In sports, the concept of “affordance perception” can mean sensing an opponent’s next move, which has implications not just for performance but also for reducing injury risk. An understanding of affordance perception also can improve the effectiveness of training.
By Julie A. Weast-Knapp, MA, and Kevin Shockley, PhD
One of the goals of perceptual-motor research is to identify the information that supports our perception of the world around us. For example, what perceptual information tells an observer if an object is within reach, or a gap wide enough to pass through? James J. Gibson, a 20th century American psychologist, proposed that humans perceive by detecting information that specifies possibilities for performing an action.1,2 That is, humans can successfully perform actions like reaching to grasp a ball or walking through a doorway because they can perceive “affordances”—possibilities for action—that change based on environmental context and the action capabilities of the observer.
These real possibilities for action are perceived through the detection of informational variables, available in structured energy patterns, to which animals are sensitive (such as structure in the optic array—the pattern of light defined with respect to the observer).1 Accurate perception of affordances requires the pickup of information that is relevant to the successful completion of a particular action. However, the pickup of the proper information for a given action often depends on the previous perceptual-motor experience of the observer with the action in question.
Affordances characterize a tight coupling between perception and action: they describe what we are capable of doing before we actually do it. Research has demonstrated that humans can perceive affordances for themselves,1,3-5 as well as for others,6-8 and that we are surprisingly accurate at doing so. Consider the affordance of “reaching-with-jump,” the perception of how high one can reach overhead while performing a vertical jump. The maximum height that can be reached while jumping is a function of the relation between properties of the environment (e.g., the height of an object) and the action (e.g., force production) capabilities of the perceiver that determine whether an action is possible for the perceiver.6,7,9
Humans are quite good at perceiving this affordance for themselves before actually performing the action, and can also perceive it for another actor without ever seeing the other person jump (with an average accuracy of 92%).6,7,10 This indicates that observers are capable of distinguishing their own affordances from those of others and are remarkably precise at predicting what the other actor is capable of doing even without any explicit information about that person’s action capabilities.6,7,11,12
Affordance perception in sport
Recently, there have been attempts to account for elite performance in fast-paced environments such as those found in sports. Perceiving affordances is crucial in sports, as athletes must be able to perceive the action capabilities of both their opponents and teammates within fractions of a second and in a dynamic context in which affordances change every instant.13,14 Athletes demonstrate a superior ability to perceive the action capabilities of others in sports such as basketball (i.e., perceiving another’s ability to jump10 as well as another’s ability to successfully make a free shot15), badminton, and squash (i.e., perceiving the direction and magnitude of an opponent’s stroke16,17). Their enhanced ability to perceive what others can do appears to be a result of long-term perceptual-motor experience that comes from playing a sport. Presumably, athletes have become more attuned to different perceptual information than novices throughout the course of their sports training.
In a study on perception of hockey stick performance, Miami University RedHawks ice hockey team players’ choice of the optimal hockey stick type for power versus precision shots differed from the preferences of non-hockey player controls.18 The preferential difference persisted even after novices were allowed to briefly practice using each stick to perform both types of shots. This is evidence that athletes may be better attuned to perceptual information specifying actions related to their sport (e.g., information discovered while wielding the hockey stick that specified whether it was best for a power or precision shot) when compared with nonathletes because of their extensive sport training—that is, perceptual-motor experience in a sport aids the discovery of information specific to a sport-relevant affordance.14,16,18,19 Years of practice mean hockey players have become attuned to information about the suitability of a hockey stick for performing a particular shot.
The influence of kinematic information
Movement appears to play an important role in the perception of certain types of affordances of other actors. Two categories of affordances have been identified—“body-scaled” and “action-scaled.”14 Body-scaled affordances capture the relationship between properties of the environment and some (usually geometric) dimension of the body of the perceiver in determining whether an action is possible for the perceiver; for example, the relation between the height of an object and a person’s arm length determines if the object is reachable for that person. Action-scaled affordances capture the relationship between properties of the environment and the action capabilities of the perceiver in determining whether an action is possible for the perceiver; for example, the relationship between an object’s height and a person’s vertical force production capability determines if the object is reachable by jumping.6,7,10,14
The distinction between these categories of affordances is important because it suggests that accurate perception of the action-scaled affordances of another person requires perceptual information about forces (or the other person’s capacity to produce them), and these affordances may be specified by information in the other’s movement patterns (i.e., kinematic information).20 Movement kinematics are implicated because the laws of physics relate motion to the forces that generated that motion, therefore information about those forces is available for perceivers in movement kinematics.21 Accordingly, when observers are permitted to see another’s walking patterns, their ability to perceive how high the other person can jump improves.6 This suggests that an actor’s walking pattern contains information about his or her capacity to produce a different action, for example, jumping to reach an object.22 These findings may have important implications for sports training programs. For example, if researchers can identify the structure in the kinematics that improves perception of affordances for others, this information could facilitate development of sports programs that train athletes to become better attuned to this structure and improve their perception of action-scaled affordances of others.
