Excerpt from Principles and Practice in Second Language Acquisition, (pgs. 20-22) by Stephen D Krashen; retrieved September 3, 2015 from http://www.sdkrashen.com/content/books/principles_and_practice.pdf
The Affective Filter hypothesis states how affective factors relate to the second language acquisition process. The concept of an Affective Filter was proposed by Dulay and Burt (1977), and is consistent with the theoretical work done in the area of affective variables and second language acquisition, as well as the hypotheses previously covered in this chapter.
Reasearch over the last decade has confirmed that a variety of affective variables relate to success in second language acquisition (reviewed in Krashen, 1981). Most of those studied can be placed into one of these three categories:
(1) Motivation. Performers with high motivation generally do better in second language acquisition (usually, but not always, "integrative"
(2) Self-confidence. Performers with self-confidence and a good self-image tend to do better in second language acquisition.
(3) Anxiety. Low anxiety appears to be conducive to second language acquisition, whether measured as personal or classroom anxiety.
In several places I have hypothesized that these attitudinal factors relate directly to acquisition and not learning, since they tend to show stronger relationships to second language achievement when communicative-type tests are used, tests that tap the acquired rather than the learned system, and when the students taking the test have used the language in "acquisition-rich" situations, situations where comprehensible input was plentiful.
The Affective Filter hypothesis captures the relationship between affective variables and the process of second language acquisition by positing that acquirers vary with respect to the strength or level of their Affective Filters. Those whose attitudes are not optimal for second language acquisition will not only tend to seek less input, but they will also have a high or strong Affective Filter--even if they understand the message, the input will not reach the part of the brain responsible for language acquisition, or the language acquisition device. Those with attitudes more conducive to second language acquisition will not only seek and obtain more input, they will also have a lower or weaker filter. They will be more open to the input, and it will strike "deeper" (Stevick, 1976).
The Affective Filter hypothesis, represented in Fig. 2.2, claims that the effect of affect is "outside" the language acquisition device proper. It still maintains that input is the primary causative variable in second language acquisition, affective variables acting to impede or facilitate the delivery of input to the language acquisition device.
The filter hypothesis explains why it is possible for an acquirer to obtain a great deal of comprehensible input, and yet stop short (and sometimes well short) of the native speaker level (or "fossilize"; Selinker, 1972). When this occurs, it is due to the affective filter.
The "affective filter", posited by Dulay and Burt (1977), acts to prevent input from being used for language acquisition. Acquirers with optimal attitudes (see text) are hypothesized to have "low" affective filters. Classrooms that encourage low filters are those that promote low anxiety among students, that keep students "off the defensive" (Stevick, 1976).
This picture does not diminish, in any way, the importance of affective variables in pedagogy. The Affective Filter hypothesis implies that our pedagogical goals should not only include supplying comprehensible input, but also creating a situation that encourages a low filter. As discussed in Chapter V, several methods focus on just this (e.g. Counseling-Learning and Suggestopedia).
The input hypothesis and the concept of the Affective Filter define the language teacher in a new way. The effective language teacher is someone who can provide input and help make it comprehensible in a low anxiety situation. Of course, many teachers have felt this way about their task for years, at least until they were told otherwise by the experts!
