Selective treatment of regular versus irregular verbs in...

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Selective treatment of regularversus irregular verbs in agrammaticaphasia: Efficacy dataYasmeen Faroqi-Shah aa Department of Hearing and Speech Sciences, University ofMaryland, College Park, MD, USAVersion of record first published: 07 Mar 2013.

To cite this article: Yasmeen Faroqi-Shah (2013): Selective treatment of regular versus irregularverbs in agrammatic aphasia: Efficacy data, Aphasiology, DOI:10.1080/02687038.2012.751577

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Aphasiology, 2013http://dx.doi.org/10.1080/02687038.2012.751577

Selective treatment of regular versus irregular verbsin agrammatic aphasia: Efficacy data

Yasmeen Faroqi-Shah

Department of Hearing and Speech Sciences, University of Maryland, CollegePark, MD, USA

Background: Production of verb morphology, especially tense marking, is frequentlyimpaired in persons with agrammatic aphasia. Very little research has examined theo-retically driven treatments for verb morphology deficits in aphasia.Aims: This study examined the relative efficacy of using regular (wash-washed,rob-robbed) versus irregular (drink-drank, keep-kept) verbs as stimuli to treat mor-phological impairments in individuals with aphasia. This comparison was motivatedby differences in the lexical organisation of regular and irregular verbs proposed inpsycholinguistic theory.Methods & Procedures: A single-participant multiple-baseline design was used to exam-ine treatment outcomes in six individuals with agrammatic aphasia. Participants receivedtraining to produce tense morphology using only either regular or irregular verbs, andthe crucial outcome measure was generalisation to untrained past tense forms (regular toirregular and vice versa).Outcomes & Results: All participants improved in the trained tenses and generalised to theproduction of regular tense morphology on untrained verbs. Generalisation to untrainedirregular past tense was relatively modest, irrespective of whether regular or irregularverbs were trained.Conclusions: The results replicate previous findings that verb morphology deficits respondto intervention, and extend the findings by suggesting that choice of stimuli may haveconsequences for generalisation effects. The implication for aphasia rehabilitation is thattense training using irregularly inflected verbs generalises to a greater variety of untrainedverb inflections (including regular past) than does the use of regular verbs.

Keywords: Aphasia; Brain damage; Inflection; Morphology; Language production;Treatment efficacy; Verb.

Address correspondence to: Yasmeen Faroqi-Shah, Department of Hearing and Speech Sciences,University of Maryland, College Park, 0100, Lefrak Hall, College Park, MD-20742, USA. E-mail:[email protected]

This project was supported by General Research Board award from the University of Maryland to YF-S.The author wishes to thank all the participants and their families for their participation and support for thisresearch. Special thanks to students who helped with various stages of data collection and analyses (listedalphabetically): Heather Alexander, Sarah Camponeschi, Isabelle Dunn, Xiomy Esteban, Lauren Graham,Melissa Graham, Jessica Greenberg, Jen Maultasch, Rachel Mont, Monica Sampson, Mohan Singh, andPascale St. Victor. Partial findings of this study were presented at the Clinical Aphasiology Conference(2008) and the Annual Convention of the American Speech Language and Hearing Association (2008).

© 2013 Taylor & Francis

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mailto:[email protected]

2 FAROQI-SHAH

Agrammatic Broca’s aphasia is characterised by syntactic and morphological diffi-culties that frequently encompass verbs. For example, verb morphology is severelyimpaired while noun morphology is relatively spared (Goodglass, Christiansen, &Gallagher, 1993; Tsapkini, Jarema, & Kehayia, 2002). A cross-linguistic pattern thathas generated considerable interest among aphasiologists is that verb morphology isselectively more impaired when expressing semantic notions such as tense rather thanwhen marking syntactic constraints such as subject–verb agreement. For instance,completing sentences that demand temporal referencing, such as Tomorrow, the boys_____ [will swim], is significantly more difficult than completing sentences in whichlocal syntactic constraints cue verb form, as in The boy(s) ___ [swim(s)] or The boyswill______ [swim] (Arabatzi & Edwards, 2002; Benedet, Christiansen, & Goodglass,1998; Faroqi-Shah & Dickey, 2009; Faroqi-Shah & Thompson, 2007; Friedmann &Grodzinsky, 1997; Kok, van Doorn, & Kolk, 2007; Varlakosta et al., 2006; Wenzlaff& Clahsen, 2004). This paper presents efficacy data for a treatment approach for verbmorphology deficits that focused on temporal reference. The treatment paradigm is areplication and extension of an earlier study (Faroqi-Shah, 2008). This study extendsprevious work by examining whether the type of stimuli used for treatment (verb withregular versus irregular past morphology) can impact treatment outcomes. A back-ground on relevant theoretical frameworks and empirical evidence is presented in thenext section. This is followed by research questions and an overview of prior treatmentresearch of verb morphology in aphasia.

THEORETICAL AND EMPIRICAL BACKGROUND

This selective impairment of tense morphology has been attributed either to arepresentational deficit for tense or to a processing limitation. Proponents of therepresentational deficit use the syntactic tree framework of generative grammariansto claim that the tense node in the mental syntactic tree is erased (Friedmann &Grodzinsky, 1997). The processing argument attributes the greater difficulty with tensemorphology to the need to integrate information between two levels of computation:conceptual intent and syntactic formulation (Avrutin, 2000, Goodglass et al., 1993).Several recent proposals have focused on the semantic functions of verb inflectionsbecause at least two syntactic functions are relatively less affected: agrammatic indi-viduals perform better on verb forms that can be selected solely by syntactic rules(Faroqi-Shah & Thompson, 2007; Goodglass et al., 1993), and judgement of syn-tactic violations is relatively spared (Linebarger et al., 1983). That is, the process oftranslating temporal information into verb morphology has been identified by multi-ple authors as a potential source of difficulty in agrammatic production (Bastiaanse,2008; Diacritical encoding and retrieval hypothesis of Faroqi-Shah & Thompson,2007; Tense Underspecification Hypothesis of Wenzlaff & Clahsen, 2004; Tense andAgreement Underspecification Hypothesis of Burchert, Swoboda-Moll, & De Bleser,2005; see also Penke, 2003, for a similar explanation based on accessing inflectionalmorphology).

Although there is a rather productive mapping between semantic notions (suchas tense/mood) and morphological structure, it is somewhat inconsistent in severalGermanic languages due to the existence of irregular verbs such as go-went, sleep-slept,and drink-drank. Patterns of performance on regular and irregular verbs have beenvariable in aphasia: some studies reported worse performance on irregulars (Balaguer,Costa, Sebastian-Galles, Juncadella, & Caramazza, 2004; Inglis, 2005; Kok et al.,

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REGULAR AND IRREGULAR VERB TREATMENT 3

2007; Miozzo, 2003; O’Conner, Obler, & Goral, 2007; Penke & Janssen, 1999), oth-ers reported worse performance on regulars (Ullman et al., 1997), or no differencesbetween regular and irregular past (Bird, Lambon Ralph, Seidenberg, McClelland, &Patterson, 2003; Druks, 2006; Faroqi-Shah & Thompson, 2007; Wenzlaff & Clahsen,2004). A meta-analysis of studies that compared regular and irregular verb per-formance revealed that more than half of the published 110 datasets showed nodifferences (Faroqi-Shah, 2007). The meta-analysis also revealed that data sets thatfound worse performance on regulars were from English speakers and the stimuliwere confounded by phonological complexity of regulars compared to irregulars. Thegeneral trend is for irregular verb morphology to be more difficult than regular mor-phology for agrammatic individuals in languages where irregulars have a subregularaffix (Penke & Janssen, 1999 in German; Balaguer et al., 2004, and O’Connor et al.,2007 in Spanish; Kok et al., 2007 for Dutch). Subregular refers to semi-productive pat-terns within the class of irregulars, such as ring-rang, sing-sang, drink-drank in English,and -e(n) suffix for feminine nouns in German irregular plurals. The crucial point isthat the putative performance differences between regulars and irregulars are over andabove the difficulty with tense morphology. That is, the tense information conveyed byboth regular and irregular verb forms (past tense in English) is essentially the same, butwhat differs is whether there is an additional influence of morphological complexity.

