Conceptual combination in schizophrenia: Contrasting property and relational interpretations

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Journal of Neurolinguistics 20 (2007) 92–110 www.elsevier.com/locate/jneuroling

Conceptual combination in schizophrenia: Contrasting property and relational interpretations Debra Titonea,, Maya Libbena, Meg Nimanb, Larissa Ranbomb, Deborah L. Levyb a

Department of Psychology, McGill University, Stewart Biology Building, 1205 Dr. Penfield Ave., Montreal, QC, Canada H3A 1B1 b Psychology Research Laboratory, McLean Hospital, Harvard Medical School, Boston, MA, USA Received 5 June 2006; accepted 8 June 2006

Abstract This study employed a conceptual combination task based on Estes and Glucksberg [(2000). Interactive property attribution in concept combination. Memory & Cognition, 28(1), 28–34] to address the question of whether semantic processing abnormalities in schizophrenia arise from deficits in semantic storage or access, or the controlled use of semantic memory representations. High thought disorder schizophrenia patients (n ¼ 25), low thought disorder schizophrenia patients (n ¼ 22), and controls (n ¼ 25) read and interpreted noun–noun combinations that varied with respect to whether the modifier noun had a salient semantic feature that could be mapped to a relevant dimension of a head noun. The percentages of property attributions, relational interpretations, and ‘‘other’’ interpretations were determined for each combination type. Subjective difficulty ratings were also collected for each response. Neither high nor low thought disorder patients differed from controls in the production of property interpretations. High thought disorder patients were significantly less likely to generate relational interpretations and significantly more likely to generate ‘‘other’’ interpretations. Subjective difficulty ratings were low for all groups, suggesting that differences in the ease of generating interpretations does not account for the results. The finding of intact property interpretations suggests that the integrity and initial access of semantic memory is spared in schizophrenia. In contrast, the reduced production of relational interpretations and increased production of ‘‘other’’ interpretations in schizophrenia suggests a

Corresponding author. Tel.: +1 514 398 1778; fax: +1 514 398 4896.

E-mail address: [email protected] (D. Titone). URL: http://www.mcgill.ca/coglab/. 0911-6044/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.jneuroling.2006.06.002

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compromised ability to engage in the controlled processing operations necessary to make flexible use of semantic material. r 2006 Elsevier Ltd. All rights reserved. Keywords: Schizophrenia; Semantics; Language; Conceptual combination

Many neurocognitive systems have been implicated in schizophrenia (SZ), but disturbances in cognition and semantic processing are predominant features of the disorder (Bleuler, 1911/1950; Kraepelin, 1919/1971). Consider, for example, the response of an individual diagnosed with SZ when asked to state what card VIII of the Rorschach looks like: ‘‘Oh man, this is out of sight. This is like a couple of y panther cats who are pink in color, who arey engaging upony some kind ofy kinghoody of a great ship, a great bar–, a greaty fishy who rules the sea, and theny he’s sailing, he’s sailing, and yet he usesy his great umy panthersy to show forth the fact thaty he comes in peace, and that he, hey he is, he isy and he’s issuing forthy a stalwarty peaceability that... that no one can put asunder in any way, shape or form, an’ he’s just happy an’ free, an’ he’s kinday got it all together, an’ he knows it.’’ In the Thought Disorder Index (TDI) scoring scheme (Johnston & Holzman, 1979; Solovay et al., 1986), this response includes several instances of idiosyncratic use of language (in bold) and the entire response would be scored as a confabulation (finding relationships between unrelated percepts and embellishing them in an unrealistic way) (Shenton, Solovay, & Holzman, 1987; Solovay, Shenton, & Holzman, 1987; Spohn et al., 1986). Tangentiality, derailment, poverty of amount and content of speech, illogicality, and incoherence also characterize aspects of schizophrenic thought disorder (Andreasen, 1979; Barch & Berenbaum, 1996; Docherty, Cohen, Nienow, Dinzeo, & Dangelmaier, 2003; Harrow, Marengo, & McDonald, 1986). Thought disorder in SZ has been linked to impaired structure and function of the superior temporal lobe (Kircher et al., 2001; Shenton et al., 1992), and to impaired executive functions such as context processing and interference resolution (Kerns & Berenbaum, 2002, 2003). Although thought disorder is not expressed exclusively through language (for example, certain behaviors may be based on delusional ideas), spoken or written language is the most common medium for conveying disturbances in thinking. In our view, the thinking anomalies associated with psychotic conditions are not, fundamentally, speech or language disorders (for a more detailed discussion see Holzman, Levy, & Johnston, 2005; Holzman, Shenton, & Solovay, 1986; Makowski et al., 1997). Rather, when language is used in an idiosyncratic way, it represents the outcome of a deviant thought process. The recognizable meaning of the word or phrase does not fit the context and therefore obscures the meaning intended by the speaker, for example—‘‘a tree head kind of person’’, ‘‘posterior pronunciations’’, ‘‘adhesive adjunctive extensions’’, ‘‘a non-verbal misrepresentation of an unformulated thought.’’ Deviant verbalizations are a predominant characteristic of the thought disorder associated with SZ, and they are present in patients independent of severity of clinical state, indicating that they are a trait characteristic of schizophrenic thought disorder (Johnston & Holzman, 1979; Solovay, Shenton, & Holzman, 1987; Spohn et al., 1986). In addition to thinking disturbances expressed in language production, SZ patients also show semantic processing abnormalities in language comprehension (Bagner, Melinder, & Barch, 2003; Condray, Steinhauer, van Kammen, & Kasparek, 2002; Kostova, Passerieux,

