Perception brings us into contact with people, objects, and places within the environment. Perception relies on sensory systems that enable humans to see, hear, feel, smell, and taste. It is estimated that one third of the human brain is dedicated to perception. Early Greek philosophers were among the first to study the science of perception. Their strong bias toward sight continues to this day, and sport psychology (SP) is no exception. For example, in addition to the wide body of research that has studied the motor dexterity of elite athletes, a growing number of researchers have studied the visual perceptual skills of these athletes. Visual perception is critical for decision making (DM); for example, to recognize an opponent’s pattern of play to assume a strategically apt position for intercepting the ball and for the guidance of action, when for instance, controlling running speed and direction in order to successfully catch a fly ball. This entry addresses perception by providing an overview of the physiology of the visual system and the two dominant theoretical approaches used to study perception: information processing and ecological psychology. In line with the typically predominant interest in visual perception, this entry uses the term perception to refer to visual perception, except where stated otherwise.
Physiology of the Visual System
Visual perception starts with rays of light, or stimulus information, falling upon the retina at the back of the eye. The retina consists of different types of light sensitive photoreceptors colloquially named rods and cones. The rods greatly outnumber the cones and are distributed across the entire retina except at the fovea, the location of highest visual resolution, where the cones are highly concentrated. The rods are more sensitive to light than cones and are involved in the perception of location and motion. Rods only provide coarse perception of the environment (i.e., low acuity). The cones function best in bright light; they are important for perceiving detail (i.e., high acuity) and color. The stimuli at the retina are relayed to the brain along the optic nerve, which consists of different populations of ganglions cells that project onto the lateral geniculate nucleus and from there to the primary visual cortex (V1) at the rear of the brain. Magnocellular ganglion cells are fast and transport stimulus information important for the perception of motion and location or distance. Parvocellular ganglion cells are much slower and transfer stimulus information about color and edges (i.e., shape). A third population of ganglion cells project directly to the subcortical areas of the visual system (i.e., the superior colliculus) to facilitate the control of eye movements. From the primary visual cortex, stimulus information is further distributed to higher cortical areas, each of which selectively processes different visual properties. For example, V2 (and V1) process orientation, V3 supports shape perception, V4 is involved in color perception, and V5 or MT is dedicated to motion perception. Importantly, beyond V1 the visual brain is organized into two distinct pathways, one toward the parietal lobe (the dorsal stream) and the other toward the temporal lobe (the ventral stream). There is fierce debate over the respective functions of the two visual systems. Traditionally, the systems have been distinguished in terms of their input: The dorsal stream is referred to as the where stream reflecting its primary function for spatial perception (i.e., the perception of motion, distance, and location), whereas the ventral stream is named the what stream consistent with the supposition that it is responsible for object perception (i.e., the perception of shape, size, and color). However, a relatively recent reinterpretation emphasizes the distinctive functions of the two streams rather than their input. Hence, the dorsal stream is proposed to be the action stream, underpinning the fast, unconscious, and online control of movement, while the ventral stream is the perception stream, a relatively slow but mostly conscious system surmising knowledge about the environment. This distinction between action and perception is particularly relevant when considering perception in sport.
Information-Processing Approach to Perception
In SP, as in most other domains of psychology, information-processing approaches have undoubtedly been the dominant theory for understanding perception. Information-processing approaches consider human perception to act in a manner similar to a digital computer. In this metaphor, the visual system is considered to be the “hardware” that underlies perception. Yet, the most distinctive feature of these approaches for understanding perception is the “software” conceived to be necessary for the different stages of information processing. In one of the earliest encompassing accounts of the information processing approach in SP, H. T. A. Whiting distinguished a series of successive and separate stages of information processing: the input, decision-making, and output stages. In the input stage, the eyes register stimulus information from the environment and transmit it to the brain. Importantly, the transmission of information is selective; because of the vast amount of stimuli, it is not possible to attend to all the stimulus information that is available at any one time.
The stimulus information in itself is inherently ambiguous. For example, the retinal size of an object varies according to the distance between the object and observer, and retinal shape varies as function of the orientation of the object relative to the observer. A single object can therefore generate an infinite number of different stimulus patterns on the retina and hence is considered to be insufficient as a basis for perception. The stimulus information needs to be interpreted or enriched. Consequently, in the decision-making stage of processing, central mechanisms in the brain must interpret and process the stimulus information to form a representation of the environment. These internal representations then provide the basis for other central mechanisms that make decisions about a new action, or adjustments in an ongoing action, to program appropriate movement responses. In the final output stage, the programmed movement responses are performed by the musculoskeletal system. Notably, for information-processing approaches, perception ends the instant that an internal perceptual representation of the environment has been created. For this reason, within the information processing approach, perception and action are conceived as largely independent processes that can be studied in isolation from one another.
