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Goh HT, Stewart J, Becker K. Fatigue Is Associated With Perceived Effort and 2-Dimensional Reach Performance After Stroke. J Neurol Phys Ther 2024:01253086-990000000-00071. [PMID: 38934610 DOI: 10.1097/npt.0000000000000483] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 06/28/2024]
Abstract
BACKGROUND AND PURPOSE Poststroke fatigue (PSF) is prevalent and often manifests as high perceived effort during activities. Little is known about how PSF influences goal-directed reaching after stroke. The purpose of this study was 2-fold (1) to evaluate how perceived effort changed when individuals with stroke performed a reaching task with various demands and (2) to determine whether PSF was associated with perceived effort during reaching and reach performance. METHODS Thirty-six individuals with chronic stroke performed 2-dimensional reach actions under varied conditions with the more and less affected arms. Perceived effort during reaching was assessed using rating of perceived exertion (RPE) and Paas Mental Effort Rating Scale (MERS). Derived reach kinematics were used to quantify reach performance. The Fatigue Severity Scale (FSS) was administered to assess fatigue severity. RESULTS Perceived effort was higher when participants reached with the more affected arm, reached toward far and small targets, and performed memory-guided reaching. Both RPE and MERS significantly correlated with the FSS score (r = 0.50 and 0.35, respectively, P < 0.05). Further, FSS correlated with movement time during the more affected arm reaching (ρ = 0.40, p < 0.05) and reach performance discrepancy between the fast and self-selected speed conditions when participants performed with the less affected arm (ρ = 0.36, P < 0.05). Exploratory analysis revealed that the relationship between fatigue and reach control appeared to be modulated by task demand. DISCUSSION AND CONCLUSIONS PSF is associated with perceived effort during reaching and reach performance after stroke. These relationships might offer insights into arm performance in the real world after stroke. VIDEO ABSTRACT for more insights from the authors Supplemental Digital Content available at http://links.lww.com/JNPT/A476.
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Affiliation(s)
- Hui-Ting Goh
- Author Affiliations: School of Physical Therapy, Texas Woman's University, Dallas, Texas (H.-T.G.); Physical Therapy Program, Department of Exercise Science. University of South Carolina, Columbus, South Carolina (J.S.); and Department of Kinesiology, Recreation, and Sport Studies. University of Tennessee, Knoxville, Tennessee (K.B.)
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Grant S, Conway ML. Deficits in Reach Planning and On-Line Grasp Control in Adults With Amblyopia. Invest Ophthalmol Vis Sci 2023; 64:45. [PMID: 38032338 PMCID: PMC10691391 DOI: 10.1167/iovs.64.14.45] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2023] [Accepted: 10/26/2023] [Indexed: 12/01/2023] Open
Abstract
Purpose Adults with amblyopia exhibit impairments when reaching to grasp three-dimensional objects. We examined whether their deficits derive from problems with feedforward planning of these prehension movements or in using visual feedback to control them on-line. Methods Twenty-one adults with mild to severe anisometropic and/or strabismic amblyopia and reduced binocularity participated, along with 21 normally sighted age- and gender-matched controls. Subjects used their preferred hand to reach for, precision grasp, and then lift cylindrical table-top objects (two sizes, two distances) using binocular, dominant eye, or amblyopic/non-sighting eye vision just to plan their movements during a 1-second task preview with vision then occluded so feedback was absent or to plan and execute them (i.e., with visual feedback fully available). Kinematic and error measures of the timing and accuracy of the reach and grasp were quantified by view and feedback and compared by ANOVA. Results The amblyopic adults performed generally worse than controls across all three views in both feedback conditions. With vision for planning only, their movement initiation and duration times were significantly increased, as were their initial reach times and error rates, especially when using the amblyopic eye alone, whatever its visual acuity loss. These relative planning deficits were only partially rectified with visual feedback available on-line. Relative grasp planning deficits were less evident in the amblyopia group, who instead produced significantly increased grip times and errors under binocular and amblyopic eye visual feedback conditions, although the subgroup with unmeasurable stereovision also formed wider (inaccurate) grasps across all conditions. Conclusions Adults with amblyopia seem to have problems constructing reliable internal spatial representations for the feedforward planning of prehension, particularly with their affected eye and mainly affecting their reach, with additional deficits in on-line grasp control related to poor binocularity.