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Laurent, & Hardy-Bayle, 2003; Ruchsow, Trippel, Groen, Spitzer, & Kiefer, 2003; Salisbury, Shenton, Nestor, & McCarley, 2002; Sitnikova, Salisbury, Kuperberg, & Holcomb, 2002; Titone, Holzman, & Levy, 2002; Titone & Levy, 2004; Titone, Levy, & Holzman, 2000). Some investigators have attributed these abnormalities to disorganized or damaged semantic memory representations or to interference with initial access to these representations (Aloia et al., 1998; Aloia, Gourovitch, Weinberger, & Goldberg, 1996; Chen Wilkins, & McKenna, 1994; Elvevag et al., 2002; Goldberg et al., 1998; McKay et al., 1996). In this conceptualization, semantic memory representations and initial access processes tend to be grouped as a general capacity for storing semantic material and gaining initial access to this material in an automatic or reflexive way. Other findings, however, suggest that semantic memory representations and initial access to them are intact in SZ, but the flexible use of semantic memory through more deliberate controlled processing operations is deficient (Chenery, Copland, McGrath, & Savage, 2004; Condray, Siegle, Cohen, van Kammen, & Steinhauer, 2003; Kerns & Berenbaum, 2002; Nestor et al., 2001; Sitnikova et al., 2002; Titone et al., 2002, 2000; Titone & Levy, 2004). Consistent with the latter view, work from our group has found that SZ patients are impaired only when the specific language comprehension situation is ambiguous and the flexible use of semantic memory requires inhibiting contextually irrelevant material. In contrast, when the language comprehension context requires only automatic retrieval of semantic memory (or lexical) representations, semantic processing is normal (Titone et al., 2000, 2002; Titone & Levy, 2004). The present study extends our work by examining patient performance on a task that involves the comprehension of ambiguous multi-word sequences: novel conceptual combinations (e.g., ‘‘zebra bag’’). Novel conceptual combinations are ubiquitous in language, and they normally elicit consistent and plausible interpretations, despite the fact that they afford several plausible (and implausible) interpretations. How this process is normally accomplished has been widely studied (Bock & Clifton Jr., 2000; Costello & Keane, 2001; Estes & Glucksberg, 2000; Gagne, 2002a; Glucksberg & Estes, 2000; Medin & Rips, 2005; Medin & Shoben, 1988; Murphy, 2002; Wisniewski & Murphy, 2005) and can increase our understanding of the nature of semantic deficits observed in individuals diagnosed with SZ. Individuals who are fluent in a language usually generate one of two types of interpretations when faced with novel conceptual combinations (Medin & Rips, 2005; Murphy, 2002). The simplest type of interpretation is a property attribution, in which some conceptual feature of the modifier noun is automatically activated during lexical retrieval and then is attributed to the head noun. In the combination ‘‘zebra bag’’, for example, a salient conceptual feature of the modifier noun, zebra, is having stripes. This feature is then attributed to the head noun bag, resulting in the interpretation, a striped bag. Another common type of interpretation is a relational interpretation. Here, the modifier noun is linked to a thematic or functional role of the head noun, for example, the notion that a bag is normally carried by an animate agent. For example, zebra bag is interpreted as a bag that a zebra carries, most likely on its back. Other kinds of interpretations of conceptual combinations occur: hybridization (e.g., a robin canary is a cross between a robin and a canary) and construal (e.g., a plastic truck is a toy). In the present study we focus on property and relational interpretations, because they are the most frequent and best understood kinds of interpretations generated for novel noun–noun combinations.

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The factors that lead comprehenders to preferentially generate property or relational interpretations have been studied by several groups. Wisniewski and colleagues (Wisniewski, 1997, 1998, 2000) found that noun–noun combinations, in which modifier nouns are similar to head nouns, lead to property interpretations more frequently than to relation interpretations (e.g., tiger panther as a panther with a black and orange pattern). This ‘‘similarity effect’’ may arise because it is easier to identify differences between two similar concepts, and thus to discover the specific properties to be mapped (although see Gagne´, 2000 for an alternative explanation of this effect). These findings were later refined to show that property attributions are more likely, and relational interpretations less likely, under two conditions: (1) when a modifier noun has a salient feature that can be attributed to a head noun, and (2) when a head noun has a relevant dimension to receive that property mapping (Estes & Glucksberg, 2000). For example, the modifier noun of the combination ‘‘zebra bag’’ has a salient feature (e.g., black and white stripes) and the head noun has a relevant dimension for accepting the mapping from that feature (e.g., an important dimension of bags is their appearance). Combinations of this type were termed high–high (HH), because they have a high salient feature as well as a highly relevant dimension. In the combination ‘‘zebra trap’’, in contrast, the modifier noun has the same salient feature, but the head noun does not have a relevant dimension for that salient feature. Such combinations are termed high–low (HL). In the combination ‘‘donkey trap’’, the modifier noun does not have a clearly salient feature that is relevant to the head noun and the head noun does not have a relevant dimension with respect to the modifier noun. Such combinations are termed low–low (LL). Estes and Glucksberg (2000) found that 79% of university students generated property attribution interpretations for HH combinations such as zebra bag, whereas 23% and 16% of students produced property interpretations for zebra trap (HL) and donkey trap (LH), respectively. The HL and LH combinations were presumed to be relational interpretations, but only property interpretations were actually scored. Thus, non-property interpretations may have been composed of relational interpretations or ‘‘other’’ types. The Estes and Glucksberg (2000) study is relevant to this study because it shows that there is a clear normative pattern for conceptual combinations comprised of equally dissimilar nouns that bias interpretations toward or away from property interpretations. The biasing effect of property and relational interpretations may help to understand the nature of semantic dysfunction in SZ. In property interpretations of the HH variety, the modifier noun possesses a highly salient feature that can be readily mapped onto a highly relevant dimension of the head noun. The mapping process places little demand on post-retrieval selection processes because the most readily activated features of the two nouns select for the property interpretation. For example, in the combination zebra bag, a highly salient feature of zebra is that it has stripes. Since bag is a noun for which appearance is an important semantic dimension, interpretation of this combination as a striped bag is relatively easy to accomplish. Indeed, property interpretations elicited by these types of combinations require only semantic access to the meanings of the modifier and head nouns. In contrast, relational interpretations require access both to semantic meaning and to post-retrieval selection processes because any two nouns possess a greater variety of relational linkages than property attributions alone can accommodate. The demands associated with a relational interpretation for donkey bag, a LH combination, are less automatic. Here, the semantics of donkey do not