Information-Processing Approach in Sport Research
In sport research, the information-processing approaches have above all been used to better understand perception and perceptual expertise in DM and anticipation. In this respect, a common feature for perception in sport is that it is performed under restrictive time constraints—for example, when attempting to interrupt the opponents’ attacking play and passing the intercepted ball to a teammate. Hence, successful performance requires perception or anticipation of the outcome of others’ actions before it is fully manifested in ball flight: a player is often too late if he or she waits until the outcome information is available. Early investigations, predating the information processing approach, assumed that expert performers must possess visual hardware that is better than in lesser-skilled performers (i.e., better visual acuity [VA], color perception, or peripheral vision). On the whole, this research failed to demonstrate a strong relationship between sport skill and the low-level physiological properties. Yet, given the recent dramatic improvement in our understanding of the visual brain, it may be premature to completely discard this proposal. For instance, measures like motion and speed perception, which purportedly reflect processing of higher cortical areas, may or may not eventually prove to distinguish athletes with different levels of skill.
More recent evidence has shown that experts possess a superior sport-specific knowledge base in addition to a superior ability to process stimulus information. These capacities speak to the very heart of the information-processing approach, which holds that the inherently insufficient information in the stimulus needs to be enriched for perception to become meaningful—that is to say, to form a high-fidelity representation of the environment. This enrichment comes about by relating the stimulus to task-specific knowledge built from past experiences via the processes of encoding (i.e., transforming stimulus information into a neural code that can be stored in the knowledge base) and retrieval (i.e., the reverse process whereby stored perception information is accessed). Perception is more truthful and rapid when the knowledge base becomes wider and when encoding and retrieval become more efficient. Indeed, experts are shown to recognize and recall patterns of play more accurately and much quicker than lesser-skilled players. In a seminal study, Adriaan D. de Groot briefly presented images of chess positions to players of different skill levels and asked them to reconstruct the positions. The expert chess players were able to recall the positions with relatively few mistakes, whereas players below master level made a large number of errors. When players in a subsequent study viewed both structured (i.e., real) and unstructured (sometimes impossible) chess positions, the recall of the experts was found only for the real configurations. This demonstrates that skilled players possess more efficient game-specific encoding and/or retrieval of chess positions rather than exceptional visual memory or speed of processing. The expert players reproduce the positions by grouping together or chunking small groups of individual pieces into larger meaningful units. This chunking allows the experts to process more information while using the same (limited) memory capacity.
The superior encoding and retrieval shown by experts in a static game like chess have been shown to also exist in more dynamic sports like basketball, field hockey, and soccer. Typically, this work presents high and low-skilled players with pictures or video clips of structured and unstructured patterns of play. Superior recognition and recall is commonly observed among high-skilled players, suggesting that expertise entails an enhanced ability to perceptually chunk the observation of individual players into larger (meaningful) units. Presumably, this allows these athletes to anticipate the outcome of patterns of play earlier, and more accurately, than lower-skilled players.
Indeed, studies employing the temporal occlusion paradigm have provided ample evidence that high-skilled players anticipate action outcomes by extracting early, pre-ball flight stimulus information (or advance cues). In the temporal occlusion paradigm, participants view video clips simulating an athlete’s view of an evolving pattern of play (e.g., an offensive move by a team) or an opponent’s action (e.g., a badminton serve). The clips are selectively occluded at predetermined times relative to a critical moment in the action sequence (e.g., ball contact). Participants predict the outcome of the action, usually by producing a verbal or a simplified movement response. High-skilled players are typically better at reliably anticipating the outcome of the occluded pattern of play or opponent’s action. Within the information-processing approach, this is taken to mean that high-skilled players distinguish themselves by their ability to use their extensive knowledge base to process early visual cues to infer the forthcoming event.
