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.

Contours produced by internal specular interreflections provide visual information for the perception of glass materials.

Two experiments are reported that investigated how the perceptual identification of glass is influenced by banding contours formed by internal specular interreflections within glass materials. Observers made material categorization judgments for images depicting glass, chrome, shiny black and shiny white objects, and for contour drawings that were created by edge filtering images of glass, chrome or textured objects. Observers rated each stimulus by adjusting four sliders to indicate their confidence that the depicted material was glass, metal, shiny black, or something else, and these adjustments were constrained so that the sum of all four settings was always 100%. The results revealed that the rendered images were all categorized correctly with a high level of confidence. The contour drawings of glass and textured materials were also categorized correctly with a high level of confidence. However, the contour drawings of chrome materials were miscategorized as glass, with an average confidence rating that was significantly lower than those obtained for the glass contours. It is hypothesized that these different contour types are perceptually distinguished from one another based on how they align with the pattern of surface curvature on an object and the smoothness of the contours.

Effects of illumination on the categorization of shiny materials.

The present research was designed to examine how patterns of illumination influence the perceptual categorization of metal, shiny black, and shiny white materials. The stimuli depicted three possible objects that were illuminated by five possible high-dynamic-range imaging light maps, which varied in their overall distributions of illuminant directions and intensities. The surfaces included a low roughness chrome material, a shiny black material, and a shiny white material with both diffuse and specular components. Observers rated each stimulus by adjusting four sliders to indicate their confidence that the depicted material was metal, shiny black, shiny white, or something else, and these adjustments were constrained so that the sum of all four settings was always 100%. The results revealed that the metal and shiny black categories are easily confused. For example, metal materials with low intensity light maps or a narrow range of illuminant directions are often judged as shiny black, whereas shiny black materials with high intensity light maps or a wide range of illuminant directions are often judged as metal. To discover the visual information on which these judgements are based, we measured several possible image statistics, and we found two that were highly correlated with the observers' confidence ratings in appropriate contexts. We also performed a spherical harmonic analysis on the different light maps to quantitatively predict how they would bias observers' judgments of metal and shiny black surfaces.

Reflections on glass.

An important phenomenon in the study of human perception is the ability of observers to identify different types of surface materials. The present article will consider a wide range of factors that can influence the perceptual identification of glass, including the structural complexity of an object, whether it is hollow or solid, and the pattern of illumination. Several illumination techniques used in the field of photography are described, and examples are provided to show how they interact with structural complexity. A single psychophysical experiment is reported to evaluate the perceptions of naïve observers using a novel categorization task designed to assess potential confusions among multiple material categories. Finally, the paper will enumerate a number of specific image features that are potentially diagnostic for the identification of glass, and it will evaluate their relative importance for human perception.

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.

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).

The visual perception of metal.

The present research was designed to examine how the presence or absence of ambient light influences the appearance of metal. The stimuli depicted three possible objects that were illuminated by three possible patterns of illumination. These were generated by a single point light source, two rectangular area lights, or projecting light onto a translucent white box that contained the object (and the camera) so that the object would be illuminated by ambient light in all directions. The materials were simulated using measured parameters of chrome with four different levels of roughness. Observers rated the metallic appearance and shininess of each depicted object using two sliders. The highest rated appearance of metal and shininess occurred for the surfaces with the lowest roughness in the ambient illumination condition, and these ratings dropped systematically as the roughness was increased. For the objects illuminated by point or area lights, the appearance of metal and shininess were significantly less than in the ambient conditions for the lowest roughness value, and significantly greater than in the ambient condition for intermediate values of roughness. We also included a control condition depicting objects with a shiny plastic reflectance function that had both diffuse and specular components. These objects were rated as highly shiny but they did not appear metallic. A theoretical hypothesis is proposed that the defining characteristic of metal (as opposed to black plastic) is the presence of specular sheen over most of the visible surface area.

Aging and Haptic-Visual Solid Shape Matching.

A total of 36 younger (mean age = 21.3 years) and older adults (mean age = 73.8 years) haptically explored plastic copies of naturally shaped objects (bell peppers, Capsicum annuum) one at a time for 7 s each. The participants' task was to then choose which of 12 concurrently visible objects had the same solid shape as the one they felt. The younger and older participants explored the object shapes using either one, three, or five fingers (there were six participants for each combination of number of fingers and age group). The outcome was different from that of previous research conducted with manmade objects. Unlike Jansson and Monaci (2006) , we found that for most objects, our participants' performance was unaffected by variations in the number of fingers used for haptic exploration. While there was no significant overall effect of the number of fingers, there was a significant main effect of age. The younger adults' shape matching performance was 48.6% higher than that of the older adults. When perceiving naturally shaped objects such as bell peppers, it appears that the usage of a single finger can be as effective as haptic exploration with a whole complement of five fingers.