There is considerable debate about the extent to which regular and irregular wordsdiffer in lexical representation, and providing a comprehensive review is beyond thescope of this paper (Bybee, 1995; Clahsen, 1999; Halle & Marantz, 1993; McClelland& Patterson, 2002; Pinker & Prince, 1991; Rumelhart & McClelland, 1986; Ullman &Pinker, 2002). Although it is not the intention of this paper to validate any one theoryof morphological processing, a review of experimental results from a variety of sourcessuch as frequency effects, priming, and child language acquisition indicates that mor-phologically regular forms are generally generated by a default mechanism of applyingaffixation rules, such as Verb (+PAST) = Verbed, while irregular forms are gener-ally retrieved from the mental lexicon1 (see also Okrent, 2004; Zimmermann, 2001).Experimental evidence from tasks such as inflectional priming and sentence matchingindicates that lexical entries are morphologically underspecified for redundant fea-tures that can be represented by a parsimonious rule, such as Verb (+PAST) = Verbed(Clahsen, Eisenbeiss, Hadler, & Sonnenstuhl, 2001; Janssen & Penke, 2002; Penke,Janssen, & Eisenbeiss, 2004). In contrast, the lexical entries of irregular verbs includeadditional specification for word structure. For instance, the lexical entry of give, willspecify the perfect form (give(+PERFECT) = given) and for the simple past form(give(+PAST) = gave). The Unique Entry Principle assumes that a general rule suchas Verb(+PAST) = Verbed is replaced by specific rules such as give(+PAST) = gavefor irregular verbs (Pinker, 1984; Pinker & Prince, 1988). In order to explain why (orhow) default rules are not universally applied to irregular verbs, thus preventing wordssuch as singed or sanged in adult speakers, a blocking mechanism is proposed (Aronoff,1976; Glass & Lau, 2003; Kiparsky, 1982; Pinker, 1999). The Blocking Principle allowsthe affixation rule to apply to irregular verbs, however, the existence of lexically storedirregular (past tense) forms blocks an over-regularised form from being produced.

1 Exceptional situations where regular forms may be stored include very high frequency forms (Alegre& Gordon, 1999). Conversely, nonword past tense generation tasks suggest the existence of subregularschemas for irregular verbs that are partially based on phonological form (Bybee & Slobin, 1982;Stemberger, 2002).

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4 FAROQI-SHAH

Figure 1. Illustration contrasting the lexical entries and morphological encoding mechanisms of regu-lar (rake) and irregular (drink) verbs. The rectangular boxes representing lexical entries illustrate theunder-specification of regular verb entries and lexical representation of irregular verb forms (unique entryprinciple). The shaded arrows represent the default affixation rule, which is proposed to be activated forboth regular and irregular verb production. The figure illustrates that production of an irregular verb entailsdefault affixation (arrows 1 & 2 for drink), and selection of the lexical entry (arrow 3 for drank) blocks (arrow4) the regularised form from entering phonological encoding (represented in ovals). The blocking mecha-nism is denoted by . Affixation rule activation during both regular and irregular verb retrieval can be usedto predict generalisation effects for aphasia.

Figure 1 illustrates the more complex nature of irregular verb lexical entries and theapplication of the blocking mechanism on an over-regularised verb after successfulretrieval of an irregular past.

The above principles can be used to make predictions about directionality effectsupon treatment of verb inflections in agrammatic aphasia. It can be hypothesisedthat, when irregular verb production is practiced by an agrammatic individual, thisnot only strengthens the practised irregular verb, but is also likely to re-activate andstrengthen the past tense affixation rule (the shaded arrows in Figure 1). Hence, theeffects of treatment with irregular inflection, via strengthening of the affixation rule,could trickle down to the production of regular past tense forms. This predicts thattreatment of irregular verb inflections could potentially improve both irregular andregular verb production. However, practice with regular verb inflections is unlikely toautomatically benefit irregular verb production. Specifically, there is a theoretical pos-sibility of asymmetrical generalisation effects, that is, treatment of tense marking usingirregular verbs may result in generalised improvement of tense marking on regulars,but not vice versa.

Another aspect that has the potential of influencing treatment effects is the pres-ence of subregular structural patterns within the class of irregulars (Bybee & Slobin,1982). One notable subregular group in English is irregulars that undergo a vowelchange (drank, sank, rang). Another subregular group is one that includes bothvowel change and addition of an alveolar consonant (henceforth referred to as suf-fixed irregulars: kept, slept, felt, and sold, told, lost). According to theories such asDistributed Morphology (Halle & Marantz, 1993), suffixed irregulars pattern bothwith vowel-change-only irregulars as well as regulars (due to alveolar consonant addi-tion). In support of this view, a priming study with unimpaired participants found thatsuffixed irregulars patterned with regulars rather than with vowel-change irregulars

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(Kierlar, Joanisse, & Hare, 2008). By this logic, treatment using suffixed irregularswould be more likely to generalise to production of regulars than treatment that usedvowel-change irregular stimuli.

This treatment study addresses the above predictions by comparing the relativeefficacy of using regular versus irregular verb stimuli in achieving within- and between-verb type generalisation. Of course, with English-speaking aphasic participants as isthe case in this study, the question is only valid for past tense (simple and perfec-tive) since present and future tense morphology is highly regular. The first questionaddressed in the present study pertained to within-verb type generalisation; that is,if tense training for any one verb type (e.g., regulars) would generalise to untrainedexemplars of the same verb type (regulars). Based on principles of affixation rulesversus storage for regular versus irregular morphology, it was predicted that train-ing regular inflections would generalise to other verbs using regular inflections (past,present, and future). However, the uniqueness of lexical entries of irregular verbswould preclude generalisation of irregular past tense training to untrained irreg-ular past verbs. The second question was whether tense training would result inbetween-verb type generalisation (regular to irregular morphology and vice versa).The blocking and unique entry principles were used to predict that training of irreg-ular past tense would inadvertently improve regular past tense production. However,between verb type generalisation would be less likely with regular verb training due tothe absence of mapping between the underspecified entries of regular verbs and thoseof irregular verbs. In other words, it was hypothesised that tense training with reg-ular verbs would promote within verb type generalisation, while tense training withirregular verbs would result in between verb type generalisation.

These two questions were addressed by training participants with either regularverbs (three participants) or with irregular verbs (three participants), while generali-sation to untrained regular and irregular verbs was tested. Given the subregularitiesamong irregulars, participants who received training with irregulars were exposed toa homogeneous set of irregulars, either vowel-change only or suffixed irregulars only.Given the proposal that suffixed irregulars actually encompass features of both vowel-change irregulars and rule based regular affixation (addition of t/d) (Halle & Marantz,1993), we decided to train vowel-change irregulars to ensure no “contamination” byaffixation rules. Hence, two out of three participants received irregular verb train-ing with vowel-change irregulars. We trained suffixed irregulars in one participant inorder to verify if the generalisation patterns obtained with vowel change irregularswere replicable with suffixed irregulars.

