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How Weight Affects the Perceived Spacing between the Thumb and Fingers during Grasping.

Butler AA, Héroux ME, Gandevia SC - PLoS ONE (2015)

Bottom Line: Results for perceived grasp aperture were compared with changes in perceived weight of objects of different sizes (5.2, 6.6, and 10 cm) but the same weight (600 g).For objects of the same weight but different widths, perceived weight decreased 42.3% [38.2 ‒ 46.4] from narrowest to widest (P < 0.001), as expected from the size-weight illusion.Given the small magnitude of this 'weight-grasp aperture' illusion, we propose the brain has access to a relatively stable 'perceptual ruler' to aid the manipulation of different objects.

View Article: PubMed Central - PubMed

Affiliation: Neuroscience Research Australia and University of New South Wales, Sydney, Australia.

ABSTRACT
We know much about mechanisms determining the perceived size and weight of lifted objects, but little about how these properties of size and weight affect the body representation (e.g. grasp aperture of the hand). Without vision, subjects (n = 16) estimated spacing between fingers and thumb (perceived grasp aperture) while lifting canisters of the same width (6.6cm) but varied weights (300, 600, 900, and 1200 g). Lifts were performed by movement of either the wrist, elbow or shoulder to examine whether lifting with different muscle groups affects the judgement of grasp aperture. Results for perceived grasp aperture were compared with changes in perceived weight of objects of different sizes (5.2, 6.6, and 10 cm) but the same weight (600 g). When canisters of the same width but different weights were lifted, perceived grasp aperture decreased 4.8% [2.2 ‒ 7.4] (mean [95% CI]; P < 0.001) from the lightest to the heaviest canister, no matter how they were lifted. For objects of the same weight but different widths, perceived weight decreased 42.3% [38.2 ‒ 46.4] from narrowest to widest (P < 0.001), as expected from the size-weight illusion. Thus, despite a highly distorted perception of the weight of objects based on their size, we conclude that proprioceptive afferents maintain a reasonably stable perception of the aperture of the grasping hand over a wide range of object weights. Given the small magnitude of this 'weight-grasp aperture' illusion, we propose the brain has access to a relatively stable 'perceptual ruler' to aid the manipulation of different objects.

No MeSH data available.


Related in: MedlinePlus

Relationship between actual and perceived grasp aperture (experiment 1), and actual and perceived weight (experiment 2).A, the relationship between actual and perceived grasp aperture for the three canisters of the same weight (600 g) but different width (5.2, 6.6, 10 cm). Data are presented as mean [95%CI]. Actual and perceived grasp aperture were linearly related with a mean R2 value of 0.99 [0.99 ‒ 1.00]. The dashed line is the line of identity. On average, grasp aperture was underestimated. B, the relationship between actual and perceived canister weight for the three canisters of the same width (6.6 cm) but different weight (300, 600, 900 g). Actual and perceived weight were linearly related with a mean R2 value of 0.98 [0.97 ‒ 0.99]. Data are presented as mean [95% CI] and the dashed line is the line of identity. On average, canister weight was underestimated.
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pone.0127983.g002: Relationship between actual and perceived grasp aperture (experiment 1), and actual and perceived weight (experiment 2).A, the relationship between actual and perceived grasp aperture for the three canisters of the same weight (600 g) but different width (5.2, 6.6, 10 cm). Data are presented as mean [95%CI]. Actual and perceived grasp aperture were linearly related with a mean R2 value of 0.99 [0.99 ‒ 1.00]. The dashed line is the line of identity. On average, grasp aperture was underestimated. B, the relationship between actual and perceived canister weight for the three canisters of the same width (6.6 cm) but different weight (300, 600, 900 g). Actual and perceived weight were linearly related with a mean R2 value of 0.98 [0.97 ‒ 0.99]. Data are presented as mean [95% CI] and the dashed line is the line of identity. On average, canister weight was underestimated.

Mentions: Subjects were able to discriminate between canisters that had the same weight but different widths. There was a strong linear relationship between canister width and perceived grasp aperture (horizontal spacing between the fingers and thumb) when subjects grasped and lifted canisters of the same weight (600 g) but different widths (mean R2 = 0.99 [0.99 ‒ 1.00]; P<0.001; Fig 2A). The mean perceived grasp aperture was 4.39 cm [4.19 ‒ 4.59] for the small 5.2-cm canister, 5.77 cm [5.45 ‒ 6.09] for the 6.6-cm mid-sized test canister, and 9.99 cm [9.76 ‒ 10.22] for the large 10-cm canister. On average, when the test canisters (6.6cm) were lifted, grasp aperture was underestimated by 0.83 cm [0.63 ‒ 1.03] (Fig 3A; P<0.001).


