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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

The effect of canister width on perceived weight of an unseen lifted object (experiment 2).A, shows the mean [95% CI] perceived weight of each of the three lifted canisters of the same weight (600 g) with varied widths. The perceived weight differed significantly with changes in canister width. The narrow canister felt much heavier than wide canisters (P < 0.001). Dashed line represents the actual canister weight (600g). B, shows the mean [95% CI] perceived weight of all trials for each subject normalised and presented as a ratio (perceived weight / mean perceived weight of all trials; squares). Individual data are indicated by grey circles. On average, perceived weight decreased by 42.3% from the narrowest to the widest canister although all canisters weighed 600 g (P<0.001).
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pone.0127983.g004: The effect of canister width on perceived weight of an unseen lifted object (experiment 2).A, shows the mean [95% CI] perceived weight of each of the three lifted canisters of the same weight (600 g) with varied widths. The perceived weight differed significantly with changes in canister width. The narrow canister felt much heavier than wide canisters (P < 0.001). Dashed line represents the actual canister weight (600g). B, shows the mean [95% CI] perceived weight of all trials for each subject normalised and presented as a ratio (perceived weight / mean perceived weight of all trials; squares). Individual data are indicated by grey circles. On average, perceived weight decreased by 42.3% from the narrowest to the widest canister although all canisters weighed 600 g (P<0.001).

Mentions: There was a linear relationship between actual and perceived weight for canisters of the same width (mean R2 = 0.98 [0.97 ‒ 0.99]; P < 0.001). Subjects were able to distinguish differences between the three canisters of the same width (6.6 cm) but varied weight; 168 g [131 ‒ 205] for the 300-g canister; 494 g [443 ‒ 545] for the 600-g canister; and 915 g [815 ‒ 979] for the 900-g canister (Fig 2B). On average, the weight of the test canisters (600 g), was underestimated by 103 g [54 ‒ 152] (Fig 4A; 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)

The effect of canister width on perceived weight of an unseen lifted object (experiment 2).A, shows the mean [95% CI] perceived weight of each of the three lifted canisters of the same weight (600 g) with varied widths. The perceived weight differed significantly with changes in canister width. The narrow canister felt much heavier than wide canisters (P < 0.001). Dashed line represents the actual canister weight (600g). B, shows the mean [95% CI] perceived weight of all trials for each subject normalised and presented as a ratio (perceived weight / mean perceived weight of all trials; squares). Individual data are indicated by grey circles. On average, perceived weight decreased by 42.3% from the narrowest to the widest canister although all canisters weighed 600 g (P<0.001).
© Copyright Policy
Related In: Results  -  Collection

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

pone.0127983.g004: The effect of canister width on perceived weight of an unseen lifted object (experiment 2).A, shows the mean [95% CI] perceived weight of each of the three lifted canisters of the same weight (600 g) with varied widths. The perceived weight differed significantly with changes in canister width. The narrow canister felt much heavier than wide canisters (P < 0.001). Dashed line represents the actual canister weight (600g). B, shows the mean [95% CI] perceived weight of all trials for each subject normalised and presented as a ratio (perceived weight / mean perceived weight of all trials; squares). Individual data are indicated by grey circles. On average, perceived weight decreased by 42.3% from the narrowest to the widest canister although all canisters weighed 600 g (P<0.001).
Mentions: There was a linear relationship between actual and perceived weight for canisters of the same width (mean R2 = 0.98 [0.97 ‒ 0.99]; P < 0.001). Subjects were able to distinguish differences between the three canisters of the same width (6.6 cm) but varied weight; 168 g [131 ‒ 205] for the 300-g canister; 494 g [443 ‒ 545] for the 600-g canister; and 915 g [815 ‒ 979] for the 900-g canister (Fig 2B). On average, the weight of the test canisters (600 g), was underestimated by 103 g [54 ‒ 152] (Fig 4A; 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