Positive and Negative Evidence in Language Acquisition

Positive and Negative Evidence in Language Acquisition

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Introduction

The necessity for input in the process of second language acquisition (SLA) is a

well-accepted fact, but the form and type that it needs to take for learning to occur

remains a controversial issue. Those subscribing to a nativist or rationalist position of

acquisition support the idea that positive evidence is all that is required for acquisition

to occur (Chomsky, 1989). They believe that human knowledge develops from

structures, processes and ideas that are in the mind at the birth. On the other hand, those

working within the interactionist paradigm see positive evidence as insufficient and

propose a role for both positive and negative evidence (Labov, 1969; Gass, 2003).

2. Positive Evidence

Positive evidence is evidence that a particular utterance is grammatical in the language

that the language that the child is learning. It consists of descriptive information about a

form or an utterance. It consists of actually occurring sequences, i.e. sentences of the

language. Various options exist for positive evidence including plentiful exemplars of

the target feature without any device to draw attention to it. For example, Trahey (1996)

developed materials consisting of stories, games, and exercises with the aim of simply

exposing learners to the subject. In this case, acquisition occurs as a result of frequent

exposure to a target feature. It involves some sort of attempt to highlight instances of the

target feature, thus drawing learners' attention to it.

Positive evidence can function entirely by itself. Learners can simply be asked to listen

to or read texts that have been provided. It can also be accompanied by some kind of

meaning-focused activity that incidentally assists learners to focus their attention on the

target feature.

For example, comprehension questions that can only be answered correctly if the

learners process the target feature. There are tasks that are designed to elicit production

of a specific target feature in the context of performing a communicative task, and tasks

that are intended to result in learners' employing some feature that has been specifically

targeted (White, 1987).

Several patterns in language have been claimed to be unlearnable from positive

evidence alone. One example is the hierarchical nature of languages. For any given set

of sentences generated by a hierarchical grammar capable of infinite recursion there are

an indefinite number of grammars that could have produced the same data. This would

make learning any such language impossible. Indeed, a proof by E. Mark Gold showed

that any formal language that has hierarchical structure capable of infinite recursion is

unlearnable from positive evidence alone,

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in the sense that it is impossible to

formulate a procedure that will discover with certainty the correct grammar given any

arbitrary sequence of positive data in which each utterance occurs at least once.

However, this does not preclude arriving at the correct grammar using typical input

sequences rather than particularly malicious sequences or arrive at an almost perfect

approximation to the correct grammar.

Another example of language pattern claimed to be unlearnable from positive evidence

alone is subject-auxiliary inversion in questions, i.e.:

?

?

You are happy.

Are you happy?

There are two hypotheses the language learner might postulate about how to form

questions: (1) The first auxiliary verb in the sentence (here: 'are') moves to the

beginning of the sentence, or (2) the 'main' auxiliary verb in the sentence moves to the

front. In the sentence above, both rules yield the same result since there is only one

auxiliary verb. But, the difference is apparent in this case:

?

Anyone who is interested can see me later.

Is anyone who interested can see me later?

Can anyone who is interested see me later?

1.

2.

Of course, the result of rule (1) is ungrammatical while the result of rule (2) is

grammatical. So, rule (2) is (approximately) what we actually have in English, not rule

(1). The claim, then, first is that children don't see sentences as complicated as this one

enough to witness a case where the two hypotheses yield different results, and second

that just based on the positive evidence of the simple sentences, children could not

possibly decide between (1) and (2). Moreover, even sentences such as (1) and (2) are

compatible with a number of incorrect rules (such as

(2) was not innately known to infants, we would expect half of the adult population to

use (1) and half to use (2). Since that doesn't occur, rule (2) must be innately known.

3. Negative Evidence

Negative evidence refers to information about which strings of words are not

grammatical sentences in the language, such as corrections or other forms of feedback

from a parent that tell the child that one of his or her utterances is ungrammatical.

Negative evidence consists of information about the impossibility and ungrammaticality

of a form or an utterance. In other words, negative evidence such as explanations,

explicit grammar teachings, and corrections of wrong sequences or ungrammatical

sentences, show what may not be done. It needs additional evidence from corrections of

impossible sequences, reading the rule-books, comprehending abstract explanations,

and so on. There are times when a learner supplies a linguistically incorrect response in

reply to a teacher's initiation; the teacher tends to provide direct, explicit, overt negative

evidence. However, Chomsky (1981) holds the idea that direct negative evidence is not

necessary for language acquisition, but indirect negative evidence may be relevant.

It's very important for us to know whether children get and need negative, because in

the absence of negative evidence, any child who hypothesizes a rule that generates a

superset of the language will have no way of knowing that he or she is wrong. If

children don't get, or don't use, negative evidence, they must have some mechanism that

either avoids generating too large a language the child would be conservative -- or that

can recover from such overgeneration.

There is also much criticism about whether negative evidence is really so rarely

encountered by children. Pullum argues that learners probably do get certain kinds of