The visual perception of exocentric distance in outdoor settings

The visual perception of long outdoor distances

Many previous studies have investigated visual distance perception, especially for small to moderate distances. Few experiments, however, have evaluated the perception of large distances (e.g., 100 m or more). The studies that have been conducted have found conflicting results (diametrically opposite conclusions). In the current experiment, the functions relating actual and perceived distance were obtained for sixteen adult observers using the method of equal appearing intervals. These functions relating perceived and actual distance were obtained for outdoor viewing in a typical University environment-the experiment was conducted along a sidewalk adjacent to a typical street where campus buildings, trees, street signs, etc., were visible. The overall results indicated perceptual compression of distances in depth so that the stimulus distance intervals appeared significantly shorter than the actual (physical) distance intervals. It is important to note, however, that there were sizeable individual differences-the judgments of half of the observers were relatively accurate, whereas the judgments of the remaining half were inaccurate to varying degrees. The results of the experiment demonstrate that there is no single function that describes how human observers visually perceive large distance intervals in outdoor environments.

Monocular information for perceiving large egocentric distance: A comparison between monocularly blind patients and normally sighted observers

The debate surrounding the advantages of binocular versus monocular vision has persisted for decades. This study aimed to investigate whether individuals with monocular vision loss could accurately and precisely perceive large egocentric distances in real-world environments, under natural viewing conditions, comparable to those with normal vision. A total of 49 participants took part in the study, divided into three groups based on their viewing conditions. Two experiments were conducted to assess the accuracy and precision of estimating egocentric distances to visual targets and the coordination of actions during blind walking. In Experiment 1, participants were positioned in both a hallway and a large open field, tasked with judging the midpoint of self-to-target distances spanning from 5 to 30 m. Experiment 2 involved a blind walking task, where participants attempted to walk towards the same targets without visual or environmental feedback at an unusually rapid pace. The findings revealed that perceptual accuracy and precision were primarily influenced by the environmental context, motion condition, and target distance, rather than the visual conditions. Surprisingly, individuals with monocular vision loss demonstrated comparable accuracy and precision in perceiving egocentric distances to that of individuals with normal vision.

How accurate is the visual estimation of bowel length by endoscopic surgeons?

Background

Measurement of small bowel length is an essential step in performing bariatric surgery. Surgeons need to measure bowel length in order to create alimentary and biliopancreatic limbs. Inaccurate bowel measurement may affect the outcome of surgery. However, it is not clear how accurate the measurement of bowel length is by surgeons.

Methods

Two image quizzes marking certain lengths of jejunum were sent to participants. They were asked to estimate the length of marked bowels in maze quizzes. The Error of estimation, prevalence of significant error (error greater than 30 percent of actual length), and the relationship between different participant characteristics was investigated.

Results

A total of 86 participants answered the questionnaire. The mean error of estimation was 4.62 cm (27%). Twenty-eight participants (33%) had significant errors in estimation of bowel length.

Conclusion

While there are surgeons that can estimate bowel length with decent accuracy, significant errors in estimation of bowel length are not uncommon among surgeons. Surgeons should consider adopting techniques for accurate measurement of the small intestine.

Monocular Perception of Equidistance: The Effects of Viewing Experience and Motion-generated Information

SIGNIFICANCE

Using static depth information, normal observers monocularly perceived equidistance with high accuracy. With dynamic depth information and/or monocular viewing experience, they perceived with high precision. Therefore, monocular patients, who were adapted to monocular viewing, should be able to perceive equidistance and perform related tasks.

PURPOSE

This study investigated whether normal observers could accurately and precisely perceive equidistance with one eye, in different viewing environments, with various optical information and monocular viewing experience.

