Poverty of stimulus in the context of language Second Semester

Russel’s Question, Plato’s problem: “How comes it that human beings, whose contacts with the world are brief and personal and limited, are nevertheless able to know as much as they know?” Assumptions Assumptions:  We know a lot; we are born not knowing all this  Our exposure to the evidence necessary to reach this knowledge is brief and limited;  Our exposure to evidence is haphazard; the necessary evidence is not presented in a systematic way.

In the domain of language: From the “blooming buzzing confusion, ‟ of the environment around them, infants learn to isolate language – isolate stretches of sound and identify them as sentences of their language -- and assign interpretation to and infinite set of these sentences.

“A human language is a system of remarkable complexity.” Argument from the poverty of the stimulus: If the stimulus is indeed poor in this way, we might assume that some innate structure mediates between us (the organism) and the environment. This will limit the kinds of hypotheses we make along the way.

As with all cognitive capacities, we need to distinguish the contribution of the environment and the contribution of the organism. E.g. The ability to distinguish between hues of different wavelengths or sounds of particular frequencies is a property of the organism. The names given to the different hues, and how many distinctions in the color spectrum are lexicalized is a property of the environment.

(1) Innate, domain-specific factors (in the case of language, what is called “universal grammar ‟ ); (2) Innate, domain-general factors; (3) External stimuli, such as nutrition, modification of visual input in very early life, exposure to distinct languages such as Japanese-vs.-English, or the like; and (4) Natural law, e.g., physical constraints such as those determining that dividing cells form spheres rather than rectangular prisms. Chomsky suggests that we distinguish between different factors which determine the course of development:

Whether domain-specific, or domain- general, the organism (child) comes equipped with SOME method of mediating between environment and (knowledge) (behavior). Abstracting away from the question of domain specificity: What is the nature of this method (learning mechanism)?

Two types of learning mechanisms: I.Sensitivity to statistical generalizations; e.g., ability to extract transitional probabilities and deduce and represent structural units from this. II.Ability to extract and represent abstract algebraic rules.

Statistical Learning by 8-Month-Old Infants Jenny R. Saffran, Richard N. Aslin, Elissa L. Newport Science 274 (1996)

“Depending on the developmental status and the task facing a particular organism, both experience-independent and experience-dependent mechanisms may be involved in the extraction of information and the control of behavior.” “Young humans are generally viewed as poor learners, suggesting that innate factors are primarily responsible for the acquisition of language.”

“… we ask whether infants are in fact better learners than has previously been assumed, thus potentially reducing the extent to which experience-independent structures must be posited.”

Words: pairings of sound and meaning is environment-dependent by all accounts. To pair chunks of sound with chunks of meaning we need to know what the chunks of each are. No indication of word boundaries in the speech signal. (No innateness theory which helps here)

Eight month olds have been shown to be able to segment fluent speech into words. What underlies this ability? No acoustic cues for word boundaries.  Sensitivity to transitional probabilities between sounds, which are much higher within words than across word boundaries.

Can 8-month-old infants extract information about word boundaries solely on the basis of the sequential statistics of concatenated speech? (Why are we interested in the abilities of such young infants?)

Experiment # month-old infants from an American- English language environment were familiarized with 2 min of a continuous speech stream consisting of four three- syllable nonsense words repeated in random order

The only cues to word boundaries were the transitional probabilities between syllable pairs, which were higher within words (1.0 in all cases) than between words (0.33 in all cases). The transitional probability of Y|X = frequency of XY frequency of X Condition A: tupiro, golabu, bidaku, and padoti; Condition B: dapiku, tilado, burobi, and pagotu.

To assess learning, each infant was presented with repetitions of one of four three syllable strings on each test trial. Two of these three-syllable strings were "words“ from the artificial language presented during familiarization, and two were three-syllable "nonwords" that contained the same syllables heard during familiarization but not in the order in which they appeared as words: tupiro, golabu, dapiku, tilado.

Experiment #2 examined whether 8-month- olds could perform the more difficult statistical computations required to distinguish words (that is, recurrent syllable sequences) from syllable strings spanning word boundaries

The test items for each infant consisted of two words and two "part-words." The part-words were created by joining the final syllable of a word to the first two syllables of another word. Thus, the part-word contained three-syllable sequences that the infant had heard during familiarization but statistically, over the corpus, did not correspond to words

Condition A words: pabiku, tibudo, golatu, and daropi; Condition B words: tudaro, pigola, bikuti, and budopa. Test stimuli: pabiku, tibudo, tudaro, and pigola.

Rule Learning by Seven-Month-Old Infants G. F. Marcus, * S. Vijayan, S. Bandi Rao, P. M. Vishton Science 283, 77 (1999).

Children might possess at least two learning mechanisms, one for learning statistical information another for learning "algebraic" rules - -open-ended abstract relationships for which we can substitute arbitrary items. For instance, we substitute any value of x into the equation y = x + 2.

Subjects were 7-month-old infants,who were younger than those studied by Saffran et al. but still old enough to be able to distinguish words in a fluent stream of speech. Experiment 1: ABA condition: e.g. “ga ti ga”; “li na li” ABB condition: e.g. “ga ti ti”; “li na na” Test condition: “wo fe wo”; “wo fe fe”

Experiment 2 controlled for repetitions of specific phonetic patterns. At test, the ABA and ABB patterns were tested, where the test words differed systematically with habituation items in phonetic features.

The 16 habituation sentences that followed the ABA pattern were "le di le," "le je le," "le li le," "le we le," "wi di wi," "wi je wi," "wi li wi," "wi we wi," "ji di ji," "ji je ji," "ji li ji," "ji we ji," "de di de," "de je de," "de li de," "de we de"; ABB items were constructed with the same vocabulary. The test trials were "ba po ba," "ko ga ko" (consistent with ABA), "ba po po," and "ko ga ga" (consistent with ABB).

Experiment 3 controlled for whether the infants were sensitive merely to a counting mechanism, or the recognition of reduplication The testers compared sentences constructed from the ABB grammar with sentences constructed from an AAB grammar

A system that was sensitive only to transitional probabilities between words could not account for any of these results, because all the words in the test sentences are novel and, hence, their transitional probabilities (with respect to the familiarization corpus) are all zero; A system that noted discrepancies with stored sequences of words could not account for the results in any of the three experiments, because both the consistent items and the inconsistent items differ from any stored sequences of words

A system that noted discrepancies with stored sequences of phonetic features could account for the results in experiment 1 but not those in experiments 2 and 3. A system that could count the number of reduplicated elements and notice sentences that differ in the number of reduplicated elements could account for the results in experiments 1 and 2, but it could not account for infants performance in experiment 3.

We propose that a system that could account for our results is one in which infants extract abstract algebra-like rules that represent relationships between placeholders (variables), such as "the first item X is the same as the third item Y," or more generally, that "item I is the same as item J."