Jessica Holmin

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.

Aging and Weight-Ratio Perception

Past research has provided evidence that older adults have more difficulty than younger adults in discriminating small differences in lifted weight (i.e., the difference threshold for older adults is higher than that of younger adults). Given this result, one might expect that older adults would demonstrate similar impairments in weight ratio perception (a suprathreshold judgment) compared to younger adults. The current experiment compared the abilities of younger and older adults to perceive weight ratios. On any given trial, participants lifted two objects in succession and were asked to provide an estimate of the objects’ weight ratio (the weight of the heavier object relative to the lighter). The results showed that while the older participants’ weight ratio estimates were as reliable as those of the younger participants, they were significantly less accurate: the older participants frequently perceived the weight ratios to be much higher than they actually were.

The effects of aging on the perception of depth from motion parallax.

Successful navigation in the world requires effective visuospatial processing. Unfortunately, older adults have many visuospatial deficits, which can have severe real-world consequences. Although some of these age effects are well documented, some others, such as the perception of depth from motion parallax, are poorly understood. Depth perception from motion parallax requires intact retinal image motion and pursuit eye movement processing. Decades of research have shown that both motion processing and pursuit eye movements are affected by age; it follows that older adults may also be less sensitive to depth from motion parallax. The goals of the present study were to characterize motion parallax depth thresholds in older adults, and to explain older adults’ sensitivity to depth from motion parallax in terms of motion and pursuit deficits. Younger and older adults’ motion thresholds and pursuit accuracy were measured. Observers’ depth thresholds across several different stimulus conditions were measured, as well. Older adults had higher motion thresholds and less accurate pursuit than younger adults. They were also less sensitive to depth from motion parallax at slow and moderate pursuit speeds. Although older adults had higher motion thresholds than younger adults, they used the available motion signals optimally, and age differences in motion processing could not account for the older adults’ increased depth thresholds. Rather, these age effects can be explained by changes in older adults’ pursuit signals.

Motion parallax thresholds for unambiguous depth perception

The perception of unambiguous depth from motion parallax arises from the neural integration of retinal image motion and extra-retinal eye movement signals. It is only recently that these parameters have been articulated in the form of the motion/pursuit ratio. In the current study, we explored the lower limits of the parameter space in which observers could accurately perform near/far relative depth-sign discriminations for a translating random-dot stimulus. Stationary observers pursued a translating random dot stimulus containing relative image motion. Their task was to indicate the location of the peak in an approximate square-wave stimulus. We measured thresholds for depth from motion parallax, quantified as motion/pursuit ratios, as well as lower motion thresholds and pursuit accuracy. Depth thresholds were relatively stable at pursuit velocities 5-20 deg/s, and increased at lower and higher velocities. The pattern of results indicates that minimum motion/pursuit ratios are limited by motion and pursuit signals, both independently and in combination with each other. At low and high pursuit velocities, depth thresholds were limited by inaccurate pursuit signals. At moderate pursuit velocities, depth thresholds were limited by motion signals.

Aging does not affect integration times for the perception of depth from motion parallax

&NA; To successfully navigate throughout the world, observers must rapidly recover depth information. One depth cue that is especially important for a moving observer is motion parallax. To perceive unambiguous depth from motion parallax, the visual system must integrate information from two different proximal signals, retinal image motion and a pursuit eye movement. Previous research has shown that aging affects both of these necessary components for motion parallax depth perception, but no research has yet investigated how aging affects the mechanism for integrating motion and pursuit information to recover depth from motion parallax. The goal of the current experiment was to assess the integration time required by older adults to process depth information. In four psychophysical conditions, younger and older observers made motion and depth judgments about stationary or translating random‐dot stimuli. Stimulus presentations in all four psychophysical conditions were followed by a high‐contrast pattern mask, and minimum stimulus presentation durations (stimulus‐to‐mask onset asynchrony, or SOA) were measured. These SOAs reflect the minimum neural processing time required to make motion and motion parallax depth judgments. Pursuit latency was also measured. The results revealed that, after accounting for age‐related delays in motion processing and pursuit onset, older and younger adults required similar temporal intervals to combine retinal image motion with an internal pursuit signal for the perception of depth. These results suggest that the mechanism for motion and pursuit integration is not affected by age. HighlightsAging affects temporal integration of motion information.Pursuit eye movement onset is slowed in older adults.Older adults have slowed processing times for depth from motion parallax.Age does not affect motion and pursuit integration for depth from motion parallax.

Implied motion produces real depth

ABSTRACT Static images taken from an animation of continuous motion, such as a photograph of a figure in a running pose, contain no real motion (RM) information. Interestingly, while imaging studies have shown that passively viewing these implied motion (IM) stimuli activate the same brain regions as RM, the perceptual effects of adding IM to RM are not fully understood. Given that IM appears to recruit the same neural mechanisms as RM, it should be possible to capitalize on this functional overlap and use IM in addition to, or in place of, RM to influence the perception of depth from motion parallax (MP). In the current study, we found that IM influenced depth-sign judgments as expected based on the geometry of MP with RM. These results bolster our understanding of the neural mechanisms of both IM and MP by demonstrating that IM coupled with pursuit eye movements generates unambiguous depth from MP.

Characterizing Motion Parallax Depth Thresholds in Older Adults

Successful navigation in the world requires effective visuospatial processing. Unfortunately, older adults have many visuospatial deficits, which can have severe real-world consequences. One visuospatial process, depth from motion parallax (MP), has been largely unexplored in older adults. Unambiguous depth from MP requires intact retinal image motion processing and an extra-retinal pursuit eye movement signal. Both the motion and eye movement systems are affected by age. Given these deficits, it follows logically that sensitivity to MP may be affected in older adults, but no one has investigated this possibility. The current study characterizes depth from MP in older adults and explores whether age-related changes in the motion and pursuit systems affect depth perception from motion parallax. Stationary younger (18-35 years) and older (60-75 years) observers performed depth-phase judgments on random-dot motion parallax stimuli. The stimuli translated laterally at one of three velocities (2.3, 10.1, and 25 deg/sec), generating the necessary pursuit signal. Dots within the stimuli translated laterally (0.013-0.92 deg/sec), generating constituent retinal image motion. The MP depth threshold at each pursuit velocity was quantified using the motion/pursuit ratio, which takes into account image motion, pursuit signal, and viewing distance. In addition, observers performed an analogous motion perception threshold task to assess age-related changes in motion perception. Age-related changes in the pursuit system were assessed with a step-ramp pursuit task at the three velocities used in the motion parallax task. Older adults have higher motion parallax thresholds at all pursuit velocities, as well as higher motion thresholds and lower pursuit gain, especially at higher velocities. We conclude that the threshold limit for unambiguous depth from MP is affected by age. Decreased sensitivity to depth from MP is tied to age-related deficits in motion perception and pursuit eye movements, both of which are necessary for unambiguous depth from MP. Meeting abstract presented at VSS 2015.