TY - JOUR
T1 - Deriving semantic structure from category fluency
T2 - Clustering techniques and their pitfalls
AU - Voorspoels, Wouter
AU - Storms, Gert
AU - Longenecker, Julia
AU - Verheyen, Steven
AU - Weinberger, Daniel R.
AU - Elvevåg, Brita
N1 - Funding Information:
WV and SV are postdoctoral fellows at the Research Foundation – Flanders. This research was supported by the Intramural Research Program of the National Institutes of Health, National Institute of Mental Health. BE was supported by the Northern Norwegian Regional Health Authority (Helse Nord RHF). None of the funding agencies had any further role in study design, data analysis and interpretation, or in the writing of the report and decision to submit for publication.
PY - 2014/6
Y1 - 2014/6
N2 - Assessing verbal output in category fluency tasks provides a sensitive indicator of cortical dysfunction. The most common metrics are the overall number of words produced and the number of errors. Two main observations have been made about the structure of the output, first that there is a temporal component to it with words being generated in spurts, and second that the clustering pattern may reflect a search for meanings such that the 'clustering' is attributable to the activation of a specific semantic field in memory. A number of sophisticated approaches to examining the structure of this clustering have been developed, and a core theme is that the similarity relations between category members will reveal the mental semantic structure of the category underlying an individual's responses, which can then be visualized by a number of algorithms, such as MDS, hierarchical clustering, ADDTREE, ADCLUS or SVD. Such approaches have been applied to a variety of neurological and psychiatric populations, and the general conclusion has been that the clinical condition systematically distorts the semantic structure in the patients, as compared to the healthy controls. In the present paper we explore this approach to understanding semantic structure using category fluency data. On the basis of a large pool of patients with schizophrenia ( n=204) and healthy control participants ( n=204), we find that the methods are problematic and unreliable to the extent that it is not possible to conclude that any putative difference reflects a systematic difference between the semantic representations in patients and controls. Moreover, taking into account the unreliability of the methods, we find that the most probable conclusion to be made is that no difference in underlying semantic representation exists. The consequences of these findings to understanding semantic structure, and the use of category fluency data, in cortical dysfunction are discussed.
AB - Assessing verbal output in category fluency tasks provides a sensitive indicator of cortical dysfunction. The most common metrics are the overall number of words produced and the number of errors. Two main observations have been made about the structure of the output, first that there is a temporal component to it with words being generated in spurts, and second that the clustering pattern may reflect a search for meanings such that the 'clustering' is attributable to the activation of a specific semantic field in memory. A number of sophisticated approaches to examining the structure of this clustering have been developed, and a core theme is that the similarity relations between category members will reveal the mental semantic structure of the category underlying an individual's responses, which can then be visualized by a number of algorithms, such as MDS, hierarchical clustering, ADDTREE, ADCLUS or SVD. Such approaches have been applied to a variety of neurological and psychiatric populations, and the general conclusion has been that the clinical condition systematically distorts the semantic structure in the patients, as compared to the healthy controls. In the present paper we explore this approach to understanding semantic structure using category fluency data. On the basis of a large pool of patients with schizophrenia ( n=204) and healthy control participants ( n=204), we find that the methods are problematic and unreliable to the extent that it is not possible to conclude that any putative difference reflects a systematic difference between the semantic representations in patients and controls. Moreover, taking into account the unreliability of the methods, we find that the most probable conclusion to be made is that no difference in underlying semantic representation exists. The consequences of these findings to understanding semantic structure, and the use of category fluency data, in cortical dysfunction are discussed.
KW - Category fluency
KW - Sampling
KW - Schizophrenia
KW - Semantic deficits
KW - Similarity
UR - http://www.scopus.com/inward/record.url?scp=84901467269&partnerID=8YFLogxK
UR - http://www.scopus.com/inward/citedby.url?scp=84901467269&partnerID=8YFLogxK
U2 - 10.1016/j.cortex.2013.09.006
DO - 10.1016/j.cortex.2013.09.006
M3 - Article
C2 - 24275165
AN - SCOPUS:84901467269
SN - 0010-9452
VL - 55
SP - 130
EP - 147
JO - Cortex
JF - Cortex
IS - 1
ER -