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PubMed2006

Perceived size and perceived distance of targets viewed from between the legs: evidence for proprioceptive theory.

We investigated, using three comparisons, perceived size and perceived distance of targets seen from between the legs. Five targets, varying from 32 to 163 cm in height, were presented at viewing distances of 2.5-45 m, and a total of 90 observers verbally judged the perceived size and perceived distance of each target. In comparison 1, 15 observers inverted their heads upside down and saw the targets between their own legs; another 15 observers viewed them while being erect on the ground. The results showed that inverting the head lowered the degree of size constancy and compressed the scale for distance. To examine whether these results were due to an inversion of retinal-image or body orientation, comparisons 2 and 3 were performed. In comparison 2, 15 observers stood upright and saw the targets with prism goggles that rotated the visual field 180 degrees , while other 15 observers stood upright, but viewed the targets with a hollow frame lacking the prisms. The results showed that, in both goggle conditions, size constancy prevailed and perceived distance was a linear function of physical distance. In comparison 3, 15 observers wore the 180 degrees rotation goggles and viewed the targets by bending their heads forwardly, and the other 15 observers viewed them while wearing hollow goggles and lying on the belly. The results showed a low degree of size constancy and compressed the scale for distance. Therefore, it is suggested that perceived size and perceived distance are affected by an inversion of body orientation, not of retinal image orientation. When path analysis and partial correlation analysis were applied to the whole data, perceived size was found to be independent of perceived distance. These results supported the direct perception model, rather than the apparent distance model.

Cues↗
PubMed2006

Distance perception in a natural outdoor setting: is there a developmental trend to overconstancy?

The main purpose of the present study was to investigate whether in natural environment, using very large physical distances, there is a trend to overconstancy for distance estimates during development. One hundred and twenty-nine children aged 5 to 13 years old and twenty-one adults (in a control group), participated as observers. The observer's task was to bisect egocentric distances, ranging from 1.0 to 296.0 m, presented in a large open field. The analyses focused on two parameters, constant errors and variable errors, such as measuring accuracy and precision, respectively. A third analysis focused on the developmental pattern of shifts in constancy as a function of age and range of distances. Constant error analysis showed that there are two relevant parameters for accuracy, age, and range of distances. For short distances, there are three developmental stages: 5-7 years, when children have unstable responses, 7-11, underconstancy, and 13 to adulthood, when accuracy is reached. For large distances, there is a two-stage development: 5-11 years, with severe underconstancy, and beyond this age, with mild underconstancy. Variable errors analyses indicate that precision is noted for 7 year-old children, independently of the range of distances. The constancy analyses indicated that there is a shift from constancy (or slightly overconstancy) to underconstancy as a function of physical distance for all age groups. The age difference is noted in the magnitude of underconstancy that occurs in larger distances, where adults presented lower levels of underconstancy than children. The present data were interpreted as due to a developmental change in cognitive processing rather than to changes in visual space perception.

Adolescent↗
PubMed1988

Overflow, first-sight, and vanishing point distances in visual imagery.

The relationship between the size of a familiar object and the distances at which it is imaged is examined in three experiments. The distance at which an imaged object overflows the visual field is linearly related to object size, a result consistent with the size-distance invariance hypothesis (Kosslyn, 1980). The distance at which an object is initially imaged, first-sight distance, is related to the object size by a power function with an exponent less than 1. In addition, time required to scan from the first-sight to the overflow distance increases as a function of the difference between the two distance estimates. The distance at which an imaged object becomes too small to be identified, vanishing point distance, is related to object size by a power function with an exponent less than 1. This result does not support predictions made from the size-distance invariance hypothesis or Kosslyn's model of visual imagery. Implications for a theory of visual imagery and memory are discussed.

Adult↗
PubMed1979

Absolute and relative cues for the auditory perception of egocentric distance.

Three experiments were performed to examine the reverberation cue to egocentric auditory distance and to determine the extent to which such a cue could provide 'absolute', as contrasted with 'relative', information about distance. In experiment 1 independent groups of blindfolded observers (200 altogether) were presented with broadband noise from a speaker at one of five different distances (0.55 to 8 m) in a normal hard-walled room. Half of each group of observers were presented with the sound at 0 deg azimuth, followed (after a delay) by the identical sound at 90 deg azimuth. The order of presentation was reversed for the remaining observers. Perceived distance varied significantly as a function of the physical distance to the speaker, even for the first presentations. The change in the binaural information between the 0 deg and 90 deg presentations did not significantly modify the results. For both orientations, near distances were overestimated and far distances were underestimated. Experiment 2 and 3 were designed to evaluate how much prior auditory exposure to the laboratory environment was necessary. A 200 Hz square-wave signal was presented from one of three distances (1, 2, or 6 m) to observers who had either minimal room information or an exposure which included talking within the room. Perceived distance varied significantly with physical distance regardless to exposure condition.

