Visually Controlled Locomotion: Its Dependence on Optic Flow,Three-Dimensional Space Perception,and Cognition

Gibson (1958/this issue) and his followers have emphasized the role of optic flow in the control of locomotion. In recent years much research has been devoted to the visual control of aiming and braking, mainly in connection with terrestrial locomotion. The goal of this article is to broaden the topic empirically and theoretically. At the empirical level, we argue that there are a number of visually controlled maneuvers that need to be addressed for their own sake, for they involve more than can be learned from research on aiming and braking. At the theoretical level, we argue that optic flow needs to be supplemented by other explanatory primitives, including the actor's perception of three-dimensional spatial layout and the actor's cognitive representations of the spatial envelope and plant dynamics of his or her body or vehicle.     

Use of landmarks and allocentric reference frames for the control of locomotion

In the present study we assessed the use of landmarks and scene layout information for the control of locomotion. Observers were presented displays simulating forward locomotion through a random dot field with the horizontal position perturbed by a sum-of-sines function and were asked to steer and null out the horizontal disturbance of the path of locomotion. The results indicate greater control gain and accuracy when presented with a repeating layout of landmarks as compared to a changing layout of landmarks. Debriefing responses suggest that observers may have implicitly learned the layout of the repeating pattern. These results suggest that observers use an allocentric representation of the scene for steering control. A model for the control of locomotion is discussed that utilizes both scene-based information and optic flow.     

What Is an Affordance?

What should and should not be considered an affordance is still an open issue. At the 2002 North American meeting of the International Society for Ecological Psychology, a symposium was held concerning this topic. The articles in this special issue are expanded versions of the papers presented at that symposium. To set the stage for those discussions, this article presents an analysis of the evolution of J. J. Gibson's thinking on this issue, from some of his earliest writings (i.e., J. J. Gibson & Crooks, 1938) through his most recent writings (i.e., J. J. Gibson, 1979/1986). It is hoped that this forum will stimulate thinking concerning this important ecological concept.     

How Is Human Gait Controlled by Vision

In his seminal article, Gibson (1958/this issue) laid the foundation for understanding the visuomotor transformations necessary for adaptive locomotor behavior. In this article, I review the work on visual control of locomotion done in our lab in Waterloo and discuss some new experiments. The major findings are put forward as three new postulates. Postulate 1: Visual exteroceptive information about the environment is used in a sampled, feed-forward mode to control locomotion. Postulate 2: Visual exproprioceptive information about the posture and movement of the lower limb is used in a sampled, online mode to control the swing phase trajectory. Postulate 3: Visual exproprioceptive information about self-motion is used in a sampled, online mode to control locomotion. Our results in most cases provide empirical support for the many insightful postulates of Gibson, in some cases amplify his statements, and in a few cases add to our understanding of how we get about by vision.     

From Gibson and Crooks to Damasio: The role of psychology in the development of driver behaviour models

This article presents a brief history and perspective of behavioural model development in traffic psychology. As one specific example of a key behavioural model, Gibson and Crooks (1938), in their classic field theoretical study, offered the first scientific attempt to deal with the issue of compensation. Two central theoretical concepts were developed: “Field of safe travel” and “Minimum stopping zone”. The interplay between the two was used to describe and explain risk compensation and illustrated by observing the impact of brakes on driver behaviour: Better brakes could make the field of safe travel – i.e. the distance to the car in front – shorter. Nearly 50 years later, the launch of Wilde’s Risk Homeostasis Theory (RHT) gave rise to a profound debate about risk homeostasis and risk compensation. The core issue in the debate was Wilde’s strict assertion that all individuals, not only car-drivers, carry an inherent target level of risk that they are seeking to maintain or restore. Gibson and Crooks fell well within psychological theories of the time, while Wilde’s RHT emerged more from control theory and economic utility theory than from psychology. In the 1990s neuroscience emerges, especially by Damasio who introduces a paradigm that has proven fruitful as a framework of more recent driver behaviour models. But neuroscience also had its forerunner in Taylor’s proposal that driver behaviour is governed by a constancy in Galvanic Skin Response (GSR) which makes driving a self-paced task aiming at keeping the GSR at a constant level. Näätänen and Summala’s integrated Taylor in their “Zero-risk model” which has persisted and still prevails as a solid and well accepted model. Psychological learning theory has, however, rarely been adequately dealt with which is quite odd given the prevalence of speeding and risk compensation which cannot escape explanations based on operant conditioning. The paper discusses the emerging role of psychology and psychological concepts that has been proposed and evolved through the development of driver behaviour models since Gibson and Crooks’ study of 1938. The views presented are subjective, they do not represent any attempt to describe the objective reality of the time.     