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readily constrain mapping to bag to give rise to a property interpretation. Rather, they bias toward a relational interpretation, because the range of plausible relational interpretations for donkey bag offers many choices (e.g., a bag carried by a donkey; a bag carrying donkey food; a bag that has a picture of a donkey; a bag made from donkey hide, etc.). Thus, compared with the easily generated property interpretation for zebra bag, a single relational interpretation for donkey bag requires additional postretrieval selection. If deficits in the integrity of semantic knowledge are a primary feature of SZ, patients should show comparable reductions in both property and relational interpretations, and a corresponding increase in ‘‘other’’ non-classifiable interpretations. Both property and relational interpretations require, at a minimum, that comprehenders activate meanings associated with each modifier and head noun. If the integrity of semantic knowledge is compromised, or if initial semantic access does not function properly, both property and relational interpretations would be compromised. In contrast, if both the integrity of semantic knowledge and immediate lexical-semantic retrieval are intact, interpretations that rely on property attributions should remain intact. However, if only an ability to use semantic knowledge in a flexible or controlled way at the post-retrieval stage is impaired, then responses that rely on relational interpretations ought to be impaired, because initial semantic access of word meanings is necessary but not sufficient for generating relational interpretations. Post-retrieval selection processes would also be necessary to select for one of a variety of plausible relational interpretations. Therefore, if only post-retrieval selection mechanisms are impaired, but property interpretations are unaffected, the ability to generate a relational interpretation would be reduced, resulting in an increase in ‘‘other’’ interpretations. We conducted a version of Estes and Glucksberg’s (2000) conceptual combination task with three participant groups: (1) individuals diagnosed with SZ with low amounts of thought disorder as measured by the TDI (SZ Low TDI), (2) individuals diagnosed with SZ with high amounts of thought disorder (SZ High TDI), and (3) individuals who were not diagnosed with a psychiatric illness (Controls). Our version differed from that of Estes and Glucksberg in two ways. First, in addition to collecting information about the kinds of interpretations generated by these groups, we asked participants to evaluate how difficult it was to generate each interpretation to determine whether any group differences in comprehension were associated with differences in subjective effort. Second, we affirmatively scored property, relational, and ‘‘other’’ interpretations, whereas only property interpretations were affirmatively scored in the Estes and Glucksberg study. Comparing patients with low and high amounts of thought disorder is important for two reasons. First, patients diagnosed with psychiatric conditions of any kind are more likely to show increased variability and poorer performance on tests of cognitive function. Thus, segregating patients according to a highly relevant clinical feature of the illness allows us to test hypotheses that are more specific to SZ and to partially control for factors that may relate to differences between patients and controls, such as medication, severity of illness, and poorer overall social functioning. Second, a number of studies have compared language-based cognitive dysfunction in patients with differing amounts of thought disorder (Barrera, McKenna, & Berrios, 2005; Kerns & Berenbaum, 2002, 2003; Leeson, Simpson, McKenna, & Laws, 2005). Thus, the results may be linked to this larger body of work.

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1. Methods 1.1. Participants The patients (n ¼ 47) were outpatients who met DSM-IV criteria for a diagnosis of SZ or schizoaffective disorder. Clinical assessments of the patients were conducted by experienced interviewers and diagnosticians independently of the experimental tasks. Consensus diagnoses were assigned by four senior clinicians on the basis of a review of a standardized interview (Structured Clinical Interview for the DSM-IV) (Spitzer, Williams, Gibbon & First, 1994), an interview narrative, and a review of all available hospital records, permitting both a cross-sectional and longitudinal evaluation. The non-psychiatric control (NC) participants (n ¼ 25) were recruited from a medical outpatient clinic and the McLean Hospital staff. The following inclusion criteria applied to all participants: native English speaker, no diagnosed organic brain disease, no substance/alcohol abuse/ dependence within the past two years, no tardive dyskinesia, no use of alcohol or recreational drugs within two weeks of testing, and an estimated verbal IQ of at least 85. Written informed consent was obtained from all participants. Thought disorder was assessed using the TDI (Coleman, Levy, Lenzenweger, & Holzman, 1996; Johnston & Holzman, 1979; Shenton et al., 1987; Shenton, Solovay, Holzman, Coleman, & Gale, 1989; Solovay et al., 1987). Responses and inquiry to a 10card Rorschach were tape recorded and transcribed verbatim. Consensus TDI scores were assigned blind to group and performance on the experimental task by a group of three expert scorers. In this study, we used the total TDI score as a measure of the quantity of formal thought disorder. The patient sample was divided into two groups based on their total TDI score. The cut-off for assigning patients to the SZ High TDI and SZ Low TDI groups was a total TDI score of 12.0, which resulted in 25 patients being assigned to the SZ High TDI group and 22 patients being assigned to the SZ Low TDI group. This cut-off was based on the overall distribution of TDI scores in the patient sample and a natural break in the distribution that would result in an approximately equal number of patients per subgroup. Table 1 presents demographic and clinical information about the groups. The groups did not differ in age, estimated verbal IQ (Wechsler, 1981), or years of education. Both patient groups had a significantly lower level of functioning as measure by Table 1

