When affordances climb into your mind: Advantages of motor simulation in a memory task performed by novice and expert rock climbers

Abstract

Does the sight of multiple climbing holds laid along a path activate a motor simulation of climbing that path? One way of testing whether multiple affordances and their displacement influence the formation of a motor simulation is to study acquired motor skills. We used a behavioral task in which expert and novice rock climbers were shown three routes: an easy route, a route impossible to climb but perceptually salient, and a difficult route. After a distraction task, they were then given a recall test in which they had to write down the sequence of holds composing each route. We found no difference between experts and novices on the easy and impossible routes, whereas on the difficult route, the performance of experts was better than that of novices. This suggests that seeing a climbing wall activates a motor, embodied simulation, which relies not on perceptual salience, but on motor competence. More importantly, our results show that the capability to form this simulation is modulated by individuals’ motor repertoire and expertise, and that this strongly impacts recall.

Introduction

Humans are able to take advantage of the objects and entities displayed in their environment in order to achieve their goals. Many behavioral studies have shown that the vision of objects, such as cups and hammers, affords simple actions, such as reaching and grasping. As a result, the notion of affordance, originally proposed by Gibson (1979), has been given new life. Affordances can be defined as action patterns activated while observing objects. The underlying neural basis for affordances can be found in the discovery, in the F5 area of the ventral premotor cortex of the monkey, of canonical neurons (Murata et al., 1997). Visuomotor canonical neurons discharge in the presence of graspable objects, when no overt response is required—the majority of neurons responds selectively to specific kinds of grips (e.g., precision vs. full hand grips). Their function probably consists in representing objects in terms of potential action patterns. Evidence in humans confirms the existence of a parietopremotor circuit active during the observation of manipulable objects (Grèzes, Tucker, Armony, Ellis, & Passingham, 2003). Brain activation results showed that the response of the left ventral premotor cortex was stronger for manipulable than for non-manipulable objects (Gerlach et al., 2002, Kellenbach et al., 2003). A number of studies with different brain activation techniques (fMRI, PET) have shown that the brain responds differently to tools compared to other objects which do not evoke actions, such as buildings, animals and faces (e.g., Boronat et al., 2005, Chao and Martin, 2000, Creem-Regehr and Lee, 2005, Grèzes and Decety, 2002, Johnson-Frey, 2003, Martin et al., 1996; for a review see Martin, 2007), and that the recall of actions associated with tools activates the left premotor cortex (Grafton, Fadiga, Arbib, & Rizzolatti, 1997). On the behavioral side, a variety of studies with compatibility paradigms have shown that the vision of objects activates a motor simulation and might even evoke overt reaching and grasping movements (Borghi, 2004, Borghi et al., 2007, Bub et al., 2003, Bub et al., 2008, Edwards et al., 2003, Fischer et al., 2008, Tipper et al., 2006, Tucker and Ellis, 1998, Tucker and Ellis, 2001, Vainio et al., 2008). Overall, both behavioral and brain imaging studies have shown that perceiving affordances activates in observers specific motor programs. This phenomenon can be interpreted as activation of a motor simulation, where ‘simulating’ means that the same sensorimotor systems that are activated during interaction with objects are activated off-line, during object observation, but without the execution of overt movements (Gallese, 2009, Jeannerod, 2006).

Indoor rock climbing consists in reaching the top of a specially-designed wall, namely a climbing wall (see Fig. 1, left), by grasping climbing holds with the hands and the foots. Climbing routes, which consist in carefully arranged sequences of climbing holds, vary in difficulties, depending on the slope of the climbing wall, the length of the route, as well as on the number, kind, and arrangement of the climbing holds. There are indeed countless artificial climbing holds that have been designed to be used in indoor rock climbing, which have different shapes, and afford different grip.

One common procedure for climbers, both during their training and during competitions, is simulating climbing routes before actually climbing them, especially when they have to climb a route for the first time (see Fig. 1, right). The simulation they build might include both information on specific affordances, i.e. the characteristics of the holds (shape, orientation, etc.), and information on their displacement, i.e. the way they are arranged on the climbing wall. Given that routes involve multiple climbing holds (see Fig. 2), clearly any simulation of a part of the route changes the way the rest of the route is perceived. For example, simulating grasping a certain hold with the right hand makes some other holds affordable to be grasped with the left hand, and some other holds out of reach. At the same time, the necessity of reaching a certain ‘goal’ hold determine which holds are affordances retrospectively, and disrupts the affordances of some holds (e.g., far holds) in the climbing wall. For all these reasons, motor simulation in rock climbing should be considered an affordance calculus rather than a response to a sequence of individual affordances. Crucially, the motor competence of climbers also determines what constitutes an affordance. Experienced climbers can hold small holds that are difficult for weak climbers to grasp, and can simulate sequences of actions that are too complex to be picked up by novice climbers, much like how expert chess players ‘see’ complex strategies. In brief, not only expert climbers are better while climbing routes, but we hypothesize that they also understand them better, where understanding should be intended as proficiency in the affordance calculus.

Our study addresses the role affordances play in the recall of routes by rock climbers. Although there is an increasing number of studies on how observing objects (or object pairs, e.g., Riddoch, Humphreys, Edwards, Baker, & Willson, 2003) activates the motor system, the role played by multiple affordances for complex actions implying a sequence of movements has not been widely investigated. In addition, the majority of studies on simulation evoked by affordances do not take into account the observers’ competence. An open issue in this field pertains to the extent to which affordances are elicited automatically, upon seeing objects, or are activated when a specific action goal is pursued. Studying recall in expert and novice climbers can contribute to showing to what extent the activation of affordances is modulated by observers’ experience and competence. Finally, we still know very little on how affordances improve recall. Acquired motor skills offer a unique way to test this question.

In our study, novice and expert climbers were asked to observe and recall the position of holds of three routes that they never climbed: an easy route (ER), a difficult route (DR), and a (motorically) impossible but perceptually salient route (IPSR). We predicted that performance would not differ between the two groups for the ER because both groups would be able to perform a motor simulation. In addition, performance would not differ for the IPSR route, when for both groups it was impossible to form a motor simulation of climbing. If this is true, this would demonstrate that the simulation formed is a motor one, and would be activated only when participants have the motor competence necessary to perform the sequence of actions. Accordingly, the performance of experts should overcome that of non-experts in the DR, when the actions required to climb the route they are shown are part of their motor repertoire.