Brita Elvevåg

Quantifying incoherence in speech: An automated methodology and novel application to schizophrenia

Incoherent discourse, with a disjointed flow of ideas, is a cardinal symptom in several psychiatric and neurological conditions. However, measuring incoherence has often been complex and subjective. We sought to validate an objective, intrinsically reliable, computational approach to quantifying speech incoherence. Patients with schizophrenia and healthy control volunteers were administered a variety of language tasks. The speech generated was transcribed and the coherence computed using Latent Semantic Analysis (LSA). The discourse was also analyzed with a standard clinical measure of thought disorder. In word association and generation tasks LSA derived coherence scores were sensitive to differences between patients and controls, and correlated with clinical measures of thought disorder. In speech samples LSA could be used to localize where in sentence production incoherence occurs, predict levels of incoherence as well as whether discourse belonged to a patient or control. In conclusion, LSA can be used to assay disordered language production so as to both complement human clinical ratings as well as experimentally parse this incoherence in a theory-driven manner.

Where have all the women gone?. Participant gender in epidemiological and non-epidemiological research of schizophrenia

Though archival literature states that schizophrenia occurs equally in males and in females, recent epidemiological studies report higher incidence of schizophrenia in men than in women. Moreover, there is longstanding evidence that women may be under-represented in non-epidemiological research literature. Our first goal was to quantify gender ratios in non-epidemiological research published in 2006. Secondly, we sought to investigate which factors contribute to high numbers of men in research studies. Our final goal was to compare gender ratios in non-epidemiological schizophrenia research to reported incidence rates. In a recent meta-analysis of incidence, there were 1.4 males for each female with schizophrenia. In non-epidemiological studies of the schizophrenia patients, there was an average of 1.94 men for every woman. Although the degree to which men outnumbered women varied according to study type and region of study, research studies included more men than women across all investigated variables. Either the incidence rates are higher for men than has previously been reported or women are less visible in research settings than in the greater community. Importantly, the discrepancy between gender ratios in epidemiological and non-epidemiological research is consistent. However, specific, identifiable factors are present when male participants are greatest, suggesting that many research environments yield a higher number of men. Thus much of our understanding of the illness and its treatment is based on research conducted disproportionately with men.

Category fluency, latent semantic analysis and schizophrenia: a candidate gene approach.

BACKGROUNDnCategory fluency is a widely used task that relies on multiple neurocognitive processes and is a sensitive assay of cortical dysfunction, including in schizophrenia. The test requires naming of as many words belonging to a certain category (e.g., animals) as possible within a short period of time. The core metrics are the overall number of words produced and the number of errors, namely non-members generated for a target category. We combine a computational linguistic approach with a candidate gene approach to examine the genetic architecture of this traditional fluency measure.nnnMETHODSnIn addition to the standard metric of overall word count, we applied a computational approach to semantics, Latent Semantic Analysis (LSA), to analyse the clustering pattern of the categories generated, as it likely reflects the search in memory for meanings. Also, since fluency performance probably also recruits verbal learning and recall processes, we included two standard measures of this cognitive process: the Wechsler Memory Scale and California Verbal Learning Test (CVLT). To explore the genetic architecture of traditional and LSA-derived fluency measures we employed a candidate gene approach focused on SNPs with known function that were available from a recent genome-wide association study (GWAS) of schizophrenia. The selected candidate genes were associated with language and speech, verbal learning and recall processes, and processing speed. A total of 39 coding SNPs were included for analysis in 665 subjects.nnnRESULTS AND DISCUSSIONnGiven the modest sample size, the results should be regarded as exploratory and preliminary. Nevertheless, the data clearly illustrate how extracting the meaning from participants responses, by analysing the actual content of words, generates useful and neurocognitively viable metrics. We discuss three replicated SNPs in the genes ZNF804A, DISC1 and KIAA0319, as well as the potential for computational analyses of linguistic and textual data in other genomics tasks.

Levels of processing effects on recognition memory in patients with schizophrenia

This study sought to characterize the performance of patients with schizophrenia, as compared with healthy participants, on a memory task that required encoding of items to different depths. Participants included 21 individuals with schizophrenia and 26 healthy controls. During the encoding phase of the study, participants processed successively presented words in two ways: perceptually (by making a decision as to whether the letter a was present in the word) or semantically (by making a living/nonliving decision for each word). During the recognition phase of the study, participants were presented with a list of words containing items that had been presented during the encoding phase (during either the letter decision task or the semantic decision task), as well as items that had not been seen before (foils). Though patients with schizophrenia performed more poorly overall on the recognition task, recognition was facilitated by semantic encoding to an equivalent degree in both groups. In other words, while significant main effects were present for group and encoding, no groupxencoding condition was present. This result is consistent with previous findings of a lack of qualitative differences in performance on learning and memory tasks between patients with schizophrenia and healthy controls. It also suggests that strategies that place constraints on the encoding processes used by patients may help improve the efficiency with which they learn and remember information.

The Evolution of the Exponent of Zipf's Law in Language Ontogeny

It is well-known that word frequencies arrange themselves according to Zipfs law. However, little is known about the dependency of the parameters of the law and the complexity of a communication system. Many models of the evolution of language assume that the exponent of the law remains constant as the complexity of a communication systems increases. Using longitudinal studies of child language, we analysed the word rank distribution for the speech of children and adults participating in conversations. The adults typically included family members (e.g., parents) or the investigators conducting the research. Our analysis of the evolution of Zipfs law yields two main unexpected results. First, in children the exponent of the law tends to decrease over time while this tendency is weaker in adults, thus suggesting this is not a mere mirror effect of adult speech. Second, although the exponent of the law is more stable in adults, their exponents fall below 1 which is the typical value of the exponent assumed in both children and adults. Our analysis also shows a tendency of the mean length of utterances (MLU), a simple estimate of syntactic complexity, to increase as the exponent decreases. The parallel evolution of the exponent and a simple indicator of syntactic complexity (MLU) supports the hypothesis that the exponent of Zipfs law and linguistic complexity are inter-related. The assumption that Zipfs law for word ranks is a power-law with a constant exponent of one in both adults and children needs to be revised.

