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Evidence for a Posterior Parietal Cortex Contribution to Spatial but not Temporal Numerosity Perception
Seda Cavdaroglu1, André Knops2,3
1Department of Psychology, Humboldt-Universität zu Berlin, Berlin, Germany.
Cerebral Cortex (New York, N.Y. : 1991)
|July 31, 2018
Summary
The posterior parietal cortex (PPC) may not have a shared neural basis for representing object numbers, whether seen at once or in sequence. This study suggests spatial numerosity processing in the PPC, but not temporal numerosity.
Area of Science:
- Cognitive Neuroscience
- Neuroimaging
Background:
- The posterior parietal cortex (PPC) is hypothesized to be a key area for representing numerical quantity (numerosity).
- A significant debate exists regarding whether the neural mechanisms for processing numerosity are independent of stimulus presentation mode (simultaneous vs. sequential).
Purpose of the Study:
- To investigate the existence of a common neural substrate for encoding numerosity across simultaneous and sequential visual stimuli using functional magnetic resonance imaging (fMRI).
- To determine if the posterior parietal cortex (PPC) exhibits mode-independent numerosity representation.
Main Methods:
- Functional magnetic resonance imaging (fMRI) was employed to measure brain activity in participants viewing visual stimuli with varying numerosities.
- Multivoxel pattern analysis (MVPA) and voxel-wise numerosity tuning functions were used to analyze brain activation patterns in specific regions of interest (ROIs).
Main Results:
- Both simultaneous and sequential numerosities activated overlapping regions in the occipital cortex.
- The PPC showed significant activation for simultaneous numerosities but not for sequential ones.
- Bilateral temporal areas were uniquely activated by sequential numerosities.
- MVPA indicated numerosity selectivity in the PPC exclusively for simultaneous stimuli, highlighting differential encoding based on presentation mode.
- An occipito-to-parietal gradient of increasing numerosity selectivity was observed for simultaneous stimuli.
Conclusions:
- The findings suggest that the parietal cortex is critically involved in processing spatial numerosity (simultaneous stimuli) but not temporal numerosity (sequential stimuli).
- The results challenge the notion of a unified, mode-independent neural circuit for numerosity representation, indicating distinct processing pathways for different stimulus types.
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