Compare and Contrast the Speech Production Models of Pim Levelt, Alfonso

Caramazza and Don MacKay.

On the surface, there appears to be a great deal of agreement between

psychologists over the process of language production. This is because the basic

structure of language production is fairly self-evident. All sensible theories agree

that semantic, syntactic and lexical form properties are distinct levels of

representation; semantics concerns meaning, syntax concerns structure and

lexical form concerns inflection (Caramazza, 1997). It is also widely agreed that

these processes occur sequentially, as each one builds upon the one before it

(Caramazza, 1997). Furthermore, there is widespread agreement that language

production occurs through two distinct phases, firstly selection of the required

lexical representation or lemma, as specified semantically and syntactically,

secondly the selection of the lexical-phonological representation or lexeme

(Caramazza, 1997 & Caramazza et al., 2004); this is because the linguistic

expression of a concept requires association of concept to sound, lemma to

lexeme.

However, there is very little agreement over the deeper processes of

language production (Caramazza, 1997). The limited scope of this essay prevents

a full analysis of the theoretical similarities and disagreements between the

models of Levelt, Caramazza and MacKay, therefore here focus shall be made on

three major theoretical concerns; whether meanings are represented holistically

or componentially, whether the stages of processing are discrete or interactive

and the function of priming in language production.

Theories of language production must be able to solve two problems, the

‘hyperonym’ and ‘hyponym’ problems (Levelt, 1992). Language production

rarely, if ever, results in the production of inaccurate hyperonyms or hyponyms,

for example the hyponym ‘tree’ will not be produced when the speaker means to

produce the hyperonym ‘plant’ and vice versa. Levelt (1992) argues that these

problems entail that representations of meaning cannot be componential as they

would require a ‘principle of specificity, which says that of all lemmas whose

conditions are satisfied by the concept-to-be-expressed the most specific one

(the most entailing one) should be selected (Levelt, 1992; pp.7). Whilst this

principle may be sound in theory, it is not obvious how it can be implemented

into a network model of language production (Levelt, 1992). Thus, Levelt

postulates that representations are holistic, that there is an individual node for

every item in the lexical item in the language, the meanings of which are

represented by lexical-concept nodes and labelled connections between the

concept nodes (Levelt, 1992).

However, MacKay and Caramazza both agree that meanings are

represented componentially (Caramazza, 1997; Levelt, 1992; MacKay, 1987;).

Caramazza argues in his 1997 that there is no need for a principle of specificity

once three sensible assumptions are made, each one of which follows logically

from the basic assumptions of componentiality. Firstly, ‘the amount of activation

passed onto the next level by any one feature is a weighted proportion of the

number of selected features’ (pp.200); thus, for a concept node to be activated,

all of the component meaning nodes of the word must be activated. Secondly,

‘the amount of activation normally needed by the activated lexemes to reach

threshold is the full unit of activation propagated from the lexical-semantic

network’ (pp.200), and finally, ‘the maximum amount of activation contributed

by a singe link to a node is a direct function of the number of links that feed into

the node’ (pp.201). These final two assumptions entail that the amount of

activation one node receives from another is proportionately weighted to the

number of links between the two nodes in the case of activating, and weighted to

the number of links between the target node and all other nodes in the case of

activation. This solves the hyperonym problem and the hyponym problem

respectively as the hyperonym and hyponym lexemes will, by definition, receive

activation from only a few of the selected nodes, not enough to reach the

activation threshold.

Unlike MacKay, both Levelt and Caramazza argue that the stages of

processing are discrete rather than interactive (Caramazza, 1997; Levelt, 1992;

MacKay, 1987 & 2004). Experimental evidence for discrete systems comes from

brain-damaged subjects found to have selective difficulties when producing

lemmas of a single grammatical class through a single modality of output

(Caramazza, 1997). That these difficulties occur in only a single modality

suggests that the lexical-semantic system still functions correctly. This, combined

with the fact that the difficulties are constrained to a single grammatical class,

suggest further that the difficulties must manifest only within the syntactic level

of representation (Caramazza, 1997). Thus, the lexical-semantic and syntactic

information must be represented independently, and therefore their systems

must be discrete (Caramazza, 1997). Furthermore, experimental evidence from

anomic subjects that are able to provide information about syntactic features of

words they are unable to produce suggest that the syntactic features of a word

and it form must also be represented independently, and thus also discrete

(Caramazza, 1997).

However, MacKay (James & MacKay, 2004) argues that experimental

evidence from research into phonological and morphological speech errors has

shown that phonology has at least some ‘retroactive’ (pp.104) effects on lexical

retrieval, effects that could not occur if the systems were discrete. This entails

that the systems must be both autonomous and interactive; a problem for

modular theories as according to Fodor modules cannot be interactive in any

way as modularity requires ‘encapsulation of processing’ (cited by MacKay,

1987; pp. 411). However, MacKay argues that modules can exist in an interactive

system, so long as priming is correctly distinguished from activation (1987).

