Definition:

Susan Gass is University Distinguished Professor Emerita of Applied Linguistics at Michigan State University, one of the most cited researchers in second language acquisition. She is known for the Input-Interaction-Output (IIO) model — a framework that synthesizes the roles of input, conversational interaction, and learner output in driving acquisition — and for co-authoring standard reference texts that have shaped how SLA is taught and researched globally.

In-Depth Explanation

Gass’s most enduring theoretical contribution is the Input-Interaction-Output model, developed through the 1980s and 1990s alongside Michael Long’s interaction hypothesis. Where Krashen’s input hypothesis focused on comprehensible input alone, and Long’s interaction hypothesis emphasized negotiation of meaning as the mechanism through which input becomes acquisitionally effective, Gass’s IIO model integrates all three phases of the information processing cycle:

1. Input — the L2 data available to the learner from the environment. Not all input becomes intake; learners selectively attend to language based on salience, frequency, and communicative need.
2. Interaction — conversational exchange in which meaning negotiation and corrective feedback make certain features of the input more noticeable, directing learner attention to form-meaning connections the learner might otherwise miss.
3. Output — learner production, which serves multiple functions beyond mere communication: it pushes learners to grammaticize meaning (where input can be processed semantically without full grammatical precision), triggers noticing of gaps in competence, and generates hypotheses about the target language.

The IIO model was influential because it provided a richer account of how acquisition proceeds than input-alone theories. It explicitly incorporated feedback loops: learner output becomes input for the interlocutor; the interlocutor’s response provides input (and often corrective feedback) to the learner; this triggers further output and, ideally, modified production. Acquisition occurs not as a passive absorption of input but through active interaction in which learners test and revise hypotheses.

Gass co-edited Input in Second Language Acquisition (1985, with Carolyn Madden) — a foundational volume that established the research agenda on input for an entire generation of SLA researchers. She later co-authored Second Language Acquisition: An Introductory Course (with Larry Selinker, and later with Jennifer Behney and Luke Plonsky) — which remains a primary graduate-level text in SLA courses.

Her methodological contributions are equally significant. Data Elicitation for Second and Foreign Language Research (with Alison Mackey, 2007) systematized the research toolkit for L2 researchers, describing and evaluating experimental and quasi-experimental designs, verbal report methods, oral production tasks, and discourse completion tasks — making it an essential reference for graduate students entering empirical SLA research.

Key Contributions

• Input-Interaction-Output (IIO) model — integrated framework linking input, interaction, and output as co-responsible drivers of acquisition
• Input in Second Language Acquisition (1985, ed. with Madden) — foundational collected volume that established the input research agenda in SLA
• Second Language Acquisition: An Introductory Course (multiple editions with Selinker et al.) — standard graduate SLA textbook
• Data Elicitation for Second and Foreign Language Research (with Mackey) — methodological reference for empirical SLA

Common Misconceptions

• Gass’s IIO model does not claim that interaction is necessary for acquisition. It claims interaction significantly facilitates acquisition by making form-meaning connections salient; learners can acquire forms through non-interactive exposure, but less efficiently.
• The IIO model is not a processing model. It describes the conditions that promote acquisition, not the cognitive mechanisms through which representations are built.

Related Terms

• Interaction hypothesis
• Input hypothesis
• Output hypothesis
• Negotiation of meaning
• Noticing hypothesis
• Recasts
• Second language acquisition

See Also

• Michael Long
• Alison Mackey
• Merrill Swain

Sources

• Gass, S.M. (1997). Input, Interaction, and the Second Language Learner. Lawrence Erlbaum — the monograph presenting the integrated IIO model; the primary theoretical source for Gass’s framework.
• Gass, S.M. & Madden, C.G. (Eds.) (1985). Input in Second Language Acquisition. Newbury House — the foundational edited volume on input in SLA; collected papers from the field’s leading researchers at the time.
• Gass, S.M., Behney, J. & Plonsky, L. (2020). Second Language Acquisition: An Introductory Course (5th ed.). Routledge — the standard introductory SLA text; covers all major frameworks with empirical grounding.