Table 1. Acoustic characteristics of the labels presented with AD prosody (Experiment 1) and ID prosody (Experiment 2).

	M F0 (Hz)	SD F0 (Hz)	Range F0 (Hz)	M Duration (sec)	SD Duration (sec)
AD labels	189.7	15.2	69.1-303.4	.826	.13
ID labels with variation	271.9	44.4	80.2-521.5	1.002	.10
ID labels without variation	310.9	5.7	91.6-499.5	1.034	.11

Notes. Fundamental frequency (F0) is an indicator of voice pitch. In all experiments, the stimuli were amplified to the same root-mean-square amplitude using Adobe Audition software. They were presented at 65 dB ± 5 dB, as measured by a digital sound level meter located at the infant’s head.