BRAIN
AND
LANGUAGE
43,
597-612 (1992)
Can Residual Lexical Knowledge Concern Word Form Rather Than Word Meaning? MARIA CATERINASILVERI, LAURA GIUSTOLISI,ANTONIO
DANIELE,
AND GUIDO GAINOTTI Institute
of Neurology,
Neuropsychology
Service,
Catholic
University,
Rome,
Italy
We described a patient with a dramatic deficit of both word comprehension and naming but with good preservation of visual pictorial semantics. On wordpicture matching, his performances were slightly better than expected based on the observed lexical semantic disorder; in addition, the patient, who maintained good preservation of his underlying phonology, showed a tendency to point to the picture phonologically related to the target. In order to interpret these data, we advanced the hypothesis that the patient, in spite of his virtually complete inability to name, would be able, in a word-picture matching task, to “covertly” (i.e., preverbally) retrieve the name from the picture and to use this name to attempt a match with the phonological form of the stimulus word. This mechanism, that we called “phonological” comprehension, would allow the identification of the correct target and would explain the choice of the phonologically related foil that was sometimes selected. 0 1~2 Academic PKSS, IIK.
INTRODUCTION Some cases are described of patients affected by severe lexical comprehension disorders who nevertheless are still able to perform tasks that presuppose at least some preserved residual knowledge about words. Warrington (1975) described three patients, all showing some degree of agnosia for words, that were able to give the superordinate response when attempting to define the words. Similarly, Deloche, Andreewski, & Desi (1981) described a patient who, although severely impaired in spoken word comprehension, performed better than chance in an “oddword-out” task in which the word, not belonging to the same class as other four words, had to be recognized, thereby showing some preserved knowledge of the superordinate category about those words. The patient reported by Albert, Yamadory, Gardner, & Howes (1973) was severely Reprint requests should be addressed to Maria Caterina Silveri, Institute of Neurology, Catholic University, Largo Agostino Gemelh 8, 00168 Rome, Italy. 597 0093-934X/92
$5.00
Copyright 0 1992 by Academic Press, Inc. All rights of reproduction in any form reserved.
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alexic but his semantic comprehension of the written word was demonstrated to be relatively preserved. A further example of residual lexical knowledge of written word was given by patient A.R. (Warrington & Shallice, 1979); although severely alexic, she preserved a surprising ability to perform categorization tasks on the words that she could not read; moreover her capacity in reading a word improved as a consequence of a semantic priming effect on that word. All these cases can be taken as evidence that the residual lexical knowledge is semantic in nature and concerns principally the more general aspects of the meaning, as the knowledge of the superordinate (Warrington, 1975; Bub, Black, Hampson, & Kertesz, 1988). This is in line with the observation that the lexical semantic breakdown of brain-damaged patients is not an “all or none” phenomenon but seems to involve firstly the more specific aspects of the meaning sparing the more general aspects of it (Warrington, 1975). Bub et al. (1988), however, described a patient, M.P., who does not completely fit this general interpretation. In this patient the residual lexical knowledge about words seemed to concern only the superordinate category; in spite of this, M.P. was to some extent able to perform a word-picture matching task in which two semantically related words (e.g., butterfly-grasshopper) had to be matched to a picture. Since the two words were members of the same category, the matching operation could not be performed only on the basis of the knowledge of their superordinate. The paradox was interpreted by suggesting that word-picture matching can be performed by checking the phonological form given by the examiner to some phonological label evoked from the picture without accessing the corresponding semantic information carried by the words. In support of this interpretation, the authors noted that M.P., although severely anemic, could judge correctly if a word rhymed or not with the name of a given picture. We describe a patient, G.P., whose main characteristic was a dramatic impairment of verbal semantics in contrast with good preservation of visual-pictorial semantics. By means of appropriate tasks we could ascertain that the patient had remarkable difficulties in accessing even the most general aspects of the meaning of the words. The existence, in a word-picture matching task, of some other form of word comprehension, in particular, the comprehension that is supposed to rely on the phonological form of the lexical items (Bub et al.,1988), was then assessed. CASE REPORT G.P., a 68-year-old right-handed man, was admitted to our neurological department on July 1988; he was educated until the fifth grade, but his actual educational level seemed to be higher than his formal one. He worked as a specialized worker in a farm and retired at age of 60. No
PHONOLOGICAL
COMPREHENSION
599
history of previous illness had been reported, except for a mild bilateral deafness of mixed type. Since August 1985 he started to complain about progressive difficulties in naming objects and in comprehension of both spoken and written language. In the last year there was a notable worsening of his language disorders and the patient gave up reading newspapers and listening to television. Nevertheless, his behavioral effectiveness in performing customary daily activities was preserved (for instance, he was still able to drive his car). A contrast-enhanced CT scan performed on April 1986 showed a slight enlargement of the frontal horn of the left lateral ventricle. An EEG performed 1 year later showed a theta slowing without any side prevalence. On admission, the neurological examination was negative. A contrast-enhanced CT scan showed an enlargement of both the left lateral ventricle and the left sylvian fissure. MRI scan showed a diffuse cortical/subcortical atrophy, mainly involving the left hemisphere, especially the left temporal lobe (Fig. 1). NEUROPSYCHOLOGICAL Language
ASSESSMENT
Spontaneous Speech
Spontaneous speech was fluent; articulation, intonation and prosody were well preserved. The sentences produced were short but syntactically correct. In spite of severe anemic difficulties, his speech conveyed a substantial amount of information. Naming
Naming was markedly impaired on all modalities (visual, tactile, and from verbal description); the patient was generally able to give information (description of use, context, attribute) about many items that he could not name, showing that he had recognized them; he never produced semantic or phonemic paraphasias. No semantic category effect was found with the exception of a clear trend to perform better on verbs as compared to nouns. Phonemic Discrimination
His ability to discriminate, in a same\different judgment task, two syllables whose first phoneme was an occlusive or two words differing in the initial phoneme was normal. Lexical Decision Task
On both auditory and visual lexical decision tasks controlled for word frequency and part of speech, G.P. was quite accurate on verbs and function words, while his performance on nouns was at chance. On visual
600
SILVER1
FIG. 1. Patient G.P.: MRI scan showing involving the left temporal lobe.
ET AL.
a diffuse
cortical-subcortical
atrophy,
mainly
PHONOLOGICAL
presentation of the stimuli, presentation.
