Brief articleAn information-based approach to action understanding
Introduction
It has been proposed that the ability to visually apprehend the goals and purposes of other agents’ actions depends on embodied simulation (ES) mechanisms that map action perception onto action execution (Gallese, 2005, Gallese and Goldman, 1998, Metzinger and Gallese, 2003, Sebanz et al., 2006, Wilson and Knoblich, 2005). Less emphasis has been placed on how action understanding and prediction may reflect a situated, on-line sensitivity to optical information, especially in the case of predicting possibilities for action (i.e., affordances; Gibson, 1986) and the outcomes of impending actions. We propose that an account emphasizing optical information about unfolding or impending actions may be able to explain findings that observers are sensitive to another actor’s body scale and action capabilities (Ramenzoni et al., 2005, Stoffregen et al., 1999) – results that seem at odds with ES, given the proposal that other agents are simulated indeterminately (Gallese, 2005; cf. Pacherie & Dokic, 2006) – and at the same time explain findings that suggest, consistent with ES, action understanding and prediction are rooted in the observer’s action capabilities (Rochat, 1995, Zaff, 1995). As an initial test of this approach we manipulated optical information about affordances for another agent.
Section snippets
Embodied simulation
The ES hypothesis was motivated by the discovery of mirror neurons. Mirror neurons, originally discovered in monkeys (Gallese et al., 1996, Rizzolatti et al., 1996a), are found in human prefrontal and parietal circuits that activate when either performing or observing goal-directed actions such as reaching (Buccino et al., 2002, Decety and Grèzes, 1999, Iacoboni et al., 1999, Rizzolatti et al., 1996a, Rizzolatti et al., 1996b). The ES hypothesis states that observing another agent perform an
Determinate, eyeheight-scaled information for action perception
Notwithstanding the claim that other agents are indeterminately simulated, determinate information about other agents’ action capabilities seems to be available to observers prior to as well as during activity of the other agent. Eyeheight-scaled optical information provides metrically determinate support for perceiving action-relevant properties of agents and objects in relation to the environment (Lee, 1974, Sedgwick, 1973, Wraga, 1999). For instance, observers use eyeheight-scaled optical
Participants
Sixteen University of Cincinnati undergraduates (9 females, 7 males) participated for course credit. Participants ranged from 18 to 22 years old (mean = 19.34 years), from 150 cm to 190 cm tall (mean = 168 cm, SD = 18.32 cm), and in reaching height from 185 cm to 229 cm (mean = 204.50 cm, SD = 19.19 cm). Participants reported to the experiment in pairs. Each pair included one participant in a shorter (150–160 cm) and one in a taller (180–190 cm) group so that participants made judgments for someone whose reaching
Results
Results are depicted in Fig. 2. Shorter participants slightly underestimated their own reaching ability in the floor condition (mean error = −3.02 cm), exhibited near-perfect accuracy in the 7.5 cm step condition (mean error = −0.01 cm), and slightly overestimated their own reaching ability in the 15 cm step condition (mean error = 3.47 cm). Expressed as gains (ratios of the increase in perceived maximum reach to the increase in eyeheight effected by each of the step conditions relative to the floor
Discussion
Overall observers exhibited a rather high degree of metrical accuracy in perceiving affordances for themselves and for agents with different action capabilities. The largest errors were made by taller participants judging what was reachable for shorter participants, though those errors ranged only 5%–9%. Taller participants also underestimated their own maximum reaching heights more so than did shorter participants. This could reflect an enhanced perceptual attunement by shorter participants to
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