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Affiliation(s)
- Simon Grant
- Centre for Applied Vision Research, School of Health & Psychological Sciences, City, University of London, London, United Kingdom
| | - Miriam L. Conway
- Centre for Applied Vision Research, School of Health & Psychological Sciences, City, University of London, London, United Kingdom
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Gao L, Liu Z, Chen Z, Pan JS, Yu M. Targeted reaching with monocular depth information and haptic feedback: Comparing between monocular patients and normally sighted observers. Vision Res 2023; 211:108274. [PMID: 37343461 DOI: 10.1016/j.visres.2023.108274] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2022] [Revised: 06/06/2023] [Accepted: 06/06/2023] [Indexed: 06/23/2023]
Abstract
Monocular blindness impairs visual depth perception, yet patients seldom report difficulties in targeted actions like reaching, walking, or driving. We hypothesized that by utilizing monocular depth information and calibrating actions with haptic feedback, monocular patients can perceive egocentric distance and perform targeted actions. We compared targeted reaching in monocular patients, monocular-viewing, and binocular-viewing normal controls. Sixty observers reached either a far or a near target, calibrating reaches to the near target with accurate or false feedback while leaving reaches to the far target uncalibrated. Reaching accuracy and precision were analyzed. Results indicated no difference in reaching accuracy between monocular patients and normal controls; all groups initially underestimated distances before until calibration. Monocular patients responded to calibration sensitively, achieving accuracy in calibrated reaches and generalizing this effect to uncalibrated distances. Thus, with monocular depth information and haptic feedback, monocular patients could perceive distance and accomplish targeted reaching.
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Affiliation(s)
- Le Gao
- State Key Laboratory of Ophthalmology, Guangdong Provincial Key Laboratory of Ophthalmology and Visual Science, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, Guangdong 510060, China
| | - Zitian Liu
- State Key Laboratory of Ophthalmology, Guangdong Provincial Key Laboratory of Ophthalmology and Visual Science, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, Guangdong 510060, China
| | - Zidong Chen
- State Key Laboratory of Ophthalmology, Guangdong Provincial Key Laboratory of Ophthalmology and Visual Science, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, Guangdong 510060, China
| | - Jing S Pan
- Department of Psychology, Sun Yat-sen University, Guangzhou 510275, China.
| | - Minbin Yu
- State Key Laboratory of Ophthalmology, Guangdong Provincial Key Laboratory of Ophthalmology and Visual Science, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, Guangdong 510060, China.
