R E S E A R C H
A R T I C L E
Effect of Body-Scaled Information on Reaching in Children With Hemiplegic Cerebral Palsy: A Pilot Study Hsiang-han Huang, ScD, OT; Terry D. Ellis, PT, PhD, NCS; Robert C. Wagenaar, PhD; Linda Fetters, PT, PhD, FAPTA Department of Occupational Therapy and Graduate Institute of Behavioral Sciences, Healthy Aging Research Center (Dr Huang), Chang Gung University, Tao-Yuan, Taiwan; Department of Physical Therapy and Athletic Training (Drs Huang, Ellis, and Wagenaar), College of Health and Rehabilitation Sciences: Sargent, Boston University, Boston, Massachusetts; Division of Biokinesiology and Physical Therapy (Drs Huang and Fetters), University of Southern California, Los Angeles, California; Department of Pediatrics (Dr Fetters), Keck School of Medicine, University of Southern California, Los Angeles, California.
Purpose: This study examined body-scaled information that specifies the reach patterns of children with hemiplegic cerebral palsy and children with typical development. Methods: Nine children with hemiplegic cerebral palsy (3-5 years) and 9 age-matched children with typical development participated in the study. They were required to reach and grasp 10 different pairs of cubes. Reach data were coded as either a 1handed reach or a 2-handed reach. Dimensionless ratios were calculated by dividing the cube size by the maximal aperture between the index finger and thumb. A critical ratio was used to establish the shift from a 1-handed to an exclusive 2-handed reach. Results: The critical ratio was not significantly different for either preferred or nonpreferred arms within and between groups. All children used an exclusive 2-handed reach at a similar dimensionless ratio. Conclusion: Our study provides evidence of the “fit” between environment (cube size) and the individual’s capabilities (finger aperture) for reaching for both groups. (Pediatr Phys Ther 2014;26:28–37) Key words: anthropometry, cerebral palsy, child, female, hand/anatomy, hand/physiology, hemiplegia, humans, male, movement/physiology, preschool, size perception, task performance and analysis INTRODUCTION Modifying the environment and task to improve the functional skills of children with cerebral palsy (CP) is a common therapeutic approach for physical and occupa0898-5669/110/261-0028 Pediatric Physical Therapy C 2014 Wolters Kluwer Health | Lippincott Williams & Copyright Wilkins and Section on Pediatrics of the American Physical Therapy Association
Correspondence: Hsiang-han Huang, ScD, OT, Department of Occupational Therapy and Graduate Institute of Behavioral Sciences, Healthy Aging Research Center, Chang Gung University, 259 Wen-Hwa 1st Rd, Kwei-Shan Tao-Yuan, Taiwan ([email protected]). At the time this article was written, Hsiang-han Huang was a student at the Department of Physical Therapy and Athletic Training, College of Health and Rehabilitation Sciences: Sargent, Boston University, Boston, Massachusetts. The authors declare no conflicts of interest. DOI: 10.1097/PEP.0000000000000008
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Huang et al
tional therapists. Recent research using “context therapy” emphasizes changing the task and environmental factors rather than changing specific child factors to achieve functional goals in the daily life of children with CP.1,2 However, adapting the task or modifying the environment is often a trial-and-error process until the child successfully accomplishes the desired goal in therapy. Our research focuses on identifying specific and quantifiable changes to the environment or task that can be made before and during therapy to support the successful completion of therapeutic goals. Identifying the specific changes to be made is complicated because actions emerge from multiple, interacting constraints, including the nervous system, the body’s mechanical properties, and properties of the environment.3,4 A constraint in this context is a variable of the person or environment that influences the emergent actions.5 Children with hemiplegic CP have altered personal constraints (eg, disturbed tactile and proprioceptive senses, increased Pediatric Physical Therapy
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins and the Section on Pediatrics of the American Physical Therapy Association. Unauthorized reproduction of this article is prohibited.
