The conflicting statements relative to the proper stimulus for eliciting the Moro reflex and the response to be expected have been discussed and a historical review of the varying points of view presented.
The present study was done in three parts. In the first part, seven infants were studied by motion picture analysis at 0-4 days, 6 weeks, and 12 weeks of age. Four stimuli were used: (1) allowing the baby's head to drop back suddenly; (2) a pin prick to the baby's foot; (3) a loud noise; (4) slapping the examining table near the baby's head. The second and third stimuli were relatively ineffective at all ages tested. The first and fourth stimuli were equally effective throughout. The outward movements of the arms were dominant throughout but the secondary inward movements were prevalent in the neonatal period, but absent at 12 weeks of age. In the second part, 30 infants were studied by motion picture analysis, only in the neonatal period using four stimuli: (1) allowing the baby's head to drop back suddenly; (2) slapping the examining table near the head of the baby; (3) suddenly tilting downward a board to which the baby was fastened; (4) sudden jarring of the same board.
A scoring scale for arm and hand movements was devised as well as a scale for the state of arousal of the infant just prior to testing. The first, second, and fourth stimuli were equally effective and all were superior to the sudden dropping of the board. It was concluded that the stimulation of the semicircular canals of the infants was not enough for a good Moro response when neck movement was prevented by the board. Neck movement seems to be essential for significant Moro response. The scores for hand response were somewhat related to those for arm responses.
In the third part of this study, a detailed scoring technique for arm and hand movements and state of arousal of the baby was devised. Forty infants were studied in the neonatal period by direct observation. Interscorer agreement between five observers rating arm and hand movements was not good. This illustrates the difficulty of carefully observing and recording the Moro reflex response without the aid of motion pictures. The hand responses did not correlate strongly with the arm responses so that one could not rely on just hand observations.
In both Parts II and III of this study, no correlation could be found between the state of arousal of the infant just prior to the administration of the stimulus and the degree of response.