Is early word-form processing stress-full? How natural variability supports recognition

Abstract

In a series of studies, we examined how mothers naturally stress words across multiple mentions in speech to their infants and how this marking influences infants' recognition of words in fluent speech. We first collected samples of mothers' infant-directed speech using a technique that induced multiple repetitions of target words. Acoustic analyses revealed that mothers systematically alternated between emphatic and nonemphatic stress when talking to their infants. Using the headturn preference procedure, we then tested 7.5-month-old infants on their ability to detect familiarized bisyllabic words in fluent speech. Stress of target words (emphatic and nonemphatic) was systematically varied across familiarization and recognition phases of four experiments. Results indicated that, although infants generally prefer listening to words produced with emphatic stress, recognition was enhanced when the degree of emphatic stress at familiarization matched the degree of emphatic stress at recognition.

Figure 1

Study 1: Graphic presentation of number of mentions by each mother across target words. The area of each dot is proportional to the number of words that a mother mentioned a given number of times. Mother 7 mentioned one word once, three words twice, five words three times, one word four times, and two words five or more times.

Figure 2

Study 1: Average duration of target words across five mentions (95% confidence intervals).

Figure 3

Study 2A: Recognition orientation times (within-subjects): alternating (emphatic/nonemphatic) familiarization stress with alternating (emphatic/nonemphatic) stress in recognition sentence sets.

Figure 4

Study 2B: Recognition orientation times (between-subjects): 1) emphatic familiarization stress and alternating (emphatic/nonemphatic) stress in recognition sentences OR 2) nonemphatic familiarization stress with alternating (emphatic/nonemphatic) stress in recognition sentence sets.

Figure 5

Study 2C: Recognition orientation times (within-subjects): 1) emphatic familiarization stress on one word and 2) nonemphatic familiarization stress on another word with alternating stress in recognition sentence sets (within-subjects).

Figure 6

Study 3: Recognition scores (between-subjects): Recognition orientation time differences for sentence sets containing familiarized words minus sentence sets containing nonfamiliarized words for matched vs. unmatched stress from familiarization to recognition.