Sources and method
Every number in this app comes from one of these. Each entry says what it is relied on for and how the figure was obtained.
24 sources
- Engle, W.A. and the Committee on Fetus and Newborn (2004). "Age terminology during the perinatal period." Pediatrics 114(5), 1362–1364.
The definitions of gestational age, chronological age, post-menstrual age and corrected age, and the convention that corrected age is measured against 40 weeks.
Definitional — a convention, not a measurement - Banks, M.S. & Salapatek, P. (1978). "Acuity and contrast sensitivity in 1-, 2-, and 3-month-old human infants." Investigative Ophthalmology & Visual Science 17(4), 361–365.
Acuity estimated a different way, from where full contrast sensitivity functions cut off, and the very low spatial frequency of peak contrast sensitivity in early infancy.
Measured — read from a table in the paper - Banks, M.S. (1980). "The development of visual accommodation during early infancy." Child Development 51(3), 646–666.
That steady-state focus error and accommodative response slope improve up to about 3–4 months, and that accommodative error does not meaningfully limit infant acuity.
Measured — read from a table in the paper - Braddick, O., Atkinson, J., French, J. & Howland, H.C. (1979). "A photorefractive study of infant accommodation." Vision Research 19(12), 1319–1330.
Consistent focusing behaviour at a low accommodative demand of about 1.3 D (≈ 75 cm) emerging between 3 and 6 months.
Measured — read from a table in the paper - Clavadetscher, J.E., Brown, A.M., Ankrum, C. & Teller, D.Y. (1988). "Spectral sensitivity and chromatic discriminations in 3- and 7-week-old human infants." Journal of the Optical Society of America A 5(12), 2093–2105.
That few 3-week-olds show reliable chromatic discrimination while most 7-week-olds do, and the long-wavelength advantage at 3 weeks.
Measured — read from a table in the paper - DeCasper, A.J. & Fifer, W.P. (1980). "Of human bonding: newborns prefer their mothers’ voices." Science 208(4448), 1174–1176.
That newborns prefer their own mother’s voice — the milestone that gives the maternal-voice level difference its meaning.
Measured — read from a table in the paper - Gerhardt, K.J. & Abrams, R.M. (2000). "Fetal exposures to sound and vibroacoustic stimulation." Journal of Perinatology 20(8 Pt 2), S21–S30.
An attenuation of roughly 30 dB above 600–1000 Hz, one of the several disagreeing published figures the app reports as a range.
Digitised — read off a published figure, so a few per cent uncertain - Haynes, H., White, B.L. & Held, R. (1965). "Visual accommodation in human infants." Science 148(3669), 528–530.
The median 19 cm focus distance in alert newborns — the origin of the "babies see 8–12 inches" claim, cited so the app can state what the paper does and does not support.
Measured — read from a table in the paper - Held, R., Birch, E.E. & Gwiazda, J. (1980). "Stereoacuity of human infants." Proceedings of the National Academy of Sciences 77(9), 5572–5574.
The abrupt onset of stereopsis between about 3 and 5 months — explained in the app and never drawn, because a flat screen cannot present it.
Measured — read from a table in the paper - Hepper, P.G. & Shahidullah, B.S. (1994). "Development of fetal hearing." Archives of Disease in Childhood 71(2), F81–F87.
The gestational progression of the audible band: first response at 19 weeks to 500 Hz, 96 % responding to 250 and 500 Hz but none to 1000 or 3000 Hz at 27 weeks, all responding at 1000 Hz by 33 weeks and 3000 Hz by 35 weeks.
Measured — read from a table in the paper - ISO 226:2003, Acoustics — Normal equal-loudness-level contours; with Fastl, H. & Zwicker, E. (2007). Psychoacoustics: Facts and Models, 3rd ed. Springer (minimum audible field).
The adult minimum-audible-field reference curve that the infant elevation is added to.
Measured — read from a table in the paper - Mohn, G. & van Hof-van Duin, J. (1986). "Development of the binocular and monocular visual fields of human infants during the first year of life." Clinical Vision Sciences 1(1), 51–64.
The restricted newborn visual field and its expansion over the first year — described in the app, deliberately not rendered as a vignette.
