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 outdoors.

We conducted an experiment to evaluate the ability of 32 younger and older adults to visually perceive distances in an outdoor setting. On any given trial, the observers viewed 2 environmental distances and were required to estimate the distance ratio-the length of the (usually) larger distance relative to that of the shorter. The stimulus distance ratios ranged from 1.0 (the stimulus distances were identical) to 8.0 (1 distance interval was 8.0 times longer than the other). The stimulus distances were presented within a 26 m × 60 m portion of a grassy field. The observers were able to reliably estimate the stimulus distance ratios: The overall Pearson r correlation coefficient relating the judged and actual distance ratios was 0.762. Fifty-eight percent of the variance in the observers' perceived distance ratios could thus be accounted for by variations in the actual stimulus ratios. About half of the observers significantly underestimated the distance ratios, while the judgments of the remainder were essentially accurate. Significant modulatory effects of sex and age occurred, such that the male observers' judgments were the most precise, while those of the older males were the most accurate.

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.

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 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.

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.

The visual perception of exocentric distance in outdoor settings.

The ability of 20 younger (mean age was 21.8years) and older adults (mean age was 71.5years) to visually perceive exocentric distances outdoors was evaluated. The observers adjusted the extent of in-depth spatial intervals until they appeared identical to fronto-parallel intervals of 4 and 8m. The frontal and in-depth intervals were viewed from a distance of 8m. Almost all of the observers' judgments were inaccurate and most reflected perceptual compressions in depth: e.g., an in-depth interval of 10m would appear to have the same extent as a physically smaller 8m frontal interval. Some observers' judgments, however, were consistent with perceptual expansions of in-depth intervals. No significant effects of age were obtained in the current study: both younger and older adults exhibited perceptual compressions and expansions of in-depth intervals. This outcome differs from that of a recent experiment conducted by our laboratory (Vision Research 109 (2015) 52-58) that found the judgments of younger adults to be less accurate than those of older adults. A comparison of the former and current results revealed that while older adults perform similarly outdoors and indoors, the accuracy of younger adults' exocentric judgements improves substantially in outdoor settings (so that the accuracy becomes similar to that exhibited by older adults).

Aging and solid shape recognition: Vision and haptics.

The ability of 114 younger and older adults to recognize naturally-shaped objects was evaluated in three experiments. The participants viewed or haptically explored six randomly-chosen bell peppers (Capsicum annuum) in a study session and were later required to judge whether each of twelve bell peppers was "old" (previously presented during the study session) or "new" (not presented during the study session). When recognition memory was tested immediately after study, the younger adults' (Experiment 1) performance for vision and haptics was identical when the individual study objects were presented once. Vision became superior to haptics, however, when the individual study objects were presented multiple times. When 10- and 20-min delays (Experiment 2) were inserted in between study and test sessions, no significant differences occurred between vision and haptics: recognition performance in both modalities was comparable. When the recognition performance of older adults was evaluated (Experiment 3), a negative effect of age was found for visual shape recognition (younger adults' overall recognition performance was 60% higher). There was no age effect, however, for haptic shape recognition. The results of the present experiments indicate that the visual recognition of natural object shape is different from haptic recognition in multiple ways: visual shape recognition can be superior to that of haptics and is affected by aging, while haptic shape recognition is less accurate and unaffected by aging.

Aging and the visual perception of exocentric distance.

The ability of 18 younger and older adults to visually perceive exocentric distances was evaluated. The observers judged the extent of fronto-parallel and in-depth spatial intervals at a variety of viewing distances from 50cm to 164.3cm. Most of the observers perceived in-depth intervals to be significantly smaller than fronto-parallel intervals, a finding that is consistent with previous studies. While none of the individual observers' judgments of exocentric distance were accurate, the judgments of the older observers were significantly more accurate than those of the younger observers. The precision of the observers' judgments across repeated trials, however, was not affected by age. The results demonstrate that increases in age can produce significant improvements in the visual ability to perceive the magnitude of exocentric distances.

Aging and visual length discrimination: sequential dependencies, biases, and the effects of multiple implicit standards.

Younger (20-25 years of age) and older (61-79 years) adults were evaluated for their ability to visually discriminate length. Almost all experiments that have utilized the method of single stimuli to date have required participants to judge test stimuli relative to a single implicit standard (for a rare exception, see Morgan, On the scaling of size judgements by orientational cues, Vision Research, 1992, 32, 1433-1445). In the current experiments, we not only asked participants to judge lengths relative to a single implicit standard, but they also compared test stimuli to two different implicit standards within the same blocks of trials. We analyzed our participants' judgments to evaluate whether significant sequential dependencies occurred. We found that while individual younger and older adults possessed similar length difference thresholds and exhibited similar overall biases, the judgments of older adults within individual blocks of trials were more strongly biased (than younger adults) by preceding responses (i.e., their judgments on any given trial were more strongly affected by responses to previously viewed stimuli). In addition, the judgments of both younger and older adults were more strongly biased by preceding responses in the blocks of trials with multiple implicit standards. Overall, our results are consistent with the operation of the tracking mechanism described by Criterion-setting theory (Lages and Treisman, Spatial frequency discrimination: Visual long-term memory or criterion setting? Vision Research, 1998, 38, 557-572).