Brain Word comprehension - Semantic Scholar · Impairments in word comprehension 613 types of...

Brain (1996), 119,611-625

Word comprehensionThe distinction between refractory and storage impairments

Elizabeth K. Warrington and Lisa Cipolotti

National Hospital for Neurology and Neurosurgery,London, UK

Correspondence to: Professor Elizabeth K. Warrington,National Hospital for Neurology and Neurosurgery, QueenSquare, London WC1N 3BG, UK

SummaryWe report a series of experiments in which we compare theresidual word comprehension skills of patients with corticaldegenerative conditions and those with an 'access' dysphasia.Using word-picture matching tasks it was shown that (i) thepresentation rate (the response-stimulus interval) affectedthe word comprehension performance of the patients with anaccess dysphasia but not of the patients with degenerativeconditions; (ii) the semantic relatedness of the stimulusarrays had a greater influence in the performance of theaccess dysphasic patients than with a degenerative condition;(Hi) word frequency was a strong determinant of theperformance of patients with degenerative conditions butnot those with an access dysphasia; and (iv) responseinconsistency was a characteristic of the patients with anaccess dysphasia, whereas this was not observed in those

with a degenerative condition. These four effects clearlydifferentiate the word comprehension performance of thesetwo types of patients. Thus, two types of word comprehensionimpairment have been identified. A unitary account of thepattern of performance in the access patients in terms ofrefractoriness has previously been proposed and it isreiterated here. Similarly, a unitary account of the patientswith degenerative conditions in terms of storage deficit isadvanced. It is speculated that these two types of deficit,refractoriness and storage, reflect two sources of damage tothe stored representations underpinning a word, rather thana dichotomy between deficits affecting the procedures ofaccessing semantic representations and the storedrepresentations themselves. The implications for neurologicaldiagnosis and therapeutic intervention are discussed.

Keywords: dysphasia; dementia; semantic memory; refractoriness/storage

Abbreviations: NART = National Adult Reading Test; WAIS-R = Wechsler Adult Intelligence Scale—Revised

IntroductionSemantic memory is a system which processes, stores andretrieves information about the meaning of words, objects,facts and concepts. However, impairments of semanticmemory may be confined to one domain of knowledge.Comprehension of the meaning of words may be gravelyimpaired in patients whose cognitive skills are otherwiserelatively preserved.

The selective impairment of semantic memory was firstdescribed in three patients with cortical degenerativeconditions (Warrington, 1975). It was observed that theirknowledge of word meanings was markedly compromised;although they were able to express themselves fluentlyand lucidly, using appropriate syntax, within the limitationsimposed by their impoverished vocabulary. Their wordcomprehension deficit was characterized by robust frequencyeffects, such that all but the most common words had becomeunfamiliar. This loss of word meaning did not appear to be

© Oxford University Press 1996

an absolute deficit, partial comprehension of words withthe relative preservation of superordinate information wasdocumented. It was also observed that they appeared to havea stable, albeit depleted, vocabulary. This consistency ofword specific knowledge over time was formally documentedin one of these patients (Coughlan and Warrington, 1981).A stable, frequency dependent, item specific, wordcomprehension impairment, preserving the superordinateknowledge, was observed in these patients. Thus a semanticstorage deficit in which there has been a degradation of thesemantic representations has been proposed to account forthis pattern of performance.

Semantic storage deficits have now been observed innumerous investigations of patients with a variety of corticaldegenerative conditions and in patients recovering fromherpes encephalitis. For example, Chertkow and Bub (1990)reported consistency and partial knowledge effects in 10

612 E. K. Warrington and L Cipolotti

Alzheimer patients. This finding was replicated by Hodgeset al. (1992A) in a larger sample of patients with dementiaof the Alzheimer type. Warrington and Shallice (1984)documented frequency, consistency and partial knowledgeeffects in two patients recovering from herpes simplexencephalitis (for review, see McKenna and Warrington, 1993).

Semantic storage deficits have been contrasted withwhat have been termed 'access' deficits, the temporaryunavailability of stored representations. An access disorderwas first identified in a patient with severe acquired dyslexiaon the grounds that from trial to trial his ability to read aloudsingle words was very inconsistent (Warrington and Shallice,1979). Indeed, it was speculated that given time an intactreading vocabulary would be elicited! In this patient and inone further dyslexic patient (Warrington, 1981) the effectsof word frequency were weak and evidence of partial wordknowledge inconclusive.

Subsequently, the concept of an access disorder has beenapplied entirely to the spoken word comprehension of someglobal dysphasic patients. The first patient described as an'access dysphasic' (V.E.R.) who had gravely impaired wordcomprehension, was investigated using word-picturematching tests (Warrington and McCarthy, 1983). In this casethe temporary unavailability of semantic information wasdocumented more directly: the crucial finding was theimportance of temporal parameters. Thus her performancewas strongly affected by presentation rate. By introducing adelay as short as 10 s after a response her performanceimproved significantly. In addition, her performance for anygiven stimulus was inconsistent from trial to trial and therewas a serial position effect such that there was a decrementin her performance with a second probe of a stimulus item.The concept of refractoriness was formulated to accountfor the temporary unavailability of semantic information.Refractoriness was operationally defined as 'the reduction inthe ability to utilize the system for a period of time followingactivation' (Warrington and McCarthy, 1983, p. 874). Thisconcept provided a basis for interpreting these empiricalobservations of rate effects and inconsistency. A furthercharacteristic of the patients' performance was a semanticrelatedness effect such that there was a decrement inperformance with stimulus arrays that were semanticallyclose. It was suggested that the semantic relatedness effectcould be accounted for by a gradient of refractoriness withina semantic field. The rate of presentation, inconsistency andsemantic relatedness effects were replicated and extended ina second case (Y.O.T.; Warrington and McCarthy, 1987).

Word frequency effects are ubiquitous in languagedisorders and strongly affect performance in semantic storagecases (Schuell et al., 1961; Poeck et al., 1973). Hints of anabsence of a frequency effect was reported in a globallydysphasic (M.E.D.; McNeil et al, 1994). This absence of afrequency effect was formally documented in a second case(H.E.C.; Cipolotti and Warrington, 1996) in which all thehallmarks of an access dysphasia were documented. Thisabsence or attenuation of frequency effects was unexpected.

Cueing or priming effects have not yet been considered inthe context of an 'access dysphasia'. Of the four 'access'dysphasic patients studied to date, three had a vascularaetiology (Warrington and McCarthy, 1983, 1987; Cipolottiand Warrington, 1995) and one was a tumour case (McNeilet al., 1995).

In summary, a number of empirical criteria have beenobserved to distinguish between deficits of semantic storageand semantic access in dysphasic patients. These are (i)presentation rate, (ii) consistency, (iii) frequency and (iv)semantic relatedness. These distinguishing criteria are not, ithas been argued, an arbitrary list but can be encompassedby the refractoriness hypothesis to provide a unitary accountof access dysphasia. Thus, refractoriness was formalized asan impairment which delays the return, following activation,of a set of representations that underpin a word, to a 'ready'state. This change was assumed to be temporary and perhapseven sporadic and will result in a reduction of the efficiencyof the system for some time following activation (Cipolottiand Warrington, 1995).

