Reconsidering the role of movement in perceiving action-scaled affordances

Many locomotor tasks require actors to choose among different categories of action, such as when deciding whether to cross the street in front of an approaching vehicle or wait until it passes. In such cases, the actor’s locomotor capabilities partly determine which actions are possible, and therefore must be taken into account. The present study was designed to re-evaluate the claim that people do not know their locomotor capabilities until they begin moving because they rely entirely on information that is picked up “on the fly” (Oudejans, Michaels, Bakker, & Dolné, 1996). Three experiments were conducted in which participants judged while stationary or moving whether it was within their capabilities to catch a fly ball or pass through a shrinking gap. The main finding was that judgments were equally accurate regardless of whether participants were stationary or allowed to move for a brief period. We conclude that stationary and moving actors know their locomotor capabilities equally well, and that actors do not rely entirely on information that is picked up on the fly.     

Doggone affordances: Canine perception of affordances for reaching

Performing any behavior requires perceiving affordances—whether and how that behavior can be performed. Perception of affordances exhibits action scaling—choices about when to transition between two different modes of behavior reflect the fit between action capabilities and environmental properties. The boundary between distances that are perceived to be reachable with an arm-only reach and those that are perceived to be reachable with an arm-plus-torso reach occurs at farther distances for long-armed than for short-armed people, but at the same ratio of object-distance-to-arm length for both groups. To the extent that perception of affordances is supported by detection of invariant stimulation patterns, perception of a given affordance ought to exhibit action scaling regardless of species. We investigated the heights at which dogs chose to transition from reaching with the head only to rearing (i.e., reaching with the head plus torso). This transition occurred at a taller height for tall than for short dogs, but at the same ratio of shoulder-height-to-treat-height for both groups. The results demonstrate a similarity in perception of affordances across species and suggest that perception of affordances is supported by detection of lawfully structured stimulation patterns that may be invariant across species.     

The perception of shrinking in apparent motion

Apparent motion was produced using two triangular patterns of different sizes, each exposed for 100 msec, with a 50-msec interstimulus interval and 200-msec recycle interval. The triangles were aligned either on center or on the midpoints of the bases. Experiment 1, filled, outline, and three-dot triangles were viewed over four backgrounds: a blank illuminated field, and texture gradients constructed from horizontal lines, perspective lines, or a combination of these (full texture). In Experiment 2, outline and dot triangles were presented in one of three orientations: base down, base right, and base up over a blank background. Subjects made two forced-choice responses: apparent size was categorized as shrinking or not shrinking, and apparent motion was categorized as motion in depth or motion in a fixed frontal plane. The type of alignment was the major determiner of responses. When the midpoints of the base were aligned, the predominant response described a shrinking object in a fixed-position in depth. When the centers were aligned, the predominant response described an object of constant size moving in depth.     

The perception of shrinking in apparent motion.

Apparent motion was produced using two triangular patterns of different sizes, each exposed for 100 msec, with a 50-msec interstimulus interval and 200-msec recycle interval. The triangles were aligned either on center or on the midpoints of the bases. In Experiment 1, filled, outline, and three-dot triangles were viewed over four backgrounds: a blank illuminated field, and texture gradients constructed from horizontal lines, perspective lines, or a combination of these (full texture). In Experiment 2, outline and dot triangles were presented in one of three orientations: base down, base right, and base up over a blank background. Subjects made two forced-choice responses: apparent size was categorized as shrinking or not shrinking, and apparent motion was categorized as motion in depth or motion in a fixed frontal plane. The type of alignment was the major determiner of responses. When the midpoints of the base were aligned, the predominant response described a shrinking object in a fixed position in depth. When the centers were aligned, the predominant response described an object of constant size moving in depth.     

