My Hand or Yours? Markedly Different Sensitivity to Egocentric and Allocentric Views in the Hand Laterality Task

Abstract

In the hand laterality task participants judge the handedness of visually presented stimuli – images of hands shown in a variety of postures and views - and indicate whether they perceive a right or left hand. The task engages kinaesthetic and sensorimotor processes and is considered a standard example of motor imagery. However, in this study we find that while motor imagery holds across egocentric views of the stimuli (where the hands are likely to be one's own), it does not appear to hold across allocentric views (where the hands are likely to be another person's). First, we find that psychophysical sensitivity, d', is clearly demarcated between egocentric and allocentric views, being high for the former and low for the latter. Secondly, using mixed effects methods to analyse the chronometric data, we find high positive correlation between response times across egocentric views, suggesting a common use of motor imagery across these views. Correlations are, however, considerably lower between egocentric and allocentric views, suggesting a switch from motor imagery across these perspectives. We relate these findings to research showing that the extrastriate body area discriminates egocentric (‘self’) and allocentric (‘other’) views of the human body and of body parts, including hands.

Motor imagery in spinal cord injury patients: Moving makes the difference

“…First, we used accuracy instead of the classical measures such as reaction times. Implementing reaction times recording, maybe with the use of an eye‐tracking equipment, could allow to extract different types of indexes such as visual effects and laterality effects (Brady et al ., ). Secondly, future studies should enlarge the clinical categories of patients taken into account, also involving the type of deafferentation (i.e., complete and incomplete).…”

“…In other words, they do not present with a disadvantage in judging hands in positions violating the real limb constraints. In fact, the simulation of the movement of one's own internal body part representation, to fit it with a hand presented in an executable grasping posture (‘ simple postures’ ), is characterized by faster reaction times and higher accuracy than when the hand is presented in unusual postures (Brady et al ., ; Conson et al ., ; Gentilucci et al ., ,b; Parsons, , ). This effect is considered a specific hallmark of MI.…”

“…This effect consists in faster response times and higher accuracy in judging body parts displayed in a position easy to reach with a real movement, i.e. simple positions (Brady et al ., ; Conson et al ., ; Parsons, , ; Parsons, Gabrieli, Phelps, & Gazzaniga, ). Conversely, for stimuli orientated in position anatomically difficult to reach, that is unusual positions , there is a disadvantage leading to slower reaction times and lower accuracy (Parsons, , ; Parsons et al ., ; Sekiyama, ).…”

“…To this aim, we relied on a modified version of the Hand Laterality Task (HLT; Fiori et al ., ; Parsons, ,b). We focused on the effect of biomechanical constraints , rather than on a simple comparison between hand orientations, as the presence of this effect is an important index of a strategy based on the active process of internally representing a motor command without an effective overt movement (Brady et al ., ; Conson et al ., ; Jackson et al ., ; Parsons, ). Consequently, some evidences suggest that the lack of this effect is indicative that the task has not been carried out using a strategy based on the simulation of the movement, but rather by means of a general VI strategy (Conson et al ., ; Nico, Daprati, Rigal, Parsons, & Sirigu, ).…”

“…Then, participant's own body part internal representation is mentally rotated to reach the position of the target stimulus (Parsons, ,b), as a function of the action‐related knowledge and of the kinematic constraints of the real body segment (Gentilucci et al ., ,b; Parsons, , ; Parsons et al ., ; Sekiyama, ). Therefore, the ability of imaging a movement is necessarily conditioned by the effect of biomechanical constrains (Brady, Maguinness, & Ni Choisdealbha, ; Conson, Pistoia, Sara, Grossi, & Trojano, ; Parsons, , ). This effect consists in faster response times and higher accuracy in judging body parts displayed in a position easy to reach with a real movement, i.e.…”