5.1 OVERVIEW
Our theoretical framework (Reichle & Perfetti, 2003) makes a general assumption that encoded memory traces of word experiences can vary in strength, quality, and quantity. Experiment 2 tests this assumption by manipulating the semantic constraint and the variability in which a new word is encountered. For this experiment, this assumption about encoded memory traces of words makes two predictions about the effects of semantic constraint and variability on meaning acquisition, and subsequent encounters with the words.
Vocabulary learning studies with adults have shown that the semantic constraint of a sentence context directly affects meaning acquisition (Bolger et al., 2008; Daneman & Green 1986) and encoding (Chaffin, et al., 2001; Williams & Morris, 2004). Highly constraining contexts, which are supportive of the word’s meaning, are better for learning a new word’s meaning than low constraint sentences. Chaffin et al. argues that greater cognitive effort is involved in processing a highly constraint context, which results in deeper encoding of the word. According to the word-instance framework, deeper encoding of a word’s meaning would result in stronger memory traces for high constraint sentences than for low constraint sentences. Our first prediction is that to the extent that word knowledge modulates familiarity, we expect that learners would be more familiar with words learned with high than low constraint sentences.
Further, because high constraint sentences are more supportive of a word’s meaning than low constraint sentences, we also expect to observe superior learning of meaning with high constraint sentences.
As addressed in Experiment 1, we are also interested in whether memory strength depends on the quantity (the sum of all traces) or the cumulative strength of repeated traces. The results from Experiment 1 indicated that familiarity and recognition were modulated by the availability of meaning knowledge, rather than by the sum or the cumulative strength of the memory traces. We test this hypothesis again by presenting learners with high or low constraint sentences in either varied or repeated contexts. Our second prediction is that high constraint sentences would be more familiar than low constraint sentences because high constraint sentences allow for a deeper encoding of the word. Specifically, if the quantity of traces affects familiarity, than varied high constraint sentences will be better than repeated high constraint contexts. If only the strength of the traces affects familiarity, then conditions with single- repeated contexts will be better than varied contexts.
Thus, the objective of Experiment 2 is to examine the effects of semantic constraint (high or low) and variability (varied or repeated content) on meaning acquisition and word processing. The following two hypotheses are addressed in this experiment:
(1) The degree of semantic constraint in which a word has been encountered will result in episodic traces that differ in strength, therefore affecting familiarity and meaning acquisition. Specifically, the effects of familiarity will be observed by differences in FN400 amplitudes, and the effects of meaning acquisition will be observed by differences of N400 amplitudes.
(2) Contextual variability will affect the strength and quantity of memory traces encoded at learning, therefore, having differential effects on word recognition processes and meaning acquisition. Specifically, the effects of recognition will be observed in differences in P600 amplitudes, and the effects of meaning acquisition will be observed by differences in N400 amplitudes.
5.2 METHODS
5.2.1 Participants
21 right-handed individuals were recruited for the study from the large lexical and comprehension battery database. These learners represented a broad range of ability on comprehension, vocabulary, and lexical skill. Participants were compensated $10/hour for their participation for the 4-hour long study. Five learners were eliminated from the final analyses due to unusable EEG data.
5.2.2 Procedure
All learners completed the three phases of the experiment; working memory assessment, word learning, and word testing.
5.2.3 Design: Word learning
In Experiment 2, the semantic constraint (high or low constraint) and the variability (varied or repeated) of word information were manipulated to test the effects of word experience on meaning acquisition and processing. This 2 x 2 design yielded four different learning conditions, as described below. The learning trial presentation was quasi-random; trials were intermixed from all four learning conditions but in a predetermined order to maintain a range of 5 to 10 trials between the first learning trial and subsequent learning trials for all words.
5.2.4 Learning Conditions
5.2.4.1 Repeated High Semantic Constraint (repeated-hi condition)
In this learning condition, learners were presented with a single-repeated sentence context of high semantic constraint (i.e., scores above 0.6 on the cloze task). The same sentence was repeated across all four learning trials. For all trials of this condition, the target word appeared on the top of the computer screen, with the sentence displayed below. A blank replaced where the target word would appear in the sentence to control for frequency of target word presentation.
5.2.4.2 Repeated Low Semantic Constraint (repeated-lo condition)
In this learning condition, learners were presented with a single-repeated sentence context of low semantic constraint (i.e. scores below 0.3 on the cloze task). The same sentence was repeated across all four learning trials. For all trials of this condition, the target word appeared on the top of the computer screen, with the sentence displayed below. A blank replaced where the target word would appear in the sentence to control for frequency of target word presentation.
5.2.4.3 Varied High Semantic Constraint (Varied-hi condition)
In this learning condition, learners were presented with four different single sentence contexts of high semantic constraint, one for each learning trial.
5.2.4.4 Varied Low Semantic Constraint (Varied-lo condition)
In this learning condition, learners were presented with four different single sentence contexts of low semantic constraint, one for each learning trial.