Stability in young infants' discrimination of optic flow

Although considerable progress has been made in understanding how adults perceive their direction of self-motion, or heading, from optic flow, little is known about how these perceptual processes develop in infants. In 3 experiments, the authors explored how well 3- to 6-month-old infants could discriminate between optic flow patterns that simulated changes in heading direction. The results suggest that (a) prior to the onset of locomotion, the majority of infants discriminate between optic flow displays that simulate only large (> 22 deg.) changes in heading, (b) there is minimal development in sensitivity between 3 and 6 months, and (c) optic flow alone is sufficient for infants to discriminate heading. These data suggest that spatial abilities associated with the dorsal visual stream undergo prolonged postnatal development and may depend on locomotor experience.     

Tactile suppression in goal-directed movement

Sharing numerous characteristics with suppression in the other senses, tactile suppression is a reliable phenomenon that accompanies movement. By investigating the simplest of movements (e.g., finger flexions), early research tried to explain the origins of the phenomenon in terms of motor command generation together with sensory reafference. Here, we review recent research that has delved into (naturalistic) goal-directed movements. In connection with goal-directed movement, tactile suppression is evident as a decrease in behavioural performance measured shortly prior to, and during, movement execution. It is also reflected in a consistent response bias highlighting the (perceptual) uncertainty of the movement. Goal-directed movement supports the forward model and establishes contextual influences as the defining influences on tactile suppression. Depending on the task at hand, people prioritize a certain percept during movement. Future research, we argue, should focus on studying naturalistic movements, or sequences of movements, that share a common meaning or goal.     

知觉场理论对面孔知觉年龄偏差效应的解释

使用融合面孔范式和倒置面孔范式来研究面孔知觉的年龄偏差效应,检验知觉场能否作为面孔整体加工的指标,并以此发展年龄偏差的整体加工解释。结果发现：（1）成人和儿童在加工正立面孔时的知觉场均大于加工倒置面孔时的知觉场;（2）在加工正立面孔时,成人加工本年龄面孔比加工他年龄面孔的知觉场更大。上述结果表明：（1）知觉场大小可以作为面孔整体加工的指标,且受面孔朝向的影响;（2）知觉场假设可以解释面孔的年龄偏差效应。     

Judgments of path, not heading, guide locomotion

To steer a course through the world, people are almost entirely dependent on visual information, of which a key component is optic flow. In many models of locomotion, heading is described as the fundamental control variable; however, it has also been shown that fixating points along or near one's future path could be the basis of an efficient control solution. Here, the authors aim to establish how well observers can pinpoint instantaneous heading and path, by measuring their accuracy when looking at these features while traveling along straight and curved paths. The results showed that observers could identify both heading and path accurately (approximately 3 degrees ) when traveling along straight paths, but on curved paths they were more accurate at identifying a point on their future path (approximately 5 degrees ) than indicating their instantaneous heading (approximately 13 degrees ). Furthermore, whereas participants could track changes in the tightness of their path, they were unable to accurately track the rate of change of heading. In light of these results, the authors suggest it is unlikely that heading is primarily used by the visual system to support active steering.     

知觉场理论对面孔知觉年龄偏差效应的解释

使用融合面孔范式和倒置面孔范式来研究面孔知觉的年龄偏差效应,检验知觉场能否作为面孔整体加工的指标,并以此发展年龄偏差的整体加工解释。结果发现：（1）成人和儿童在加工正立面孔时的知觉场均大于加工倒置面孔时的知觉场;（2）在加工正立面孔时,成人加工本年龄面孔比加工他年龄面孔的知觉场更大。上述结果表明：（1）知觉场大小可以作为面孔整体加工的指标,且受面孔朝向的影响;（2）知觉场假设可以解释面孔的年龄偏差效应。     

The flip side of perception-action coupling: locomotor experience and the ontogeny of visual-postural coupling.

