A new empirical challenge for local theories of consciousness

Local theories of consciousness state that one is conscious of a feature if it is adequately represented and processed in sensory brain areas, given some background conditions. We challenge the core prediction of local theories based on recently discovered long-lasting postdictive effects demonstrating that features can be represented for hundreds of milliseconds in perceptual areas without being consciously perceived. Unlike previous empirical data aimed against local theories, proponents of local theories cannot explain these effects away by conjecturing that subjects are phenomenally conscious of features that they cannot report. Only a strong and counterintuitive version of this claim can account for long-lasting postdictive effects. Although possible, we argue that adopting this strong version of the “overflow hypothesis” would have the effect of nullifying the weight of the evidence taken to support local theories of consciousness in the first place. We also discuss several alternative explanations that proponents of local theories could offer

Is the primary visual cortex necessary for blindsight-like behavior? Review of transcranial magnetic stimulation studies in neurologically healthy individuals

The visual pathways that bypass the primary visual cortex (V1) are often assumed to support visually guided behavior in humans in the absence of conscious vision. This conclusion is largely based on findings on patients: V1 lesions cause blindness but sometimes leave some visually guided behaviors intact-this is known as blindsight. With the aim of examining how well the findings on blindsight patients generalize to neurologically healthy individuals, we review studies which have tried to uncover transcranial magnetic stimulation (TMS) induced blindsight. In general, these studies have failed to demonstrate a completely unconscious blindsight-like capacity in neurologically healthy individuals. A possible exception to this is TMS-induced blindsight of stimulus presence or location. Because blindsight in patients is often associated with some form of introspective access to the visual stimulus, and blindsight may be associated with neural reorganization, we suggest that rather than revealing a dissociation between visually guided behavior and conscious seeing, blindsight may reflect preservation or partial recovery of conscious visual perception after the lesion

Inattentional Blindness: Neural Correlates and Theoretical Progress

Consciousness has remained one of the most perplexing enigmas of science and philosophy. Modern neuroscientific research seeks to understand how consciousness emerges within biological systems through identifying the necessary mechanisms that enable sensory information to be consciously experienced. Inattentional blindness (IB), the failure to notice something right in front of you, offers a profound means of studying consciousness, as it highlights the indistinct boundary between the conscious and the unconscious. The primary goal of the current thesis was to contribute to a scientific understanding of consciousness through advancing knowledge on IB. To this end, two reviews and four empirical studies were conducted. The first review provides a qualitative synthesis of empirical literature on IB that has employed neuroscientific methodology. Findings suggest that neural correlates of consciousness under conditions of IB may favour early sensory views of consciousness, however more research is needed. The second review provides a systematic review of the behavioural literature on IB, with focus on its two leading theories. Findings highlight that no theory can yet fully account for IB, and a model of IB is proposed based on the partial awareness hypothesis. Study one investigates the relation between alpha-band neural activity and IB via electroencephalography (EEG). Results indicate that a reduction in alpha activity in the pre- and post-stimulus interval correlates with consciousness of the critical stimulus during IB. Study two employs transcranial alternating current stimulation (tACS) to examine a causal role of alpha activity in IB. Findings indicate that, relative to control conditions, those stimulated at alpha frequency were more likely to be subject to IB. Study three extends on study two by implementing auditory tone trains at various frequencies during IB. Results show no difference in rates of IB based on auditory tone frequency. Study four then addresses the degree to which semantic processing, as indexed via the N400, can occur under conditions of IB. Findings show that no significant N400 activity is observed when the eliciting stimuli are rendered unconscious via IB. Overall, the implications of the current thesis are that alpha activity has a reliable, and potentially causal, relationship with IB; that a coherent explanation of IB is yet to exist, but may be found in reconsidering the traditional view of visual consciousness more broadly; and that the endowment of meaning to sensory information may be a key function of consciousness

