Semantic ambiguity and epilepsy

Cognitive impairment in epilepsy is frequently reported by neuropsychological studies assessing functions such as short-term memory, language, fine motor activity and executive functions. With regard to language, specific abilities such as writing, reading, auditory discrimination, word and sentence comprehension, and word recognition have been frequently assessed. The majority of these neuropsychological studies regarding language function in epilepsy utilize words that have a precise and specific meaning. Nevertheless, the ability of processing semantically ambiguous words in this population has not been extensively investigated. Semantic ambiguity refers to the phenomenon of a single word corresponding to two or even more possible meanings. For example, the noun 'fan' means either a ventilator or an adherent. The purpose of this paper is to review the studies related to the phenomenon of semantic ambiguity in neurologically impaired patients focusing on epilepsy. Firstly, an attempt to a short introduction of the linguistic phenomenon of semantic ambiguity and its connection with lexical features such as contextual information, word frequency, form-class and imageability is made. These are some important variables that are considered to affect meaning selection and word recognition processes. Secondly, several studies concerned with the role of cerebral hemispheres and, more precisely, with the contribution of distinct cerebral regions in the resolution of semantic ambiguity are presented. Converging data suggest that the role of the right hemisphere is to maintain all the alternative meanings of an ambiguous word, whereas the role of the left hemisphere is to select and integrate the appropriate word meaning into context. This finding suggests that both cerebral hemispheres possess a crucial role in the neurolinguistic ability of interpreting ambiguous words. Furthermore, it is well known that distinct cerebral regions associate with semantic processing. This neural network is presented, discussed in terms of lexical ambiguity resolution and compared with the resolution of precise lexical items. Finally, the few available studies regarding the resolution of semantically ambiguous words and semantic knowledge in epilepsy are presented. In a recent study, we propose that the specific type of epileptic seizures affects to a certain degree the semantic processing of ambiguous and non-ambiguous lexical items. In particular, it is found that patients with partial epilepsy have a quite severely disturbed ability to interpret ambiguous and specific (non-ambiguous) lexical items, while patients with generalized epilepsy have a difficulty in processing specific kinds of words, particularly in ambiguous verbs and specific low imageability words. Therefore, the problem found in patients with generalized epilepsy seems to be related with words that have complex representations in the 'mental lexicon', in contrast with patients with partial epilepsy who have difficulty in processing all kinds of the administered lexical items. Further investigation of this interesting observation is suggested in order to specify more precisely whether there are differences between patients with an epileptogenic focus in left or right cerebral hemisphere and in different cerebral regions.

Key words: Semantic ambiguity, semantic processing, epilepsy.