Our brains handle vast amounts of information incoming through our senses.
Continuously exposed to sensory input, the sense of touch, however, may miss tactile stimuli, no matter how much attention we pay to them. In four empirical studies, this thesis tested (1) the feasibility of investigating undetectable stimulation by electrical finger nerve pulses, (2) how its neural correlates dissociate from detectable stimulation and (3) whether and how selective somatosensory attention nevertheless affects the neural representation of undetectable stimuli. The first two studies showed that there is a natural
range of electrical stimulation intensities that cannot be detected. A rigorous statistical evaluation with Bayes factor analysis indicated that the evidence of chance performance after undetectable stimulation reliably outweighed evidence of above-chance performance. A subsequent study applying electroencephalography (EEG) revealed qualitative differences between the processing of detectable and undetectable stimulation, which is evident in altered event-related potentials (ERP). Specifically, undetectable stimulation evokes a single component that is not predictive of stimulus detectability but lacks a
subsequent component, which correlates with upcoming stimulus detection. The final study showed that attention nevertheless affects neural processing of undetectable stimuli in a top-down manner as it does for detectable stimuli and fosters the view of attention and awareness being two separate and mostly independent mechanisms. The influence of the pre-stimulus oscillatory (~10 Hz) alpha amplitude—a putative marker of attentional deployment—on the ERP depended on the current attentional state and indicates that both processes are interacting but not functionally matching.:1 Touch, Consciousness, And Attention – Theoretical Considerations ........ 1-11
1.1 A Neural Account To (Un-) Consciousness ............................................ 1-12
1.2 Controlling detectability of external stimulation ...................................... 1-14
1.3 Thresholds in the light of signal detection theory ................................... 1-17
1.4 Selective attention in touch .................................................................... 1-19
1.5 Research questions ............................................................................... 1-21
2 Empirical Evidence .................................................................................... 2-25
2.1 General methods .................................................................................... 2-25
2.1.1 Stimulation ........................................................................................... 2-25
2.1.2 Threshold assessment procedure ....................................................... 2-25
2.1.3 Behavioral analysis .............................................................................. 2-26
2.1.4 Electrophysiological measurement ...................................................... 2-28
2.1.5 Analysis of event-related potentials ..................................................... 2-30
2.1.6 Spectral Analysis resolved over time ................................................... 2-30
2.2 Psychophysical assessment of subthreshold stimulation ........................ 2-33
2.2.1 A method for assessing the individual absolute detection threshold
(ADTH) ......................................................................................................... 2-33
2.2.2 Validation of absolute detection threshold assessment by signal
detection theory measures and Bayesian Null-Hypothesis testing ................ 2-39
2.3 Non-invasive neural markers of unconscious perception ....................... 2-47
2.3.1 Neural Correlates of Undetectable Somatosensory Stimulation in EEG
and fMRI ...................................................................................................... 2-47
2.3.2 Prediction of stimulus perception by features of the evoked potential for
different stimulation intensities along the psychometric function ................. 2-51
2.4 The role of Rolandic Alpha Activity in Somatosensation and its Relation
to Attention ................................................................................................. 2-75
3 General Discussion and Conclusions ...................................................... 3-101
3.1 Summary of empirical results ................................................................ 3-101
3.2 Neural processing of undetectable stimulation ..................................... 3-102
3.3 Attention, awareness and neural oscillatory activity ............................. 3-104
3.4 Limits of the current studies and future perspectives ........................... 3-109
References .................................................................................................... 113
Summary ....................................................................................................... 137
Zusammenfassung ........................................................................................ 143
Curriculum Vitae ............................................................................................ 151
Selbständigkeitserklärung ............................................................................. 155
Nachweis über die Anteile der Co-Autoren .................................................... 157
| Identifer | oai:union.ndltd.org:DRESDEN/oai:qucosa:de:qucosa:35146 |
| Date | 26 August 2019 |
| Creators | Forschack, Norman |
| Contributors | Universität Leipzig |
| Source Sets | Hochschulschriftenserver (HSSS) der SLUB Dresden |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/publishedVersion, doc-type:doctoralThesis, info:eu-repo/semantics/doctoralThesis, doc-type:Text |
| Rights | info:eu-repo/semantics/openAccess |
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