muscle stiffness, and decreased range of motion).6,7 These constraints influence their interactions with the environment and hence their emergent actions.8 Specific actions depend on the “fit” between the child’s constraints and the environmental constraints (ie, context for action).3,9 This fit between a person and the environment was termed an “affordance” by Gibson.10 Affordances are specified through body-scaled information within the context of the task. For example, we have found that both children with typical development (TD) and adults use a 2-handed reach at the ratio of 1.0 to 1.15 (ie, the size of the object is equal or slightly larger than the maximal index finger and thumb aperture).11 This perceived information is termed “bodyscaled information” and the ratio is termed a “dimensionless ratio.” Perceiving this body-scaled information is the foundation of successful functional actions.3,12-14 Very few studies have explored the use of body-scaled information by children with CP.15,16 van der Meer and colleagues15 have found that the body-scaled information of “passability,” when walking under a horizontal bar for children with hemiplegic CP, is influenced by personal constraints. They scaled environmental properties (eg, barrier height) in relation to personal constraints (eg, head height and postural control). Children with hemiplegic CP compensated for their insufficient ability to control the head/trunk vertical position in space by allowing a greater safety margin than children with TD when walking or running under a horizontal bar. Several studies have specified the “fit” of reaching and grasping patterns for children with TD,17-19 but no comparable research for children with hemiplegia was found. Identifying the “fit” between reachable objects and constraints of the reaching hand and arm, for both the paretic and nonparetic limbs, will provide us with a principled approach to enhancing movement and not merely a trialand-error process during therapy. If children with CP use the same relative information as children with TD (ie, the ratio of the index finger–thumb aperture in relation to the object size, for 1-handed vs 2-handed reach), then this ratio can be incorporated into therapy. A 2-handed reach should emerge automatically if the object size in relation to the hand size exceeds a specific ratio. Switching between a 1-handed and a 2-handed reach during therapy then emerges as the therapist changes object sizes. This switching behavior can be practiced intensely at the boundaries of this ratio. The objective of this study was to examine the relationship between hand size (personal characteristics) and object size (environmental characteristics) and the effect of this relationship on the emergent reaching patterns for children with hemiplegic CP and children with TD. In this study, we defined the dimensionless ratio as the ratio of the cube size to the maximal index finger–thumb aperture (active movement) for each cube size. We hypothesized that the dimensionless ratio that specifies this change from a 1-handed to a 2-handed reach would differ between children with CP and children with TD because of different personal constraints affecting their perceived affordance. Pediatric Physical Therapy
Children with CP may use a 2-handed pattern at a smaller dimensionless ratio (ie, the object size is much smaller than the hand size) than children with TD. The results of this study will provide a further understanding of the relationship between children with CP and their environment, which can be applied in a therapeutic program to improve the fit between the child, task, and environment and support emergent action patterns.
METHODS Participants This is a cross-sectional prospective study. Participants in the study were children with hemiplegic CP (n = 9) between the ages of 3 and 5 years. The comparison group was age-matched children with TD (n = 9) (Table 1). Ages were matched within 4 months, achieving as close a match as feasible. Children with mild to severe CP may have different levels of impairments that influence motor capabilities and development.7,20 Therefore, the inclusion criteria were
TABLE 1 Demographic and Clinical Characteristics of the Participantsa
Age (mean) Sex Male Female Race White African American Hispanic Asian Weight, lb Height, inch Preferred/nonparetic arm Right Left Maximal index finger–thumb, cm Preferred/nonpreferred
Baseline hand function MACS I II III AHA (logits)
Children With CP (n = 9)
Children With TD (n = 9)
4 yrs and 0 mo
3 yrs and 11 mos
7 (78%) 2 (22%)
5 (56%) 4 (44%)
2 (22%) 0 7 (78%) 0 38.89 (8.55) 39.28 (2.59)
1 (11%) 0 5 (56%) 3 (33%) 35.50 (5.87) 40.12 (2.25)
1 (11%) 8 (89%)
9 (100%) 0
7.74 (1.22)/6.80 (1.47)b,c
9.10 (1.62)/8.69 (1.20)
8 (89%) 1 (11%) 0 5.67 (3.01)
NA NA NA NA
Abbreviations: AHA, Assisting Hand Assessment; CP, cerebral palsy; MACS, Manual Ability Classification System; NA, nonapplicable; TD, typical development. a Data are means (standard deviation) except for sex, race, preferred arm and MACS, which are totals and group percentages. b Difference is significant (P < .05) between preferred and nonpreferred hands. c Difference is significant (P < .05) between children with CP and TD.
