"Compare and contrast the Garden Path Model and the

Constraint Based Model of sentence processing. What are

their relative strengths and weaknesses?"

Dionne Angela Donnelly

Module Code: PSYC214

Word Count: 1786

Sentence processing (or parsing) is thought to be best examined by assessing our performance on

understanding ambiguous sentences. This is usually tested by comparing eye movements on

ambiguous and non-ambiguous sentences. Two opposing models of parsing have emerged from

such analyses. These are the garden-path model (GPM) which is an autonomous, two-stage model

of parsing, and the constraint based model (CBM) which is an interactive one-stage model. There

is an abundance of research on these two models, which both support or contest each one

depending on their individual strengths and weaknesses. This research points to both theories

being at least partially correct, but the GPM being the better theory of the two.

The GPM was proposed by Frazier (1979, 1987; Frazier & Rayner, 1982, cited in Jay, 2003), and

it dictates that sentence processing is an autonomous two-stage process. It is autonomous because

the first stage (or pass) involves making initial attachments based on syntactic processing only,

and only one (the simplest) syntactical structure is considered at a time (Eysenck & Keane, 2005).

This stage involves attachments being made based on two of Kimball’s (1973, cited in Garman,

1990) principles: Minimal attachment and late closure. The minimal attachment principle involves

choosing the structure which when adding new lexical items to the sentence leads to the fewest

nodes (Jay, 2003). Late closure involves new words being attached to the current phrase/clause if

it is grammatically sound (Eysenck & Keane, 2005). Of these two principles, minimal attachment

takes precedence (Harley, 2001). The GPM is deemed a two-stage process because if the sentence

to be parsed is ambiguous and requires a second pass, pragmatic, semantic and thematic

information is used to revise the parse tree (Harley, 2001). In contrast to the above model, the

CBM (MacDonald, Pearlmutter & Seidenberg, 1994, cited in Eysenck & Keane, 2005) states that

sentence processing is a one-stage process involving an interaction of semantic, syntactic,

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discourse, and frequency-based information (also referred to as ‘constraints’) (Harley, 2001). All

of these are available to the parser immediately, with all possible interpretations being available at

the same time, and these are ordered depending upon their “strength of activation” (Eysenck &

Keane, 2005, pg. 364). This strength is determined by the number of constraints which support

each structure. ‘Garden-pathing’ is thought to arise when the correct structure receives less

activation that an incorrect structure (Eysenck & Keane, 2005; Harley, 2001).

Research which provided support for the principles of the GPM (and which therefore opposes the

CBM) was conducted by Rayner and Frazier (1987), who found (using eye movement data) that

processing was faster for nonminimal attachment sentences that contained complementisers such

as ‘that’ in order to reduce ambiguity, than for sentences that did not contain complementisers. For

example in the sentences:

(1) “The criminal confessed that his sins harmed many people”

(2) “The criminal confessed his sins harmed many people”

Subjects, using the principle of minimal attachment, found (1) to be unambiguous as the parser

sees ‘his sins’ as the subject of the complement ‘harmed many people’ (Pine, 2010), whereas (2)

resulted in a garden path when the reader reached ‘harmed’ (the disambiguating region) as the

reader treats ‘his sins’ as the direct object of the verb ‘confessed’ (Pine, 2010). This study shows

that without such complementisers we read past the clause boundary and fail to close the clause

correctly (Jay, 2003). An example of a similar study which instead provides support for the CBM

was conducted by Trueswell, Tanenhaus & Kello (1993). They compared reading times and eye

movement data for parsing of garden path sentences that made either direct object reading more or

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less likely (Pine, 2010). The results showed that the complementiser effect seen above was due to

how strongly a verb is associated with the ‘that’ complementiser, and was not because of syntactic

misanalysis as proposed by the GPM.

The principle of late closure has also been supported by research, which again contradicts the

predictions of the CBM. Frazier and Rayner (1982, cited in Pine, 2010), studied the reading times

for sentences which were either consistent or inconsistent with late closure, for example:

(3) Since Jay always jogs a mile and a half this seems a short distance to him.

(4) Since Jay always jogs a mile and a half seems a short distance to him.

Sentence (3) requires reader to keep VP ‘jogs’ open and attach NP ‘a mile and a half’, which

according to the GPM model should be easy for the parser. Sentence (4) requires reader to close

VP after ‘jogs’ which should have caused a garden path effect at ‘seems’ (Pine, 2010). Reading

times were longer for (4), which indicates that the parser spent longer attempting to process the

sentence. This contradicts the predictions of the CBM as if all the possible constraints were

considered simultaneously, reading times would have been the same for both the ambiguous and

the unambiguous sentences.

One of the major contrasts between the CBM and the GPM which has received a considerable

amount of interest from researchers is whether semantic information is used by the parser in the

first pass. The GPM argues that no semantic information is used. This has received support from

studies such as the one conducted by Ferreira & Clifton (1986). They compared eye movement for

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sentences in which minimal attachment would lead to an ambiguous or unambiguous

interpretation. They found that there was a bias for syntactic processing even when such sentences

did not make thematic sense and the reader had to reanalyse the whether the verb should have

been a main verb or a verb of reduced relative. One again, similar research by Truesman,

Tanenhaus and Garnsey (1994) yielded a different conclusion, in favour of the CBM. They used

the sentences:

(5) The author read by the student was very difficult to understand

(6) The book read by the student was very difficult to understand.

