Correlation Analysis of Finger Movement Patterns .1 Introduction

Kinematic Analysis of Hand Function

4.3 Correlation Analysis of Finger Movement Patterns .1 Introduction

4.3 Correlation Analysis of Finger Movement Patterns

4.3.1 Introduction

The analysis of hand movement presents one significant challenge when computing and assessing kinematic variables: the natural movements of the hand rarely involve motion or rotation at a single joint. Previous studies have shown that a small number of joint motions can account for most of the variance in hand movement patterns and postures (kinematic synergies) [12], [23], [25], [26], [123].

Anatomical factors, such as inter-digit webbings, connections between various tendons, insertions of extrinsic finger muscles, and neuronal connections result in mechanical and neural couplings between various joints. The sum of mechanical and neural coupling generates coordinated movements between various joints [22], [25], [123]. Thus, the proficient grasping of an object entails simultaneous motion at multiple joints, with correlated rotations. Correlated motion at multiple hand joints has been studied during complex tasks, such as typing [8], playing the piano [28], and haptic interactions [29], but a standard procedure to assess such movement synergies has not been developed. Moreover, previous studies involved sets of tasks and hand postures or force patterns that were not specific enough to be immediately translated into assessment practice [22], [25], [40].

The purpose of this experimental study was to objectively identify and examine finger movement patterns as one of the underlying features of dexterity and their relation with performance of daily living tasks.

Finger landmark positions obtained from motion capture, within and across digits 2–5 (index to little finger) were processed to obtain instantaneous joint angles from healthy participants performing the Purdue Pegboard Test, Variable Dexterity Test, and a selection of tasks related to activities of daily living. The study focused on the three main grip styles identified from the literature as the most frequently used grasping patterns: precision, cylinder, and spherical.

4.3.2 Data Analysis

The analysis of joint angles correlations consisted of the computation of the cross-correlation coefficient matrix for all instantaneous flexion joint angles of interest obtained from motion capture data. A matrix X, whose rows are observations (instantaneous joint angles) and whose columns are variables (degree of freedom), was defined from data from the last trial of each task for each subject in order to reduce error due to learning effect and provide stability to the data.

78 The matrix R of correlation coefficients was calculated from the matrix X. The matrix R is related to the covariance matrix C by:

! !, ! =

^{! !,!}

! !,! ! !,!

( 6 )

Where R, is the zeroth lag of the normalized covariance function.

Significance of the correlation values was examined for p < 0.5, and for all correlation coefficients n = 10, df = 15.

The matrix R was calculated for three stages of each trial, splitting tasks into: formation of the grip, manipulation, and release; this approach increases the precision of the analysis.

providing insight into the range of strategies across grasping patterns.

The stages were defined by visual inspection of data and video. The formation stage was defined as the portion of the task between the start of the movement and the first contact with the object. The manipulation stage was defined as the period of the task between the first contact of the dominant hand with the object and the moment no contact between the hand and the object is detected. Finally, the release stage was defined as the portion of the task starting when the hand stops making contact with the object and ending with the hand back in the resting posture (Figure 4.11).

The correlation coefficients across tasks and participants were then analysed aiming to identify the relationship between finger movement patterns and dexterity. Additionally, correlation patterns from both dexterity tests were compared to the related ADL looking to

FIGURE 4.11 PREDEFINED TASKS' STAGES: A) FORMATION OF THE GRIP, B) MANIPULATION, C) RELEASE (TAKEN FROM EXPERIMENTAL FOOTAGE)

79 investigate the degree with which these tests truly reflect finger movement patterns and hand function.

4.3.3 Results

Purdue Pegboard Test

Formation stage: In the Purdue Pegboard Test experiment the metacarpophalangeal (MCP) joints of the index and middle fingers showed high correlation coefficients between them (0.8 - 0.95) during the formation stage of the task (Table 4.11). The MCP of the thumb, however, had low correlation coefficients with respect to the MCP of index and middle fingers.