The possible role of motor development on psychological function is once again a topic of great theoretical and practical importance. The revival of this issue has stemmed from a different approach to the topic, away from Gesell's interest in the long-term prediction of psychological functions from early motoric assessments, toward an attempt to understand how the acquisition of motor skills orchestrates psychological changes. This paper describes how the acquisition of one motor skill, prone locomotion, has been linked to developmental changes in an infant's ability to regulate posture based on information available in patterns of optic flow. It is argued that the onset of prone locomotion presses the infant to differentiate spatially delimited regions of optic flow to effectively and efficiently control the important subtasks nested within the larger task of locomotion, namely, steering, attending to the surface of support, and maintaining postural control. Following this argument, a research program is described that aims to determine if locomotor experience is causally linked to improvements in the ability to functionalize peripheral optic flow for postural control or whether locomotor experience is merely a maturational forecaster of such improvements. Finally, a hypothesis is put forward that links the emergence of wariness of heights to infants' ability to regulate posture on the basis of peripheral optic flow. The paper's overarching theoretical point is the principle of probabilistic epigenesis, which states that one developmental acquisition produces experiences that bring about a host of new developmental changes in the same and different domains.     

1966 and All That: James Gibson and Bottom-Down Theory

ABSTRACT

The “later” James Gibson is widely misrepresented as an extreme stimulus–response theorist. In fact, Gibson's 1966 book presents a radical alternative to stimulus–response theory. “Perceptual systems” are not passive and receptive but “organs of active attention” (1966/1968, p. 58). Perceivers “reach out” into the world. This commentary examines some of the implications of Gibson's systems-cum-functionalist-cum-ecological approach, including the relations between the senses; the concept of “sensationless” perception; and most fundamentally, the nature of perceptual systems as extending beyond the body. I conclude that an adequate understanding of perception cannot be limited to the already severely limited domain of psychology. If Gibson is right, “ecological psychology” is a contradiction in terms.     

Meta-Invariant Structure in Stimulus Arrays: A Response to Mace's Zetetic Challenge to Ecological Perceptual Researchers

ABSTRACT

Ecological perception, per James Gibson's theory, avows that perception depends on informative structure in stimulus arrays, where information is defined as stimulus array invariants. Gibson, however, was somewhat vague about the nature of such structure. Consequently, ecological perceptual research—even acknowledging some remarkable successes—has generally been ad hoc: Lacking principled heuristics, researchers examine array structure, which, by some means, they have come to discover as (or believe to be) informative. Here, I propose a series of heuristic principles potentially useful for the discovery of informative structure in stimulus arrays, with examples to suggest how those principles might apply. The major benefit of principled search for stimulus array invariants is more efficient elaboration of their function in perception. While admittedly preliminary, the principles outlined may both guide perceptual investigations and prompt additional consideration of how to approach the search for stimulus array invariants.     

Separating perceptual processes from decisional processes in identification and categorization

Four observers completed perceptual matching, identification, and categorization tasks using separable-dimension stimuli. A unified quantitative approach relating perceptual matching, identification, and categorization was proposed and tested. The approach derives from general recognition theory (Ashby & Townsend, 1986) and provides a powerful method for quantifying the separate influences of perceptual processes and decisional processes within and across tasks. Good accounts of the identification data were obtained from an initial perceptual representation derived from perceptual matching. The same perceptual representation provided a good account of the categorization data, except when selective attention to one stimulus dimension was required. Selective attention altered the perceptual representation by decreasing the perceptual variance along the attended dimension. These findings suggest that a complete understanding of identification and categorization performance requires an understanding of perceptual and decisional processes. Implications for other psychological tasks are discussed.     

The influence of anxiety on processing capacity for threat detection

In the present study, we explored the proposition that an individual’s capacity for threat detection is related to his or her trait anxiety. Using a redundant signals paradigm with concurrent measurements of reaction times and eye movements, participants indicated the presence or absence of an emotional target face (angry or happy) in displays containing no targets, one target, or two targets. We used estimates of the orderings on the hazard functions of the RT distributions as measures of processing capacity (Townsend & Ashby, 1978; Wenger & Gibson, Journal of Experimental Psychology. Human Perception and Performance, 30,708–719, 2004) to assess whether self-reported anxiety and the affective state of the face interacted with the level of perceptual load (i.e., the number of targets). Results indicated that anxiety was associated with fewer eye movements and increased processing capacity to detect multiple (vs. single) threatening faces. The data are consistent with anxiety influencing threat detection via a broadly tuned attentional mechanism (Eysenck, Derakshan, Santos, & Calvo, Emotion, 7,336–353, 2007).     

