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Electrophysiological correlates of consciousness
Stockholm University, Faculty of Social Sciences, Department of Psychology.ORCID iD: 0000-0001-9924-5486
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

How does the brain enable us to experience seeing or hearing a stimulus? If a stimulus is repeatedly presented at the awareness threshold, subjects will report that they are aware of the stimulus on half of the presentations. Electroencephalography (EEG) can be used to non-invasively record neural activity as event-related potentials (ERPs). The contrastive analysis of neural activity to trials rated as aware minus neural activity to trials rated as unaware reveals the neural correlates of consciousness (NCC). Research on the NCC in vision has resulted in two ERPs: an early negative difference wave (visual awareness negativity, VAN) and a subsequent late positivity (LP). Visual awareness may be reflected by one or both of these ERPs. However, the contrastive analysis (aware minus unaware) may not isolate the NCC because it arguably compares aware processing with a combination of unaware processing and no processing. In support, previous research that tried to isolate a comparison between aware processing and unaware processing found that LP was the only NCC. However, subsequent replications suggested VAN and LP as NCC. Because of these mixed results, we followed up on these studies in Study I with a preregistered design that manipulated stimulus size. Results showed VAN and LP as NCC. The findings provide evidence for VAN as an early NCC.

Another main goal of this thesis was to investigate auditory awareness. In Study II, an auditory threshold task was used, and the contrastive analysis revealed an early negative difference wave (auditory awareness negativity, AAN) and LP. These ERPs are comparable to VAN and LP in vision. Because post-perceptual processes related to responding may confound the NCC in contrastive analysis, no-response tasks can be used to isolate awareness-related activity. In vision, a previous study in which the manual response requirement was manipulated showed effects on LP but not on VAN. In Study III, we used a similar task with auditory stimuli at the awareness threshold. Results suggested that AAN and LP are unaffected by the response manipulation. However, the present no-response task may not be optimal for removing post-perceptual processing because subjects need to reflect on their experience even if they do not need to respond manually. Additional analyses that attempted source localization of the AAN suggested that it is generated in auditory cortex.

From a theoretical perspective, one view of these results is that VAN and AAN reflect local recurrent processing and that this is the neural signature of awareness, whereas LP reflects global recurrent processing that enables reporting. Other views suggest that VAN and AAN merely reflect preconscious processes, whereas LP and global recurrent processing reflect consciousness. The studies described in this thesis do not support one theory over the other but provide robust evidence for early neural correlates of visual and auditory awareness.

Place, publisher, year, edition, pages
Stockholm: Department of Psychology, Stockholm University , 2019. , p. 70
Keywords [en]
neural correlates of consciousness, electroencephalography, event-related potentials, visual awareness negativity, auditory awareness negativity, recurrent processing, phenomenal consciousness, access consciousness
National Category
Psychology (excluding Applied Psychology)
Research subject
Psychology
Identifiers
URN: urn:nbn:se:su:diva-172804ISBN: 978-91-7797-795-7 (print)ISBN: 978-91-7797-796-4 (electronic)OAI: oai:DiVA.org:su-172804DiVA, id: diva2:1350713
Public defence
2019-10-30, David Magnussonsalen (U31), Frescati Hagväg 8, Stockholm, 09:00 (English)
Opponent
Supervisors
Available from: 2019-10-07 Created: 2019-09-12 Last updated: 2019-09-18Bibliographically approved
List of papers
1. Visual awareness negativity is an early neural correlate of awareness: A preregistered study with two Gabor sizes
Open this publication in new window or tab >>Visual awareness negativity is an early neural correlate of awareness: A preregistered study with two Gabor sizes
2018 (English)In: Cognitive, Affective, & Behavioral Neuroscience, ISSN 1530-7026, E-ISSN 1531-135X, Vol. 18, no 1, p. 176-188Article in journal (Refereed) Published
Abstract [en]

Electrophysiological recordings are commonly used to study the neural correlates of consciousness in humans. Previous research is inconsistent as to whether awareness can be indexed with visual awareness negativity (VAN) at about 200 ms or if it occurs later. The present study was preregistered with two main aims: First, to provide independent evidence for or against the presence of VAN, and second, to study whether stimulus size may account for the inconsistent findings. Subjects were shown low-contrast Gaussian filtered gratings (Gabor patches) in the four visual quadrants. Gabor size (large and small) was varied in different sessions and calibrated to each subject’s threshold of visual awareness. Event-related potentials were derived from trials in which subjects localized the Gabors correctly to capture the difference between trials in which they reported awareness versus no awareness. Bayesian analyses revealed very strong evidence for the presence of VAN for both Gabor sizes. However, there was no evidence for or against an effect of stimulus size. The present findings provide evidence for VAN as an early neural correlate of awareness.