COMPREHENSION
601
the performances were better than on auditory
Lexical-Semantic Comprehension
Comprehension of lexical items (nouns) was dramatically impaired independently of the modalities of presentation of the stimuli: on classical matching-to-sample tasks his performances were not far from chance on both auditory and visual presentation of the lexical item. When semantic and phonological distracters were presented at the same time among the alternatives in a word matching task (Gainotti, Altagirone, & Ibba, 1975), G.P. showed the tendency to point more often to the phonological foil than to the semantic foil, in spite of his good performances on the phonemic discrimination task. Syntactic Comprehension
On multiple choice sentence comprehension tasks (Miceli et al., 1991), G.P. obtained a good score. He was in fact quite able to process syntactic and morphological aspects of the sentences; on this task, most errors were produced when the comprehension of lexical semantic components was crucial for sentence comprehension. Transcoding Tasks
Reading aloud, writing to dictation and repetition showed a certain amount of errors all compatible with a “superficial” transcoding. The patient was usually conscious of his inability to access the meaning of the words he had to read, write, or repeat, sometimes verbalizing that he could recognize the word but that he had no idea about its meaning. Visual-Pictorial Semantic Tasks Semantic knowledge about pictures was explored by means of tasks that did not require any verbal input or output. The performance obtained by G.P. was normal on tasks of categorization of pictures, including “Class Inclusion” (Gainotti, Carlomagno, Craca, & Silveri, 1986), and only the performance on “Class Intersection” (Gainotti et a1.,1986) was slightly impaired. Memory G.P. scored at normal level on a task of immediate and delayed recognition of meaningful pictures among semantic, visual, and unrelated distracters. Verbal span was five for digits and three for words. On a memory probe for words his performance was quite good. Rey’s Test (free recall of 15 words), as expected, could not be performed. The patient did not show any sign of constructional, limb, or oral
Syntax comprehension
Verb comprehension (1 verb-3 pictures)
Lexical comprehension (1 word-l semantically-l lated pictures)
phonologically-3
Lexical comprehenshion (1 word-3 semantically related pictures)
Visual
Lexical decision task Auditory
Naming
Language
unre-
MAIN
TABLE
1
Spoken Written Spoken Written
Spoken (Errors: Written (Errors:
EXAMINATION
word word stimulus stimulus
word 2 semantic; 6 phonemic; 5 unrelated) word 3 semantic; 3 phonemic; 5 unrelated)
Spoken word Written word
Words Non-words Words Non-words
Object Actions
DATA ON NEUROPSYCHOLOGICAL
62% 58% 82% 84%
45% 9120 15124 14/24 49160 36143
35%
40% 45%
60% 95% 72% 95%
32%
7120
8120 9120
24140 38/40 29140 38/40
o/20 21166
Correct
Absence 415 5 213
Verbal memory (recall) Digit span
Errors
Visual semantics
o/20 4/20 6/20
Categorization of pictures Class Inclusion (Gainotti et al., 1986)
Class Intersection (Gainotti et al., 1986)
l/2 19120 24135
Word span Non-word span Visual memory recognition of pictures Raven colored matrices
Forward Backward
Correct
Words Non-words Words Non-words Words Non-words
116/120 40/40 20/20 39145 13/18 20/46 6/10 78192 39/45
Memory
Reading
Writing
Phonemic discrimination On syllables On syllables On words Repetition
(Normal for education) (Slight impairment)
96% 100% 100% 87% 72% 43% 60% 85% 87%
i 8 !z LT F2 2
z F 8 ij $
604
SILVER1
ET AL.
apraxia; other non-verbal tasks such as drawing (copy and from memory) or recognition of gestures and pantomimes were performed without particular difficulties. Calculation was moderately impaired. Visual spatial analysis and perceptual skill were unimpaired. His performance on Raven Colored Matrices ‘47 were within the range of normal subjects matched for age and educational level (Table 1). EXPERIMENTAL INVESTIGATION Experiment 1 On the lexical-semantic comprehension tasks administered as part of the general neuropsychological examination, G.P. performed, as mentioned above, not far from chance level, thus showing a very severe lexical comprehension disorder. In order to explore if at least the more general aspects of the meaning of words could be accessed, we devised two wordpicture matching tasks (one word-three pictures) in which we compared the two following conditions: -lexical comprehension among semantically related items (e.g., three pictures:pear, apple, grapes; stimulus word: apple) (Task 1A); -lexical comprehension among semantically unrelated items (e.g., three pictures: bicycle, pen, glass; stimulus word: pen) (Task 1B). Each task comprised 40 items; the stimulus word was presented on both spoken and written form in two different sessions. Our hypothesis was that if some residual lexical semantic knowledge was available, the choice among semantically unrelated alternatives should be easier than the one restricted within a semantic domain, since in the former case, partial semantic knowledge, namely the knowledge of the superordinate category, would be sufficient to successfully perform the task. The comparison between the scores obtained on the two tasks, on both auditory and visual presentation of the stimulus word, failed to confirm the hypothesis. The performances obtained on Tasks A and B did not significantly differ from each other (Task 1A auditory modality vs. Task 1B auditory modality: 2 = .O, n.s.; Task 1A visual modality vs. Task 1B visual modality: x2 = .45, n.s.) (Table 2). This result suggests that even very general aspects of the meaning, in this case the superordinate class, had been lost or could not be accessed; the patient, in fact, was not facilitated by the condition in which (Task 1B) the mere identification of the superordinate of the stimulus word would have allowed the rejection of the semantically unrelated pictures. The good performance obtained by G.P. on the visual-pictorial tasks described in the general neuropsychological examination ruled out the possibility that the difficulties in performing Tasks 1A and 1B could be
PHONOLOGICAL
COMPREHENSION TABLE
EXPERIMENT
Task 1A: one word-three
1:
PICTURE-WORD
2 MATCHING
TASK
pictures (the target and two semantically related alternatives) Correct responses
Auditory modality (N = 40) Visual modality (N = 40) Task 1B: one word-three alternatives)
605
20 (50%) 21 (52.5%)
pictures (the target and two semantically unrelated Correct responses
Auditory modality (N = 40) Visual modality (N = 40)
20 (50%) 24 (60%)
due to agnosia for the pictures used in the two tasks or to some generalized semantic disruption concerning both the verbal and the visual-semantic knowledge. Experiment 2
Even if the results obtained in Experiment 1 seemed to show that no partial semantic knowledge about the superordinate class of the stimulus word was available to our patient, we could not rule out the possibility that some residual semantic knowledge regarding the superordinate or other aspects of the meaning could be culled by different experimental procedures. We therefore devised two tasks (Task 2A and Task 2B), in which other aspects of the lexical semantic knowledge could be directly explored by means of yes/no tasks. In Task 2A we used a picture as a target and we explored the knowledge that G.P. had of the corresponding lexical label and of its superordinate; in Task 2B the target was a word and we explored the knowledge of the superordinate and of an attribute of the corresponding object. In Task 2A, pictures were presented one-by-one to the patient and, for each picture the patient received in random order, four words were presented in the auditory modality: the correct lexical label of the picture; a contrast coordinate; the superordinate category; and a false superordinate (an example is reported on Table 3, top section). The patient was requested every time to decide if each word did or not match the picture. We expected “yes” responses on the first and on the third type of question, “no” responses on the second and on the fourth type of question. G.P. gave mainly “no” responses because of an
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SILVER1 ET AL. TABLE 3 EXPERIMENT 2
Task 2A: Lexical knowledge of the lexical label of a picture (is this picture a. . . ?; e.g., bee) (yes/no task) Correct responses (%) 1) Recognition of the correct lexical label (is this a bee?) 2) Rejection of a contrast coordinate (is this a butterfly?) 3) Recognition of the correct superordinate (is this an animal?) 4) Rejection of an unrelated item (is this a piece of furniture?)
