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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

Experimental set-up.A, in both experiments 1 and 2, subjects grasped and lifted a range of standard cylindrical canisters of different weights and widths. The canisters were lifted with the right hand with movement at the wrist, elbow or shoulder. Throughout all experiments, the canisters and the subject’s arm were screened from view. B, shows the canisters of different dimensions lifted in both experiments. For experiment 1, the mid-sized test canisters (width 6.6 cm) were used to measure perceived horizontal spacing between the fingers and thumb (perceived grasp aperture) during a lift. These four test canisters ranged in weight from 300g–1200g. The narrow and wide canisters from experiment 2 each weighed 600g and were used as distractors (see Methods). For experiment 2, the test canisters included the narrow, mid-sized and wide canisters which each weighed 600g and ranged in size from 5.2cm–10cm. During the lift subjects reported the weight, they perceived to be lifting. Two mid-sized canisters from experiment 1 of 300 g and 900 g were used as distractors (see Methods). C, in experiment 1, subjects reported their perceived grasp aperture using an A3 sized visual chart with 22 numbered horizontal lines of different lengths that represented the grasp aperture of the hand. D, in experiment 2, subjects reported the weight of milk they perceived to be lifting using a coloured vertical scale marked on a one-litre carton with ten 1.9-cm coloured increments, each divided into upper, middle and lower portions for each colour. Each portion represented 33.3 g.
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pone.0127983.g001: Experimental set-up.A, in both experiments 1 and 2, subjects grasped and lifted a range of standard cylindrical canisters of different weights and widths. The canisters were lifted with the right hand with movement at the wrist, elbow or shoulder. Throughout all experiments, the canisters and the subject’s arm were screened from view. B, shows the canisters of different dimensions lifted in both experiments. For experiment 1, the mid-sized test canisters (width 6.6 cm) were used to measure perceived horizontal spacing between the fingers and thumb (perceived grasp aperture) during a lift. These four test canisters ranged in weight from 300g–1200g. The narrow and wide canisters from experiment 2 each weighed 600g and were used as distractors (see Methods). For experiment 2, the test canisters included the narrow, mid-sized and wide canisters which each weighed 600g and ranged in size from 5.2cm–10cm. During the lift subjects reported the weight, they perceived to be lifting. Two mid-sized canisters from experiment 1 of 300 g and 900 g were used as distractors (see Methods). C, in experiment 1, subjects reported their perceived grasp aperture using an A3 sized visual chart with 22 numbered horizontal lines of different lengths that represented the grasp aperture of the hand. D, in experiment 2, subjects reported the weight of milk they perceived to be lifting using a coloured vertical scale marked on a one-litre carton with ten 1.9-cm coloured increments, each divided into upper, middle and lower portions for each colour. Each portion represented 33.3 g.

Mentions: Without vision, subjects grasped and lifted a range of cylindrical canisters of different sizes and weights with their right hand and made judgements on the perceived horizontal spacing between their fingers and thumb (perceived grasp aperture; experiment 1) or perceived weight of the lifted object (experiment 2). Fig 1 shows the experimental set-up. Subjects sat comfortably with their right forearm and hand resting on a table, both of which were concealed from view by a screen. With the subject’s arm in a relaxed position, the experimenter placed each canister between the subject’s fingers and thumb. All fingers contacted the canister and were opposed to the thumb, as if lifting a glass. Subjects were told to vertically lift the canister ~3 cm above the table for ~5 s, and not to feel or explore other aspects of the canister with their fingers.


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

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

Experimental set-up.A, in both experiments 1 and 2, subjects grasped and lifted a range of standard cylindrical canisters of different weights and widths. The canisters were lifted with the right hand with movement at the wrist, elbow or shoulder. Throughout all experiments, the canisters and the subject’s arm were screened from view. B, shows the canisters of different dimensions lifted in both experiments. For experiment 1, the mid-sized test canisters (width 6.6 cm) were used to measure perceived horizontal spacing between the fingers and thumb (perceived grasp aperture) during a lift. These four test canisters ranged in weight from 300g–1200g. The narrow and wide canisters from experiment 2 each weighed 600g and were used as distractors (see Methods). For experiment 2, the test canisters included the narrow, mid-sized and wide canisters which each weighed 600g and ranged in size from 5.2cm–10cm. During the lift subjects reported the weight, they perceived to be lifting. Two mid-sized canisters from experiment 1 of 300 g and 900 g were used as distractors (see Methods). C, in experiment 1, subjects reported their perceived grasp aperture using an A3 sized visual chart with 22 numbered horizontal lines of different lengths that represented the grasp aperture of the hand. D, in experiment 2, subjects reported the weight of milk they perceived to be lifting using a coloured vertical scale marked on a one-litre carton with ten 1.9-cm coloured increments, each divided into upper, middle and lower portions for each colour. Each portion represented 33.3 g.
© Copyright Policy
Related In: Results  -  Collection

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

pone.0127983.g001: Experimental set-up.A, in both experiments 1 and 2, subjects grasped and lifted a range of standard cylindrical canisters of different weights and widths. The canisters were lifted with the right hand with movement at the wrist, elbow or shoulder. Throughout all experiments, the canisters and the subject’s arm were screened from view. B, shows the canisters of different dimensions lifted in both experiments. For experiment 1, the mid-sized test canisters (width 6.6 cm) were used to measure perceived horizontal spacing between the fingers and thumb (perceived grasp aperture) during a lift. These four test canisters ranged in weight from 300g–1200g. The narrow and wide canisters from experiment 2 each weighed 600g and were used as distractors (see Methods). For experiment 2, the test canisters included the narrow, mid-sized and wide canisters which each weighed 600g and ranged in size from 5.2cm–10cm. During the lift subjects reported the weight, they perceived to be lifting. Two mid-sized canisters from experiment 1 of 300 g and 900 g were used as distractors (see Methods). C, in experiment 1, subjects reported their perceived grasp aperture using an A3 sized visual chart with 22 numbered horizontal lines of different lengths that represented the grasp aperture of the hand. D, in experiment 2, subjects reported the weight of milk they perceived to be lifting using a coloured vertical scale marked on a one-litre carton with ten 1.9-cm coloured increments, each divided into upper, middle and lower portions for each colour. Each portion represented 33.3 g.
Mentions: Without vision, subjects grasped and lifted a range of cylindrical canisters of different sizes and weights with their right hand and made judgements on the perceived horizontal spacing between their fingers and thumb (perceived grasp aperture; experiment 1) or perceived weight of the lifted object (experiment 2). Fig 1 shows the experimental set-up. Subjects sat comfortably with their right forearm and hand resting on a table, both of which were concealed from view by a screen. With the subject’s arm in a relaxed position, the experimenter placed each canister between the subject’s fingers and thumb. All fingers contacted the canister and were opposed to the thumb, as if lifting a glass. Subjects were told to vertically lift the canister ~3 cm above the table for ~5 s, and not to feel or explore other aspects of the canister with their fingers.

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