Time, tone and the brain: Behavioral and neurophysiological studies on time reference and grammatical tone in Akan

Languages of the world have several ways of expressing time reference. Many languages such as those in the Indo-European group express time reference through tense. Asian languages such as Chinese express time reference through aspectual adverbs, while Akan (spoken in Ghana) does so through grammatical tone. The goal of this dissertation was to investigate grammatical tone and time reference processing in Akan brain damaged speakers with and without aphasia, as well as healthy Akan speakers. Using behavioral and neurophysiological methods, the results of this project showed that grammatical tone processing is problematic for individuals with brain damage. However, the problems with grammatical tone processing, particularly in individuals with brain damage leading to agrammatic aphasia, was largely driven by past time reference deficit, and not grammatical tone per se. That is, individuals with agrammatic aphasia showed more difficulties in processing past verbs than the non-past verbs. This is because past time reference requires extra processing load compared to the non-past time reference. The dissociation between the past and non-past processing was also confirmed by the electrophysiological brain response of the healthy Akan speakers. The conclusion is that regardless of how time reference is expressed, whether through affixes (in Indo-European languages), aspectual adverbs (in Chinese) or tone (in Akan), the processing of past and non-past time reference show different underlying neural processes. Therefore, the findings of this project highlight the need for cross-linguistic studies, especially in understudied languages, in order to test and broaden the already existing neuro-linguistic theories.