- How do we understand the words we hear?
- Semantic memory
- Organization of the lexicon
1. How do we understand the words we hear?
Language comprehension occurs rather effortlessly for most of
us, and at the same time is the result of complex mechanisms.
These mechanisms have been identified by the
three main ways of discovering cognitive mechanisms. Like
most areas of cognition, the bulk of the evidence for language
comprehension mechanisms comes from reaction time and accuracy
studies, although some of these findings have been replicated
with neuroimaging techniques, whose importance has grown tremendously
recently in a relatively short period of time. Research with patients
who have language impairments have also been conducted with reaction
time and other performance tasks, and these tasks have also begun
to be carried out in the scanner with patients.
Conducting imaging studies with patients who have had impairments
but are later able to recover some function allows us to be able
to identify areas that might become responsible for neuronal firing
when normal pathways have been lesioned, as well as monitor any
recovery of the lesioned area. In people who have been permanently
debilitated, one might expect to see little or no activation in
the regions other imaging studies have found to be activated;
however, these are hypotheses waiting to be explored.
The three methods of inquiry provide information about how comprehension
occurs. If you were building a comprehension machine, what components
would you think necessary to include? First, it would need a way
to take the sounds it hears and recognize them as being a word
and not just noise. It would need to have a collection of recognizable
words already stored in its memory, and it would need to be able
to connect these words to the mental representations (stored knowledge)
of the objects that they name.
Additionally, to facilitate comprehension, you would need to
understand the words in relation to each other. For example, if
someone told you that she were going to the store, your comprehension
would be more complete if you knew not only that a store is a
place to buy goods and not a place to go skiing, but if you also
understood what the items in the store were. You would also need
to know that a place where gas is sold is not called a store,
but has its own name, "gas station"; you would have
to build in the ability to distinguish among different stored
words (lexical entries) that share the same or similar senses.
When your friend arrived at the store, she would also need to
know that toasters can be found in the appliances section and
flashlights in the hardware section. Thus, your comprehension
machine would need to understand relationships among the concepts
2. Semantic memory
As mentioned earlier, words can be typified as stored in networks
in memory. The relationship between words and the objects they
represent is called reference. When a word refers to an object,
the word connects to a concept of the object in your mental dictionary
or lexicon; for example, the sound of the word dog refers to the
concept of domestic canines, along with attributes you have stored
for the concept dog, such as furry or possessing a tail.
The relationship that words have with other words is called sense.
Words can be related to each other in many ways, including being
antonyms, synonyms, hypernyms (if X is a kind of Y, X is a hypernym
of Y) and metonyms, meronyms. WordNet, created by George Miller
and his colleagues at Princeton University is a large database
of words that are linked to each other according to their senses,
primarily synonym, hypernym, meronym, and hyponym relations.
For an illustration of how many relationships one
word can have to another,
visit Princeton University's WordNet. Hint: Try the word arm
and the word hanger. How might frequency and the number of senses
a word has be related?
The store of concepts and the words that name them comprise the
lexicon. The process by which we call up a word from memory is
called lexical access.
A number of factors can influence the rate at which words are
retrieved, including how often the word appears in print or speech,
commonly referred to as frequency, (e.g., Rubenstein, Garfield,
& Milliken, 1970) or how people rate a word for familiarity
(Gilhooly & Logie, 1980). Although familiarity plays a large
role in language processing and can account for effects that frequency
does not, the effects of frequency have been most extensively
reported and are robust.
One task in which the influence of frequency has been investigated
is lexical decision. In one version of this task, words and strings
of letters that form non-words, e.g. SHRUK, appear one at a time
on a computer screen. For example, research participants might
read SHOE NEWT BARL FROMP. After seeing each letter string, participants
decide as quickly and as accurately as they can if the string
of letters formed a word or a non-word, and they press a key to
indicate their decision.
Before we tell you much more about this lexical
decision task, try
it for yourself.
In the lexical decision task, you responded to both words and
non-words. A strong finding in the literature is that words are
responded to much more quickly than non-words because words have
already been encountered and have formed representations in memory.
In addition, words that are accessed more often are accessed more
quickly; hence words that are high in frequency are typically
responded to faster than other words and produce fewer errors.