Here, the GPM would state that a garden-path effect should occur regardless of the meaning of the

‘author’ or ‘book’ which would change whether the verb ‘read’ would become a main verb or a

reduced relative. However, Truesman, Tanenhaus and Garnsey found that when a semantic

constraint is strongly activated, reduced relatives are just as easy to process as any other structure.

This contradicts the idea that the parser would have to backtrack and reanalyse ‘read’ due to its

ambiguous syntactical structure. Furthermore, the CBM predicts that eye movement studies will

show how the ambiguity of part of a sentence affects processing, until there is enough contextual

information to allow “perceptual suppression” of the other possible interpretations (Mackay, 1970,

cited in Garman, 1990, pg. 359). Support for the CBM comes from a study by Pickering and

Traxler (1998, cited in Eysenck & Keane, 2005), which the following sentences were used:

(7) As the woman edited the magazine amused the reporters.

(8) As the woman sailed the magazine amused the reporters.

As these sentences are syntactically the same, if interpreted using the GPM they would both cause

the parser the same difficulty. But, if interpreted by the CBM this would not be the case due to the

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semantic bias toward the wrong structure in sentence (1). Eye movement analysis showed that

more regressions and longer fixations in the disambiguating region whilst reading sentence (1).

This could be interpreted as showing that semantic information was available to the parser in order

for them to parse (8) more easily than they could parse (7), and this clearly contradicts the

predictions of the GPM. However, Ferreira and Clifton (n.d., cited in Harey, 2001) argued that

semantic information does not help to either prevent or cause the garden-path effect, but instead

aids recovery from it. Nonetheless, CBM proponents argue that contexts are never semantically

neutral, we always have prior knowledge and expectations of what is likely to appear next in a

sentence or what words are likely to appear together (Harley, 2001).

Despite the above research showing a similar amount of support for each model, there are

differences between the two models regarding their theoretical basis. The CBM has a number of

theoretical problems which mean that it is almost impossible to test scientifically. Unlike the

GPM, the CBM is very vague and offers so many potential constraints that it is almost impossible

for them all to be wrong. Therefore, the CBM should make clearer predictions about which

constraints are most salient to the parser and if there are any exceptions to such a rule. The GPM

makes clear predictions that syntactic structure is most important to the parser, and such

predictions can be clearly supported or refuted by the evidence. In contrast to this, researchers

aiming to support the CBM can claim almost any results fit the predictions of the model due to

their vagueness. Also, the CBM should be more specific (as the GPM is) about when interaction

effects occur (Pine, 2010) as it is probable that all constraints are not needed at all times as this

would increase working memory demands (Pine, 2010). The GPM accounts for this problem as

the parser minimises demand by using the principles of minimal attachment and late closure.

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These generalisations usually work because we only rarely encounter ambiguous structures that

are not the correct syntactic structure. If the CBM were more specific, it would allow it to be

tested in its own right, rather than by using procedures designed to test the GPM (Pine, 2010).

Furthermore, the CBM does not make clear whether constraint information is present immediately

or if it only appears soon after reading begins. In relation to this, the semantic effects seen in the

above research by Truesman, Tanenhaus and Garnsey (1994) and Pickering and Traxler (1998,

cited in Eysenck & Keane, 2005) may just show that the first stage of the GPM is extremely short

or difficult to identify using the above procedures (Pine, 2010).

In conclusion, the above empirical research does not indicate whether one model is better at

explaining parsing of ambiguous structures than the other. It only shows that they both receive

similar amounts of support depending on the types of sentences/syntactical structures used. Garrett

(1970, cited in Garman, 1990) reviewed the evidence and concluded that there was enough

empirical support for the validity of both models. He also observed that the research which

supports the CBM predominantly involves tasks that facilitate immediate processing, and the

studies which provide support for the GPM require judgements subsequent to the sentence being

processed and stored in memory. Despite this, the consideration of the theoretical difficulties of

the CBM leads one to believe that whilst both models may be are partially correct, the GPM is the

more theoretically sound and scientifically testable theory of the two.

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References

Eysenck, M. W. & Keane, M. T. (2005). Cognitive Psychology A Student’s Handbook. Hove:

Psychology Press.

Garman, M. (1990). Psycholinguistics. Cambridge: Cambridge University Press.

Harley, T. (2001). Psychology of Language From Data To Theory (2nd Ed.). Hove: Psychology

Press.

Jay, T. B. (2003). The Psychology of Language. New Jersey: Prentice Hall.

Pine, J. (2010). Autonomous and interactive models of sentence processing. PSYC214 Language

& Thought Lecture Slides.

Rayner, K. & Frazier, L. (1987). Parsing temporarily ambiguous complements. The Quarterly

Journal of Experimental Psychology, 39(4), 657-673.

Trueswell, J. C., Tanenhaus, M. K. & Kello, C. (1993). Verb-specific constraints in sentence

processing: Separating effects of lexical preference from garden-paths. Journal of Experimental

Psychology: Learning, Memory, and Cognition, 19(3), 528-553.

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