Past exam of the developmental science course of the year 2 of the psychology (experimental) course of the University of Oxford / 2022 / 5 / Solution

Children detect distributional structure at several levels: variation within speech sounds, sequential relations that help identify word-sized units, dependencies across intervening words, and word–referent co-occurrences across scenes. These findings challenge the claim that language is acquired without powerful learning from experience. They do not, by themselves, show that linguistic representations, perceptual constraints or specialised learning biases are dispensable. A learning algorithm and the representations over which it operates are different parts of an explanation.

At the phonetic level, Jessica Maye and colleagues familiarised six- and eight-month-olds with tokens from a speech-sound continuum. Exposure concentrated near one region or around two regions, creating unimodal versus bimodal frequency distributions. Only the bimodally exposed group subsequently discriminated the tested endpoints. Holding the range of speech sounds while changing their frequency profile gives a causal manipulation of distributional input, supporting a mechanism through which experience could tune phonetic categories. Endpoint discrimination is still not equivalent to acquiring the full phoneme inventory of a natural language, and infants' prior perceptual organisation constrains what distributions are available to learn.^[ref]

At the word-boundary level, Jenny R. Saffran and colleagues exposed eight-month-olds for two minutes to a continuous artificial speech stream with repeated trisyllabic units but no pauses marking their boundaries. A head-turn preference procedure then measured responses to familiar units and comparison sequences. Infants differentiated units supported by the stream's sequential regularities. The arrangement matters: after a central light attracted attention, a side light and loudspeaker supported a controlled measure of how long the infant maintained orientation. Masking sound for the accompanying adult and observer reduced inadvertent cueing. This made a nonverbal test of sequence learning possible well before children could explain a segmentation strategy.^[ref]

The relevant statistic can be expressed as the conditional probability $P(s_{t+1}\mid s_t)$ of the next syllable given the current one. High predictability within a recurring unit and lower predictability across units can supply boundary information. This is a candidate computation, not a claim that infants explicitly calculate numerical fractions. Association strength, chunk formation or predictive processing can produce related behavioural discrimination, and a preference test alone may not identify which algorithm was used. Recognition of a recurrent sound sequence also does not yet make it a meaningful word.

Rebecca L. Gómez extended learning beyond adjacent pairs. Adults and eighteen-month-olds heard three-element artificial-language strings whose first and last elements were related while the middle element varied. Adjacent dependencies were matched between the languages; the discriminating information lay in the nonadjacent relation. Greater variability in the middle position helped reveal the invariant outer relation. This shows that variability can improve learning rather than merely introducing noise, and that distributional sensitivity can extend over an intervening element. It remains a constrained sequence-learning result, not a demonstration that infants have induced hierarchical syntax or every long-distance dependency of natural grammar.^[ref]

At the lexical–semantic interface, Linda B. Smith and Chen Yu presented twelve- and fourteen-month-olds with ambiguous picture–word situations. A single encounter contained two objects and two words, so it did not uniquely specify which word referred to which object. Across encounters, the correct word–object pairings recurred more consistently. At test, a spoken label elicited greater looking to its associated target than to a distractor. Accumulating evidence across individually ambiguous scenes therefore supports learning several mappings without a uniquely informative naming event on each trial. The result does not show whether each infant maintained competing associations or tested a single candidate hypothesis, and the controlled visual scenes simplify the attentional problem of everyday word learning.^[ref]

These levels address different uncertainty problems. A distribution over acoustic tokens can alter discriminability; a sequence distribution can identify recurring units; nonadjacent relations can support dependency learning; cross-situational co-occurrence can link forms to referents. None entails that the others are solved automatically. To explain a natural language, an account must specify how learners select relevant features, integrate conflicting cues, remember the necessary history and move from surface regularities to productive representations. Successful learning of a small artificial input establishes capacity under those conditions, not that the available natural input necessarily suffices for every proposed grammatical generalisation.

Evidence against exclusive linguistic specialisation comes from transfer of the statistical problem to nonlinguistic materials. In a 1999 study, Saffran and colleagues arranged tones into continuous streams with analogous boundary structure. Eight-month-olds and adults segmented those streams using their regularities. Thus the relevant capacity is not restricted to syllables. This supports a domain-general contribution but does not prove identical neural implementation, equal learnability for every stimulus class or the absence of specialisation elsewhere in language.^[ref]

The strongest version of an encapsulated linguistic module, if it claims that such acquisition cannot exploit general sequence learning, must accommodate this evidence or be revised. A weaker linguistic toolkit can remain compatible with it. Constraints on representations, attention to particular acoustic dimensions, biases about possible dependencies and socially guided selection of referents can determine the input on which an otherwise general learner operates. Experience can also produce increasing specialisation, so a specialised mature system does not entail a fully specified innate one. Conversely, learning some regularities early does not demonstrate a blank slate: a learner needs a perceptual space, memory and inductive assumptions before any frequency can be counted.

To distinguish these accounts, studies should compare linguistic and carefully matched nonlinguistic materials, separate frequency from conditional predictability, test generalisation to new items, and establish which cues children actually exploit in less constrained settings. A model that fits a familiarisation preference but cannot learn or generalise beyond that particular stream has not explained language acquisition. Evidence of reliable cross-domain learning constrains claims of exclusivity; evidence for selective biases constrains an unrestricted domain-general model. By 2022, the warranted position was to retain distributional learning as a demonstrated part of the toolkit while treating the scope, representational format and degree of specialisation as empirical questions.