Acoustic Stimulation↗
PubMed1982

The effect of familiar size at familiar distances.

The effect of familial size as a distance cue was tested with familiar objects at familiar distances. Experiment 1 showed that there were no uncontrolled distance cues available and that in their absence the retinal image did not affect depth or size perception. Under these conditions, size and distance judgments were essentially indeterminate and independent of each other. In experiment 2 a paradigm was employed which allowed a direct determination of whether equivalent changes either in size of a familiar object or in its true distance produced equivalent changes in its perceived distance. The results showed that there were no uncontrolled distance cues, and that subjects perceived the familiar object as having its familiar size. Moreover, changing the retinal image of the objects had almost exactly the same effect on their perceived distance as did changing their true distance. Hence, familial size does effectively govern the perception of distance when there are no competing cues.

Cues↗
PubMed1988

Accommodation and apparent distance.

The ability to judge egocentric distance was assessed in sixteen normal observers under conditions where monocular blur-driven accommodation provided the only source of information regarding changes in target dioptric distance. Accommodation and apparent distance were measured over an optical range of 2 to 6 D for each of three targets which differed in their effectiveness as accommodative stimuli (excellent, moderate, and poor). For the excellent and moderate accommodative targets, apparent distance decreased as accommodation increased, with both targets sharing a common linear function. Apparent distance, however, tended to exceed accommodative distance and was relatively compressed in scale. As expected, accommodative response and apparent distance diminished in range as target effectiveness was reduced. The poor accommodative target represented the limiting case wherein accommodation failed to deviate from the tonic level, and apparent distance remained constant. There were considerable intersubject differences in the ability to judge distances on the basis of accommodation. The results indicate that accommodation can indeed serve as a source of distance information, particularly for some individuals.

Accommodation, Ocular↗
PubMed1992

Cognitive strategies and short-term memory for movement distance and location.

A number of researchers (e.g. Kerr, 1978; Walsh, Russell, Imanaka, & James, 1979) have previously demonstrated interference between location and distance information in motor short-term memory. This interference manifests itself in a characteristic pattern of undershooting and overshooting, with reproduction movement location being drawn in the direction of criterion movement distance and, conversely, the distance of reproduction movements being influenced by the terminal location of the criterion movement. We investigated the effects of different cognitive strategies upon the appearance of this location-distance interference during the reproduction of movement location (Experiment 1) and distance (Experiments 2 and 3) in a linear arm positioning task. Experiment 1 compared performance in location reproduction between two strategy groups differing in the availability of explicit information about the change in starting position. The characteristic undershooting-overshooting interference pattern was observed for the group without the explicit information about the change in starting position but disappeared for the group in which explicit information about the change in starting position was provided. Experiment 2 examined the systematic undershooting-overshooting pattern in distance reproduction for a location strategy (involving some extrapolation of the start and end locations), a counting strategy, and a distance sense strategy (involving the use of visual imagery). The systematic response bias pattern disappeared when the subjects used a location strategy but was clearly observed for the subjects using the other two strategies. This finding was generally confirmed by Experiment 3, which showed a typical undershooting-overshooting pattern in distance reproduction for a counting/distance sense strategy but not for two location strategies (a general location and an explicit location strategy). The location strategies differed in the availability of explicit information about starting and end locations for both the criterion and reproduction movements. The results from these three experiments indicate that explicit information about the start and/or end locations prevents the usual interference between location and distance information from arising in movement reproduction. The notions of automatic and controlled processing and cerebral hemispheric specialization are discussed as potential explanations of these results and of the interference typically observed in motor short-term memory between distance and location information.

Adolescent↗
PubMed1993

Neuronal specification of direction and distance during reaching movements in the superior precentral premotor area and primary motor cortex of monkeys.