PRIOR TREATMENTS OF INFLECTIONAL MORPHOLOGY

In spite of the pervasive occurrence of verb inflection impairments in nonfluentaphasia, and the widespread empirical and theoretical interest in this impairment,there has been a relative dearth of treatment studies for inflectional deficits. The ear-liest treatment study for verb inflections used Garrett’s (1988) framework of languageproduction (Mitchum & Berndt, 1994). As per Garrett’s proposal that verb inflec-tions are embedded in sentence frames, Mitchum and Berndt trained present, past,and future tenses such as The noun is verbing, The noun has verbed, and The nounwill verb in one aphasic individual. It is noteworthy that the trained sentences were

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6 FAROQI-SHAH

morphosyntactically similar in including an auxiliary and verb, but were semanti-cally varied in the type of aspectual markers, with progressive aspect for present tense,and perfective aspect for past tense, but no aspect trained for future tense. One halfof the trained verbs had a regular perfective maker (has closed) while the other halfwere irregular (has eaten). After treatment the patient improved in the production ofboth untrained regular and irregular past perfect tense. Another tense treatment studyused computerised icons and trained a combination of regular and irregular verbs inthree nonfluent aphasic individuals (Weinrich, Shelton, Cox, & McCall, 1997; see alsoBoser, Weinrich, & McCall, 2000). The stimuli differed in two aspects from those ofMitchum and Berndt. First, simple past tense was trained, and second, irregular verbswith a variety of transformations were used. All participants improved in the produc-tion of untrained regular past tense, while improvements for untrained irregular pasttense were limited. Weinrich and colleagues attributed the limited generalisability ofirregulars to the use of heterogeneous irregulars in treatment. The present study differsfrom these two past studies by training only regular or irregular verbs in any one apha-sic participant. Also, all training was strictly for simple tense forms and no aspectualmarking was included.

In a prior study, the relative efficacy of training verb form production(morphophonological treatment) versus semantic aspects of verb forms(morphosemantic treatment) was compared in four individuals with agrammaticaphasia (Faroqi-Shah, 2008). Only the morphosemantic treatment resulted inincreased accuracy of verb inflections, although both treatments improved the num-ber and variety of inflected verbs produced. Hence agrammatic individuals benefitedmaximally from practice in mapping tense features (e.g., +PAST, +PRESENT,+FUTURE) onto semantically matched verb forms (folded, folds, will fold). Practicewith verb form production in the absence of semantic context was less successful.Hence the present study used the morphosemantic procedure of tense trainingproposed by Faroqi-Shah (2008).

METHOD

Participants

Six individuals with aphasia were recruited for the current study (age range:44–65 years). All participants gave written informed consent using proceduresapproved by the institutional review board of the University of Maryland, CollegePark, and hence this study was performed in accordance with the ethical standards laiddown in the 1964 Declaration of Helsinki. All participants had a single left hemispherelesion in the region of the middle cerebral artery resulting from a cerebrovascular acci-dent (CVA) and were at least 1 year post-onset of the CVA. One of the participants(P6) had a history of grand mal seizures, and none of the other participants had anycomplicating neurological conditions such as prior neurosurgery, degenerative or psy-chiatric conditions, or a history of substance abuse. They passed puretone audiometricscreening at 500, 1000, 2000, and 4000 Hz at 40 dBHL ANSI: 1969 in both ears andpassed a vision screen, defined as at least 20/40 corrected or uncorrected vision ona Snellen’s chart and the absence of spatial neglect and visual field deficits (as perself-report). All participants were native speakers of English, right-handed before theCVA, and had at least a high school diploma. Demographic and neurological detailsof all participants are given in Table 1.

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TABLE 1Demographic and neurological information of participants, sorted by treatment verb type

Participant Age/genderYears

education Occupation LesionMonths

post-onset

Regular verb treatmentP1 37/M 18 Police officer Left MCA infarct involving the

frontal and parietal regions84

P2 44/M 19 Softwareengineer

Left MCA infarct, involvingfrontal, subcortical, and basalganglia

16

P3 55/M 18 Admiral inNavy

Left MCA involving thetemporo-parietal andextending into the occipitalregion

29

Irregular verb treatmentP4 56/M 17 Insurance

adjusterLeft MCA infarct 19

P5 55/F 18 Homemaker Left MCA territory infarct andocclusion of the left ICA

26

P6 39/M 14 Financialanalyst

Left MCA territory infarctresulting in a paucity of distalbranches. No major branchocclusion

25

MCA = middle cerebral artery; ICA = internal carotid artery.

Language testing

In order to establish their diagnosis of non-fluent aphasia with agrammatic speechand morphological impairments, all aphasic participants completed a variety of testsincluding: (1) Western Aphasia Battery (WAB, Kertesz, 1982), (2) narrative andoral expression sections of the Boston Diagnostic Aphasia Examination (BDAE,Goodglass, Kaplan, & Barresi, 2001), (3) six sequences from the Narrative StoryCards (Helm-Estabrooks & Nicholas, 2003), and (4) Verb Inflection Test (Faroqi-Shah, unpublished). The narratives obtained from the tests described above weretranscribed and coded using the Systematic Analysis of Language Transcripts (SALT)(Miller, 2004) for lexical and syntactic measures as described in Faroqi-Shah (2008).Using SALT the narratives were analysed to determine rate of speech and mean lengthof utterance. The first 50 utterances were used to compute the proportion of sentences,proportion of grammatical sentences, noun–verb ratio, open–closed class ratio, pro-portion of suffixed verbs (the ratio of suffixed verbs to the total number of verbs thatrequire affixation in contexts where affixation was possible), diversity of tense marking(type–token ratio of tense computed as the ratio of unique tense-aspect markings tothe total number of verbs), and accuracy of tense marking. The first 50 utterances wereused to compute these values so that comparisons across participants and pre- versuspost-treatment measures could be made over a consistent number of utterances. Thesemeasures were used not only to determine the presence of agrammatic speech, butalso as general outcome measures that could be compared across studies in the future.The Verb Inflection Test (Faroqi-Shah, unpublished) elicited 20 sentences in past,present, and future tenses using a picture description with adverbial cues (Tomorrow,

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8 FAROQI-SHAH

Right now, Yesterday, and Every day/Nowadays).2 In addition single word repetition of20 regular and irregular past tense verbs was tested using stimuli matched for phono-logical structure (taken from Bird et al., 2003). Individual participant scores are givenin Table 2.

Inclusionary criteria from these tests were: (1) a profile of non-fluent aphasia withrelatively spared comprehension (all participants were classified as having Broca’saphasia as per the WAB), (2) agrammatic sentence production gleaned from nar-ratives and defined as the presence of fragmented utterances, decreased proportionof sentences, paucity of grammatical morphemes and verbs, (3) difficulty with verbmorphology, defined as an accuracy below 60% on the Verb Inflection Test, (4) nosignificant differences in the production of regular and irregular past tense verbs,determined from tests of sentence production and single word repetition, (5) absenceof significant apraxia or dysarthria as per the oral expression subtests of the BDAEand the checklist of apraxic symptoms listed in the Apraxia Battery for Adults-2ndedition (Dabul, 2000), and (6) functional reading abilities as per the single word read-ing subtests of the WAB. The inclusionary criterion of comparable performance forregular and irregular past verbs prior to the onset of treatment was necessary toexamine between-verb type generalisation effects after treatment and also because ofdiscussions in prior literature about whether regular and irregular verbs are dissociatedin aphasia (Bird et al., 2003; Faroqi-Shah, 2007; Faroqi-Shah & Thompson, 2007).

Upon determination of eligibility, participants were assigned to receive treatmentwith either irregular or regular verbs. Although it was not possible to make exactpairwise matches, we used a pseudo-random assignment method so that participantsreceiving regular versus irregular treatment did not vary dramatically in three respects:severity of the aphasia quotient (AQ) calculated from the WAB, accuracy of verb tenseproduction calculated from the Verb Inflection Test, and age at the time of the study.This is evident from the language scores in Table 2: participants who received treat-ment with regular past tense verbs (P1, P2, P3) did not differ in the above criteria fromthe participants who received treatment with irregular past tense verbs (P4, P5, P6) interms of overall aphasia severity.

