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  Decoding monkey's conscious experience during ambiguous and unambiguous motion percept reveals initial non-conscious spike activity and later neuronal correlates of consciousness in area MT

Tsuchiya, N., Maier, A., Logothetis, N., & Leopold, D. (2008). Decoding monkey's conscious experience during ambiguous and unambiguous motion percept reveals initial non-conscious spike activity and later neuronal correlates of consciousness in area MT. In Eighth Biennial Tucson Conference:Toward a Science of Consciousness 2008 (pp. 89).

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Item Permalink: http://hdl.handle.net/21.11116/0000-0003-AA2B-E Version Permalink: http://hdl.handle.net/21.11116/0000-0003-AA2C-D
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Tsuchiya, N, Author
Maier, A1, 2, Author              
Logothetis, NK1, 2, Author              
Leopold, D1, 2, Author              
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1Department Physiology of Cognitive Processes, Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_1497798              
2Max Planck Institute for Biological Cybernetics, Max Planck Society, ou_1497794              

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 Abstract: The class of ambiguous stimuli, such as the Necker cube or the Rubin’s vase, is a powerful tool to study the neuronal correlates of consciousness; under the constant physical stimulation, the conscious experience of the stimulus spontaneously flips back and forth over time. Provided with careful and strict control measures, it is possible to train monkeys to report their percepts as they see such an ambiguous stimulus, which allows us to record neuronal activity directly related to the conscious experience [Leopold,Maier, and Logothetis 2003 Journal of Consciousness Studies]. Previous electrophysiological studies with concurrent behavioral measurements during ambiguous percepts concentrated on the trial-by-trial relationship between the activity of isolated single neurons and monkeys’ reports. In these studies, either the stimulus or the recorded neuron was carefully selected so that the two alternative conscious experiences maximally differentiate the spike counts of the recorded neurons. Focusing on single neurons ignores a potentially information-rich signal: the temporal correlation in the spikes of neighboring neurons. We were interested to learn how and when the firing of many neurons began to reflect the conscious perception of an ambiguous stimulus over time. Specifically, we wanted to learn the extent towhich we could track the development over time of a neural correlate of consciousness. To address this issue, we trained two monkeys to report their percepts while they were seeing an ambiguous structure-from-motion stimulus. We recorded neuronal activity from the motion sensitive areaMT, with 8-10 microelectrodes, each of which was independently mobilized by micro-drives. We used a decoding approach to quantify howmonkeys’ reports are correlated with the activity of the simultaneously recordedmultiple neurons over time. For the decoding analysis, we trained a pattern classifier (regularized least square classifier) using 70\% of trials and decoded the percepts fromneural activity for a test set (the rest of 30\% of trials). The output from the classifier in the test set was submitted to signal detection analysis to obtain non-parametric bias free measure of decoding performance (area under the curve, A’). We used spike counts with a bin size of 100 msec and combined the counts from multiple neurons in each time bin in an optimal manner with linear weights estimated by the classifier. The time resolved decoding performance was compared between ambiguous and unambiguous conditions. The ambiguity was manipulated via binocular disparity. The decoding performance attained with >100 neurons in both conditions were very accurate (A’>.9. Chance decoding performance is A’=.5), although a significant difference emerged between the ambiguous and unambiguous conditions over time. For the unambiguous condition the decoding performance was very accurate from shortly after the stimulus onset (A’>.9) and remained high throughout the stimulus presentation. In a stark contrast, the decoding performance for the ambiguous condition built up gradually (almost linearly) over time, and reached at the peak (A’\verb=~=.9) at around.4-.8 sec after the stimulus onset. Our results show that the initial neuronal activity evoked by the onset of a stimulus reflects the physical properties of the input and thus is less correlated with conscious percept, while the later activity is increasingly reflective of the conscious percept of the animal.

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 Dates: 2008-04
 Publication Status: Published online
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Title: Eighth Biennial Tucson Conference:Toward a Science of Consciousness 2008
Place of Event: Tucson, AZ, USA
Start-/End Date: 2008-04-08 - 2008-04-12

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Title: Eighth Biennial Tucson Conference:Toward a Science of Consciousness 2008
Source Genre: Proceedings
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Pages: - Volume / Issue: - Sequence Number: 109 Start / End Page: 89 Identifier: -