Hand anthropometry and the limits of aperture separation determine the utility of Weber’s law in grasping and manual estimation

Ayala, Naila; Binsted, Gordon; Heath, Matthew

doi:10.1007/s00221-018-5311-6

Cited by 10 publications

(8 citation statements)

References 22 publications

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“…This result provides a direct replication of Ganel et al (2012) and supports the PAM's assertion that the dorsal pathway provides the visuomotor system absolute visual information to mediate metrically precise hand-target interactions (for review, see Goodale & Milner, 2018). Thus, the present findings, PANTOMIME-GRASPS AND VISUAL RESOLUTION those of Ganel et al (2012) and the extant grasping literature (for reviews, see Goodale, 2011;Smeets & Brenner, 1999) demonstrate that PGAs scale to veridical target size across stimuli that are below-and above (see Ayala et al, 2018;-the Weber's fraction for the discrimination of line length. Notably, however, pantomime-grasp PGAs for the 40.0 mm and 40.5 mm targets did not reliably differ and a TOST statistic indicated that values were within an equivalence boundary.…”

Section: Discussionsupporting

confidence: 86%

Distinct visual resolution supports aperture shaping in natural and pantomime-grasping.

Heath¹,

Ayala²,

Hamidi³

et al. 2022

Canadian Journal of Experimental Psychology / Revue canadienne

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Pantomime-grasping is a "simulated" motor response wherein an individual grasps to an area dissociated from a physical target. The task has been used in the apraxia literature as a proxy for natural grasping (i.e., physically grasping a target); however, it is important to recognize that the task's decoupled spatial relations between stimulus and response renders the top-down processing of target features (e.g., size) that accumulating evidence has shown to be mediated by visual information functionally distinct from natural grasping. Here, we examined whether the visual information supporting pantomime-grasps exhibits a visual resolution power commensurate with natural grasps. Participants were presented with a target and nontarget that differed in size below the perceptual threshold (i.e., 0.5 mm or ∼1.3%) and were asked to make a perceptual judgment about the target (i.e., "smaller" or "larger" than the nontarget) before and after completing natural and pantomime-grasps. Results showed that perceptual judgments "before" and "after" natural and pantomime-grasps did not reliably distinguish between target and nontarget. Natural grasp peak grip apertures (PGAs) scaled to target size and were comparable for "before" and "after" perceptual judgment trials-a result indicating that haptic feedback from physically grasping the target did not "boost" perceptual accuracy. Most notably, pantomime-grasp PGAs were insensitive to target size; that is, responses elicited a visual resolution power less than natural grasps. These results provide convergent evidence that pantomime-grasps are mediated by the same visual information as obligatory perceptions and do not provide a proxy for natural grasps. Public Significance StatementThe visual information we use to identify an apple in a bowl of fruit (i.e., a perception) is distinct from the visual information we use to grasp the apple (i.e., an action). The main finding from the present study is that a simulated grasping response (so-called pantomime) is supported by the same visual information as that supporting perceptions.

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Section: Discussionsupporting

confidence: 86%

Distinct visual resolution supports aperture shaping in natural and pantomime-grasping.

Heath¹,

Ayala²,

Hamidi³

et al. 2022

Canadian Journal of Experimental Psychology / Revue canadienne

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“…Another seemingly challenging finding for the biomechanical account was recently reported by Ayala et al (2018). In this study, they used object sizes that were adjusted to the size of participants’ hands.…”

Section: Introductionmentioning

confidence: 87%

Bimanual Grasping Adheres to Weber's Law

et al. 2021

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Weber's law states that our ability to detect changes in stimulus attributes decreases linearly with their magnitude. This principle holds true for many attributes across sensory modalities but appears to be violated in grasping. One explanation for the failure to observe Weber's law in grasping is that its effect is masked by biomechanical constraints of the hand. We tested this hypothesis using a bimanual task that eliminates biomechanical constraints. Participants either grasped differently sized boxes that were comfortably within their arm span (action task) or estimated their width (perceptual task). Within each task, there were two conditions: One where the hands’ start positions remained fixed for all object sizes (meaning the distance between the initial and final hand-positions varied with object size), and one in which the hands’ start positions adapted with object size (such that the distance between the initial and final hand-position remained constant). We observed adherence to Weber's law in bimanual estimation and grasping across both conditions. Our results conflict with a previous study that reported the absence of Weber's law in bimanual grasping. We discuss potential explanations for these divergent findings and encourage further research on whether Weber's law persists when biomechanical constraints are reduced.