The Visual Aesthetics of Snowflakes.

In two experiments, participants evaluated the perceived beauty of snowflakes and solid objects. The snowflake silhouettes used as experimental stimuli were created from photographs of natural snowflakes. Both the snowflake silhouettes and computer-generated solid objects varied in complexity. In Experiment 1, 204 participants selected the single snowflake and single solid object that was the most beautiful. In Experiment 2, 33 participants rated the perceived complexity and beauty of the entire set of 100 snowflakes and solid objects. When considered as a group, the participants' results for the solid objects replicated previous findings: The most and least complex objects were perceived as being the most beautiful. This pattern did not necessarily occur, however, for individual participants. Some participants in Experiment 2, for example, found only complex solid objects to be most beautiful ( N = 10); other participants found only the simple solid objects to be most beautiful ( N = 11). Additional participants perceived both the most and least complex solid objects to be beautiful ( N = 10), while one participant only found moderately complex solid objects to be most beautiful. The results for the snowflakes were more uniform: 91% of participants perceived only the complex snowflakes as being most beautiful.

Aging and the Haptic Perception of Material Properties.

The ability of 26 younger (mean age was 22.5 years) and older adults (mean age was 72.6 years) to haptically perceive material properties was evaluated. The participants manually explored (for 5 seconds) 42 surfaces twice and placed each of these 84 experimental stimuli into one of seven categories: paper, plastic, metal, wood, stone, fabric, and fur/leather. In general, the participants were best able to identify fur/leather and wood materials; in contrast, recognition performance was worst for stone and paper. Despite similar overall patterns of performance for younger and older participants, the younger adults' recognition accuracies were 26.5% higher. The participants' tactile acuities (assessed by tactile grating orientation discrimination) affected their ability to identify surface material. In particular, the Pearson r correlation coefficient relating the participants' grating orientation thresholds and their material identification performance was -0.8: The higher the participants' thresholds, the lower the material recognition ability. While older adults are able to effectively perceive the solid shape of environmental objects using the sense of touch, their ability to perceive surface materials is significantly compromised.

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.

Aging and temporal integration in the visual perception of object shape.

It has been known for more than 160 years that highly occluded objects that would normally be visually unrecognizable can be successfully identified when they move. This anorthoscopic perception relies on the visual system's ability to integrate information over time to complete the perception of an entire object's shape. In this experiment, 16 younger and older adults (mean ages were 20.5 and 74.6 years, respectively) were familiarized with the (unoccluded) shapes of five naturally-shaped objects (bell peppers, Capsicum annuum) until they could be easily identified (i.e., with accuracies of at least 90 percent correct). All observers then viewed the stimulus objects anorthoscopically as they moved behind narrow slits; only small object fragments could be seen at any given time, because the objects were almost totally occluded from view. Even though the object identification performance for all observers was equivalent when whole object shapes were visible, a large age-related deficit in object identification emerged during anorthoscopic viewing such that the younger adults' identification performance was 45.4 percent higher than that of the older adults. This first ever study of aging and anorthoscopic perception demonstrates that there is an age-related deficit in performing the temporal integration needed for successful object recognition.

Solid shape discrimination from vision and haptics: natural objects (Capsicum annuum) and Gibson's "feelies".

A set of three experiments evaluated 96 participants' ability to visually and haptically discriminate solid object shape. In the past, some researchers have found haptic shape discrimination to be substantially inferior to visual shape discrimination, while other researchers have found haptics and vision to be essentially equivalent. A primary goal of the present study was to understand these discrepant past findings and to determine the true capabilities of the haptic system. All experiments used the same task (same vs. different shape discrimination) and stimulus objects (James Gibson's "feelies" and a set of naturally shaped objects--bell peppers). However, the methodology varied across experiments. Experiment 1 used random 3-dimensional (3-D) orientations of the stimulus objects, and the conditions were full-cue (active manipulation of objects and rotation of the visual objects in depth). Experiment 2 restricted the 3-D orientations of the stimulus objects and limited the haptic and visual information available to the participants. Experiment 3 compared restricted and full-cue conditions using random 3-D orientations. We replicated both previous findings in the current study. When we restricted visual and haptic information (and placed the stimulus objects in the same orientation on every trial), the participants' visual performance was superior to that obtained for haptics (replicating the earlier findings of Davidson et al. in Percept Psychophys 15(3):539-543, 1974). When the circumstances resembled those of ordinary life (e.g., participants able to actively manipulate objects and see them from a variety of perspectives), we found no significant difference between visual and haptic solid shape discrimination.

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.

Aging and the perception of tactile speed.

