The essential role of optical flow in the peripheral visual field for stable quiet standing: Evidence from the use of a head-mounted display

Abstract

It has long been thought that vision is the most essential factor in maintaining stable quiet standing compared to other sources (i.e., vestibular and somatosensory inputs) of information. Specifically, several vision studies on postural control have shown evidence for the importance of the visual system, particularly peripheral vision rather than central vision, and optical flow. Nevertheless, to date, no study has manipulated both visual field and optical flow concurrently. In the present study, we experimentally manipulated both the visual field (the central and peripheral visual fields) and the occurrence of optical flow during quiet standing, examining the effects of the visual field and optical flow on postural sway measured in terms of the center of pressure (CoP). Stationary random dot stimuli were presented exclusively in either the central or peripheral visual field, while the occurrence of optical flow was manipulated using a desktop (DTD) or a head-mounted (HMD) display. The optical flow that occurred while using the DTD was a function of the postural sway during quiet standing, while for the HMD, no optical flow occurred even when the body/head swayed during quiet standing. Our results show that the extent of postural sway (e.g., CoP area) was smaller when visual stimuli were presented in the peripheral visual field than that in the central visual field; this was the case while using the DTD alone, with no effects of the peripheral vision on the extent of postural sway while using the HMD. It is therefore suggested that the optical flow occurring in the peripheral visual field is essential for stable quiet standing.

Fig 1. Images of the original and dummy HMDs used.

The original (left figure) and dummy (right figure) head-mounted displays (HMD) were respectively worn at HMD and Desktop display (DTD) conditions.

Fig 2. Sample images of the visual stimuli.

Sample images of visual stimuli at four visual field conditions (full vision [FV], central vision [CV], peripheral vision [PV], and no dot [ND] condition) presented at the desktop display (DTD) and head-mounted display (HMD) conditions.

Fig 3. Results for envelopment area.

Envelopment area for the four visual conditions (full vision [FV], central vision [CV], peripheral vision [PV], and no dot [ND] condition) for both the desktop display (DTD) and head-mounted display (HMD) conditions. The x-axis denotes the visual condition, with the y-axis denoting the size of the envelopment area. Error bars indicate the standard deviation (SD).

Fig 4. Results for rectangular area.

Rectangular area for the four visual conditions (full vision [FV], central vision [CV], peripheral vision [PV], and no dot [ND] condition) for both the desktop display (DTD) and head-mounted display (HMD) conditions. The x-axis denotes the visual condition, with the y-axis denoting the size of the envelopment area. Error bars indicate the standard deviation (SD).

Fig 5. Results for root mean square area.

Root mean square area for the four visual conditions (full vision [FV], central vision [CV], peripheral vision [PV], and no dot [ND] condition) for both the desktop display (DTD) and head-mounted display (HMD) conditions. The x-axis denotes the visual condition, with the y-axis denoting the size of the envelopment area. Error bars indicate the standard deviation (SD).

Fig 6. Results for total CoP length.

Total length of center of pressure (CoP) displacement for the four visual conditions (full vision [FV], central vision [CV], peripheral vision [PV], and no dot [ND] condition) for both the desktop display (DTD) and head-mounted display (HMD) conditions. The x-axis denotes the visual condition, with the y-axis denoting the total length of CoP displacement per area. Error bars indicate the standard deviation (SD).

Fig 7. Results for total CoP length over displacement area.

Total length of center of pressure (CoP) displacement per area for the four visual conditions (full vision [FV], central vision [CV], peripheral vision [PV], and no dot [ND] condition) for both the desktop display (DTD) and head-mounted display (HMD) conditions. The x-axis denotes the visual condition, with the y-axis denoting the total length of CoP displacement per area. Error bars indicate the standard deviation (SD).