1. Single-unit neuronal activity was recorded in the primary motor and superior precentral premotor areas of two rhesus monkeys during an arm reaching task. The task involved moving a cursor displayed on a video terminal using a draftsman's arm-type manipulandum. From a centrally located start box the animal was required to move to 1 of 48 target boxes at eight different directions (0-360 degrees in 45 degrees intervals) and six distances (1.4-5.4 cm in 0.8-cm increments). Both direction and distance for the upcoming movement were unpredictable. 2. The activity of 197 arm movement-related cells was recorded and evaluated for each of the 48 targets. Histological examination showed the cells to be primarily in the primary motor cortex or in the premotor area around the superior precentral sulcus. Each cell's discharge was aligned on movement onset and averaged over five trials for each target. Movement kinematics including hand path velocity were also determined. The task time was divided into three epochs, a premovement period (PT), a movement period (MT), and total time (TT = PT+MT). For each epoch the average firing was correlated with the direction and distance of the movement using various regression procedures. 3. An analysis of variance (ANOVA) showed that the majority of neurons were modulated significantly by movement direction in each of the three time periods, PT (73.7%), MT (68.3%), and TT (78.5%). The relationship of the firing to direction was fit to a cosine tuning function for each significantly modulated cell. In 86.3% of the cells the firing was correlated significantly with a cosine function of movement direction in TT. A cell's preferred direction varied little for different movement distances. The mean difference in preferred direction for the smallest possible change in distance (0.8 cm) was 12.8 +/- 11.4 degrees (SD) and 17.1 +/- 14.7 degrees for the largest change in distance (4.0 cm). 4. Correlation analysis revealed that the activity of the majority of cells was modulated significantly by distance along at least one direction in each of the three time periods, PT (46.8%), MT (68.8%), and TT (67.7%). Subsequently, a univariate linear regression model was used to quantify a cell's discharge as a function of distance. For the regressions of firing with distance with a statistically significant correlation (r > 0.8), the mean slope was 3.59 +/- 0.17 spikes.s-1.cm-1 for the total time. The existence of a significant distance modulation was not invariably correlated with a cell's preferred movement direction.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2003

Interpersonal distance in schizophrenic patients: relationship to negative syndrome.

BACKGROUND: Personal space is the area individuals maintain around themselves into which others cannot intrude without arousing discomfort. OBJECTIVE: We tested the hypotheses that psychological distancing of patients with schizophrenia would be a characteristic of 1) diagnosis and/or 2) syndrome. METHODS: For this aim, 30 schizophrenic and 30 age matching normal males established comfortable interpersonal distances for 20 word-stimuli representing family members, significant others, self-images, emotionally neutral and threatening surroundings. The distances were assessed by a paper-and-pencil projective measure, the Comfortable Interpersonal Distance scale and the patients' psychopathological symptoms were quantified by the Positive and Negative Syndrome Scale. t-tests and correlational analyses were employed to examine the relationships between the parameters of interest. RESULTS: The rank order (hierarchy) of preferable interpersonal distances of patients with schizophrenia was similar to that of normal subjects. At the same time, psychological distance from family members and themselves was substantially larger among the patients. There were no significant correlations between any kind of interpersonal distance and positive syndrome of schizophrenia, while negative syndrome showed significant inverse association with distances from emotionally neutral and threatening figures and positive correlation with family member and self-image distances. CONCLUSION: The results suggest that the negative syndrome of schizophrenia attenuates the differences between interpersonal distances from generally close and distant persons.

Adult↗
PubMed2001

The independence of size perception and distance perception.

Research on distance perception has focused on environmental sources of information, which have been well documented; in contrast, size perception research has focused on familiarity or has relied on distance information. An analysis of these two parallel bodies of work reveals their lack of equivalence. Furthermore, definitions of familiarity need environmental grounding, specifically concerning the amount of size variation among different tokens of an object. To demonstrate the independence of size and distance perception, subjects in two experiments were asked to estimate the sizes of common objects from memory and then to estimate both the sizes and the distances of a subset of such objects displayed in front of them. The experiments found that token variation was a critical variable in the accuracy of size estimations, whether from memory or with vision, and that distance had no impact at all on size perception. Furthermore, when distance information was good, size had no effect on distance estimation; in contrast, at far distances, the distances to token variable or unknown objects were estimated with less accuracy. The results suggest that size perception has been misconceptualized, so that the relevant research to understand its properties has not been undertaken. The size-distance invariance hypothesis was shown to be inadequate for both areas of research.

Adult↗
PubMed2002

Contribution of extraretinal signals to the scaling of object distance during self-motion.

We investigated the role of extraretinal information in the perception of absolute distance. In a computer-simulated environment, monocular observers judged the distance of objects positioned at different locations in depth while performing frontoparallel movements of the head. The objects were spheres covered with random dots subtending three different visual angles. Observers viewed the objects ateye level, either in isolation or superimposed on a ground floor. The distance and size of the spheres were covaried to suppress relative size information. Hence, the main cues to distance were the motion parallax and the extraretinal signals. In three experiments, we found evidence that (1) perceived distance is correlated with simulated distance in terms of precision and accuracy, (2) the accuracy in the distance estimate is slightly improved by the presence of a ground-floor surface, (3) the perceived distance is not altered significantly when the visual field size increases, and (4) the absolute distance is estimated correctly during self-motion. Conversely, stationary subjects failed to report absolute distance when they passively observed a moving object producing the same retinal stimulation, unless they could rely on knowledge of the three-dimensional movements.

