Origins of the specialization for letters and numbers in ventral occipitotemporal cortex

doi:10.1016/j.tics.2015.05.006

Trends in Cognitive Sciences

Volume 19, Issue 7, July 2015, Pages 374-382

https://doi.org/10.1016/j.tics.2015.05.006 Get rights and content

Highlights

•
The VWFA and NFA are areas specializing in letter and number recognition, respectively.
•
The locations of these symbol form areas are conserved in blind participants.
•
Their existence cannot be explained by evolutionary changes or visual constraints.
•
Symbol form areas may emerge from connectivity biases and/or shape feature preferences.

Deep in the occipitotemporal cortex lie two functional regions, the visual word form area (VWFA) and the number form area (NFA), which are thought to play a special role in letter and number recognition, respectively. We review recent progress made in characterizing the origins of these symbol form areas in children or adults, sighted or blind subjects, and humans or monkeys. We propose two non-mutually-exclusive hypotheses on the origins of the VWFA and NFA: the presence of a connectivity bias, and a sensitivity to shape features. We assess the explanatory power of these hypotheses, describe their consequences, and offer several experimental tests.

Section snippets

The puzzle of symbol form areas in the brain

Written symbols such as letters or numbers are a late but far-reaching addition to the mental toolkit of humanity. It should therefore be no surprise that the brain dedicates significant resources to recognizing them. More surprising is that these resources, the VWFA and the NFA, are always localized and highly reproducible in the occipitotemporal cortex across subjects, fonts, and even sensory modalities. This is especially puzzling because letters and numbers are such recent cultural

Two hypotheses for symbol form areas in vOTC

We spell out two hypotheses on the initial conditions that lead to the maturation of the letter and number form areas depicted in Figure 1. These hypotheses are not mutually exclusive but have distinct consequences.

Concluding remarks

Symbol form areas are highly reproducible in vOTC across subjects of different cultures, and localized proto-symbol form areas also consistently emerge in IT cortex after training juvenile macaques. Nonetheless, these areas could not have specifically evolved for processing symbols, and their locations, which are conserved in congenitally blind humans, cannot proceed from purely visual constraints. Our analysis of the available data suggests that two hypotheses, the biased connectivity and the

Acknowledgments

The research leading to these results has received funding from the European Commission Seventh Framework Programme (FP7/2007-2013) under grant agreement 604102 (Human Brain Project), from the program ‘Investissements d’Avenir’ ANR-10-IAIHU-06, and was supported by INSERM, the CEA, the Collège de France, and the Bettencourt-Schueller foundation. A.A. is a European Research Council (ERC) fellow and is supported by ERC-ITG grant (310809) as well as the Gatsby Charitable Foundation and a James S.

Glossary

Deep convolutional networks: neural network systems inspired from the primate brain, which classify patterns using a hierarchy of layers with restricted receptive fields, and interleaved pooling and sampling units.
Diffusion tensor imaging (DTI)/tractography: DTI is a brain-imaging technique whereby the properties of neural tissues are inferred from the pattern of diffusion of water molecules as measured by MRI. Tractography is the application of computerized algorithms to DTI images of white matter

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Trends in Cognitive Sciences

OpinionOrigins of the specialization for letters and numbers in ventral occipitotemporal cortex

Highlights

Section snippets

The puzzle of symbol form areas in the brain

Two hypotheses for symbol form areas in vOTC

Concluding remarks

Acknowledgments

Glossary

Trends Cogn. Neurosci.

Neuron

Neuroimage

Trends Cogn. Sci.

Neuron

Neuroimage

Neuron

Trends Cogn. Sci.

Neuron

Neuroimage

Neuroimage

Neuroimage

Curr. Biol.

Neurosci. Lett.

Neuroimage

Prog. Brain. Res.

Brain Res. Bull.

Cogn. Brain Res.

Curr. Biol.

Prog. Brain Res.

Neural Netw.

Neuron

Neuroimage

Reading in the Brain

Towards an anatomical and functional model of number processing

Math. Cogn.

A brain area for visual numerals

J. Neurosci.

Contribution à l’étude anatomo-pathologique et clinique des différentes variétés de cécité verbale

Mem. Soc. Biol.

Number processing in pure alexia: the effect of hemispheric asymmetries and task demands

Neurocase

Cerebral networks for number processing: evidence from a case of posterior callosal lesion

Neurocase

Number reading in pure alexia – a review

Neuropsychologia

A number-form area in the blind

Nat. Commun.

EyeMusic: introducing a ‘visual’ colorful experience for the blind using auditory sensory substitution

Restor. Neurol. Neurosci.

Representation of number in the brain

Annu. Rev. Neurosci.

The visual word form area: spatial and temporal characterization of an initial stage of reading in normal subjects and posterior split-brain patients

Brain

Letter binding and invariant recognition of masked words: behavioral and neuroimaging evidence

Psychol. Sci.

Adding words to the brain's visual dictionary: novel word learning selectively sharpens orthographic representations in the VWFA

J. Neurosci.

The visual word form area. A prelexical representation of visual words in the fusiform gyrus

Neuroreport

Auditory selective attention to speech modulates activity in the visual word form area

Cereb. Cortex

How learning to read changes the cortical networks for vision and language

Science

The development of cortical sensitivity to visual word forms

J. Cogn. Neurosci.

Beyond hemispheric dominance: brain regions underlying the joint lateralization of language and arithmetic to the left hemisphere

J. Cogn. Neurosci.

The left ventral occipito-temporal response to words depends on language lateralization but not on visual familiarity

Cereb. Cortex

Different activation patterns in the visual cortex of late and congenitally blind subjects

Brain

A ventral visual stream reading center independent of visual experience

Curr. Biol.

The fusiform face area: a module in human extrastriate cortex specialized for the perception of faces

J. Neurosci.

Separate face and body selectivity on the fusiform gyrus

J. Neurosci.

The functional architecture of the ventral temporal cortex and its role in categorization

Nat. Rev. Neurosci.

Cortical representations of symbols, objects, and faces are pruned back during early childhood

Opinion
Origins of the specialization for letters and numbers in ventral occipitotemporal cortex