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Methods to Explore the Influence of Top-down Visual Processes on Motor Behavior
Published on: April 16, 2014
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Differential modulation of visual object processing in dorsal and ventral stream by stimulus visibility
Karin Ludwig1, Philipp Sterzer2, Norbert Kathmann3
1Visual Perception Laboratory, Department of Psychiatry and Psychotherapy, Campus Charité Mitte, Charité - Universitätsmedizin Berlin, Germany; Department of Psychology, Humboldt-Universität zu Berlin, Germany.
Summary
The influential "two visual systems" hypothesis suggests distinct roles for dorsal and ventral visual streams in awareness. This study found both streams are linked to visual awareness, but ventral areas more closely reflect graded awareness differences.
Area of Science:
- Neuroscience
- Cognitive Neuroscience
- Visual Perception
Background:
- The "two visual systems" hypothesis posits separate dorsal (action) and ventral (perception) visual streams.
- A key assumption is that ventral stream processing is linked to awareness, while dorsal stream processing is not.
Purpose of the Study:
- To investigate the relationship between stimulus visibility and neural information processing in both dorsal and ventral visual streams.
- To test the differential involvement of visual streams in visual awareness using fMRI.
Main Methods:
- Functional magnetic resonance imaging (fMRI) was used in human observers.
- Stimulus visibility was parametrically modulated using a continuous flash suppression (CFS) paradigm with varying mask contrasts.
- Stimulus-related information in fMRI response patterns was analyzed in relation to visibility measures.
Main Results:
- Stimulus visibility decreased linearly with increasing CFS mask contrast, confirmed by objective and subjective measures.
- Ventral visual areas showed a linear decrease in stimulus-related information with increasing mask contrast.
- Dorsal visual areas exhibited a step-like decrease in stimulus-related information, rather than a linear one.
Conclusions:
- Both ventral and dorsal visual streams are associated with visual awareness.
- Neural activity in ventral areas more accurately reflects graded changes in visual awareness compared to dorsal areas.
- The findings challenge the strict dichotomy of awareness proposed by the "two visual systems" hypothesis.
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