(N = 50)
44.4%
(N = 45)
93.3%
(N = 49)
43%
(N = 46)
89%
Task 2B: Lexical knowledge of a written word (is this word . . . (yes/no task)
. ?; e.g., banana) Correct responses (%)
1) Recognition of the correct superordinate (is this item fruit?) 2) Rejection of a false superordinate (is this item furniture?) 3) Recognition of the correct attribute (is this item yellow?) 4) Rejection of a false attribute (is this item red?)
(N = 32)
37%
(N = 32)
68%
(N = 32)
15%
(N = 32)
43%
extremely conservative strategy. The performance was analyzed according to the “Signal Detection Theory” (Parks, 1966) and transformed into accuracy scores (McNichol, 1972), ranging from 50 (random performance) to 100 (maximum accuracy). The responses (Table 3, top section) were clearly beyond chance. G.P. in fact showed some ability to recognize the correct lexical label and the superordinate of the picture without any difference between the two performances (accuracy scores: 81 and 78, respectively). An analogous procedure was adopted in Task 2B. In this case the patient was presented with written words instead of pictures; for each written word he received in random order four words in auditory modality: the superordinate; a false superordinate; an attribute; a false attribute of each target (an example is given in Table 3, bottom section). The patient had to decide if the word spoken to him was or was not in relation with the written word. In this case we also expected “yes” responses on the first and on the third type of question and “no” responses on the second and on the fourth type of question. The performances obtained, transformed into accuracy scores according to the methodology reported above, were
PHONOLOGICAL
COMPREHENSION
607
lower than those in Task 2A (Table 3, bottom section); accuracy scores were in fact 68 on the superordinate and 60 on the attribute. The percentage of correct responses (both expected “yes” and expected “no” responses) was significantly higher in Task 2A than in Task 2B (Task 2A vs. Task 2B, x2 = 14.8, p < .OOl). How does one reconcile the differences between the performances obtained in the two conditions? Why did G.P. show some preserved lexical semantic ability when the target was a picture while he performed near the chance level when the target was a word? The relatively high level of accuracy reached on Task 2A with respect to Task 2B suggested that the patient received some “cue” by having a picture as a target. We thus hypothesized that G.P. was able to understand the meaning of the picture (we already demonstrated that G.P. did not have a problem in processing pictorial material) and sometimes he was able to covertly retrieve some feature of the phonological form of its lexical label. This phonological form could not be transcoded into a phonological output, such as requested to perform a naming task (G.P. was completely unable to name) but that preverbal code would facilitate a match with the phonological form of the stimulus word. The hypothesis of a “covert retrieval” of the name from picture, as in Bub et al.? (1988) patient, could be directly explored by a rhyming task in which a subject is requested to judge if a word spoken to him rhymes or not with the name of picture that he is unable to name. Because of his severe comprehension deficit, we did not succeeded in getting G.P. to understand the rhyming task. Thus, we devised a less difficult task that nevertheless could provide us some information on the plausibility of our hypothesis. Experiment 3 A series of colored pictures was given one-by-one to the patient; for each target picture he received in random order four spoken words corresponding respectively to a)the correct lexical label of the target; b)a word phonologically related to the target; c)a word semantically related to the target; and d)a word without phonological or semantic relations with the target. The task consisted in asking the patient if the word spoken to him was or was not the lexical label of the picture. The results are summarized in Table 4. As in other yes/no tasks G.P. showed a strong tendency to give “no” responses (observed “no” vs. expected “no”: x2 = 5.27; p = .02); in spite of his conservative strategy, he recognized 13/34 correct lexical labels. The number of “yes” responses given on the correct lexical label was significantly higher than the number of “yes” responses obtained on phonological, semantic, and unrelated items (Fisher’s exact test: a vs. b, p = .OOl; a vs. c and d, p. = .0003). It was interesting to note that in four cases he accepted as correct the phonological alternative even if
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SILVER1 ET AL. TABLE EXPERIMENT
3:
LEXICAL
KNOWLEDGE
4
OF THE LEXICAL
LABEL
OF A PICTURE
(is this picture a. . . ? e.g., dog) Yes/no task (34 expected “yes” responses; 102 expected “no” responses) Responses
Correct Lexical Item [cane (dog)] (N = 34) Lexical Item phonologically related to the target [pane (bread)] (N = 34) Lexical Item semantically related to the target [gatto (cat)] (N = 34) Lexical Item unrelated to the target [sole (sun)] (N = 34)
Yes
No
13 (38%)
21 (62%)
4 (12%)
30 (88%)
1 (3%)
33 (97%)
1 (3%)
33 (97%)
this tendency did not reach significance in respect to the “yes” responses given on the semantic and unrelated distracters (Fisher’s exact test: p = .15). This slight tendency to consider as correct the phonological associate rather than the semantic or the unrelated alternative can be interpreted on the basis of our hypothesis. This is so because the lexical label can often be “covertly” (pre-verbally) derived from the picture and utilized in a word-picture matching task, both to reject the semantically related foil and the unrelated distracters (that are in fact phonologically very different from the correct lexical label) as well as to select as correct not only the proper lexical label but also, albeit only occasionally, the phonologically related foils. The alternative interpretation of this tendency, which is that the patient sometimes confounds the correct with the phonologically related alternative, and which would therefore adumbrate a defective apprehension of the phonological structure of the stimulus word, is not tenable. In fact, G.P.‘s successful performance on phonemic discrimination tasks and on transcoding tasks would appear to rule out disorders at the phonological level. Also, the phonological errors that G.P. produced in the word-picture matching task in which alternatives semantically and phonologically related to the target were included (mentioned earlier in the general neuropsychological examination) could be due to this partial “covert” retrieval of the name from the stimulus picture. In this task as well, in fact, as in the above described experiment, we were reluctant to accept an explanation based on the poor phonological processing of the stimulus word. This word-picture match, however, had not been devised in order to explore this specific issue, and we could not therefore rule out the possibility that uncontrolled factors, such as word frequency (word frequency
PHONOLOGICAL
609
COMPREHENSION
TABLE 5 EXPERIMENT 4: PICTURE-WORD MATCHING One word-three picture (the target and one semantically related and one phonologically related picture) Type of error
Auditory modality (N = 22) Visual modality (N = 22)
Correct responses
Phonemic
Semantic
10 (45.4%)
7
5
10 (45.4%)
9
3
of the phonological foils higher than word frequency of the semantic foils), could have influenced the results. Hence, we designed Experiment 4 in order to exclude this possibility. Experiment
4
We administered a word-picture matching task in which each target picture was contrasted with both a semantic and a phonological distractor matched for word frequency and familiarity. The stimulus word was given in both spoken and in written form on two separate sessions of 22 items each. The performances are summerized in Table 5. The tendency to point more to the phonological than to the semantic distractor was confirmed on both the auditory (7 phonological vs. 5 semantic) and the visual (9 phonological vs. 3 semantic;) modalities. The total number of phonological errors produced in the two modalities was higher than the total number of semantic errors with a strong tendency toward significance (x2 = 3.6, p = .052)