Correlation coefficients between all the joints analysed fell during the final segment of the formation stage, when the hand approached the object and prepared to make contact with the board, this was particularly noticeable in the correlation coefficients between the MCP joint of the thumb and the same joint of the index and middle fingers (Figure 4.12, Table 4.2).

Manipulation stage: During the manipulation stage, the MCP joint of the thumb had low correlation values with respect to the MCP joints of both the index and middle fingers (0.2 - 0.5) (Table 4.11). The MCP joints of index and middle fingers showed higher correlation values between them during the first part of the manipulation stage. The last part of the manipulation stage, which includes the insertion of the peg into the hole, produced low correlation values for all the joints under analysis (0.3 - 0.5) (Table 4.2, Appendix D).

FIGURE 4.12 COLOUR MAP SHOWING THE CORRELATION COEFFICIENTS BETWEEN ALL MEASURED MOVEMENTS FROM SUBJECT 4 DURING THE FORMATION STAGE OF THE PURDUE PEGBOARD TEST. RED COLOUR INDICATES LOW CORRELATION. SIGNIFICANCE OF THE CORRELATION COEFFICIENTS WAS EXAMINED FOR P < 0.5. THE IMAGE ON THE RIGHT SHOWS THE POSTURE OF THE HAND ACCORDING TO THE CROSS-CORRELATION MAP, WITH INDEX FINGER AND THUMB MOVING INDEPENDENTLY FROM THE REST OF THE FINGERS (RED AND ORANGE COLOURED AREAS CORRESPONDING TO FLEXION MOVEMENTS OF THESE DIGITS).

80 Release stage: During the release stage of the test correlation values between the MCP joints of index and middle fingers raised to levels above 0.8 for most subjects, while correlation coefficients from movements involving the thumb increased when compared with previous stages, showing a smooth and coordinated extension of this fingers during the dissolution of the grasping pattern (Table 4.2, 4.11, Appendix D).

Variable Dexterity Test - Precision

Formation stage: Data obtained from the performance of the VDT-Precision revealed high correlation between the MCP flexion of index and middle fingers during the formation stage of the task, as the fingers flexed to perform a precision grip. Correlation between the thumb and both index and middle fingers was generally lower across participants, with values below 0.8 for 90% of the subjects (Table 4.3, 4.11).

TABLE 4.2 MEANS AND S.D. VALUES OF THE CORRELATION COEFFICIENTS FROM MCP JOINTS FOR ALL SUBJECTS DURING THE THREE STAGES OF THE PURDUE PEGBOARD TEST

MCP Flexion Index MCP Flexion Middle MCP Flexion Index MCP Flexion Thumb MCP Flexion Middle MCP Flexion Thumb Subject

MCP Flexion Index MCP Flexion Middle MCP Flexion Index MCP Flexion Thumb MCP Flexion Middle MCP Flexion Thumb 1

81 Manipulation stage: Correlation coefficients during the manipulation stage of the VDT-Precision task were from moderate to high between the index finger’s MCP and middle finger’s MCP flexion with respect to the rest of the joints. Thumb flexion had moderate correlation with respect to the rest of the movements under analysis for all participants (Table 4.3), indicating the manipulation of the VDT object required higher thumb flexion interdependence with the index and middle fingers across subjects (Table 4.11).

Release stage: The release stage resulted in correlation coefficients below 0.8 for all participants and movements. Index and middle fingers MCP flexion had the highest correlation coefficients across participants, although these values were rarely above 0.75, indicating low finger interdependence across all degrees of freedom, as the fingers extended, and the hand returned to the starting position (Table 4.3, 4.11, Appendix D).

TABLE 4.3 MEAN VALUES OF THE CORRELATION COEFFICIENTS FROM MCP JOINTS FOR ALL SUBJECTS DURING THE THREE STAGES OF THE VARIABLE DEXTERITY TEST-PRECISION TASK.

