Table 2.
Mean (SD) vowel space area in mels2 and vowel space dispersion in mels for infant-directed (ID) and adult-directed (AD) speech at three longitudinal intervals (Study 1) and at four cross-sectional intervals (Study 2).
| Study | Interval | AD | ID |
|---|---|---|---|
| Study 1 | |||
| Area | 3 months | 123399 (22508) | 123574 (25280) |
| 6 months | 111763 (24742) | 113739 (20865) | |
| 9 months | 104335 (30153) | 118778 (33082) | |
| Dispersion | 3 months | 393 (27) | 395 (24) |
| 6 months | 386 (16) | 399 (35) | |
| 9 months | 374 (36) | 390 (37) | |
| Study 2 | |||
| Area | 3 months | 110990 (23513) | 109293 (25576) |
| 9 months | 117860 (26098) | 109247 (22875) | |
| 13 months | 113386 (19883) | 114137 (26531) | |
| 20 months | 104631 (22937) | 103975 (30412) | |
| Dispersion | 3 months | 389 (35) | 388 (33) |
| 9 months | 382 (29) | 389 (28) | |
| 13 months | 391 (29) | 403 (23) | |
| 20 months | 379 (42) | 380 (47) | |