Effects of postural support on eye hand interactions across development

Abstract

Reaching to grasp an object of interest requires a complex sensorimotor transformation-involving eye, head, hand, and postural systems. We show here that discontinuities in development of movement in these systems are dependent not only on age but also vary according to task constraints. Providing external postural support allows us to examine the differential influences of the eye on the hand and the hand on the eye as the ability to isolate and coordinate each system changes with age. Children 4-6 years old had significant difficulty isolating eye movement from head or hand movement, whereas children 7-9 years old showed improved ability to isolate the eye, and by 10-15 years children became proficient in isolating hand movements from eye movements. Postural support had differential effects on the processes of initiation and execution of eye-hand movements. The addition of postural support decreased the time needed for planning the movement, especially in the youngest children, and contributed to increased speed of isolated movements, whereas it caused differential slowing of coordinated movements depending on the child's developmental level. We suggest that the complexity of the results reflects the complexity of changing task requirements as children transition from simpler ballistic control of all systems to flexible, independent but coordinated control of multiple systems.

Figure 1

Experimental setup: children sat in front of a computer monitor in a darkened room, hands resting on a table. Supported postural condition included hip straps that keep the pelvis aligned vertically and a rigid support around the thoracic spine ~ 1 inch below arm pit. The straps were released and support bar removed for the unsupported condition. Magnetic sensors were attached to a headband and to the index finger of dominant hand.

Figure 2

Data was collected during completion of 4 tasks a) control task, maintain visual fixation on center target (frog image) do not look at peripheral distracter (butterfly images) b)eye only task, begin with central fixation quickly look at peripheral target when it appears c) eye hand task, begin with central fixation quickly look at and touch peripheral target when it appears d) maintain central fixation, quickly touch peripheral target without looking at it.

Figure 3

Group means for eye peak velocity during isolated (a) vs. paired (b) eye movements made with postural support (filled squares) and without support (unfilled diamonds).

Figure 4

Group means for hand RT during isolated (a) vs. paired (b) hand movements made with postural support (filled squares) and without support (unfilled diamonds).

Figure 5

Group means for hand peak velocity during isolated (a) vs. paired (b) hand movements made with postural support (filled squares) and without support (unfilled diamonds).

Figure 6

Group means for hand submovements (# of zero acceleration crossings) during isolated (a) vs. paired (b) hand movements made with postural support (filled squares) and without support (unfilled diamonds).