Experiment 5 The last experiment was designed to obtain additional evidence that the choice of the phonological distractor in word-picture matching tasks is based on the ability to “covertly” retrieve the name from the picture stimulus, thus ultimately rejecting the possibility that such a tendency could be traced to a disrupted apprehension of the phonological structure of the stimulus word (Experiment 5). The experiment (Experiment 5) consisted of two word-picture matching tasks, where the stimulus words were given verbally. In Task 5A, the target had semantic and unrelated foils; in Task 5B the target had phonological and unrelated foils. If G.P. could retrieve some information about the name of the picture, we should expect to obtain on Task 5A a performance only slightly above chance (the information obtained about the name of the picture target has some possibility of being correctly matched
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SILVER1 ET AL. TABLE EXPERIMENT
Task 5A: One word-three alternative)
6
5: PICTURE-WORD
MATCHING
pictures (the target, one semantic and one unrelated Type of errors
Auditory modality first administration (N = 44) Task 5B: One word-three alternative)
Correct responses
Semantic
Unrelated
19 (43.2%)
13 (29%)
12 (27%)
pictures (the target, one phonologic and one unrelated Type of errors
Auditory modality first administration (N = 44)
Correct responses
Phonologic
Unrelated
28 (63.3%)
13 (29%)
3 (7%)
with the stimulus word) with no differences between semantic and unrelated errors. On the second task (5B), however, the patient should point more often to the correct and the phonological distractor than to the unrelated one. Note that we admit that the phonologically related distractor and the target could sometimes be confused because of their phonological similarity. We hypothesized that in a word-picture matching task, when the names of two pictures (the target and the phonologically related foils) were “similar,” the choice of the form-related foil had greater likelihood of occurrence. Our findings confirmed the expectancy: as shown in Table 6, only a nonsignificant (x2 = 1.031, p = 0.31) tendency to point more to the correct picture (43.2%) than to the semantic and unrelated foils was observed. On Task 5B, on the contrary, the distribution of the responses was significantly different from that expected by chance (x2 = 8.41, p = .004) since the great majority of choices consisted either of correct or of phonologically similar responses, whereas the number of unrelated responses was very low. It is interesting to note that the condition in which the target had a phonological foil (Task 5B) seems to “facilitate” the task rather than to increase the difficulties, as it might be expected if G.P. were unable to appreciate the phonological structure of the stimulus word in some covert or pre-verbal fashion. GENERAL DISCUSSION The most striking deficit in G.P. was his dramatic difficulty accessing semantic information through the lexical items, both in spoken or written
PHONOLOGICAL
COMPREHENSION
611
form. This deficit could not be attributed to alteration in perception or to decoding the words, since his performance in discrimination tasks and in transcoding ruled out a phonological impairment. The processing and the categorization of visual-pictorial stimuli was also quite good. Therefore, the possible role of visual agnosic factors or of amodal semantic disorders in tasks where lexical comprehension is assessed by means of word-picture matching could be excluded as well. In other words, G.P’s deficit was specifically lexical semantic in nature, comprising severe difficulties in the appreciation of more general aspects of lexical meaning, such as the superordinate. It was surprising to note that G.P. in word-picture matching showed a clear tendency to point to the phonological distractor (the distractor that shares phonological features with the target). This tendency could not be explained by an altered decoding of the stimulus word. Hence, the interpretation given here is that the phonological foils were chosen because of their phonological resemblance to the target. The crucial question is as follows: is it possible that, in a pointing task that requires a match between the lexical stimulus and the lexical label activated by the picture, our patient could rely exclusively on the phonological structure of the stimulus? According to Bub et al. (1988) this is plausible assuming that the phonological form of a word, whose meaning is not accessible, could be matched with a phonological label evoked from the picture. The possibility of evoking a correct phonological label from a picture despite being unable to name the picture has been demonstrated in two patients, S.P. (Marin, Saffran, & Schwartz, 1976) who was able to decide if the referents of pictures that he could not name rhymed or not and, similarly, in M.P. (Bub et al., 1988) who, although affected by severe naming deficit, could nevertheless decide if a word rhymed or not with a picture. Although less concise than a rhyming task, our Task 3 is also suggestive for this hypothesis. G.P.‘s performance was, in fact, clearly better than chance in the recognition of the correct lexical label of a given picture and showed in addition, the tendency to accept, as correct, the phonologically similar word. The results obtained from Experiment 5 further confirmed our hypothesis. The “covert” retrieval of the name from a stimulus picture can explain the facilitation obtained by G.P. on the task where the target was contrasted with a phonologically related foil and an unrelated foil, as opposed to the condition in which the target is contrasted with semantically related and unrelated foils. In summary, we think that the crucial condition that allows, in wordpicture matching, the observation of a residual “phonological” comprehension is the occurrence of some “covert label selection”, that is, a preserved ability to evoke some phonological information about the spoken label of a picture item, while at the same time being unable to successively convert that representation into a phonological output. The second condition reouired is a breakdown nf the lexirnl cmnnntir wn~-P-
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SILVER1 ET AL.
sentation, or an inability to access it. Consequently, the subject is only able to rely upon the above hypothesized mechanism, to reach some form of lexical comprehension. Both these conditions seem to be present in M.P. (Bub et al., 1988) and in G.P. The subjects are the only two who are demonstrated to preserve, in a word-picture matching task, some capacity to “understand” lexical items without relying upon semantics but only upon the phonological form of the stimulus word. To conclude, our hypothesis is that the phenomenon we call “residual phonological” comprehension is actually the consequence of a severe lexical semantic breakdown at the comprehension level, in the presence of some residual lexical semantic ability in the production process. REFERENCES Albert, M. L., Yamadory, A., Gardner, H., & Howes, D. 1973. Comprehension in alexia. Brain, 96, 317-328. Bub, D. N., Black, S., Hampson, E,. & Kertesz, A. 1988. Semantic encoding of pictures and words: Some neuropsychological Observations. Cognitive Neuropsychology, 5, 2766.
Deloche, G., Andreewsky, E., & Desi, M. 1981. Lexical meaning: A case report. Some striking phenomena, theoretical implications. Cortex, 17, 147-152. Gainotti, G., Caltagirone, C., & Ibba, A. 1975. Semantic and phonemic aspects of auditory language comprehension in aphasia. Linguistics, W/155, 15-29. Gainotti G., Carlomagno, S., Craca, A., & Silveri, M. C. 1986. Disorders of classificatory activity in aphasia. Brain and Language, 28, 181-195. Marin, 0. M., Saffran, E. M., & Schwartz, M. F. 1976. Dissociation of language in aphasia: Implications for normal function. In H. B. Steklis, S. R. Harnard, & J. Lancaster (Eds). , Origins and evolution of language and speech. New York: New York Academy of Sciences. McNichol, D. 1972. A primer of the Signal Detection Theory. Sydney: Australian Publishing. Miceli, G., Laudanna, A., & Burani, C. 1991. Batteria per l’analisi dei deficit afasici. Milano: Associazione per le ricerche neuropsicologiche. Parks, T. E. 1966. Signal Detectability Theory of recognition memory performance. Psychological
Warrington,
Review,
of Experimental
Warrington,
73, 44-58.
