Related Work
In this chapter, I will detail a selection of projects and areas of research that I regard as relevant to this thesis.
Attentive user interfaces and gaze tracking
A specific research field of eye-based interaction that is closely related to this thesis is the field of 'Attentive User Interfaces' (AUIs) 49 - closing the eyes can serve as an indicator for a (visually) non-attentive user. Currently, AUIs gather information about the user's attention through eye gaze tracking 50 51 52 48 53.
When eye gaze tracking 55 54 arose as a field of research 56, it was novel that the eye, a sensory organ, was used as an input. Eye gaze tracking is currently being used as an analysis tool for user behaviour (i.e. to investigate the usability of a system 57) and as an input modality. Interfaces that employ the gaze direction as an input are, depending on context and user, augmenting or replacing commonplace inputs, i.e. to help a surgeon to access patient information without using his hands or to ensure the accessibility of a system for disabled user groups 58. Especially in 'hands free' applications, prolonged blinks can be used as a replacement for clicking.
Eye communication
Furthermore, eye gaze plays an important, though at times quite subtle part in human communication. Research has been undertaken to transfer these communication principles into the HCI field 59, reaching from the interaction with on-screen agents 41 42, the recognition of facial gestures 60 61 and the tracking of eyebrow movements 62. These projects show how existing knowledge about eye communication can be used in human-computer interaction.
Multimodality
Multimodal interfaces are are an emerging topic in the HCI field 63. They combine different modalities, such as vision, sound and touch. A multimodal browser is currently under development by Opera and IBM 64, using 3D sound and head position tracking.
Especially in a mobile context, users are mostly focused on navigating within their environment - this makes it important to create interfaces that are visually as little demanding as possible 65 66 67, as, for example, in the AudioGPS project 68, which shows an application for the 'non-visual' modality. Already, some research has been undertaken in the area of 'non-visual' interfaces. In 69, a 'bull's eye menu' is found to be a effective non-visual replacement for visual linear menus. The non-visual modality will play an important role in the course of this thesis.
Fatigue and sleep
An existing and widespread usage for eyelid tracking is the diagnosis of fatigue 70. Spontaneous eye-blink is considered to be an ample indicator for drowsiness. Various research has been undertaken in this area, assessing the 'increase of blink frequency as a function of the time-on-task' 71, both in general 72 73 and in diverse applications like aviation 74 75, driving 76 77, reading 78 or vigilance tasks 79 (examples as cited by 71).
The recently launched Philips Wake-up Light Clock 80 demonstrates another relation of eyelids and sleep: light does wake us up. The Wake-up Light is also an example of what will later in this document be introduced as 'through-the-eyelid display'.
Entertainment and art
A 'niche market' of specific relevance to this project is the field of 'audiogames', or video games without video. The achievements in this area are considerable 81 - when played with closed eyes, they provide a good impression of how intense the non-visual state can feel 82 83 84. Further research is undertaken to make games accessible to visually impaired children, a practical example is the 'Blindstation' 85.
Andrew Schneider, wearing the BlinkCam 86
Lastly, 'BlinkCam' should be mentioned. It is a camera mounted on a helmet, taking a picture of its wearer whenever he blinks. According to the project's creator, 192 hours pass without visual perception every year, for each of us - while blinking. 'BlinkCam' gives a very practical example of new ways of eye closure-based interaction 86.
