Probabilistic Adaptation and Voluntary Attention

The following experiments considered the general phenomenon of behavioural adaptation in response to statistical regularities—which we refer to as probability learning (PL). In particular, these experiments focused on spatial PL and its relationship with spatial attention. Evidence suggests that the set of neural mechanisms responsible for spatial PL might intersect with those which mediate the voluntary expression of spatial attention. Furthermore, inductions of spatial PL are typically successful in the absence of explicit awareness on the behalf of participants. These findings raise the question of whether spatial PL inductions can be used to subtly alter voluntary behaviour by altering attentional biases. If this is the case, spatial PL inductions could have a wide range of applications—for example as tools in skill training and marketing. We investigated a potential cross-task influence of spatial PL on voluntarily expressed patterns of spatial attention. We used a behavioural task based on the Tse Illusion to measure voluntary shifts in spatial attention (Illusion Task; Tse, Caplovitz, & Hsieh, 2006). We used a feature discrimination task (PL Task) derived from Druker and Anderson (2010) to induce spatial PL. Experiments 1, 2, and 3 combined the Illusion Task with the PL Task in a pre-test/post-test design. Experiment 3’s inclusion of eye tracking permitted us to explore mechanistic hypotheses concerning the cross-task translation of behavioural adaptation. All three experiments revealed that condition-specific variation of the PL Task’s spatial probability distribution produced predictable changes in PL Task performance. Experiment 3 supported the utility of eye-tracking as a tool for understanding the processes underlying spatial PL along with the impact of spatial PL on voluntary attention. We found that we could reliably induce spatially-specific changes in involuntary attention. We produced consistent and robust estimates of the impact of such spatial PL on our feature discrimination task—and, found the effect to be largely driven by changes in eye-movement generation and consequently target acquisition. Finally, we discovered that spatial PL did not influence the expression of voluntary attention in a subsequent task

Measuring gaze and pupil in the real world: object-based attention,3D eye tracking and applications