When basketball players are exposed to another’s walking patterns, they improve their ability to accurately perceive the maximum reach-with-jump height for the other person more so than nonbasketball players; however, they do not improve their ability to accurately perceive the other person’s maximum standing-reach height.10 Basketball players, then, are not generally more sensitive to perceptual information. Rather, there is structure in an actor’s walking kinematics (e.g., in the motion of the joint centers on the actor’s body16) that is informative about his or her ability to jump to reach an object,6,22 and basketball players are better able than novices to capitalize on that structure and perceive the actor’s action-scaled affordance of reach-with-jump. Thus, athletic experience seems to enhance sensitivity to certain types of perceptual information, in particular to kinematic information available in another’s movement patterns.
Elite athletes, then, may have highly developed capacities for perception of affordances related to their sport compared with nonathletes or athletes with limited experience.14 When observing video of a basketball player performing a free shot (with an interruption in the video before the ball reaches the basket), for example, basketball players are better than novices at predicting whether the shot will be sucessful.15 They are also able to make accurate predictions earlier in the video—even before seeing the ball leave the hands of the shooter—than controls.15 Again, it seems the players are more sensitive than controls to kinematic information in the movement patterns of the actor that specifies the outcome of the free shot.
Interestingly, basketball players are also better at predicting the outcome of the free shot than coaches and sports journalists, two groups with just as much experience watching people jump as the players themselves.15 Basketball players appear to rely on the movements of the shooter (even if they never see the ball leave his hands) to predict the success of the shot, while novices appear to rely instead on the trajectory of the basketball.15
Thus, visual experience with a sport is not sufficient for perceiving affordances of others. Something about the players’ own perceptual-motor experience enable them to more accurately predict the shooting abilities of others compared with controls. Indeed, it has been shown that providing nonvisual motor-training to individuals for a novel body movement (i.e., allowing motor practice of the movement but not letting individuals see themselves perform the action) improves visual recognition of the learned action in another’s movement.23 If motor experience is necessary for perceptual-motor expertise, sports training programs may emphasize “doing” rather than “watching” in skill instruction, and sports researchers should focus on applied research of expertise development.24,25
Similarly, a focus on improving the perception of affordances for others could result in injury prevention. For example, postural adjustments and rapid reflex responses while playing a sport produce unanticipated sudden movements that can result in injuries such as anterior cruciate ligament tears.26 If athletes can improve their ability to perceive the affordances of their opponents and team members, they may be better able to anticipate the actions of others and adjust their own perceptual-motor responses accordingly.
Conclusions and implications
In the realm of athletic expertise, Abernethy et al, writing in the journal Perception, noted that perceptual learning by athletes appears “to be characterized by progressive perceptual discrimination, increased attunement to particular structure in the opponent’s kinematics and, likely, the optimization of attention to the essential informative features.”16 Athletes’ perceptual sensitivity presumably reflects attunement to the appropriate informational variables available as a result of perceptual-motor experience in their sport.16,18,19 Enhanced affordance perception by basketball players, for example, is evidence that athletes, when compared with nonathletes, are better attuned to salient kinematic information about affordances for others.10,13,14
What the particular information is remains unclear: the specific kinematic structure to which basketball players might be attuned has not yet been identified. For example, a particular relation among the moving joints and the corresponding (e.g., forward and/or vertical) motion of the actor may specify the force production capabilities of the actor to the observer, and it may be this information to which basketball players are more sensitive. Future studies of perception of affordances in sport must attempt to identify the informational variables in the movement patterns of others that improve perception of affordances for another, as sensitivity to relevant perceptual information about action-scaled affordances is essential for an athlete’s success in a sport.14
Julie Weast-Knapp, MA, is a doctoral student in the Department of Psychology at the University of Cincinnati, OH. Kevin Shockley, PhD, is an associate professor at the University of Cincinnati and director of experimental training in its Department of Psychology.
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