E. K. 1975. The selective impairment of semantic memory. Quarterly Psychology,
Journal
27, 635-657.
E. K., & Shallice, T. 1979. Semantic access dyslexia. Brain,
102, 43-63.
AND
LANGUAGE
43,
597-612 (1992)
Can Residual Lexical Knowledge Concern Word Form Rather Than Word Meaning? MARIA CATERINASILVERI, LAURA GIUSTOLISI,ANTONIO
DANIELE,
AND GUIDO GAINOTTI Institute
of Neurology,
Neuropsychology
Service,
Catholic
University,
Rome,
Italy
We described a patient with a dramatic deficit of both word comprehension and naming but with good preservation of visual pictorial semantics. On wordpicture matching, his performances were slightly better than expected based on the observed lexical semantic disorder; in addition, the patient, who maintained good preservation of his underlying phonology, showed a tendency to point to the picture phonologically related to the target. In order to interpret these data, we advanced the hypothesis that the patient, in spite of his virtually complete inability to name, would be able, in a word-picture matching task, to “covertly” (i.e., preverbally) retrieve the name from the picture and to use this name to attempt a match with the phonological form of the stimulus word. This mechanism, that we called “phonological” comprehension, would allow the identification of the correct target and would explain the choice of the phonologically related foil that was sometimes selected. 0 1~2 Academic PKSS, IIK.
INTRODUCTION Some cases are described of patients affected by severe lexical comprehension disorders who nevertheless are still able to perform tasks that presuppose at least some preserved residual knowledge about words. Warrington (1975) described three patients, all showing some degree of agnosia for words, that were able to give the superordinate response when attempting to define the words. Similarly, Deloche, Andreewski, & Desi (1981) described a patient who, although severely impaired in spoken word comprehension, performed better than chance in an “oddword-out” task in which the word, not belonging to the same class as other four words, had to be recognized, thereby showing some preserved knowledge of the superordinate category about those words. The patient reported by Albert, Yamadory, Gardner, & Howes (1973) was severely Reprint requests should be addressed to Maria Caterina Silveri, Institute of Neurology, Catholic University, Largo Agostino Gemelh 8, 00168 Rome, Italy. 597 0093-934X/92
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alexic but his semantic comprehension of the written word was demonstrated to be relatively preserved. A further example of residual lexical knowledge of written word was given by patient A.R. (Warrington & Shallice, 1979); although severely alexic, she preserved a surprising ability to perform categorization tasks on the words that she could not read; moreover her capacity in reading a word improved as a consequence of a semantic priming effect on that word. All these cases can be taken as evidence that the residual lexical knowledge is semantic in nature and concerns principally the more general aspects of the meaning, as the knowledge of the superordinate (Warrington, 1975; Bub, Black, Hampson, & Kertesz, 1988). This is in line with the observation that the lexical semantic breakdown of brain-damaged patients is not an “all or none” phenomenon but seems to involve firstly the more specific aspects of the meaning sparing the more general aspects of it (Warrington, 1975). Bub et al. (1988), however, described a patient, M.P., who does not completely fit this general interpretation. In this patient the residual lexical knowledge about words seemed to concern only the superordinate category; in spite of this, M.P. was to some extent able to perform a word-picture matching task in which two semantically related words (e.g., butterfly-grasshopper) had to be matched to a picture. Since the two words were members of the same category, the matching operation could not be performed only on the basis of the knowledge of their superordinate. The paradox was interpreted by suggesting that word-picture matching can be performed by checking the phonological form given by the examiner to some phonological label evoked from the picture without accessing the corresponding semantic information carried by the words. In support of this interpretation, the authors noted that M.P., although severely anemic, could judge correctly if a word rhymed or not with the name of a given picture. We describe a patient, G.P., whose main characteristic was a dramatic impairment of verbal semantics in contrast with good preservation of visual-pictorial semantics. By means of appropriate tasks we could ascertain that the patient had remarkable difficulties in accessing even the most general aspects of the meaning of the words. The existence, in a word-picture matching task, of some other form of word comprehension, in particular, the comprehension that is supposed to rely on the phonological form of the lexical items (Bub et al.,1988), was then assessed. CASE REPORT G.P., a 68-year-old right-handed man, was admitted to our neurological department on July 1988; he was educated until the fifth grade, but his actual educational level seemed to be higher than his formal one. He worked as a specialized worker in a farm and retired at age of 60. No
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history of previous illness had been reported, except for a mild bilateral deafness of mixed type. Since August 1985 he started to complain about progressive difficulties in naming objects and in comprehension of both spoken and written language. In the last year there was a notable worsening of his language disorders and the patient gave up reading newspapers and listening to television. Nevertheless, his behavioral effectiveness in performing customary daily activities was preserved (for instance, he was still able to drive his car). A contrast-enhanced CT scan performed on April 1986 showed a slight enlargement of the frontal horn of the left lateral ventricle. An EEG performed 1 year later showed a theta slowing without any side prevalence. On admission, the neurological examination was negative. A contrast-enhanced CT scan showed an enlargement of both the left lateral ventricle and the left sylvian fissure. MRI scan showed a diffuse cortical/subcortical atrophy, mainly involving the left hemisphere, especially the left temporal lobe (Fig. 1). NEUROPSYCHOLOGICAL Language
ASSESSMENT
Spontaneous Speech
Spontaneous speech was fluent; articulation, intonation and prosody were well preserved. The sentences produced were short but syntactically correct. In spite of severe anemic difficulties, his speech conveyed a substantial amount of information. Naming
Naming was markedly impaired on all modalities (visual, tactile, and from verbal description); the patient was generally able to give information (description of use, context, attribute) about many items that he could not name, showing that he had recognized them; he never produced semantic or phonemic paraphasias. No semantic category effect was found with the exception of a clear trend to perform better on verbs as compared to nouns. Phonemic Discrimination
His ability to discriminate, in a same\different judgment task, two syllables whose first phoneme was an occlusive or two words differing in the initial phoneme was normal. Lexical Decision Task
On both auditory and visual lexical decision tasks controlled for word frequency and part of speech, G.P. was quite accurate on verbs and function words, while his performance on nouns was at chance. On visual
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FIG. 1. Patient G.P.: MRI scan showing involving the left temporal lobe.
ET AL.
a diffuse
cortical-subcortical
atrophy,
mainly
PHONOLOGICAL
presentation of the stimuli, presentation.