The proposed distinction between access and storagedeficits has been challenged (Humphreys et al., 1988; Rappand Caramazza, 1993). In particular, Rapp and Caramazzahave criticized both the theoretical and empirical validity ofthe distinction. From a theoretical point of view, they arguedthat the access—storage proposal was not presented in thecontext of a 'fully-worked-out theory'. This, they suggest,prevents the possibility of evaluating 'the putatively relevantevidence'. They have also demonstrated elegantly that eachof the single criteria could be conceptualized, according todifferent theories, in a manner that contradicted the inferencesengaged by Warrington and colleagues. The authors alsosuggested that the empirical basis of the access-storagedistinction was not robust. They argued that because not allof the patients have been tested on all of the relevant criteriait is not possible to know whether the refractory hypothesisis indeed a unifying concept. They therefore claim that thetwo patterns of impairments are not clear-cut and did notrepresent a '. . . phenomenon in search of an explanation . . .that may have provided constraints on the theories that couldbe invoked to account for such phenomena . . .' (Rapp andCaramazza, 1993, p. 133).

Rapp and Caramazza's analysis of access and storageimpairments did bring to light a potential empirical weakness.Some effects claimed to be relevant only for accessimpairments have never, in fact, been assessed in patientsheld to have a storage deficit. For example, rate of presentationhas never been manipulated in a semantic storage case. Inaddition, the methods used to assess word comprehensionhave been rarely comparable in the two types of deficit,particularly with regard to semantic relatedness. In thiscontext it may be inappropriate to compare performance onword-picture matching tests that are commonly used toinvestigate access dysphasia with verbal definition tasks thatare more often used in semantic storage cases. Analyses ofconsistency also have not been comparable in these two

Impairments in word comprehension 613

types of impairments. Thus, the four criteria held todifferentiate access and storage deficits still require fullempirical substantiation.

The aim of the present study was to investigate wordcomprehension deficits observed in patients with corticaldegenerative conditions using identical procedures that havepreviously been used to assess access dysphasia. We reporta series of experiments using word-picture matchingprocedures to assess the effects of rate of presentation, wordfrequency, semantic relatedness and consistency in fourdegenerative cases and two access dysphasics. We willdemonstrate that these effects are important for differentiatingbetween disorders of access and storage. These phenomenaare empirically strong and clear-cut. Indeed we will arguethat they might provide, if not a fully worked out theory, atleast the constraints for developing a more fully specifiedtheoretical framework for understanding the organization andoperation of semantic memory.

SubjectsDegenerative casesPatients attending a special clinic for degenerative conditionsare routinely referred to the Psychology Department fora comprehensive neuropsychological assessment. Althoughmany of these patients have global cognitive impairments,in a few cases they may present with a discrepancy betweentheir verbal and nonverbal skills. Four patients withselectively impaired verbal skills were identified and availableto take part in this series of experiments.

Case SIMr W.E. a 67-year-old retired businessman was referred toDr Rossor in July 1992 for investigation of his cognitivedifficulties. There was a 3-year history of language andmemory problems. Other than the cognitive impairmentsdescribed below, there were no neurological signs of note.The MR1 scan demonstrated focal left hemisphere atrophy(see Fig. 1). The clinical diagnosis was probable Pick'sdisease.

W.E. was first assessed on the Wechsler Adult IntelligenceScale—Revised (WAIS-R) in July 1992. At that time heobtained an average verbal IQ of 103 and a high averageperformance IQ of 112. His reading IQ equivalent on theNational Adult Reading Test (NART) was average (28 outof 50 correct). His recognition memory for both verbal andvisual material was very impaired [Recognition MemoryTest—Warrington, 1984]. His verbal comprehension andword retrieval skills were very impaired and he failed toscore on the Graded Naming Test (McKenna and Warrington,1980). A neuropsychological assessment was repeated inDecember 1992 and again in September 1993 (see Table 1).Although still able to function at an above average level onnonverbal tasks, his verbal skills were globally affected and

Fig. 1 Patients scans: (A) Patient SI; (B) Patient S2; (C) PatientS3; (D) Patient S4; (E) Patient Al; (F) Patient A2.

his word comprehension and word retrieval skills wereprofoundly impaired.

Case S2Mrs R.L. was a 59-year-old teacher who was first referredto Dr Rossor with a 4-year history of forgetfulness, especiallyfor names of places and people. Neurological examinationwas entirely normal except for the cognitive deficits describedbelow. The MRI scan showed atrophy of the left temporal


Table 1 Cognitive test scores

Verbal IQPerformance IQDigit spanVocabularyArithmeticSimilaritiesPicture completionPicture arrangementBlock design

RM wordsRM facesOldfieldGNTNARTGDSObject decisionIncomplete letters

SISept.-Nov. '93

92108155

10799

16

10/2515/2511/300/30

28/5023/30NT19/20

S2May '93

10092131011879

11

34/5031/5010/300/30

36/5016/3016/20NT

S3Oct. '93

74101

8644

109

12

17/2542/50

1/300/304/503/30

18/20NT

S4May '94

76104

85669

159

14/2523/253/300/30

12/503/30

17/2019/20

NT = not tested; BPVT = British Picture Vocabulary Test; RM = Recognition Memory; GNT = GradedNaming Test; NART = National Adult Reading Test; GDS = Graded Difficulty Spelling Test.

lobe (see Fig. 1). The clinical diagnosis was probable Pick'sdisease.

R.L. was first assessed on the WAIS-R in September 1992when she obtained a verbal IQ of 97 and a performance IQof 95. Her reading IQ equivalent on the NART was at a highaverage level (32 out of 50 correct). Her recognition memoryfor both verbal and visual material was impaired. The mostnotable feature at this time was a grave nominal dysphasia.She failed to name any item from the Graded NamingTest and only 10 out of 30 of the Oldfield pictures. Theinvestigations of her word comprehension began nearly1 year later, in May 1993. A formal neuropsychologicalassessment was repeated at this time (see Table 1). Therehad been little change in her cognitive status during thisperiod. As previously, the most notable feature was her graveword comprehension difficulties (sparing abstract words) andher very marked nominal dysphasia.

Case S3Mr S.M. a 58-year-old right-handed educator was referred toDr Rossor in July 1993 for investigation of increasingmemory and language difficulties over a 4-year period.Other than the cognitive difficulties described below hisneurological system was entirely normal. The MRI scandemonstrated focal left temporal atrophy (see Fig. 1). Theclinical diagnosis was probable Pick's disease.

