Spoken number words and Arabic digits are the most commonly used numerical symbols. We often transcode numerals from one to another, thus, the correspondence between them should become over-learned and automatic after years of usage. It has been shown that an integration usually exists when pairing of stimulus is over-learned, and is often reflected in the mismatch negativity (MMN). The current thesis conducted two behavioural experiments (Chapter 2) and three EEG experiments (Chapter 3 - 5) to systematically investigate the cross-modal correspondence, i.e., the integration, between spoken number words and Arabic digits in adult participants. In the behavioural experiments, a clear distance effect is shown in an audiovisual matching task. This suggests that an amodal, shared magnitude representation is activated for cross-modal numerals during a matching judgment. Moreover, the distance effect is modulated by stimulus onset asynchrony (SOA). That is, the distance effect becomes smaller with the increase of SOA. This is similar to the data pattern of a common integration effect because an integration usually shows when cross-modal stimuli are temporally close. However, a disadvantage of a behavioural task is that the RTs could be influenced by response-selection or response-execution. Hence, I then used an oddball paradigm in which no responses are required for the cross-modal numerals in my EEG experiments. The results of three EEG experiments showed that an early integration effect exists between spoken number words and Arabic digits in the mismatch negativity (MMN). This result is first to show the presence of a cross-format integration between spoken number words and Arabic digits. However, the integration effect is also modulated by distance as well as stimulus onset asynchrony (SOA), which may suggest that the cross-modal correspondence between audiovisual numerals is more complicated than other kinds of audiovisual stimuli, such as letters and speech sounds
