The present dissertation focuses on the question of how humans acquire syntactic knowledge without intending to and without awareness of what they have learned. The aim is to apply the theoretical concepts and the methodological framework provided by implicit learning research to the investigation of language acquisition. The results of six experiments are reported. In terms of design, all experiments consisted of (i) a training phase, during which subjects were trained on a miniature linguistic system by means of different exposure conditions, (ii) an unexpected testing phase, during which learning and awareness were assessed, and (iii) a debriefing session. A semi-artificial grammar, which consisted of English words and German syntax, was employed to generate the stimulus material for experiments 1, 2, 3, 5 and 6; in the case of experiment 4, nonsense syllables were used instead of English words. The linguistic focus was on verb placement rules. Native speakers of English with no background in German (or any other V2 language) were recruited to take part in the experiments.

Participants in experiments 1-5 were exposed to the semi-artificial system under incidental learning conditions by means of different training tasks. In experiments 1 and 2, an auditory plausibility judgment task was used to expose participants to the stimulus sentences. In experiment 3, elicited imitations were used in addition to the plausibility judgment task. The training phase in experiment 4 consisted solely of elicited imitations, while training in experiment 5 consisted of a classification task which required participants to identify the syntactic structure of each stimulus item, followed by plausibility judgments. Participants in experiment 6, on the other hand, were exposed to the semi-artificial grammar under intentional learning conditions. These participants were told that the word order of the stimulus sentences was governed by a complex rule-system and instructed to discover syntactic rules. After training, participants in all six experiments took part in a testing phase which assessed whether learning took place and to what extent they became aware of the knowledge they had acquired. Grammaticality judgments were used as a measure of learning. Awareness was assessed by means of verbal reports, accuracy estimates, confidence ratings and source attributions. Control participants did not take part in the training phase.

The results of the experiments indicate that adult learners are able to acquire syntactic structures of a novel language under both incidental and intentional learning conditions, while processing sentences for meaning, without the benefit of corrective feedback and after short vi exposure periods. That is, the findings demonstrate that the implicit learning of natural language is not restricted to infants and child learners. In addition, the experiments also show that subjects are able to transfer their knowledge to stimuli with the same underlying structure but new surface features. The measures of awareness further suggest that, in experiments 3 to 6 at least, learning resulted in both conscious and unconscious knowledge. While subjects did not become aware of all the information they have acquired, it was clear that higher levels of awareness were associated with improved performance.

The findings reported in this dissertation have several implications for our understanding of language acquisition and for future research. Firstly, while the precise form of the knowledge acquired in these experiments is unclear, the findings provided no evidence for rule learning in the vast majority of subjects. It suggests that subjects in these types of experiments (and perhaps in natural language acquisition) do not acquire linguistic rules. The results support Shanks (1995; Johnstone & Shanks, 2001), who argues against the possibility of implicit rule learning. Secondly, while adults can acquire knowledge implicitly, the work reported in this dissertation also demonstrates that adult syntactic learning results predominantly in a conscious (but largely unverbalizable) knowledge base. Finally, from a methodological perspective, the results of the experiments confirm that relying on verbal reports as a measure of awareness is not sufficient. The verbal reports collected at the end of the experiment were helpful in determining what aspects of the semi-artificial grammar subjects had consciously noticed. At the same time, verbal reports were clearly not sensitive enough to assess whether subjects were aware of the knowledge they had acquired. Confidence ratings and source attributions provided a very useful method for capturing low levels of awareness and to observe the conscious status of both structural and judgment knowledge. Future experiments on language acquisition would benefit from the introduction of this relatively simple, but effective way of assessing awareness.