# Female/Male Age (years) Education (years) Estimated verbal IQ BPRS GASb Medication amount (CPZ equivalent units) TDI Total scorec a

NC ðn ¼ 25Þ

SZ LOW TDI ðn ¼ 22Þ

SZ HIGH TDI ðn ¼ 25Þ

18/7 30.5 (11.8)a 15.5 (2.6) 105.8 (8.5) NA 78.3 (8.4)

11/11 34.9 (8.3) 14.3 (3.1) 105.9 (12.1) 40.8 (13.0) 40.8 (13.0)

10/15 34.1 (9.9) 14.4 (2.0) 102.0 (9.8) 43.3 (13.6) 40.7 (10.3)

NA 4.2 (6.2)

509.4 (299.8) 4.9 (3.8)

578.8 (327.3) 29.0 (17.4)

Mean (SD). NC vs. SZ Low TDI, F ð1; 44Þ ¼ 136:0, po.001; NC vs. SZ High TDI, F ð1; 44Þ ¼ 194:7, po.001. c NC vs. SZ High TDI, F ð1; 44Þ ¼ 38:4, po.001; SZ Low TDI vs. SZ High TDI, F ð1; 45Þ ¼ 40:3, po.001. b

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the Global Assessment Scale (GAS) (Endicott, Spitzer, Fliess, & Cohen, 1976) than NC, but did not differ from each other. The two patient groups did not differ from each other in symptom severity as assessed using the Brief Psychiatric Rating Scale (BPRS) (Overall & Gorham, 1962), or in daily dose of medication (chlorpromazine, CPZ, equivalent units). The two patient groups differed significantly from each other only in average total TDI scores. 1.2. Materials and procedure Stimuli consisted of 24 sets of noun–noun conceptual combinations taken from Estes and Glucksberg (2000). Three different types of noun–noun pairs were counterbalanced across the 24 items. In the first type of combination the modifier noun had a semantic feature that was highly salient, and the head noun had a semantic dimension that was highly relevant for that feature (HH; e.g., zebra bag). The HH pairs were thus designed to provide a high degree of contextual constraint for a property interpretation. The two other types of pairs were designed to impose a contextual constraint favoring a relational interpretation over a property interpretation. In the second type of combination, the modifier noun had a semantic feature that was highly salient but the head noun did not have a semantic dimension that was highly relevant for that feature (HL; e.g., zebra trap). In the third type of combination, the modifier noun did not have a semantic feature that was highly salient, but used the head noun from the HH pair that had a relevant dimension in the context of the HH pair (LH; e.g., donkey bag). Three rating forms were created in order to counterbalance each item across the three conditions of the experiment (i.e., HH, HL, LH). Only one rating form was given to each participant. Thus, no list contained the same pair more than once, and pairs of each type were included in approximately equal numbers on each list. Participants were instructed to write their interpretation of each pair on the line provided below the pair. They were also instructed to rate (on a scale of 1–5) how difficult it was to create that interpretation. The task was not timed, and it took approximately 15 min to complete. A scoring system was devised to classify participants’ responses into three broad response categories: property interpretation, relational interpretation, and ‘‘other’’ (i.e., neither property nor relational) interpretations. We based the coding scheme on that used by Estes and Glucksberg (2000), but elaborated upon it as well. For example, Estes and Glucksberg reported only results for property interpretations. We report results for property interpretations, relational interpretations, and non-classifiable (i.e., ‘‘other’’) interpretations. Estes and Glucksberg also restricted their classification of property interpretations to only those responses that exactly matched what the combination was meant to bias, whereas we scored property interpretations using a more liberal criterion (i.e., any property interpretation generated). Examples of each interpretation type and additional subdivisions of each category are presented in Table 2. The completed rating forms were scored by four of the authors who obtained extensive training in this coding scheme and were blind to participant group status at the time of scoring (DT, ML, MN, LR). The coded responses were transformed into percentage of responses in each major interpretation category (i.e., property, relational, other) for each combination type (i.e., HH, HL, LH). The difficulty ratings were averaged for each participant as a function of each combination type and interpretation category.

