Numerical reasoning pervades modern human culture and depends on a fronto-parietal network, a key node of which is the intraparietal sulcus (IPS). In this dissertation I investigate how visual experience shapes the cognitive and neural basis of numerical thinking by studying numerical cognition in congenitally blind individuals.
In Chapter 2, I ask how the cognitive basis of numerical thinking is shaped by visual experience. I test whether the precision of approximate number representations develops normally in the absence of vision and test whether the relationship between numerical approximation and math abilities is preserved in congenital blindness.
In Chapter 3, I ask how the neural basis of symbolic number reasoning is modified by visual experience by studying neural responses to symbolic math in congenitally blind individuals. This initial investigation revealed that the fronto-parietal number system is preserved in blindness but that some “visual” cortices are recruited for symbolic number processing in blindness. The following chapters unpack these two patterns preservation and plasticity.
In Chapter 4, I use resting-state data to ask whether functional connectivity with higher-cognitive networks is a potential mechanism by which “visual” cortices are reorganized in blindness. In Chapter 5, I work with individuals who became blind as adults to determine whether visual cortex plasticity for numerical functions is possible in the adult cortex or whether it is restricted to sensitive periods in development.
In Chapter 6, I investigated whether the IPS and newly identified number-responsive “visual” area of congenitally blind individuals possess population codes that distinguish between different quantities.
I find that the behavioral signatures of numerical reasoning are indistinguishable across congenitally blind and sighted groups and that the fronto-parietal number network, in particular the IPS, is preserved in the absence of vision. A dorsal occipital region showed the same functional profile as the IPS number system in congenitally blind individuals. Number-related plasticity was restricted to a sensitive period in development as it was not observed in adult-onset blind individuals. Furthermore, in congenital blindness, sub-specialization of the “visual” cortex for math and language processing followed the functional connectivity patterns of “visual” cortex
