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Identifying To What People Attend When Perceiving Others’ Maximum Vertical Reach

Assistive robots need to understand when people need help. Therefore, they need to understand peoples’ action capabilities. One way to enable robots to do so is to program them to attend to the same information that people utilize when perceiving other people’s action capabilities (Jones & Garcia, 2021; Jones & Schmidlin, 2011). Past studies demonstrated that 1) people who are perceiving others’ action capabilities (e.g., ability to climb a stair) attend to relevant properties of the other person (e.g., leg length) in relation to relevant properties of the other person’s environment (e.g., stair riser height), and 2) relevant properties of the other person can include the other person’s physical dimensions, their movements, or both (see Jones & Garcia, 2021 for a review). Such studies provide important insights, but they do not indicate to what exactly do people attend when perceiving whether another person can perform a given action. Toward that end, the current experiment investigated to what do people attend when perceiving whether someone else can reach an object. To do so, 80 participants viewed a set of point-light displays (Johansson, 1973). Each depicted either a tall or short actor and a to-be-reached object. Markers were placed on either the actor’s whole body, upper body, lower body, or ankles; the to-be-reached object was represented by a single point of light. Actors either moved or were still. Participants instructed the experimenter to adjust the height of the to-be-reached object to where the actor could just barely reach it while keeping their feet flat on the ground and standing still (i.e., the actor’s maximum vertical reach height). If participants are sensitive to actors’ action capabilities, then they should judge that the tall actor could reach higher than the short actor. If participants attend to specific body segments when judging the actors’ maximum vertical reach heights, then their judgments should degrade when information about those body segments is unavailable. If participants attend to movements of body segments, then their judgments should degrade when actors do not move. The study utilized a one-within two-between mixed factorial design. The within-subjects factor was Actor Height, which consisted of two levels: Tall Actor and Short Actor. The first between-subjects factor was Actors’ Movement, which consisted of two conditions: Movement Present or Movement Absent. The second between-subjects factor was Actor PointLight Marker Configuration, which consisted of four conditions: Full Body, Upper Body, Lower Body, and Ankles. The dependent variables were the 1) participants’ judgments of the maximum height that the actor could reach and 2) percentage of absolute judgment error. The results revealed that participants were sensitive to actors’ action capabilities, which replicates past findings (Mark, 2007; Stoffregen et al., 1999). Further participants attended to a) something present when either actors’ upper or lower bodies were visible, b) something not present when only actors’ ankles were visible, and c) something present when actors did not move. What might that be? One possibility is object height in relation to actor height. In the Upper Body condition, participants may have attended to the relation between object height and the top of actors’ heads. In the Lower Body condition, participants may have attended to the relation between object height and the length of actors’ legs. Leg length is highly correlated (e.g., r = .88-.90) with overall height (Clarke, 1957), so the relation between object height and actors’ leg lengths should be highly correlated with the relation between object height and actors’ heights. Participants may have utilized the relation between object height and actors’ leg lengths as information about the relation between object height and actors’ heights. In the Ankles condition, participants were not presented with information about actor height. The present results move us towards a better understanding of to what exactly do people attend when perceiving others’ action capabilities and thus closer to being able to program assistive robots to perceive people’s action capabilities (Jones & Garcia, 2021; Jones & Schmidlin, 2011). Continued research in this area will enable assistive robots that can perceive a wide array of human action capabilities.