chapter 9 Development of Manipulative Skills

Manipulative Skills and the Model of Constraints What makes humans unique in performing manipulative skills? What structural constraints contribute to this uniqueness? How might these constraints change over the life span?

Reaching and Grasping Proficient performers execute the reach and the grasp as a single skill. Study here is of grasping first, then reaching.

Grasping Prehension is the grasping of an object. Halverson proposed 10 phases of development in –Transition from power to precision grips –Imposition of one task, one set of environmental conditions Hohlstein (1982): Object size and shape influence type of grasp (by 9 months, infants shape hand to match object as they reach).

Halverson’s Phases of Grasping Development See figure 9.1 on page 171 of the textbook.

More on Grasping How do you shape your hand to pick up the following? –Pen –Quarter –Heavy book –Bottle of water –Crystal vase What is the role of vision in grasping?

Body Scaling in Grasping Grip movements are body scaled (Newell, Scully, Tenenbaum, & Hardiman, 1989). –Key is hand size relative to object size. –More research is needed in infancy. Ratio of hand size to object size is consistent for transitioning from using one hand to using two hands to pick up object.

Reaching What drives infants to transition from random arm movements to purposeful reaches? Does learning to reach involve learning to visually match hand and object or learning to control the arm?

Hand–Mouth Movements At 3 to 4 months, infants become consistent in moving the hand to the mouth. By 5 months, they open the mouth in anticipation of the hand’s arrival.

Bimanual Reaching and Manipulation At 2 months, infants show bilateral arm extension and reaching. Around 4.5 months, infants reach for objects with both arms (usually one hand reaches and grasps object first). During year 1, infants alternate between predominantly unimanual and predominantly bimanual reaching. (continued)

Bimanual Reaching and Manipulation (continued) By 12 months, we see pulling apart and insertion actions. Early in year 2, infants use objects as tools. After 18 months, infants manipulate objects cooperatively with both hands. By end of year 2, we see complementary activities.

Bimanual Manipulation What activities do you perform that require complementary use of the hands? What challenges would you face in completing these tasks with one wrist in a cast?

Role of Posture Reaching improves when infants can maintain postural control. What postural constraints could serve as limiters to the rate of development of reaching?

Manual Performance in Adulthood Kauranen & Vanharanta (1996) –Manual performance declined after age 50. –Movements slowed; coordination scores declined. Hughes et al. (1997) –Strength declined. –More individuals exceeded time thresholds. Some loss in coordination of handwriting Accuracy maintained, especially in well- practiced tasks

Rapid Aiming Movements Involve an initiation and acceleration to peak velocity, then a deceleration and termination phase. Young adults tend to have symmetrical phases; older adults move less far in acceleration phase, thus have longer deceleration phase.

Fundamental Manipulative Skills Performer gains possession or control of an object. Catching is the most common.

Catching Ideally, objects are caught in the hands so they can be manipulated. Needing to intercept an object makes catching more difficult. Children initially position arms and hands rigidly, sometimes trap ball against chest. Children sometimes turn their head away or close their eyes.

Beginning Catching

Proficient Catching Hands “give” with the ball to gradually absorb force. Catcher moves from side to side or forward and back to intercept the ball. Fingers are pointed up for high balls and down for low balls. (continued)

Proficient Catching (continued)

Developmental Changes in Catching Note: Task and environmental constraints greatly affect the difficulty of catching. Arm action 1. Little response 2. Hugging 3. Scooping 4. Arms “give” (continued)

Developmental Changes in Catching (continued) Hand action 1.Palms up 2.Palms in 3.Palms adjusted Body action 1.No adjustment 2.Awkward adjustment 3.Proper adjustment

Model of Constraints and Catching Consider various objects to catch and various task and environmental constraints for catching tasks. What makes some catching tasks more difficult than others?

Anticipation Anticipation is involved in many manipulative tasks and interception skills. Studies often involve coincidence- anticipation tasks (anticipating completion of movement to coincide with arrival of moving object).

Development of Coincidence Anticipation Interception success is often related to ball size, speed, trajectory, and other task and environmental constraints. Why might studies on coincidence- anticipation reflect limits of perception more than real-world catching skill?

Perception–Action Perspective Two characteristics of person–environment system for catching involve constant patterns of change. –Invariants: stable patterns –Expanding optical array: visual pattern that expands or constricts on the retina Invariance in moving sideways was investigated through the constant bearing angle strategy. (continued)

Perception–Action Perspective (continued) Do catchers intercept a moving ball by keeping a ratio (based on an angle of gaze) at or near zero? (McLeod and Dienes, 1993, 1996) Do catchers keep the vertical optical acceleration of the ball close to zero? (Michaels & Oudejans, 1992; Oudejans et al., 1996)

How Do Children Arrive at the Right Place? Perhaps children learn that the ratio is zero when they stand still and catch a ball. Eventually they learn to move to keep the ratio at zero. Experience is important in learning to move to catch. Parents, teachers, and coaches can manipulate information constraints during exploratory practice. Identifying important sources of information might also help novice adults.

Catching in Older Adulthood Little research is available. Catching might be influenced by factors affecting movement speed or ability to reach. Older adults are somewhat less accurate and more variable on coincidence- anticipation tasks. Older adults can improve with practice.

Driving and Piloting What changing structural constraints might affect performance by older adults who drive cars or pilot boats or planes? What task and environmental constraints could prove challenging to older adults? What compensatory strategies could be used by older adults to offset these challenges?

Manipulative Skills: Summary Manipulative skills set humans apart. Infants become skilled at reaching and grasping. Children are accomplished catchers by 11 or 12 years of age, but catching tasks that require movement are difficult. Aging probably affects getting to a ball more than it affects manipulative aspects of catching.

Assessment of Catching For comparisons, task and environmental constraints must be consistent. The number of catches in a set of attempts can be scored. The developmental sequence can provide information about the movement process.