Basic prediction mechanisms as a precursor for schizophrenia studies

Traditionally, early visual cortex (V1-3) was thought of as merely a relay centre for feedforward retinal input, providing entry to the cortical visual processing steam. However, in addition to feedforward retinal input, V1 receives a large amount of intracortical information through feedback and lateral connections. Human visual perception is constructed from combining feedforward inputs with these feedback and lateral contributions. Feedback connections allow the visual cortical response to feedforward information to be affected by expectation, knowledge, and context; even at the level of early visual cortex. In Chapter 1 we discuss the feedforward and feedback visual processing streams. We consider historical philosophical and scientific propositions about constructive vision. We introduce modern theories of constructive vision, which suggest that vision is an active process that aims to infer or predict the cause of sensory inputs. We discuss how V1 therefore represents not only retinal input but also high-level effects related to constructive predictive perception. Visual illusions are a ‘side effect’ of constructive and inferential visual perception. For the vast majority of stimulus inputs, integration with context and knowledge facilitates clearer, more veridical perception. In illusion these constructive mechanisms produce incorrect percepts. Illusory effects can be observed in early visual cortex, even when there is no change in the feedforward visual input. We suggest that illusions therefore provide us with a tool to probe feedforward and feedback integration, as they exploit the difference between retinal stimulation and resulting perception. Thus, illusions allow us to see the changes in activation and perception induced only by feedback without changes in feedforward input. We discuss a few specific examples of illusion generation through feedback and the accompanying effects on V1 processing. In Schizophrenia, the integration of feedback and feedforward information is thought to be dysfunctional, with unbalanced contributions of the two sources. This is evidenced by disrupted contextual binding in visual perception and corresponding deficits in contextual illusion perception. We propose that illusions can provide a window into constructive and inferential visual perception in Schizophrenia. Use of illusion paradigms could help elucidate the deficits existing within feedback and feedforward integration. If we can establish clear effects of illusory feedback to V1 in a typical population, we can apply this knowledge to clinical subjects to observe the differences in feedback and feedforward information. Chapter 2 describes a behavioural study of the rubber hand illusion. We probe how multimodal illusory experience arises under varying reliabilities of visuotactile feedforward input. We recorded Likert ratings of illusion experience from subjects, after their hidden hand was stimulated either synchronously or asynchronously with a visible rubber hand (200, 300, 400, or 600ms visuotactile asynchronicity). We used two groups, assessed by a questionnaire measuring a subject’s risk of developing Schizophrenia - moderate/high scorers and a control group of zero-scorers. We therefore consider how schizotypal symptoms contribute to rubber hand illusory experience and interact with visuotactile reliability. Our results reveal that the impact of feedforward information on higher level illusory body schema is modulated by its reliability. Less reliable feedforward inputs (increasing asynchronicity) reduce illusion perception. Our data suggests that some illusions may not be affected on a spectrum of schizotypal traits but only in the full schizophrenic disorder, as we found no effect of group on illusion perception. In Chapter 3 we present an fMRI investigation of the rubber hand illusion in typical participants. Cortical feedback allows information about other modalities and about cognitive states to be represented at the level of V1. Using a multimodal illusion, we investigated whether crossmodal and illusory states could be represented in early visual cortex in the absence of differential visual input. We found increased BOLD activity in motion area V5 and global V1 when the feedforward tactile information and the illusory outcome were incoherent (for example when the subject was experiencing the illusion during asynchronous stimulation). This is suggestive of increased predictive error, supporting predictive coding models of cognitive function. Additionally, we reveal that early visual cortex contains pattern representations specific to the illusory state, irrespective of tactile stimulation and under identical feedforward visual input. In Chapter 4 we use the motion-induced blindness illusion to demonstrate that feedback modulates stimulus representations in V1 during illusory disappearance. We recorded fMRI data from subjects viewing a 2D cross array rotating around a central axis, passing over an oriented Gabor patch target (45°/ 135°). We attempted to decode the target orientation from V1 when the target was either visible or invisible to subjects. Target information could be decoded during target visibility but not during motion-induced blindness. This demonstrates that the target representation in V1 is distorted or destroyed when the target is perceptually invisible. This illusion therefore has effects not only at higher cortical levels, as previously shown, but also in early sensory areas. The representation of the stimulus in V1 is related to perceptual awareness. Importantly, Chapter 4 demonstrated that intracortical processing can disturb constant feedforward information and overwrite feedforward representations. We suggest that the distortion observed occurs through feedback from V5 about the cross array in motion, overwriting feedforward orientation information. The flashed face distortion illusion is a relatively newly discovered illusion in which quickly presented faces become monstrously distorted. The neural underpinnings of the illusion remain unclear; however it has been hypothesised to be a face-specific effect. In Chapter 5 we challenged this account by exploiting two hallmarks of face-specific processing - the other-race effect and left visual field superiority. In two experiments, two ethnic groups of subjects viewed faces presented bilaterally in the visual periphery. We varied the race of the faces presented (same or different than subject), the visual field that the faces were presented in, and the duration of successive presentations (250, 500, 750 or 1000ms per face before replacement). We found that perceived distortion was not affected by stimulus race, visual field, or duration of successive presentations (measured by forced choice in experiment 1 and Likert scale in experiment 2). We therefore provide convincing evidence that FFD is not face-specific and instead suggest that it is an object-general effect created by comparisons between successive stimuli. These comparisons are underlined by a fed back higher level model which dictates that objects cannot immediately replace one another in the same retinotopic space without movement. In Chapter 6 we unify these findings. We discuss how our data show fed back effects on perception to produce visual illusion; effects which cannot be explained through purely feedforward activity processing. We deliberate how lateral connections and attention effects may contribute to our results. We describe known neural mechanisms which allow for the integration of feedback and feedforward information. We discuss how this integration allows V1 to represent the content of visual awareness, including during some of the illusions presented in this thesis. We suggest that a unifying theory of brain computation, Predictive Coding, may explain why feedback exerts top-down effects on feedforward processing. Lastly we discuss how our findings, and others that demonstrate feedback and prediction effects, could help develop the study and understanding of schizophrenia, including our understanding of the underlying neurological pathologies

