Academic journal article Attention, Perception and Psychophysics

Duck! Scaling the Height of a Horizontal Barrier to Body Height

Academic journal article Attention, Perception and Psychophysics

Duck! Scaling the Height of a Horizontal Barrier to Body Height

Article excerpt

Recent research shows that the body is used to scale environmental extents. We question whether the body is used to scale heights as measured by real actions (Experiments 1 and 2) or by judgments about action and extent made from a single viewpoint (Experiments 3 and 4). First, participants walked under barriers naturally, when wearing shoes, or when wearing a helmet. Participants required a larger margin of safety (they ducked at shorter heights) when they were made taller. In follow-up experiments, participants visually matched barrier heights and judged whether they could walk under them when wearing shoes or a helmet. Only the helmet decreased visually matched estimates; action judgments were no different when participants' eye height increased. The final experiment suggested that the change in matched estimates may have been due to lack of experience wearing the helmet. Overall, the results suggest that perceived height is scaled to the body and that when body height is altered, experience may moderate the rescaling of height.

Gibson (1979) hypothesized that perception was directly related to action. Specifically, actors can directly perceive what the environment affords them (affordances). What an environment affords an individual is determined by the characteristics of the environment (height, width, etc.) and by the capability of the actor. For example, a doorway affords walking under upright if the height of the doorway is sufficiently higher than the upright height of the actor.

Some research has demonstrated that people can perceive whether the width of an aperture affords passage. Warren and Whang (1987) found that participants scaled their decision of whether an aperture afforded passage to the width of their shoulders. Specifically, when the ratio of aperture-to-shoulder width was 1.16 or larger, participants indicated that they could pass through an aperture. Wagman and Taylor (2005) found that participants who were asked to hold or view objects of different sizes when anticipating walking through an aperture adjusted their judgments of passability to take into account the size of the object. Ishak, Adolph, and Lin (2008) also investigated participants' ability to judge whether they could reach into an aperture to retrieve candy. Their findings showed that participants scaled their decisions to their hand size. Ishak et al. also varied the size of the hand by placing a prosthesis on participants. The participants, in turn, adjusted their reachability judgments accordingly, showing that they were sensitive to the new size of their hand.

Although much has been done to assess how people perceive whether they can fit through an aperture, fewer studies have determined how people perceive whether they can walk under a barrier. Perceiving whether an aperture affords passing under is reliant on perceiving the height of the aperture or barrier in relation to the height of the body. We will first review the literature that describes how people normatively estimate heights, and then we will discuss the literature that suggests that a certain aspect of the body, eye height, seems to be the most likely reference for deciding whether one can pass under a barrier or not.

Normative Estimation of Heights

Sinai, Ooi, and He (1998) found that participants who stood at the top of heights (~6 ft or 2 m in size) overestimated the vertical distance to the ground by about 50% (see also Jackson & Cormack, 2007; Stefanucci & Proffitt, 2009, for more overestimation of taller heights). They concluded that this overestimation was likely due to a misperception of eye height, but they did not include a situation in which participants viewed the height from the ground. Yang, Dixon, and Proffitt (1999) also tested perception of the height of short objects (such as a light pole or a door) and found approximately 6% overestimation. Their results suggested that taller objects (buildings) were overestimated more than were shorter objects (doors), even when the visual angle to all of the objects from the viewing position of the observer was held constant. …

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