Visual and haptic perception of postural affordances in children and adults

The present study compared how children and adults perceived affordances for upright stance when information was available either visually or haptically. 12 adults (mean age=26.5 years) and 13 children (mean age=4.5 years) examined an adjustable wooden platform that was randomly set at five different degrees of inclination (17, 22, 27, 33, 39). In the haptic condition, a masking curtain excluded vision of the platform and the surface was explored with a hand-held, wooden dowel. Results showed that for both children and adults there was closer agreement between perceptual judgments and action capabilities in the visual condition. Children overestimated their ability to stand on the steeper slopes, took equal amounts of time to make their judgments across all slopes, and were equally confident in their judgments across all slopes. In contrast, adults were more accurate than children at judging the affordances for upright stance, took longer to respond close to the actual action boundary, and were less confident close to the action boundary. Furthermore, adults took longer to respond and were less confident in the haptic condition whereas children had similar response times and were equally confident in both conditions. These important differences between adults and children in the perception of a basic affordance are discussed with reference to the coupling between perception and action at different phases of the lifespan and to the factors that might influence the organization of this coupling. Finally, implications are drawn for the prevention of accidents and the promotion of basic motor competence in children.     

Changing affordances in stair climbing: the perception of maximum climbability in young and older adults.

This experiment extended Warren's leg-length model by investigating the relevance of leg strength and joint flexibility on perceptual judgments of climbability. From a set of 8 stairs (riser heights: 38-91 cm), 24 older and 24 young adults were asked to identify the highest stair they could climb without using their hands or knees. Ss then attempted to climb the selected stair. Tall and short young observers perceived similar action boundaries despite leg-length differences. Tall and short older adults had divergent action boundaries when a single-scale leg-length model was applied. A regression model that used flexibility and leg-strength measurements provided a better fit of the older adult data, indicating that models applying functional (kinematic and kinetic) criteria might be useful in describing lawful relationships between organisms and the environment.     

Direct perception and the predictive mind

Predictive approaches to the mind claim that perception, cognition, and action can be understood in terms of a single framework: a hierarchy of Bayesian models employing the computational strategy of predictive coding. Proponents of this view disagree, however, over the extent to which perception is direct on the predictive approach. I argue that we can resolve these disagreements by identifying three distinct notions of perceptual directness: psychological, metaphysical, and epistemological. I propose that perception is plausibly construed as psychologically indirect on the predictive approach, in the sense of being constructivist or inferential. It would be wrong to conclude from this, however, that perception is therefore indirect in a metaphysical or epistemological sense on the predictive approach. In the metaphysical case, claims about the inferential properties of constructivist perceptual mechanisms are consistent with both direct and indirect solutions to the metaphysical problem of perception (e.g. naïve realism, representationalism, sense datum theory). In the epistemological case, claims about the inferential properties of constructivist perceptual mechanisms are consistent with both direct and indirect approaches to the justification of perceptual belief. In this paper, I demonstrate how proponents of the predictive approach have conflated these distinct notions of perceptual directness and indirectness, and I propose alternative strategies for developing the philosophical consequences of the approach.     

Direct perception in the intersubjective context

This paper, in opposition to the standard theories of social cognition found in psychology and cognitive science, defends the idea that direct perception plays an important role in social cognition. The two dominant theories, theory theory (TT) and simulation theory (ST), both posit something more than a perceptual element as necessary for our ability to understand others, i.e., to “mindread” or “mentalize.” In contrast, certain phenomenological approaches depend heavily on the concept of perception and the idea that we have a direct perceptual grasp of the other person’s intentions, feelings, etc. This paper explains precisely what the notion of direct perception means, offers evidence from developmental studies, and proposes a non-simulationist interpretation of the neuroscience of mirror systems.     

The effect of gap depth on the perception of whether a gap is crossable

Four experiments were performed in order to examine the effect of gap depth on human observers’ perception of whether or not a gap is crossable. Experiments 1 and 2 showed that as the gap’s depth increased, observers tended to increasingly underestimate the maximum width of a gap they could step across. Experiments 3 and 4 clarified this finding: The observed covariation of perceived gap crossability and gap depth depended on the observer’s direction of gaze, rather than on the physical depth of the gap. The optical relations to which observers might be attending are discussed, as well as the possibility that cognitive-affective processes might have contributed to observers’ underestimation of their actual capabilities.     