Stimuli

Black and white line drawings in three tenses were made by an artist for 40 regular and40 irregular imageable verbs (an example of the verb steal is shown in Figure 2 and theverb list is given in Appendix A). A total of 20 regular verbs were used as treatmentstimuli and the remaining 20 regular verbs were used to test generalisation. The irreg-ular verbs included an equal number of verbs with vowel change and suffixed verbs.Verbs with two acceptable past tense forms (such as dove-dived) were avoided to theextent possible. As explained earlier, one research question pertained to between verb-type generalisation: whether training of irregulars would generalise to regulars, andso we wanted to train irregulars that had little overlap with regulars. Hence two par-ticipants (P4, P5) received training on vowel-change irregulars. The third participant(P6) received training on suffixed irregulars in order to replicate the generalisationpatterns obtained with vowel change irregulars. Treatment and generalisation verbswere matched in logarithmic lemma frequency as per CELEX word frequency counts(Baayen, Piepenbrock, & van Rijn, 1993).

2 All participants were pre-tested for comprehension of temporal adverbs using a calendar pointingtask, on which they had to identify yesterday, today, tomorrow, next month, etc.

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TAB

LE2

Pre-

and

po

st-t

reat

men

tsc

ore

so

nla

ng

uag

eo

utc

om

em

easu

res

Reg

ular

verb

str

aine

dIr

regu

lar

verb

str

aine

d

P1

P2

P3

P4

P5

P6

Pre

Pos

tP

reP

ost

Pre

Pos

tP

reP

ost

Pre

Pos

tP

reP

ost

aW

AB

AQ

(max

.=10

0)77

.492

.1#

45.6

75.8

#61

.867

.8#

80.5

93.7

#22

.761

.9#

71.8

74.1

bV

erb

infle

ctio

nT

est

(%)

5525

3025

55

Wor

dre

peti

tion

(max

=10)

Reg

ular

past

89

510

59

Irre

gula

rpa

st9

107

1010

10c N

arra

tive

Spee

chR

ate

(wor

dspe

rm

inut

e)21

.649

.258

.844

.427

.632

.419

7.4

265.

855

.219

.855

.833

Mea

nle

ngth

ofut

tera

nce

3.74

3.12

1.92

3.61

1.68

1.91

2.84

3.4

1.54

2.8

2.94

4.28

Pro

port

ion

sent

ence

s0.

480.

460.

220.

61∗

0.1

0.39

0.4

0.44

0.1

0.62

∗0.

360.

62∗

Ope

n:C

lose

dC

lass

1.14

1.3

4.33

1.95

∗3.

531.

59∗

1.28

0.95

∗15

1.47

∗0.

840.

9P

ropo

rtio

nve

rbs

0.16

0.19

0.19

0.2

0.15

0.14

0.09

0.08

0.09

0.11

0.07

0.11

∗P

ropo

rtio

nsu

ffixe

dve

rbs

0.63

0.66

0.83

0.77

0.54

0.83

∗0.

851∗

0.14

0.6∗

0.8

0.87

Var

iety

ofte

nse

0.82

0.77

0.08

0.18

∗0

0.89

∗0.

860.

95∗

00.

6∗0.

790.

67A

ccur

acy

ofte

nse

0.22

0.2

11

00.

38∗

0.17

0.1

00.

110.

270.

14

aW

este

rnA

phas

iaB

atte

ry(K

erte

sz,

1982

);A

Q-A

phas

iaQ

uoti

ent;

bF

aroq

i-Sh

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10 FAROQI-SHAH

Figure 2. Example of stimuli. The verb illustrated here is steal. Lexical items were provided by the tester toelicit sentences. For example, the past tense was elicited using the following verbatim instructions: “In thesethree pictures, the action is steal and here is a man and a thief . Here the action is about to happen, here it isgoing on, and here it is done. Now use a sentence to describe this picture [while pointing to the third picturein the sequence].”

Design and procedures

This study primarily used a single-participant design, although descriptive between-group comparisons were made to assess generalisation patterns. Data collectionconsisted of three phases: baseline, treatment, and follow-up. During each base-line probe, a picture description task was used to elicit 30 sentences distributedacross present, past, and future tenses with the treatment and generalisation verbs.Participants received between four and eight baseline probes (ranging from 120 to240 sentences total) in order to demonstrate that treatment effects were unrelatedto repetitive exposure to baseline probes. The number of baseline sessions was ran-domly assigned to each participant. Participants received individual morphosemantictreatment 4 days a week in 1–2-hour sessions. Criteria for cessation of treatment weretreatment probe accuracies exceeding 80% over at least two sessions and a minimumof 12 sessions. Post-treatment testing was conducted immediately following the cessa-tion of treatment and consisted of a re-administration of treatment and generalisationprobes, WAB, and narrative measures. Follow-up testing was done twice, at 2 weeks(F1) and 2 months (F2) after the cessation of treatment, during which treatment andgeneralisation probes were administered. The typical duration of involvement in thestudy (excluding follow-up testing) was 6 weeks.

Experimental control was achieved using varying numbers of baseline measuresacross participants, thus documenting the absence of spontaneous improvement anddemonstrating treatment-induced improvement regardless of the amount of exposureto baseline measures.

Treatment. Each treatment session began with administration of the treatmentprobes, in which the 20 sentences with training verbs were elicited in varioustenses. Generalisation probes were administered every fourth session and consistedof regular and irregular past tense as well as present and future tenses of theseverbs. The procedure for morphosemantic treatment focused on learning the seman-tic implications of various verb forms and has been described in detail elsewhere(Faroqi-Shah, 2008). The following steps were completed for each verb using threepictures, which depicted past, present, and future actions. (1) Confrontation naming:

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In this step the participant was asked to name the action depicted in the three pic-ture sequences (e.g., steal or stealing for Figure 2). (2) Grammaticality judgement:The experimenter read sentences that contained the action elicited in step (1) andthe participant responded whether or not the sentences were grammatically correct(e.g., Yesterday the woman rang the bell, Tomorrow the woman rang the bell). The pri-mary emphasis was on learning to match the temporal adverb with the verb inflection.(3) Comprehension. In this step the experimenter randomly staggered the three pic-tures and read a sentence. The participant was asked to match the sentence with itscorresponding picture (e.g., The man steals the wallet). (4) In the written sentencecompletion task the participant was given a printed sentence with the inflected verbomitted (e.g., Yesterday the lion ________) and the participant was asked to write theappropriate verb inflection that matched a given picture. Assistance with spelling wasprovided. (5) Sentence anagram: In this step the participant was asked to select wordanagrams (The man/ stole/ steals/ will steal/ the wallet) that matched a given pictureand arrange these to form a sentence. Each step was followed by feedback regardingaccuracy and an accompanying explanation. The above steps were repeated for eachof the 20 treatment verbs. After the first few treatment sessions all participants wereable to complete two iterations of 20 verbs during each session. Consistent with theprocedure of Faroqi-Shah (2008), none of the steps listed above required extensiveoral production of verb morphology.3 All three tenses were trained in the followingsequence: past, present (third person singular, Verb+s), and future (will Verb). Onlysimple tenses were trained without introducing aspectual markers. Participants had toachieve an accuracy of 90% in the written sentence completion step (see (iv) above) toproceed to the next tense.