Reaching in Children With Hemiplegia
29
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins and the Section on Pediatrics of the American Physical Therapy Association. Unauthorized reproduction of this article is prohibited.
established to optimize homogeneity among participants relative to severity of impairments. This study was reviewed and approved by the institutional review boards of Boston University and the University of Southern California. Written parental permissions giving informed consent for their children to participate were obtained before participation. Inclusion criteria for children with CP were as follows: (1) children had a diagnosis of CP resulting in hemiparesis; (2) children’s ages were between 3 and 5 years; (3) children had spasticity in the elbow, wrist, and finger flexors of the paretic limb from zero to moderate on the Modified Ashworth Scale (MAS)21 assessed by the first author; (4) severity of fine motor function was at level I to III according to the Manual Ability Classification System (MACS)22 assessed by the first author; (5) children had the ability to reach and grasp a peg on a board using the paretic limb; (6) children had the ability to understand and follow 2 to 3 step commands; (7) the team obtained the consent of the parents for their child to participate in the testing procedures and the experiments at the lab, clinic, or home. Although the MAS is the most common and frequently used measure of spasticity in children with CP, both in research and in clinical practice, the reliability and validity of the MAS is not well-established.23,24 Therefore, we also provided the MACS23 to assess the participant’s hand function. The MACS is a 5-level classification system designed to classify how children with CP use their hands to handle objects in their daily life.22,25 Higher MACS levels indicate more severe disability of hand function for daily activities. Procedures Testing was conducted by the first author in the Development of Infant Motor Performance Laboratory, Division of Biokinesiology and Physical Therapy, University of Southern California or at the child’s home or clinic. Parents were with their child at all times during testing. Baseline Assessments Bimanual hand function was evaluated with the Assisting Hand Assessment (AHA)26 by the first author who is reliable and certified in administration, scoring, and interpretation of the AHA. The AHA is currently the only reliable and valid assessment for measuring the effectiveness of use of the paretic arm in the performance of bimanual activity for children with hemiplegic CP.27,28 Stereognosis, proprioception, and tactile discrimination as measured by 2-point discrimination (2PD) were assessed by the first author at baseline. The tests were modified versions of the methods of Cooper et al7 and van Heest et al.29 The stereognosis and 2PD tests were found to be reliable. The reported interrater reliability of stereognosis (for children with TD) and 2PD tests (for children with CP) was 93.75%,7,30 and ranged from 0.96 to 0.99,31,32 respectively. Reliability and validity for testing proprioception in these 2 studies7,29 was not reported. 30
Huang et al
The tests were administered by a therapist in the Cooper et al7 study, but no specific information about the tester was provided by van Heest et al.29 In our version, we used 3 objects (a shirt-button, key, and pencil) which were used in van Heest et al’s study29 to substitute for candy in a wrapper, diamond, and octagon in Cooper’s method.7 We also decreased the number of trials assessed in the proprioception test.7,29 These changes were made because the original versions were developed for older children with CP and required higher cognitive and attentional demands than were feasible for the preschool children in our study. Stereognosis was examined for both preferred and nonpreferred hands by asking subjects to identify 10 objects (eg, circle, triangle, square, toothbrush, tennis ball, 4-inch comb, large cup, a shirt-button, key, and pencil). Participants manipulated each object by reaching with 1 hand into a bag (vision occluded), and subsequently pointing to a corresponding picture with the other hand.7 Each participant’s stereognosis was graded as intact (9-10 objects correct), mildly deficient (6-8 objects correct), moderately deficient (3-5 objects correct), or severely deficient (0-2 objects correct).29 The test of proprioception involved moving the participant’s shoulder, elbow, wrist, proximal phalanges of the thumb and index finger with his/her eyes closed, and asking the participant to perform the same movements on the other hand. The movements were in the range of 30 degrees of flexion or extension. The proprioception score was determined as the number of joint movement directions that the blindfolded participant correctly replicated out of 3 trials for each joint. Proprioception was graded as follows: intact, 3 trials correct; impaired, 1 to 2 trials correct; absent, no trials correct.29 The threshold cutoff value between intact and deficient for 2PD tests was set at 3 mm for all fingertips for children with CP.33 Reaching Experiment The detailed setup of the experiment was described in a previous study.11 Each participant was seated on a chair and required to reach and grasp 10 cube pairs of different sizes, which were made of foam board and sized from 0.8 (
A R T I C L E
Effect of Body-Scaled Information on Reaching in Children With Hemiplegic Cerebral Palsy: A Pilot Study Hsiang-han Huang, ScD, OT; Terry D. Ellis, PT, PhD, NCS; Robert C. Wagenaar, PhD; Linda Fetters, PT, PhD, FAPTA Department of Occupational Therapy and Graduate Institute of Behavioral Sciences, Healthy Aging Research Center (Dr Huang), Chang Gung University, Tao-Yuan, Taiwan; Department of Physical Therapy and Athletic Training (Drs Huang, Ellis, and Wagenaar), College of Health and Rehabilitation Sciences: Sargent, Boston University, Boston, Massachusetts; Division of Biokinesiology and Physical Therapy (Drs Huang and Fetters), University of Southern California, Los Angeles, California; Department of Pediatrics (Dr Fetters), Keck School of Medicine, University of Southern California, Los Angeles, California.