Haptically creating affordances: the user-tool interface

Successful use of a hand-held tool requires overcoming the rotational inertia of the hand-plus-tool system. Where an object is grasped affects this rotational inertia. Appropriate choice of grip position may be crucial in the safe, effective, and efficient control of a hand-held tool. In 3 experiments, the authors investigated how choice of grip position on a tool was constrained by task demands. The results suggest that choice of grasp position serves to establish relationships among 3 variables derived from the inertial ellipsoid of the hand-object system (volume, symmetry, and eigenvector angle) in a way that specifically reflected the power or precision constraints of the given task. These variables have previously been shown to play a role in haptic perception of tool function. Changing grasp position on a tool is a way to exert control over the nuances of the user-tool interface.     

Direct and indirect perception of size

Three experiments, using a reaction time paradigm, examine the direct (stimulus bound) and indirect (mediational inference) approaches to size perception. Subjects determine which of two stimuli is the larger when the two can be at different egocentric distances. The effects of two variables on reaction times are examined—distal ratio, the ratio of physical sizes of the stimuli, and proximal ratio, the ratio of the angular projections of the stimuli on the retina. In Experiment 1, both ratios are found to affect reaction times, with the proximal ratios yielding the larger effect, more in line with the predictions of the indirect approach. But the results of Experiments 2 and 3 indicate that distance is taken into greater account, the more similar the distal sizes of the stimuli. In one stimulus condition, distance appears not to affect reaction times. It is suggested that direct size perception occurs for large stimulus differences, indirect size perception for smaller differences. The identical results of the two experiments, one with and one without texture, point to some variable other than texture occlusion or interception as the stimulus for direct size perception. Some aspect of distance from the eye-level plane is suggested as an alternative.     

Direct perception in context: radical empiricist reflections on the medium

Synthese - Radical empiricists at the turn of the twentieth century described organisms as experiencing the relations they maintain with their surroundings prior to any analytic separation from...     

Kinetic potential influences visual and remote haptic perception of affordances for standing on an inclined surface

The ability of a perceiver–actor to perform a particular behaviour depends on their ability to generate and control the muscular forces required to perform that behaviour. If an intended behaviour is to be successful, perception must be relative to this ability. We investigated whether perceiver–actors were sensitive to how changes in their mass distribution influenced their ability to stand on an inclined surface. Participants reported whether they would be able to stand on an inclined surface while wearing a weighted backpack on their back, while wearing a weighted backpack on their front, and while not wearing a weighted backpack. In addition, participants performed this task by either viewing the surface or exploring it with a hand-held rod (while blindfolded). The results showed that perception of affordances for standing on the inclined surface depended on how the backpack influenced the ability of the participant to stand on the surface. Specifically, perceptual boundaries occurred at steeper inclinations when participants wore the backpack on their front than when they wore it on their back. Moreover, this pattern occurred regardless of the perceptual modality by which the participants explored the inclined surface.     

The perception of offset: A problem of decision criteria

Robinson (1974) has presented a simple form of a hypothesis which assumes that the sensory response to a stimulus persists for a period of time exceeding its physical duration. He uses this hypothesis to predict Efron’s (1970) results concerning the delayed perception of offset of brief stimuli. We propose a natural extension of this hypothesis that assumes that each subject adopts a “personal” criterion in order to judge offset. This model not only provides predictions consistent with Efron’s data, but can also predict data of quite dissimilar appearance, including the data of the present study.

     

Balance of power and the problem of perception 1

The concept of balance of power can have considerable heuristic and explanatory power over the full range of conflict systems. But the concept requires analysis, to clarify both what it means and the conditions under which it can obtain. An empirically faithful analysis of ‘balance of power’ must take account of, among other things, the perceptions the opposing parties have of one another. These perceptions have structural and psychological determinants, and an analysis of their operations in power systems provides a necessary part of the analysis of ‘balance of power’. In terms of the frame of reference employed it is concluded that there is only one situation in which balance might obtain, though not for any length of time.