Getting a grasp on action-specific scaling: A response to Witt (2017).

Can higher level cognition directly influence visual spatial perception? Many recent studies have claimed so, on the basis that manipulating cognitive factors (e.g., morality, emotion, action capacity) seems to directly affect perception. However, Firestone and Scholl (Behavioral and Brain Sciences, 39, 1-77, 2016) argued that such studies often fall prey to at least one of six pitfalls. They further argued that if an effect could be accounted for by any of these pitfalls, it is not a true demonstration of a top-down influence of cognition on perception. In response to Firestone and Scholl (Behavioral and Brain Sciences, 39, 1-77, 2016), Witt (Psychonomic Bulletin & Review, 24(4), 999-1021, 2017) discussed four action-specific scaling effects which, she argued, withstand all six pitfalls and thus demonstrate true perceptual changes caused by differences in action capacity. Her third case study was the influence of apparent grasping capacity on perceived object size. In this article, we provide new interpretations of previous findings and assess recent data which suggest that this effect is not, in fact, perceptual. Instead, we believe that many earlier studies showing this effect are subject to one or more of the pitfalls outlined by Firestone and Scholl (Behavioral and Brain Sciences, 39, 1-77, 2016). We substantiate our claims with recent empirical evidence from our laboratory which suggests that neither actual nor perceived grasping capacity directly influence perceived object size. We conclude that studies manipulating grasping capacity do not provide evidence for the action-specific account because variation in this factor does not directly influence size perception.