Purpose: This study examined body-scaled information that specifies the reach patterns of children with hemiplegic cerebral palsy and children with typical development. Methods: Nine children with hemiplegic cerebral palsy (3-5 years) and 9 age-matched children with typical development participated in the study. They were required to reach and grasp 10 different pairs of cubes. Reach data were coded as either a 1handed reach or a 2-handed reach. Dimensionless ratios were calculated by dividing the cube size by the maximal aperture between the index finger and thumb. A critical ratio was used to establish the shift from a 1-handed to an exclusive 2-handed reach. Results: The critical ratio was not significantly different for either preferred or nonpreferred arms within and between groups. All children used an exclusive 2-handed reach at a similar dimensionless ratio. Conclusion: Our study provides evidence of the “fit” between environment (cube size) and the individual’s capabilities (finger aperture) for reaching for both groups. (Pediatr Phys Ther 2014;26:28–37) Key words: anthropometry, cerebral palsy, child, female, hand/anatomy, hand/physiology, hemiplegia, humans, male, movement/physiology, preschool, size perception, task performance and analysis INTRODUCTION Modifying the environment and task to improve the functional skills of children with cerebral palsy (CP) is a common therapeutic approach for physical and occupa0898-5669/110/261-0028 Pediatric Physical Therapy C 2014 Wolters Kluwer Health | Lippincott Williams & Copyright Wilkins and Section on Pediatrics of the American Physical Therapy Association
Correspondence: Hsiang-han Huang, ScD, OT, Department of Occupational Therapy and Graduate Institute of Behavioral Sciences, Healthy Aging Research Center, Chang Gung University, 259 Wen-Hwa 1st Rd, Kwei-Shan Tao-Yuan, Taiwan ([email protected]). At the time this article was written, Hsiang-han Huang was a student at the Department of Physical Therapy and Athletic Training, College of Health and Rehabilitation Sciences: Sargent, Boston University, Boston, Massachusetts. The authors declare no conflicts of interest. DOI: 10.1097/PEP.0000000000000008
28
Huang et al
tional therapists. Recent research using “context therapy” emphasizes changing the task and environmental factors rather than changing specific child factors to achieve functional goals in the daily life of children with CP.1,2 However, adapting the task or modifying the environment is often a trial-and-error process until the child successfully accomplishes the desired goal in therapy. Our research focuses on identifying specific and quantifiable changes to the environment or task that can be made before and during therapy to support the successful completion of therapeutic goals. Identifying the specific changes to be made is complicated because actions emerge from multiple, interacting constraints, including the nervous system, the body’s mechanical properties, and properties of the environment.3,4 A constraint in this context is a variable of the person or environment that influences the emergent actions.5 Children with hemiplegic CP have altered personal constraints (eg, disturbed tactile and proprioceptive senses, increased Pediatric Physical Therapy
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins and the Section on Pediatrics of the American Physical Therapy Association. Unauthorized reproduction of this article is prohibited.