Adolescent↗
PubMed2005

A distance education in undergraduate dietetic education.

Distance education is an exploding phenomenon that allows people to pursue higher education on their own time, at a pace that meets their needs, in locations where there are no colleges and universities, or where there is not a desired program of study. This study examined the use of distance education in undergraduate dietetic education programs and the opportunities for obtaining an undergraduate degree in dietetics solely via distance education. A survey was sent to all directors (n = 279) of undergraduate programs accredited/approved by the Commission on Accreditation for Dietetics Education to determine the current status and projected future use of distance education in their institutions' on-campus programs. The survey had a 54% response rate. Approximately 32% (n = 150) of undergraduate dietetics programs offer distance education courses in some format. Institutions that offer nondietetics distance education courses were more likely to offer dietetics distance education courses. The most common distance education format utilized in dietetics was 100% Internet courses (48%). The most common distance education dietetics course offered was a basic or introductory nutrition course (31%). From the data of courses offered, or permitted to be transferred, it would not be possible for a student to complete an undergraduate degree in dietetics solely via distance education methodologies at the time this study was conducted.

Education, Distance↗
PubMed2003

Genetic maps of microsatellite and single-nucleotide polymorphism markers: are the distances accurate?

Genetic maps play an important role in gene mapping. Inaccurate genetic maps can hinder gene mapping by biasing lod scores and reducing the power to map a trait to a particular region. Although sequence-based physical maps can provide a unique order for markers, they do not provide information on genetic map distances. By simulation studies, I investigated how many meioses are necessary to accurately estimate genetic map distances for maps constructed from microsatellite and single-nucleotide polymorphism (SNP) markers for various intermarker distances and marker heterozygosity. To evaluate the accuracy of the generated genetic maps, the length of the 95% confidence interval for intermarker genetic distances was examined. In addition, the power to separate two adjacent markers by a nonzero map distance was investigated. The number of meioses necessary to accurately estimate map distances depends greatly not only on intermarker distances but also on marker heterozygosity. For example, for a genetic map with intermarker distances of 0.5 cM generated with 1,000 meioses, when marker heterozygosity was high (0.90), for 96% of the markers there was a nonzero map distance between adjacent markers. However, when marker heterozygosity was low (0.32), only 48% of the markers mapped to a unique position. For identical numbers of meioses and intermarker distances, genetic maps constructed from microsatellite markers will be more precise than maps assembled from SNP markers, due to the higher levels of heterozygosity for microsatellite markers.

Adult↗
PubMed1999

The size-distance paradox is a cognitive phenomenon.

The perceived size of a fixated object is known to be a function of the perceived fixation distance. The size-distance paradox has been posited as evidence that the perceived distance of a fixated object is, in turn, influenced by the object's perceived size. If this is correct then it challenges a widely accepted account (modified weak fusion) of how the nervous system combines multiple sources of information. We hypothesised that the influence of perceived size on the perception of distance is likely to be restricted to conscious perceptual judgements. If our hypothesis is correct then the size-distance paradox should not be observed when observers make action-based distance judgements. In line with this expectation we observed the size-distance paradox when participants made verbal reports on target distance but found no paradoxical judgements in a group who were asked to point at the target. We therefore suggest that the size-distance paradox should not be taken as evidence that perceived size feeds back into distance perception.

Adult↗
PubMed1999

[Retroequatorial myopexy combined with bimedial recession for near-distance disparity esotropia].

PURPOSE: In cases of esotropia combined with a high AC/A ratio, partly accommodative convergence excess or with nonaccommodative convergence excess, two methods of surgical therapy are possible: recession of the medial recti (Parks) and retroequatorial myopexy (Cüppers). Our aim was to answer the question whether retroequatorial myopexy alone and in combination with bimedial recession are appropriate methods of reducing the strabismic angle at near and distant fixation to values under 10 PD and near-distance disparity to less than 10 PD to form the basis for single binocular vision without bifocals. PATIENTS AND METHODS: Eighty-three patients, aged 2-14 years (39 boys and 44 girls), were included in the study: 37 children (group A) with early-onset near-distance esotropia of 14-48 PD for distance and 26-65 PD for near objects and 46 children (group B) with acquired near-distance esotropia of 8-45 PD for distance and 26-70 PD for near objects. Inclusion criteria were a near-distanced disparity of at least 10 PD (range 10-33 PD), a follow-up of at least 3 months (median 5 months, range 3-69 months), retinoscopy in cycloplegia and full refractive correction. The amount of conventional surgery was chiefly based on the distance angle of esotropia. The myopexy was placed 12, 13 and 14 mm behind the insertion of the medial rectus. RESULTS: In 73 of 83 patients (88%) we were able to reduce the strabismic angle for distance and near fixation to less than 10 PD and in 73 cases even under 5 PD. In 77 of 83 patients (93%) the near-distance disparity was reduced to less than 10 PD and in 72 patients (87%) even under 5 PD. Postoperatively, 9 children had bifocals, but 3 of them have meanwhile discarded them. Two cases were slightly ocvercorrected and 1 case undercorrected. Seventy children (84%) attained grade of binocularity. CONCLUSION: Retroequatorial myopexy (fadenoperation) alone and combined with bimedial recession is an effective procedure in treating esotropia with abnormal near-distance disparity.

