Abstract:
The Triple Code Model (TCM) is the most prominent and influential model of numerical cognition and its neurocognitive foundations. Relying on experimental psychological, neuropsychological, and neurofunctional data, its major contribution for a better understanding of number processing is the assignment of domain-specific structure-function-relationships to the proposed numerical codes. The TCM assumes three distinct codes which interact bi-directionally with each other but can be selectively impaired: a visual Arabic number code attributed to bilateral fusiform gyrus, an auditory verbal code associated with left perisylvian language areas, and an analogue magnitude code to be found in bilateral intraparietal sulcus (IPS). Thus, domain-specific functions are associated with specific neural structures. Nevertheless, two important aspects were less in the focus of the TCM: On the one hand, the involvement of domain-general processes and their complex interplay with domain-specific processes involved in numerical cognition received only little attention. On the other hand, as a structural model the TCM describes the processes involved in numerical cognition with high spatial resolution based on neuropsychological and neurofunctional data, while temporal aspects were left largely unnoticed so far. However, research of recent years emphasized the relevance of both the complex interplay of domain-specific and domain-general processes as well as good spatial and good temporal resolution of these processes to adequately understand processes and mechanisms involved in numerical cognition.
To pursue this issue, the present thesis focused on these so far underspecified issues in two sections. As part of the tertiary association cortex, bilateral IPS is not only involved in domain-specific number processing, but also in other rather domain-general cognitive functions. For this reason, Section 1 addresses domain-specific numerical and domain-general processes in parietal cortex involved in numerical cognition in two fMRI and one behavioral study with the aim to complement functions associated with the parietal cortex by the TCM. Section 1 shows that i) relative magnitude information is processed comparably to absolute magnitude information in intraparietal brain areas, ii) parietal brain regions are also involved in domain-general processes related to, but beyond magnitude processing, and iii) specific aspects of complex number concepts (e.g., multi-symbol numbers) are associated with space only with increasing experience with this specific concept. Section 2, for its part, focuses on aspects of temporal dynamics of number processing distinguishing between early automatic bottom-up mechanisms on the conceptual level and later cognitively controlled top-down mediated processes as revealed by eye-tracking.
Based on the present findings and the existing literature, a model extension of the TCM is proposed, which aims at specifying the assumptions of the TCM for domain-specific numerical and domain-general processes (principally independent from temporal aspects and time-critical methods) and enriching the TCM with early bottom-up and later top-down mediated processing stages (based on findings of time-critical methods). In doing so, three distinct processing stages are assumed: an initial visual input stage in occipital brain areas, an early largely automatic and stimulus-driven conceptual processing stage in parietal regions, and a later top-down and cognitively controlled processing stage recruiting fronto-parietal areas.
This model extension provides a first attempt to complement neurofunctional correlates of domain-specific numerical and domain-general processes with aspects of temporal dynamics of number processing.