muscle stiffness, and decreased range of motion).6,7 These constraints influence their interactions with the environment and hence their emergent actions.8 Specific actions depend on the “fit” between the child’s constraints and the environmental constraints (ie, context for action).3,9 This fit between a person and the environment was termed an “affordance” by Gibson.10 Affordances are specified through body-scaled information within the context of the task. For example, we have found that both children with typical development (TD) and adults use a 2-handed reach at the ratio of 1.0 to 1.15 (ie, the size of the object is equal or slightly larger than the maximal index finger and thumb aperture).11 This perceived information is termed “bodyscaled information” and the ratio is termed a “dimensionless ratio.” Perceiving this body-scaled information is the foundation of successful functional actions.3,12-14 Very few studies have explored the use of body-scaled information by children with CP.15,16 van der Meer and colleagues15 have found that the body-scaled information of “passability,” when walking under a horizontal bar for children with hemiplegic CP, is influenced by personal constraints. They scaled environmental properties (eg, barrier height) in relation to personal constraints (eg, head height and postural control). Children with hemiplegic CP compensated for their insufficient ability to control the head/trunk vertical position in space by allowing a greater safety margin than children with TD when walking or running under a horizontal bar. Several studies have specified the “fit” of reaching and grasping patterns for children with TD,17-19 but no comparable research for children with hemiplegia was found. Identifying the “fit” between reachable objects and constraints of the reaching hand and arm, for both the paretic and nonparetic limbs, will provide us with a principled approach to enhancing movement and not merely a trialand-error process during therapy. If children with CP use the same relative information as children with TD (ie, the ratio of the index finger–thumb aperture in relation to the object size, for 1-handed vs 2-handed reach), then this ratio can be incorporated into therapy. A 2-handed reach should emerge automatically if the object size in relation to the hand size exceeds a specific ratio. Switching between a 1-handed and a 2-handed reach during therapy then emerges as the therapist changes object sizes. This switching behavior can be practiced intensely at the boundaries of this ratio. The objective of this study was to examine the relationship between hand size (personal characteristics) and object size (environmental characteristics) and the effect of this relationship on the emergent reaching patterns for children with hemiplegic CP and children with TD. In this study, we defined the dimensionless ratio as the ratio of the cube size to the maximal index finger–thumb aperture (active movement) for each cube size. We hypothesized that the dimensionless ratio that specifies this change from a 1-handed to a 2-handed reach would differ between children with CP and children with TD because of different personal constraints affecting their perceived affordance. Pediatric Physical Therapy
Children with CP may use a 2-handed pattern at a smaller dimensionless ratio (ie, the object size is much smaller than the hand size) than children with TD. The results of this study will provide a further understanding of the relationship between children with CP and their environment, which can be applied in a therapeutic program to improve the fit between the child, task, and environment and support emergent action patterns.
METHODS Participants This is a cross-sectional prospective study. Participants in the study were children with hemiplegic CP (n = 9) between the ages of 3 and 5 years. The comparison group was age-matched children with TD (n = 9) (Table 1). Ages were matched within 4 months, achieving as close a match as feasible. Children with mild to severe CP may have different levels of impairments that influence motor capabilities and development.7,20 Therefore, the inclusion criteria were
TABLE 1 Demographic and Clinical Characteristics of the Participantsa
Age (mean) Sex Male Female Race White African American Hispanic Asian Weight, lb Height, inch Preferred/nonparetic arm Right Left Maximal index finger–thumb, cm Preferred/nonpreferred
Baseline hand function MACS I II III AHA (logits)
Children With CP (n = 9)
Children With TD (n = 9)
4 yrs and 0 mo
3 yrs and 11 mos
7 (78%) 2 (22%)
5 (56%) 4 (44%)
2 (22%) 0 7 (78%) 0 38.89 (8.55) 39.28 (2.59)
1 (11%) 0 5 (56%) 3 (33%) 35.50 (5.87) 40.12 (2.25)
1 (11%) 8 (89%)
9 (100%) 0
7.74 (1.22)/6.80 (1.47)b,c
9.10 (1.62)/8.69 (1.20)
8 (89%) 1 (11%) 0 5.67 (3.01)
NA NA NA NA
Abbreviations: AHA, Assisting Hand Assessment; CP, cerebral palsy; MACS, Manual Ability Classification System; NA, nonapplicable; TD, typical development. a Data are means (standard deviation) except for sex, race, preferred arm and MACS, which are totals and group percentages. b Difference is significant (P < .05) between preferred and nonpreferred hands. c Difference is significant (P < .05) between children with CP and TD.
