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Unconscious Number Discrimination in the Human Visual System
Ché Lucero1, Geoffrey Brookshire1, Clara Sava-Segal1
1Department of Psychology, University of Chicago, Chicago, IL 60637, USA.
Cerebral Cortex (New York, N.Y. : 1991)
|June 16, 2020
Summary
Humans compute approximate number within the visual system, not solely in higher brain areas. This study shows visual processing differentiates numerical ratios even without conscious awareness.
Area of Science:
- Cognitive Neuroscience
- Visual Perception
- Numerical Cognition
Background:
- The exact neural basis of approximate number system (ANS) computation remains debated.
- One theory posits amodal representations in the intraparietal sulcus, independent of sensory input.
- An alternative suggests initial computation within specific sensory systems.
Purpose of the Study:
- To investigate whether the human visual system can process approximate number.
- To determine if ANS computation occurs independently of conscious awareness and higher-order brain regions.
Main Methods:
- Used steady-state visual evoked potentials (SSVEPs) to measure brain activity.
- Presented participants with rapidly alternating dot clouds (10-20 dots) at 15 Hz, employing backward masking.
- Recorded electroencephalography (EEG) over the occipital lobe (Oz) to analyze spectral amplitude at 15 Hz.
Main Results:
- A positive correlation was found between spectral amplitude at 15 Hz over the occipital lobe and the numerical ratio of dot clouds.
- This correlation persisted even when non-numerical stimulus attributes were controlled.
- Participants could not consciously discriminate the numerosities, indicating disrupted reentrant feedback.
Conclusions:
- The visual system demonstrates sensitivity to approximate number, processing numerical ratios.
- Approximate number computation appears to occur within the visual system, preceding conscious awareness.
- Findings challenge the exclusive role of the intraparietal sulcus for initial ANS processing.
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