The top panel is a spectrum (distribution of intensity over frequency) for /s/ and the bottom one a spectrum for /∫/. The peak location for /∫/ is usually much lower than that for /s/.
Histogram of peak location values (in kHz) collapsing across /s/ and /∫/ tokens in a caregiver with high /s/ peak location.
Average discrimination scores (error bars show standard errors) by median group and age group.
Individual data are plotted on the left panel, sorted by /s/ peak location. For each dyad, peak location in the caregiver’s speech is noted with squares (/s/ = dark; /∫/ = light; both plotted on the kilohertz scale shown on the far left; error bars indicate standard errors); and the infant’s discrimination score is plotted with a white circle in the same vertical line (using the scale between the two panels). The right panel shows a histogram for infants’ discrimination score (on the same scale). The dotted horizontal line crossing both panels signals the 0.5 proportion level for the discrimination scores, above which there would be an evidence of successful discrimination. The other two horizontal lines, crossing only the left panel, represent the average peak location for the /s,∫/ stimuli used in the infant test (/s/ = dark, /∫/ = light).
Objects selected to elicit the target sibilants and vowels through the object label and “primed” words (given in italics below the relevant items).
Average (SD; min-max) of the number of segments tagged (short /s/ and /∫/ are those excluded for being shorter than 40 ms) in each of the median groups.
Average (and SD) of each of the median groups for relevant acoustic correlates, as well as the outcome measure. The first two columns show peak location for the sibilants in kilohertz and the following two columns show measures of distance between the two categories within each talker’s speech: D(a) (distance between the means divided by the average variance) and Welch’s t (distance between the means divided by frequency-weighted variance); the fifth rightmost column displays the outcome of discrimination scores. These averages are given for the whole sample (overall) and also separating infants in their age groups; in the last line of each of these three groupings is the t-value of an unequal variance, two-tailed test across the two median groups is shown together with its significance level (***p < 0.001; **p < 0.01; *p < 0.05).
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