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Simon-Martinez C, Antoniou MP, Bouthour W, Bavelier D, Levi D, Backus BT, Dornbos B, Blaha JJ, Kropp M, Müller H, Murray M, Thumann G, Steffen H, Matusz PJ. Stereoptic serious games as a visual rehabilitation tool for individuals with a residual amblyopia (AMBER trial): a protocol for a crossover randomized controlled trial. BMC Ophthalmol 2023; 23:220. [PMID: 37198558 DOI: 10.1186/s12886-023-02944-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2023] [Accepted: 04/25/2023] [Indexed: 05/19/2023] Open
Abstract
BACKGROUND Amblyopia is the most common developmental vision disorder in children. The initial treatment consists of refractive correction. When insufficient, occlusion therapy may further improve visual acuity. However, the challenges and compliance issues associated with occlusion therapy may result in treatment failure and residual amblyopia. Virtual reality (VR) games developed to improve visual function have shown positive preliminary results. The aim of this study is to determine the efficacy of these games to improve vision, attention, and motor skills in patients with residual amblyopia and identify brain-related changes. We hypothesize that a VR-based training with the suggested ingredients (3D cues and rich feedback), combined with increasing the difficulty level and the use of various games in a home-based environment is crucial for treatment efficacy of vision recovery, and may be particularly effective in children. METHODS The AMBER study is a randomized, cross-over, controlled trial designed to assess the effect of binocular stimulation (VR-based stereoptic serious games) in individuals with residual amblyopia (n = 30, 6-35 years of age), compared to refractive correction on vision, selective attention and motor control skills. Additionally, they will be compared to a control group of age-matched healthy individuals (n = 30) to account for the unique benefit of VR-based serious games. All participants will play serious games 30 min per day, 5 days per week, for 8 weeks. The games are delivered with the Vivid Vision Home software. The amblyopic cohort will receive both treatments in a randomized order according to the type of amblyopia, while the control group will only receive the VR-based stereoscopic serious games. The primary outcome is visual acuity in the amblyopic eye. Secondary outcomes include stereoacuity, functional vision, cortical visual responses, selective attention, and motor control. The outcomes will be measured before and after each treatment with 8-week follow-up. DISCUSSION The VR-based games used in this study have been conceived to deliver binocular visual stimulation tailored to the individual visual needs of the patient, which will potentially result in improved basic and functional vision skills as well as visual attention and motor control skills. TRIAL REGISTRATION This protocol is registered on ClinicalTrials.gov (identifier: NCT05114252) and in the Swiss National Clinical Trials Portal (identifier: SNCTP000005024).
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Affiliation(s)
- Cristina Simon-Martinez
- University of Applied Sciences Western Switzerland (HES-SO) Valais-Wallis, Rue de Technopole 3, 3960, Sierre, Switzerland.
- Department of Ophthalmology, University Hospitals of Geneva, Geneva, Switzerland.
- The Sense Innovation and Research Center, Lausanne and Sion, Sion, Switzerland.
- Experimental Ophthalmology, University of Geneva, Geneva, Switzerland.
| | - Maria-Paraskevi Antoniou
- University of Applied Sciences Western Switzerland (HES-SO) Valais-Wallis, Rue de Technopole 3, 3960, Sierre, Switzerland
- Department of Ophthalmology, University Hospitals of Geneva, Geneva, Switzerland
- The Sense Innovation and Research Center, Lausanne and Sion, Sion, Switzerland
- Experimental Ophthalmology, University of Geneva, Geneva, Switzerland
| | - Walid Bouthour
- Department of Ophthalmology, University Hospitals of Geneva, Geneva, Switzerland
- Experimental Ophthalmology, University of Geneva, Geneva, Switzerland
| | - Daphne Bavelier
- Faculty of Psychology and Education Sciences, University of Geneva, Geneva, Switzerland
| | - Dennis Levi
