Download Many types of variation can be found in the analysis of agrammatic

In press in Brain and Language
Generalizations on variations in comprehension and production:
A further source of variation and a possible account
Naama Friedmann, Tel Aviv University, [email protected]
Many types of variation can be found in agrammatic aphasia. Drai and Grodzinsky (in press)
presented a convincing account for variations between syntactic structures, between individuals
and across languages. However, there is one source of variation that is not accounted for by their
approach: the variation that exists within individuals with agrammatism between different
structures that are derived by movement. Such variation can be found in comprehension mainly
between passive sentences and object relative clauses.
Drai and Grodzinsky show that whether or not a sentence is derived by movement of a noun
phrase is a critical factor in whether individuals with agrammatism understand it or not. However,
both passive sentences and object relatives involve movement of noun phrases, and yet for some
individuals, the comprehension of object relatives is impaired (showing chance performance)
whereas the comprehension of passives is unimpaired or above chance. Some other (maybe most)
individuals with agrammatism are impaired in both passives and object relatives. Interestingly,
individuals who are above chance in object relatives but at chance in passives are not reported.
This dissociation can be seen in several studies, for example, Sherman and Schweickert (1989)
reported 5 individuals with agrammatism, two of them were above chance in the comprehension
of reversible passives, but at-chance on reversible center-embedding object relatives. Berndt,
Mitchum and Wayland (1997) reported 5 individuals with agrammatism, 3 of them were above
chance on passives, and at chance on object relatives. This pattern can also be seen in studies that
were not interested in the comparison of passives and object relatives. For example, Ballard and
Thompson (1999) report the baseline comprehension results of 5 individuals with agrammatism
prior to treatment. Two of them, participants 1 and 4, were above chance on passives and at
chance on object relatives. The same was found in the baseline performance of two of the four
participants reported by Thompson, Shapiro, Kiran and Sobecks (2003), RM and DL: they had
above chance performance on passives, and chance performance on object relatives. Three of the
participants reported in Love and Oster (2003) were above chance on passives and at chance on
object relatives (only for one of them, BJ, object relatives significantly differed from the passives).
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The rest of the participants in all these studied were at chance on both passives and object relatives
(except for one participant in Berndt et al. who was above chance on both). Finally, Piñango
(1999) reported an individual, RD, who showed a dissociation of a similar nature: he was above
chance in the comprehension of alternating unaccusatives (which include movement of the subject
from object to subject position) and at chance on object relatives.
What can account for such pattern? It might have been a sheer statistical coincidence, but the clear
asymmetric pattern of passives better than object relatives seems to call for a principled treatment,
similar to the treatment Drai and Grodzinsky gave other types of variations. What we need is an
account that will be able to account both for the dissociation found between passives and object
relatives, as well as for the asymmetrical pattern of this dissociation: either both passives and
object relatives impaired, or passives unimpaired and object relatives impaired, but not the
opposite.
One direction for such account is to try and apply the Tree Pruning Hypothesis, which was
originally suggested for agrammatic production, also to agrammatic comprehension. The Tree
Pruning Hypothesis proved useful in accounting for variation between individuals with
agrammatism who show different degrees of severity in production (Friedmann, 2001, 2005, in
press). Similarly to the pattern in comprehension, variation within individuals was found in
production: Some showed a dissociation in production between good tense inflection and impaired
production of questions and embedding, and some were impaired in both. In a study of 19
Hebrew- and Palestinian Arabic-speaking individuals with agrammatism, three distinct patterns of
performance were found. Five individuals had a relatively mild deficit, which impaired their
ability to produce Wh questions, embedded sentences and verb movement to second position, but
not their ability to inflect verbs for tense and agreement; 13 were more severely impaired, and
their deficit extended to both their ability to produce Wh questions, embedded sentences and V-C
movement, and to inflect verbs for tense; One participant, who was in the early stages of her
recovery, was even more severely impaired, and for her not only the abilities to produce Wh
questions, embedded sentences, V-C movement, and tense inflection were impaired, but also
agreement inflection.
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I suggested that these differences in production can be accounted for by the height on the
syntactic tree that a patient can access: the higher the patient can climb on the tree, the milder the
impairment. A few words about the syntactic tree are necessary here before we proceed to the
account.
