scholarly journals Why some size illusions affect grip aperture

2019 ◽  
Author(s):  
Jeroen B.J. Smeets ◽  
Erik Kleijn ◽  
Marlijn van der Meijden ◽  
Eli Brenner
Keyword(s):  
Extensive Literature ◽  
Object Size ◽  
Ebbinghaus Illusion ◽  
Grip Aperture ◽  
Size Information

AbstractThere is an extensive literature debating whether perceived size is used to guide grasping. A possible reason for not using judged size is that using judged positions might lead to more precise movements. As this argument does not hold for small objects, and all studies showing an effect of the Ebbinghaus illusion on grasping used small objects, we hypothesized that size information is used for small objects but not for large ones. Using a modified diagonal illusion, we obtained an effect of about 10% on perceptual judgements, without an effect on grasping, irrespective of object size. We therefore reject our precision hypothesis. We discuss the results in the framework of grasping as moving digits to positions on an object. We conclude that the reported disagreement on the effect of illusions is because the Ebbinghaus illusion not only affects size, but –unlike most size illusions– also affects perceived positions.

scholarly journals Deep ugrizY imaging and DEEP2/3 spectroscopy: a photometric redshift testbed for LSST and public release of data from the DEEP3 Galaxy Redshift Survey

2019 ◽  
Vol 488 (4) ◽  
pp. 4565-4584 ◽  
Author(s):  
Rongpu Zhou ◽  
Michael C Cooper ◽  
Jeffrey A Newman ◽  
Matthew L N Ashby ◽  
James Aird ◽  
...  
Keyword(s):  
Object Size ◽  
Random Forest Regression ◽  
Photometric Redshifts ◽  
Size Information ◽  
Photometric Redshift ◽  
Point Spread ◽  
Spread Function ◽  
Redshift Survey ◽  
Galaxy Redshift ◽  
Empirical Tests

ABSTRACT We present catalogues of calibrated photometry and spectroscopic redshifts in the Extended Groth Strip, intended for studies of photometric redshifts (photo-z’s). The data includes ugriz photometry from Canada–France–Hawaii Telescope Legacy Survey (CFHTLS) and Y-band photometry from the Subaru Suprime camera, as well as spectroscopic redshifts from the DEEP2, DEEP3, and 3D-HST surveys. These catalogues incorporate corrections to produce effectively matched-aperture photometry across all bands, based upon object size information available in the catalogue and Moffat profile point spread function fits. We test this catalogue with a simple machine learning-based photometric redshift algorithm based upon Random Forest regression, and find that the corrected aperture photometry leads to significant improvement in photo-z accuracy compared to the original SExtractor catalogues from CFHTLS and Subaru. The deep ugrizY photometry and spectroscopic redshifts are well suited for empirical tests of photometric redshift algorithms for LSST. The resulting catalogues are publicly available at http://d-scholarship.pitt.edu/36064/. We include a basic summary of the strategy of the DEEP3 Galaxy Redshift Survey to accompany the recent public release of DEEP3 data.

The Effect of Pictorial Illusion on Prehension and Perception

1998 ◽  
Vol 10 (1) ◽  
pp. 122-136 ◽  
Author(s):  
Angela M. Haffenden ◽  
Melvyn A. Goodale
Keyword(s):  
Visual Perception ◽  
Three Dimensional ◽  
Object Size ◽  
Strongly Correlated ◽  
Visually Guided ◽  
Grip Aperture ◽  
Physical Size ◽  
Disk Size ◽  
Dimensional Version ◽  
Size Contrast

The present study examined the effect of a size-contrast illusion (Ebbinghaus or Titchener Circles Illusion) on visual perception and the visual control of grasping movements. Seventeen right-handed participants picked up and, on other trials, estimated the size of fipoker-chipfl disks, which functioned as the target circles in a three-dimensional version of the illusion. In the estimation condition, subjects indicated how big they thought the target was by separating their thumb and forefinger to match the target's size. After initial viewing, no visual feedback from the hand or the target was available. Scaling of grip aperture was found to be strongly correlated with the physical size of the disks, while manual estimations of disk size were biased in the direction of the illusion. Evidently, grip aperture is calibrated to the true size of an object, even when perception of object size is distorted by a pictorial illusion, a result that is consistent with recent suggestions that visually guided prehension and visual perception are mediated by separate visual pathways.