S.M. was first assessed on the WAIS-R in July 1993 whenhe obtained a verbal IQ of 76 and a performance IQ of 87.His reading IQ equivalent on the NART was defective (fiveout of 50 correct). His recognition memory for verbal materialwas impaired (recognition memory—words 28 out of 50);however, his recognition memory for visual material was

average (recognition memory—faces 43 out of 50). At thistime his language skills were globally impaired. In additionto a profound nominal dysphasia (Graded Naming Test zeroout of 30, Oldfield four out of 30) he was dyslexic anddysgraphic. The investigations of his word comprehensionskills began in October 1993 and at this time a formalneuropsychological assessment was repeated (see Table 1).His verbal IQ has remained static, whereas there was someimprovement in his performance IQ which was attributed toa practice effect. He was now virtually unable to nameto confrontation and this naming deficit appeared to beunderpinned by a profound comprehension deficit.

Case S4Mr T.M. a 58-year-old business man was referred to DrMorgan-Hughes in January 1993 with an 18-month historyof progressive memory and language decline. Neurologicalexamination was normal except for the cognitive deficitsdescribed below. The EEG examination was within normallimits. The CT scan showed mild generalized cerebral andcerebellar involutional changes, together with more severeatrophy of the left temporal lobe (see Fig. 1). The clinicaldiagnosis was probable Pick's disease.

T.M. was first assessed on the WAIS-R in January 1993when he obtained a verbal IQ of 89 and a performance IQof 101. At this time his reading was mildly impaired (NARTscore 15 correct) and could not therefore be used to estimatehis optimum level. His recognition memory for words wassignificantly impaired (17 out of 25), although his recognitionmemory for faces was at an average level (short versionof Recognition Memory Test; E. Warrington, unpublishedresults)^ His spelling and arithmetic were also weak. His


word comprehension and word retrieval skills were seriouslyimpaired.

He was only able to name nine out of 30 items from theOldfield naming test and he scored below the fifth percentileon a synonym test of comprehension (E. Warrington,unpublished results). The investigations of his wordcomprehension impairment began 15 months later in March1994 when a formal neuropsychological assessment wasrepeated (see Table 1). There had been further decline inhis verbal skills during this period although his nonverbalcognitive skills had remained static at an average level

SummaryThe clinical histories of these four patients were very similarindeed. An early feature was word retrieval difficulties inthe context of fluent speech. Formal neuropsychologicalassessment confirmed that the impairment of word retrieval,and in addition word comprehension deficits were a prominentfeature. The series of experiments reported here werecompleted during three or four sessions over a 1-2 monthperiod.

Access dysphasic casesPreviously, access dysphasia has been identified on the basisof clinical criteria, the core feature being a severe wordcomprehension deficit which was described as inconsistentand deteriorating with repeated testing.

Two such 'access dysphasic' patients were identified bythese criteria and available to take part in this series ofexperiments.

Case AlMr M.H., a businessman and company director was admittedto the West Middlesex Hospital after a left-sided cerebro-vascular accident on November 29, 1992, which resulted ina dense right hemiplegia and a dysphasia. During the earlyrecovery period he sustained a myocardial infarction. He wastransferred to the Regional Rehabilitation Unit for intensivephysiotherapy and speech therapy. On examination he wasdensely hemiplegic (though mobile in a wheelchair) andglobally dysphasic. A CT scan demonstrated a large area ofinfarction in the territory of the left middle cerebral artery(see Fig. 1).

He had no useful language production. More striking washis failure to comprehend spoken and written language evenat the single word level. He was unable to attempt any ofthe verbal subtests of the WAIS-R. On a shortened form ofthe performance scale he obtained a performance IQ of 86.On a recognition memory test for faces he obtained anaverage score (44 out of 50). His performance on the Testfor the Reception of Grammar (Bishop, 1982) was very poorand the task was abandoned. He was unable to read or write.On the British Picture Vocabulary Scale (Dunn et al., 1982)

he scored 26 correct on the first 50 items. His performancewas very erratic and not obviously related to word frequency.

Case A2Mr R. S. a 64-year-old painter-decorator was admitted to theNational Hospital for Neurology and Neurosurgery in January1994 under the care of Professor M. Ron. He had beentreated for depression for the last 3 years. Six weeks earlierthere was a sudden deterioration in his mental status; hebecame confused and his speech became impaired. Onexamination, in addition to his cognitive deficits, there wasa right homonymous hemianopia. He had a global dysphasiaand his comprehension was very limited. An MRI scanshowed a multifocal intrinsic cerebral tumour in the leftparietal white matter and in the left posterior temporal lobeoccipital lobe and splenium of the corpus callosum. At biopsya grade IV malignant astrocytoma was demonstrated (seeFig. 1).

A formal neuropsychological assessment was carried outon January 26, 1994. He obtained a verbal IQ of 67 and aperformance IQ of 76 on the WAIS-R. On Raven's ColouredMatrices he obtained a good average score (28 out of 36).On an easy three-choice recognition memory test for pictureshe scored 30 out of 30. He had global language difficulties.Although normally articulated, his expressive language wassparse; he had profound naming difficulties, scoring only oneout of 30 on the Oldfield naming test. He was unable to readany words from the NART, he could spell only two wordsfrom the Schonell graded spelling test. On informal oneword-picture matching tests his performance was veryinconsistent and especially poor for a second or thirdpresentation of the same item.

General proceduresIn all the following experiments, residual comprehensionskills were assessed using matching to sample techniques.Patients were required to match either a spoken word or apicture to a stimulus item in an array displayed on a desk.The arrays comprised four, five and six stimulus items andeach stimulus item was probed three times.

The response-stimulus interval was strictly timed and,unless otherwise stated, a 1 -s rate was adopted. It should benoted that the patient was under no pressure to respond atspeed; 'rate' of successive stimuli was determined entirelyfrom the time a response had been made.

Experiment 1: picture-picture matchingOur aim in the following series of experiments was tocompare patterns of verbal comprehension deficits in patientswith cortical degenerative conditions with those with anaccess dysphasia, using word-picture matching tests. Themain criteria for inclusion in these experiments was theidentification of a verbal comprehension deficit in a patient

616 E. K. Warrington and L. Cipolotti

Table 2 Experiment 1: number and percentage of correctresponses on picture-picture matching tasks

Patient Objects Animals

Table 3 Experiment 2: effect of rate of presentation on thespoken word-picture matching task (number andpercentage correct)

Patient Fast (1 s) Slow (15 s) X2(df-AlA2

SIS2S3S4

75/75 (100%)74/75 (99%)

66/75 (88%)73/75 (97%)75/75 (100%)74/75 (99%)

75/75 (100%)70/75 (93%)

64/75 (85%)60/75 (80%)70/75 (93%)72/75 (96%)

AlA2

SIS2S3

71/144(49%)84/144 (58%)

96/144 (67%)91/144 (63%)93/144 (64%)91/144 (63%)

105/144 (73%)110/144(76%)

99/144 (69%)95/144 (66%)

100/144 (69%)100/144 (69%)

16.8910.6

0.1430.240.771.25

<0.001<0.01

n.s.n.s.n.s.n.s.

whose nonverbal skills were relatively intact. First it wasconsidered necessary to establish that visual processing wassufficiently intact to use word-picture matching tests to assessverbal comprehension.

