exclusion of stigmatized others and is illustrated by cognitive distancing, institutional distancing (in education, housing, health care, legal assistance, politics, and public policy), and interpersonal distancing. The adoption of the Resolution on Poverty and Socioeconomic Status by the American Psychological Association Council of Representatives in August 2000 is cited as an important step in the direction of eliminating the invisibility of low-income persons in psychological research and theory.

Humans↗
PubMed1989

Two operations for "ratios" and "differences" of distances on the mental map.

Ss judged "ratios of distances" and "differences of distances" between pairs of U.S. cities. Results fit the theory that Ss used two comparison processes as instructed. A ratio scale of distances between cities was constructed from the 2 rank orders. From this scale, an interval scale of the city locations on an east-west continuum was derived. This scale agrees with the subtractive model fit to "ratios" and "differences" of easterliness and westerliness, and it also agrees with multidimensional scaling of judged distances between cities. These findings are consistent with the theory that Ss use subtraction when instructed to judge either "ratios" or "differences," but that they can use both ratio and difference operations when the stimuli (in this case, distances) constitute a ratio scale on the subjective continuum.

Adult↗
PubMed1991

Perceiving the vertical distances of surfaces by means of a hand-held probe.

Nine experiments were conducted on the haptic capacity of people to perceive the distances of horizontal surfaces solely on the basis of mechanical stimulation resulting from contacting the surfaces with a vertically held rod. Participants touched target surfaces with rods inside a wooden cabinet and reported the perceived surface location with an indicator outside the cabinet. The target surface, rod, and the participant's hand were occluded, and the sound produced in exploration was muffled. Properties of the probe (length, mass, moment of inertia, center of mass, and shape) were manipulated, along with surface distance and the method and angle of probing. Results suggest that for the most common method of probing, namely, tapping, perceived vertical distance is specific to a particular relation among the rotational inertia of the probe, the distance of the point of contact with the surface from the probe's center of percussion, and the inclination at contact of the probe to the surface. They also suggest that the probe length and the distance probed are independently perceivable. The results were discussed in terms of information specificity versus percept-percept coupling and parallels between selective attention in haptic and visual perception.

Adult↗