Abstract
Linkenauger, Witt, and Proffitt (Journal of Experimental Psychology: Human Perception and Performance, 37(5), 1432–1441, 2011, Experiment 2) reported that right-handers estimated objects as smaller if they intended to grasp them in their right rather than their left hand. Based on the action-specific account, they argued that this scaling effect occurred because participants believed their right hand could grasp larger objects. However, Collier and Lawson (Journal of Experimental Psychology: Human Perception and Performance, 43(4), 749–769, 2017) failed to replicate this effect. Here, we investigated whether this discrepancy in results arose from demand characteristics. We investigated two forms of demand characteristics: altering responses following conscious hypothesis guessing (Experiments 1 and 2), and subtle influences of the experimental context (Experiment 3). We found no scaling effects when participants were given instructions which implied the expected outcome of the experiment (Experiment 1), but they were obtained when we used unrealistically explicit instructions which gave the exact prediction made by the action-specific account (Experiment 2). Scaling effects were also found using a context in which grasping capacity could seem relevant for size estimation (by asking participants about the perceived graspability of an object immediately before asking about its size on every trial, as was done in Linkenauger et al., 2011; Experiment 2). These results suggest that demand characteristics due to context effects could explain the scaling effects reported in Experiment 2 of Linkenauger et al. (2011), rather than either hypothesis guessing, or, as proposed by the action-specific account, a change in the perceived size of objects.
Highlights
These results suggest that demand characteristics due to context effects could explain the scaling effects reported in Experiment 2 of Linkenauger et al (2011), rather than either hypothesis guessing, or, as proposed by the action-specific account, a change in the perceived size of objects
Action-specific scaling effects suggest that perception may be cognitively penetrable—so perception can be directly influenced by higher-level cognition
If action-specific scaling effects truly reflect changes in what is perceived in this strong sense, this has major implications for standard, modular theories of vision, which hold that perception is encapsulated and separate from cognition (Pylyshyn, 1999; for a recent review, see Firestone & Scholl, 2015)
Summary
Participants’ responses may not reflect differences in what they perceive; rather, their spatial estimates may be affected by nonperceptual influences such as their beliefs about the purpose of the experiment. Firestone and Scholl (2014) found that when participants were given a convincing reason for holding the rod, their estimates of aperture width did not differ from participants who did not hold the rod These results suggest that if participants are not given an explanation for a salient manipulation, they may attempt to figure out the experimental hypothesis and that this, in turn, can influence their responses
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