COMPREHENSION
601
the performances were better than on auditory
Lexical-Semantic Comprehension
Comprehension of lexical items (nouns) was dramatically impaired independently of the modalities of presentation of the stimuli: on classical matching-to-sample tasks his performances were not far from chance on both auditory and visual presentation of the lexical item. When semantic and phonological distracters were presented at the same time among the alternatives in a word matching task (Gainotti, Altagirone, & Ibba, 1975), G.P. showed the tendency to point more often to the phonological foil than to the semantic foil, in spite of his good performances on the phonemic discrimination task. Syntactic Comprehension
On multiple choice sentence comprehension tasks (Miceli et al., 1991), G.P. obtained a good score. He was in fact quite able to process syntactic and morphological aspects of the sentences; on this task, most errors were produced when the comprehension of lexical semantic components was crucial for sentence comprehension. Transcoding Tasks
Reading aloud, writing to dictation and repetition showed a certain amount of errors all compatible with a “superficial” transcoding. The patient was usually conscious of his inability to access the meaning of the words he had to read, write, or repeat, sometimes verbalizing that he could recognize the word but that he had no idea about its meaning. Visual-Pictorial Semantic Tasks Semantic knowledge about pictures was explored by means of tasks that did not require any verbal input or output. The performance obtained by G.P. was normal on tasks of categorization of pictures, including “Class Inclusion” (Gainotti, Carlomagno, Craca, & Silveri, 1986), and only the performance on “Class Intersection” (Gainotti et a1.,1986) was slightly impaired. Memory G.P. scored at normal level on a task of immediate and delayed recognition of meaningful pictures among semantic, visual, and unrelated distracters. Verbal span was five for digits and three for words. On a memory probe for words his performance was quite good. Rey’s Test (free recall of 15 words), as expected, could not be performed. The patient did not show any sign of constructional, limb, or oral
Syntax comprehension
Verb comprehension (1 verb-3 pictures)
Lexical comprehension (1 word-l semantically-l lated pictures)
phonologically-3
Lexical comprehenshion (1 word-3 semantically related pictures)
Visual
Lexical decision task Auditory
Naming
Language
unre-
MAIN
TABLE
1
Spoken Written Spoken Written
Spoken (Errors: Written (Errors:
EXAMINATION
word word stimulus stimulus
word 2 semantic; 6 phonemic; 5 unrelated) word 3 semantic; 3 phonemic; 5 unrelated)
Spoken word Written word
Words Non-words Words Non-words
Object Actions
DATA ON NEUROPSYCHOLOGICAL
62% 58% 82% 84%
45% 9120 15124 14/24 49160 36143
35%
40% 45%
60% 95% 72% 95%
32%
7120
8120 9120
24140 38/40 29140 38/40
o/20 21166
Correct
Absence 415 5 213
Verbal memory (recall) Digit span
Errors
Visual semantics
o/20 4/20 6/20
Categorization of pictures Class Inclusion (Gainotti et al., 1986)
Class Intersection (Gainotti et al., 1986)
l/2 19120 24135
Word span Non-word span Visual memory recognition of pictures Raven colored matrices
Forward Backward
Correct
Words Non-words Words Non-words Words Non-words
116/120 40/40 20/20 39145 13/18 20/46 6/10 78192 39/45
Memory
Reading
Writing
Phonemic discrimination On syllables On syllables On words Repetition
(Normal for education) (Slight impairment)
96% 100% 100% 87% 72% 43% 60% 85% 87%
i 8 !z LT F2 2
z F 8 ij $
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ET AL.
apraxia; other non-verbal tasks such as drawing (copy and from memory) or recognition of gestures and pantomimes were performed without particular difficulties. Calculation was moderately impaired. Visual spatial analysis and perceptual skill were unimpaired. His performance on Raven Colored Matrices ‘47 were within the range of normal subjects matched for age and educational level (Table 1). EXPERIMENTAL INVESTIGATION Experiment 1 On the lexical-semantic comprehension tasks administered as part of the general neuropsychological examination, G.P. performed, as mentioned above, not far from chance level, thus showing a very severe lexical comprehension disorder. In order to explore if at least the more general aspects of the meaning of words could be accessed, we devised two wordpicture matching tasks (one word-three pictures) in which we compared the two following conditions: -lexical comprehension among semantically related items (e.g., three pictures:pear, apple, grapes; stimulus word: apple) (Task 1A); -lexical comprehension among semantically unrelated items (e.g., three pictures: bicycle, pen, glass; stimulus word: pen) (Task 1B). Each task comprised 40 items; the stimulus word was presented on both spoken and written form in two different sessions. Our hypothesis was that if some residual lexical semantic knowledge was available, the choice among semantically unrelated alternatives should be easier than the one restricted within a semantic domain, since in the former case, partial semantic knowledge, namely the knowledge of the superordinate category, would be sufficient to successfully perform the task. The comparison between the scores obtained on the two tasks, on both auditory and visual presentation of the stimulus word, failed to confirm the hypothesis. The performances obtained on Tasks A and B did not significantly differ from each other (Task 1A auditory modality vs. Task 1B auditory modality: 2 = .O, n.s.; Task 1A visual modality vs. Task 1B visual modality: x2 = .45, n.s.) (Table 2). This result suggests that even very general aspects of the meaning, in this case the superordinate class, had been lost or could not be accessed; the patient, in fact, was not facilitated by the condition in which (Task 1B) the mere identification of the superordinate of the stimulus word would have allowed the rejection of the semantically unrelated pictures. The good performance obtained by G.P. on the visual-pictorial tasks described in the general neuropsychological examination ruled out the possibility that the difficulties in performing Tasks 1A and 1B could be
PHONOLOGICAL
COMPREHENSION TABLE
EXPERIMENT
Task 1A: one word-three
1:
PICTURE-WORD
2 MATCHING
TASK
pictures (the target and two semantically related alternatives) Correct responses
Auditory modality (N = 40) Visual modality (N = 40) Task 1B: one word-three alternatives)
605
20 (50%) 21 (52.5%)
pictures (the target and two semantically unrelated Correct responses
Auditory modality (N = 40) Visual modality (N = 40)
20 (50%) 24 (60%)
due to agnosia for the pictures used in the two tasks or to some generalized semantic disruption concerning both the verbal and the visual-semantic knowledge. Experiment 2
Even if the results obtained in Experiment 1 seemed to show that no partial semantic knowledge about the superordinate class of the stimulus word was available to our patient, we could not rule out the possibility that some residual semantic knowledge regarding the superordinate or other aspects of the meaning could be culled by different experimental procedures. We therefore devised two tasks (Task 2A and Task 2B), in which other aspects of the lexical semantic knowledge could be directly explored by means of yes/no tasks. In Task 2A we used a picture as a target and we explored the knowledge that G.P. had of the corresponding lexical label and of its superordinate; in Task 2B the target was a word and we explored the knowledge of the superordinate and of an attribute of the corresponding object. In Task 2A, pictures were presented one-by-one to the patient and, for each picture the patient received in random order, four words were presented in the auditory modality: the correct lexical label of the picture; a contrast coordinate; the superordinate category; and a false superordinate (an example is reported on Table 3, top section). The patient was requested every time to decide if each word did or not match the picture. We expected “yes” responses on the first and on the third type of question, “no” responses on the second and on the fourth type of question. G.P. gave mainly “no” responses because of an
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Task 2A: Lexical knowledge of the lexical label of a picture (is this picture a. . . ?; e.g., bee) (yes/no task) Correct responses (%) 1) Recognition of the correct lexical label (is this a bee?) 2) Rejection of a contrast coordinate (is this a butterfly?) 3) Recognition of the correct superordinate (is this an animal?) 4) Rejection of an unrelated item (is this a piece of furniture?)
