Compromised mobility, balance, and muscle strength contribute to the likelihood of falling. Falls often result in serious injuries, decreased mobility, and loss of independence. Given the aging population, and statistics showing that almost 1 in 3 adults aged over 65 y will experience a fall every year, effective countermeasures are necessary. Here we showed that a brief light intervention was capable of altering measures with relevance to fall-risk (static balance and rapid motor responses) in older adults. Specifically, the ability to rapidly respond and re-plant the foot following a disturbance could decrease the likelihood of falling. The fastest PVT score explained ~20% of the variance in this measure of movement coordination.
An impaired ability to redress postural perturbance is likely a major contributor to falls. Here we show that the time taken to lift a leg in response to an unexpected visual stimulus was enhanced following the VISUAL intervention, with a large positive effect on this measure of motor function relative to the PLA condition. Previous research has demonstrated that short-wavelength blue-light is capable of improving reaction times in computer-based tasks [4, 7, 14] The neurophysiology that mediates the effects of short wavelength light is not well understood, but blue-light has been shown to affect the superchiasmatic nucleus and high-frequency alpha activity associated with the circadian drive for alertness . Currently, strategies for reducing fall risk in older adults use a multifactorial clinical approach including gait and balance assessment, and strength exercises . Optimizing the light environment could provide an adjunct approach to reduce fall risk via improved motor coordination. Speculatively, the improvements in motor coordination may also have ramifications for other aspects of human performance, driving, and physical exercise.
The balance data showed an interesting, albeit non-significant, result whereby the visual blue-light intervention decreased the AoS in older adults in the eyes open condition. Greater amounts of postural sway and mean sway area have previously been positively correlated with fall risk . The greater AoS in fallers may represent an inferior strategy when attempting to acquire a stable solution with excessive sway responses having been previously suggested to indicate a deterioration in the sensorimotor underpinnings of balance . Although research has indicated some potential for force plate measures to offer a predictive value of future falls , it has been noted that no single measure of postural sway is capable of detecting differences between faller and non-faller groups . Currently, there are a wide variety of stance, duration, and other posturographic protocol variables such as surface, as well as a paucity of prospective studies. Thus, it is difficult to make firm conclusions regarding the predictive nature of static force platform-based testing variables on fall risk .
Also of note was the lack of negative impact of the COUNT task on the AoS metric, given that postural stability has been shown to be affected by tasks that apply a cognitive load . Bergamin and coworkers  demonstrated that a simple backwards counting task had little effect on sway area, while a mental arithmetic task decreased sway area. It is possible that the counting task attenuated the potential for conscious interference of typically automated motor control processes harnessed during postural control. We note that the predisposition for conscious involvement in movement of a given individual, as outlined in the Theory of Reinvestment [23, 24], has the potential to mediate balance task responses .
In contrast to our earlier research , no effect of any light intervention was observed in the measure of cognitive function. It is worth noting that the duration of each cycle of testing was approximately 12 minutes and the cognitive task was always performed last. Thus, by the time a participant completed the final PVT test, it had been >10 min since the light intervention. As the persistence of any effect of the current protocols are currently unknown, there is the potential that any modulation of performance effects had dissipated. However, differences in psychomotor performance parameters have been reported to persist for up to an hour after light exposure .
We also acknowledge that the duration of the VISUAL stimulus may have been sub-optimal, as the duration of exposure was matched with the AURAL exposure that was dictated by the manufacturer’s recommendations. Future work may address the optimization of the visual stimulus and attempt to objectively quantifying the persistence of any beneficial physiological effects. We also note that there was no evidence to suggest any benefit related to either the individual or combined use of the AURAL intervention. Furthermore, it is worth noting that force plates can provide numerous posturographic measures, albeit not all measures are considered reliable ; thus, other metrics therefore may be worth examining further, including medio-lateral sway  and sample entropy . Importantly, the brief VISUAL light intervention affected measures associated with the prevention of falls in older adults. Novel light interventions may provide a potential countermeasure to decrease the financial and human costs of falls. Additional positive effects via altered lighting environments could include improved sleep quality  and mood .