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Table 2 Response category

Response sub-category

Explanation

Example

Property interpretation

Property as defined by Estes and Glucksberg (2000) Property/non-salient

Demonstrates a salient feature and relevant dimension Demonstrates a property interpretation, but not involving the relevant dimension Demonstrates a property interpretation for the relevant dimension, but not for the salient feature

Zebra bag—a bag with black and white stripes

Property/non-salient/ relevant dimension

Property/salient/nonrelevant dimension

Property/switched head

Demonstrates a property interpretation: mentions salient feature but places it in a nonrelevant dimension Property attribution from the head to the modifier

Octopus tray—a tray shaped like an octopus (salient property is # of legs) Turtle jumper—a person who is quick to finish a task (salient feature is slowness: the dimension of speed was used but not the salient feature) Octopus table—a table with eight place settings (relevant dimension was legs of the table) Blimp eagle—a blimp in the shape of an eagle

Relation interpretation

Relation as defined by Estes and Glucksberg (2000)

Relation is created between the head and modifier: usually no mention of salient feature or relevant dimension

Skunk scraps—pieces of dead skunk

‘‘Other’’ interpretation

Ambiguous word interpretation

One of the words is given an unintended meaning by using a homonym of the intended word

Vague

The logic is not apparent, or there is not enough information to determine a classification The response is vague, but some logic is apparent The only words used are the head and the modifier

Frog pen—an enclosure in which to keep frogs (where intended meaning of pen pertained to writing implement) Cotton luggage— luggage that is only the essentials

Vague/associated

Vague/no information

Turtle jumper—a hard job Cherry grease—grease of a cherry

1.3. Results Property interpretations: Fig. 1 presents the percentage of property interpretations across the three participant groups. We computed a 3 (pair type: HH, HL, LH)  3 (group:

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100

Percentage of Property Interpretations

80

HH

HL

LH

70 60 50 40 30 20 10 0 Controls (n = 25)

SZ Low TDI (n = 22)

SZ High TDI (n = 25)

Fig. 1. Percentage of property interpretations (plus or minus 1 standard error of the mean) for controls, SZ Low TDI, and SZ High TDI, as a function of pair type.

Controls, SZ Low TDI, SZ High TDI) mixed-design ANOVA, with pair type as a withinsubjects factor and group as a between-subjects factor. The only significant effect was a main effect of pair type (F ð2; 138Þ ¼ 169:4, po.0001). Across the three groups, the percentage of property interpretations was significantly higher for HH pairs (mean ¼ 66:5; SD ¼ 24) than for HL pairs (mean ¼ 25:3; SD ¼ 19) and LH pairs (mean ¼ 19:5; SD ¼ 16) (HH vs. HL, F ð1; 138Þ ¼ 219:7, po.0001; HH vs. LH, F ð1; 138Þ ¼ 284:4, po.0001)). The percentage of property interpretations was also significantly higher for HL pairs than for LH pairs (HL vs. LH, F ð1; 138Þ ¼ 4:2, po.05), although the magnitude of this effect is much smaller than the difference between HH pairs and HL or LH. The absence of a main effect of group indicated that both subgroups of SZ and the controls were more likely to produce property interpretations for noun–noun combinations that were biased to elicit property interpretations (e.g., HH combinations) than noun–noun combinations that were biased against property interpretations (e.g., HL and LH). The finding that HL pairs were associated with significantly more property interpretations than LH pairs indicates that the presence of a highly salient feature in the modifier noun slightly but significantly favored property interpretations over relational interpretations. These results suggest that the capacity to create property-based interpretations for novel noun–noun combinations is intact in SZ and does not vary as a function of the amount of independently rated thought disorder. Note that the overall pattern of results is the same when the more restrictive definition of property interpretations used by Estes and Glucksberg (2000) is applied to the data. Relational interpretations: Fig. 2 presents the percentage of relational interpretations across the three participant groups. We computed a 3 (pair type: HH, HL, LH)  3 (group: Controls, SZ Low TDI, SZ High TDI) mixed-design ANOVA, with pair type as a within-subjects factor and group as a between-subjects factor. The results yielded a main effect of group (F ð2; 69Þ ¼ 5:1, po.01), a main effect of pair type (F ð2; 138Þ ¼ 103:3, po.0001), and a group  pair-type interaction (F ð4; 138Þ ¼ 2:5, po.05). Inspection of Fig. 2 shows that this interaction was driven by significantly fewer relational responses for

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HH

HL

101

LH

Percentage of Relational Interpretations

80 70 60 50 40 30 20 10 0 Controls (n = 25)

SZ Low TDI (n = 22)

SZ High TDI (n = 25)

Fig. 2. Percentage of relational interpretations (plus or minus 1 standard error of the mean) for controls, SZ Low TDI, and SZ High TDI, as a function of pair type.

80 Percentage of Other Interpretations

HH

HL

LH

70 60 50 40 30 20 10 0 Controls (n = 25)

SZ Low TDI (n = 22)

SZ High TDI (n = 25)

Fig. 3. Percentage of ‘‘other’’ interpretations (plus or minus 1 standard error of the mean) for controls, SZ Low TDI, and SZ High TDI, as a function of pair type.

the HL and LH pairs in the SZ High TDI group than in the SZ Low TDI or the NC groups, who did not differ from each other. A sub-ANOVA comparing the SZ High TDI group and the controls confirmed a significant group  pair-type interaction (F ð2; 96Þ ¼ 4:6, po.05): these two groups differed significantly for HL and LH pairs (po.05) but not for HH pairs. The group  pair-type interaction was not significant in comparison of SZ Low TDI participants and NC.

