Simulating Infant Senses with Age-Tuned Networks

Somesh Mohapatra

Figure 1: Sensory milestones from birth to 24 months, by sense. Each dot is a typical age at which a capacity is reported in group studies; individual babies vary by weeks to months. Touch: responsiveness and reflexes at birth, exploration with hands and mouth, then with fingers [ 11 ] . Taste and smell: preference at birth for odours of the mother’s diet in late pregnancy [ 44 ] . Hearing: preference for the mother’s voice at birth [ 12 ] , recognition of own name at about 4.5 months [ 33 ] , vowel perception shaped by the home language by 6 months [ 27 ] , decline of non-native consonant discrimination by 10–12 months [ 54 ] . Vision: preference for face-like patterns at birth [ 14 , 23 ] , smooth pursuit developing between 2 and 3 months [ 51 ] and colour discrimination improving over the first months [ 2 , 10 ] , binocular depth (stereopsis) at about 4 months [ 19 ] , face perception narrowing to familiar species and groups by 9 months [ 42 , 25 ] . Second year: walking alone, with touch and body sense guiding balance, and following one-step spoken directions by about 18 months [ 59 ] ; comprehension of hundreds of words by 24 months [ 15 , 59 ] . Horizontal bars mark gradual refinement without a single milestone age: locating touch in space [ 11 ] , sound localisation and listening in noise [ 56 ] , and visual acuity [ 37 , 47 ] . No later taste or smell milestone was found in the sources we could verify. Shading marks the first year, the range of the main networks; the second year is covered by the website’s tables and by one follow-up run (Fig. 7 a).

Sense	Birth	3 months	6 months	12–24 months
Vision: detail	$\approx$ 1 cycle/degree (20/600); sees bold shapes at 20–30 cm	2.6 (looking) to 4 (evoked) cycles/degree	4.8 (looking) to 15 (evoked) cycles/degree	7.5–10.5 (looking); evoked responses near adult; fine detail improves into preschool
Vision: contrast, colour	only strong contrasts; colour limited	medium contrasts; colour much improved	most everyday contrasts; colour near adult	contrast near adult
Vision: motion, depth, faces	notices motion; prefers face-like patterns	smooth pursuit; stereopsis begins (3–5 months)	adult-like motion; uses depth when reaching	face perception narrowed to familiar faces (9 months)
Hearing	hears from before birth; quiet sounds missed; prefers mother’s voice	thresholds still well above adult	many basic abilities near adult; vowels tuned to home language	non-native consonants harder (10–12 months); localisation and hearing in noise keep improving
Touch and body sense	most mature sense; responds everywhere; rooting and grasp	explores with hands and mouth	explores textures with fingers; combines body sense and vision in reaching	fine touch keeps sharpening; body sense supports standing and walking
Taste and smell	prefers odours met in the womb	–	–	– (not modelled)

Table 1: What each sense can do, by age. Values are typical for groups of babies; individual babies vary widely. For vision, two numbers are given where behavioural (preferential looking) and evoked-potential measures differ. Sources are given in the text; the numbers used by the simulations are in Fig. 2 .

Figure 2: Age-tuned front ends used by the simulations and the website. a , Visual acuity. Solid line: the evoked-potential-style table used by the models, which rises steeply in the first year [ 39 ] ; dashed line and band: behavioural acuity-card values, shown with the roughly one-octave normal range on either side [ 37 , 47 ] ; dotted line, 30 cycles/degree (adult reference). b , Contrast sensitivity. c , Colour saturation relative to adult (a simplification of chromatic sensitivity). d – f , Hearing: extra attenuation standing for raised thresholds [ 56 ] , reduced high frequencies, and the fraction of the adult left-right (interaural) difference. Values between the listed ages are interpolated linearly. The vision tables follow published infant data; the hearing tables are coarse anchors that respect the direction of known changes, not fitted values; Fig. 6 compares them with threshold data. The evoked-potential acuity, contrast and colour values at 0, 3, 6 and 12 months are the same as the vision front-end table of the companion paper [ 38 ] ; the behavioural acuity curve, the extension to 24 months and the hearing parameters used on real audio ( d – f ) are new here. Values beyond 12 months are used by the website and by the follow-up runs of Fig. 7 a; the evoked-potential acuity, contrast and colour tables are held constant after 12 months (colour after 5), and only behavioural acuity and hearing change in the second year.

Figure 3: What the input allows and what a network learned, by age. a , Vision: toy position decoded from a self-supervised prediction network trained through four age stages (solid; mean

\pm

1 s.d., 5 seeds; probe fitted and tested on input of the stage’s own age), against a supervised network given only that age’s filtered frames (dashed; one network per age). b , The same for hearing. c , Touch: toy identity from the supervised ceiling, high from birth (chance 0.25). Same training runs as the main study of the companion paper [ 38 ] , which reports these vision and hearing values in its development figure; this figure is a new plot that sets the learned and available values side by side for each sense.

