for the degree of Master of Philosophy
at The University of Hong Kong
in August, 2010
Motor and perceptual timing studies have discovered a network of sub-cortical and cortical regions involved in temporal processing, including the cerebellum (Keele & Ivry, 1990; Xu et al., 2006), basal ganglia (Harrington et al., 1998; Rao et al., 2001), supplementary motor area (Macar, Coull & Vidal, 2006) and the prefrontal cortex (Lewis & Miall, 2006). Yet these motor and perceptual timing experiments have a serious confounder in that the stimuli vary in physical dimension between the control and experimental conditions. Using language as experimental materials to study time processing does not have this caveat, in that the temporal information contained within it is explicit but physical properties of stimuli can be perfectly matched. In this thesis, a series of three studies use functional magnetic resonance imaging was used to show the overlap between regions that mediate motor and perceptual timing and those that mediate the processing of time in language.
Experiments 1 and 2 used language to study temporal processing. In Experiment 1, seventeen native mandarin speakers were scanned whilst they performed a task with three different conditions: time condition, life condition and a baseline condition. In the time condition, participants judged if a word presented to them contained time information, such as "yesterday", or did not contain time information, such as "book". The life condition used a similar task but required the participants to judge if the word referred to a living creature, such as "butterfly" or not. In the baseline task, participants judged if two characters that were semantically, phonologically and orthographically unrelated were the same font-size or not. All tasks were conducted in simplified Chinese. In experiment 2, participants did the same tak as in Experiment 1, but the stimuli was only presented for 100ms, and followed by a complex visual mask. Experiment 3 was used for comparison purposes and consisted of a motor time task adopted from Bueti et. al.'s (2006) study.
The supplementary motor area (SMA), thalamus and insula were activated for both Experiment 1 and 3, suggesting that these regions were involved in the processing of temporal information both in and out of language. However, these activations are not seen in Experiment 2, suggesting that temporal regions were only activated when participants had ample time to read the stimuli. The results from this study suggest that it is possible that the SMA, insula and thalamus may be part of a domain-general mechanism for the processing of time.