Cognitive differences between men and women: a comparison of patients with schizophrenia and healthy volunteers

Gender modulates cognition such that women display advantages in certain domains while men excel in others tasks. Similar patterns have been seen in patients with schizophrenia. We derived six cognitive factor domain scores from a cognitive battery and examined gender-based cognitive differences in patients with schizophrenia and controls. There were strikingly different effects of gender in patients as compared to controls. The large sample size and broad range of tests in our study add important findings to the neuropsychological literature of schizophrenia, which serve to reinforce some aspects of past research on gender differences in cognition, while questioning others.

Automated computerized analysis of speech in psychiatric disorders.

Purpose of review Disturbances in communication are a hallmark feature of severe mental illnesses. Recent technological advances have paved the way for objectifying communication using automated computerized semantic, linguistic and acoustic analyses. We review recent studies applying various computer-based assessments to the natural language produced by adult patients with severe mental illness. Recent findings Automated computerized methods afford tools with which it is possible to objectively evaluate patients in a reliable, valid and efficient manner that complements human ratings. Crucially, these measures correlate with important clinical measures. The clinical relevance of these novel metrics has been demonstrated by showing their relationship to functional outcome measures, their in-vivo link to classic ‘language’ regions in the brain, and, in the case of linguistic analysis, their relationship to candidate genes for severe mental illness. Summary Computer-based assessments of natural language afford a framework with which to measure communication disturbances in adults with severe mental illnesses. Emerging evidence suggests that they can be reliable and valid, and overcome many practical limitations of more traditional assessment methods. The advancement of these technologies offers unprecedented potential for measuring and understanding some of the most crippling symptoms of some of the most debilitating illnesses known to humankind.

Latent semantic variables are associated with formal thought disorder and adaptive behavior in older inpatients with schizophrenia

INTRODUCTIONnFormal thought disorder is a hallmark feature of schizophrenia in which disorganized thoughts manifest as disordered speech. A dysfunctional semantic system and a disruption in executive functioning have been proposed as possible mechanisms for formal thought disorder and verbal fluency impairment. Traditional rating scales and neuropsychological test scores might not be sensitive enough to distinguish among types of semantic impairments. This has lead to the proposed used of a natural language processing technique, Latent Semantic Analysis (LSA), which offers improved semantic sensitivity.nnnMETHODnIn this study, LSA, a computational, vector-based text analysis technique to examine the contribution of vector length, an LSA measure related to word unusualness and cosines between word vectors, an LSA measure of semantic coherence to semantic and phonological fluency, disconnectedness of speech, and adaptive functioning in 165 older inpatients with schizophrenia.nnnRESULTSnIn stepwise regressions word unusualness was significantly associated with semantic fluency and phonological fluency, disconnectedness in speech, and impaired functioning, even after considering the contribution of premorbid cognition, positive and negative symptoms, and demographic variables.nnnCONCLUSIONSnThese findings support the utility of LSA in examining the contribution of coherence to thought disorder and the its relationship with daily functioning. Deficits in verbal fluency may be an expression of underlying disorganization in thought processes.

Detecting order–disorder transitions in discourse: Implications for schizophrenia

Several psychiatric and neurological conditions affect the semantic organization and content of a patients speech. Specifically, the discourse of patients with schizophrenia is frequently characterized as lacking coherence. The evaluation of disturbances in discourse is often used in diagnosis and in assessing treatment efficacy, and is an important factor in prognosis. Measuring these deviations, such as loss of meaning and incoherence, is difficult and requires substantial human effort. Computational procedures can be employed to characterize the nature of the anomalies in discourse. We present a set of new tools derived from network theory and information science that may assist in empirical and clinical studies of communication patterns in patients, and provide the foundation for future automatic procedures. First we review information science and complex network approaches to measuring semantic coherence, and then we introduce a representation of discourse that allows for the computation of measures of disorganization. Finally we apply these tools to speech transcriptions from patients and a healthy participant, illustrating the implications and potential of this novel framework.

Metaphor interpretation and use : a window into semantics in schizophrenia

The nature of putative semantic anomalies in schizophrenia is controversial. Metaphor interpretation and use provide a useful methodology with which to probe semantics since metaphors are critical in reasoning processes and in how conceptual knowledge is organized. The first study examined free speech for figurative language. The second study explored whether emotional versus non-emotional metaphorical language interpretation elicits differences in the tendencies to produce idiosyncratic (bizarre) or literal interpretations or use of other metaphors to describe the meaning of a metaphor. The third study examined the interpretation of time metaphors. We expected the time perspective in ambiguous sentences to be differentially influenced by previously presented unambiguous sentences of a specific perspective, either events moving relative to a stationary observer (moving-time) or an observer moving relative to a stationary event (moving-ego). First, we found that patients used a similar amount of figurative language as control participants. Second, we did not find any difference between the groups in terms of idiosyncratic interpretations, although patients did interpret more metaphors literally and controls utilized more figurative language. Third, we did not find evidence of a difference between the groups in terms of time perspectives influencing ambiguous target sentences differentially. As operationalized here, the interpretation and use of metaphors is similar in patients with schizophrenia to that of healthy control participants. To the extent that metaphors recruit semantic processes this area of cognition is generally intact in schizophrenia.