Implicit statistical learning in language processing: word predictability is the key

Abstract

Fundamental learning abilities related to the implicit encoding of sequential structure have been postulated to underlie language acquisition and processing. However, there is very little direct evidence to date supporting such a link between implicit statistical learning and language. In three experiments using novel methods of assessing implicit learning and language abilities, we show that sensitivity to sequential structure - as measured by improvements to immediate memory span for structurally-consistent input sequences - is significantly correlated with the ability to use knowledge of word predictability to aid speech perception under degraded listening conditions. Importantly, the association remained even after controlling for participant performance on other cognitive tasks, including short-term and working memory, intelligence, attention and inhibition, and vocabulary knowledge. Thus, the evidence suggests that implicit learning abilities are essential for acquiring long-term knowledge of the sequential structure of language - i.e., knowledge of word predictability - and that individual differences on such abilities impact speech perception in everyday situations. These findings provide a new theoretical rationale linking basic learning phenomena to specific aspects of spoken language processing in adults, and may furthermore indicate new fruitful directions for investigating both typical and atypical language development.

Figure 1

Depiction of the visual implicit learning task used in Experiments 1 and 3, similar to that used in previous work (Conway et al., 2007; Karpicke & Pisoni, 2004). Participants view a sequence of colored squares (700-msec duration, 500-msec ISI) appearing on the computer screen (top) and then, 2000-msec after sequence presentation, they must attempt to reproduce the sequence by pressing the touch-panels in correct order (bottom). The next sequence occurs 2000-msec following their response.

Figure 2

Artificial grammar used in Experiment 2. Each numeral was mapped onto one of four spoken nonwords.

Figure 3

Depiction of the auditory implicit learning task used in Experiment 2. Participants listened to nonword sequences (700-msec duration, 500-msec ISI) through headphones and then, 2000-msec after sequence presentation, they must attempt to verbally reproduce the sequence by speaking into a microphone. The next sequence occurs 2000-msec following their response.

Figure 4

Scatterplot of data from Experiments 1 and 2 (n=40). The x-axis displays the implicit learning scores; the y-axis displays the word predictability difference scores for the spoken sentence perception task. The best-fit line was drawn using SPSS 16.0.

Figure 6

Scatterplot of data from Experiment 3 (n=59). The x-axis displays the implicit learning scores; the y-axis displays the word predictability difference scores for the spoken sentence perception task. The best-fit line was drawn using SPSS 16.0.