3. Organization of the lexicon
Collins and Quillian (1969)
proposed that concepts are stored hierarchically in our mental
dictionary of words, or mental lexicon. Property relations are
represented within the hierarchy; for example, the concept of
"animal" would be stored at a node that is above "bird",
which would be stored above "canary". Connected to each
category node are properties, such as "has skin" and
"can move around" for "animal".
Figure 1. Collins and Quillian's
hierarchical model of mental lexicon
Collins and Quillian predicted that the more closely situated
on the hierarchy the concepts were, the faster they would activate
each other; that is, people should be faster to say that the proposition
"Birds have feathers" is true than they would say that
"Birds eat" is true. This pattern of reaction times
in the verification task was obtained, although for a reason different
from that proposed by Collins and Quillian. Conrad (1972) conducted
a similar property verification task, but he manipulated the frequency
with which the category and its properties were associated. Rather
than distance, the frequency of the relationships was responsible
for the faster responses.
When you comprehend a word, other words can become active in
your mental lexicon as well. This finding was made famous by a
study by Meyer and Schvaneveldt in 1971. Meyer and Schvaneveldt
presented research participants with words and non-words, one
item at a time. Participants were instructed to press a particular
key if they saw a word, and a different key if they saw a non-word,
and their response times were measured. This task is called a
lexical decision task, and it was designed to be a measure of
the concepts activated in memory. Reading times for a word may
be influenced by a preceding word. When the word NURSE appeared
before the word DOCTOR, participants were faster to indicate that
DOCTOR is a word compared to when the word BUTTER preceded DOCTOR.
The fact that response times were facilitated suggests that the
relatedness of words is represented in the mental lexicon. In
particular, once a word is activated in memory, it can spread
activation to related words.
Although we are still investigating how spread of activation
is actually represented neurally, it is possible that related
concepts are stored in nearby places, or that neural connections
that are commonly made occur quickly. Consistent findings have
been obtained suggesting that nouns are stored in the temporal
lobe, and verbs are stored in the frontal lobe. Additionally,
ERP studies have suggested that, when processed in sentence contexts,
function words are activated in brain areas separate from content
words, with greater left activation for function words.
English is a language that contains a predominance of ambiguous
words; that is, it is composed of words that have more than one
meaning. According to Merriam-Websters online Dictionary,
for example, the verb "to run" has 68 different meanings.
Chinese dialects such as Mandarin are even more ambiguous than
English, for example. The occurrence of ambiguous words in a language
is not a universal characteristic. How do we access the appropriate
meaning of "run" when we hear the sentence, "Bert
likes to run in the museum"? Right away you might think that
frequency plays a role, and you would be rightto an extent.
The most common meaning of "run" is the physical exercise
sense, but a secondary sense is readily available when you read,
"The optimistic undergraduate plans to run for office".
Although you may experience no confusion, research suggests that
multiple meanings of words can be active in memory during the
first few hundred seconds after reading a word. Thus, we cannot
always be conscious of having to deal with multiple meanings,
and that is quite a good thing if your language is English or
Mandarin! Although research in the area of lexical ambiguity has
looked at this question for more than twenty-five years, there
is strong evidence that both frequency and the context in which
ambiguous words are presented determine your success at arriving
at the intended meaning. (So the next time someone tells you a
bad pun, and you dont get it, dont feel badthe
teller might not have given you the appropriate context and is
perhaps referring to an infrequent sense). The findings of one
respected researcher indicate that an ambiguous word presented
outside of a context that could sway interpretation leads to activation
of multiple meanings regardless of the frequency of the meaning;
but, when a context is provided, only the appropriate meaning
is activated for the dominant sense, and multiple meanings are
activated when it is the subordinate sense that is intended.
Activation of meanings as they occur in the brain has been studied
by presenting ambiguous words in solely the right or left visual
fields and measuring response times to dominant and subordinate
meanings (for example, "bank" is presented and is followed
by either "money" or "river"). Immediately
following presentation of an ambiguous word, both meanings are
activated in both hemispheres. After a short time, however, only
the dominant meaning is available in the left hemisphere, whereas
both meanings are still available in the right. Evidence from
neuroimaging studies indicates that word processing in the right
hemisphere occurs in analogous positions to those in the left