- Herbert Wertheim School of Optometry & Vision Science, Helen Wills Neuroscience Institute, University of California Berkley, Berkley, CA, USA
| | - Benjamin T Backus
- Vivid Vision, Inc, 424 Treat Ave., Ste B, San Francisco, CA, 94110, USA
| | - Brian Dornbos
- Vivid Vision, Inc, 424 Treat Ave., Ste B, San Francisco, CA, 94110, USA
| | - James J Blaha
- Vivid Vision, Inc, 424 Treat Ave., Ste B, San Francisco, CA, 94110, USA
| | - Martina Kropp
- Department of Ophthalmology, University Hospitals of Geneva, Geneva, Switzerland
- Experimental Ophthalmology, University of Geneva, Geneva, Switzerland
| | - Henning Müller
- University of Applied Sciences Western Switzerland (HES-SO) Valais-Wallis, Rue de Technopole 3, 3960, Sierre, Switzerland
| | - Micah Murray
- The Sense Innovation and Research Center, Lausanne and Sion, Sion, Switzerland
- Institute of Health Sciences, School of Health Sciences, HES-SO Valais-Wallis, Sion, Switzerland
- Laboratory for Investigative Neurophysiology, Department of Radiology, Lausanne University Hospital, University of Lausanne (CHUV-UNIL), Lausanne, Switzerland
| | - Gabriele Thumann
- Department of Ophthalmology, University Hospitals of Geneva, Geneva, Switzerland
- Experimental Ophthalmology, University of Geneva, Geneva, Switzerland
| | - Heimo Steffen
- Department of Ophthalmology, University Hospitals of Geneva, Geneva, Switzerland
- Experimental Ophthalmology, University of Geneva, Geneva, Switzerland
| | - Pawel J Matusz
- University of Applied Sciences Western Switzerland (HES-SO) Valais-Wallis, Rue de Technopole 3, 3960, Sierre, Switzerland
- Department of Ophthalmology, University Hospitals of Geneva, Geneva, Switzerland
- The Sense Innovation and Research Center, Lausanne and Sion, Sion, Switzerland
- Experimental Ophthalmology, University of Geneva, Geneva, Switzerland
- Institute of Health Sciences, School of Health Sciences, HES-SO Valais-Wallis, Sion, Switzerland
- Laboratory for Investigative Neurophysiology, Department of Radiology, Lausanne University Hospital, University of Lausanne (CHUV-UNIL), Lausanne, Switzerland
- Department of Hearing & Speech Sciences, Vanderbilt University Medical Center, Nashville, TN, USA
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Peckre LR, Fabre AC, Wall CE, Pouydebat E, Whishaw IQ. Evolutionary History of food Withdraw Movements in Primates: Food Withdraw is Mediated by Nonvisual Strategies in 22 Species of Strepsirrhines. Evol Biol 2023. [DOI: 10.1007/s11692-023-09598-0] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/28/2023]
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Niechwiej-Szwedo E, Colpa L, Wong A. The role of binocular vision in the control and development of visually guided upper limb movements. Philos Trans R Soc Lond B Biol Sci 2023; 378:20210461. [PMID: 36511416 PMCID: PMC9745875 DOI: 10.1098/rstb.2021.0461] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2022] [Accepted: 06/16/2022] [Indexed: 12/15/2022] Open
Abstract
Vision provides a key sensory input for the performance of fine motor skills, which are fundamentally important to daily life activities, as well as skilled occupational and recreational performance. Binocular visual function is a crucial aspect of vision that requires the ability to combine inputs from both eyes into a unified percept. Summation and fusion are two aspects of binocular processing associated with performance advantages, including more efficient visuomotor control of upper limb movements. This paper uses the multiple processes model of limb control to explore how binocular viewing could facilitate the planning and execution of prehension movements in adults and typically developing children. Insight into the contribution of binocularity to visuomotor control also comes from examining motor performance in individuals with amblyopia, a condition characterized by reduced visual acuity and poor binocular function. Overall, research in this field has advanced our understanding of the role of binocular vision in the development and performance of visuomotor skills, the first step towards developing assessment tools and targeted rehabilitation for children with neurodevelopment disorders at risk of poor visuomotor outcomes. This article is part of a discussion meeting issue 'New approaches to 3D vision'.