This dissertation contains studies on visual attention, as measured by gaze orientation, and the use of mobile eye-tracking and pupillometry in applications. It combines the development of methods for mobile eye-tracking (studies II and III) with experimental studies on gaze guidance and pupillary responses in patients (studies IV and VI) and healthy observers (studies I and V). Object based attention / Study I What is the main factor of fixation guidance in natural scenes? Low-level features or objects? We developed a fixation-predicting model, which regards preferred viewing locations (PVL) per object and combines these distributions over the entirety of existing objects in the scene. Object-based fixation predictions for natural scene viewing perform at par with the best early salience model, that are based on low-level features. However, when stimuli are manipulated so that low-level features and objects are dissociated, the greater prediction power of saliency models diminishes. Thus, we dare to claim, that highly developed saliency models implicitly obtain object-hood and that fixation selection is mainly influenced by objects and much less by low-level features. Consequently, attention guidance in natural scenes is object-based. 3D tracking / Study II The second study focussed on improving calibration procedures for eye-in-head positions with a mobile eye-tracker.We used a mobile eye-tracker prototype, the EyeSeeCam with a high video-oculography (VOG) sampling rate and the technical gadget to follow the users gaze direction instantaneously with a rotatable camera. For a better accuracy in eye-positioning, we explored a refinement in the implementation of the eye-in-head calibration that yields a measure for fixation distance, which led to a mobile eye-tracker 3D calibration. Additionally, by developing the analytical mechanics for parametrically reorienting the gaze-centred camera, the 3D calibration could be applied to reliably record gaze-centred videos. Such videos are suitable as stimuli for investigating gaze-behaviour during object manipulation or object recognition in real worlds point-of-view (PoV) perspective. In fact, the 3D calibration produces a higher accuracy in positioning the gaze-centred camera over the whole 3D visual range. Study III, eye-tracking methods With a further development on the EyeSeeCam we achieved to record gaze-in-world data, by superposing eye-in-head and head-in-world coordinates. This novel approach uses a combination of few absolute head-positions extracted manually from the PoV video and of relative head-shifts integrated over angular velocities and translational accelerations, both given by an inertia measurement unit (IMU) synchronized to the VOG data. Gaze-in-world data consist of room-referenced gaze directions and their origins within the environment. They easily allow to assign fixation targets by using a 3D model of the measuring environment – a strong rationalisation regarding fixation analysis. Applications Study III Daylight is an important perceptual factor for visual comfort, but can also create discomfort glare situations during office work, so we developed to measure its behavioural influences. We achieve to compare luminance distributions and fixations in a real-world setting, by also recording indoor luminance variations time-resolved using luminance maps of a scenery spanning over a 3pi sr. Luminance evaluations in the workplace environment yield a well controlled categorisation of different lighting conditions and a localisation as well as a brightness measure of glare sources.We used common tasks like reading, typing on a computer, a phone call and thinking about a subject. The 3D model gives the possibility to test for gaze distribution shifts in the presence of glare patches and for variations between lighting conditions. Here, a low contrast lighting condition with no sun inside and a high contrast lighting condition with direct sunlight inside were compared. When the participants are not engaged in any visually focused task and the presence of the task support is minimal, the dominant view directions are inclined towards the view outside the window under the low contrast lighting conditions, but this tendency is less apparent and sways more towards the inside of the room under the high contrast lighting condition. This result implicates an avoidance of glare sources in gaze behaviour. In a second more extensive series of experiments, the participants’ subjective assessments of the lighting conditions will be included. Thus, the influence of glare can be analysed in more detail and tested whether visual discomfort judgements are correlated in differences in gaze-behaviour. Study IV The advanced eye-tracker calibration found application in several following projects and included in this dissertation is an investigation with patients suffering either from idiopathic Parkinson’s disease or from progressive supranuclear palsy (PSP) syndrome. PSP’s key symptom is the decreased ability to carry out vertical saccades and thus the main diagnostic feature for differentiating between the two forms of Parkinson’s syndrome. By measuring ocular movements during a rapid (< 20s) procedure with a standardized fixation protocol, we could successfully differentiate pre-diagnosed patients between idiopathic Parkinson’s disease and PSP, thus between PSP patients and HCs too. In PSP patients, the EyeSeeCam detected prominent impairment of both saccade velocity and amplitude. Furthermore, we show the benefits of a mobile eye-tracking device for application in clinical practice. Study V Decision-making is one of the basic cognitive processes of human behaviours and thus, also evokes a pupil dilation. Since this dilation reflects a marker for the temporal occurrence of the decision, we wondered whether individuals can read decisions from another’s pupil and thus become a mentalist. For this purpose, a modified version of the rock-paper-scissors childhood game was played with 3 prototypical opponents, while their eyes were video taped. These videos served as stimuli for further persons, who competed in rock-paper-scissors. Our results show, that reading decisions from a competitor’s pupil can be achieved and players can raise their winning probability significantly above chance. This ability does not require training but the instruction, that the time of maximum pupil dilation was indicative of the opponent’s choice. Therefore we conclude, that people could use the pupil to detect cognitive decisions in another individual, if they get explicit knowledge of the pupil’s utility. Study VI For patients with severe motor disabilities, a robust mean of communication is a crucial factor for well-being. Locked-in-Syndrome (LiS) patients suffer from quadriplegia and lack the ability of articulating their voice, though their consciousness is fully intact. While classic and incomplete LiS allows at least voluntary vertical eye movements or blinks to be used for communication, total LiS patients are not able to perform such movements. What remains, are involuntarily evoked muscle reactions, like it is the case with the pupillary response. The pupil dilation reflects enhanced cognitive or emotional processing, which we successfully observed in LiS patients. Furthermore, we created a communication system based on yes-no questions combined with the task of solving arithmetic problems during matching answer intervals, that yet invokes the most solid pupil dilation usable on a trial-by-trial basis for decoding yes or no as answers. Applied to HCs and patients with various severe motor disabilities, we provide the proof of principle that pupil responses allow communication for all tested HCs and 4/7 typical LiS patients. Résumé Together, the methods established within this thesis are promising advances in measuring visual attention allocation with 3D eye-tracking in real world and in the use of pupillometry as on-line measurement of cognitive processes. The two most outstanding findings are the possibility to communicate with complete LiS patients and further a conclusive evidence that objects are the primary unit of fixation selection in natural scenes

Change blindness: eradication of gestalt strategies

Arrays of eight, texture-defined rectangles were used as stimuli in a one-shot change blindness (CB) task where there was a 50% chance that one rectangle would change orientation between two successive presentations separated by an interval. CB was eliminated by cueing the target rectangle in the first stimulus, reduced by cueing in the interval and unaffected by cueing in the second presentation. This supports the idea that a representation was formed that persisted through the interval before being 'overwritten' by the second presentation (Landman et al, 2003 Vision Research 43149–164]. Another possibility is that participants used some kind of grouping or Gestalt strategy. To test this we changed the spatial position of the rectangles in the second presentation by shifting them along imaginary spokes (by ±1 degree) emanating from the central fixation point. There was no significant difference seen in performance between this and the standard task [F(1,4)=2.565, p=0.185]. This may suggest two things: (i) Gestalt grouping is not used as a strategy in these tasks, and (ii) it gives further weight to the argument that objects may be stored and retrieved from a pre-attentional store during this task

