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"Shiffrar, Maggie"
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Fitts's Law Holds for Action Perception
Fitts's law is one of the most well-established principles in psychology. It captures the relation between speed and accuracy in performed and imagined movements. The aim of this study was to determine whether this law also holds during the perception of other people's actions. Subjects were shown apparent motion displays of a person moving his arm between two identical targets. Target width, the separation between targets, and movement speed were varied. Subjects reported whether the person could move at the perceived speed without missing the targets. The movement times reported as being just possible were exactly those predicted by Fitts's law (r² = .96). A subsequent experiment demonstrated the same lawful relation for the perception of a robot arm (r² = .93). To our knowledge, this makes Fitts's law the first motor principle that holds in imagery and the perception of biological and nonbiological agents.
Journal Article
Hand movement observation by individuals born without hands: phantom limb experience constrains visual limb perception
Increasing evidence suggests that the visual analysis of other people's actions depends upon the observer's own body representation or schema. This raises the question of how differences in observers' body structure and schema impact their perception of human movement. We investigated the visual experiences of two persons born without arms, one with and the other without phantom sensations. These participants, plus six normally-limbed control observers, viewed depictions of upper limb movement under conditions of apparent motion. Consistent with previous results (Shiffrar M, Freyd JJ (1990) Psychol Sci 1:257), normally-limbed observers perceived rate-dependent paths of apparent human movement. Specifically, biologically impossible motion trajectories were reported at rapid display rates while biologically possible trajectories were reported at slow display rates. The aplasic individual with phantom experiences showed the same perceptual pattern as control participants, while the aplasic individual without phantom sensations did not. These preliminary results suggest that phantom experiences may constrain the visual analysis of the human body. These results further suggest that it may be time to move beyond the question of whether aplasic phantoms exist and instead focus on the question of why some people with limb aplasia experience phantom sensations while others do not. In this light, the current results suggest that somesthetic representations are not sufficient to define body schema. Instead, neural systems matching action observation, action execution and motor imagery likely contribute to the definition of body schema in profound ways. Additional research with aplasic individuals, having and lacking phantom sensations, is needed to resolve this issue.
Journal Article
Detecting deception in a bluffing body: The role of expertise
Studies of deception detection traditionally have focused on verbal communication. Nevertheless, people commonly deceive others through nonverbal cues. Previous research has shown that intentions can be inferred from the ways in which people move their bodies. Furthermore, motor expertise within a given domain has been shown to increase visual sensitivity to other people’s movements within that domain. Does expertise also enhance deception detection from bodily movement? In two psychophysical studies, experienced basketball players and novices attempted to distinguish deceptive intentions (fake passes) and veridical intentions (true passes) from an observed individual’s actions. Whereas experts and novices performed similarly with postural cues, only experts could detect deception from kinematics alone. These results demonstrate a link between action expertise and the detection of nonverbal deception.
Journal Article
The visual perception of motion by observers with autism spectrum disorders: A review and synthesis
Traditionally, psychological research on autism spectrum disorder (ASD) has focused on social and cognitive abilities. Vision provides an important input channel to both of these processes, and, increasingly, researchers are investigating whether observers with ASD differ from typical observers in their visual percepts. Recently, significant controversies have arisen over whether observers with ASD differ from typical observers in their visual analyses of movement. Initial studies suggested that observers with ASD experience significant deficits in their visual sensitivity to coherent motion in random dot displays but not to point-light displays of human motion. More recent evidence suggests exactly the opposite: that observers with ASD do not differ from typical observers in their visual sensitivity to coherent motion in random dot displays, but do differ from typical observers in their visual sensitivity to human motion. This review examines these apparently conflicting results, notes gaps in previous findings, suggests a potentially unifying hypothesis, and identifies areas ripe for future research.
Journal Article
Apparent Motion of the Human Body
Observers viewed pairs of alternating photographs of a human body in different positions. Shortest-path motion solutions were pitted against anatomically possible movements. With short stimulus onset asynchronies (SOAs), observers tended to report the shortest path despite violations of anatomical constraints. However, with longer SOAs observers became increasingly likely to report the anatomically possible, but longer, paths. This finding, in conjunction with those from a second study, challenges the accepted wisdom that apparent motion paths are independent of the object. Instead, our findings suggest that when given enough time and appropriate stimuli, the visual system prefers at least some object-appropriate apparent motion paths.
Journal Article
Expecting to lift a box together makes the load look lighter
The action abilities of an individual observer modulate his or her perception of spatial properties of the environment and of objects. The present study investigated how joint action abilities shape perception. Four experiments examined how the intention to lift an object with another individual affects perceived weight. In Experiments 1, 2a, and 2b, participants judged the perceived weight of boxes while expecting to lift them either alone or with a co-actor. In Experiment 3, the co-actor was healthy or injured. Participants intending to lift a box with a co-actor perceived the box as lighter than participants intending to lift the same box alone, provided that the co-actor appeared healthy and therefore capable of helping. These findings suggest that anticipated effort modulates the perception of object properties in the context of joint action. We discuss implications for the role of action prediction and action simulation processes in social interaction.
Journal Article
Perception, as you make it
The main question that Firestone & Scholl (F&S) pose is whether “what and how we see is functionally independent from what and how we think, know, desire, act, and so forth” (sect. 2, para. 1). We synthesize a collection of concerns from an interdisciplinary set of coauthors regarding F&S's assumptions and appeals to intuition, resulting in their treatment of visual perception as context-free.
Journal Article