Outcome measures and scoring

The measure that determined cessation of treatment was tense accuracy of treatmentsentences. Generalisation probes—that is, tense accuracy of both regular and irreg-ular generalisation verbs (in all three tenses)—were the primary dependent variablethat specifically addressed the research questions. A significant generalisation effectwas operationally defined as a statistically significant difference between baseline andpost-treatment probes (McNemar’s change test, p < .05). Generalisation probes wereadministered every fourth session for two reasons: to limit improvement in accuracyas a result of repetitive daily exposure, and because of the time required to adminis-ter the very large number of generalisation items (N = 120). The method of elicitingsentences for these treatment and generalisation probes was identical and involveddescribing one of three pictures in a sequence (see Figure 2). The nouns and verbs inthe pictures were provided by the experimenter in order to avoid confounds createdby lexical retrieval difficulties. Responses that minimally contained a noun and a verbwere scored, and the target verb was scored as correct if the verb morphology matchedthe tense being elicited even if the entire sentence was not grammatically well formed.That is, “Woman peeled” was considered for scoring and scored as correct because the

3 Given that the primary purpose of the Faroqi-Shah (2008) study was to compare the relative efficacy ofmorphosemantic and morphophonological treatments, oral production was minimised for morphosemantictreatment to preclude any morphophonological practice. The same protocol was repeated for the currentstudy although the lack of oral practice has no direct implications for the research questions in the currentstudy. Fidelity with the treatment protocol between studies serves to replicate and extend the findings ofFaroqi-Shah (2008).

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12 FAROQI-SHAH

target past tense morphology was produced even though the determiner for “woman”and the noun argument (the potatoes) were not produced.

Participants were given the choice of writing their responses if they experienced dif-ficulty with oral production, and both oral and written responses were accepted. Allparticipants preferred orally producing their responses. However, three participantswere limited by intermittent oral production difficulties specifically for verb endings(P2, P5, and P6) and would orally perseverate on a single ending. All three participantswould self-correct after oral production by writing out their intended verb morphol-ogy (this happened for a total of 5%, 20%, and 17% of all probes for P2, P5, andP6 respectively). No feedback regarding accuracy was provided. Additionally, narra-tive measures and the WAB were repeated at the end of treatment as general outcomemeasures that would enable future comparison with the outcomes of other treatmentstudies.

Reliability

Inter-rater reliability was obtained for 30% of all selected dependent measures, includ-ing scoring of treatment and generalisation probes, as well as transcription andcoding of narrative samples. Additionally, reliability was obtained for 30% of treat-ment sessions for accuracy of administration of the treatment procedure, which isthe independent variable. Reliability measures were obtained using audio recordings,video recordings and/or on-line scoring. Point to point inter-rater agreement for allmeasures exceeded 90% (Cohen’s Kappa statistic, 1960, K > 0.95).

Data analysis

Each participant’s percent accuracy scores were calculated for treatment and general-isation probes for each of the three phases of the study (i.e., baseline, treatment, andfollow-up). Our primary research question pertained to generalisation to untrainedverb morphology and hence the percent accuracy of past tense sentences among thegeneralisation probes was also separately calculated. McNemar’s change test was usedto determine statistically significant change in level for each participant by comparingmean baseline accuracy with post-treatment accuracy (see Boo & Rose, 2011; Conroy,Sage, & Lambon Ralph, 2009; Edmonds & Babb, 2011; for a similar use of McNemar’stest). Two effect size measures were computed, effect size for change in level (Busk& Serlin, 1992) and effect size including slope (Olive & Smith, 2005). The effectsize for change in level (SMDpre-post) was computed by subtracting each participant’smean baseline accuracy from the final treatment session accuracy. This difference wasdivided by that participant’s baseline standard deviation. To compute the effect sizefor slope, mean accuracy was computed over all treatment sessions (hence SMDall).This effect size (SMDall) was calculated by subtracting mean baseline accuracy frommean treatment accuracy and dividing this number by the baseline standard deviation(Olive & Smith, 2005). SMDall values are typically smaller than SMDpre-post becauseprobe accuracies during the treatment phase are lower than post-treatment accuracy.One participant (P4) had zero percent accuracy for baseline probes and hence effectsizes could not be calculated.4

4 In cases of zero-standard deviation during baseline, Busk and Serlin (1992) proposed calculation ofstandard deviation by combining baseline and follow-up scores if both phases have similar performance.Since P4 improved significantly following treatment, Busk and Serlin’s condition for calculation of pooledstandard deviation was not met.

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RESULTS

The mean accuracy of baseline sessions was 3.4% (range: 0–35), and all participantsshowed relatively stable baselines with a small standard deviation. During baselinetesting, regular and irregular past tense probes were of comparable accuracy for allparticipants with the exception of P1 who showed better performance in irregular pastcompared to regular past (14/20 versus 6/20); χ2(N = 40) = 4.9, p < .05. The num-bers of baseline sessions, treatment sessions, and total hours of treatment are givenfor each participant in Table 3. The average number of treatment sessions was 15. Theaverage final treatment accuracy for trained verbs was 93.4% (range: 87–100) showinga significant treatment effect, Paired t-test, t(5) = 9.9, = p < .001. In the following sec-tions results of each treatment verb type will be presented separately. This is followedby scores on general outcome measures, namely narratives and WAB.

Regular verb treatment

The treatment trajectories of P1, P2, and P3 are presented in Figure 3. The durationof treatment and effect sizes are given in Table 3. All three participants showed signif-icant gains in trained verbs (McNemar’s change test, p < .001) with an average finaltreatment accuracy of 95%. As for the first research question (within-verb type gen-eralisation), Figure 3 shows that all three participants generalised treatment effects tountrained regular past tense, and the scores for untrained regular past in the final treat-ment session were near ceiling (Mean = 96.7%). Effect sizes did not differ from that oftrained regular past tense (Fisher’s exact test, p >1 for all three participants). The datafor other trained tenses (which includes combined scores for simple present and futuretenses) were also near ceiling (Mean = 96.6%), and effect sizes did not differ fromthat of trained regular past tense (Fisher’s exact test, p > 1 for all participants). Thesecond research question regarding between-verb type generalisation was examinedwith accuracy of irregular past tense. The effects are mixed: P1 and P2 improved by30% points in the production of irregular past tense (pre- to final-treatment accuracyfor P1 is 70% to 100%; McNemar’s change test, p < .05; pre- to final-treatment accu-racy for P2 is 0% to 30%; McNemar’s change test, p < .05). P3 remained unchangedfor irregular verbs (pre- and final-treatment accuracy = 0%). To summarise, partici-pants were able to apply trained morphology (regular past, simple present, future) tountrained verbs, but did not improve consistently in untrained morphology (irregularpast).

All participants maintained the effects of treatment in follow-up testing (data pointsF1 and F2 in Figure 3), with a mean follow up accuracy score of 87.1% (range =75–100). This accuracy was significantly greater than baseline accuracy (McNemar’schange test, p < .05). While there was a slight decline from final treatment sessionaccuracy, this difference was not statistically significant (McNemar’s change test,p > 1).

Irregular verb treatment

Figure 4 and Table 3 show the treatment trajectories of P4, P5, P6, and other relevantdata respectively. All three participants achieved 80% accuracy criterion for treatmentprobes with an average final treatment accuracy of 95% (McNemar’s change test, p< .01). Data pertaining to the first research question (within-verb type generalisa-tion), show that all three participants improved significantly in accuracy of untrained

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14 FAROQI-SHAH

TAB

LE3

Trea

tmen

td

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for

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Figure 3. Percent accuracy for participants who received tense training with regular verbs (P1, P2, P3) dur-ing baseline (B), treatment (T), and follow-up (F). During baseline, combined scores for both verb types(regular, irregular) and all three tenses (simple past, simple present, future) are plotted for the sake of visualsimplicity. The treatment data (Tx Reg All tense) reflect combined accuracies for all trained verbs (threetenses). The generalisation data are separately plotted for regular and irregular past (Gen Reg Past, Gen IrrPast) and for other tenses, which include simple present and future tense (Gen Other Tense).

