Amanda M. Beers

Aging and the haptic perception of 3D surface shape

Two experiments evaluated the ability of older and younger adults to perceive the three-dimensional (3D) shape of object surfaces from active touch (haptics). The ages of the older adults ranged from 64 to 84 years, while those of the younger adults ranged from 18 to 27 years. In Experiment 1, the participants haptically judged the shape of large (20 cm diameter) surfaces with an entire hand. In contrast, in Experiment 2, the participants explored the shape of small (5 cm diameter) surfaces with a single finger. The haptic surfaces varied in shape index (Koenderink, Solid shape, 1990; Koenderink, Image and Vision Computing, 10, 557–564, 1992) from −1.0 to +1.0 in steps of 0.25. For both types of surfaces (large and small), the participants were able to judge surface shape reliably. The older participants’ judgments of surface shape were just as accurate and precise as those of the younger participants. The results of the current study demonstrate that while older adults do possess reductions in tactile sensitivity and acuity, they nevertheless can effectively perceive 3D surface shape from haptic exploration.

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.

Effective 3-D shape discrimination survives retinal blur.

A single experiment evaluated observers’ ability to visually discriminate 3-D object shape, where the 3-D structure was defined by motion, texture, Lambertian shading, and occluding contours. The observers’ vision was degraded to varying degrees by blurring the experimental stimuli, using 2.0-, 2.5-, and 3.0-diopter convex lenses. The lenses reduced the observers’ acuity from −0.091 LogMAR (in the no-blur conditions) to 0.924 LogMAR (in the conditions with the most blur; 3.0-diopter lenses). This visual degradation, although producing severe reductions in visual acuity, had only small (but significant) effects on the observers’ ability to discriminate 3-D shape. The observers’ shape discrimination performance was facilitated by the objects’ rotation in depth, regardless of the presence or absence of blur. Our results indicate that accurate global shape discrimination survives a considerable amount of retinal blur.

Characterizing Perceptual Alternations During Binocular Rivalry in Children

Although binocular rivalry has been examined thoroughly in young adults, we know relatively little about its developmental trajectory. To address this issue, we created a child-friendly task, in which we presented pairs of orthogonal, oblique sine wave gratings to 7-, 9-, 11-year-olds, and young adults (mean = 21.25 years). Stimulus size (diameter = 1.4 or 4.4) and contrast level (0.2 or 0.8), factors with well-known effects on rivalry in young adults, varied across trials. On each trial, participants recorded their alternations among percepts (each of the two exclusive, mixed, and fading/other) with a handheld button box. To measure accuracy of reported percepts, we intermixed pseudo-rivalry with experimental trials. For experimental trials, dependent measures included the average duration and proportion of time participants reported viewing each type of percept. Children spent a significantly greater proportion of time viewing exclusive percepts and less time viewing mixed percepts compared to young adults, a finding that provides evidence against the prediction of increased mixed percepts in children (Kovacs & Eisenberg, 2005). Sequential patterns of alternations between percepts also varied between children and young adults. For example, the proportion of return transitions increased from childhood to adulthood, specifically for low contrast conditions. Average durations for exclusive percepts did not differ significantly across age groups, contrary to previous reports suggesting faster alternation rates in children (Kovacs & Eisenberg, 2005; Hudak et al., 2011). Average durations for mixed percepts were shorter in children compared to young adults. No differences were observed between 7-, 9-, and 11-year-olds for any dependent measure. These are the first reports of several characteristics of binocular rivalry in children, specifically measures of mixed percepts and sequential transitions. Meeting abstract presented at VSS 2015.