1. A model for word production
- A model for word production
- Applying the model to a patient
- Speech-error evidence
Language production might be thought of as the flip side of language
comprehension; that is, in comprehension, you have to take the sounds,
i.e., phonemes, that you hear, group them into words, and arrive
at their meaning. In production, you begin with a meaning that you
wish to convey, and you have to select the appropriate words before
transforming them into sounds.
How might you arrive at a blueprint, or model, of how language
is produced? The above description specifies roughly the stages
involved in production and mentions at least on type of unit that
is processed in the stages, phonemes. If you were building a talker,
what other kinds of information would it process?
Figure 1 is a depiction of a model of how language is produced
(Bock & Levelt, 1994). Production begins when a message-level
representation is formulated. Here a speaker forms a pre-linguistic
concept of what he or she would like to say; for example, the
speaker might decide to tell you about what she did last night,
but has not specified which words she will use. The next step
is to select the words that are appropriate for the meaning (the
lexical-semantic level), followed by specifying the sound of the
word (phonological form) and eventually outputting the utterance
via the articulatory organs in the mouth, throat, and nose.
Figure. 1 Adapted from Bock & Levelt (1994) Model
of Language Production
(Image of sheep courtesy of
2. Applying the model to a patient
Now that we have the steps of production specified, how can
we know more about what occurs at those levels, as well as the
units that are processed by them? One way to get evidence for
the levels in a model of speech production is with patient data.
Individuals who have suffered some sort of damage to their brains
can provide insight into how language production normally works
by showing us what they can and cannot produce.
One person who has been studied for his patterns of production
is MS (Martin, Lesch, & Bartha, 1999). MS suffers from encephalitis,
which has led to damage in the bilateral temporal areas of his
brain. This impairment has caused him some difficulty with producing
language, which he has generously and good-naturedly agreed to
allow researchers to study.
In one task, he was asked to name simple pictures
(taken from the Philadelphia Naming Test; Roach, A., Schwartz,
M. F., Martin, N., Grewal, R. S., & Brecher, A., 1996). To
listen to his responses to the pictures of three items (Cane,
Train, and Comb), click here.
An overall impression you might have of his responses is that
he seems to know a lot about the meaning of a pictured item, but
he just cant seem to access the correct word to convey that
meaning. He can describe what a cane looks like and how it functions,
but he cant say the word, "cane". A preponderance
of such responses suggests that he has difficulty advancing from
the lexical-semantic level to the phonological level; it may be
that the connections between the two levels are impaired.
Connections can be bidirectional; that is, information can spread
downward or upward. Refer again to the model of production in
Figure 1. What path did he take to be able to respond correctly
to "comb" in the end? After saying, "I use it to
comb", he then had the correct phonological form and constituent
phonemes, and they provided feedback to the lexical-semantic level
to activate the correct noun entry.
3. Speech-error evidence
MSs data are consistent with the models depiction
of the levels of speech production. By showing how a system in
a patient has broken down, we saw how semantic and phonological
levels can be separate. How might we get evidence for the units
that are processed by those levels?
Before reading on, try the following demonstration.
You will see two single words appear, side by side, and you should
name each pair to yourself as quickly as you can. Once in a while
the word, "RESPOND" will appear. When you see this word,
say out loud the word pair that preceded it as quickly as you
here to begin!
The experience you just had attempted to get your production
system to break down (with no permanent damage done!) to suggest
what the units of production are. Did you make any errors? How
can you typify them? This task does a good job of creating the
processing circumstances that lead to error in everyday conversation;
e.g, having a limit on time, or trying to talk quickly. Any errors
you made probably involved switching phonemes around; but phonemes,
morphemes (the smallest meaningful unit in a word; e.g, the word
"walked" has two morphemes, "walk" and "ed"
), and words move around, suggesting that they are individual
units that are processed at various stages in production. In experiments
conducted in laboratories, errors are elicited about 10-30% of
the time. About how often did you err?