MCP Flexion Index MCP Flexion Middle MCP Flexion Index MCP Flexion Thumb MCP Flexion Middle MCP Flexion Thumb Subject

MCP Flexion Index MCP Flexion Middle MCP Flexion Index MCP Flexion Thumb MCP Flexion Middle MCP Flexion Thumb 1

82 Pick-up Coin task

Formation stage: During the coin experiment, the (MCP) joints of the thumb, index and middle fingers had high correlation values between them in the formation stage (0.8 - 0.95).

The MCP joint of the thumb showed lower correlation values with respect to index and middle MCP joints (0.2 - 0.4) for 90% of the subjects (Table 4.4, 4.11).

Manipulation stage: The manipulation stage of the coin task showed high correlation values between the MCP joints of the thumb, index and middle fingers (0.8 - 0.95), indicating a smooth and coordinated grasp and controlled manipulation of the coin across all subjects (Table 4.4, 4.11).

Release stage: In the release stage of the task, the MCP joint of the thumb had the lowest correlation coefficients with respect to the index and middle fingers’ MCP joint, fluctuating between 0.2 and 0.8. Additionally, the correlation coefficients between index and middle fingers decreased with respect to previous stages of the task, indicating the dissolution of the grasping pattern presented low coordination between the fingers involved, particularly between the thumb and the index and middle fingers (Table 4.4, 4.11, Appendix D).

TABLE 4.4 MEAN VALUES OF THE CORRELATION COEFFICIENTS FROM MCP JOINTS FOR ALL SUBJECTS DURING THE THREE STAGES OF THE COIN TASK.

MCP Flexion Index MCP Flexion Middle MCP Flexion Index MCP Flexion Thumb MCP Flexion Middle MCP Flexion Thumb Subject

MCP Flexion Index MCP Flexion Middle MCP Flexion Index MCP Flexion Thumb MCP Flexion Middle MCP Flexion Thumb 1

83 Buttoning task

Formation stage: In the buttoning experiment, the MCP joints of the index and middle fingers had moderate to high correlation coefficients between them throughout the formation stage of the task (0.75 - 0.90) for 90% of the participants, suggesting a coordinated movement between these MCP joints as the fingers flexed to perform a precision grip (Table 4.5).

Correlation coefficients between thumb flexion and both index and middle fingers flexion were lower during this stage, with values below 0.75 for most participants (Table 4.11).

Manipulation stage: During the manipulation stage of the buttoning task, correlation coefficients decreased when compared to the formation stage, particularly index and middle fingers MCP flexion, with coefficients at or below 0.76 for 90% of participants (Table 4.5, 4.11).

Movement correlation between the thumb and index, and middle fingers decreased to levels below 0.65 for all participants. This trend may suggest the finer nature of the task required the fingers to move in an independent manner in order to proficiently complete the task.

Release stage: The release stage was characterised by high correlation coefficients between the index and middle fingers’ MCP flexion. 80% of participants had correlation coefficients above 0.80 for the release stage (Table 4.5). Correlation between index and middle finger’s flexion with thumb flexion was significantly lower, with 90% of the subjects having coefficients below 60% during this stage of the task. This results may indicate index and middle finger tend to move interdependently when releasing the object, and extending to return to a relaxed posture, while the thumb tends to move in a more independent pattern, normally being the last finger to return to the resting posture (Table 4.11).

suggesting a coordinated finger flexion as the hand prepared the hand posture to manipulate the lid. A variety of precision grips were observed from participants as they reached forward to hold the bottle. extend in a more independent manner.

