Jan Ehlers

Pupil Size Changes as an Active Information Channel for Biofeedback Applications

Pupil size is usually regarded as a passive information channel that provides insight into cognitive and affective states but defies any further control. However, in a recent study (Ehlers et al. 2015) we demonstrate that sympathetic activity indexed by pupil dynamics allows strategic interference by means of simple cognitive techniques. Utilizing positive/negative imaginings, subjects were able to expand pupil diameter beyond baseline variations; albeit with varying degrees of success and only over brief periods. The current study provides a comprehensive replication on the basis of considerable changes to the experimental set-up. Results show that stricter methodological conditions (controlled baseline settings and specified user instructions) strengthen the reported effect, whereas overall performance increases by one standard deviation. Effects are thereby not restricted to pupillary level. Parallel recordings of skin conductance changes prove a general enhancement of induced autonomic arousal. Considering the stability of the results across studies, we conclude that pupil size information exceeds affective monitoring and may constitute an active input channel in human–computer interaction. Furthermore, since variations in pupil diameter reliably display self-induced changes in sympathetic arousal, the relevance of this parameter is strongly indicated for future approaches in clinical biofeedback.

Age-specific mechanisms in an SSVEP-Based BCI scenario: evidences from spontaneous rhythms and neuronal oscillators

Utilizing changes in steady-state visual evoked potentials (SSVEPs) is an established approach to operate a brain-computer interface (BCI). The present study elucidates to what extent development-specific changes in the background EEG influence the ability to proper handle a stimulus-driven BCI. Therefore we investigated the effects of a wide range of photic driving on children between six and ten years in comparison to an adult control group. The results show differences in the driving profiles apparently in close communication with the specific type of intermittent stimulation. The factor age gains influence with decreasing stimulation frequency, whereby the superior performance of the adults seems to be determined to a great extent by elaborated driving responses at 10 and 11 Hz, matching the dominant resonance frequency of the respective background EEG. This functional interplay was only partially obtained in higher frequency ranges and absent in the induced driving between 30 and 40 Hz, indicating distinctions in the operating principles and developmental changes of the underlying neuronal oscillators.

Real-Time Feedback Towards Voluntary Pupil Control in Human-Computer Interaction: Enabling Continuous Pupillary Feedback

Since the late 90’s pupil size variations have been considered a possible input channel in Human-Computer Interaction [7]. [4, 5] showed that it is possible to manipulate pupil size via self-induced regulation strategies. A training based on graphical real-time pupillary feedback supported the learning process towards voluntary pupil size control. For successful learning the feedback has to be reliable, stable and on time. Taking this into account, spontaneous blinking poses one important problem during real-time feedback. This paper presents the process and elaboration of real-time data filtering methods. The final implementation consists of a two-state process. Blink replacement is achieved with a data-driven threshold. The filter was programed and tested in the framework of a study by [3]. The testing results were promising.

Multistable perception in children: Prefrontal delta oscillations in the developing brain

The prefrontal cortex (PFC) is considered to be the primary source of attentional control during elementary visual processing as exemplified in perceptual ambiguity. Assuming that multistable perception activates a fronto-parietal network, we contrast the results of mature and developing cognitive systems to deduce the developmental status of underlying structures from behavioral performances and functional EEG parameters. We analyzed the topographical distribution, amplitude characteristics and inter-trial variability of a reversal-related delta response that accompanies perceptual switches between the two alternative percepts of an ambiguous motion pattern. Fourteen ten-year old children and an adult control group indicated changes of perceived motion directions by a button-press. EEG was recorded from frontal, central, parietal, and occipital locations of both hemispheres. Behavioral data shows a considerably lower reversal rate within the children sample, suggesting that the related mechanisms are not yet operating on an adult level. In contrast to findings in adults, the involved delta component emerges as part of an unspecific posterior activation, suggesting that a cortical specialization process has not been accomplished yet. On frontal locations the ten-year old children fail to yield a stable component. The synchronized fronto-parietal activity in adults may constitute the result of a specialization process that determined connection patterns and functionally tuned the involved areas. This implies a deficit in timing and temporal sequencing of neuronal activity in children, mainly attributable to a less functional differentiated PFC that has not been fully integrated yet into the cognitive ensemble.

Pupil-Assisted Target Selection (PATS).