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16 FAROQI-SHAH

Figure 4. Percent accuracy for participants who received tense training with irregular verbs (P4, P5, P6) dur-ing baseline (B), treatment (T), and follow-up (F). During baseline, combined scores for both verb types(regular, irregular) and all three tenses (simple past, simple present, future) are plotted for the sake of visualsimplicity. The treatment data (Tx Reg All tense) reflect combined accuracies for all trained verbs (threetenses). The generalisation data are separately plotted for regular and irregular past (Gen Reg Past, Gen IrrPast) and for other tenses, which include simple present and future tense (Gen Other Tense).

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irregular past forms (overall pre- to final-treatment accuracy: 0–48.3%; P4: 0–80%;P5: 0–30%; P6: 0–35%; McNemar’s change test, p < .01 for P4, p < .05 for P5 andP6). Table 3 shows that the effect sizes for untrained irregulars were relatively smallwhen compared to the effect sizes for trained irregulars (0.5 versus 6.6 for P5 and1.9 versus 7 for P6). For the second research question (between-verb type generali-sation), accuracy of regular past tense showed a statistically significant gain for allthree participants, with a mean final treatment accuracy of 93.3% compared to 7.7%at baseline testing (McNemar’s change test, p < .01). The effect sizes for regular pastare larger in magnitude than the corresponding trained irregular and untrained irreg-ular effect sizes (see Table 3). Production of future and present tense morphology onuntrained verbs also improved significantly for all three participants (Mean pre- andfinal treatment scores are: 12% and 87.6%; McNemar’s change test, p < .01 for allthree participants). The participant who received treatment with suffixed irregulars(P6) showed no significant advantage over the participants who received treatment onvowel-change irregulars (P4, P5). To summarise, treatment using irregular verbs pro-duced generalisations in untrained regular and irregular verb morphology. However,the gain in untrained irregular past verb forms was lower in magnitude than that forregular morphology.

All participants maintained the effects of treatment in follow-up testing, withan average accuracy score of 80.8% for trained irregulars (data points F1 andF2 in Figure 4; range = 66–100). While mean follow-up accuracy was significantlygreater than baseline accuracy (McNemar’s change test, p < .05), the decline fromfinal-treatment session accuracy was significant (McNemar’s change test, p < .05).

Regular versus irregular verb treatment

Table 3 shows that quantitative aspects such as the mean number treatment ses-sions required to reach criterion (14.4 versus 15.6), treatment effect sizes (SMDpre-post:11.1 versus 11.8), and the number of treatment hours (24.5 versus 19.2) showed noconsistent advantage for any group. However, there were differences in the patternand magnitude of generalisation to untrained verb types, which can be compared inthe accuracy scores of final treatment and follow-up sessions across Figures 3 and 4.As for the first research question, the mean within-verb type generalisation, computedas the difference between average baseline and final treatment session accuracy, was99.5% for the regular-trained group (gains of 100%, 99%, and 99.5% for P1, P2, andP3 respectively) and 48.3% for the irregular-trained group (gains of 80%, 30%, and35% for P4, P5, and P6 respectively). Mean between-verb type generalisation (regu-lar trained → irregular tested, and vice versa) was 20% for the regular trained group(gains of 30%, 30%, and 0% for P1, P2, and P3 respectively) and 79% for the irreg-ular trained group (gains of 60%, 98%, and 79% for P4, P5, and P6 respectively).That is, while within-verb type generalisation was of higher magnitude for the regulartrained group, between-verb type generalisation was larger for the irregular trainedgroup. In other words, irrespective of whether regular or irregular verbs are used intraining, generalisation to untrained regular morphology was consistently found andwas larger in magnitude than for irregular verb morphology. It is also noteworthythat there were no remarkable differences in generalisation patterns between the twoparticipants who received treatment with vowel change irregulars and the participantwho received treatment on suffixed irregulars.

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18 FAROQI-SHAH

Other outcome measures

Post-treatment scores of the WAB and narratives are given in Table 2. Five out ofsix participants (with the exception of P6) significantly improved in their WAB AQ(McNemar’s change test, p < .05). For the most part, these changes were in the flu-ency score, and additionally in a variety of subtests. Normative values of narrativemeasures are given in Appendix B for comparison. Given that typical statistical testscannot be used for most narrative measures, an a priori criterion of change greaterthan two standard deviations of the normative sample was used as threshold for sig-nificant change (Rochon, Laird, Bose, & Scofield, 2005). The post-treatment narrativemeasures in Table 2 show that rate of speech was higher than the pre-treatment samplefor three participants (P1, P3, P4) and was decreased for the other three participants(P2, P5, P6). All participants except one (P1) showed a quantitative increase in meanlength of utterance (MLU) although this was not a significant change (< 2 SD ofnormative sample). All except one participant (P1) had a higher proportion of sen-tences in the post-treatment sample, and this was significant for P2, P5, and P6. Theratio of open-class to closed-class words showed a significant post-treatment decrease(agrammatic participants have abnormally high ratios, hence a decrease is a favourablechange) in four participants (all except P1 and P6). All participants except P4 showeda quantitative increase in the proportion of verbs, and this change was significant forone participant (P6). Three participants (P3, P4, P5) increased significantly in the pro-portion of suffixed verbs. Four participants improved significantly in the variety oftense (all except P1 and P6). Only one participant (P3) improved significantly on theaccuracy of tense measure. The pre-treatment accuracy of tense is relatively high insome participants (P2) because of the over-use of the present progressive morphology(is Ving).

DISCUSSION

The primary aim of this study was to investigate the relative extent of within- andbetween-verb generalisation that could be achieved with morphosemantic treatmentof tense using regular or irregular verb stimuli. This is a first study that directlycompares the relative efficacy of using regular and irregular verbs in verb tense train-ing, and is a phase II investigation of morphosemantic treatment (Robey, Schultz,Crawford, & Sinner, 1999; WHO). The data show that morphosemantic training ofboth verb types results in significant gains in trained items for all participants. Themorphosemantic treatment also promotes generalised improvement in tenses that areconveyed by predictable and regular morphological markers (such as V+d, V+s, willV ). On the other hand, generalisation to untrained irregular past forms is partial,irrespective of whether regular or irregular verbs are trained. For most participantsthere were also changes in related narrative measures such as variety of tense. In thefollowing sections we discuss the implications of these findings for aphasia rehabili-tation, the understanding of verb tense impairments in agrammatism, and the lexicalrepresentation of verb morphology.

Implications for aphasia therapy

First, this study adds to the body of research that demonstrates the efficacy of targetedaphasia treatment in individuals with chronic aphasia (Holland, Fromm, DeRuyter,& Stein, 1996). Morphosemantic treatment, as described here and in previous work

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(Faroqi-Shah, 2008), results in significantly improved production of verb tense mor-phology in elicited speech and modest improvements in narrative speech. The data onregular rule recovery and generalisation show that all six aphasic individuals were ableto re-learn rules or patterns and generalise the use of V+d, V+s, will V in the correcttemporal context to untrained items.

Given that three tenses for each verb were sequentially trained, it is worth ques-tioning if it is even necessary to train all tenses (or verb forms). In other words, if it issufficient to train only one tense and obtain generalisation to untrained tenses (or verbforms). Two prior studies provide answers to this question. Bastiaanse, Hurkmans,and Links, (2006) trained only non-finite or finite verbs in two Dutch-speaking par-ticipants. The key treatment step was sentence completion and training of temporalreference was not a part of this treatment. The authors used the Complexity Accountof Treatment Efficacy (Thompson, Shapiro, Kiran, & Sobecks, 2003) to predict thatfinite verb treatment would generalise to non-finite verbs since the former are syntac-tically more complex than the latter. Both participants showed limited improvementof trained verb types and failed to improve in the untrained verb type. Thompsonet al. (2006) trained either past tense morphology (V+ed) or agreement morphology(V+s) in a group of 12 participants, and examined generalisation to the untrainedmorphology. Temporal context was utilised in this treatment with adverbs Yesterdayand Nowadays. Thompson et al. found mixed patterns of generalisation, with an equalnumber of participants generalising or failing to generalise to the untrained morphol-ogy. To summarise, the results so far reveal weak generalisation across verb forms,suggesting that each verb tense and its corresponding form (V+ed, V+s, will V )might need to be trained before participants will apply the morphological patternto untrained verbs in the appropriate temporal context. The exception in generali-sation to untrained verb forms are the three participants (P4, P5, P6) who improvedsignificantly in the regular past form even though regular past was not trained andone participant (P1) who improved on irregular past when only regulars were trained.This finding of generalisation across past tense verb forms is further discussed in thefollowing sections.