Adolescent↗
PubMedDate not supplied

Distance discrimination during active electrolocation in the weakly electric fish Gnathonemus petersii.

Weakly electric fish use active electrolocation for orientation at night. They emit electric signals (electric organ discharges) which generate an electrical field around their body. By sensing field distortions, fish can detect objects and analyze their properties. It is unclear, however, how accurately they can determine the distance of unknown objects. Four Gnathonemus petersii were trained in two-alternative forced-choice procedures to discriminate between two objects differing in their distances to a gate. The fish learned to pass through the gate behind which the corresponding object was farther away. Distance discrimination thresholds for different types of objects were determined. Locomotor and electromotor activity during distance measurement were monitored. Our results revealed that all individuals quickly learned to measure object distance irrespective of size, shape or electrical conductivity of the object material. However, the distances of hollow, water-filled cubes and spheres were consistently misjudged in comparison with solid or more angular objects, being perceived as farther away than they really were. As training continued, fish learned to compensate for these 'electrosensory illusions' and erroneous choices disappeared with time. Distance discrimination thresholds depended on object size and overall object distance. During distance measurement, the fish produced a fast regular rhythm of EOD discharges. A mechanisms for distance determination during active electrolocation is proposed.

Animals↗
PubMed1992

Comparison of the intercondylar distance and the interfacial width as used with the electronic pantograph.

The electronic pantograph (Pantronic) records mandibular movements and computes the articulator settings. The Pantronic pantograph does not determine the intercondylar distance but approximates it from the interfacial width at the condyles. An average distance of 12.5 mm is subtracted from each side to determine the intercondylar distance. This study recorded 45 patients' articulator intercondylar distances that had been set from a mechanical pantograph and they were compared with the Pantronic's approximation. The difference between the interfacial width and the actual intercondylar distance was 15.1 mm on the right side and 14.9 mm on the left side. A numerical value of 15.0 mm was statistically superior to the Pantronic's 12.5 mm in estimating the average distance between the intercondylar distance and the surface of the skin at the condyle. No statistically significant difference was found between the differences of interfacial width and intercondylar distance values for men and women (p greater than 0.05). The mean intercondylar distance was 56.5 mm on the right side and 56.7 mm on the left side. A statistically significant difference was found between the mean intercondylar distances of men and women (p less than 0.05).

Adult↗
PubMed1989

The proximity of DNA sequences in interphase cell nuclei is correlated to genomic distance and permits ordering of cosmids spanning 250 kilobase pairs.

The physical distance between DNA sequences in interphase nuclei was determined using eight cosmids containing fragments of the Chinese hamster genome that span 273 kb surrounding the dihydrofolate reductase (DHFR) gene. The distance between these sequences at the molecular level has been determined previously by restriction enzyme mapping (J.E. Looney and J.L. Hamlin, 1987, Mol. Cell Biol. 7: 569-577; C. Ma et al., 1988, Mol. Cell Biol. 8: 2316-2327). Fluorescence in situ hybridization was used to localize the DNA sequences in interphase nuclei of cells bearing only one copy of this genomic region. The distance between DNA sequences in interphase nuclei was correlated to molecular distance over a range of 25 to at least 250 kb. The observed relationship was such that genomic distance could be predicted to within 40 kb from interphase distance. The correct order of seven probes was derived from interphase distances measured for 19 pair-wise combinations of the probes. Measured distances between sequences approximately 200 kb apart indicate that the DNA is condensed 70- to 100-fold in hybridized nuclei relative to a linear DNA helix molecule. Cell lines with chromosome inversions were used to show that interphase distance increases with genomic distance in the 50-90 Mb range, but less steeply than in the 25-250 kb range.

Animals↗