ProcedureThe picture-picture matching test described by Cipolotti andWarrington (1995) was administered. The stimuli consistedof 25 pairs of pictures of objects and 25 pairs of pictures ofanimals. For each object and for each animal there were twovisually different representations. The stimuli were arrangedin 10 five-item arrays of semantically similar items. Thepatients were required to match each picture with its 'pair'in the array. Each item in each array was probed three times.

ResultsThe number and percentage correct for each category ofstimulus for each patients is given in Table 2. The performanceof all the four 'degenerative patients' (Cases SI, S2, S3 andS4), and the two 'access patients' (Cases Al and A2) is fairlyintact (and we will refer to these two types of patients, thus,throughout). Furthermore, there is little suggestion that thepatients with degenerative conditions are less intact on thistask than the patients with access dysphasia.

CommentThe very satisfactory performance of our two types ofpatient on this visual-visual matching test indicates that theiridentification of pictorial stimuli was adequate for the word-picture matching procedures adopted in this series ofexperiments. We are satisfied that this test was a fairlystringent test of the integrity of our patients' processing inthe visual domain. Indeed, one further degenerative patientwith comparable poor verbal skills to that of the patientsreported in this series of experiments, showed a clear categoryeffect on this task (objects 85% correct, animals 50%); andwas therefore not included in this study.

Experiment 2: spoken word-picture matching(the effect of rate of presentation, semanticrelatedness and word frequency)It has been reported that in patients with an access dysphasia,there are effects of rate of presentation and semantic

relatedness and no effects of word frequency. Our aim was,first, to replicate these effects in the two access patients and,secondly, to compare their pattern of performance with thatof the degenerative patients. These three effects were assessedin the context of three major semantic categories: objects,animals and foods.

ProcedureThis word-picture matching test described in detail byCipolotti and Warrington (1995) consists of coloured picturesof 16 objects, 16 animals and 16 foods. These were arrangedwithin categories in four sets of four-item arrays. For eachcategory there was an array of high frequency words and anarray of low frequency words. For each level of frequencythere was a semantically closely related array and asemantically distant array, that did not cross a major categoryboundary. Thus there were four types of array for each ofthe three categories {see Appendix). Each array was testedboth at a slow presentation rate (response-stimulus interval =15 s) and at a fast presentation rate (response-stimulusinterval = 1 s). Each item in each array was probed threetimes at each rate. The 12 arrays were tested in apredetermined order such that the slow and the fast ratealternated, successive arrays differed in category, frequencyand semantic relatedness.

ResultsThe number and percentage correct for each rate ofpresentation (summing across category, levels of frequencyand semantic relatedness) for each patient are given inTable 3. For the four degenerative patients, there was asignificant impairment at both rates of presentation but theeffect of rate per se was negligible. By contrast, for the twoaccess patients there was a significant effect of rate ofpresentation. Indeed there was a very clear groups Xconditions interaction since there was no overlap in the scoresof the two types of patient at either the fast or the slow rate.

The number and percentage correct for each level offrequency (summing across category, rate and semanticrelatedness) for each patient is given in Table 4. The resultsof the previously reported access dysphasic (H.E.C.) (seeCipolotti and Warrington, 1995) are also included for

Table 4 Experiment 2: effect of word frequency on thespoken word-picture matching task (number andpercentage correct)


Table 5 Experiment 2: effect of semantic relatedness onthe spoken word-picture matching task (number andpercentage correct)

Patient

H.E.C.

AlA2

SIS2S3S4

High

110/144(76%)

89/144 (62%)93/144 (64%)

139/144 (96%)125/144 (87%)133/144 (92%)139/144 (97%)

Low

112/144(78%)

87/144 (60%)101/144 (70%)

56/144 (39%)61/144 (42%)58/144 (40%)52/144 (36%)

X2(d-f. 1)

0.07

0.0031.01

109.4062.1787.44

117.65

P

n.s.

n.s.n.s.

A

A

A A

o o

o

o8

88

8

Patient

H.E.C.

AlA2

SIS2S3S4

Close

102/144(71%)

69/144 (48%)86/144 (60%)

99/144 (69%)98/144 (68%)85/144 (59%)97/144 (67%)

Distant

120/144 (83%)

107/144 (74%)108/144 (75%)

94/144 (65%)88/144 (61%)

106/144 (74%)99/144 (69%)

X2 (d.f. 1)

6.36

21.097.64

0.391.516.850.06

P

<0.02

<0.001<0.01

n.s.n.s.<0.01n.s.

comparison (see also Tables 5-7). There was a massive effectof word frequency in the four degenerative patients. For theaccess patients, including H.E.C, there was no effect offrequency. Again a groups X conditions interaction has beenobserved, since the degenerative patients are superior to theaccess patients with high frequency array, yet score at a verymuch lower level on the low word frequency arrays.

The number and percentage correct for the close anddistant arrays (summing across category, rate and frequency)for each patient is given in Table 5. For three of the fourdegenerative patients, there were no significant differencesbetween their performance on the close and distant arrays.In the fourth patient a semantic relatedness effect wasobserved. However, this was only present with the low wordfrequency arrays. There was a significant effect of semanticrelatedness for the access patients.

The number and percentage correct for each category(summing across levels of word frequency, relatedness andrate) for each patient are given in Table 6. A minor categoryeffect emerged in one of the access patients (A2) and in twoof the degenerative patients (SI, S3) (see Table 6).

CommentIn the two access patients we have obtained similar resultsas in the previously reported access dysphasic (H.E.C).Robust effects of presentation rate and semantic relatednesswere documented. However, there was no effect of frequency.This pattern of performance stands in contrast to that of thefour degenerative patients in whom we have documented theconverse effects. In these patients, performance was notsensitive to rate of presentation. The semantic relatednesseffect was not observed in three of the four patients andrestricted in the fourth case to the low frequency items.However, there was a very striking effect of word frequency.These results cannot be dismissed as a trivial consequenceof severity of deficit. The performance of the degenerativepatients are both superior and inferior to the access patientsdepending on word frequency and inferior on the lowfrequency. It is also quite implausible that these distinctivepatterns of performance can be attributed to some complexinteraction with category specific effects. In neither group

were category effects striking nor was there any hint ofceiling or floor effects restricted to a particular category.

Experiment 3In Experiment 2 we obtained evidence for two very distinctivepatterns of performance in the access patients compared withthe degenerative patients. Our aim in this experiment was toreplicate the rate of presentation, semantic relatedness andword frequency effects using a different set of stimulusmaterials.