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Affiliation(s)
- Ewa Niechwiej-Szwedo
- Kinesiology and Health Sciences, University of Waterloo, 200 University Avenue, Waterloo, ON, Canada N2L 3G1
| | - Linda Colpa
- Department of Ophthalmology and Vision Sciences, The Hospital for Sick Children, 555 University Avenue, Toronto, ON, Canada M5G 1X8
| | - Agnes Wong
- Department of Ophthalmology and Vision Sciences, The Hospital for Sick Children, 555 University Avenue, Toronto, ON, Canada M5G 1X8
- University of Toronto, 27 King's College Circle, Toronto, ON, Canada M5S 1A4
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Kelly KR, Norouzi DM, Nouredanesh M, Jost RM, Cheng-Patel CS, Beauchamp CL, Dao LM, Luu BA, Stager DR, Tung JY, Niechwiej-Szwedo E. Temporal Eye–Hand Coordination During Visually Guided Reaching in 7- to 12-Year-Old Children With Strabismus. Invest Ophthalmol Vis Sci 2022; 63:10. [DOI: 10.1167/iovs.63.12.10] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Affiliation(s)
- Krista R. Kelly
- Retina Foundation of the Southwest, Dallas, TX, United States
- Department of Ophthalmology, UT Southwestern Medical Center, Dallas, TX, United States
| | | | - Mina Nouredanesh
- School of Rehabilitation Science, McMaster University, Hamilton, Ontario, Canada
| | - Reed M. Jost
- Retina Foundation of the Southwest, Dallas, TX, United States
| | | | | | - Lori M. Dao
- ABC Eyes Pediatric Ophthalmology, PA, Dallas, TX, United States
| | - Becky A. Luu
- Pediatric Ophthalmology & Adult Strabismus, PA, Plano, TX, United States
| | - David R. Stager
- Pediatric Ophthalmology & Adult Strabismus, PA, Plano, TX, United States
| | - James Y. Tung
- Department of Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo, Ontario, Canada
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Hou SW, Zhang Y, Christian L, Niechwiej‐Szwedo E, Giaschi D. Evaluating visuomotor coordination in children with amblyopia. Dev Psychobiol 2022; 64:e22270. [DOI: 10.1002/dev.22270] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Revised: 02/05/2022] [Accepted: 02/20/2022] [Indexed: 11/08/2022]
Affiliation(s)
- Sabrina W. Hou
- Department of Ophthalmology and Visual Sciences University of British Columbia Vancouver British Columbia Canada
| | - Yan Zhang
- Department of Ophthalmology and Visual Sciences University of British Columbia Vancouver British Columbia Canada
| | - Lisa Christian
- Department of Optometry and Vision Science University of Waterloo Waterloo Ontario Canada
| | | | - Deborah Giaschi
- Department of Ophthalmology and Visual Sciences University of British Columbia Vancouver British Columbia Canada
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Sheppard WEA, Dickerson P, Baraas RC, Mon-Williams M, Barrett BT, Wilkie RM, Coats RO. Exploring the effects of degraded vision on sensorimotor performance. PLoS One 2021; 16:e0258678. [PMID: 34748569 PMCID: PMC8575268 DOI: 10.1371/journal.pone.0258678] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2021] [Accepted: 10/02/2021] [Indexed: 11/19/2022] Open
Abstract
PURPOSE Many people experience unilateral degraded vision, usually owing to a developmental or age-related disorder. There are unresolved questions regarding the extent to which such unilateral visual deficits impact on sensorimotor performance; an important issue as sensorimotor limitations can constrain quality of life by restricting 'activities of daily living'. Examination of the relationship between visual deficit and sensorimotor performance is essential for determining the functional implications of ophthalmic conditions. This study attempts to explore the effect of unilaterally degraded vision on sensorimotor performance. METHODS In Experiment 1 we simulated visual deficits in 30 participants using unilateral and bilateral Bangerter filters to explore whether motor performance was affected in water pouring, peg placing, and aiming tasks. Experiment 2 (n = 74) tested the hypothesis that kinematic measures are associated with visuomotor deficits by measuring the impact of small visual sensitivity decrements created by monocular viewing on sensorimotor interactions with targets presented on a planar surface in aiming, tracking and steering tasks. RESULTS In Experiment 1, the filters caused decreased task performance-confirming that unilateral (and bilateral) visual loss has functional implications. In Experiment 2, kinematic measures were affected by monocular viewing in two of three tasks requiring rapid online visual feedback (aiming and steering). CONCLUSIONS Unilateral visual loss has a measurable impact on sensorimotor performance. The benefits of binocular vision may be particularly important for some groups (e.g. older adults) where an inability to complete sensorimotor tasks may necessitate assisted living. There is an urgent need to develop rigorous kinematic approaches to the quantification of the functional impact of unilaterally degraded vision and of the benefits associated with treatments for unilateral ophthalmic conditions to enable informed decisions around treatment.
