Perceptions of Passability Through Dynamically Moving Gaps

Introduction. A critical aspect of daily locomotion and mobility is the successful navigation of apertures. The ability to determine which openings an individual can and cannot fit through is useful when walking through doors or hallways, when keeping a vehicle inside lane markers, and when navigating through a crowd. Successful locomotion, including actions such as passing through openings, relies on accurate affordance perception. Affordances, or action capabilities, represent the relationship between properties of the actor and characteristics of the environment (Gibson, 1979). The majority of affordance research on aperture passability has studied the actor within a static environment (Warren & Whang, 1987; Wagman & Taylor, 2005; Franchak & Adolph, 2014). However, realistic interactions between the actor and environment must be considered within a dynamic context. Other actors and vehicles in the environment move around, and inanimate objects can be moved mechanically, thrown, or blown by the wind, all while being subjected to the laws of physics. To successfully pass through a dynamic gap, the actor must avoid collision with the moving edges of the gap. Research on the dynamic affordance of gap crossing has assessed tasks such as walking through oscillating or closing doors (Cinelli, Patla, & Allard, 2009; Fajen & Matthis, 2011; Grechkin, Plumert, & Kearney, 2014) and crossing streets with oncoming traffic (Chihak et al., 2010; O’Neal et al., 2018; Plumert & Kearney, 2014). Most research on dynamic affordances has taken the assumption that the environment is always moving in a predictable way. Cars in the road-crossing experiments were always travelling at constant velocities, and in door closing experiments the door always followed a patterned movement (completely open to completely closed). However, natural dynamic environments may be complex and unpredictable. A worker navigating through a factory setting may have to walk through two machines which are moving in complex patterns, and driving a vehicle may require one to pass a bicyclist whose balance and lateral movement is more or less complex. These examples represent a yet unstudied dynamic affordance task; one in which the gap remains partially open at all times, and the size of the gap fluctuates around some base width. Considering this type of task, there are two key metrics that would appropriately quantify properties of the dynamic gap; the amplitude (or magnitude) of the oscillation and the determinism (or complexity/predictability) of the oscillation pattern. The amplitude of an oscillation can be quantified by taking the Standard Deviation (SD) of the oscillation sequence. The determinism of an oscillation can be quantified by calculating the Sample Entropy (SampEn) of the oscillation, which measures the sequential dependence of a time series (Kuznetsov, 2014). The current experiment assessed the extent to which the amplitude and determinism of a gap whose width is fluctuating impacts an actor’s judgments of their ability to pass through the gap.