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The neural representation of Arabic digits in visual cortex.

Peters L, De Smedt B, Op de Beeck HP - Front Hum Neurosci (2015)

Bottom Line: In this study, we investigated how Arabic digits are represented in the visual cortex, and how their representation changes throughout the ventral visual processing stream, compared to the representation of letters.However, the activity in this region might have been confounded by string length-number words contain more characters than digits.We found an alteration in representations throughout the ventral processing stream from clustering based on amount of visual information in primary visual cortex (V1) towards clustering based on symbolic stimulus category higher in the visual hierarchy.

View Article: PubMed Central - PubMed

Affiliation: Parenting and Special Education Research Unit, KU Leuven Leuven, Belgium, Europe.

ABSTRACT
In this study, we investigated how Arabic digits are represented in the visual cortex, and how their representation changes throughout the ventral visual processing stream, compared to the representation of letters. We probed these questions with two functional magnetic resonance imaging (fMRI) experiments. In Experiment 1, we explored whether we could find brain regions that were more activated for digits than for number words in a subtraction task. One such region was detected in lateral occipital cortex. However, the activity in this region might have been confounded by string length-number words contain more characters than digits. We therefore conducted a second experiment in which string length was systematically controlled. Experiment 2 revealed that the findings of the first experiment were task dependent (as it was only observed in a task in which numerosity was relevant) or stimulus dependent (as it was only observed when the number of characters of a stimulus was not controlled). We further explored the characteristics of the activation patterns for digit and letter strings across the ventral visual processing stream through multi-voxel pattern analyses. We found an alteration in representations throughout the ventral processing stream from clustering based on amount of visual information in primary visual cortex (V1) towards clustering based on symbolic stimulus category higher in the visual hierarchy. The present findings converge to the conclusion that in the ventral visual system, as far as can be detected with fMRI, the distinction between Arabic digits and letter strings is represented in terms of distributed patterns rather than separate regions.

No MeSH data available.


Mean activation elicited by the three format conditions in the three regions of interest in Experiment 1. Error bars represent standard error of the mean.
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Figure 7: Mean activation elicited by the three format conditions in the three regions of interest in Experiment 1. Error bars represent standard error of the mean.

Mentions: Next, we analyzed the data in our three visual regions of interest, i.e., V1, LOC and VWFA. (Figures 7–8). In V1, dot arrays and number words elicited more activation than Arabic digits did (both p’s < 0.001), whereas dot arrays and number words did not differ in terms of activation (p = 0.07). The same pattern was found, though with smaller effect size, in LOC: dot arrays and number words activated this region more than Arabic digits did (p = 0.003 and p = 0.01, respectively), whereas dot arrays and number words did not differ in terms of activation (p = 0.91). Furthermore, this analysis revealed that the lateral occipital region specifically activated by Arabic symbols was not overlapping with our functionally defined LOC. Finally, in the third a priori defined region of interest, the VWFA, we found significantly more activation for number words than for digits (p < 0.001), and higher activation for digits than for dot arrays (p = 0.005).


The neural representation of Arabic digits in visual cortex.

Peters L, De Smedt B, Op de Beeck HP - Front Hum Neurosci (2015)

Mean activation elicited by the three format conditions in the three regions of interest in Experiment 1. Error bars represent standard error of the mean.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4585091&req=5

Figure 7: Mean activation elicited by the three format conditions in the three regions of interest in Experiment 1. Error bars represent standard error of the mean.
Mentions: Next, we analyzed the data in our three visual regions of interest, i.e., V1, LOC and VWFA. (Figures 7–8). In V1, dot arrays and number words elicited more activation than Arabic digits did (both p’s < 0.001), whereas dot arrays and number words did not differ in terms of activation (p = 0.07). The same pattern was found, though with smaller effect size, in LOC: dot arrays and number words activated this region more than Arabic digits did (p = 0.003 and p = 0.01, respectively), whereas dot arrays and number words did not differ in terms of activation (p = 0.91). Furthermore, this analysis revealed that the lateral occipital region specifically activated by Arabic symbols was not overlapping with our functionally defined LOC. Finally, in the third a priori defined region of interest, the VWFA, we found significantly more activation for number words than for digits (p < 0.001), and higher activation for digits than for dot arrays (p = 0.005).

Bottom Line: In this study, we investigated how Arabic digits are represented in the visual cortex, and how their representation changes throughout the ventral visual processing stream, compared to the representation of letters.However, the activity in this region might have been confounded by string length-number words contain more characters than digits.We found an alteration in representations throughout the ventral processing stream from clustering based on amount of visual information in primary visual cortex (V1) towards clustering based on symbolic stimulus category higher in the visual hierarchy.

View Article: PubMed Central - PubMed

Affiliation: Parenting and Special Education Research Unit, KU Leuven Leuven, Belgium, Europe.

ABSTRACT
In this study, we investigated how Arabic digits are represented in the visual cortex, and how their representation changes throughout the ventral visual processing stream, compared to the representation of letters. We probed these questions with two functional magnetic resonance imaging (fMRI) experiments. In Experiment 1, we explored whether we could find brain regions that were more activated for digits than for number words in a subtraction task. One such region was detected in lateral occipital cortex. However, the activity in this region might have been confounded by string length-number words contain more characters than digits. We therefore conducted a second experiment in which string length was systematically controlled. Experiment 2 revealed that the findings of the first experiment were task dependent (as it was only observed in a task in which numerosity was relevant) or stimulus dependent (as it was only observed when the number of characters of a stimulus was not controlled). We further explored the characteristics of the activation patterns for digit and letter strings across the ventral visual processing stream through multi-voxel pattern analyses. We found an alteration in representations throughout the ventral processing stream from clustering based on amount of visual information in primary visual cortex (V1) towards clustering based on symbolic stimulus category higher in the visual hierarchy. The present findings converge to the conclusion that in the ventral visual system, as far as can be detected with fMRI, the distinction between Arabic digits and letter strings is represented in terms of distributed patterns rather than separate regions.

No MeSH data available.