Abstract
Speech sound discrimination in 72 infants aged 6-12 wk was studied using contingent and noncontingent methods of sound presentation. In the contingent condition a high-amplitude suck was reinforced with the presentation of a speech sound. In the 2 noncontingent conditions speech sounds were presented at either random or periodic intervals independent of infant sucking. Under all 3 conditions, following a period of sucking decrement, there was either a change in the sound presented (sound-change group) or the same sound continued to be presented (no-change group). A significant difference in postdecrement sucking rate between sound-change and no-change groups was found only under the contingent condition. Significant differences in the elimination of subjects from the experimental population for reasons of state change were also found across conditions of sound presentation.

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