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Although participants in all three groups were more likely to create relational interpretations for novel noun–noun combinations designed to elicit relational interpretations (e.g., HL and LH combinations) than for noun–noun combinations designed to elicit property interpretations (e.g., HH combinations), the percentage of relational interpretations was inversely related to amount of thought disorder in SZ. SZ High TDI patients created significantly fewer relational interpretations than NC, whereas SZ Low TDI patients and NC did not differ in percentage of relational interpretations. ‘‘Other’’ interpretations: Fig. 3 presents the percentage of other interpretations across the three participant groups. We computed a 3 (pair type: HH, HL, LH)  3 (group: Controls, SZ Low TDI, SZ High TDI) mixed-design ANOVA, with pair type as a withinsubjects factor and group as a between-subjects factor. The results yielded significant main effects of group (F ð2; 69Þ ¼ 6:5, po.01) and pair type (F ð2; 138Þ ¼ 5:7, po.01). SZ High TDI participants created significantly more ‘‘other’’ responses (mean ¼ 26:9, SD ¼ 27) than NC (mean ¼ 10:8, SD ¼ 14) (po.05), but SZ Low TDI participants (mean ¼ 13:1, SD ¼ 19) and NC did not differ. HH combinations elicited significantly fewer ‘‘other’’ responses (mean ¼ 12:3, SD ¼ 18) than the HL (mean ¼ 19:6, SD ¼ 21) or LH combinations (mean ¼ 19:5, SD ¼ 25) (contrasts with HH combinations, respectively, F ð1; 38Þ ¼ 8:8, po.01; F ð1; 138Þ ¼ 8:2, po.01) in all groups. HL and LL combinations did not differ in proportion of ‘‘other’’ responses. These results indicate that SZ High TDI participants were more likely than SZ Low TDI and NC to create interpretations for novel noun–noun combinations that could not be classified as either property or relational interpretations, and thus were only vaguely or tangentially related to a plausible interpretation of the pair. This tendency was somewhat more pronounced for the HL and LH combinations, but the group  pair-type interaction was not significant. To illustrate the kinds of responses that were observed for the three groups, Table 3 presents example property, relational, and ‘‘other’’ responses from the patient groups for several combinations. Mean difficulty ratings: SZ High TDI participants were less likely than the other groups to create relational interpretations for noun–noun pairs designed to elicit relational interpretations and more likely to create ‘‘other’’ interpretations. To evaluate the possibility that SZ High TDI found HL and LH pairs more difficult to process relationally

Table 3 Property example

Relation example

Other example

Zebra bag (HH)

Striped purse

A fun accessory

Zebra trap (HL)

Mouse car (HH)

Black and white cage Bag shaped like a donkey Very small car

Mouse truck (HL)

Small truck

Cat car (LH)

Car that looks like a cat

Bag made from zebra skin Trap to catch zebras Saddlebag for a donkey A car that mice drive Truck that carries mice Toy car for cats

Donkey bag (LH)

Referee with a gun Saddle for a donkey A car trapped by something Used at Disneyworld to empty trash Automobile of fancy women

ARTICLE IN PRESS Average Difficulty Ratings (1 = low; 5 = high)

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3

(a)

Property Interpretation

Average Difficulty Ratings (1 = low; 5 = high)

Relational Interpretation

2.5

2

1.5

1 HH

Average Difficulty Ratings (1 = low; 5 = high)

103

3

(b)

HL

Property Interpretation

LH

Relational Interpretation

2.5

2

1.5

1 HH 3

HL

Property Interpretation

(c)

LH

Relational Interpretation

2.5

2

1.5

1 HH

HL

LH

Fig. 4. (a) Average difficulty ratings (1 ¼ low; 5 ¼ high) for property and relational interpretations (plus or minus 1 standard error of the mean) as a function of pair type for controls. (b) Average difficulty ratings (1 ¼ low; 5 ¼ high) for property and relational interpretations as a function of pair type for SZ Low TDI. (c) Average difficulty ratings (1 ¼ low; 5 ¼ high) for property and relational interpretations as a function of pair type for SZ High TDI.