Visual Cortex

The neurosciences have experienced tremendous and wonderful progress in many areas, and the spectrum encompassing the neurosciences is expansive. Suffice it to mention a few classical fields: electrophysiology, genetics, physics, computer sciences, and more recently, social and marketing neurosciences. Of course, this large growth resulted in the production of many books. Perhaps the visual system and the visual cortex were in the vanguard because most animals do not produce their own light and offer thus the invaluable advantage of allowing investigators to conduct experiments in full control of the stimulus. In addition, the fascinating evolution of scientific techniques, the immense productivity of recent research, and the ensuing literature make it virtually impossible to publish in a single volume all worthwhile work accomplished throughout the scientific world. The days when a single individual, as Diderot, could undertake the production of an encyclopedia are gone forever. Indeed most approaches to studying the nervous system are valid and neuroscientists produce an almost astronomical number of interesting data accompanied by extremely worthy hypotheses which in turn generate new ventures in search of brain functions. Yet, it is fully justified to make an encore and to publish a book dedicated to visual cortex and beyond. Many reasons validate a book assembling chapters written by active researchers. Each has the opportunity to bind together data and explore original ideas whose fate will not fall into the hands of uncompromising reviewers of traditional journals. This book focuses on the cerebral cortex with a large emphasis on vision. Yet it offers the reader diverse approaches employed to investigate the brain, for instance, computer simulation, cellular responses, or rivalry between various targets and goal directed actions. This volume thus covers a large spectrum of research even though it is impossible to include all topics in the extremely diverse field of neurosciences

Conscious and unconscious somatosensory perception and its modulation by attention

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 .................................................... 15