TABLE 4.5 MEAN VALUES OF THE CORRELATION COEFFICIENTS FROM MCP JOINTS FOR ALL SUBJECTS DURING THE THREE STAGES OF THE BUTTONING TASK

MCP Flexion Index MCP Flexion Middle MCP Flexion Index MCP Flexion Thumb MCP Flexion Middle MCP Flexion Thumb Subject

MCP Flexion Index MCP Flexion Middle MCP Flexion Index MCP Flexion Thumb MCP Flexion Middle MCP Flexion Thumb 1

85 Release Stage: The release stage resulted in low correlation coefficients between the MCP joints of the thumb and the index and middle fingers’, indicating the dissolution of the grip style was completed with a low degree of interdependencies between the fingers involved in the activity, this behaviour could be generally observed from 80% of the subjects (Table 4.6, 4.11, Appendix D).

Variable Dexterity Test – Cylinder

Formation stage: The highest correlation coefficients during the formation stage of the VDT-Cylinder were observed between middle and ring fingers’ MCP flexion, with values varying between 0.60 and 0.94. Coefficients between movements from digits 2-5 were generally larger than those between movements involving the thumb. However, most correlation coefficients were from low to moderate, indicating the formation of the cylinder grip involved mostly independent finger movements before making contact with the object (Table 4.7).

Manipulation stage: During the manipulation stage, the VDT-Cylinder task had moderate to high correlation coefficients for most movements under analysis. Particularly, flexion

TABLE 4.6 MEAN VALUES OF THE CORRELATION COEFFICIENTS FROM THE MCP JOINTS FOR ALL SUBJECTS DURING THE THREE STAGES OF THE BOTTLE OPENING TASK.

MCP Flexion Index MCP Flexion Middle MCP Flexion Index MCP Flexion Thumb MCP Flexion Middle MCP Flexion Thumb Subject

MCP Flexion Index MCP Flexion Middle MCP Flexion Index MCP Flexion Thumb MCP Flexion Middle MCP Flexion Thumb 1

86 movements involving digits 2-4 had high correlation coefficients during this stage. Flexion movements involving the thumb had higher correlation when compared to the formation stage, with moderate values (0.6-0.69) from most participants (Table 4.7). Correlation coefficients between MCP flexion of index, middle and ring fingers were the highest from the movements under analysis. These results suggest the manipulation of the cylinder object required little finger independent movement, particularly from digits 2-5 (Table 4.11).

Release stage: During the release stage of the VDT-Cylinder task, flexion movements across fingers were moderately correlated, with values between 0.6 and 0.85 from 90% of the subjects. Correlation coefficients between the index, middle, and ring fingers MCP flexion had the highest correlation among the movements under analysis. Furthermore, movements involving the thumb had higher correlation coefficients when compared to the formation and manipulation stages, suggesting the release was made of coordinated, interdependent extension from most joints as the hand returned to the resting position (Table 4.7, 4.11,

MCP Flexion Index MCP Flexion Middle MCP Flexion Index MCP Flexion Thumb MCP Flexion Middle MCP Flexion Thumb MCP Flexion Middle MCP Flexion Ring Subject

MCP Flexion Index MCP Flexion Middle MCP Flexion Index MCP Flexion Thumb MCP Flexion Middle MCP Flexion Thumb MCP Flexion Middle MCP Flexion Ring 1

87 Drinking from a glass task

Formation stage: During the formation stage of the glass task, correlation coefficients between MCP flexion from index, middle, and ring fingers were from moderate to high (0.71 – 0.95) for most participants, while correlation from movements involving the thumb and little finger was between low and moderate (0.45 - 0.69). Results and observation suggest the formation of the cylinder grip required to drink from the glass was generally made of coordinated flexion movements, as the fingers prepared for the specific size of the glass (Table 4.8, 4.11).

Manipulation stage: The manipulation stage was characterised by low correlation coefficients from the little finger’s MCP, PIP, and DIP flexion (0.1 – 0.4) with respect to the rest of the fingers. Movement from digits 2-4 were moderately or highly correlated across subjects during the manipulation of the glass, indicating the object was firmly under control with coordinated movements from these digits. Additionally, movement correlation from MCP thumb flexion was between 0.5 and 0.7 for most subjects, indicating low to moderate coordination between digits 2-5 and the thumb when holding and transporting the glass (Table 4.8).

