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

Virtual Hand Illusion in younger and older adults

Introduction

Embodiment involves experiencing ownership over our body and localizing it in space and is informed by multiple senses (visual, proprioceptive and tactile). Evidence suggests that embodiment and multisensory integration may change with older age. The Virtual Hand Illusion (VHI) has been used to investigate multisensory contributions to embodiment, but has never been evaluated in older adults. Spatio-temporal factors unique to virtual environments may differentially affect the embodied perceptions of older and younger adults.

Methods

Twenty-one younger (18–35 years) and 19 older (65+ years) adults completed the VHI paradigm. Body localization was measured at baseline and again, with subjective ownership ratings, following synchronous and asynchronous visual-tactile interactions.

Results

Higher ownership ratings were observed in the synchronous relative to the asynchronous condition, but no effects on localization/drift were found. No age differences were observed. Localization accuracy was biased in both age groups when the virtual hand was aligned with the real hand, indicating a visual mislocalization of the virtual hand.

Conclusions

No age-related differences in the VHI were observed. Mislocalization of the hand in VR occurred for both groups, even when congruent and aligned; however, tactile feedback reduced localization biases. Our results expand the current understanding of age-related changes in multisensory embodiment within virtual environments.

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

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.

The life-span trajectory of visual perception of 3D objects

Deriving a 3D structural representation of an object from its 2D input is one of the great challenges for the visual system and yet, this type of representation is critical for the successful recognition of and interaction with objects. Perhaps reflecting the importance of this computation, infants have some sensitivity to 3D structural information, and this sensitivity is, at least, partially preserved in the elderly population. To map precisely the life-span trajectory of this key visual computation, in a series of experiments, we compared the performance of observers from ages 4 to 86 years on displays of objects that either obey or violate possible 3D structure. The major findings indicate that the ability to derive fine-grained 3D object representations emerges after a prolonged developmental trajectory and is contingent on the explicit processing of depth information even in late childhood. In contrast, the sensitivity to object 3D structure remains stable even through late adulthood despite the overall reduction in perceptual competence. Together, these results uncover the developmental process of an important perceptual skill, revealing that the initial, coarse sensitivity to 3D information is refined, automatized and retained over the lifespan.