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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., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

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)., (Copyright © 2014 Elsevier Ltd. All rights reserved.)

Two experiments evaluated the ability of 50 older, middle-aged, and younger adults to discriminate the 3-dimensional (3-D) shape of curved surfaces defined by optical motion. In Experiment 1, temporal correspondence was disrupted by limiting the lifetimes of the moving surface points. In order to discriminate 3-D surface shape reliably, the younger and middle-aged adults needed a surface point lifetime of approximately 4 views (in the apparent motion sequences). In contrast, the older adults needed a much longer surface point lifetime of approximately 9 views in order to reliably perform the same task. In Experiment 2, the negative effect of age upon 3-D shape discrimination from motion was replicated. In this experiment, however, the participants' abilities to discriminate grating orientation and speed were also assessed. Edden et al. (2009) have recently demonstrated that behavioral grating orientation discrimination correlates with GABA (gamma aminobutyric acid) concentration in human visual cortex. Our results demonstrate that the negative effect of age upon 3-D shape perception from motion is not caused by impairments in the ability to perceive motion per se, but does correlate significantly with grating orientation discrimination. This result suggests that the age-related decline in 3-D shape discrimination from motion is related to decline in GABA concentration in visual cortex., (Copyright © 2013 Elsevier B.V. All rights reserved.)

Two experiments evaluated the ability of 30 older and younger adults to discriminate the curvature of simple object surfaces from static and dynamic touch. The ages of the older adults ranged from 66 to 85 years, while those of the younger adults ranged from 20 to 29 years. For each participant in both experiments, the minimum curvature magnitude needed to reliably discriminate between convex and concave surfaces was determined. In Experiment 1, participants used static touch to make their judgments of curvature, while dynamic touch was used in Experiment 2. When static touch was used to discriminate curvature, a large effect of age occurred (the thresholds were 0.67 & 1.11/m for the younger and older participants, respectively). However, when participants used dynamic touch, there was no significant difference between the ability of younger and older participants to discriminate curvature (the thresholds were 0.58 & 0.59/m for the younger and older participants, respectively). The results of the current study demonstrate that while older adults can accurately discriminate surface curvature from dynamic touch, they possess significant impairments for static touch.