Release stage: Correlation coefficients from movements involving the index, middle, and ring fingers were high for most subjects during the release stage of the task (0.8 - 0.95). Thumb flexion movements were moderately correlated with both index and middle fingers for 80% of participants, suggesting the dissolution of the cylinder grasping patterns was mostly made of interdependent finger flexion-extension movements. Moreover, results suggest the drinking task was generally made of well coordinated and interdependent finger movements during its three pre-defined stages (Table 4.8, 4.11, Appendix D).

Variable Dexterity Test – Spherical

Formation stage: During the formation stage of the VDT-Spherical task the MCP flexion movements of both middle and ring fingers had moderate to high correlation coefficients (0.75 – 0.95). In addition, correlation coefficients between MCP flexion movements of the thumb and index and middle fingers were low to moderate (0.5 – 0.75) suggesting movements from digits 2-5 were made of coordinated flexion-extension as the hand reached forward and extends, forming the required spherical grip (Table 4.9).

Manipulation stage: The manipulation stage of the VDT-Spherical task had high correlation coefficients between movements involving digits 2-5 (0.8 – 0.95) from 90% of participants.

Movements involving the thumb had considerably lower correlation coefficients, indicating an independent role of thumb flexion as the hand transports the circular object to the target position while maintaining the spherical posture (Table 4.9).

TABLE 4.8 MEAN VALUES OF THE CORRELATION COEFFICIENTS FROM THE MCP JOINTS FOR ALL SUBJECTS DURING THE THREE STAGES OF THE DRINKING TASK.

MCP Flexion Index MCP Flexion Middle MCP Flexion Index MCP Flexion Thumb MCP Flexion Middle MCP Flexion Thumb MCP Flexion Middle MCP Flexion Ring Subject

MCP Flexion Index MCP Flexion Middle MCP Flexion Index MCP Flexion Thumb MCP Flexion Middle MCP Flexion Thumb MCP Flexion Middle MCP Flexion Ring 1

89 Release stage: The release stage of the VDT-Spherical task showed a similar pattern of high correlation between digits 2-4, with coefficients ranging between 0.8 – 0.95 in 90% of participants (Table 4.9, Appendix D).

TABLE 4.9 MEAN VALUES OF THE CORRELATION COEFFICIENTS FROM THE MCP JOINTS FOR ALL SUBJECTS DURING THE THREE STAGES OF THE VDT-SPHERICAL TASK.

Jar Opening task

Formation stage: The formation stage of the jar task was made of highly correlated flexion movements of digits 2-4 (0.8 – 0.95). Correlation of flexion movements involving the thumb were moderately correlated across the stage for most participants, suggesting a highly coordinated movement from most subjects whilst forming the spherical grip required to interact with the lid (Table 4.10).

Manipulation stage: During the manipulation phase correlation between relevant movements associated with the spherical grip remained moderate to high (0.6 – 0.95). Index, middle, and ring fingers MCP flexion were particularly high during this stage, with correlation coefficients above 0.8 for 90% of participants. Manipulation of the jar was characterised by interdependent movements of all fingers involved, as the dominant hand had firm control over the lid (Table 4.10, 4.11).

MCP Flexion Index MCP Flexion Middle MCP Flexion Index MCP Flexion Thumb MCP Flexion Middle MCP Flexion Thumb MCP Flexion Middle MCP Flexion Ring Subject

MCP Flexion Index MCP Flexion Middle MCP Flexion Index MCP Flexion Thumb MCP Flexion Middle MCP Flexion Thumb MCP Flexion Middle MCP Flexion Ring 1

MCP Flexion Index MCP Flexion Middle MCP Flexion Index MCP Flexion Thumb MCP Flexion Middle MCP Flexion Thumb MCP Flexion Middle MCP Flexion Ring

In document Development of a dexterity assessment method (Page 77-97)