How Weight Affects the Perceived Spacing between the Thumb and Fingers during Grasping.

Butler AA, Héroux ME, Gandevia SC - PLoS ONE (2015)

Relationship between actual and perceived grasp aperture (experiment 1), and actual and perceived weight (experiment 2).A, the relationship between actual and perceived grasp aperture for the three canisters of the same weight (600 g) but different width (5.2, 6.6, 10 cm). Data are presented as mean [95%CI]. Actual and perceived grasp aperture were linearly related with a mean R2 value of 0.99 [0.99 ‒ 1.00]. The dashed line is the line of identity. On average, grasp aperture was underestimated. B, the relationship between actual and perceived canister weight for the three canisters of the same width (6.6 cm) but different weight (300, 600, 900 g). Actual and perceived weight were linearly related with a mean R2 value of 0.98 [0.97 ‒ 0.99]. Data are presented as mean [95% CI] and the dashed line is the line of identity. On average, canister weight was underestimated.
© Copyright Policy
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4440696&req=5

pone.0127983.g002: Relationship between actual and perceived grasp aperture (experiment 1), and actual and perceived weight (experiment 2).A, the relationship between actual and perceived grasp aperture for the three canisters of the same weight (600 g) but different width (5.2, 6.6, 10 cm). Data are presented as mean [95%CI]. Actual and perceived grasp aperture were linearly related with a mean R2 value of 0.99 [0.99 ‒ 1.00]. The dashed line is the line of identity. On average, grasp aperture was underestimated. B, the relationship between actual and perceived canister weight for the three canisters of the same width (6.6 cm) but different weight (300, 600, 900 g). Actual and perceived weight were linearly related with a mean R2 value of 0.98 [0.97 ‒ 0.99]. Data are presented as mean [95% CI] and the dashed line is the line of identity. On average, canister weight was underestimated.
Mentions: Subjects were able to discriminate between canisters that had the same weight but different widths. There was a strong linear relationship between canister width and perceived grasp aperture (horizontal spacing between the fingers and thumb) when subjects grasped and lifted canisters of the same weight (600 g) but different widths (mean R2 = 0.99 [0.99 ‒ 1.00]; P<0.001; Fig 2A). The mean perceived grasp aperture was 4.39 cm [4.19 ‒ 4.59] for the small 5.2-cm canister, 5.77 cm [5.45 ‒ 6.09] for the 6.6-cm mid-sized test canister, and 9.99 cm [9.76 ‒ 10.22] for the large 10-cm canister. On average, when the test canisters (6.6cm) were lifted, grasp aperture was underestimated by 0.83 cm [0.63 ‒ 1.03] (Fig 3A; P<0.001).

Bottom Line: Results for perceived grasp aperture were compared with changes in perceived weight of objects of different sizes (5.2, 6.6, and 10 cm) but the same weight (600 g).For objects of the same weight but different widths, perceived weight decreased 42.3% [38.2 ‒ 46.4] from narrowest to widest (P < 0.001), as expected from the size-weight illusion.Given the small magnitude of this 'weight-grasp aperture' illusion, we propose the brain has access to a relatively stable 'perceptual ruler' to aid the manipulation of different objects.

View Article: PubMed Central - PubMed

Affiliation: Neuroscience Research Australia and University of New South Wales, Sydney, Australia.

ABSTRACT
We know much about mechanisms determining the perceived size and weight of lifted objects, but little about how these properties of size and weight affect the body representation (e.g. grasp aperture of the hand). Without vision, subjects (n = 16) estimated spacing between fingers and thumb (perceived grasp aperture) while lifting canisters of the same width (6.6cm) but varied weights (300, 600, 900, and 1200 g). Lifts were performed by movement of either the wrist, elbow or shoulder to examine whether lifting with different muscle groups affects the judgement of grasp aperture. Results for perceived grasp aperture were compared with changes in perceived weight of objects of different sizes (5.2, 6.6, and 10 cm) but the same weight (600 g). When canisters of the same width but different weights were lifted, perceived grasp aperture decreased 4.8% [2.2 ‒ 7.4] (mean [95% CI]; P < 0.001) from the lightest to the heaviest canister, no matter how they were lifted. For objects of the same weight but different widths, perceived weight decreased 42.3% [38.2 ‒ 46.4] from narrowest to widest (P < 0.001), as expected from the size-weight illusion. Thus, despite a highly distorted perception of the weight of objects based on their size, we conclude that proprioceptive afferents maintain a reasonably stable perception of the aperture of the grasping hand over a wide range of object weights. Given the small magnitude of this 'weight-grasp aperture' illusion, we propose the brain has access to a relatively stable 'perceptual ruler' to aid the manipulation of different objects.

No MeSH data available.


Related in: MedlinePlus