According to syntactic theories within the generative tradition (e.g., Chomsky, 1995), sentences
are represented as phrase markers or syntactic trees (see Figure 1 and ignore for now the arches on
the tree). These syntactic trees include functional nodes, which are responsible for the syntactic
structure of the sentence. These functional nodes include, among others, inflectional nodes: an
agreement phrase (AgrsP), the lowest functional node, which represents agreement between the
subject and the verb in person, gender and number, and a tense phrase (TP) above it, representing
tense inflection of the verb. Finite verbs move from V0, their base-generated position within the
VP, to Agr0 and then to T0 in order to check (or collect) their inflection. The highest phrasal node
in the tree is the Complementizer Phrase (CP). This node hosts complementizers such as “that”,
Wh morphemes like “who” and “what” that moved from the base-generated position within the
VP, and the auxiliary in yes/no questions or the verb, which in some languages moves to second
position in the sentence.
Thus, the ability to correctly inflect verbs for agreement and tense crucially depends on the AgrP
and TP nodes respectively and the ability to move the verb to these nodes; The construction of
embedded sentences, Wh-questions and movement of verbs to second position depends on the CP
node being intact and accessible.
Crucially, the nodes in the syntactic tree are hierarchically ordered – the lowest node is the Verb
Phrase, the nodes above it are the Agreement Phrase and the Tense Phrase (in this order according
to Pollock, 1989), and the Complementizer Phrase is placed at the highest point of the syntactic
tree. Now, if we look at this theoretical construct, the syntactic tree, as a Guttman scale (Guttman,
1944), the hierarchy of functional nodes defines what are possible and impossible patterns of
agrammatic deficit in production. It defines what can be a possible agrammatic deficit, and derives
the three patterns of impairment in production that we found, and, perhaps more importantly, it
defines patterns of agrammatism that are logically possible but that are not expected according to
this hierarchy.
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If access to a high node entails access to all nodes below it, and a deficit in a low node implies a
deficit in all nodes above it, then we can explain the three patterns of deficit in production (see
Figure 1) by postulating a single principle that distinguishes them from one another, the level in
the syntactic tree at which the pruning occurs. The five individuals with impairment in Wh
questions and embedding are only impaired at CP, but can access the nodes below it. The 13 more
severely impaired individuals could not access TP, and therefore could not inflect verbs for tense
and also could not access any higher node. The inaccessibility of the higher node resulted in an
impairment also in structures that relate to the higher node CP. Finally, the most severely impaired
individual could not even access the AgrP node, and therefore could not inflect verbs correctly for
agreement, and also could not access the higher nodes TP and CP. Given that inaccessibility to a
certain node prevents access to higher nodes, we do not expect to find individuals with impaired
functions that relate to TP, but with intact CP functions such as Wh question production, and
production of CP-embedded sentences. Similarly, if agreement-related structures are impaired, we
expect both TP and CP to be impaired. And indeed, no agrammatic participant showed an
impairment in TP without an impairment in CP, or impairment in AgrP without an impairment in
TP and CP.
CP
Milder: 5 individuals
C'
(Wh-question)
C
TP
(complementizer)
Severe: 13 individuals
T'
T
AgrP
(tense)
Agr'
VP
Agr
(agreement)
Severest: 1 individual
V'
NP
V
NP
Figure 1. Degrees of agrammatic severity in production on the syntactic tree.
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Returning to the variation in comprehension, a possible way to account for the within-subject
variation of impaired object relatives and above-chance performance on passives is to relate the
performance in comprehension to the position of each sentence type on the tree. The highest node
that passive sentences, as well as SV sentences with unaccusatives, require is the TP node (termed
IP by some analyses that do not split Agr and T). Relative clauses, on the other hand, require CP,
and actually build a tree even above the CP of the embedded clause.1 If a limitation in access to a
node on the tree holds not only for production but also for comprehension, the difference between
individuals who understand neither object relatives nor passives, and individuals who fail to
understand object relatives but who understand passives (and unaccusatives) will be how high
they can get on the tree. Those who can access TP but not CP would understand passives but not
object relatives; those who cannot even access TP, and therefore also not CP, would not
understand both types of sentences. This also explains why the dissociation goes only this way: if
passives are impaired it usually means that TP is impaired (morphological deficits that are not
agrammatic aside), and this requires CP to also be impaired, and therefore causes a failure in
object relatives as well.
So it seems that this additional source of variation in comprehension can also be accounted for.
This opens several questions - can Tree Pruning account in general for the deficit in
comprehension as well as in production? Should we assume tree pruning in comprehension in
addition to a deficit in movement? And finally - is there a relation between variation in
comprehension and production – Namely, if a patient is unable to access TP in production, does it
mean that she will not be able to understand passives?
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A further interesting question relates to whether pruning can occur not only at AgrP, TP or CP, but also
above CP, and therefore manifest only in embedded sentences. This would cause an additional source of
variation between structures that involve nodes above CP and structures that involve only CP. This would
cause a dissociation for some individuals between monoclausal topicalization sentences and Wh-questions
on the one hand and relative clauses and embedded Wh questions on the other hand.
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