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than the other groups, we analyzed the subjective ratings for each pair on the difficulty associated with creating each kind of interpretation. Figs. 4a–c present the mean difficulty ratings for Controls, SZ Low TDI, and SZ High TDI participants, respectively, as a function of pair type and interpretation category. We computed a 3 (pair type: HH, HL, LH)  3 (group: Controls, SZ Low TDI, SZ High TDI)  2 (interpretation category: property, relation) mixed-design ANOVA, with pair type and interpretation categories as within-subjects factors and group as a betweensubjects factor. The mean ratings for ‘‘other’’ interpretations were not included in this analysis because of the relatively infrequency of these responses across the groups. The results revealed a significant pair type  interpretation category interaction (F ð2; 138Þ ¼ 8:2, po.001), and a significant three-way pair type  interpretation category  group interaction (F ð4; 138Þ ¼ 3:5, p o.01). We computed sub-ANOVAs for each subject group to explore the nature of these significant interactions. Among NC, there were main effects of pair type (F ð2; 38Þ ¼ 4:1, po.05) and interpretation category (F ð1; 24Þ ¼ 8:1, po.01), and the pair type  interpretation category interaction just missed statistical significance (F ð2; 48Þ ¼ 2:9, p ¼ :07). As shown in Fig. 4a, these effects reflect the finding that property interpretations for HL pairs were rated as more difficult than the other pair types and interpretation categories (po.05). Thus, although the average difficulty ratings were quite low overall (i.e., between 2 and 2.5 on a 5 point scale), controls found it more difficult to interpret combinations when the modifier noun for a combination that had a salient feature mapped to a head noun that did not have a relevant dimension for that feature than when a relevant dimension was present as in the HH pair. Among SZ Low TDI patients there were no significant effects. Difficulty ratings were also low overall (i.e., averaging approximately 2 on a 5 point scale) (see Fig. 4b), and did not discriminate between pair types and interpretation categories. Among SZ High TDI participants the sub-ANOVA yielded a significant pair type  interpretation category interaction (F ð2; 48Þ ¼ 13:5, po.001). Subjective perceptions of response difficulty covaried with the dominant response tendency in each category (Fig. 4c). Thus, difficulty ratings for HH combinations designed to elicit property interpretations were significantly higher when property interpretations were created than when relational interpretations were created for the same pairs (po.05). In contrast, difficulty ratings for HL combinations and LH combinations designed to elicit relational interpretations were significantly higher when relational interpretations were created than when property interpretations were created for the same pairs. Importantly, difficulty ratings for SZ High TDI participants were as low overall as those of the other groups (i.e., averaging approximately 2–2.5 on a 5 point scale). Thus, these data suggest that the significant reduction in relational responses for SZ High TDI participants did not arise because the patients found the specific word combinations to be more difficult subjectively. In support of this interpretation, when the original omnibus ANOVA was computed only for SZ High TDI and Control participants, there was a significant main effect of interpretation category (F ð1; 46Þ ¼ 6:2, po.05) and pair type  interpretation category interaction (F ð2; 96Þ ¼ 10:8, po.001), but no significant main effect of group. 2. General discussion This study employed a conceptual combination task to address the question of whether semantic processing abnormalities in SZ arise from deficits in semantic storage or access,

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or the controlled use of semantic memory representations. The results of this study suggest that the integrity and initial access of semantic memory is spared in SZ, whereas the ability to engage in the controlled processing operations necessary to make flexible use of semantic material, once retrieved, is impaired. Neither high nor low TDI patients differed from controls in how they interpreted noun–noun combinations designed to elicit property interpretations. However, high TDI SZ patients produced significantly fewer relational interpretations for combinations designed to elicit relational interpretations and significantly more ‘‘other’’ unclassifiable interpretations than low TDI patients and controls. Differences in subjective difficulty across the different pairs or interpretation types did not account for the selective deficit involving relational interpretations. Moreover, the specificity of this deficit in high TDI SZ was unrelated to severity of illness, global level of functioning, or dose of medication. The findings from the present study are consistent with our previous work in suggesting that semantic processing impairments in SZ arise when the flexible and contextually appropriate use of semantic memory representations is required to resolve ambiguous input (Titone et al., 2000, 2002; Titone & Levy, 2004). Titone et al. (2000), for example, found that SZ patients and controls showed semantic priming for the less frequent meaning of lexically ambiguous words when the sentence context moderately or strongly biased the less frequent meaning (e.g., the dance meaning of ball for the sentence, ‘‘Because it lasted all night, she really liked the ball’’). However, unlike controls, SZ patients showed continued priming of the contextually irrelevant dominant meaning of lexically ambiguous words when the sentence context moderately biased the less frequent subordinate interpretation. For example, SZ patients showed significant priming of the toy meaning of ball for the sentence, ‘‘Because it lasted all night, she really liked the ball’’, suggesting that the patients failed to inhibit the contextually irrelevant meaning. These findings suggested that SZ patients made use of sentence contexts to activate intact semantic memory representations, but were impaired in flexibly modulating activation of semantic memory as a function of context. A study that examined processing at a lexical rather than semantic level reported a similar pattern of results (Titone & Levy, 2004). SZ patients were impaired in identifying spoken English words that sounded similar to many other high-frequency words, but intact in identifying words that had relatively few lexical competitors. We obtained a similar pattern of results in a study that examined the comprehension of non-literal idiomatic sequences in SZ (Titone et al., 2002). The study of non-literal, or figurative, language processing has a long history in SZ, in that a number of clinical tests of ‘‘thought disorder’’ involve the interpretation of familiar proverbs (e.g., a rolling stone gathers no moss). Non-literal idiomatic sequences do not comprise a homogeneous class of expressions; however, they vary along a number of linguistic dimensions that may affect how idioms are normally processed (Titone & Connine, 1994a,b 1999). For example, some idioms are literally plausible such as ‘‘skate on thin ice’’, whereas other idioms are literally implausible, such as ‘‘pay through the nose’’. Using a cross modal priming paradigm, Titone et al. (2002) found that SZ patients showed reduced semantic priming for literally plausible idiomatic expressions (e.g., ‘‘skate on thin ice’’), but intact semantic priming for literally implausible idiomatic expressions (e.g., ‘‘pay through the nose’’). Thus, the storage of non-literal sequences was not impaired, but SZ patients had difficulty settling on a single interpretation after semantic representations were retrieved into working memory. The results of this series of studies are consistent with meta-analyses showing that post-lexical or strategic aspects of semantic processing are impaired, whereas semantic storage and

