A Brain Area for Visual Numerals

Abstract

Is there a distinct area within the human visual system that has a preferential response to numerals, as there is for faces, words, or scenes? We addressed this question using intracranial electrophysiological recordings and observed a significantly higher response in the high-frequency broadband range (high γ, 65–150 Hz) to visually presented numerals, compared with morphologically similar (i.e., letters and false fonts) or semantically and phonologically similar stimuli (i.e., number words and non-number words). Anatomically, this preferential response was consistently localized in the inferior temporal gyrus and anterior to the temporo-occipital incisure. This region lies within or close to the fMRI signal-dropout zone produced by the nearby auditory canal and venous sinus artifacts, an observation that may account for negative findings in previous fMRI studies of preferential response to numerals. Because visual numerals are culturally dependent symbols that are only learned through education, our novel finding of anatomically localized preferential response to such symbols provides a new example of acquired category-specific responses in the human visual system.

Mapping human temporal and parietal neuronal population activity and functional coupling during mathematical cognition

“…We refer to this numeral-selective pITG site as the "number form area" (NFA). These findings in a new subcohort of subjects confirmed our previous report of a numeral-selective brain region (37).…”

“…Our analyses were aimed first at characterizing the response properties of subregions within the VTC and LPC to confirm the presence of numeral-and/or math-selective neuronal populations that we and other groups have reported previously (20,22,23,37,39,40). Next, we measured the relative timing of the activation of each of these regions during arithmetic computations.…”

“…Recently, our group used intracranial electrocorticography (ECoG) to confirm the existence of a site within the posterior inferior temporal gyrus (pITG) that selectively responds to visual numerals relative to letters, false fonts, number words, and words (37). This pITG site is located in an area subject to strong susceptibility artifact with fMRI (38,39); however, numeral selectivity within the pITG has since been demonstrated with fMRI using advanced techniques to increase the signal-to-noise ratio in this region (38,39).…”

Music and words in the visual cortex: The impact of musical expertise

“…In humans, there is also evidence for segregated activations for letters and numerals in the fusiform gyrus (Polk et al, 2002;Shum et al, 2013;Abboud et al, 2015), and for Chinese vs alphabetic stimuli in the early visual cortex (Szwed et al, 2014). There are also some indications of segregated activations for printed words and musical notation in the occipitotemporal cortex (Wong and Gauthier, 2010a), but this evidence is controversial (Muayqil et al, 2015) and is not supported by statistical comparisons of activation topography between words and music.…”

Is VIRTU4L larger than VIR7UAL? Automatic processing of number quantity and lexical representations in leet words.

“…The idea was that neural overlap would imply sharing resources whereas non-overlapping neural representations would imply separate representational resources (Cohen et al, 2014). In the present experiment, one can formulate a parallel explanation: When presented with leet words, letters are normalized in the "visual word-form" area (Cohen et al, 2000, Polk et al, 2002, whereas digits would be (independently) recognized in the inferior temporal gyrus (the "visual number-form" area; see Shum et al, 2013). If so, a leet word like VIR7UAL would partially activate these two brain areas.…”