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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 weight on perceived grasp aperture of an unseen lifted object (experiment 1).A, filled symbols represent mean [95% CI] perceived grasp aperture for each of the four test canisters lifted, using movement at the elbow (black circles), wrist (grey squares) and shoulder (black diamonds). The test canisters had the same width (6.6cm) but varied in weight (300–1200 g). Perceived grasp aperture was narrower when heavier canisters were lifted compared to lighter ones (P<0.001). Results are similar with movement at the wrist, elbow or shoulder (P = 0.16). Dashed horizontal line represents the actual canister width (6.6cm) which was consistently underestimated. B, data are presented as ratios normalised to the mean perceived grasp aperture of all four lifted weights for each subject at each joint (perceived grasp aperture/mean perceived grasp aperture of all trials). Individual data are shown as grey circles. Squares show the mean ratio pooled across the three types of movement used to lift the canister [95% CI]. For the pooled data, perceived grasp aperture is significantly narrower (4.8%) when the heavier canisters are lifted compared to the lighter canisters of the same width (P < 0.001).
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pone.0127983.g003: The effect of canister weight on perceived grasp aperture of an unseen lifted object (experiment 1).A, filled symbols represent mean [95% CI] perceived grasp aperture for each of the four test canisters lifted, using movement at the elbow (black circles), wrist (grey squares) and shoulder (black diamonds). The test canisters had the same width (6.6cm) but varied in weight (300–1200 g). Perceived grasp aperture was narrower when heavier canisters were lifted compared to lighter ones (P<0.001). Results are similar with movement at the wrist, elbow or shoulder (P = 0.16). Dashed horizontal line represents the actual canister width (6.6cm) which was consistently underestimated. B, data are presented as ratios normalised to the mean perceived grasp aperture of all four lifted weights for each subject at each joint (perceived grasp aperture/mean perceived grasp aperture of all trials). Individual data are shown as grey circles. Squares show the mean ratio pooled across the three types of movement used to lift the canister [95% CI]. For the pooled data, perceived grasp aperture is significantly narrower (4.8%) when the heavier canisters are lifted compared to the lighter canisters of the same width (P < 0.001).

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)

The effect of canister weight on perceived grasp aperture of an unseen lifted object (experiment 1).A, filled symbols represent mean [95% CI] perceived grasp aperture for each of the four test canisters lifted, using movement at the elbow (black circles), wrist (grey squares) and shoulder (black diamonds). The test canisters had the same width (6.6cm) but varied in weight (300–1200 g). Perceived grasp aperture was narrower when heavier canisters were lifted compared to lighter ones (P<0.001). Results are similar with movement at the wrist, elbow or shoulder (P = 0.16). Dashed horizontal line represents the actual canister width (6.6cm) which was consistently underestimated. B, data are presented as ratios normalised to the mean perceived grasp aperture of all four lifted weights for each subject at each joint (perceived grasp aperture/mean perceived grasp aperture of all trials). Individual data are shown as grey circles. Squares show the mean ratio pooled across the three types of movement used to lift the canister [95% CI]. For the pooled data, perceived grasp aperture is significantly narrower (4.8%) when the heavier canisters are lifted compared to the lighter canisters of the same width (P < 0.001).
© Copyright Policy
Related In: Results  -  Collection

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

pone.0127983.g003: The effect of canister weight on perceived grasp aperture of an unseen lifted object (experiment 1).A, filled symbols represent mean [95% CI] perceived grasp aperture for each of the four test canisters lifted, using movement at the elbow (black circles), wrist (grey squares) and shoulder (black diamonds). The test canisters had the same width (6.6cm) but varied in weight (300–1200 g). Perceived grasp aperture was narrower when heavier canisters were lifted compared to lighter ones (P<0.001). Results are similar with movement at the wrist, elbow or shoulder (P = 0.16). Dashed horizontal line represents the actual canister width (6.6cm) which was consistently underestimated. B, data are presented as ratios normalised to the mean perceived grasp aperture of all four lifted weights for each subject at each joint (perceived grasp aperture/mean perceived grasp aperture of all trials). Individual data are shown as grey circles. Squares show the mean ratio pooled across the three types of movement used to lift the canister [95% CI]. For the pooled data, perceived grasp aperture is significantly narrower (4.8%) when the heavier canisters are lifted compared to the lighter canisters of the same width (P < 0.001).
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