Priming is both automatic and unencapsulated within modules, whilst activation

occurs through sequencing and timing nodes encapsulated within modules

(MacKay, 1987); thus priming allows interaction between modules whilst

sequencing keeps them distinct.

There is such a wealth of experimental evidence of the effects of priming

that few would argue with its phenomenological existence; however, Levelt and

Caramazza disagree with MacKay on exactly how important the process is during

language production (Caramazza, 1997; Levelt, 2001; MacKay, 1987). They argue

that node activation can be facilitated by priming, but is in no way dependent on

it (Caramazza, 1997; Levelt, 2001). In their models the lexical selection system

selects the appropriate nodes ‘under competition’ (Levelt, 2001; pp. 13464) with

other syntactically identical but semantically different nodes, without the need

for separate processes of priming and sequencing. Activation spreads

unidirectionally, for example, to the phonological nodes connected to the lemma

node only, rather than indiscriminately to all other connected nodes; the

phonological nodes of related lemmas are not activated at all (Levelt, 2001). The

creation of a lexical selection network provides a group of relevant lemmas, and

perspective taking obtains the most relevant of the group (Levelt, 2001). The

target lemma node will most likely be the first to reach its activation threshold

and become fully activated, thus activating the phonological nodes connected to

the lemma node.

However, MacKay’s model of language production requires that every

node involved in the utterance of a specific word undergoes separate processes

of priming and activation; priming is the sole process by which a node is

prepared for activation (Burke et al., 1991). This preliminary or subthreshold

stimulation spreads from an individual node to all other nodes connected to it,

regardless of their place in the system hierarchy (Burke, MacKay, et al., 1991).

Priming spreads quickly amongst the nodes regardless of their content and thus

causes the priming of many irrelevant nodes; however, the most relevant nodes

will experience the highest level of subthreshold stimulation as they are

connected to the greatest number of other primed nodes (Burke, MacKay et al.,

1991). The primed nodes are then activated by a separate system of domain-

specific sequence nodes that repeatedly multiply the levels of priming across an

entire domain (Burke, MacKay et al., 1991); the node with the highest level of

priming within each domain, the most relevant node, will be the first to reach the

activation threshold and be expressed. Thus, MacKay’s theory produces the same

outcome as that of Caramazza and Levelt, the activation of the target lemma

node, but by different means.

Thus it can be clearly seen that models of language production, although

similar in their general structure, can vary a great deal in terms of the more

detailed underlying processes. Levelt’ theory argues that meanings are

represented holistically due to the hyperonym/hyponym problem, whilst

MacKay concurs with Caramazza arguments that show that simple assumptions

that follow naturally from those of componentiality itself can solve the problem

much more sensibly. Both Levelt and Caramazza argue that the stages of

processing are discrete, but MacKay points out evidence for interaction between

the stages and is able to integrate the evidence into his theory. Unlike Levelt and

Caramazza, MacKay’s theory argues that the processes of priming and activation

are very important in language production. Indeed, it is this distinction that

divided the three theories most fully. Of the three, it would appear that MacKay’s

theory is the strongest. Not only is his theory the only one of the three that is

consistent with all the experimental evidence mentioned here, but also his is the

only theory that allows activation to spread from a node to all its connect nodes,

and thus does not require that each node performs selective activation of other

connected nodes, a much more intuitive proposition.

Bibliography:

Burke, D., MacKay, D., Worthley, J. & Wade, E. (1991). ‘On the Tip of the Tongue:

What Causes Word Finding Failures in Young and Older Adults?’ Journal of

Memory and Language, 30, pp. 542-579.

Caramazza, A. (1997). ‘How many Levels of Processing are there in Lexical

Access?’ Cognitive Neuropsychology, 14(1), pp. 177-208.

Caramazza, A., Costa, A. & Miozzo, M. (2004). ‘What Determines the Speed of

Lexical Access: Homophone or Specific-Word Frequency? A Reply to Jescheniak

et al. (2003).’ Journal of Experimental Psychology: Learning, Memory, and

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Levelt, W. (1992). ‘Accessing Words in Speech Production: Stages, Processes and

Representations.’ Cognition, 42, pp. 1-22.

Levelt, W. (2001). ‘Spoken Word Production: A Theory of Lexical Access.’

Proceedings of the National Academy of Sciences of the United States of America,

98(23), pp. 13464-13471.

James, L. & MacKay, D. (2004). ‘Sequencing, Speech Production, and Selective

Effects of Aging on Phonological an Morphological Speech Errors.’ Psychology

and Aging, 19(1), pp. 93-107.

MacKay, D. (1987). ‘Constraints on Theories of Sequencing and Timing in

Language Perception and Production.’ Language Perception and Production,

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