Studies of the Sucking Reflex

A second area in which habituation and sensitization responses have been
the subject of extensive investigation is the sucking reflex exhibited by human
infants. When the cheeks or lips of a young child are touched with a
nipple or finger, the infant will automatically begin sucking. In a study designed
to explore how various stimuli affect this reflex, it was shown that babies
respond much more vigorously to a bottle nipple than to the end of a
piece of rubber tubing. In addition, repeated presentation of a bottle nipple
causes an increase in sucking response, whereas repeated stimulation with
rubber tubing causes a decrease in sucking. The sensitized or elevated response
to a rubber nipple is a result of activation of the state system, which
increases the baby’s awareness and readiness to respond. Sensitization, however,
does not occur when the baby is stimulated with rubber tubing, and instead
the child habituates to this stimulus.