Orienting Under Load: Intrinsic Dynamics and Postural Affordances for Visual Perception

Abstract

Orientation toward one's surroundings is necessary for prospective control of action, and constraints on orienting activity have consequences for animal survival. Physically coupled load is a constraint for humans wearing protective equipment (firefighters, soldiers, etc.). The consequences of load on postural affordances while transitioning to upright stance was used to quantify the impact of different soldier configurations. Eight participants established upright posture in 4 relevant load configurations (5.0 to 79.2 lb). Load affected the accessibility of optical information at a distance as evidenced by increasing downward head angles and reductions in postural coordination. Reductions in the variability of time to establish upright stance with load suggests a loss of functional adaptability. Load asymmetries played a significant role as the most asymmetric configuration (not the heaviest) had the most detrimental effect on postural affordances. Center of Pressure (CoP) dynamics reflected the consequences of asymmetric loading on postural regulation as greater power and fluctuations across frequencies were observed. Physically coupled load induces significant constraints on orienting activity, and load asymmetry contributes significantly to the detrimental effects of protective equipment on action-perception coupling during whole-body movements.

Notes

¹The term Field of Regard is used specifically because its definition includes the dynamic Field of View across head movements rather than the static definition most closely associated with the term Field of View (SIMTECH Inc., 1998). Moreover, Field of Regard is more closely tied with the concept of “what your head is inside of” (Mace, 1977) rather than what's inside your head.

*Significantly less than Weapon (p ≤ .044).

‡Significantly less than Helmet & Vest (p ≤ .004).

§Significantly less than Helmet, Vest, & Pack (p < .001).

*Significantly greater than Vest or Pack (p = .0073).

*Significantly greater than all other configurations (p < .0001).

§Significantly less than all other configurations (p ≤ .0273).

‡Trend for Pack to have significantly more bimodal distributions (p = .0739).