ProcedureThis word-picture matching test described by Cipolotti andWarrington (1995) consists of coloured pictures of 16 objectsand 16 foods. These were arranged within categories in foursets of four-item arrays. For each of the two categories therewas both a high and a low word frequency array and asemantically close and a semantically distant array. As inExperiment 2 the items in the 'distant' arrays did notcross major category boundaries. Each of the four possiblecombinations (close, high frequency; close, low frequency;distant, high frequency; distant, low frequency) for eachcategory was tested at two presentation rates (reponse-stimulus interval = 1 s and 15 s). The eight arrays weretested in a predetermined order such that the fast andslow rates alternated; successive arrays differed in category,frequency level and semantic relatedness. Each stimulus ineach array was probed three times in a pseudo-random order.

ResultsThe number and percentage correct for each rate (summingacross categories, frequency and semantic relatedness) foreach patient are given in Table 7. For the four degenerativepatients there was no significant effect of rate of presentation.In contrast, the performance of the two access patientswas significantly worse with the fast than with the slowpresentation rate.

The number and percentage correct for each level offrequency (summing across the two rates, levels of semantic


Table 6 Experiment 2: effect of category on the spoken word-picture matching task (numberand percentage correct)

Patient

H.E.C.

AlA2

SIS2S3S4

Objects

73/96 (76%)

58/96 (60%)67/96 (70%)

71/96 (74%)64/96 (67%)83/% (86%)65/96 (68%)

Animals

78/% (81%)

53/% (55%)74/% (77%)

50/% (52%)59/% (61%)54/% (56%)69/% (72%)

Foods

71/% (74%)

65/% (68%)53/% (55%)

74/96 (77%)64/% (67%)51/% (58%)56/% (58%)

X2d.f. 1)

1.53

3.110.8

16.20.7

28.04.1

P

n.s.

n.s.<0.01

<0.001n.s.<0.001n.s.

Table 7 Experiment 3: effect of rate of presentation on thespoken word-picture matching task (number andpercentage correct)

Patient Fast (1 s) Slow (15 s) X2(d-f- 1)

AlA2

SIS2S3S4

59/% (61%)65/% (68%)

46/% (48%)58/% (60%)64/% (66.6%)61 /% (59%)

71/% (74%)77/% (80%)

3.433.89

51 /% (53%) 0.5253/% (55%) 0.5360/% (68.8%) 0.3661/% (59%)

<0.05

n.s.n.s.n.s.n.s.

Table 8 Experiment 3: effect of word frequency on thespoken word-picture matching task (number andpercentage correct)

Patient High Low X2(d.f. 1) P

H.E.C. 81 /% (84%) 73/% (76%)

AlA2

SIS2S3S4

60/% (62%)75/% (78%)

65/% (68%)87/% (90%)88/% (91%)92/% (%%)

68/% (71%)68/% (71%)

32/% (33%)25/% (26%)36/% (39.5%)30/% (31%)

2.1

1.(51.34

22.682.361.(586.4

n.s.n.s.n.s.

<0.001<0.001<0.001<0.001

relatedness and categories) for each patient is given in Table 8.The results of the previously reported access dysphasic patient(H.E.C.) are also included for comparison {see also Tables 9and 10). There was a highly significant effect of wordfrequency for all the four degenerative patients. In contrastthe effect of word frequency was absent in the access patients.There was a significant semantic relatedness effect in accesspatients. In contrast, there was no semantic relatedness effectin any of the four degenerative patients {see Table 9). Nocategory effects were observed in any patient (see Table 10).

CommentThis experiment replicates and extends the results ofExperiment 2. The degenerative patients were stronglyaffected by the word frequency manipulation but not by rateof presentation or semantic relatedness. Conversely, theaccess patients were affected by the rate and the semantic

Table 9 Experiment 3: effect of semantic relatedness onthe spoken word—picture matching task (number andpercentage correct)

Patient Close Distant X2(d.f. 1) P

H.E.C. 68/% (71%) 86/96 (89%)

AlA2

SIS2S3S4

47/% (49%)64/% (67%)

47/% (49%)55/% (57%)57/96 (59%)63/% (66%)

81/96 (84%)79/96 (82%)

50/% (52%)57/% (59%)67/96 (69.8%)59/% (61%)

10.6

27.096.16

0.180.082.270.36

<0.01

<0.001<0.01

n.s.n.s.n.s.n.s.

Table 10 Experiment 3: effect of category on the spokenword-picture matching task (number and percentagecorrect)

Patient Animals Foods X2(d.f. 1) P

H.E.C. 80/% (83%) 74/% (77%) 0.25

AlA2

SIS2S3S4

60/% (62%)69/% (72%)

46/% (48%)50/96 (52%)66/96 (68%)60/% (63%)

66/% (69%)73/% (76%)

51/% (53%)61/96 (63%)58/96 (60%)62/96 (65%)

0.830.43

0.522.581.450.09

n.s.n.s.n.s.

n.s.n.s.n.s.n.s.

relatedness but not by word frequency. These distinctivepatterns cannot be attributed to severity of deficit, since withall four manipulations the performance of the degenerativepatients and the access patients overlapped depending on theprecise conditions. These are clearly robust and distinctivepatterns of performance.

Experiment 4In Experiments 2 and 3 the absence of (or very weak) effectsof semantic relatedness was observed in the degenerativecases. However, it should be noted that the items in the'close' and 'distant' arrays were not the same. Our aim inthis experiment was to assess the semantic relatedness effectmore rigorously by probing the same items both in thecontext of a 'close' and of a 'distant' array using highlyfamiliar stimuli.


Table 11 Experiment 4: number of correct responses onspoken word-picture and spoken word-picture matchingtasks (effect of semantic relatedness)

Table 12 Experiment 5: number and percentage correctresponses on spoken word-picture matching tasks (effect ofsemantic relatedness)

Patient

H.E.C.

AlA2

SIS2S3S4

Close

65/108 (60%)

33/108 (30%)NT

102/108 (84%)108/108 (100%)106/108 (98%)103/108 (95%)

Distant

95/108 (88%)

81/108 (75%)NT

107/108 (99%)108/108 (100%)107/108 (98%)104/108 (96%)

X2(d.f. 1)

21.69

42.79

P

<0.001

<0.001

n.s.n.s.n.s.n.s.

Patient

AlA2

SIS2S3S4

Distant

59/72 (82%)NT

26/72 (36%)22/72 (30%)27/72 (37%)28/72 (39%)

Very distant

69/72 (96%)NT

58/72 (80%)69/72 (96%)71/72(99%)65/72 (90%)

X2 (d-f- 1)

7.03

29.265.961.841.5

P

<0.01

<0.001<0.001<0.001<0.001

ProcedureThe category 'inanimate objects' is very broad indeed. Thisword-picture matching test described by McCarthy andWarrington (1987) consists of six highly familiar stimuliselected from six subcategories of inanimate objects. Thesewere office stationery, clothes, household utensils, kitchenutensils, furniture and vehicles. The pictures were arrangedin six-item arrays. There were a total of 12 arrays, six closearrays in which all items were from the same subcategoryand six distant arrays which consisted of one item from eachof six subcategories. Each item was probed three times at astandard 1-s rate.

