Ledge and wedge: younger and older adults’ perception of action possibilities

Abstract

The current study investigated whether younger (college-age) and older adults (60+ years) differ in their ability to perceive safe and unsafe motor actions. Participants decided whether to walk through openings varying in width in two penalty conditions: In the doorway condition, if participants attempted to squeeze through impossibly narrow openings, the penalty for error was entrapment. In the ledge condition, if participants attempted to inch along impossibly narrow ledges, the penalty for error was falling. Results showed that across the lifespan, people consider falling to be a more severe penalty than getting stuck: Both younger and older adults made more conservative decisions when the penalty for error was falling, and older women were especially leery of falling. In both age groups, abilities and decisions were based on dynamic properties of the body, such as compressed body size in the doorway condition and balance in the ledge condition. Findings indicate that failure to perceive possibilities for action is unlikely to be the cause of the increased prevalence of falling in older adults.

Affordances as Probabilistic Functions: Implications for Development, Perception, and Decisions for Action

“…For safety reasons, we did not measure pregnant women’s compressed body dimensions. However, in other work we found that younger and older (non-pregnant) adults’ torsos compress by 3–4 cm, and measurements of compressed body size closely match affordance thresholds (Comalli, Franchak, Char, & Adolph, 2012). …”

“…When verbal judgments about affordances for passage were assessed using the same curve-fitting procedure, variability for judgments about horizontal openings was greater than variability for vertical openings. Similarly, affordances for squeezing through doorways are less variable than those for navigating along ledges, and perceptual judgments for squeezing through doorways are less variable than those for navigating ledges (Comalli et al, 2012). Moreover, rapid pointing studies show that actors are sensitive to motor variability: They adjust their aim according to their individual motor variability and even adapt to artificial perturbations that increase motor noise (Trommershäuser, Gepshtein, Maloney, Landy, & Banks, 2005).…”

“…Indeed, actors weigh the probability of success against the cost of errors. Seventeen-month-old infants, college-aged adults, and older adults (65+ years) make more cautious decisions when navigating ledges where the penalty for errors is falling compared to fitting through doorways where the penalty for errors is entrapment (Comalli et al, 2012; Franchak & Adolph, 2012b). Similarly, participants report that they would allow a greater safety margin for ducking under a barrier made of foam compared to one of metal (Wagman & Malek, 2009).…”

“…Moreover, actors’ perceptual judgments are better scaled to the actual affordance than to shoulder width, meaning that perceivers detect information that accounts for the dynamics of walking in addition to shoulder width when they judge affordances for passage. Other affordances, such as squeezing through tight spaces, also depend on dynamic aspects of the body such as compression (Comalli et al, 2012). Given that affordances depend on the characteristics of the body in motion, attempts to identify perceptual information rooted in body dynamics, such as stride length and head sway (Fath & Fajen, 2011), might be more fruitful than information based on the static geometry of the body.…”

Exploratory behaviors and recalibration: What processes are shared between functionally similar affordances?

“…Past work highlights a unique aspect of the squeezing task that differs from other fitting affordances: Squeezing through doorways depends not only on body size, but also on body compression (Comalli, Franchak, Char, & Adolph, 2013;Franchak & Adolph, 2014b;Franchak, van der Zalm, & Adolph, 2010). Like friction (Joh, Adolph, Campbell, & Eppler, 2006;Joh, Adolph, Narayanan, & Dietz, 2007), compression is an emergent property: How much the body (or the body while modified by a backpack or pregnancy pack) compresses can only be understood given the opposing surface (like a doorway) and the amount of force applied.…”