The development of the parachute reaction: a visuo-vestibular response.

The development of the parachute reaction as a postural response has been tested under various optic stimuli in normal and statomotorically retarded infants. Complete reaction consists in symmetric extension of the arms with extension and spreading of the fingers on quick approach to visual surface. Using a glass plate with three different sized stimulus patterns the parachute response is scored as complete or incomplete. The complete reaction to large visual surface develops significantly earlier than to small visual surface. The response also requires simultaneously a visual and a vestibular sensory input. The developmental course of the parachute reaction is statistically significant linear correlated in double logarithmic transformation to the stimulus pattern and to the age indicating a complex biological maturating process. When the whole retinal area was stimulated by moving visual scenes similar to normal environmental conditions the reaction starts with about 4 months of age and is fully developed from 9 months onwards. The time of quickest development is around 6.3 months of age, a period where locomotor abilities shift from horizontal postiion to active verticalisation of the body. In statomotorically retarded infants the response develops significantly later according to their active motor behaviour. Brain integration and computing centers of sensory afferent input could be multilevel from reticular formation to cerebral cortex, wherein the latter, probable the parietal lobe should play the major role. It is concluded that the parachute reaction results from a combined visuovestibular mechanism of interaction in connection with sufficient kinesthetic experience in visuo-motor behaviour.