ResultsThe number and percentage correct score for each type ofarray for each patient is given in Table 11. The results of thepreviously reported access dysphasic (H.E.C.) are includedfor comparison. The degenerative patients' performance wasat ceiling on both the 'close' and the 'distant' arrays. Theeffect of semantic relatedness was significant for the accessPatient Al (Patient A2 was not tested).

CommentThe observation that the access patients' performance wasstrongly affected by semantic relatedness replicated thefindings of Experiments 2 and 3. It is not possible to drawany comparison with the degenerative cases since all fourscored at ceiling on this task. Nevertheless, their near perfectscores provide evidence that if the stimuli are highly familiarthese degenerative patients can perform at a superior levelto the access patients.

Experiment 5In this series of experiments the effects of semanticrelatedness were clear-cut in the access patients, but werenot observed, except in the most attenuated form, in thedegenerative patients. However, it would be premature toconclude that the degenerative patients are immune to theeffects of semantic relatedness. In Experiments 2, 3 and 4

the distant arrays were, in fact, all relatively close insofar asall items shared the same broad superordinate category. Thus,if in the degenerative patients there was only preservation ofbroad superordinate information of items in these categories,there would be no benefit of distant over close arrays. Ouraim in this experiment was to explore a wider range ofsemantic relatedness than had been achieved in the previousthree experiments by crossing category boundaries. Theselection of low frequency items would allow a more adequateassessment of semantic relatedness in the degenerativepatients whose low word frequency vocabulary wasimpoverished.

ProcedureThis word-picture matching test consists of coloured picturesof nine objects, nine vegetables and nine animals. The samestimuli were arranged within and across categories in threesets of three-item arrays. The within-category arrays weresimilar (there was some overlap in stimuli) but not identicalto the stimuli of distant arrays used in Experiment 2. Theacross-category arrays consisted of one object, one vegetableand one animal. Thus, there were 18 arrays in all, nine'distant' and nine 'very distant'. The distant and very distantarrays were alternated and each item was probed three timesat a standard 1-s rate.

ResultsThe number and percentage correct score for each type ofarray is given in Table 12. There was a highly significanteffect of semantic relatedness in all four degenerative patients.The access patient Al's performance (patient A2 was nottested) on the 'distant' arrays was at a similarly good levelas was observed in Experiments 2 and 3. In this experimentwith the very distant arrays, both the access patient anddegenerative patients with one exception (SI) were closeto ceiling.

CommentIn this experiment we have compared performance on distantarrays with very distant arrays. We have now, for the firsttime in this series of experiments, observed a semantic


Tbble 13 Error analysis: from Experiments 2 and 3

ConsistencyAl

A2

SI

S2

S3

S4

ObservedExpectedObservedExpected

ObservedExpectedObservedExpectedObservedExpectedObservedExpected

Serial position—McNemarAlA2

SIS2S3S4

/ / /

20112619

3917362034224121

X X X

14985

235

154

123

174

*y /

19312435

934143220358

35

yx

2416

97

157

x x y

27292222

923152114191420

xy

618

714117

X2 (d.f. 3)

6.6

3.82

40.8

18.9

12.8

32.5

X2(d-f. 1)

0.0312.03

0.061.710.340.00

P

n.s.

n.s.

<0.001

<0.001

<0.01

<0.001

P

n.s.<0.0001

n.s.n.s.n.s.n.s.

relatedness effect in the degenerative patients. We will argue(see below) that there is a different basis for the semanticrelatedness effects in the two types of patient. In thedegenerative cases it is only observed with arrays that crosscategories. This suggests that the gain on the very distantarrays can be attributed to the preservation of superordinateinformation in these patients.

Error analysisIn Experiments 2 and 3, the fast condition summing acrosscategories and frequency yielded a high error rate for boththe access and degenerative patients. The data obtained fromthis condition in these two experiments has been amalgamatedand analysed in terms of response consistency and in termsof a serial position effect.

Response consistencyResponse consistency across the three probes of each stimulusitem was computed (assuming independence over trials)using the binomial expansion to generate the expecteddistribution for a chance probability of a wrong responsegiven the known probability of a correct response. Theobserved and expected values of each pattern of correct andincorrect responses for each patient are given in Table 13. AX2 test was computed to assess the significance of thedifference between the observed and expected values (seeTable 13). It was found that the distribution of the accesspatients' responses did not significantly differ from thatexpected by the binomial expansion indicating a degree

of response inconsistency across trials. In contrast, thedistribution of the degenerative patients' responses didsignificantly differ from that expected by the binomialexpansion indicating a highly consistent pattern ofresponding.

Serial position analysisThe number of times the first probe was correct and secondprobe incorrect and the converse pattern of response, incorrectfirst probe and correct second probe, were analysed. Thenumber of each pattern of response for each patient is givenin Table 13. The McNemar test was used to assess thesignificance of these differences. There was no bias in favourof the first or second response for any of the degenerativepatients. For one access patient (A2) there was a clear biasin favour of the first response and in the other access patient(Al) this was not observed.

DiscussionOur aim in this series of experiments was to assess thevalidity of the distinction between 'semantic access' andsemantic storage in patients with impairments of wordcomprehension. Performance of patients with corticaldegenerative conditions was compared with the performanceof access dysphasics on word-picture matching tasks. Fourcriteria (rate of presentation, consistency, frequency andsemantic relatedness), that are considered to differentiatebetween access and storage deficits, were investigated. Inprevious studies, word-picture matching tasks have not been


used to assess the comprehension deficits of patients withcortical degenerative conditions. In addition, there are noprevious reports in which investigators have assessed accessand storage cases using the same stimuli or even the sameprocedures.

Our findings were consistent and clear-cut. Significantrates of presentation effects were observed in the accesspatients but not in the degenerative patients (Experiments 2and 3). By introducing a short interval between the patient'sresponse and the presentation of the next stimulus, theaccuracy of the access group increased dramatically. Thus,with a normal presentation rate, the access patients werescoring at a worse level than the degenerative patients,whereas at the slow rate they were scoring at a better level.

Our analysis of consistency also showed differential effectsin the two patient groups. Response inconsistency was notdemonstrated in the four degenerative cases, nor was thereany evidence of a serial position effect. However, responseinconsistency was observed in the two access patients andin one of these patients there was also a serial position effect.

Robust frequency effects were observed in the degenerativepatients. In contrast, the performance of the access patientswas equally compromised for both high and low frequencywords (Experiments 2 and 3). Consequently, a paradoxicalresult emerged. With a high frequency vocabulary, thedegenerative cases were at ceiling, whereas the access patientshad a significant deficit. With the low frequency vocabularythe performance of the degenerative cases plummeted to alevel inferior to that of the access patients.