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automatic semantic processing seem to be spared, in SZ (Barrera et al., 2005; Kerns & Berenbaum, 2002, 2003; Leeson et al., 2005; Minzenberg, Ober, & Vinogradov, 2002). The key variable linked to the reduction in relational interpretations in the present study was quantity of thought disorder. Interestingly, impaired lexical processing was also significantly correlated with increased thought disorder as assessed with the TDI (Titone & Levy, 2004). We did not examine whether impairments in idiomatic processing and lexical ambiguity resolution are more severe for SZ High TDI participants (Titone et al. 2000, 2002). It is intriguing to consider why impairments in relational interpretations would be associated with increased amounts of thought disorder in SZ. Combinatory thinking, one characteristic of schizophrenic thought disorder, involves creating relationships between unrelated percepts. It seems reasonable to presume that the predisposition to make relational interpretations that are inappropriate interferes with the ability to make relational interpretations that are not only appropriate, but are called for by the context of a particular noun–noun combination. Thus, a core deficit in the ability to inhibit contextually irrelevant semantic representations may lead to the selection of less coherent relational interpretations. This interference effect is particularly pronounced in contexts that are semantically less constrained (i.e., relational) compared with contexts that are semantically more constrained (i.e., property). These results bear on studies of conceptual combination in other populations that have semantic processing deficits. In a recent study examining conceptual combination in individuals with Alzheimer’s disease (AD), the pattern of deficits was the opposite of that found in SZ patients in the present study (Taler, Chertkow, & Saumier, 2005). Taler et al. asked three groups of AD patients, age-matched controls, and young adults to select which of three interpretations best matched noun–noun combinations, although the compounds were undifferentiated with respect to the HH, HL, and LH dimensions. The possible choices on each trial consisted of a property interpretation (termed integration interpretations), or a relational interpretation (termed association interpretations). AD patients and older adult controls made relational interpretations with equivalent frequency, but AD patients were less likely to make property interpretations and more likely to choose the semantic foils than older adult controls. Although the stimuli and procedures are not entirely comparable to those used in the present study, we found that SZ High TDI were impaired in making relational interpretations and intact in making property interpretations. The possible double dissociation between property and relational interpretation deficits in AD and SZ High TDI patients in these two studies suggests that multiple processes that operate independently may be involved in conceptual combination. Such a conclusion is consistent with other work on conceptual combination in normals. A number of studies support the notion that conceptual combination is governed by at least two independent processes that proceed in parallel (Estes, 2003; Wisniewski, 1997; Wisniewski & Love, 1998), although some models propose one cognitive mechanism for the full range of combination interpretations (Gagne, 2002a; Gagne & Shoben, 2002). Support for multiple processes in conceptual combination is also found in a recent electrophysiological study (Kounios et al., 2003), although the kinds of combinations and interpretations studied do not perfectly map onto the property and relational interpretation distinction made here. Thus, data from the present study and previous studies suggest that distinct neural processes may lead to qualitatively different kinds of conceptual combination interpretations. Further work is necessary to resolve this issue more fully.

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It is possible that the kinds of property interpretations examined in the present study and in the Estes and Glucksberg (2000) study have lexical rather than conceptual processing origins. That is, the HH combinations (e.g., zebra bag) were designed so that the modifier noun had a salient feature that could be mapped to the head noun. Therefore, the processes involved in generating a property attribution for these combinations are likely to be by-products of the normal word recognition and semantic activation process (Estes, 2003; Gagne, 2002b). Indeed, it is this view of property interpretations that motivated our prediction that comprehension of combinations that were biased towards property interpretations would be intact in SZ. It is also possible, however, that comprehenders may generate property interpretations for conceptual combinations that do not have a particularly salient feature of the modifier noun or relevant dimension of the head noun differently from those that do. In that case property interpretations could arise from conceptual rather than lexical processes. Thus, property interpretations may be comprised of two types: those that are based on lexical-semantic saliency, as in the HH combinations used by us as well as Estes and Glucksberg (2000), and those that are conceptually based, for example, when a property interpretation is generated for HL, LH combinations, or other kinds of combinations. Thus, the double dissociation between AD and SZ High TDI patients may solely rest on the comparison of lexically driven property interpretations and relational interpretations. Further work is needed to clarify the range of possible interpretations of conceptual combinations and whether they arise from similar or dissimilar neurocognitive systems. To conclude, the present study demonstrated that individuals with SZ with high amounts of thought disorder were impaired in generating relational interpretations of conceptual combinations. These impairments were specific to noun–noun pairs that were designed to preferentially bias relational interpretations. Thus, SZ patients with high amounts of thought disorder are not globally impaired on semantic tasks, but rather show impairments only under circumstances that required controlled and flexible use of material retrieved from semantic memory. Notably, the predominant features of the thought disorder shown by the high thought disorder subgroup of patients involved finding unrealistic relationships between unrelated things and idiosyncratic semantics. In contrast, individuals with SZ were not impaired in generating property attribution interpretations of conceptual combinations that were designed to preferentially bias property interpretations. Thus, when a semantic task required that information be retrieved from semantic memory, individuals with SZ performed normally, suggesting that the structure and initial access of their semantic memory representations were intact. Further work will be necessary to clarify which components of thought disorder are responsible for these impairments, and to determine which neural systems that underlie these processes are compromised in SZ. Acknowledgments We gratefully acknowledge support from the Canada Research Chairs program, NSERC, NARSAD, the Essel Foundation, the Canadian Foundation for Innovation, the McGill Research Development Fund, NIMH Grants MH31340 and MH49487, and the Stanley Scholar Fund. We are grateful to Dr. Philip S. Holzman and Michael Coleman for their assistance in scoring thought disorder protocols using the Thought Disorder Index.

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