Proceedings of the 2009 Joint Workshop of Fraunhofer IOSB and Institute for Anthropomatics, Vision and Fusion Laboratory

The joint workshop of the Fraunhofer Institute of Optronics, System Technologies and Image Exploitation IOSB, Karlsruhe, and the Vision and Fusion Laboratory (Institute for Anthropomatics, Karlsruhe Institute of Technology (KIT)), is organized annually since 2005 with the aim to report on the latest research and development findings of the doctoral students of both institutions. This book provides a collection of 16 technical reports on the research results presented on the 2009 workshop

The computational neurology of active vision

In this thesis, we appeal to recent developments in theoretical neurobiology – namely, active inference – to understand the active visual system and its disorders. Chapter 1 reviews the neurobiology of active vision. This introduces some of the key conceptual themes around attention and inference that recur through subsequent chapters. Chapter 2 provides a technical overview of active inference, and its interpretation in terms of message passing between populations of neurons. Chapter 3 applies the material in Chapter 2 to provide a computational characterisation of the oculomotor system. This deals with two key challenges in active vision: deciding where to look, and working out how to look there. The homology between this message passing and the brain networks solving these inference problems provide a basis for in silico lesion experiments, and an account of the aberrant neural computations that give rise to clinical oculomotor signs (including internuclear ophthalmoplegia). Chapter 4 picks up on the role of uncertainty resolution in deciding where to look, and examines the role of beliefs about the quality (or precision) of data in perceptual inference. We illustrate how abnormal prior beliefs influence inferences about uncertainty and give rise to neuromodulatory changes and visual hallucinatory phenomena (of the sort associated with synucleinopathies). We then demonstrate how synthetic pharmacological perturbations that alter these neuromodulatory systems give rise to the oculomotor changes associated with drugs acting upon these systems. Chapter 5 develops a model of visual neglect, using an oculomotor version of a line cancellation task. We then test a prediction of this model using magnetoencephalography and dynamic causal modelling. Chapter 6 concludes by situating the work in this thesis in the context of computational neurology. This illustrates how the variational principles used here to characterise the active visual system may be generalised to other sensorimotor systems and their disorders

Developing implant technologies and evaluating brain-machine interfaces using information theory

Brain-machine interfaces (BMIs) hold promise for restoring motor functions in severely paralyzed individuals. Invasive BMIs are capable of recording signals from individual neurons and typically provide the highest signal-to-noise ratio. Despite many efforts in the scientific community, BMI technology is still not reliable enough for widespread clinical application. The most prominent challenges include biocompatibility, stability, longevity, and lack of good models for informed signal processing and BMI comparison. To address the problem of low signal quality of chronic probes, in the first part of the thesis one such design, the Neurotrophic Electrode, was modified by increasing its channel capacity to form a Neurotrophic Array (NA). Specifically, single wires were replaced with stereotrodes and the total number of recording wires was increased. This new array design was tested in a rhesus macaque performing a delayed saccade task. The NA recorded little single unit spiking activity, and its local field potentials (LFPs) correlated with presented visual stimuli and saccade locations better than did extracted spikes. The second part of the thesis compares the NA to the Utah Array (UA), the only other micro-array approved for chronic implantation in a human brain. The UA recorded significantly more spiking units, which had larger amplitudes than NA spikes. This was likely due to differences in the array geometry and construction. LFPs on the NA electrodes were more correlated with each other than those on the UA. These correlations negatively impacted the NA's information capacity when considering more than one recording site. The final part of this dissertation applies information theory to develop objective measures of BMI performance. Currently, decoder information transfer rate (ITR) is the most popular BMI information performance metric. However, it is limited by the selected decoding algorithm and does not represent the full task information embedded in the recorded neural signal. A review of existing methods to estimate ITR is presented, and these methods are interpreted within a BMI context. A novel Gaussian mixture Monte Carlo method is developed to produce good ITR estimates with a low number of trials and high number of dimensions, as is typical for BMI applications