Is the size of the useful field of view affected by postural demands associated with standing and stepping?

The useful field of view (UFOV) is the visual area from which information is obtained at a brief glance. While studies have examined the effects of increased cognitive load on the visual field, no one has specifically looked at the effects of postural control or locomotor activity on the UFOV. The current study aimed to examine the effects of postural demand and locomotor activity on UFOV performance in healthy young adults. Eleven participants were tested on three modified UFOV tasks (central processing, peripheral processing, and divided-attention) while seated, standing, and stepping in place. Across all postural conditions, participants showed no difference in their central or peripheral processing. However, in the divided-attention task (reporting the letter in central vision and target location in peripheral vision amongst distracter items) a main effect of posture condition on peripheral target accuracy was found for targets at 57° of eccentricity (p=.037). The mean accuracy reduced from 80.5% (standing) to 74% (seated) to 56.3% (stepping). These findings show that postural demands do affect UFOV divided-attention performance. In particular, the size of the useful field of view significantly decreases when stepping. This finding has important implications for how the results of a UFOV test are used to evaluate the general size of the UFOV during varying activities, as the traditional seated test procedure may overestimate the size of the UFOV during locomotor activities.

Visually evoked whole-body turning responses during stepping in place in a virtual environment.

Humans use a specific sequence of reorientation of the eyes, head and body to perform turning and redirections while walking. Gaze (eye and head) rotation in a new direction of travel precedes body rotation by as much as 1.5s and provides a stable reference frame that guides subsequent whole-body redirection. The purpose of the current study was to determine whether a visually presented rotation of the external environment can induce whole-body turning lead by gaze redirection in a new travel direction. Five healthy young adults performed a stepping in place task while watching a virtual scene that moved as if they were walking down a hallway, thus providing participants with a perception of forward self motion. While "forward" stepping, the virtual scene would gradually turn around a 90 degrees corner. As a result the turn could be anticipated by the participants. Significant horizontal eye movements and head and body rotation magnitudes were observed in response to the virtual visual turning cue. Onset of eye, head and body redirection revealed a sequenced order and timing of segment rotation that is characteristic of steering behaviour in real world turning situations. The results of this study provide support for the hypothesis that gaze redirection may be an essential subcomponent to steering behaviour. The link between visual redirection and coordinated body turning implies instability when turning may result from visual and/or oculomotor deficits.

The relationship between postural stability and virtual environment adaptation.

Currently little is known about how adaptive responses to virtual environments are different between individuals who experience sickness related symptoms and those who do not. It is believed that sensory interactions between visually perceived self-motion and static inertial cues from vestibular and/or proprioceptive sensory systems contribute to the development of adaptation symptoms. The aim of this study was to evaluate the relationship between adaptation symptoms and postural stability in a virtual environment (VE) driving simulator. In addition, the role of sensory interaction was assessed using direct electrical stimulation techniques of the vestibular and cutaneous sensory systems. Posture performance was measured using centre of pressure measures of single leg stance tests during eyes open and eyes closed conditions. Correlation analysis of postural measures and symptom scores were conducted, as well as analysis of variance of posture performance between SICK and WELL individuals. Results indicate that posture stability is negatively correlated to symptom reporting. WELL individuals displayed the greatest decrease in postural stability during eyes open single leg stance following VE simulation. Application of a secondary sensory stimulation (vestibular or cutaneous) resulted in increased visual dependency for postural control following simulation. Combined, these results suggest that sensory interactions drive postural changes that are observed following VE simulation and are related to how visual information is used to control posture.