Measured — read from a table in the paper - Neijzen, C.M., de Wit, F.M., et al. (2025). "Reference values for the Teller Acuity Cards II (TAC II) in infants and preverbal children, a meta-analysis." Acta Ophthalmologica. doi:10.1111/aos.17447.
The behavioural binocular grating-acuity curve the app renders, and its stated uncertainty of approximately 0.16 log10 units, flat with age.
Measured — read from a table in the paper - Norcia, A.M. & Tyler, C.W. (1985). "Spatial frequency sweep VEP: visual acuity during the first year of life." Vision Research 25(10), 1399–1408.
The swept-VEP acuity curve reported alongside the behavioural one as an upper bound, and the 24.3 c/deg adult reference measured in the same apparatus.
Measured — read from a table in the paper - Norcia, A.M., Tyler, C.W. & Hamer, R.D. (1990). "Development of contrast sensitivity in the human infant." Vision Research 30(10), 1475–1486.
Contrast threshold at low spatial frequency falling from 7 % at 2–3 weeks to a 0.5 % asymptote by 9 weeks, against an adult 0.32–0.22 %, and the two-phase shape of contrast development.
Measured — read from a table in the paper - Olsho, L.W., Koch, E.G., Carter, E.A., Halpin, C.F. & Spetner, N.B. (1988). "Pure-tone sensitivity of human infants." Journal of the Acoustical Society of America 84(4), 1316–1324.
The primary pure-tone threshold dataset underlying the infant audiogram.
Measured — read from a table in the paper - Peeples, D.R. & Teller, D.Y. (1975). "Color vision and brightness discrimination in two-month-old human infants." Science 189(4208), 1102–1103.
Established red/white chromatic discrimination at two months of age.
Measured — read from a table in the paper - Querleu, D., Renard, X., Versyp, F., Paris-Delrue, L. & Crèpin, G. (1988). "Fetal hearing." European Journal of Obstetrics & Gynecology and Reproductive Biology 28(3), 191–212.
The low-pass character of the abdominal transfer function, with frequencies below about 400 Hz well preserved and increasing attenuation above.
Digitised — read off a published figure, so a few per cent uncertain - Regal, D.M. (1981). "Development of critical flicker frequency in human infants." Vision Research 21(4), 549–555.
Low critical flicker fusion frequency in the first weeks reaching near-adult values within months — described, not rendered.
Measured — read from a table in the paper - Richards, D.S., Frentzen, B., Gerhardt, K.J., McCann, M.E. & Abrams, R.M. (1992). "Sound levels in the human uterus." Obstetrics & Gynecology 80(2), 186–190.
Measured inside the human uterus: the mother’s own voice enhanced by 5.2 dB, an external male voice attenuated 2.1 dB and an external female voice 3.2 dB.
Measured — read from a table in the paper - Skelton, A.E., Maule, J. & Franklin, A. (2022). "Infant colour perception: Insight into perceptual development." Child Development Perspectives 16(2), 90–95.
The review timeline placing the emergence of colour vision between about 3 weeks and 3 months.
Derived — computed from the source by a stated relation - Varner, D., Cook, J.E., Schneck, M.E., McDonald, M. & Teller, D.Y. (1985). "Tritan discriminations by 1- and 2-month-old human infants." Vision Research 25(6), 821–831.
Demonstrable tritan (S-cone) discrimination at 1 and 2 months, which is why the app does not dramatise a months-long absence of blue-yellow vision.
Measured — read from a table in the paper - Werner, L.A. (2002). "Infant auditory capabilities." Current Opinion in Otolaryngology & Head and Neck Surgery 10(5), 398–402.
Behavioural thresholds of 40–55 dB SPL at 1 month falling to 10–30 dB SPL by 6–12 months; a 4 kHz threshold only ~10 dB above adult at 6 months while low frequencies mature into childhood; and that cochlear function is mature at term, so the elevation is middle-ear and central.
Measured — read from a table in the paper - World Health Organization. "Preterm birth" fact sheet. Definition: birth before 37 completed weeks of gestation.
The 37-week threshold that separates preterm from term birth.
Definitional — a convention, not a measurement
Where studies disagree, this app says so rather than picking one quietly. Two accepted ways of measuring what a baby can resolve differ by a factor of about three to six and a half at the same age.
This is not a vision or hearing test. If anything worries you, speak to your paediatrician or a paediatric eye doctor.