METHODS

Sixteen normally sighted observers monocularly perceived the distance (5 to 30 m) between a target and the self and replicated it either in some hallways that contained ample static monocular depth information but had a limited field of view or on a lawn that contained less depth information but had a large field of view. Participants remained stationary or walked 5 m before performing the task, as a manipulation of the availability of dynamic depth information. Eight observers wore eye patches for 3 hours before the experiment and gained monocular viewing experience, whereas the others did not. Both accuracy and precision were measured.

RESULTS

As long as static monocular depth information was available, equidistance perception was effectively accurate, despite minute underestimation. Perception precision was improved by prior monocular walking and/or experience with monocularity. Accuracy and precision were not affected by the viewing environments.

CONCLUSIONS

Using static and dynamic monocular depth information and/or with monocular experience, normal observers judged equidistance with reliable accuracy and precision. This implied that patients with monocular vision, who are better adapted than participants of this study, should also be able to perceive equidistance and perform distance-dependent tasks in natural viewing environments.

Visual distance perception indoors, outdoors, and in the dark

The ability to visually perceive distances in depth was evaluated in two experiments. In both experiments, the observers were required to bisect a distance interval oriented in depth (8 m total extent in Experiment 1 and 7 m in Experiment 2). The purpose of Experiment 1 was to examine the effects of environmental context (indoors in the dark, indoors in the light, and outdoors) and monocular versus binocular viewing. The purpose of Experiment 2 was to manipulate linear perspective to determine its importance for perceiving depth interval magnitudes. In the outdoor environment, the observers' bisection judgments indicated perceptual compression of farther distances similar to that obtained in many previous studies. In contrast, the observers' judgments in the indoor lighted environment were consistent with the perceptual expansion of farther distances. There was also a beneficial effect of binocular viewing upon the precision of the observers' repeated judgments, but the size of this effect was large only within the dark environment. Finally, linear perspective was found to significantly modulate the observers' bisection judgments such that they became accurate only when perspective was available.

The Visual Perception of Large-Scale Distances Outdoors

The ability of 32 younger (ages ranged from 19 to 32 years) and older adults (ages ranged from 65 to 83 years) to visually perceive outdoor distances was evaluated; we used the method of equal-appearing intervals. On any given trial, the observers adjusted five distance intervals in depth so that they all appeared equivalent in magnitude (and equal to a standard initial egocentric distance of 6 m). The judgments of approximately two thirds of the younger and older observers exhibited varying degrees of perceptual compression, while those of the remaining one third were essentially accurate. Unlike a number of previous studies that evaluated the perception of shorter distances, no significant effects of age were obtained in the current experiment. In particular, there were no significant effects of age upon either accuracy or precision. The ability of human observers to evaluate large-scale distances outdoors is well maintained with increasing age.

Effects of orientation change during environmental learning on age-related difference in spatial memory

It has been suggested that older adults suffer a greater degree of decline in environmental learning when navigating in an environment than when reading a map of the environment. However, the two types of spatial learning differ not only in perspectives (i.e., navigation is done with a ground-level perspective; a map is read from an aerial perspective) but also in orientations (i.e., orientations vary during navigation; spatial information is drawn from a single orientation in a map), making it unclear which factor critically affects older adults' spatial learning. The present study addressed this issue by having younger and older participants learn the layout of a large-scale environment through an aerial movie that contained changes in orientations from which the environment was depicted. Results showed that older participants' memories for the environmental layout were as distorted as those created through a ground-level movie (which involved the same orientation changes), whereas they formed more accurate memories through another aerial movie in which an orientation was fixed. By contrast, younger participants learned the environment equally well from the three movies. Taken together, these findings suggest that there is age-related alteration specifically in the ability to process multiple orientations of an environment while encoding its layout in memory. It is inferred that this alteration stems from functional deterioration of the medial temporal lobe, and possibly that of posterior cingulate areas as well (e.g., the retrosplenial cortex), in late adulthood.