Eighteen younger and older adults (mean ages were 20.4 and 72.8 years, respectively) participated in a tactile speed matching task. On any given trial, the participants felt the surfaces of rotating standard and test wheels with their index fingertip and were required to adjust the test wheel until its speed appeared to match that of the standard wheel. Three different standard speeds were utilized (30, 50, and 70 cm/s). The results indicated that while the accuracy of the participants' judgments was similar for younger and older adults, the precision (i.e., reliability across repeated trials) of the older participants' judgments deteriorated significantly relative to that exhibited by the younger adults. While adverse effects of age were obtained with regards to both the precision of tactile speed judgments and the participants' tactile acuity, there was nevertheless no significant correlation between the older adults' tactile acuities and the precision of their tactile speed judgments.

Aging and the detection of moving objects defined by common fate.

Grouping by common fate plays an important role in how human observers perceive environmental objects. In this study, the effect of aging upon the ability to utilize common fate was evaluated. Twenty-two younger and older adults (mean ages were 23.4 and 74.7 years, respectively) participated in two experiments. On any given trial, the participants sequentially viewed two apparent motion sequences and were required to indicate which temporal interval contained a coherently moving dotted line embedded in noisy random background motion. In Experiment 1, the number of dots defining the target was varied, while in Experiment 2, the target interpoint spacing was varied. The younger adults outperformed the older adults by 19.4 percent in Experiment 1 and 50.5 percent in Experiment 2. The older and younger adults were similarly affected by variations in the number of target dots and the target interpoint spacing. The individual older participants' object detection accuracies were highly correlated with their individual chronological ages, such that the performance of the younger old participants was much higher than that exhibited by the older old. Increases in age systematically affect the ability of older adults to detect and visually perceive objects defined by common fate.

Aging and the visual perception of object size.

An experiment evaluated the ability of 30 younger and older adults to visually judge object size under three conditions: (1) full cue, (2) in the dark, with linear perspective, and (3) in complete darkness. Each observer made repeated judgments for the same square stimuli (the task was to adjust a separation until it matched the perceived size of the squares), enabling an evaluation of precision as well as accuracy. The judgments were just as accurate in the dark with linear perspective condition as in the full cue condition, indicating that linear perspective serves as an important source of optical information to support the perception of object size). In contrast, in complete darkness (where linear perspective information was unavailable), the accuracy of the observers' judgments was poor. Finally, there was no difference in either the accuracy or the precision of the observers' judgments between the two age groups, despite the fact that the older adults were more than 50 years older than the younger adults (mean age of the younger and older adults was 22.3 and 74.1 years, respectively). The ability to visually perceive object size is well maintained with increasing age, unlike a number of other important visual abilities.

Anterior regions of monkey parietal cortex process visual 3D shape.

The intraparietal cortex is involved in the control of visually guided actions, like reach-to-grasp movements, which require extracting the 3D shape and position of objects from 2D retinal images. Using fMRI in behaving monkeys, we investigated the role of the intraparietal cortex in processing stereoscopic information for recovering the depth structure and the position in depth of objects. We found that while several areas (CIP, LIP, and AIP on the lateral bank; PIP and MIP on the medial bank) are activated by stereoscopic stimuli, AIP and an adjoining portion of LIP are sensitive only to depth structure. Furthermore, only these two regions are sensitive to both the depth structure and the 2D shape of small objects. These results indicate that extracting 3D spatial information from stereo involves several intraparietal areas, among which AIP and anterior LIP are more specifically engaged in extracting the 3D shape of objects.

Temporal integration in the perception and discrimination of solid shape.

Two experiments evaluated the importance of temporal integration for the perception and discrimination of solid object shape. In Experiment 1, observers anorthoscopically viewed moving or stationary cast shadows of naturally shaped solid objects (bell peppers, Capsicum annuum) through narrow (4-mm wide) slits. At any given moment, observers could only see a very small portion of the overall object shape (generally less than 10%). The results showed that the observers' discrimination performance for the moving cast shadows was much higher than that obtained for the stationary shadows, demonstrating the ability to temporally integrate the piecemeal momentary information about shape that was available through the narrow apertures. In a second experiment, estimates of the strength of the observers' impressions of solid shapes rotating in depth were obtained as well as discrimination accuracies; perceptions of the original moving condition were compared with a new condition where the frames of the apparent motion sequences depicting solid objects in continuous motion (behind the slits) were randomly scrambled. The observers perceived the anorthoscopic displays as depicting solid objects rotating in depth, but only in the continuous motion condition. Interestingly, the discrimination performance in the scrambled condition remained relatively high-observers were still able to integrate information across the multiple scrambled frames in order to produce discrimination performance that was significantly higher than that obtained in the stationary shadow condition. This study was the first to thoroughly evaluate whether and to what extent human observers can effectively discriminate and perceive solid object shape anorthoscopically.