Hand movement observation by individuals born without hands: phantom limb experience constrains visual limb perception

Abstract

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.

Interdependence of movement and anatomy persists when amputees learn a physiologically impossible movement of their phantom limb

“…1B). This is consistent with data from healthy participants-one normally perceives the hand moving between the two positions through the long, physiological movement if the rate at which the two images alternate is equal to or slower than the speed at which they can perform the movement themselves (13). After training, the four successful participants perceived the impossible movement regardless of the rate at which images alternated but only for images of the amputated side.…”

Projecting the self outside the body: Body representations underlying proprioceptive imagery

“…The Body and Proprioceptive Imagery 16 slower to mentally rotate their hands or feet into awkward postures than into postures that are biomechanically easier to achieve (Parsons, 1987(Parsons, , 1994Shenton et al, 2004;Funk et al, 2005). For example, judging the laterality of a picture of the palm of a hand orientated 90 o away from the medial axis (with the thumb pointing away from the body) is more difficult than for the same picture orientated towards the medial axis (Parsons, 1994).…”

“…Research has suggested that participants perform this task by mentally rotating their hand from its current posture to match the seen hand (Parsons, 1987). Indeed, when the posture of the participant's own hand does not match that of the picture, responses are slowed (Shenton, Schwoebel, & Coslett, 2004;Funk, Shiffrar, & Brugger, 2005;Ionta, Fourkas, Fiorio, & Aglioti, 2007). The…”

Incarnation and animation: physical versus representational deficits of body integrity

“…1). In a paradigm investigating "apparent motion of body parts" (Shiffrar and Freid 1990), we compared AZ's performance with that of CL, a 43-year-old journalist born without arms, but who had never experienced any phantom sensations (Funk et al 2005). In this paradigm, what is seen is determined by what can be performed with one's limbs.…”