Sex and age modulate the visual perception of distance

An experiment was conducted to evaluate the ability of 28 younger and older adults to visually bisect distances in depth both indoors and outdoors; half of the observers were male and half were female. Observers viewed 15-m and 30-m distance extents in four different environmental settings (two outdoor grassy fields and an indoor hallway and atrium) and were required to adjust the position of a marker to place it at the midpoint of each stimulus distance interval. Overall, the observers' judgments were more accurate indoors than outdoors. In outdoor environments, many individual observers exhibited perceptual compression of farther distances (e.g., these observers placed the marker closer than the actual physical midpoints of the stimulus distance intervals). There were significant modulatory effects of both age and sex upon the accuracy and precision of the observers' judgments. The judgments of the male observers were more accurate than those of the female observers and they were less influenced by environmental context. In addition, the accuracies of the younger observers' judgments were less influenced by context than those of the older observers. With regard to the precision of the observers' judgments, the older females exhibited much more variability across repeated judgments than the other groups of observers (younger males, younger females, and older males). The results of our study demonstrate that age and sex are important variables that significantly affect the visual perception of distance.

The Aging Navigational System

The discovery of neuronal systems dedicated to computing spatial information, composed of functionally distinct cell types such as place and grid cells, combined with an extensive body of human-based behavioral and neuroimaging research has provided us with a detailed understanding of the brain's navigation circuit. In this review, we discuss emerging evidence from rodents, non-human primates, and humans that demonstrates how cognitive aging affects the navigational computations supported by these systems. Critically, we show 1) that navigational deficits cannot solely be explained by general deficits in learning and memory, 2) that there is no uniform decline across different navigational computations, and 3) that navigational deficits might be sensitive markers for impending pathological decline. Following an introduction to the mechanisms underlying spatial navigation and how they relate to general processes of learning and memory, the review discusses how aging affects the perception and integration of spatial information, the creation and storage of memory traces for spatial information, and the use of spatial information during navigational behavior. The closing section highlights the clinical potential of behavioral and neural markers of spatial navigation, with a particular emphasis on neurodegenerative disorders.

Aging and visual 3-D shape recognition from motion

Two experiments were conducted to evaluate the ability of younger and older adults to recognize 3-D object shape from patterns of optical motion. In Experiment 1, participants were required to identify dotted surfaces that rotated in depth (i.e., surface structure portrayed using the kinetic depth effect). The task difficulty was manipulated by limiting the surface point lifetimes within the stimulus apparent motion sequences. In Experiment 2, the participants identified solid, naturally shaped objects (replicas of bell peppers, Capsicum annuum) that were defined by occlusion boundary contours, patterns of specular highlights, or combined optical patterns containing both boundary contours and specular highlights. Significant and adverse effects of increased age were found in both experiments. Despite the fact that previous research has found that increases in age do not reduce solid shape discrimination, our current results indicated that the same conclusion does not hold for shape identification. We demonstrated that aging results in a reduction in the ability to visually recognize 3-D shape independent of how the 3-D structure is defined (motions of isolated points, deformations of smooth optical fields containing specular highlights, etc.).

The visual perception of distance ratios in physical space

Past studies have consistently demonstrated that human observers cannot accurately perceive environmental distances. Even so, we obviously detect sufficient spatial information to meet the demands of everyday life. In the current experiment, ten younger adults (mean age was 21.8years) and ten older adults (mean age was 72.3years) estimated distance ratios in physical space. On any given trial, observers judged how long one distance interval was relative to another. The 18 stimulus ratios ranged from 1.0 to 9.5; the observers judged each stimulus ratio three times. The average correlation coefficient relating actual distance ratios to perceived ratios was identical (r=0.87) for both younger and older age groups. Despite this strong relationship between perception and reality, the judgments of many individual observers were inaccurate. For example, ten percent of the observers overestimated the stimulus ratios, while fifty percent underestimated the stimulus ratios. Although both under- and overestimation occurred in the current experiment, the results nevertheless demonstrate that human adults can reliably compare environmental distances in different directions.