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Affiliation(s)
| | - Polly Dickerson
- Department of Ophthalmology, York Teaching Hospital NHS Foundation Trust, North Yorkshire, United Kingdom
| | - Rigmor C. Baraas
- Department of Optometry, Radiography and Lighting Design, National Centre for Optics, Vision and Eye Care, University of South-Eastern Norway, Kongsberg, Norway
| | - Mark Mon-Williams
- School of Psychology, University of Leeds, Leeds, West Yorkshire, United Kingdom
- Department of Optometry, Radiography and Lighting Design, National Centre for Optics, Vision and Eye Care, University of South-Eastern Norway, Kongsberg, Norway
- Bradford Institute of Health Research, Bradford Teaching Hospital NHS Foundation Trust, West Yorkshire, United Kingdom
| | - Brendan T. Barrett
- Faculty of Life Sciences, School of Optometry & Vision Science, University of Bradford, West Yorkshire, United Kingdom
| | - Richard M. Wilkie
- School of Psychology, University of Leeds, Leeds, West Yorkshire, United Kingdom
| | - Rachel O. Coats
- School of Psychology, University of Leeds, Leeds, West Yorkshire, United Kingdom
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Mroczkowski CA, Niechwiej-Szwedo E. Stereopsis contributes to the predictive control of grip forces during prehension. Exp Brain Res 2021; 239:1345-1358. [PMID: 33661370 DOI: 10.1007/s00221-021-06052-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2020] [Accepted: 01/29/2021] [Indexed: 11/26/2022]
Abstract
Binocular viewing is associated with a superior prehensile performance, which is particularly evident in the latter part of the reach as the hand approaches and makes contact with the target object. However, the visuomotor mechanisms through which binocular vision serves prehension are not fully understood. This study assessed the role of stereopsis in the predictive control of grasping by measuring grip force. Twenty participants performed a precision reach-to-grasp task in four viewing conditions: binocular, monocular, and with reduced stereoacuity (200 arc sec, > 400 arc sec). Monocular, compared to binocular viewing, was associated with a fourfold increase in grasp errors, a 56% increase in grasp duration, 22% decrease in grip force at 50 ms following grasp initiation, and the time of peak force occurred 40% later after grasp initiation (all p < 0.05). Grasp performance was also disrupted when viewing with reduced stereoacuity. Notably, grip force at the time of object lift-off was comparable between all viewing conditions. These results demonstrate that binocular stereopsis contributes to the efficient programming of grip forces. Specifically, stereopsis may provide important sensory information that enables the central nervous system to engage in predictive control of grasping.
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Affiliation(s)
- Corey A Mroczkowski
- Department of Kinesiology, University of Waterloo, 200 University Ave W, Waterloo, ON, N2L 5G1, Canada
| | - Ewa Niechwiej-Szwedo
- Department of Kinesiology, University of Waterloo, 200 University Ave W, Waterloo, ON, N2L 5G1, Canada.
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Abstract
Since Kepler (1604) and Descartes (1637), 'vergence' (the angular rotation of the eyes) has been thought of as one of our most important absolute distance cues. But vergence has never been tested as an absolute distance cue divorced from obvious confounding cues such as binocular disparity. In this article, we control for these confounding cues for the first time by gradually manipulating vergence and find that observers fail to accurately judge distance from vergence. We consider several different interpretations of these results and argue that the most principled response to these results is to question the general effectiveness of vergence as an absolute distance cue. Given that other absolute distance cues (such as motion parallax and vertical disparities) are limited in application, this poses a real challenge to our contemporary understanding of visual scale.
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Affiliation(s)
- Paul Linton
- Centre for Applied Vision Research, City, University of London, Northampton Square, Clerkenwell, London, EC1V 0HB, UK.
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