The visual perception of distance ratios outdoors

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.

Aging and the perception of global structure

A single experiment required 40 younger and older adults to discriminate global shape as depicted by Glass patterns (concentric and radial organizations). Such patterns have been widely used for decades, because in order to successfully perceive the depicted shape, the visual system has to detect both locally oriented features (dipoles) and their alignments across extended regions of space. In the current study, we manipulated the number of constituent dipoles in the stimulus patterns (40 or 200), the noise-to-signal ratio (zero, 1.0, & 5.0), and the pattern size (6.0 & 25.0 degrees visual angle). The observers’ shape discrimination accuracies (d’ values) decreased markedly as the amount of noise increased, and there were smaller (but significant) effects of both overall pattern size and the number of stimulus dipoles. Interestingly, while there was a significant effect of age, it was relatively small: the overall d’ values for older and younger adults were 2.07 and 2.34, respectively. Older adults therefore retain an effective ability to visually perceive global shape, even for sparsely-defined patterns embedded in noise.

Aging and the Perception of Motion-Defined Form

A single experiment required 26 younger and older adults to discriminate global shape as defined only by differences in the speed of stimulus element rotation. Detection of the target shape required successful perceptual grouping by common fate. A considerable adverse effect of age was found: In order to perceive the target and discriminate its shape with a d’ value of 1.5, the older observers needed target element rotational speeds that were 23.4% faster than those required for younger adults. In addition, as the difference between the rotation speeds of the background and target stimulus elements increased, the performance of the older observers improved at a rate that was only about half of that exhibited by the younger observers. The results indicate that while older adults can perceive global shape defined by similarity (and differences) in rotational speed, their abilities are nevertheless significantly compromised.

Tests of the abilities to judge ratios of extensive and intensive sensory magnitudes

The assumption that people are able to numerically judge ratios of sensory magnitude is often used to scale sensations. In this study, we tested this assumption for the extensive sensation of length and the intensive sensations of heaviness and brightness. A ratio model fit judged length ratios accurately and fit judged heaviness and brightness ratios inaccurately. Also, most participants could not judge brightness ratios, even if they seemed able to respond nonverbally to the brightness ratios. These results suggest that people may generally be able to judge extensity ratios but not intensity ratios. Participants used auxiliary judgment operations to compensate for their lack of ability to judge intensity ratios. These auxiliary, nonratio operations were found to yield linear scales of intensive sensory magnitude.

Haptic Distance Ratio Estimation: The Geometry of Space Within the Hands

In the current study of haptic distance perception, 20 younger (median age: 22 years) and 20 older adults (median age: 72 years) used active touch to estimate distance ratios(one length relative to another). Nine tactile stimuli were created from wooden dowels; each consisted of two perpendicular dowels. The stimulus distance ratios ranged from 1.0 to 5.0. Each participant used both hands (without vision) to actively explore (30 s) a single stimulus object on every trial. The task was to numerically estimate the distance ratio. Overall, the participants’ judgments were precise; the overall magnitude of the Pearson r correlation coefficient was 0.943 and did not differ for younger and older adults. While the participants’ judgments were precise, they were not completely accurate: The average slope (of the relationship between actual and judged distance ratios) for all participants was significantly greater than 1.0 (1.15). Surprisingly, differences in manual dexterity had no apparent effect on distance ratio estimates. Older adults apparently retain an excellent ability to perceive distances using their sense of touch. Our results also demonstrate that the geometry of haptic space (at the scale of the hand) is approximately Euclidean in nature (and certainly not merely topological, projective, or affine).

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.

Aging and the Visual Perception of Motion Direction: Solving the Aperture Problem

An experiment required younger and older adults to estimate coherent visual motion direction from multiple motion signals, where each motion signal was locally ambiguous with respect to the true direction of pattern motion. Thus, accurate performance required the successful integration of motion signals across space (i.e., accurate performance required solution of the aperture problem) . The observers viewed arrays of either 64 or 9 moving line segments; because these lines moved behind apertures, their individual local motions were ambiguous with respect to direction (i.e., were subject to the aperture problem). Following 2.4 seconds of pattern motion on each trial (true motion directions ranged over the entire range of 360° in the fronto-parallel plane), the observers estimated the coherent direction of motion. There was an effect of direction, such that cardinal directions of pattern motion were judged with less error than oblique directions. In addition, a large effect of aging occurred—The average absolute errors of the older observers were 46% and 30.4% higher in magnitude than those exhibited by the younger observers for the 64 and 9 aperture conditions, respectively. Finally, the observers’ precision markedly deteriorated as the number of apertures was reduced from 64 to 9.

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.).