The influence of visual flow and perceptual load on locomotion speed

Visual flow is used to perceive and regulate movement speed during locomotion. We assessed the extent to which variation in flow from the ground plane, arising from static visual textures, influences locomotion speed under conditions of concurrent perceptual load. In two experiments, participants walked over a 12-m projected walkway that consisted of stripes that were oriented orthogonal to the walking direction. In the critical conditions, the frequency of the stripes increased or decreased. We observed small, but consistent effects on walking speed, so that participants were walking slower when the frequency increased compared to when the frequency decreased. This basic effect suggests that participants interpreted the change in visual flow in these conditions as at least partly due to a change in their own movement speed, and counteracted such a change by speeding up or slowing down. Critically, these effects were magnified under conditions of low perceptual load and a locus of attention near the ground plane. Our findings suggest that the contribution of vision in the control of ongoing locomotion is relatively fluid and dependent on ongoing perceptual (and perhaps more generally cognitive) task demands.     

What factors determine the preferred gait transition speed in humans? A review of the triggering mechanisms

Human locomotion is a fundamental skill that is required for daily living, yet it is not completely known how human gait is regulated in a manner that seems so effortless. Gait transitions have been analyzed to gain insight into the control mechanisms of human locomotion since there is a known change that occurs as the speed of locomotion changes. Specifically, as gait speed changes, there is a spontaneous transition between walking and running that occurs at a particular speed. Despite the growing body of research on the determinants of this preferred transition speed and thus the triggering mechanisms of human gait transitions, a clear consensus regarding the control mechanisms of gait is still lacking. Therefore, this article reviews the determinants of the preferred transition speed using concepts of the dynamic systems theory and how these determinants contribute to four proposed triggers (i.e. metabolic efficiency, mechanical efficiency, mechanical load and cognitive and perceptual) of human gait transitions. While individual anthropometric and strength characteristics influence the preferred transition speed, they do not act to trigger a gait transition. The research has more strongly supported the mechanical efficiency and mechanical load determinants as triggering mechanisms of human gait transitions. These mechanical determinants, combined with cognitive and perceptual processes may thus be used to regulate human gait patterns through proprioceptive and perceptual feedback as the speed of locomotion changes.     

Effects of optic flow on the kinematics of human gait: a comparison of young and older adults

This experiment studied the effect of imposed optic flow on human locomotion. Six young and 6 older adults were exposed to various patterns of optic flow while walking in a moving hallway. Results showed few cases of impaired postural control (staggers, parachute reactions). No falls were recorded. Kinematic patterns of gait were altered when vision was absent or inconsistent optic flow was presented: Ninety two percent of the subjects' mean step velocity differed from their step velocities under normal vision. Compared with imposed central flow, peripheral optic flow was not dominant in inducing kinematic changes. Characteristic gait profiles were obtained, depending on flow direction. Global backward flow tended to slow down step velocity, whereas subjects' step velocity increased during conditions of forward flow. The results suggest that subjects attempted to match their own walking speed to the velocity of the moving visual scenes. It is concluded that in an uncluttered environment, imposed optic flow has a modulating rather than a destabilizing effect on human locomotion.     

Path integration from optic flow and body senses in a homing task

We examined the roles of information from optic flow and body senses (eg vestibular and proprioceptive information) for path integration, using a triangle completion task in a virtual environment. In two experiments, the contribution of optic flow was isolated by using a joystick control. Five circular arenas were used for testing: (B) both floor and wall texture; (F) floor texture only, reducing information for rotation; (W) wall texture only, reducing information for translation; (N) a no texture control condition, and (P) an array of posts. The results indicate that humans can use optic flow for path integration and are differentially influenced by rotational and translational flow. In a third experiment, participants actively walked in arenas B, F, and N, so body senses were also available. Performance shifted from a pattern of underturning to overturning and exhibited decreased variability, similar responses with and without optic flow, and no attrition. The results indicate that path integration can be performed by integrating optic flow, but when information from body senses is available it appears to dominate.