Semantic relatedness within a category had a strongdeleterious effect for the access patients (Experiments 2 and3). However, this effect was only present in one of thedegenerative patients in one of the two experiments. However,when the semantic distance was increased to cross categoryboundaries (Experiment 5), a different pattern of performanceemerged. In this condition, all four degenerative patientsshowed a massive effect of semantic relatedness.

These qualitatively different patterns of performancecannot be attributed to differences in the severity of theword comprehension impairment in access and degenerativepatients. It was the testing conditions themselves whichdetermined their pattern of performance.

Thus, we conclude that these four criteria held todifferentiate between deficits of semantic access and semanticstorage are borne out in the comparison of word compre-hension in patients with cortical degenerative conditions andthose with an access dysphasia. The effects of presentationrate, consistency, frequency, and semantic relatednessproduced clear-cut contrasts in the two patient groups. Wewould, therefore, argue that the empirical basis of the access-storage distinction is robust and that contrary to Rapp andCaramazza's (1993) position, these patterns of performanceare indeed phenomena in search of an explanation.

We have previously articulated a unitary account thatprovides a basis for interpreting the observed effects of thesefour variables in the syndrome of access dysphasia (Cipolotti

and Warrington, 1995). Following Warrington and McCarthy(1987) we put forward the concept of refractoriness. Byrefractoriness we assume that following activation, there isa delay in the return to a 'ready' state of the semanticrepresentations underpinning the meaning of a word. Thisrefractoriness is assumed to be temporary and perhaps evensporadic, and will result in the reduction of the efficiency ofthe system for some time following activation. The effect ofrate of presentation is clearly central to this account. Atslower presentation rates there would be a greater probabilitythat the activation levels would have returned to a 'readystate'. Subsequent presentation of the same stimuli wouldresult in a further delay of the return of the semanticrepresentations to their 'ready state', hence the possibility ofa serial position effect. Such delayed return to a 'ready state'would be independent of the frequency or familiarity of thesemantic representations, hence the lack of a frequency effect.Assuming that semantically related words share semantic'space', then the deleterious effect of the activation ofparticular representations would appear to extend tosemantically close words, hence the semantic relatednesseffect.

Similarly we would wish to propose a tentative unitaryaccount of the effects of these four variables in our corticaldegenerative patients. We would suggest that these patientshave suffered a storage impairment such that the semanticrepresentations themselves are lost or degraded rather thanbeing in a refractory state. If the stored representationsthemselves are damaged or lost there could obviously be nogain with a slower presentation rate. Similarly, if the storedrepresentations themselves are damaged or lost, theprobability of a correct response would be independent ofthe number of preceding trials. Thus, performance would notbe characterized by inconsistency by a serial position effect.

Although the psychological basis of frequency orfamiliarity is ill understood, it is a significant factor formany cognitive functions (Schuell et al., 1961; Oldfield andWingfield, 1965; Poeck and Stachowiak, 1975). This isobserved in both normal experimental studies and inneuropsychological investigations. Such frequency effectsare often conceptualized in abstract terms of increased 'tracestrength' or 'greater redundancy'. There are some hints thatthere may be more cells underpinning frequent than infrequentstimuli. For example, in the domain of face perception, ithas been reported that there are more cells optimally tunedto the characteristic front view of the head than the back view(Perretef al., 1991). Thus, in a system that is deteriorating, theobservation of strong word frequency effects would not beunexpected.

In three of the four degenerative patients, a semanticrelatedness effect was only observed when semanticallyvery distant arrays crossing major category boundaries werecompared with within-category arrays. Here we would assumethat semantic knowledge loss is not all or none, but ratherthat some partial knowledge of a concept may be retained.It has been shown previously that superordinate knowledge


is less vulnerable to degradation than subordinate knowledge(e.g. Warrington, 1975; Chertkow and Bub, 1990; Hodgesetai, 1992a, b, 1994). Therefore, in the arrays that comprisedacross-category items, superordinate knowledge wouldincrease the probability of a correct response The fourthpatient is of some interest in so far as his performance onthe within-category arrays was sensitive to the close anddistant dimension and this effect interacted with frequency(at least in one experiment). This, we argue, provides someevidence that the superordinate/subordinate distinction is nota firm dichotomy but depending on the degree of degradationof the semantic system, a gradation of superordinateinformation will be observed. Thus, the lower the itemfrequency, the greater the semantic distance that will benecessary for a given probability of a correct response.

To summarize, we propose that there can be two sourcesof damage to the stored semantic representations underpinninga word. In the one case, the semantic representations are ina refractory state. In the other, there has been loss ordegradation of the semantic representations themselves. Inthis context we wish to introduce a caveat. The observationsthat not all patients with impairments of word comprehensiondo not conform exactly to one or other pattern, present noproblem for our account. Indeed, it is more likely that themajority of cases (other than cortical degenerative conditions)could be expected to have sustained damage that causes bothdegradation and refractoriness of the semantic representa-tions. If this formulation is correct then the two types ofdeficit 'storage' and 'access' reflect the two types of structuraldamage sustained by the semantic representation. Hitherto ithas been supposed that storage and access deficits reflect twofacets of the semantic system, the procedures of accessingthe semantic representations and the storage of semanticrepresentations (Warrington and Shallice, 1979; Shallice,1988; Rapp and Caramazza, 1993). Indeed, the fact that thedegenerative cases are so immune to semantic relatednesseffects with high frequency items and the access cases soimmune to the effects of frequency, suggests that we areobserving the effects of two different sources of structuraldamage to the semantic system. Thus, it would seem moreappropriate to capture this distinction by the terms'refractoriness' and 'storage'. The extent to which thisdistinction can be applied to other subcomponents of thelanguage system such as word retrieval and word productionis an open empirical question.

We now wish to consider briefly the possible aetiology ofthese two types of impairment in neurophysiological terms.First, it should be noted that storage deficits have beenreported not only in the type of degenerative conditioninvestigated here but also in patients with a herpes simplexencephalitis. Similarly, access deficits have been observed inpatients with cerebrovascular disease and in tumour cases.We would speculate that a critical distinction could tentativelybe drawn between a reduction of neuronal conductivity andthe damage or loss of neural structures themselves.

At the physiological level, activity in the broadest sense—

the passage of action potentials and the release oftransmitters—is an energy dependent process. Energy failuredue to anoxia will impair the maintenance of the neuron'smembrane potential resulting in a number of possibleconduction abnormalities, depending upon the severity andduration of the insult. This could include an increase in theperiod when the neuron is refractory to transmission of animpulse or release of neurotransmitter. The psychologicalrefractory data described here could be captured in thisphysiological refractory period. Presumably it would be invascular and tumour cases, in which there may be a penumbraof dysfunction in the region of damage, that a refractorypattern of impairment would be observed. In contrast, astorage disorder would not be captured by a neuro-physiological deficit that impaired conductivity. It wouldrather be characterized by structural neuronal damage eitheracquired or genetically determined. Presumably it would benecessary to damage an entire class of neurons, an eventmost likely with genetic and degenerative disorders ratherthan vascular disease and neoplasms. This, we assume, woulddestroy the substrata of the semantic representations and bereflected in the storage pattern of impairment.

