PROJECT SUMMARY
Human postural control involves multiple sensory integrations from visual, somatosensory, and vestibular inputs.
Due to a decline in somatosensation and vestibular function that occurs with aging, vision becomes the dominant
sensory input used to maintain balance in elderly adults. Studies have used optic flow (OF) to examine the effect
of visual input on postural control. While optic flow stimulus can be presented through traditional PC monitor
setups, the advent of consumer grade virtual reality (VR) head mounted displays has provided new options. An
immersive VR environment is advantageous because it can provide OF stimulus to induce a self-motion illusion
that provokes postural responses while also isolating the subject from outside stimuli. In addition to visual
information, attention is critical for older individuals to maintain good balance. Studies have used dual-task
paradigms, such as performing a concurrent cognitive task along with a balance task, to examine the cognitive
demands associated with postural control. However, the mechanisms of sensory integration processing and
neural resource allocation in the human brain have not been fully investigated in real balance tasks with
concurrent cognitive tasks. A novel neuroimaging method, functional near-infrared spectroscopy (fNIRS),
provides us the opportunity to explore the underlying mechanism of postural control in the human brain. The
purpose of this research is to investigate physiological limitations when processing OF information and observe
the neural resource allocation during dual-task conditions. In this study, healthy younger adults (aged 25-45 y.o.,
n = 24), healthy older adults (aged 65-85 y.o., n = 24), and older adults at risk of falling based on the STEADI
and clinical balance/gait assessments (aged 65-85 y.o., n = 24) will be recruited. In the first visit subjects will be
asked to wear a VR head mounted display that will present the OF stimulation. Particle movement speed will
vary between six levels, 0 m/s (static), 5m/s, 10 m/s, 15 m/s, 20 m/s, and 25 m/s. The nonstatic OF speeds will
be contracted to the static OF (0 m/s) in a block design, (A1-B-A2), for a total of six conditions. Each block will
last for 30 seconds. In the second visit, the subjects will perform two auditory reaction time tasks while receiving
OF stimulation at the speeds of 5 m/s and 20 m/s. During the two study visits fNIRS will be used to measure
brain activity in regions of interest (ROIs) including the bilateral prefrontal cortices, superior temporal areas, and
temporoparietal junctions. We will compare the group, gender, and hemisphere differences in the ROIs. A
repeated measure ANOVA will be used to analyze the reaction time and postural sway data to examine the
effects of Group (younger, older, and older adults with fall risks), OF speed (six OF speeds), Block (A1, B, and
A2), and their interactions.