This study differed from previous verb morphology treatment research in severalrespects (Bastiaanse et al., 2006; Mitchum & Berndt, 1994; Thompson et al., 2006;Weinrich et al., 1997). First, past tense training involved only one verb type for anyparticipant, making it relatively straightforward to examine production of past tenseacross untrained regular and irregular verbs. Another previous study examined gen-eralisation across regular-irregular morphology (Weinrich et al., 1997), and differedfrom the present study in three ways: training used computerised icons, both regu-lar and irregular verbs, and trained six irregular verbs which had different subpatterns(while the present study trained a homogeneous set of irregulars: vowel change only orsuffixed only). The findings were consistent with the present study: improved produc-tion of regular past morphology on untrained verbs, but limited improvements withuntrained irregular past (see also participants TP, PP and SK in Faroqi-Shah, 2008,for similar findings). While rule-based generalisation for regular morphology was dis-cussed earlier, there are at least two possible explanations for irregular verb outcomes.From a psycholinguistic perspective, irregular verbs are unlikely to have strong inter-linkages with each other in the mental lexicon (Pinker, 1999) and hence exert limitedinfluence on other irregulars. Second, composition of stimuli used for irregular verbtraining presents a caveat: while the present study tested generalisation for irregularverb types that were not used for training (that is, suffixed irregulars were tested when

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vowel change irregulars were trained and vice versa), Weinrich et al. (1997) trainedsix heterogeneous irregulars. No study has yet trained and tested generalisation withinthe same subfamily of irregulars, and therefore this possibility for stronger irregularverb generalisation remains to be explored.

A second difference with prior treatment studies is the de-emphasis on oral pro-duction in the treatment steps. The outcomes showed that there was a generalimprovement in oral production of verb morphology even though this was not anexplicit part of the treatment (as mentioned in the section on scoring, P2, P5, andP6 provided written responses for 5–20% of probes). This finding is consistent withFaroqi-Shah (2008), who found that accuracy of tense production failed to improvewhen participants received extensive oral practice (morphophonological training) buttraining on temporal context was not provided. A third difference from prior stud-ies was the inclusion of treatment steps that tapped input processing (grammaticalityjudgement and comprehension). The motivation for including these steps was drawnfrom prior research showing poor performance in such tasks (Dickey, Milman, &Thompson, 2008; Faroqi-Shah & Dickey, 2009). Given that Bastiaanse et al. (2006)failed to find significant treatment gains, and their treatment included oral sentencecompletion without any input processing steps, one can infer that the input stepsused in the present study may be augmenting the treatment outcomes. However, it ispreliminary to make definitive statements about the benefit of using input processingsteps without systematically comparing outcomes of morphosemantic treatment withand without input steps. A final difference with prior treatment studies is the robustimprovement in narrative measures across most participants (except P1).

The implications for aphasia therapy based on the current study and previousfindings are that: (1) morphosemantic training of verb morphology is a promisingtreatment approach for tense deficits for participants whose aphasia profile is similarto those reported in this study and Faroqi-Shah (2008), that is, those with agrammaticaphasia and minimal apraxia of speech, (2) contextually accurate use of regular verbmorphology can be trained quite successfully. Further, use of regular past ending ishighly likely to improve even when it is not explicitly trained. Findings to date areless conclusive about generalisation to untrained irregular verb stimuli, irrespective ofwhether regular or irregular verbs are used for training, (3) oral practice may not benecessary for improved outcomes, (4) use of input processing steps may be respon-sible for the positive outcomes (although this final point needs further verification),and (5) each tense may need to be trained for generalisation of that tense to untrainedverbs.

The findings of this study also have implications for the Complexity Account ofTreatment Efficacy, which states that the “linguistic complexity of materials selectedfor treatment will influence learning and generalisation patterns” (Thompson et al.,2003, p. 602). In other words, treatment of complex linguistic processes is expectedto produce generalised improvement of linguistically related less complex processes.Most evidence for the complexity account comes from syntactic (Thompson &Shapiro, 2007) and semantic treatments (Kiran, 2007). The present study adds mor-phological treatment to the body of research that supports the complexity account;namely, the mental representation of irregular verbs is more complex (as per theevidence presented in the Introduction) and treatment of irregular past tense gener-alises to the production of regular past tense. Given that P1, the patient with leastsevere pre-treatment verb inflection scores, showed improvement for the more complexirregulars following regular training, further research is necessary to examine theapplicability of CATE to intervention of verb morphology.

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Obviously much more research is warranted to validate the above clinical recom-mendations. First, although we found improvement in regular past tense for patientswho were trained on irregulars, a caveat is that all patients were also trained onfuture and present tenses, which are morphologically regular. In future work, weintend to examine the potential for generalisation to regular past following expo-sure to irregular past and no training of other regular morphology. It also remainsto be seen if morphosemantic treatment is a viable treatment approach for individualswho speak inflectionally rich languages (such as Italian, French, Spanish, Kannada)where verb morphology represents additional information such as mood, number, andperson. The patterns of generalisation across regular and irregular verbs and verbswith different conjugations in other languages are also worth investigating. Finally,morphosemantic treatment in its current form does not emphasise oral production.It remains to be seen if incorporating oral practice (such as oral sentence completionor sentence repetition) would enhance treatment outcomes.

Implications for lexical organisation and theories of morphologicalprocessing

The significant improvement in regular past tense production in the irregular trainedgroup provides neuropsychological support for activation of the regularisation ruleduring irregular production and is consistent with theories that invoke either theBlocking mechanism (Aronoff, 1976; Kiparsky, 1982; Pinker, 1999) or parallelaccess of rule-based and storage mechanisms (Augmented Addressed Morphology:Caramazza, Laudanna, & Romani, 1988; Frauenfelder & Schreuder, 1992; Schreuder& Baayen, 1995). However, a confound that limits the interpretation of automaticactivation of regularisation rules in the presence of irregulars is that the irregulartreatment group was exposed to other regularisation rules (V+s). In future researchexclusively training irregular past without accompanying simple present or futuretense training will better elucidate if regularisation rules are automatically strength-ened with exposure to irregulars. A second point from these results is that theeffectiveness of generalisation to regulars did not vary with the type of irregulartrained (vowel change for P4 and P5 versus suffixed irregulars for P6). This is incon-sistent with models that postulate a gradation between regulars and irregulars on thebasis of phonological shape (such as the Distributed Morphology of Halle & Marantz,1993; and the single route account of Eddington, 2002). This finding is also inconsis-tent with priming data on unimpaired individuals where suffixed irregulars patternedwith regulars while vowel change irregulars did not (Kielar et al., 2008). It is likelythat there are multiple principles of organisation in the mental lexicon and the vari-ous experimental tasks tapped different organisational principles. The third theoreticalimplication comes from the finding that untrained irregulars only partially improvedwith irregular treatment. The Unique Entry Principle and its recent variants (Glass &Lau, 2003) propose the relative independence of each irregular verb entry and hencecan accommodate this finding related to limited irregular verb generalisation.

