The role of learning mechanisms in understanding spoken language

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In recent years there have been several notable demonstrations that the ability to learn about words and their meanings continues to be important throughout our adult life (1). Not only do learning mechanisms allow us to acquire entirely new information (e.g., the social-networking meaning of the word "twitter" (2), see associated studentship), but they can also modify our existing knowledge about words that we already know in order to enhance their subsequent processing. One case where such a learning mechanism would be of clear benefit is to facilitate the processing of words like "bark" that have multiple meanings. This form of ambiguity is ubiquitous in language, with over 80% of words having more than one dictionary definition (3). Learning mechanisms could make an important contribution to our ability to understand these tricky words by adjusting the availability of their meanings on the basis of experience. For example the word "spade" can refer to either a "digging tool" or "card suit", and our preferred interpretation of this word could be influenced by whether we had recently taken up gardening or card-playing as a hobby. By learning from our recent experience with such words, we can make better predictions about which meaning is more likely to be encountered in the future. There are several reasons to believe that such learning mechanisms do indeed make an important contribution to understanding ambiguous words. First, numerous studies have shown a strong processing benefit for the meaning that is most frequent in the language as a whole (4), such that the word "pen" is easier to understand in a phrase like "the blue pen", which uses its dominant meaning compared a with the phrase like "the pig pen" where its low frequency meaning is used. These findings suggest, indirectly, that that we are sensitive to the overall frequency with which we encounter alternative word meanings across our life-time. In addition, we have recently provided the first direct evidence that listeners' preferences for word meanings are strongly influenced by a single recent encounter with one of its meanings, such that the low-frequency meaning of "pen" would become more readily available after hearing a sentence like "the farmer put the sheep in the pen"(5).Despite this evidence that learning mechanisms play a key role in our ability to understand ambiguous words, current models of ambiguity resolution are remarkably inadequate when it comes to explaining these mechanisms. The primary aim of the proposed research is to obtain comprehensive empirical evidence about how and when listeners can use their experience to adjust their preferences for individual word meanings. First we will establish whether listeners learn from all encounters with an ambiguous word or if particular conditions necessary for learning to occur (Experiment 1, 6). Second, we will measure the relative contributions of listeners' recent and longer-term experience with ambiguous words to determine how we integrate information acquired across our lifespan (Experiments 2-5, 9). Finally we will explore whether meaning preferences can be modulated by factors such as the identity or accent of the speaker (Experiments 7, 8). These data will guide the development of a new model of ambiguity resolution which specifies the nature of these learning mechanisms. This novel line of research offers an opportunity to make rapid progress on this important topic, and may lead to a radically different understanding of this critical aspect of language comprehension.By understanding how these processes operate within healthy adults we will also provide the empirical evidence that will allow future research to assess the contributions of both processing and learning deficits in those individuals who are known to have difficulties understanding sentences that contain ambiguous words (see Impact Summary).