The Semantic Feature Model

To address some of the shortcomings of models like Collins and Quillian’s (1969), Smith and colleagues (1974) developed a model that viewed the meanings of words as sets of semantic features or attributes (Smith et al., 1974). These features can be broken down into two types: characteristic and defining. Defining features are ones that are essential to distinguishing a concept from others (their most salient feature), while characteristic features are ones that are not essential to this. For example, a defining feature of “robin” is that it is “red-breasted,” while a characteristic feature is that it is "small.” The more defining features concepts share, the closer together they are organized in the mental lexicon. Thus, looking at the defining features shared between “bird,” “robin,” and “ostrich,” we see that “robin” and “bird” share 3, while “ostrich and “bird” share 2, meaning that “robin” would be grouped closer to “bird” than “ostrich” (see Figure). A hierarchical model, by contrast, would organize “ostrich” and “robin” equally close to “bird.” Thus, this model allows for more flexibility and levels in connections between nodes (lexical entries). Another key aspect of this model is that the more concrete a concept is, the more defining features it has, and the easier it is to make a semantic decision about it when compared with another concept. For example, when performing a semantic categorization task, it is easier to make a decision about the question, “Is a dog a toaster?” than, “Is an animal a thinker?”

The process of our brain

Knowledge of words is embedded in a set of weights on connections between processing units encoding orthographic, phonological, and semantic properties of words, and the correlations between these properties.

Thus, when any of the properties they mention (phonology, orthography and meaning) are activated at once the connections between them become stronger, like neurons firing and wiring together in the brain. These connections are mediated in a bottom-up process via a small number of “hidden units,” which are connected to the much more numerous “input units” that represent orthography, phonology and meaning. The hidden units cluster together inputs that co-occur (or “fire”) together. When connectionist models are tested on the computer, as the weights between units are refined over time, they tend to group words based on categories such as “noun,” “verb,” “animal” etc.This logical grouping of words that occurs via a completely bottom-up process flies in the face of the models discussed previously, which tend to operate in a more top-down manner. This approach, therefore, suggests that words are organized purely by associations between words as they are encountered in the world, with no "hard-wired" rules for organizing them in the brain, as suggested by the next approach we will discuss.


EXAMPLE:

The fact that a speaker can mentally find the word that he/she wants in less than 200 milliseconds, and in certain cases, even before it is heard, is proof that the mental lexicon is ordered in such a way as to facilitate access and retrieval.

What is Mental Lexicon?

Psycholinguistics is about how language works in the brain. A specific question that one might ask on this topic is, "How are the words we use connected to the thoughts they serve to express?" The answer to such a seemingly simple question is actually quite complicated and far from conclusive. In order for one to transform his or her abstract thoughts into physical words (spoken, written, or signed), these words must first be mentally represented and organized in a systematic, easily accessible way.

Why is necessary this systematic organization of the words?

The mental lexicon is necessary because without it, linguistic production would be long, laborious and would not accurately represent one's thoughts. An analogy that is often used to illustrate the concept of the mental lexicon is that of a printed dictionary, which is similar to a lexicon. This analogy breaks down very quickly, however, in that the use of language in humans is very multi-faceted and does not occur in a robotic, dictionary-like fashion. Dictionaries only allow one to access words by their alphabetically ordered spelling, which is often accidental in a language and does not allow for them to be accessed by any of their other properties (e.g., their meaning) (Fellbaum, 1998). What the more flexible models of the mental lexicon try to do is explain the patterns and regularities that underlie people's knowledge and (sometimes irregular) use of words.