It is beyond the scope of this paper to embark on a detailedexamination of models of the organization and operation ofsemantic systems. However, it is clear that these two syn-dromes offer the potential to investigate organization of thestored semantic representations. Focusing on the phenomenonof partial knowledge observed in the degenerative casescould provide a means of testing theories of the architectureof semantic representations. In particular, it should be possibleto pit 'feature' models (e.g. Smith et al., 1974) against the'tree' models (e.g. Collins and Quinlan, 1970) which are, atpresent, without an adequate empirical test. Exploration ofthe semantic relatedness phenomenon observed in the accesscases could provide more fine grain evidence of theorganization of the semantic representations. These effectsat present point to a strict categorical organization of thesystem. We would also suggest that further investigation ofthe interaction of frequency with the partial knowledgeand the semantic relatedness phenomena would yield sometestable hypotheses. Meanwhile, the data we have presentedserves to constrain certain models of semantic knowledgesystems and must, at any rate, be taken into account in anyformulation of their organization and operation. We wouldwish to harness our observations to temper ad hocspeculations (Rapp and Caramazza, 1993) and to suggesthypotheses that could be put to the test.

Finally, we would suggest that refractory and storageimpairments have significant diagnostic and therapeuticimplications. First, considering the diagnostic issues, wewould predict that patients whose word comprehensionperformance is characterized by a rate of presentation effectwould be more likely to have vascular or space occupyinglesions. Further, we would predict that the rate effect wouldnot occur in patients with pure cortical degenerativeconditions. Secondly, considering the therapeutic issues we


would claim that for patients with a refractory impairment,contrary to most treatment procedures and indeed commonsense, it would appear that repetition of an item is notbeneficial. Indeed it may even be deleterious if the repetitionis too frequent. Rather than focus on a small vocabularywhich might cause serious refractoriness, a wide vocabularymight be more advantageous for these patients.

In conclusion, in this study we have achieved full empiricalsubstantiation for the distinction between refractory andstorage impairments. We have argued that such a distinctionis clear-cut and may provide constraints for models describingthe architecture of the semantic system. We have alsosuggested that such a distinction, which has diagnostic andtherapeutic implications, might be underpinned by two typesof damage at a neurophysiological level.

AcknowledgementsWe wish to thank Dr M. N. Rossor for permission to studypatients under his care and for providing us with facilities tocarry out the investigation, Professor M. Ron for permissionto study a patient under her care, Dr F. Clegg for giving usaccess to a patient undergoing neurorehabilitation, Dr N. Foxfor his advice in interpreting the individual patients' scansand Dr P. Rudge for helpful discussion and advice in thepreparation of this manuscript.

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Collins AM, Quillian MR. Experiments on semantic memory andlanguage comprehension. In: Gregg LW, editor. Cognition in learningand memory. New York: John Wiley, 1972: 117-37.

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McKenna P, Warrington EK. Testing for nominal dysphasia. JNeurol Neurosurg Psychiatry 1980; 43: 781-8.

McKenna P, Warrington EK. The neuropsychology of semanticmemory. In: Boiler F, Grafman J, editors. Handbook of neuro-psychology, Vol. 8. Amsterdam: Elsevier, 1993: 193-213.

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Poeck K, Hartje W, Kerschensteiner M, Orgass B. Sprachverstand-nisstorungen bei aphasischen und nicht aphasischen Himkranken.Dtsche Med Wochenschr 1973; 98: 139-47.

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Received June 15, 1995. Revised October 11, 1995.Accepted November 15, 1995


Appendix: Experiment 2Animals: high frequency

Close SRI (mean = 4.08; SD = 0.8)CDR SF

Distant SRI (mean = 2.4; SD = 0.8)CDR SF

RabbitDonkeyCowLambMean(SD)

20915626394

180.5(72.3)

5.4(1.1)4.5 (1.3)5.1 (1.4)5.1 (0.9)5.04(1.2)

BeeDogHorseSwanMean(SD)

12813801263

29700

(720.3)

5.05 (1)6.5 (0.8)5.52(1.1)4.82(1.23)5.4(1.2)

Animals: low frequency

Close SRI (mean = 4.2; SD = 07)CDR SF

Distant SRI (mean = 2; SD = 0.7)CDR SF

StarfishLobsterCrabOctopusMean(SD)

469

621934(24.3)

3.12(1.2)3.8(1.1)3.8(1.4)3.1 (0.9)3.4(1.1)

KoalaShrimpBisonWalrusMean(SD)

329182117.7(10.8)

3.2(1.2)3.6 (1.2)2.7 (1)2.8 (0.8)3.1(1.1)

Objects: high frequency



TrousersBlouseDressJacketMean(SD)

6064

396143165.7(158.1)

6.35(1.1)5.52(1.3)6.05 (1.4)6.2 (0.8)6.05(1.1)

TeapotKeyHatGlassesMean(SD)

21652511150333.5(296.8)

5.8(1.5)6.3(1)6 (0.8)6.2 (0.9)6.1(0

Objects: low frequency



PliersHoeAxeRakeMean(SD)

1433273727.7(10)

4.2(1.2)3.6(1.4)4.2(1.3)3.6(1.3)3.8(1.3)

FunnelEarphonesBarometerPianoMean

731342

418136.5(189.2)

4.0(1)3.4(1.4)2.8(1)4.8 (1.2)3.7(1.4)

Foods: high frequency



AppleBananasOrangePearMean(SD)

29411322132

165(115.7)

6.5 (0.7)5.9(1.5)6.0(1.4)5.2(1.4)5.9(1.3)

GrapesPotatoesCabbageCherriesMean(SD)

8827413971

143(91.9)

5.1 (1.2)6.3 (0.7)5.0 (1.45)5.2 (1.3)5.3(1-3)


Foods: low frequency

Close SRI (mean

RaspberriesBlackberriesGooseberriesBlueberriesMean(SD)

= 4.8; SDCDR

1493

1610.5(5.8)

= 0.3)SF

4.8 (1.5)4.5 (1.4)3.7 (1.6)3.8 (1.6)4.2(1.5)

Distant SRI (mean

RhubarbPeachDatesOlivesMean(SD)

= 3.1;SDCDR

376

1094257.5

(45.4)

= 0.7)SF

3.8 (1.3)4.8 (1.2)3.6 (1.5)4.2(1.2)4.0(1.3)

The values given for SF are mean (SD). SRI = semantic relatedness index; SF = subjective frequency count. For further details of thesemeasurements see Cipolotti and Wamngton, 1995. CDR = Carroll et al. (1971) word frequency count.

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