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“…Given the ubiquity of Weber's law it was very astounding when researchers reported that grasping—a central human ability—does not obey Weber's law ( Ganel et al., 2008 ). The main experimental result leading to this claim has been replicated many times, and far-reaching theoretical consequences for the understanding of the functional architecture of the brain were derived ( Ayala, Binsted, & Heath, 2018 ; Christiansen, Christensen, Grünbaum, & Kyllingsbæk, 2014 ; Freud, Culham, Namdar, & Behrmann, 2019 ; Ganel et al., 2008 ; Hadad, Avidan, & Ganel, 2012 ; Heath, Mulla, Holmes, & Smuskowitz, 2011 ; Heath, Holmes, Mulla, & Binsted, 2012 ; Heath, Manzone, Khan, & Davarpanah Jazi, 2017 ; Heath & Manzone, 2017 ; Holmes, Mulla, Binsted, & Heath, 2011 ; Holmes & Heath, 2013 ; Hosang, Chan, Jazi, & Heath, 2016 ; Jazi & Heath, 2017 ; Löwenkamp, Gärtner, Haus, & Franz, 2015 ; Namdar, Algom, & Ganel, 2018 ; Ozana, Berman, S., & Ganel, 2018 ; Ozana & Ganel, 2017 ; Ozana & Ganel, 2018 ; Utz, Hesse, Aschenneller, & Schenk, 2015 ).…”

Section: Introductionmentioning

confidence: 87%

“…First, we conducted our experiment with a grasping and a manual estimation task. The design was optimized to investigate Weber's law: (a) we minimized biomechanical constraints by using functionally “graspable” object sizes between 20 and 50 mm ( Ayala et al., 2018 ; Heath & Manzone, 2017 ; Heath et al., 2017 ); (b) each object was repeated 50 times (instead of the usual ≤20 repetitions in such experiments; cf. Appendix D ) to improve the parameter estimates; and (c) we used a relatively large sample size of N = 20 participants.…”

Section: Experiments 1: Weber's Law In Grasping and Manual Estimationmentioning

confidence: 99%

Grasping follows Weber's law: How to use response variability as a proxy for JND

2022

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Weber's law is a fundamental psychophysical principle. It states that the just noticeable difference (JND) between stimuli increases with stimulus magnitude; consequently, larger stimuli should be estimated with larger variability. However, visually guided grasping seems to violate this expectation: When repeatedly grasping large objects, the variability is similar to that when grasping small objects. Based on this result, it was often concluded that grasping violated Weber's law. This astonishing finding generated a flurry of research, with contradictory results and potentially far-reaching implications for theorizing about the functional architecture of the brain. We show that previous studies ignored nonlinearities in the scaling of the grasping response. These nonlinearities result from, for example, the finger span being limited such that the opening of the fingers reaches a ceiling for large objects. We describe how to mathematically take these nonlinearities into account and apply this approach to our own data, as well as to the data of three influential studies on this topic. In all four datasets, we found that—when appropriately estimated—JNDs increase with object size, as expected by Weber's law. We conclude that grasping obeys Weber's law, as do essentially all sensory dimensions.

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Hand anthropometry and the limits of aperture separation determine the utility of Weber’s law in grasping and manual estimation

Cited by 10 publications

References 22 publications

Distinct visual resolution supports aperture shaping in natural and pantomime-grasping.

Distinct visual resolution supports aperture shaping in natural and pantomime-grasping.

Bimanual Grasping Adheres to Weber's Law

Grasping follows Weber's law: How to use response variability as a proxy for JND

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