Prehension Movements in the Macaque Monkey: Effects of Object Size and Location

2002 ◽  
Vol 88 (3) ◽  
pp. 1491-1499 ◽  
Author(s):  
Alice C. Roy ◽  
Yves Paulignan ◽  
Martine Meunier ◽  
Driss Boussaoud
Keyword(s):  
Three Dimensional ◽  
Large Degree ◽  
Macaque Monkey ◽  
Task Demands ◽  
Object Size ◽  
Grip Aperture ◽  
Location Task ◽  
Prehension Movements ◽  
Size Task ◽  
Behaving Monkeys

Prehension movements were examined in freely behaving monkeys and compared with the well-known characteristics of human movements. The degree of independence of the components of movements (i.e., reaching and grasping) was investigated in animals trained to reach for and grasp three-dimensional objects. To this aim, the kinematics of prehension movements was recorded using an Optotrak system in two tasks. In one task, monkeys grasped a small or a large object (size task), in the other, they grasped an object of constant size placed at three different spatial locations (location task). We found that object size and its location affected both reaching and grasping. In particular, in the size task, we found that the maximum grip aperture strongly depended on the selection of the grip and not only on the size of an object. Our results also revealed that, in monkeys as well as in humans, the reaching parameters are highly sensitive to task-related constraints such as accuracy demands. The results of the location task showed a difference between rightward and leftward movements, a pattern of grip aperture that varied across animals, and a large degree of coordination between the two components. These findings argue against a strict postulate of independence between the visuo-motor channels, favoring instead the idea of variable degrees of coordination between the reach and grasp components depending on the task demands. Finally, this work emphasizes the relevance of studying monkey's prehension movements as a useful step to the understanding of visuo-motor control in humans.

scholarly journals Decreased attention to object size information in scale errors performers

2017 ◽  
Vol 47 ◽  
pp. 72-82 ◽  
Author(s):  
Beata J. Grzyb ◽  
Angelo Cangelosi ◽  
Allegra Cattani ◽  
Caroline Floccia
Keyword(s):  
Object Size ◽  
Size Information

scholarly journals Grasp aperture corrections in reach-to-grasp movements do not reliably alter size perception

PLoS ONE ◽  
2021 ◽  
Vol 16 (9) ◽  
pp. e0248084
Author(s):  
Vonne van Polanen
Keyword(s):  
Visual Information ◽  
Discrimination Performance ◽  
Perceptual Bias ◽  
Size Perception ◽  
Object Size ◽  
Haptic Information ◽  
Reach To Grasp ◽  
Grip Aperture ◽  
Reaching Movement ◽  
The Difference

When grasping an object, the opening between the fingertips (grip aperture) scales with the size of the object. If an object changes in size, the grip aperture has to be corrected. In this study, it was investigated whether such corrections would influence the perceived size of objects. The grasping plan was manipulated with a preview of the object, after which participants initiated their reaching movement without vision. In a minority of the grasps, the object changed in size after the preview and participants had to adjust their grasping movement. Visual feedback was manipulated in two experiments. In experiment 1, vision was restored during reach and both visual and haptic information was available to correct the grasp and lift the object. In experiment 2, no visual information was provided during the movement and grasps could only be corrected using haptic information. Participants made reach-to-grasp movements towards two objects and compared these in size. Results showed that participants adjusted their grasp to a change in object size from preview to grasped object in both experiments. However, a change in object size did not bias the perception of object size or alter discrimination performance. In experiment 2, a small perceptual bias was found when objects changed from large to small. However, this bias was much smaller than the difference that could be discriminated and could not be considered meaningful. Therefore, it can be concluded that the planning and execution of reach-to-grasp movements do not reliably affect the perception of object size.

scholarly journals Are reaching and grasping effector-independent? Similarities and differences in reaching and grasping kinematics between the hand and foot

2021 ◽  
Author(s):  
Yuqi Liu ◽  
James Caracoglia ◽  
Sriparna Sen ◽  
Ella Striem-Amit
Keyword(s):  
Peak Velocity ◽  
Object Size ◽  
Body Parts ◽  
Acceleration Phase ◽  
Grip Aperture ◽  
Deceleration Phase ◽  
Neural Representations ◽  
Maximum Grip Aperture ◽  
Similarities And Differences ◽  
Maximum Grip

While reaching and grasping are highly prevalent manual actions, neuroimaging studies provide evidence that their neural representations may be shared between different body parts, i.e. effectors. If these actions are guided by effector-independent mechanisms, similar kinematics should be observed when the action is performed by the hand or by a cortically remote and less experienced effector, such as the foot. We tested this hypothesis with two characteristic components of action: the initial ballistic stage of reaching, and the preshaping of the digits during grasping based on object size. We examined if these kinematic features reflect effector-independent mechanisms by asking participants to reach toward and to grasp objects of different widths with their hand and foot. First, during both reaching and grasping, the velocity profile up to peak velocity matched between the hand and the foot, indicating a shared ballistic acceleration phase. Secondly, maximum grip aperture and time of maximum grip aperture of grasping increased with object size for both effectors, indicating encoding of object size during transport. Differences between the hand and foot were found in the deceleration phase and time of maximum grip aperture, likely due to biomechanical differences and the participants' inexperience with foot actions. These findings provide evidence for effector-independent visuomotor mechanisms of reaching and grasping that generalize across body parts.

