Number-form synesthetes consciously experience numbers in spatially-defined locations. For non-synesthete individuals, a similar association of numbers and space appears in the form of an implicit mental number line as signified by the distance effect–reaction time decreases as the numerical distance between compared numbers increases. In the current experiment, three number-form synesthetes and two different non-synesthete control groups performed a number comparison task. Synesthete participants exhibited a sizeable distance effect only when presented numbers were congruent with their number-form. In contrast, the (...) controls exhibited a distance effect regardless of congruency or presentation type. The findings suggest that: number-form synesthesia impairs the ability to represent numbers in a flexible manner according to task demands; number-form synesthesia is a genuine tangible experience, triggered involuntarily; and the classic mental number line can be more pliable than previously thought and appears to be independent of cultural-lingo direction. (shrink)

In their target article, Rips et al. have presented the view that there is no necessary dependency between natural numbers and internal magnitude. However, they do not give enough weight to neuroimaging and neuropsychological studies. We provide evidence demonstrating that the acquisition of natural numbers depends on magnitude representation and that natural numbers develop from a general magnitude mechanism in the parietal lobes.

Cohen Kadosh & Walsh (CK&W) neglect the solid empirical evidence for a convergence of notation-specific representations onto a shared representation of numerical magnitude. Subliminal priming reveals cross-notation and cross-modality effects, contrary to CK&W's prediction that automatic activation is modality and notation-specific. Notation effects may, however, emerge in the precision, speed, automaticity, and means by which the central magnitude representation is accessed.

Numbers are fundamental to our understanding of, and survival in, the environment. Not surprisingly, numbers represent an important psychological dimension in triggering synaesthetic experiences, such as in digit-colour synaesthesia, or number-space synaesthesia. Another important consideration is directionality in synaesthesia, in that we might ask whether the stimulus and response in any given synaesthetic variant can also work on the opposite way. Most studies have documented the typical direction of the synaesthetic experience from the inducer to the concurrent. However, it seems (...) that some synaesthetes do show bi-directionality, that is, their concurrent might also trigger the inducer either at an implicit level, or even at the explicit level that reaches perceptual awareness. We discuss these two issues in this book chapter. We will first explore synesthesia and automaticity where numbers are concerned, followed by a discussion on synaesthesia and directionality. (shrink)

Numbers are vital to so many areas of life: in science, economics, sports, education, and many aspects of everyday life from infancy onwards. This handbook brings together the different research areas that make up the vibrant field of numerical cognition in one comprehensive and authoritative volume.

In this commentary we make two rejoinders to Jung & Haier (J&H). First, we highlight the response selection component in tasks as a confounding variable that may explain the parieto-frontal involvement in studies of human intelligence. Second, we suggest that efficient response selection may be an integral part of the definition of intelligence.

We concur with Cohen Kadosh & Walsh (CK&W) that representation of numbers in the parietal cortex is format dependent. In addition, we suggest that all formats do not automatically, and equally, access analog magnitude representation in the intraparietal sulcus (IPS). Understanding how development, learning, and context lead to differential access of analog magnitude representation is a key question for future research.