User:Mentalexicon/sandbox

Introduction

The mental lexicon is a construct used in linguistics and psycholinguistics to refer to individual speakers’ lexical, or word, representations. However, not all scientists agree as to the utility of the mental lexicon as a scientific construct.

The mental lexicon differs from the lexicon in that it is not just a general collection of words; instead, it deals with how those words are activated, stored, processed, and retrieved by each speaker. An individual’s mental lexicon changes and grows as new words are learned and is always developing, but there are several theorists that argue exactly how this occurs. Some theories about the mental lexicon include the Spectrum Theory, the Dual Coding Theory, and Chomsky’s Nativist theory. Scientists also study the areas of the brain involved in lexical representations. The following addresses some of the physiological, social, and linguistic aspects of the mental lexicon.

Methods of Inquiry

Although the mental lexicon is often called a mental “dictionary,” in actuality, research suggests that it differs greatly from a dictionary. For example, the mental lexicon is not organized alphabetically like a dictionary; rather, it seems to be organized in a more complex manner, with links between phonologically and semantically related lexical items. This is suggested by evidence of phenomena such as slips of the tongue, which showed that replacing words such as anecdote for antidote. Research is continuing to identify the exact way that words are linked and accessed. Two common methods are lexical decision and priming.

Theories and Perspectives

Not all linguists and psychologists believe in the mental lexicon’s existence and there is much controversy over the concept. One theory about the mental lexicon states that it organizes our knowledge about words “in some sort of dictionary.” Another states that the mental lexicon is “a collection of highly complex neural circuits.” In this theory the frequency of words (“frequency effect”), similarity between words (“neighbourhood effect”), and the priming effect impacts how fast words “activate” the mental lexicon. In the spectrum theory, at one end “each phonological form is connected to one complex semantic representation,” at the opposite end, homonyms and polysemes have their “own semantic representation[s].” The middle of the spectrum contains the theories that “suggest that related senses share a general or core semantic representation.” The “dual coding theory (DCT)” contrasts multiple and common coding theories. DCT is “an internalized nonverbal system that directly represents the perceptual properties and affordances of nonverbal objects and events, and an internalized verbal system that deals directly with linguistic stimuli and responses.” Similarly, we do not observe words “as elements in a data structure” that are “retrieved from memory, but rather as stimuli that alter mental states.” Others work around Chomsky’s theory that “all syntactic and semantic features are included directly in the abstract mental representation of a lexical word.”

Development

Average vocabulary size of an English-speaking child by age.

One aspect of research on the development of the mental lexicon has focused on vocabulary growth. Converging research suggests that at least English children learn several words a day throughout development. The figure at left illustrates the growth curve of a typical English speaking child’s vocabulary size.

The words acquired in the early stages of language development tend to be nouns or nounlike, and there are some similarities in first words across children (e.g. mama, daddy, dog). Research suggests that, despite the fast mapping hypothesis, words are not just learned as soon as we are exposed to them, each word needs some type of activation and/or acknowledgement before it is permanently and effectively stored. For young children, the word may be accurately stored in their mental lexicon, and they can recognize when an adult produces the incorrect version of the word, but they may not be able to produce the word accurately.

Brain and the Mental Lexicon

Studies have shown that the temporal and parietal lobes in the left hemisphere are particularly relevant for the processing of lexical items.

The following are some hypotheses pertaining to semantic comprehension in the brain:

1. Organized Unitary Content Hypothesis (OUCH): this hypothesis posits that lexical items that co-occur with high frequency are stored in the same area in the brain.
2. Domain-Specific Hypothesis: this hypothesis uses the theory of evolution to posit that certain categories that have an evolutionary advantage over others (such as useful items like tools) have their specialized and functionally dissociated neural circuits in the brain.
3. Sensory/Functional Hypothesis: this hypothesis posits that the ability to identify (i.e. be able to recognize and name) living things depends on visual information, while the ability to identify non-living things depends on functional information. Thus this hypothesis implies that modality-specific subsystems compose an overarching semantic network of lexical items.

Impaired Access to the Mental Lexicon

Anomic aphasia, aphasia (expressive aphasia + receptive aphasia) and Alzheimer’s disease can all affect recalling or retrieving words. Anomia renders a person completely unable to name familiar objects, places and people. Anomia involves specific naming difficulties and have difficulties recalling words. Anomia is a severe form of the "tip-of-the-tongue" phenomenon where the brain cannot recall the desired word. Stroke, head trauma and brain tumors can cause anomia.

Expressive and receptive aphasia are neurological language disorders. Expressive aphasia limits the ability to convey thoughts through the use of speech, language or writing. Receptive aphasia affects a person's ability to comprehend spoken words, causing disordered sentences that have little or no meaning and which can include addition of nonce words.

Harry Whitaker states that Alzheimer’s disease patients are forgetful of proper names. Patients have difficulty generating names, especially with phonological tasks such as words starting with a certain letter. They also have word-retrieval difficulties in spontaneous speech but still have relatively preserved naming of presented stimuli. Later, loss of naming of low-frequency lexical items occurs. Eventually, the loss of ability to comprehend and name the same lexical item indicates semantic loss of the lexical item.