scholarly journals A review of grasping as the movements of digits in space

2019 ◽  
Vol 122 (4) ◽  
pp. 1578-1597 ◽  
Author(s):  
Jeroen B. J. Smeets ◽  
Katinka van der Kooij ◽  
Eli Brenner
Keyword(s):  
Neural Control ◽  
The Other ◽  
Reach To Grasp ◽  
Grip Aperture ◽  
Trade Off ◽  
Size Information ◽  
Direct Support ◽  
Speed Accuracy ◽  
Hand Transport ◽  
Fast Responses

It is tempting to describe human reach-to-grasp movements in terms of two, more or less independent visuomotor channels, one relating hand transport to the object’s location and the other relating grip aperture to the object’s size. Our review of experimental work questions this framework for reasons that go beyond noting the dependence between the two channels. Both the lack of effect of size illusions on grip aperture and the finding that the variability in grip aperture does not depend on the object’s size indicate that size information is not used to control grip aperture. An alternative is to describe grip formation as emerging from controlling the movements of the digits in space. Each digit’s trajectory when grasping an object is remarkably similar to its trajectory when moving to tap the same position on its own. The similarity is also evident in the fast responses when the object is displaced. This review develops a new description of the speed-accuracy trade-off for multiple effectors that is applied to grasping. The most direct support for the digit-in-space framework is that prism-induced adaptation of each digit’s tapping movements transfers to that digit’s movements when grasping, leading to changes in grip aperture for adaptation in opposite directions for the two digits. We conclude that although grip aperture and hand transport are convenient variables to describe grasping, treating grasping as movements of the digits in space is a more suitable basis for understanding the neural control of grasping.

scholarly journals Grasp Aperture Corrections in Reach-to-Grasp Movements Do Not Alter Size Perception

2021 ◽  
Author(s):  
Vonne van Polanen
Keyword(s):  
Visual Information ◽  
Discrimination Performance ◽  
Perceptual Bias ◽  
Size Perception ◽  
Object Size ◽  
Haptic Information ◽  
Reach To Grasp ◽  
Grip Aperture ◽  
Reaching Movement ◽  
The Difference

ABSTRACTWhen grasping an object, the opening between the fingertips (grip aperture) scales with the size of the object. If an object changes in size, the grip aperture has to be corrected. In this study, it was investigated whether such corrections would influence the perceived size of objects. The grasping plan was manipulated with a preview of the object, after which participants initiated their reaching movement without vision. In a minority of the grasps, the object changed in size after the preview and participants had to adjust their grasping movement. Visual feedback was manipulated in two experiments. In experiment 1, vision was restored during reach and both visual and haptic information was available to correct the grasp and lift the object. In experiment 2, no visual information was provided during the movement and grasps could only be corrected using haptic information. Participants made reach-to-grasp movements towards two objects and compared these in size. Results showed that participants adjusted their grasp to a change in object size from preview to grasped object in both experiments. However, a change in object size did not bias the perception of object size or alter discrimination performance. In experiment 2, a small perceptual bias was found when objects changed from large to small. However, this bias was much smaller than the difference that could be discriminated and could not be considered meaningful. Therefore, it can be concluded that the planning and execution of reach-to-grasp movements do not affect the perception of object size.

scholarly journals Some illusions are more inconsistent than others

2019 ◽  
Author(s):  
Jeroen B. J. Smeets ◽  
Eli Brenner
Keyword(s):  
Motion Aftereffect ◽  
Apparent Size ◽  
Ebbinghaus Illusion ◽  
Reach To Grasp ◽  
Grip Aperture ◽  
Maximum Grip Aperture ◽  
Pencil And Paper ◽  
Maximum Grip

Illusions are characterized by inconsistencies. For instance, in the motion aftereffect, we see motion without an equivalent change in position. We used a simple pencil-and-paper experiment to determine whether illusions that influence an object’s apparent size give rise to equivalent changes in apparent positions along the object’s outline. We found different results for two equally strong size illusions. The Ebbinghaus illusion affected perceived positions in a way that was consistent with its influence on perceived size, but a modified diagonal illusion did not affect perceived positions. This difference between the illusions might explain why there are so many conflicting reports about the effects of size illusions on the maximum grip aperture during reach-to-grasp movements.

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