Academic journal article Attention, Perception and Psychophysics

Perception of the End Position of a Limb Loaded with a Weight

Academic journal article Attention, Perception and Psychophysics

Perception of the End Position of a Limb Loaded with a Weight

Article excerpt

Published online: 9 November 2011

© Psychonomic Society, Inc. 2011

Abstract We examined the effect of loading a weight on the perception of the end position of the limb. The participants haptically perceived where the end of their limb was located while they swung the limb or statically held it. The results showed that the loading of a weight influenced participants' perception only when they swung the limb; when the weight was attached to a participant's hand, the position was perceived to be farther from the body than when the weight was attached to the forearm or no weight was attached. We also found that the end position was generally underestimated when the participants swung their limb. On the other hand, when the participants statically held their limb, the perceived position was not affected by the loading of the weight and was rather precise. These results suggest that the perceptual system for limb end position is sensitive to changes in the surrounding haptic information caused by moving the limb.

Keywords Dynamic touch . Haptic perception . Perception and action

The ability to haptically perceive the position of our body parts is very important in daily life. For example, it helps us control our body parts smoothly without visual information. The haptic perception of body position occurs through mechanical stimulation of the mechanoreceptors (e.g., muscle spindles and Golgi tendon organs) present in our muscles and tendons.

It has been reported that vibrations sent to muscles and tendons (de Vignemont, Ehrsson, & Haggard, 2005; Lackner, 1988; Longo, Kammers, Gomi, Tsakiris, & Haggard, 2009) can change the spatial perception of the size of a body part, as can anesthetization of a finger (Gandevia & Phegan, 1999). It is also possible to perceive sensations for body configurations that we have never experienced before (e.g., the Pinocchio illusion; Lackner, 1988). It can therefore be assumed that in addition to stored knowledge on body shape, information regarding online haptic stimulus changes is important in perceiving the shapes and spatial dimensions of our body (Pagano & Turvey, 1998).

It has been hypothesized that common information is used for the haptic perception of spatial dimensions of both body segments and rod-shaped objects because both are basically cylindrical in shape and the haptic perception of both is caused by the stimulation of mechanoreceptors (Pagano & Turvey, 1998; Turvey, 1996). For example, if the body segment from shoulder to fingertip is considered a rod, the length perception of the limb will be similar to that of a handheld rod.

The perception of the properties of handheld objects based on the stimulation of mechanoreceptors is called dynamic touch (Turvey, 1996). Many studies have investigated the length perception of a grasped rod by dynamic touch (e.g., Burton & Turvey, 1990; Carello, Santana, & Burton, 1996; Chan, 1994; Kingma, Beek, & van Dieën, 2002; Kingma, van de Langenberg, & Beek, 2004; Menger & Withagen, 2009; Solomon & Turvey, 1988; Stephen & Arzamarski, 2009; Stroop, Turvey, Fitzpatrick, & Carello, 2000; van de Langenberg, Kingma, & Beek, 2006). In the typical task used in these studies, participants had to perceive the far end position of a grasped rod while the rod was occluded from view by a screen. The manipulations in the studies were based on the resistance of the rods and took into account both rod mass and rod mass distribution. The length perception of a grasped rod changes depending on the manipulation of the mass distribution, even if the mass and rod length remain the same. For example, when a weight is attached to the rod farther away from the rotational point (e.g., the wrist), the perceived rod length is longer (i.e., the perceived end position is farther) than when the weight is attached closer to the rotational point, because resistance to rotational accelerations is larger in the former case. …

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