Figure 4: Perceptual signatures in age-tuned networks. a , b , One recurrent prediction network trained behind a newborn and a 12-month front end in each sense: how well object identity can be read out ( a ) and how surprised the network is when an object jumps ( b ,

d_{z}

). Vision changes most; touch hardly changes. c , A critical period: final fine-detail accuracy after a 3-month window of heavy blur placed at different ages, each window followed by 8 months of clear input; only the earliest window leaves a lasting loss. d , e , Perceptual narrowing in a run where only two of four identities ever appear. In vision ( d ), surprise at a change between the two never-seen identities (violet) rises and then falls, while the familiar pair (black) keeps rising and a control that saw all identities (dashed) does not fall. In hearing ( e ) the same pattern appears in how separable the unfamiliar identities are (

d^{\prime}

), not in surprise. Mean over 3 seeds ( a – c ) with

\pm

1 s.d. bars or bands. Drawn for this paper from the raw results of the project’s cross-sense and age-modelling studies; this figure does not appear in the companion paper [ 38 ] .

Figure 5: The Baby Senses Lab. a , Age profile at 3 months: plain-language descriptions of seeing, hearing, and touch and body sense (thinking, social and movement are in a separate section), and the numbers behind them, opened from the section below the descriptions, including both acuity measures and the smallest detail resolvable at 30 cm. b , “See like a baby”: an image shown as an adult sees it and as a 2-month-old might at 30 cm, using the front end of Fig. 2 a–c, and the same image across the first year (newborn to 12 months). Users can load their own photos and videos. Screenshots of the live site.

Figure 6: Hearing front end compared with infant threshold data. Points: infant-minus-adult pure-tone thresholds from group studies [ 40 , 55 , 56 ] ; filled markers low frequencies (250–500 Hz), open markers high frequencies (4–8 kHz); grey, the pooled 6- and 12-month value. Review values that differ from the primary study [ 56 ] are shown but not fitted. Orange line: exponential fit to the mean of low and high frequencies over the range of the data (dotted beyond it). Dashed line: the attenuation anchors used by the models and the website (Fig. 2 d). There are no data at birth or in the second year.

Figure 7: Training beyond 12 months, and predicting latents instead of pixels. a , Toy position decoded from the main-study networks (own-age linear probe; mean

\pm

1 s.d., 5 seeds) continued to 18 and 24 months (shaded), for vision with the evoked-potential (dark blue) and behavioural (light blue) acuity tables and for hearing (orange); dashed lines, supervised information ceiling for the same input. b , Vision on the 0–12 month schedule: pixel prediction (the main-study objective) against latent prediction with a slowly updated target encoder, with and without variance–covariance regularisation; dashed line, information ceiling. New runs for this paper.

Study	Senses and input	Networks and objective	Seeds
Main study (Fig. 3 )	Vision (32 $\times$ 32 colour), binaural hearing (2 $\times$ 32 bands), touch (8 $\times$ 8 patch), body position; one toy, a moving hand and an occluding screen	Encoder, residual dynamics over a memory window and decoder; reconstruct and predict next frame; four age stages in one run; supervised information ceiling per age	5
Cross-sense study (Fig. 4 a, b, d, e)	Vision (12 $\times$ 12), hearing (24 bands), touch (16 taxels) rendered from one latent world	Recurrent, transformer, predictive-coding and latent-prediction networks at $\approx$ 20k core parameters; next-step prediction	3 (5 for onset order)
Age-modelling study (Fig. 4 c)	Vision (shape-versus-texture gratings); vision plus audio for onset order	Compact convolutional networks, fixed or growing; classification; blur windows of 3–9 months	3–7
Follow-up runs (Fig. 7 )	As the main study; vision and hearing	Main-study networks continued to 18 and 24 months; and latent prediction against pixel prediction, 0–12 months	3

Table 2: Modelling studies summarised in this paper.

Simulating Infant Senses with Age-Tuned Networks

Abstract

Figures & tables

Human Visual Perception

Making Sense of Touch from the Child's View for Contrastive Learning

Vision Models Capture Complementary Representations in Children That Converge in Adults

Sensing Intelligence as a Trainable Metamaterial Property

Abstract

Human Visual Perception

Explore similar work

Making Sense of Touch from the Child's View for Contrastive Learning

Vision Models Capture Complementary Representations in Children That Converge in Adults

Sensing Intelligence as a Trainable Metamaterial Property