Some have argued that the expert perceptual advantage in sport is not limited to the processing of stimulus information but that it also entails the ability to better attend to relevant stimuli or cues. High-skilled athletes appear to be able to visually search the environment in a more efficient manner by selectively fixating longer on those areas that are relevant for successful task performance. Yet, visual search has also proven to be highly sport and task-specific, rendering it hazardous to make inferences about general skill-related characteristics for visual search. Nonetheless, it is fair to conclude that athletes’ visual search is not only driven by environmental events, but is also directed by their internal knowledge base. Experts know what are the most informative aspects of an evolving pattern of play or an opponent’s action, and what aspects are less relevant for further processing.
The Ecological Approach to Perception
The central notion of the information-processing approach is that the environment is perceived indirectly via an internal representation constructed by cognitive processes that add meaning to inherently ambiguous stimuli. In contrast, the ecological approach holds that visual perception is direct. It claims that all the information that is needed for perception (and action) is “out there” in the environment. James J. Gibson argued that the optic array, which refers to the ambient light that is lawfully patterned by the surfaces of the environment, carries information that is rich and sufficient for perception. Because information in the optic array is specific to the properties of the environment (or the observer-environment system), internal processes of enrichment are redundant. Visual perception therefore entails the pickup or extraction of specifying information that resides in the optic array. As a rule, information is granted by virtue of the observer’s movements. For instance, a moving observer generates a global expansion pattern in the optic array, the focus of which is specific to the direction of locomotion. Importantly, these movement-induced patterns in the optic array (denoted invariants) also form the basis for the visual guidance of action. Accordingly, when steering, the only thing a cyclist needs to do is to move or steer in such a manner that the focus of expansion remains at a position farther down the road. Within the ecological approach this is referred to as perception– action coupling (or sometimes, and perhaps more appropriately, information–movement coupling). A critical corollary of this intricate coupling of perception with action is that the available information, and hence perception, is grounded in action: Perception and action cannot—and should not—be understood and studied as independent processes. Accordingly, the primary objects of perception are thought to be so-called affordances, or opportunities to act.
Within the ecological approach, perceptual learning is described as convergence or education of attention, a process along which perceivers learn to pick up specifying information. Early in the learning process, perceivers can be expected to attend to less useful nonspecifying information (i.e., information that is not specific to the environmental property of interest), resulting in misperception. During learning, however, the observer comes to attend to the specifying information that will enhance perceptual accuracy. Moreover, accurate perception (or action) not only requires the pickup of specifying information but also an appropriate scaling or calibration of perception or action to the exploited information. Hence, proponents of the ecological approach posit that in addition to the education of attention, perceptual learning entails a process of calibration.
The Ecological Approach in Sport Research
The concept of perception–action coupling in particular has had, and continues to have, a powerful influence on research in perception in sport.
The baseball outfielder trying to catch a fly ball is a paradigmatic example. Rather than inferring the location that the ball will land based on the perception of its current distance and velocity and internal knowledge of ball flight characteristics, the outfielder should—according to proponents of the ecological approach—simply run in a manner that generates systematic changes in the optic array. During early ball flight, the optical height of the ball changes according to the location the ball will land relative to the outfielder. The ball will land behind the outfielder when there is vertical optical acceleration. Conversely, in the case of vertical optical deceleration it will land in front of them. This invariant not only specifies what the situation affords for action (i.e., running forward or backward) but also how to run to get in the right place at the right time to intercept the ball. That is, catchers have been shown to run in a manner that zeroes out or negates optical acceleration or deceleration and keeps optical velocity constant.
The outfielder catching a ball underlines that perception and perceptual expertise cannot be investigated separate from action (i.e., without action, optical acceleration cannot be negated). Accordingly, the ecological approach has criticized information-processing approaches for doing just that: studying perceptual expertise in sport using experimental designs that isolate perception from action. Soccer goalkeepers, for instance, demonstrate superior anticipation (and interception) when diving to save real penalty kicks (in situ) when compared to making verbal responses in response to video clips (as typically required within the temporal occlusion paradigm). Importantly, these differences in anticipation are reflected by critically different gaze patterns. In addition, faster and more agile goalkeepers are found to wait longer before moving to block the ball when tested in situ. In doing so, the pickup of information supporting anticipation of the kick can be based on (potentially less deceptive) information that is only available in the latter part the penalty taker’s actions. Consequently, perceptual expertise can only manifest itself relative to dexterity in action. Neurophysiologically, this would suggest that skilled athletes rely on interacting and complementary contributions from the ventral (perception) and dorsal (action) visual streams. Therefore ecological psychologists consider it impossible, or perhaps even misleading, to try capturing (or achieving) perceptual expertise in sport by examining (or practicing) perception on its own, decoupled from action.