Reaching in Children With Hemiplegia
29
Copyright © 2014 Wolters Kluwer Health | Lippincott Williams & Wilkins and the Section on Pediatrics of the American Physical Therapy Association. Unauthorized reproduction of this article is prohibited.
established to optimize homogeneity among participants relative to severity of impairments. This study was reviewed and approved by the institutional review boards of Boston University and the University of Southern California. Written parental permissions giving informed consent for their children to participate were obtained before participation. Inclusion criteria for children with CP were as follows: (1) children had a diagnosis of CP resulting in hemiparesis; (2) children’s ages were between 3 and 5 years; (3) children had spasticity in the elbow, wrist, and finger flexors of the paretic limb from zero to moderate on the Modified Ashworth Scale (MAS)21 assessed by the first author; (4) severity of fine motor function was at level I to III according to the Manual Ability Classification System (MACS)22 assessed by the first author; (5) children had the ability to reach and grasp a peg on a board using the paretic limb; (6) children had the ability to understand and follow 2 to 3 step commands; (7) the team obtained the consent of the parents for their child to participate in the testing procedures and the experiments at the lab, clinic, or home. Although the MAS is the most common and frequently used measure of spasticity in children with CP, both in research and in clinical practice, the reliability and validity of the MAS is not well-established.23,24 Therefore, we also provided the MACS23 to assess the participant’s hand function. The MACS is a 5-level classification system designed to classify how children with CP use their hands to handle objects in their daily life.22,25 Higher MACS levels indicate more severe disability of hand function for daily activities. Procedures Testing was conducted by the first author in the Development of Infant Motor Performance Laboratory, Division of Biokinesiology and Physical Therapy, University of Southern California or at the child’s home or clinic. Parents were with their child at all times during testing. Baseline Assessments Bimanual hand function was evaluated with the Assisting Hand Assessment (AHA)26 by the first author who is reliable and certified in administration, scoring, and interpretation of the AHA. The AHA is currently the only reliable and valid assessment for measuring the effectiveness of use of the paretic arm in the performance of bimanual activity for children with hemiplegic CP.27,28 Stereognosis, proprioception, and tactile discrimination as measured by 2-point discrimination (2PD) were assessed by the first author at baseline. The tests were modified versions of the methods of Cooper et al7 and van Heest et al.29 The stereognosis and 2PD tests were found to be reliable. The reported interrater reliability of stereognosis (for children with TD) and 2PD tests (for children with CP) was 93.75%,7,30 and ranged from 0.96 to 0.99,31,32 respectively. Reliability and validity for testing proprioception in these 2 studies7,29 was not reported. 30
Huang et al
The tests were administered by a therapist in the Cooper et al7 study, but no specific information about the tester was provided by van Heest et al.29 In our version, we used 3 objects (a shirt-button, key, and pencil) which were used in van Heest et al’s study29 to substitute for candy in a wrapper, diamond, and octagon in Cooper’s method.7 We also decreased the number of trials assessed in the proprioception test.7,29 These changes were made because the original versions were developed for older children with CP and required higher cognitive and attentional demands than were feasible for the preschool children in our study. Stereognosis was examined for both preferred and nonpreferred hands by asking subjects to identify 10 objects (eg, circle, triangle, square, toothbrush, tennis ball, 4-inch comb, large cup, a shirt-button, key, and pencil). Participants manipulated each object by reaching with 1 hand into a bag (vision occluded), and subsequently pointing to a corresponding picture with the other hand.7 Each participant’s stereognosis was graded as intact (9-10 objects correct), mildly deficient (6-8 objects correct), moderately deficient (3-5 objects correct), or severely deficient (0-2 objects correct).29 The test of proprioception involved moving the participant’s shoulder, elbow, wrist, proximal phalanges of the thumb and index finger with his/her eyes closed, and asking the participant to perform the same movements on the other hand. The movements were in the range of 30 degrees of flexion or extension. The proprioception score was determined as the number of joint movement directions that the blindfolded participant correctly replicated out of 3 trials for each joint. Proprioception was graded as follows: intact, 3 trials correct; impaired, 1 to 2 trials correct; absent, no trials correct.29 The threshold cutoff value between intact and deficient for 2PD tests was set at 3 mm for all fingertips for children with CP.33 Reaching Experiment The detailed setup of the experiment was described in a previous study.11 Each participant was seated on a chair and required to reach and grasp 10 cube pairs of different sizes, which were made of foam board and sized from 0.8 (
