number form
{{Use American English|date = February 2019}}
{{Short description|Mental map of numbers}}
{{about|the neurological phenomenon|Unicode numbers|Number Forms}}
{{Technical|date=November 2019}}
A number form is a mental map of numbers, which automatically and involuntarily appears whenever someone who experiences number-forms thinks of numbers. Numbers are mapped into distinct spatial locations and the mapping may be different across individuals. Number forms were first documented and named by Sir Francis Galton in his The Visions of Sane Persons.{{cite book |last1=Galton |first1=Francis |title=The Visions of Sane Persons |date=1881 |url=http://galton.org/cgi-bin/searchImages/search/essays/pages/galton-1881-fort-rev-visions-sane-persons_2.htm}} Later research has identified them as a type of synesthesia.{{cite journal |last1=Seron |first1=X. |last2=Pesenti |first2=M. |last3=Noël |first3=M. P. |last4=Deloche |first4=G. |last5=Cornet |first5=J. A. |title=Images of numbers, or "When 98 is upper left and 6 sky blue" |journal=Cognition |date=August 1992 |volume=44 |issue=1–2 |pages=159–196 |doi=10.1016/0010-0277(92)90053-k |pmid=1511585 |s2cid=26687757 |url=https://pubmed.ncbi.nlm.nih.gov/1511585/ |issn=0010-0277}}{{cite journal |last1=Sagiv |first1=Noam |last2=Simner |first2=Julia |last3=Collins |first3=James |last4=Butterworth |first4=Brian |last5=Ward |first5=Jamie |title=What is the relationship between synaesthesia and visuo-spatial number forms? |journal=Cognition |date=August 2006 |volume=101 |issue=1 |pages=114–128 |doi=10.1016/j.cognition.2005.09.004 |pmid=16288733 |s2cid=1948034 |url=https://pubmed.ncbi.nlm.nih.gov/16288733/ |issn=0010-0277}}
Neural mechanisms
It has been suggested that number-forms are a result of cross-activation between regions of the parietal lobe that are involved in numerical cognition and angular gyrus for spatial cognition.{{cite journal |last1=Ramachandran |first1=V. S. |last2=Hubbard |first2=E. M. |title=Synaesthesia—A Window Into Perception, Thought and Language |journal=Journal of Consciousness Studies |volume=8 |issue=12 |pages=3–34 |date=2001 |url=http://psy.ucsd.edu/~edhubbard/papers/JCS.pdf |access-date=2018-02-27 |archive-date=2006-05-27 |archive-url=https://web.archive.org/web/20060527085838/http://psy.ucsd.edu/~edhubbard/papers/JCS.pdf |url-status=dead }}{{cite journal |last1=Hubbard |first1=Edward M. |last2=Piazza |first2=Manuela |last3=Pinel |first3=Philippe |last4=Dehaene |first4=Stanislas |title=Interactions between number and space in parietal cortex |journal=Nature Reviews. Neuroscience |date=June 2005 |volume=6 |issue=6 |pages=435–448 |doi=10.1038/nrn1684 |pmid=15928716 |s2cid=1465072 |url=https://pubmed.ncbi.nlm.nih.gov/15928716/ |issn=1471-003X}} Since the areas that process numerical and spatial representations are close to each other, this may contribute to the increased cross-activation. Synesthetes display larger P3b amplitudes for month cues compared to non-synesthetes, but similar N1 and P3b responses for arrow (← or →) and word (left or right) cues.{{cite journal |last1=Teuscher |first1=Ursina |last2=Brang |first2=David |last3=Ramachandran |first3=Vilayanur S. |last4=Coulson |first4=Seana |title=Spatial cueing in time-space synesthetes: An event-related brain potential study |journal=Brain and Cognition |date=October 2010 |volume=74 |issue=1 |pages=35–46 |doi=10.1016/j.bandc.2010.06.001 |pmid=20637536 |s2cid=15082643 |url=https://pubmed.ncbi.nlm.nih.gov/20637536/ |issn=1090-2147}}
Reaction time research
Reaction time studies have shown that number-form synesthetes are faster to say which of two numbers is larger when the numbers are arranged in a manner consistent with their number-form, suggesting that number forms are automatically evoked.{{cite journal |last1=Piazza |first1=M. |last2=Pinel |first2=P. |last3=Dehaene |first3=S. |title=Objective correlates of an unusual subjective experience: A single-case study of number-form synaesthesia |journal=Cognitive Neuropsychology |date=1 December 2006 |volume=23 |issue=8 |pages=1162–1173 |doi=10.1080/02643290600780080 |pmid=21049372 |s2cid=12570398 |url=https://pubmed.ncbi.nlm.nih.gov/21049372/ |issn=0264-3294}} This can be thought of as a spatial Stroop task, in which space is not relevant to the task, but which can hinder performance despite its irrelevance. The fact that synesthetes cannot ignore the spatial arrangement of the numbers on the screen demonstrates that numbers are automatically evoking spatial cues. The reaction times for valid cues are smaller than invalid cues (words and arrows), but in synesthetes the response time differences for months are larger than those of non-synesthetes.
Differences with number line
These number forms can be distinguished from the non-conscious mental number lines by the fact that they are conscious, idiosyncratic and stable across the person's lifespan. Although this form of synesthesia has not been as intensively studied as grapheme–color synesthesia, Hubbard and colleagues have argued that similar neural mechanisms might be involved, but acting in different brain regions.