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Perceiving Affordances for Fitting Through Apertures Shaziela Ishak, Karen E. Adolph, and Grace C. Lin

Summary: Perceiving Affordances for Fitting Through Apertures
Shaziela Ishak, Karen E. Adolph, and Grace C. Lin
New York University
Affordances--possibilities for action--are constrained by the match between actors and their environ-
ments. For motor decisions to be adaptive, affordances must be detected accurately. Three experiments
examined the correspondence between motor decisions and affordances as participants reached through
apertures of varying size. A psychophysical procedure was used to estimate an affordance threshold for
each participant (smallest aperture they could fit their hand through on 50% of trials), and motor
decisions were assessed relative to affordance thresholds. Experiment 1 showed that participants scale
motor decisions to hand size, and motor decisions and affordance thresholds are reliable over two blocked
protocols. Experiment 2 examined the effects of habitual practice: Motor decisions were equally accurate
when reaching with the more practiced dominant hand and less practiced nondominant hand. Experiment
3 showed that participants recalibrate motor decisions to take changing body dimensions into account:
Motor decisions while wearing a hand-enlarging prosthesis were similar to motor decisions without the
prosthesis when data were normalized to affordance thresholds. Across experiments, errors in decisions
to reach through too-small apertures were likely due to low penalty for error.
Keywords: affordance, aperture, perception-action, psychophysics, reaching
Possibilities for motor action--or what Gibson (1979) termed
affordances--depend on the match between environmental con-
ditions and actors' physical characteristics (e.g., Adolph & Berger,


Source: Adolph, Karen - Center for Neural Science & Department of Psychology, New York University


Collections: Biology and Medicine