R ETHINKING THE L EXICAL P ATTERNS

In the last section I have explained how to build a VSM, including the essential components and the supporting theories. I have also discussed how we can represent our linguistic knowledge through the two implementations. It is now sufficient for us to say that VSM is actually one powerful and promising tool for researchers to simulate human language ability in NLP. However, despite the impressive

performance demonstrated in those works, it is still left unanswered what aspect of lexical relation we are looking at when we apply lexical patterns as a medium to have a good grasp of what relations may be like in our mind. The assumption that lexical patterns can be treated as embodiment of lexical relations is rarely examined in works

that are preoccupied with solving specific tasks. Therefore now it is time for us to look deeper into the lexical patterns.

2.3.1 Capturing Conceptual Nature in Lexical Patterns

In Section 2.1.1, I have pointed out the conceptual nature of lexical relations based on the metalexical treatment. It’s evident that our knowledge about lexical relations is a conceptual one, which means it combines not just lexical entries or meanings, but concepts about words that are built upon our understanding of what we have

experienced, conceived, and learned. Three aspect of this conceptual knowledge was discussed: (a) lexical relations are productive, (b) they are context-dependent, and (c) they display the prototypicality effect. Given that in NLP it is assumed that lexical patterns are the linguistic representations of lexical relations, it follows naturally that we can postulate that this conceptual nature can also be observed in and extracted from the lexical patterns. This also suggests that the three aspects should be able to account for behavior of lexical patterns.

To begin with, lexical patterns can be productive. To be more specific, the words that are connected by patterns are not arbitrary or idiosyncratic since we can produce potentially limitless new pairs without hearing or reading them before. For example, the expression your word is the opposite of nutrient makes sense to people who hear it for the first time. The pattern is the opposite of can be used in such a way that the hearer fully grasps the intended meaning by applying his/her concepts about nutrients, that is, any substance that nourishes an organism. Actually, it is also argued by Murphy (2003:49) that the metalexical account of lexical relations can explain our ubiquitous metaphorical use of words.

Secondly, lexical patterns display the prototypicality effect. People can

naturally make metalinguistic judgment about what are the better substrings that serve as the indication of word relations. This is also supported by the findings of Jones (2002) that there exist some typical lexisyntatic frames in which antonyms co-occur such as instead of.

Lexical patterns are also context-based, which means the meaning of words connected by these patterns can vary according to different context of background.

Cultural difference, geological distinction, and economic gap can all affect how speakers and listeners perceive the meaning of words connected by the patterns. For instance, the same expression this place is the opposite of Africa can be interpreted distinctly when the utterer is in the context of an international economic conference and a frosty cold street. In the former the economic development divide is possibly the main subject of discussion while in the latter it is more likely that the climate difference is the topic of conversation. This suggests that Africa in the example is actually treated as one concept that covers all information we have about the continent. Therefore the lexical pattern serves as a bridge that connects the speaker and hearer’s world and their knowledge about Africa.

Now it’s evident that lexical patterns, just like lexical relations, connect concepts of what we know about the word. However, to my limited knowledge, there is currently no such a theory that accounts for this conceptual nature in lexical

patterns. Considering the growing importance of lexical pattern in various applications simulating human behavior, a theory for it is obviously in need.

When we characterize lexical patterns as our conceptual knowledge, we mean that these patterns can be understood and produced through reference to a structured background of experience, culture, and worldview. Just as I have argued in Section

2.1.1 that these factors determine the validity of treating lexical relations as our knowledge beyond lexicon, it stands to reason that we can’t derive a detailed picture of lexical patterns based solely on information in lexicon. Then where should we look for it?

To answer that question, we can draw some inspiration from studies on free association response in psychology. In these experiments, subjects’ most immediate response words to the stimulus words are recoded in association norms. To account for certain preferred choices of words, it is often argued that objects and events that are experienced together tend to become associated in human imagination. Also, according to experiments done by Spence and Owens (1990) and Wettler et al.

(2005), this human associative response can be explained in terms of contiguities between words in language use. In other words, our conceptual knowledge can be investigated by analyzing the co-occurring words in the linguistic context. More specifically, if we can gather the co-occurring words of a lexical pattern, it is

plausible that we can thereby capture the elements involved in our concepts about the corresponding words. We can now state concisely that:

The conceptual lexical pattern hypothesis: Lexical patterns that represent word relations are a kind of human conceptual knowledge whose contents during application can be captured in co-occurring words.

This conceptual lexical pattern hypothesis is important for it sets standard for computational models that apply lexical patterns to calculate relational similarity. In other words, if two lexical patterns encode different concepts, no matter how similar

they are in terms of frequency distribution, they should not be put into the same cluster that is supposed to represent one specific lexical relation.