Atypical associations to abstract words in Broca’s aphasia

Abstract 

Introduction

Left frontal brain lesions are known to give rise to aphasia and impaired word associations. These associations have previously been difficult to analyze. We used a semantic space method to investigate associations to cue words. The degree of abstractness of the generated words and semantic similarity to the cue words were measured.

Method

Three subjects diagnosed with Broca’s aphasia and twelve control subjects associated freely to cue words. Results were evaluated with latent semantic analysis (LSA) applied to the Swedish Parole corpus.

Results

The aphasic subjects could be clearly distinguished from controls by a lower degree of abstractness in the words they generated. The aphasic group’s associations showed a negative correlation between semantic similarity to cue word and abstractness of cue word.

Conclusions

By developing novel semantic measures, we showed that Broca’s aphasic subjects’ word production was characterized by a low degree of abstractness and low degree of coherence in associations to abstract cue words. The results support models where meanings of concrete words are represented in neural networks involving perceptual and motor areas, whereas the meaning of abstract words is more dependent on connections to other word forms in the left frontal region. Semantic spaces can be used in future developments of evaluative tools for both diagnosis and research purposes.

Keywords: Aphasia, LSA, Latent semantic analysis, Concreteness, Abstractness