Keywords
visual awareness, event-related potentials, visual awareness negativity, late positivity, Gabor size
National Category
Psychology (excluding Applied Psychology)
Research subject
Psychology
Identifiers
urn:nbn:se:su:diva-152248 (URN)10.3758/s13415-018-0562-z (DOI)000425984100014 ()
Available from: 2018-01-29 Created: 2018-01-29 Last updated: 2019-09-12Bibliographically approved
2. Auditory awareness negativity is an electrophysiological correlate of awareness in an auditory threshold task
Open this publication in new window or tab >>Auditory awareness negativity is an electrophysiological correlate of awareness in an auditory threshold task
2019 (English)In: Consciousness and Cognition, ISSN 1053-8100, E-ISSN 1090-2376, Vol. 71, p. 70-78Article in journal (Refereed) Published
Abstract [en]

One theory of visual awareness proposes that electrophysiological activity related to awareness occurs in primary visual areas approximately 200 ms after stimulus onset (visual awareness negativity: VAN) and in fronto-parietal areas about 300 ms after stimulus onset (late positivity: LP). Although similar processes might be involved in auditory awareness, only sparse evidence exists for this idea. In the present study, we recorded electrophysiological activity while subjects listened to tones that were presented at their own awareness threshold. The difference in electrophysiological activity elicited by tones that subjects reported being aware of versus unaware of showed an early negativity about 200 ms and a late positivity about 300 ms after stimulus onset. These results closely match those found in vision and provide convincing evidence for an early negativity (auditory awareness negativity: AAN), as well as an LP. These findings suggest that theories of visual awareness are also applicable to auditory awareness.

Keywords
Awareness, Consciousness, Auditory, Electroencephalography, Threshold, Auditory awareness negativity, Late positivity
National Category
Psychology
Research subject
Psychology
Identifiers
urn:nbn:se:su:diva-169269 (URN)10.1016/j.concog.2019.03.008 (DOI)000466834200006 ()30928900 (PubMedID)
Available from: 2019-06-11 Created: 2019-06-11 Last updated: 2019-09-12Bibliographically approved
3. Effects of a Manual Response Requirement on Early and Late Correlates of Auditory Awareness
Open this publication in new window or tab >>Effects of a Manual Response Requirement on Early and Late Correlates of Auditory Awareness
2019 (English)In: Frontiers in Psychology, ISSN 1664-1078, E-ISSN 1664-1078, Vol. 10, article id 2083Article in journal (Refereed) Published
Abstract [en]

In hearing, two neural correlates of awareness are the auditory awareness negativity (AAN) and the late positivity (LP). These correlates of auditory awareness are typically observed with tasks in which subjects are required to report their awareness with manual responses. Thus, the correlates may be confounded by this manual response requirement. We manipulated the response requirement in a tone detection task (N = 52). Tones were presented at each subject’s individual awareness threshold while high-density electroencephalography (EEG) activity was recorded. In one response condition, subjects pushed a button if they were aware of the tone and withheld responding if they were unaware of the tone. In the other condition, subjects pushed a button if they were unaware of the tone and withheld responding if they were aware of the tone. To capture AAN and LP, difference waves were computed between aware and unaware trials, separately for trials in which responses were required and trials in which responses were not required. Results suggest that AAN and LP are unaffected by the response requirement. These findings imply that in hearing, early and late correlates of awareness are not confounded by a manual response requirement. Furthermore, the results suggest that AAN originates from bilateral auditory cortices, supporting the view that AAN is a neural correlate of localized recurrent processing in early sensory areas.

Keywords
auditory awareness negativity, late positivity, consciousness, response requirement, source analysis
National Category
Psychology (excluding Applied Psychology)
Research subject
Psychology
Identifiers
urn:nbn:se:su:diva-172802 (URN)10.3389/fpsyg.2019.02083 (DOI)000484968300002 ()
Available from: 2019-09-10 Created: 2019-09-10 Last updated: 2019-10-14Bibliographically approved

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