Self-motion perception in the elderly

Abstract

Self-motion through space generates a visual pattern called optic flow. It can be used to determine one's direction of self-motion (heading). Previous studies have already shown that this perceptual ability, which is of critical importance during everyday life, changes with age. In most of these studies subjects were asked to judge whether they appeared to be heading to the left or right of a target. Thresholds were found to increase continuously with age. In our current study, we were interested in absolute rather than relative heading judgments and in the question about a potential neural correlate of an age-related deterioration of heading perception. Two groups, older test subjects and younger controls, were shown optic flow stimuli in a virtual-reality setup. Visual stimuli simulated self-motion through a 3-D cloud of dots and subjects had to indicate their perceived heading direction after each trial. In different subsets of experiments we varied individually relevant stimulus parameters: presentation time, number of dots in the display, stereoscopic vs. non-stereoscopic stimulation, and motion coherence. We found decrements in heading performance with age for each stimulus parameter. In a final step we aimed to determine a putative neural basis of this behavioral decline. To this end we modified a neural network model which previously has proven to be capable of reproduce and predict certain aspects of heading perception. We show that the observed data can be modeled by implementing an age related neuronal cell loss in this neural network. We conclude that a continuous decline of certain aspects of motion perception, among them heading, might be based on an age-related progressive loss of groups of neurons being activated by visual motion.

Motion perception as a model for perceptual aging

“…Warren, Blackwell, and Morris (1989) reported only a minimal increase in heading detection thresholds varying the deviation from a central focus of expansion, i.e., from 1.18 in young adults and 1.98 in older adults. In contrast, a more recent study by Lich and Bremmer (2014) found that older adults are less accurate in identifying heading direction using a reference ruler. Thus, more refined measurements might be needed to reveal effects of age in optic flow perception.…”

The Aging Navigational System

“…For example, Warren and colleagues (Warren et al, 1989) found a small but significant age-related decline of about 1–2° in the ability to perceive heading direction, and subsequent studies have reported similar results with a range of optic flow stimuli (Kavcic et al, 2011; Lich and Bremmer, 2014). Importantly, such deficits are also observed when self-motion is computed from body-based cues and used to regulate walking speed (Lalonde-Parsi and Lamontagne, 2015; Roditi and Crane, 2012).…”

“…First, neuron loss or reduced GABAergic inhibition in areas VIP and MT/MST (Lich and Bremmer, 2014) increase the level of noise and decrease the directional tuning of motion sensitive neurons (Liang et al, 2010). Such deficits can be further enhanced by altered eye movement behavior (Dowiasch et al, 2015), which changes the way older adults sample the outside world.…”

Heading Perception Depends on Time-Varying Evolution of Optic Flow

“…Stereoscopic depth should enhance the reliability of dp/dt, leading to less variable and/or less biased heading estimates, under our account. This is borne out in human behavior (37,38,(63)(64)(65) and might be mediated by the responses of neurons that signal heading and exhibit tuning for both binocular disparity and global motion patterns (66)(67)(68)(69). The small heading biases that we (and others) have observed may be reduced when stereo cues are also available.…”