When perception intrudes on 2D grasping: evidence from Garner interference
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ORIGINAL ARTICLE
When perception intrudes on 2D grasping: evidence from Garner interference Tzvi Ganel1 · Aviad Ozana1 · Melvyn A. Goodale2 Received: 14 March 2019 / Accepted: 8 June 2019 © Springer-Verlag GmbH Germany, part of Springer Nature 2019
Abstract When participants reach out to pick up a real 3-D object, their grip aperture reflects the size of the object well before contact is made. At the same time, the classical psychophysical laws and principles of relative size and shape that govern visual perception do not appear to intrude into the control of such movements, which are instead tuned only to the relevant dimension for grasping. In contrast, accumulating evidence suggests that grasps directed at flat 2D objects are not immune to perceptual effects. Thus, in 2D but not 3D grasping, the aperture of the fingers has been shown to be affected by relative and contextual information about the size and shape of the target object. A notable example of this dissociation comes from studies of Garner interference, which signals holistic processing of shape. Previous research has shown that 3D grasping shows no evidence for Garner interference but 2D grasping does (Freud & Ganel, 2015). In a recent study published in this journal (Löhr-Limpens et al., 2019), participants were presented with 2D objects in a Garner paradigm. The pattern of results closely replicated the previously published results with 2D grasping. Unfortunately, the authors, who appear to be unaware the potential differences between 2D and 3D grasping, used their findings to draw an overgeneralized and unwarranted conclusion about the relation between 3D grasping and perception. In this short methodological commentary, we discuss current literature on aperture shaping during 2D grasping and suggest that researchers should play close attention to the nature of the target stimuli they use before drawing conclusions about visual processing for perception and action.
Introduction The objects in our immediate environment that we interact with every day—our coffee cup, our pen, and the apple in the fruit bowl—are all are 3D stimuli. A long history of research has revealed critical differences between the visual processing (and the underlying visual pathways) that mediate the perception of those 3D objects and the control of grasping movements directed towards them (for review, see Goodale, 2011). At the same time, we interact with 2D stimuli as well. The recent proliferation of smartphones, tablets, and touch screens has made such interactions all the more frequent and consequential for many aspects of our lives. These technological advancements have led to the emergence of a new form of goal-directed action performed not towards actual * Tzvi Ganel [email protected] 1
Psychology Department, Ben-Gurion University of the Negev, 8410501 Beer‑Sheva, Israel
The Brain and Mind Institute, The University of Western Ontario, London, ON N6A 5B7, Canada
2
3D objects but rather to 2D and virtual stimuli (presented on screens) and virtual objects in vir
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