The role of contrast sensitivity in global motion processing deficits in the elderly

Abstract

This study compared the effects of age on the perception of translational, radial, and rotational global motion patterns. Motion coherence thresholds were measured for judging the direction of each motion type as a function of contrast (visibility) and temporal sampling rate in young and elderly participants. Coherence thresholds decreased as dot contrast increased asymptoting at high dot contrasts but were higher in elderly compared to young participants. This equated to global motion impairment in the elderly of a factor of around 2, characterized by a shift of the threshold vs. contrast function along the horizontal axes (dot contrast). The effect of contrast interacted with the temporal sampling rate. Old participants were deleteriously affected by reduced temporal sampling particularly at low contrasts. The findings suggest that age-related changes in global motion perception may be driven principally by deficits in contrast encoding, rather than by deficits in motion integration and suggest a role for increased internal noise in the older visual system.

Psychophysical correlates of global motion processing in the aging visual system: A critical review

“…Even in instances where there is a minimal effect of age, decreasing dot contrast has a more profoundly deleterious effect on performance levels of older participants. As mentioned previously, Allen et al (2010) have shown that when high contrast dots move at 5.6 deg/sec, older and younger adults' motion discrimination performance is comparable. However reducing dot contrast led to elevated motion coherence thresholds (impaired performance) for older, compared to younger adults.…”

“…Even when age-related optical factors such as lenticular yellowing and decreased pupil diameter have been accounted for, problems in spatial and temporal vision persist (e.g. Elliott, Whitaker, & MacVeigh, 1990;Whitaker & Elliott, 1992;Elliott, Choi, Doble, Hardy, Evans & Werner, 2009;Allen et al, 2010). Moreover, Ball and Sekuler (1986) assessed the effects of positive optical blur (0.00 to + 4.00 dioptres) on visual acuity and global motion discrimination in young participants.…”

“…In addition, evidence that older adults' performance is more markedly affected by local dot contrast (e.g. Allen et al 2010) probably reflects contrast-dependent input from area V1 to area V5/MT, demonstrating the importance of other factors such as changes in contrast sensitivity with aging.…”

Feature-Selective Attention in Healthy Old Age: A Selective Decline in Selective Attention?

“…Although the stimulus parameters used here should be above older adults' thresholds (Snowden and Kavanagh, 2006), we ruled out a relationship between measured contrast sensitivity and detection performance, which suggests that optical differences did not contribute to our results (cf. Allen et al, 2010). Older adults were overall slower to respond to targets, but we found no differential effect of task (detect/select), suggesting that this age difference reflects general age-related slowing rather than a deficit specific to the attentional task.…”

Visual Motion: From Cortex to Percept

“…With regard to the weaker spatial suppression reported in older observers (Betts et al, 2005), subsequent studies have failed to replicate this effect (Karas & McKendrick, 2011) and other studies, again using stimuli designed to selectively target V5, have concluded that any motion deficits in older observers are primarily a result of contrast sensitivity loss (Allen et al, 2010). Intrigued by the counterintuitive idea that older observers were performing better than their younger counterparts, we carried out a series of experiments in which we reproduced a "suppressive" effect in younger observers very similar to that of Tadin et al, and we also showed that this effect was absent in older observers, akin to the study of Betts et al ).…”