Implications for theories of tense deficits in agrammatism

The patterns of acquisition and generalisation obtained in this study and prior treat-ment studies provide some insight into the nature of tense deficits in agrammaticaphasia. Given that training on associating temporal context with verb morphology

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resulted in improved production of tense morphology, the findings are generally con-sistent with theoretical accounts of agrammatic aphasia that attribute difficulty withsemantic or extrasentential aspects of tense morphology (Faroqi-Shah & Thompson,2007; Wenzlaff & Clahsen, 2004). The pattern of tense deficits in this study isinconsistent with Bastiaanse’s (2008) proposal that only computation of past tensemorphology is impaired in agrammatic aphasia. Our findings of impaired present,future, and past tense morphology are instead consistent with findings of a generalisedtense impairment (Burchert et al., 2005; Thompson et al., 2006; Wenzlaff & Clahsen,2004).

The occurrence of over-regularisation errors for irregular targets during the courseof treatment and generalisation testing needs to be accounted for. After producing anover-regularised verb, participants frequently commented on their unfamiliarity withthe uttered word, but were still unable to generate the correct form. Less frequently,production of an over-regularised form was followed by production of an accurateirregular target. Although this over-regularisation pattern has not been reported forEnglish-speaking agrammatic participants, it is consistent with data from German andDutch agrammatic participants described by Penke and Westermann (2006). Theirdata, obtained using a sentence completion task (for example in German: Ich schreibe.Ich habe __ [geschrieben] [I am writing. I have ___ [written]]), revealed 81% and 98%over-regularisation errors for German and Dutch participles respectively. It is alsonoteworthy that the difficulty with irregulars was reported for participles, which arenon-finite (untensed), with the tense information having been conveyed by an alreadyexisting auxiliary (habe or hebben) in the sentence completion task. This predominantpattern of over-regularisation errors cannot be explained without invoking difficultieswith word form access. A further indication of difficulty with word form access comesfrom the limited generalisation to untrained irregulars found in our study. That is,production of irregular morphology was not facilitated by tense training alone. A thirdpointer to word form access is the influence of lexical frequency on the production ofirregular (Penke & Westermann, 2006) and regular verb inflections (Faroqi-Shah &Thompson, 2004). It is widely reported in psycholinguistic literature that the languageproduction process most robustly influenced by lexical frequency is word form access(e.g., Levelt, Roelofs, & Meyer, 1999).

In their present form, two accounts can accommodate a verb form retrieval deficit.Penke (2003), using the framework of lexicalist approaches to inflectional morphol-ogy, proposed that problems in accessing inflectional affixes were at the core ofagrammatic speech. Penke cited two patterns of data in German agrammatic patientsto support this argument: inflectional errors were more likely with lower-frequencyverb forms and in inflectional paradigms with fewer members. Agrammatic errors inGerman, such as clause-final verb placement and inflectional errors in the second verbwere argued to be accommodated by this account (Penke, 2001). Additionally, theDiacritical Encoding and Retrieval (DER) hypothesis can accommodate a word formretrieval problem that is likely to underlie the over-regularisation errors with irregulartargets. The DER identifies two potential deficits: selection of diacritical features thatcorrespond to the intended message (+PAST, +PLURAL, etc.) and/or selection ofverb forms that correspond to these diacritics (Faroqi-Shah & Thompson, 2007). Thelatter deficit can explain why, despite training with (and knowledge of) past tense, ourparticipants were unable to retrieve the irregular past and instead applied the defaultpast tense affixation rule. Faroqi-Shah and Thompson (2004) argued that agrammaticparticipants are unable to retrieve verb forms that match the intended tense, and hence

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resort to producing the most easily accessible verb form. In most cases verb formswith higher word frequencies or higher affix frequencies are thus produced (see alsoCenteno, Obler, Cairns, Garro, & Merrifield, 1996 for consistent data from Spanish,and Luzzatti, Mondini, & Semenza, 2001 for data from Italian). The data with irregu-lar verbs suggest that representational differences between verbs add another level ofcomplexity that can impact the production of inflections.

Accounts of verb inflection deficits are incomplete if they fail to address anotherfacet: that of morphophonological complexity, which is often implicated to under-mine the production of regular inflections in English (Bird et al., 2003; Braber,Patterson, Ellis, & Lambon Ralph, 2005; Druks, 2006; Ullman et al., 1997). Druks(2006) suggested that morphosyntactic (tense and agreement encoding) difficultiesmight interact with morphophonological encoding such that only those inflectionsthat are morphosyntactically impaired experience additional deficits at the level ofmorphophonology. This was proposed to account for the relatively spared productionof plural and progressive markers in comparison to that of past tense inflections, anda greater deficit for regular past versus irregular past tense inflections observed forDruks’ patient.

In sum, agrammatic participants described here and in previous studies evince mul-tiple levels of difficulties with verb inflections: morphosemantic (diacritical featurespecification), morphosyntactic (as in subject–verb agreement), morpholexical (as inverb form access/encoding), and morphophonological (Bird et al., 2003; Burchertet al., 2005; Druks, 2006; Faroqi-Shah & Thompson, 2004, 2007; Friedmann &Grodzinsky, 1997; Luzzatti & De Blaser, 1996; Wenzlaff & Clahsen, 2004). The emerg-ing pattern is that, while morphosemantic deficits are pervasive (with tense diacriticsmost frequently impaired), these may or may not co-occur with other deficits in vary-ing combinations. There is a cascading complexity effect, where deficits at any levelget magnified by deficits at ensuing levels. The recent computational load accountof agrammatic production (Kok et al., 2007) reveals that task demands add anotherdimension to this complexity cascade and is not incompatible with the data presentedhere.

Conclusions

Psycholinguistic, neuroimaging, and neuropsychological differences in the process-ing of regularly and irregularly inflected verbs in Germanic languages have playeda central role in theories of linguistic processing. However, there have been hardlyany attempts to apply these findings to rehabilitation of morphological deficitsin aphasia (but see Thompson et al., 2006, for application of linguistic theory).This study presents one such attempt in which representational differences betweenverbs were used as a framework to guide treatment. The primary finding is thatre-learning of morphological rules is quite successful in persons with agrammaticaphasia with morphosemantic treatment (within-verb type generalisation). The poten-tial for improvement in rule-based morphology following training with irregular verbs(between-verb type generalisation) is promising, but needs further research beforeconclusive statements can be made.

Manuscript received 16 September 2011Manuscript accepted 12 November 2012

First published online 7 March 2013

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APPENDIX A

Verbs used for treatment and generalisation testing, listed by verb type and participantconditions.

Regular verbs Irregular verbs

Treatment for P1,P2, P3

Generalisation for allparticipants

Treatment for P4,P6Generalisation for

P1, P2, P3, P5

Treatment for P5Generalisation for all other

participants

rake iron ring sleeppeel water sing keepwrap plant swim sellshave climb sink sweeppull mow break dealwash comb wear weepkick push tear leavesmoke empty steal buyhug kiss drink hearrob vacuum wake kneelplay jump sit creepfold open eat losejuggle bake drive leapsew clean light fleeski cross dig catchpaint pour fly tellcarry sail write dreamdry wipe throw feeltie save lead teachskate scrub bite payD

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APPENDIX B

Normative values for narrative speech obtained from 13 age-matched healthy normaladults.

Mean SD

Rate (words per minute) 136.06 26.53MLU 10.80 1.63Proportion sentences 0.97 0.03Open:closed class ratio 0.79 0.07Proportion verbs 0.15 0.02Proportion suffixed verbs 0.63 0.07Variety of tense 0.08 0.02Accuracy of tense 0.94 0.08

Age range = 46 to 66 years, Mean age: 56.6; seven females, Mean years of education = 18.1.

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