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Visions

• Augmenting Human Intellect: A Conceptual Framework (Engelbart 1996)

Theoretical Backbone

Here we list references that will represent the theoretical side to inform our research. The augmented interactions framework provides us with (1) a vocabulary to articulate our interactions, (2) a starting point for our conceptual work. Implicit interaction provides us with a means to describe our interaction in terms of foreground and background, which means we can think of chords as a background interaction that augments foreground actions.

• Augmented Interactions: A Framework for Adding Expressive Power to GUI Widgets? (Cechanowicz and Gutwin, 2009)
• The Design of Implicit Interactions: Making Interactive Systems Less Obnoxious? (Ju et al., 2008)

Ergonomics

The papers listed here talk about one-handed and two-handed mobile use. We also have a more general paper that looks at how people use their hands to grasp physical objects. For one-handed usage, the focus is the physical limitations of the thumb in being unable to reach the edges comfortably, thus having an optimal area and a not-so-optimal area. Two handed use is not as constrained, as a user is able to use free movements with the hand performing the interaction.

• Modeling the functional Area of the Thumb on mobile Touchscreen Surfaces? (Bergstrom-Lehtovirta and Oulasvirta, 2014)
• How Do Users Really Hold Mobile Devices?? (Hoober, 2013)
• The Prehensible Movements of the Human Hand? (Napier, 1956)
• The Fat Thumb: Using the Thumb's Contact Size for Single-Handed Mobile Interaction? (Boring et al., 2012)

Back of the Device Interaction and Chords on Mobile Phones

Back of Device Interaction

These papers focus on using the back of the phone to interact with the content on the screen. Dual-Surface input proposes leveraging the index finger at the back for more fine-grained selection operations. I think there's also a theme of being able to use the centre of the contact point as a precise pointer.

• Back-of-Device Interaction Allows Creating Very Small Touch Devices? (Baudisch and Chu, 2009)
• Dual-Surface Input: Augmenting One-Handed Interaction with Coordinated Front and Behind-the-Screen Input? (Yang et al., 2009)
• LucidTouch: A See-Through Mobile Device? (Wigdor et al., 2007)

Text Entry

A big chunk of work on mobile chording focuses on text entry. This use case makes sense and shows an example of using chords as a trigger as opposed to being an augmentation

• RearType: Text Entry Using Keys on the back of a Device? (Scott et al, 2010)
• A Comparison of Consecutive and Concurrent Input Text entry on Mobile Phones? (Wigdor et al., 2004)
• A model of Two-Thumb Chording on a Phone Keypad? (Patel et al., 2009)
• Design and Evaluation of Innovative Chord Input for Mobile Phones? (Wu et al., 2009)
• Twiddler Typing: One-Handed Chording Text Entry for Mobile Phones? (Lyons et al., 2004)

Bimanual Interaction

These papers use bimanual interaction in the context of mobile devices, where often one hand 'holds' and the other one 'interacts'. These I haven't read into very much.

• BiTouch and BiPad: Designing Bimanual Interaction for Hand-held Tablets? (Wagner et al., 2012)
• The Hold-and-Move Gesture for Multi-touch Interfaces? (Kulik et al., 2012)

Chord Learnability

• Arpege: Learning Multitouch Chord Gestures Vocabularies? (Ghomi et al., 2013)
• Multi-finger Chords for Hand-held Tablets: Recognizable and Memorable? (Wagner et al., 2014)

Mobile Interaction Techniques for Mode Switching, Menu Navigations and Expert Use

• Faster Command Selection on Tablets with FastTap? (Gutwin et al., 2014)
• The Fat Thumb: Using the Thumb's Contact Size for Single-Handed Mobile Interaction? (Boring et al., 2012)
• Side pressure for Bidirectional Navigation on Small Devices? (Spelmezan et al., 2013)
• Controlling Widgets with One Power-Up Button? (Spelmezan et al, 2013)
• Pinch-to-zoom-plus: an enhanced pinch-to-zoom that reduces clutching and panning? (Avery et al., 2014)
• Understanding Shortcut Gestures on Mobile Devices? (Poppinga et al., 2014)
• Acoustruments: Passive, Acoustically-Driven, Interactive Controls for Handheld Devices (Laput et al., 2015)

Chords and Gestures on Traditional Keyboards / Piano

These papers are a bit varied - one looks at using keyboards as a chord; the next looks at using gestures like swiping to perform action; the last one looks at using a piano for keyboard entry, where chords serve to trigger commonly used words. These all show usage of (1) chording to perform common actions and (2) leveraging user expertise.

• Typing With a Two-Hand Chord Keyboard: Will the QWERTY Become Obsolete?? (Gopher and Raij, 1987)
• GestKeyboard: Enabling Gesture-Based Interaction on Ordinary Physical Keyboard? (Zhang and Li, 2014)
• PianoText: Redesigning the Piano Keyboard for Text Entry?(Feit, Oulasvirta, 2014)
• Case Study 2: Chorded Keyboards (Buxton, In Preparation). Chapter 6 in Human Input to Computer Systems: Theories, Techniques and Technology. Cambridge: Cambridge University Press.