(N = 50)
44.4%
(N = 45)
93.3%
(N = 49)
43%
(N = 46)
89%
Task 2B: Lexical knowledge of a written word (is this word . . . (yes/no task)
. ?; e.g., banana) Correct responses (%)
1) Recognition of the correct superordinate (is this item fruit?) 2) Rejection of a false superordinate (is this item furniture?) 3) Recognition of the correct attribute (is this item yellow?) 4) Rejection of a false attribute (is this item red?)
(N = 32)
37%
(N = 32)
68%
(N = 32)
15%
(N = 32)
43%
extremely conservative strategy. The performance was analyzed according to the “Signal Detection Theory” (Parks, 1966) and transformed into accuracy scores (McNichol, 1972), ranging from 50 (random performance) to 100 (maximum accuracy). The responses (Table 3, top section) were clearly beyond chance. G.P. in fact showed some ability to recognize the correct lexical label and the superordinate of the picture without any difference between the two performances (accuracy scores: 81 and 78, respectively). An analogous procedure was adopted in Task 2B. In this case the patient was presented with written words instead of pictures; for each written word he received in random order four words in auditory modality: the superordinate; a false superordinate; an attribute; a false attribute of each target (an example is given in Table 3, bottom section). The patient had to decide if the word spoken to him was or was not in relation with the written word. In this case we also expected “yes” responses on the first and on the third type of question and “no” responses on the second and on the fourth type of question. The performances obtained, transformed into accuracy scores according to the methodology reported above, were
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COMPREHENSION
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lower than those in Task 2A (Table 3, bottom section); accuracy scores were in fact 68 on the superordinate and 60 on the attribute. The percentage of correct responses (both expected “yes” and expected “no” responses) was significantly higher in Task 2A than in Task 2B (Task 2A vs. Task 2B, x2 = 14.8, p < .OOl). How does one reconcile the differences between the performances obtained in the two conditions? Why did G.P. show some preserved lexical semantic ability when the target was a picture while he performed near the chance level when the target was a word? The relatively high level of accuracy reached on Task 2A with respect to Task 2B suggested that the patient received some “cue” by having a picture as a target. We thus hypothesized that G.P. was able to understand the meaning of the picture (we already demonstrated that G.P. did not have a problem in processing pictorial material) and sometimes he was able to covertly retrieve some feature of the phonological form of its lexical label. This phonological form could not be transcoded into a phonological output, such as requested to perform a naming task (G.P. was completely unable to name) but that preverbal code would facilitate a match with the phonological form of the stimulus word. The hypothesis of a “covert retrieval” of the name from picture, as in Bub et al.? (1988) patient, could be directly explored by a rhyming task in which a subject is requested to judge if a word spoken to him rhymes or not with the name of picture that he is unable to name. Because of his severe comprehension deficit, we did not succeeded in getting G.P. to understand the rhyming task. Thus, we devised a less difficult task that nevertheless could provide us some information on the plausibility of our hypothesis. Experiment 3 A series of colored pictures was given one-by-one to the patient; for each target picture he received in random order four spoken words corresponding respectively to a)the correct lexical label of the target; b)a word phonologically related to the target; c)a word semantically related to the target; and d)a word without phonological or semantic relations with the target. The task consisted in asking the patient if the word spoken to him was or was not the lexical label of the picture. The results are summarized in Table 4. As in other yes/no tasks G.P. showed a strong tendency to give “no” responses (observed “no” vs. expected “no”: x2 = 5.27; p = .02); in spite of his conservative strategy, he recognized 13/34 correct lexical labels. The number of “yes” responses given on the correct lexical label was significantly higher than the number of “yes” responses obtained on phonological, semantic, and unrelated items (Fisher’s exact test: a vs. b, p = .OOl; a vs. c and d, p. = .0003). It was interesting to note that in four cases he accepted as correct the phonological alternative even if
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SILVER1 ET AL. TABLE EXPERIMENT
3:
LEXICAL
KNOWLEDGE
4
OF THE LEXICAL
LABEL
OF A PICTURE
(is this picture a. . . ? e.g., dog) Yes/no task (34 expected “yes” responses; 102 expected “no” responses) Responses
Correct Lexical Item [cane (dog)] (N = 34) Lexical Item phonologically related to the target [pane (bread)] (N = 34) Lexical Item semantically related to the target [gatto (cat)] (N = 34) Lexical Item unrelated to the target [sole (sun)] (N = 34)
Yes
No
13 (38%)
21 (62%)
4 (12%)
30 (88%)
1 (3%)
33 (97%)
1 (3%)
33 (97%)
this tendency did not reach significance in respect to the “yes” responses given on the semantic and unrelated distracters (Fisher’s exact test: p = .15). This slight tendency to consider as correct the phonological associate rather than the semantic or the unrelated alternative can be interpreted on the basis of our hypothesis. This is so because the lexical label can often be “covertly” (pre-verbally) derived from the picture and utilized in a word-picture matching task, both to reject the semantically related foil and the unrelated distracters (that are in fact phonologically very different from the correct lexical label) as well as to select as correct not only the proper lexical label but also, albeit only occasionally, the phonologically related foils. The alternative interpretation of this tendency, which is that the patient sometimes confounds the correct with the phonologically related alternative, and which would therefore adumbrate a defective apprehension of the phonological structure of the stimulus word, is not tenable. In fact, G.P.‘s successful performance on phonemic discrimination tasks and on transcoding tasks would appear to rule out disorders at the phonological level. Also, the phonological errors that G.P. produced in the word-picture matching task in which alternatives semantically and phonologically related to the target were included (mentioned earlier in the general neuropsychological examination) could be due to this partial “covert” retrieval of the name from the stimulus picture. In this task as well, in fact, as in the above described experiment, we were reluctant to accept an explanation based on the poor phonological processing of the stimulus word. This word-picture match, however, had not been devised in order to explore this specific issue, and we could not therefore rule out the possibility that uncontrolled factors, such as word frequency (word frequency
PHONOLOGICAL
609
COMPREHENSION
TABLE 5 EXPERIMENT 4: PICTURE-WORD MATCHING One word-three picture (the target and one semantically related and one phonologically related picture) Type of error
Auditory modality (N = 22) Visual modality (N = 22)
Correct responses
Phonemic
Semantic
10 (45.4%)
7
5
10 (45.4%)
9
3
of the phonological foils higher than word frequency of the semantic foils), could have influenced the results. Hence, we designed Experiment 4 in order to exclude this possibility. Experiment
4
We administered a word-picture matching task in which each target picture was contrasted with both a semantic and a phonological distractor matched for word frequency and familiarity. The stimulus word was given in both spoken and in written form on two separate sessions of 22 items each. The performances are summerized in Table 5. The tendency to point more to the phonological than to the semantic distractor was confirmed on both the auditory (7 phonological vs. 5 semantic) and the visual (9 phonological vs. 3 semantic;) modalities. The total number of phonological errors produced in the two modalities was higher than the total number of semantic errors with a strong tendency toward significance (x2 = 3.6, p = .052)
