The Role of Central and Peripheral Vision in the Control of Upright Posture

1. Results Effects on Absolute-Filtered RMS AP Sway • There was greater absolute sway during the full/peripheral FOVs than during the central condition (Figure 2, Table 1). • There was greater sway during sway-referencing due to an attenuation of somatosensory inputs. • The FOV*Frequency and FOV*Platform interactions were primarily due to the reduction in sway at 0.25 Hz when the central FOV was presented (especially during sway-referencing). Low-Frequency Sway During Quiet Stance is a Confounding Factor. • Sway obtained during moving-scene trials is a superposition of the response at the stimulus frequency and quiet-stance (QS) sway (Figure 3). • The mean QS sway at 0.1 Hz was greater than the QS sway at 0.25 Hz. • Therefore, absolute RMS sway (Figure 2) includes the subjects’ QS sway and their response to the stimulus. • In order to determine how much the subjects reacted to the stimulus, we normalized their RMS values by subtracting out the QS component at the stimulus frequency (Figure 4). • Methods • Twenty healthy subjects (mean age: 24  3 years) • 3 Fields of View (FOVs) • Full: Central Rings and Peripheral Checkers (see Figure 1) • Central Rings only • Peripheral Checkers only • 2 Frequencies: 0.1 and 0.25 Hz • 1 Amplitude: 16 cm peak-to-peak • 2 Support Surfaces: Fixed and Sway-Referenced • 3 Quiet-Stance (QS) trials (one for each FOV), during which the scene was stationary Figure 3. Mean Power Spectral Densities of Sway During QS and During the Two Stimulus Frequencies • Data Collection and Analysis: • Recorded head movement using Polhemus Fastrak™ system • Performed a statistical test to determine whether there was a significant response at the stimulus frequency (Percival 1994). Subjects who passed the test during the majority of their trials were considered “responders” • Filtered the responders’ data with a bandpass at the stimulus frequency (± 0.05 Hz), and calculated the Root-Mean-Square (RMS) amplitudes of their AP sway • Performed a repeated-measures ANOVA to test for the effects of FOV, Frequency, and Surface condition, as well as the interactions ( = 0.05) Effects on Normalized-Filtered RMS AP Sway • Normalization accentuated the FOV effect. The central stimulus elicited little response, regardless of the frequency or platform condition (Figure 4, Table 1). • During the full and peripheral FOVs, the 0.25 Hz stimuli caused a greater increase in sway than those moving at 0.1 Hz. This was true for both support-surface conditions. • The central-peripheral differences were greater during sway-referencing than when the support surface was fixed. Figure 4. Normalized-Filtered RMS AP Sway Responders only (n = 10) Figure 1. Visual environment encompassed 180 deg. X 70 deg. (horiz. X vert.) of the subjects’ FOV. The Role of Central and Peripheral Vision in the Control of Upright Posture During Anterior-Posterior Optic Flow Jeff G. Jasko1,4, Patrick J. Loughlin1,2, Mark S. Redfern1,4, and Patrick J. Sparto 1,3,4 Departments of Bioengineering1, Electrical Engineering2, Physical Therapy3, and Otolaryngology4 University of Pittsburgh, Pittsburgh, PA, USA Introduction Several theories have been developed in an attempt to characterize the functional roles of central and peripheral vision in maintaining postural equilibrium (Bardy et al. 1999). While some findings suggest that peripheral vision dominates postural control, others suggest that central vision is equally important in the perception of self-motion. Given these diverging results, further research is needed to clarify this issue. In addition, previous research has demonstrated the postural system to be less responsive to optic flow as frequency increases. Specific Aim: To investigate the influences of central and peripheral vision on upright posture during anterior-posterior (AP) optic flow at different frequencies. Figure 2. Absolute-Filtered RMS AP Sway Responders only (n = 10) • Conclusions • The peripheral stimulus caused significantly more sway than the central stimulus. Therefore, given a sufficient stimulus amplitude, the postural system is more sensitive to movement in the peripheral FOV. • There was a greater response to the 0.25 Hz stimuli in the full and peripheral FOV conditions, after accounting for typical postural responses during quiet stance. This challenges the idea that people are more sensitive to lower-frequency optic flow stimuli. Table 1. ANOVA results of FOV, Frequency, and Surface condition on absolute and normalized RMS head sway. Only p-values less than 0.05 are indicated. • References • Bardy, B.G. et al. (1999). Perception & Psychophysics. 61, 1356-68. • Percival, D.B. (1994). `Spectral Analysis of Univariate and Bivariate Time Series,' in Statistical Methods for Physical Science. Academic Press. • Peterka, R.J. et al. (1995). Experimental Brain Research. 105, 101-10. • van Asten, W.N. et al. (1988). Experimental Brain Research. 73, 371-83. Acknowledgements This research was supported by grants from NIH/NIA-1K25 AG01049, NIH/NIDCD-DC02490, and the Eye and Ear Foundation.