Physiological signals such as pupil size changes promise improvements for human-computer-interaction. However, the pupil response is known to be rather slow and unspecific. This hinders its application in target selection up to now. Nevertheless, there are indications for fast diameter changes accompanying cognitive processing already at early stages so that pupil effects can even precede psycho-motor activity. Building on these findings, we investigated the potential of short-latency pupil size changes for improving target selection in a search and select task. Pupil assisted target selection (PATS) was shown to be competitive to both, purely pupil-based and to dwell-time based selection modes in regard to selection times, but at the cost of more false positives than for a dwell-time approach in a search and select task. This demonstrates the usefulness of PATS as a means for target selection. The observed pupil dynamics correspond to early signal courses in basic research. Pupil dynamics also suggest room for further improvements of the integrated concept of pupil-assisted target selection.

Better Than You Think: Head Gestures for Mid Air Input

This paper presents a systematical comparison of pointing gestures in the context of controlling home appliances in smart homes. The pointing gestures were conducted with head, hand, arm and a computer mouse serving as baseline. To the best of our knowledge, we are the first to report on such a systematical comparison of the mentioned modalities. Our results indicate that although being overall slower and more inaccurate than hand and arm gestures, head gestures are more suitable for mid air input than previous research indicated. We show that disadvantages like slowness and inaccuracy can be compensated by a larger target size. In addition, head gestures have the largest learning effect. Considering our results and the possibilities head gestures would provide in daily life, we recommend thinking of head gestures as a feasible input modality besides hand and arm gestures.

Slow Trends

As of recently, research efforts are intensified to operationalize pupil dynamics for cognitive and affective classification in human-machine interaction. However, signal analysis of pupil diameter changes is problematic since the respective dynamics consist of three essential components that have to be disentangled: Very slow diameter changes, slow and high frequencies. The current paper discusses the amount of slow trends in pupillary signal courses and the effects on functional parameters of pupil dilations. Thereby we confront our data with linear detrending approaches and reveal various forms of trend progressions that differ over time and cannot be fixed with conventional linear procedures.

Training facilitates cognitive control on pupil dilation

Physiological responses are generally involuntary; however, real-time feedback enables, at least to a certain extent, to voluntary control automatic processes. Recently, it was demonstrated that even pupil dilation is subject to controlled interference. To address effects of training on the ability to exercise control on pupil dilation, the current study examines repeated exercise over seven successive days. Participants utilize self-induced changes in arousal to increase pupil diameter, real-time feedback was applied to evaluate and improve individual performance. We observe inter-individual differences with regard to responsiveness of the pupillary response: six of eight participants considerably increase pupil diameter already during the first session, two exhibit only slight changes, and all showed rather stable performance throughout training. There was a trend towards stronger peak amplitudes that tend to occur increasingly early across time. Hence, higher cognitive control on pupil dilations can be practiced by most users and may therefore provide an appropriate input mechanism in human-computer interaction.

A view to a click: Pupil size changes as input command in eyes-only human-computer interaction

Abstract In the field of Human-Computer Interaction (HCI), affective computation extends parameterization by including implicit user information, e.g. galvanic skin responses or heart rate variability. Physiological responses are generally involuntary and measurements primarily derive emotional features to differentiate cognitive and affective states. Biofeedback applications externalize covert physiological responses and allow interference by means of simple cognitive techniques. Here, signal responses do not necessarily indicate cognitive or affective dispositions but depict a users intention. As demonstrated recently, even pupil diameter is subject to explicit control, albeit with individually varying degrees of success. The current study explores to what extent users can transfer implicit events (here: pupil size changes) into explicit input requests. In Experiment 1 we carried out biofeedback sessions to determine individual strategies to achieve cognitive control on pupil dilation. In Experiment 2 we applied explicit pupil dilations as input commands in a visual search-and-select task. Implementation of varying thresholds ensured the involvement of different levels of cognitive effort to exceed selection criteria. Results show that a short period of freely exploring the mechanisms of action enabled most subjects to achieve cognitive control on pupil dilation, even during increased tonic activation provoked by high task load. Hence, the associated dynamics no longer define automatic events but indicate the degree of explicitness to be imposed upon implicit processing. During pupil-based object selection, a strict criterion was associated with a high cognitive load, prolonged selection times and a notable number of time-outs, whereas a soft criterion correlated with fast selections and low cognitive demands. Together with the outcome of a user survey, the current findings suggest explicit pupil size changes constitute an appropriate selection mechanism for HCI even in the context of high cognitive workload.