Abstract
Perception and action are tightly linked: objects may be perceived not only in terms of visual features, but also in terms of possibilities for action. Previous studies showed that when a centrally located object has a salient graspable feature (e.g., a handle), it facilitates motor responses corresponding with the feature's position. However, such so-called affordance effects have been criticized as resulting from spatial compatibility effects, due to the visual asymmetry created by the graspable feature, irrespective of any affordances. In order to dissociate between affordance and spatial compatibility effects, we asked participants to perform a simple reaction-time task to typically graspable and non-graspable objects with similar visual features (e.g., lollipop and stop sign). Responses were measured using either electromyography (EMG) on proximal arm muscles during reaching-like movements, or with finger key-presses. In both EMG and button press measurements, participants responded faster when the object was either presented in the same location as the responding hand, or was affordable, resulting in significant and independent spatial compatibility and affordance effects, but no interaction. Furthermore, while the spatial compatibility effect was present from the earliest stages of movement preparation and throughout the different stages of movement execution, the affordance effect was restricted to the early stages of movement execution. Finally, we tested a small group of unilateral arm amputees using EMG, and found residual spatial compatibility but no affordance, suggesting that spatial compatibility effects do not necessarily rely on individuals' available affordances. Our results show dissociation between affordance and spatial compatibility effects, and suggest that rather than evoking the specific motor action most suitable for interaction with the viewed object, graspable objects prompt the motor system in a general, body-part independent fashion.
Highlights
The idea that an object is perceived by its visual features, and by the potential motor actions it affords has captured the attention and imagination of both scientists (e.g., Tucker and Ellis, 1998, 2004) and philosophers (Gibson, 1979). In support of this notion, a series of behavioral studies have shown that when a centrally located object has a salient graspable feature, it facilitates motor responses corresponding with the feature position: When participants were asked to perform simple key-press responses with both hands, the response time of the hand most suited to perform a reach-and-grasp movement toward the object handle was speeded
These results suggest that both spatial compatibility and affordance effects are www.frontiersin.org response (A), maximum amplitude of EMG response (B), and button press responses (C)
The prevalent account of affordances, based on speeded reaction times (RTs) for graspable objects oriented toward the responding hand, suggests lateralized facilitation of the hand toward which the central object’s handle is oriented (Tucker and Ellis, 1998; Phillips and Ward, 2002; McBride et al, 2012)
Summary
The idea that an object is perceived by its visual features, and by the potential motor actions it affords (object affordances) has captured the attention and imagination of both scientists (e.g., Tucker and Ellis, 1998, 2004) and philosophers (Gibson, 1979). Objects that facilitate different kinds of grasping (e.g., power grip or precision grip), prime different motor actions (“micro affordances”; Ellis and Tucker, 2000; Tucker and Ellis, 2004) This line of evidence led researchers to conclude that object affordances automatically activate codes for actions appropriate for the utilization of that object, even when these responses are irrelevant. For example Symes et al (2005) simultaneously manipulated the spatial location of objects and the orientation of their handles, and found that each produced a distinct compatibility effect These results were taken as an indication that affordance effects and the Simon effect are independent (see Riggio et al, 2008; Pellicano et al, 2010). It is still possible that these www.frontiersin.org
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