Augmentation of Brain Function: Facts, Fiction and Controversy. Volume III: From Clinical Applications to Ethical Issues and Futuristic Ideas

The final volume in this tripartite series on Brain Augmentation is entitled “From Clinical Applications to Ethical Issues and Futuristic Ideas”. Many of the articles within this volume deal with translational efforts taking the results of experiments on laboratory animals and applying them to humans. In many cases, these interventions are intended to help people with disabilities in such a way so as to either restore or extend brain function. Traditionally, therapies in brain augmentation have included electrical and pharmacological techniques. In contrast, some of the techniques discussed in this volume add specificity by targeting select neural populations. This approach opens the door to where and how to promote the best interventions. Along the way, results have empowered the medical profession by expanding their understanding of brain function. Articles in this volume relate novel clinical solutions for a host of neurological and psychiatric conditions such as stroke, Parkinson’s disease, Huntington’s disease, epilepsy, dementia, Alzheimer’s disease, autism spectrum disorders (ASD), traumatic brain injury, and disorders of consciousness. In disease, symptoms and signs denote a departure from normal function. Brain augmentation has now been used to target both the core symptoms that provide specificity in the diagnosis of a disease, as well as other constitutional symptoms that may greatly handicap the individual. The volume provides a report on the use of repetitive transcranial magnetic stimulation (rTMS) in ASD with reported improvements of core deficits (i.e., executive functions). TMS in this regard departs from the present-day trend towards symptomatic treatment that leaves unaltered the root cause of the condition. In diseases, such as schizophrenia, brain augmentation approaches hold promise to avoid lengthy pharmacological interventions that are usually riddled with side effects or those with limiting returns as in the case of Parkinson’s disease. Brain stimulation can also be used to treat auditory verbal hallucination, visuospatial (hemispatial) neglect, and pain in patients suffering from multiple sclerosis. The brain acts as a telecommunication transceiver wherein different bandwidth of frequencies (brainwave oscillations) transmit information. Their baseline levels correlate with certain behavioral states. The proper integration of brain oscillations provides for the phenomenon of binding and central coherence. Brain augmentation may foster the normalization of brain oscillations in nervous system disorders. These techniques hold the promise of being applied remotely (under the supervision of medical personnel), thus overcoming the obstacle of travel in order to obtain healthcare. At present, traditional thinking would argue the possibility of synergism among different modalities of brain augmentation as a way of increasing their overall effectiveness and improving therapeutic selectivity. Thinking outside of the box would also provide for the implementation of brain-to-brain interfaces where techniques, proper to artificial intelligence, could allow us to surpass the limits of natural selection or enable communications between several individual brains sharing memories, or even a global brain capable of self-organization. Not all brains are created equal. Brain stimulation studies suggest large individual variability in response that may affect overall recovery/treatment, or modify desired effects of a given intervention. The subject’s age, gender, hormonal levels may affect an individual’s cortical excitability. In addition, this volume discusses the role of social interactions in the operations of augmenting technologies. Finally, augmenting methods could be applied to modulate consciousness, even though its neural mechanisms are poorly understood. Finally, this volume should be taken as a debate on social, moral and ethical issues on neurotechnologies. Brain enhancement may transform the individual into someone or something else. These techniques bypass the usual routes of accommodation to environmental exigencies that exalted our personal fortitude: learning, exercising, and diet. This will allow humans to preselect desired characteristics and realize consequent rewards without having to overcome adversity through more laborious means. The concern is that humans may be playing God, and the possibility of an expanding gap in social equity where brain enhancements may be selectively available to the wealthier individuals. These issues are discussed by a number of articles in this volume. Also discussed are the relationship between the diminishment and enhancement following the application of brain-augmenting technologies, the problem of “mind control” with BMI technologies, free will the duty to use cognitive enhancers in high-responsibility professions, determining the population of people in need of brain enhancement, informed public policy, cognitive biases, and the hype caused by the development of brain- augmenting approaches