Abstract
Fear of heights occurs when a visual stimulus causes the apprehension of losing balance and falling. A moderate form of visual height intolerance (vHI) affects about one third of the general population and has relevant consequences for the quality of life. A quantitative evaluation of balance mechanisms in persons susceptible to vHI during height exposure is missing. VHI‐related changes in postural control were assessed by center‐of‐pressure displacements and electromyographic recordings of selected leg, arm, and neck muscles in 16 subjects with vHI while standing at heights on an emergency balcony versus standing in the laboratory at ground level. Characteristics of open‐ and closed‐loop postural control were analyzed. Body sway and muscle activity parameters were correlated with the subjective estimates of fear at heights. During height exposure, (1) open‐loop control was disturbed by a higher diffusion activity (P < 0.001) and (2) the sensory feedback threshold for closed‐loop control was lowered (P < 0.010). Altered postural control was predominantly associated with increased co‐contraction of leg muscles. Body sway and leg and neck muscle co‐contraction correlated with the severity of subjective anxiety (P < 0.050). Alterations in postural control diminished if there were nearby stationary contrasts in the visual surrounding or if subjects stood with eyes closed. The performance of a cognitive dual task also improved impaired balance. Visual heights have two behavioral effects in vHI subjects: A change occurs in (1) open‐ and closed‐loop postural control strategy and (2) co‐contraction of anti‐gravity leg and neck muscles, both of which depend on the severity of evoked fear at heights.
Highlights
Individual responses to visual stimulation of heights vary within a continuum ranging from physiological visual height imbalance to acrophobia, the severest end of the spectrum (Salassa and Zapala 2009)
Acrophobia is defined to be a specific phobia by ICD-10 (WHO 1993) and DSM-V (APA 2013), implying that an anticipatory fear leads to avoidance of heights
Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society
Summary
Individual responses to visual stimulation of heights vary within a continuum ranging from physiological visual height imbalance to acrophobia, the severest end of the spectrum (Salassa and Zapala 2009). Physiological visual height imbalance is experienced by everyone and results from a mismatch between visual distance cues and the perception of self-movement when the distance between the eyes and nearest objects in the environment reaches a certain threshold (Brandt et al 1980; Salassa and Zapala 2009). Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society
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