Experiment 5 The last experiment was designed to obtain additional evidence that the choice of the phonological distractor in word-picture matching tasks is based on the ability to “covertly” retrieve the name from the picture stimulus, thus ultimately rejecting the possibility that such a tendency could be traced to a disrupted apprehension of the phonological structure of the stimulus word (Experiment 5). The experiment (Experiment 5) consisted of two word-picture matching tasks, where the stimulus words were given verbally. In Task 5A, the target had semantic and unrelated foils; in Task 5B the target had phonological and unrelated foils. If G.P. could retrieve some information about the name of the picture, we should expect to obtain on Task 5A a performance only slightly above chance (the information obtained about the name of the picture target has some possibility of being correctly matched
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SILVER1 ET AL. TABLE EXPERIMENT
Task 5A: One word-three alternative)
6
5: PICTURE-WORD
MATCHING
pictures (the target, one semantic and one unrelated Type of errors
Auditory modality first administration (N = 44) Task 5B: One word-three alternative)
Correct responses
Semantic
Unrelated
19 (43.2%)
13 (29%)
12 (27%)
pictures (the target, one phonologic and one unrelated Type of errors
Auditory modality first administration (N = 44)
Correct responses
Phonologic
Unrelated
28 (63.3%)
13 (29%)
3 (7%)
with the stimulus word) with no differences between semantic and unrelated errors. On the second task (5B), however, the patient should point more often to the correct and the phonological distractor than to the unrelated one. Note that we admit that the phonologically related distractor and the target could sometimes be confused because of their phonological similarity. We hypothesized that in a word-picture matching task, when the names of two pictures (the target and the phonologically related foils) were “similar,” the choice of the form-related foil had greater likelihood of occurrence. Our findings confirmed the expectancy: as shown in Table 6, only a nonsignificant (x2 = 1.031, p = 0.31) tendency to point more to the correct picture (43.2%) than to the semantic and unrelated foils was observed. On Task 5B, on the contrary, the distribution of the responses was significantly different from that expected by chance (x2 = 8.41, p = .004) since the great majority of choices consisted either of correct or of phonologically similar responses, whereas the number of unrelated responses was very low. It is interesting to note that the condition in which the target had a phonological foil (Task 5B) seems to “facilitate” the task rather than to increase the difficulties, as it might be expected if G.P. were unable to appreciate the phonological structure of the stimulus word in some covert or pre-verbal fashion. GENERAL DISCUSSION The most striking deficit in G.P. was his dramatic difficulty accessing semantic information through the lexical items, both in spoken or written
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COMPREHENSION
611
form. This deficit could not be attributed to alteration in perception or to decoding the words, since his performance in discrimination tasks and in transcoding ruled out a phonological impairment. The processing and the categorization of visual-pictorial stimuli was also quite good. Therefore, the possible role of visual agnosic factors or of amodal semantic disorders in tasks where lexical comprehension is assessed by means of word-picture matching could be excluded as well. In other words, G.P’s deficit was specifically lexical semantic in nature, comprising severe difficulties in the appreciation of more general aspects of lexical meaning, such as the superordinate. It was surprising to note that G.P. in word-picture matching showed a clear tendency to point to the phonological distractor (the distractor that shares phonological features with the target). This tendency could not be explained by an altered decoding of the stimulus word. Hence, the interpretation given here is that the phonological foils were chosen because of their phonological resemblance to the target. The crucial question is as follows: is it possible that, in a pointing task that requires a match between the lexical stimulus and the lexical label activated by the picture, our patient could rely exclusively on the phonological structure of the stimulus? According to Bub et al. (1988) this is plausible assuming that the phonological form of a word, whose meaning is not accessible, could be matched with a phonological label evoked from the picture. The possibility of evoking a correct phonological label from a picture despite being unable to name the picture has been demonstrated in two patients, S.P. (Marin, Saffran, & Schwartz, 1976) who was able to decide if the referents of pictures that he could not name rhymed or not and, similarly, in M.P. (Bub et al., 1988) who, although affected by severe naming deficit, could nevertheless decide if a word rhymed or not with a picture. Although less concise than a rhyming task, our Task 3 is also suggestive for this hypothesis. G.P.‘s performance was, in fact, clearly better than chance in the recognition of the correct lexical label of a given picture and showed in addition, the tendency to accept, as correct, the phonologically similar word. The results obtained from Experiment 5 further confirmed our hypothesis. The “covert” retrieval of the name from a stimulus picture can explain the facilitation obtained by G.P. on the task where the target was contrasted with a phonologically related foil and an unrelated foil, as opposed to the condition in which the target is contrasted with semantically related and unrelated foils. In summary, we think that the crucial condition that allows, in wordpicture matching, the observation of a residual “phonological” comprehension is the occurrence of some “covert label selection”, that is, a preserved ability to evoke some phonological information about the spoken label of a picture item, while at the same time being unable to successively convert that representation into a phonological output. The second condition reouired is a breakdown nf the lexirnl cmnnntir wn~-P-
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sentation, or an inability to access it. Consequently, the subject is only able to rely upon the above hypothesized mechanism, to reach some form of lexical comprehension. Both these conditions seem to be present in M.P. (Bub et al., 1988) and in G.P. The subjects are the only two who are demonstrated to preserve, in a word-picture matching task, some capacity to “understand” lexical items without relying upon semantics but only upon the phonological form of the stimulus word. To conclude, our hypothesis is that the phenomenon we call “residual phonological” comprehension is actually the consequence of a severe lexical semantic breakdown at the comprehension level, in the presence of some residual lexical semantic ability in the production process. REFERENCES Albert, M. L., Yamadory, A., Gardner, H., & Howes, D. 1973. Comprehension in alexia. Brain, 96, 317-328. Bub, D. N., Black, S., Hampson, E,. & Kertesz, A. 1988. Semantic encoding of pictures and words: Some neuropsychological Observations. Cognitive Neuropsychology, 5, 2766.
Deloche, G., Andreewsky, E., & Desi, M. 1981. Lexical meaning: A case report. Some striking phenomena, theoretical implications. Cortex, 17, 147-152. Gainotti, G., Caltagirone, C., & Ibba, A. 1975. Semantic and phonemic aspects of auditory language comprehension in aphasia. Linguistics, W/155, 15-29. Gainotti G., Carlomagno, S., Craca, A., & Silveri, M. C. 1986. Disorders of classificatory activity in aphasia. Brain and Language, 28, 181-195. Marin, 0. M., Saffran, E. M., & Schwartz, M. F. 1976. Dissociation of language in aphasia: Implications for normal function. In H. B. Steklis, S. R. Harnard, & J. Lancaster (Eds). , Origins and evolution of language and speech. New York: New York Academy of Sciences. McNichol, D. 1972. A primer of the Signal Detection Theory. Sydney: Australian Publishing. Miceli, G., Laudanna, A., & Burani, C. 1991. Batteria per l’analisi dei deficit afasici. Milano: Associazione per le ricerche neuropsicologiche. Parks, T. E. 1966. Signal Detectability Theory of recognition memory performance. Psychological
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