Information Capacity of Full-Body Movements

March 17, 2014 by

Information Capacity of Full-Body Movements

Antti Oulasvirta (acm) (google)

If you’re going to remember one(?) thing:

A modern take of Fitts. Rather than just looking at distance to target, this paper looks at the information carrying capacity of movements. And applies this to areas as diverse as gestures and rehersed dance moves.

The problem of designing interfaces with full-body control is that the number of possible movements is too enormous to study empirically. Our solution is to ask a user to produce an overlearned motor act, such as signing one’s name, in each condition. The overlearned motor act is a surrogate for any complex movement that a user could produce with practice.

The user could express genuine information with two-hand interaction: Throughput was 182.7 bps with dominant hand removed, 217.8 bps with non-dominant hand removed, and 322.1 bps with both hands. Thus, bimanual gesturing genuinely increased TP from that of singlehanded gesturing.


This method accommodates continuous movement of multiple limbs. Throughput (TP) is calculated as mutual information in repeated motor sequences. It is affected by the complexity of movements and the precision with which an actor reproduces them.
The new metric extends Fitts-TP metric by considering

• the shape of continuous trajectory as the source of information instead of target width and distance and
• the accuracy of the reproduced movement as the source of noise instead of end-point variation.

Moreover, the speed of performance affects the rate of information, as in Fitts-TP.

The metric allows researchers to examine any scenario wherein users’ motion can be represented as a sequence of vectors of movement features, from mouse movements to full-body motion. Naturally occurring movement can be analyzed, with the precondition that the data include matchable repetitions. The known extensions of Fitts’ law from discrete to continuous movements are predictive models of MT and do not carry an interpretation in information theory. Moreover, they are incapable of dealing with multi-feature arbitrary trajectories in 3D space.


To assess joint human–computer performance, the “tempting but naïve” solution is to examine average speed and accuracy in a task. This approach, however, overlooks the fact that data from easy and from difficult motor acts are incommensurable. Information theory has contributed to the measurement of user performance in HCI by providing a metric that collapses data on speed and accuracy into a single metric: throughput.

Information capacity denotes the rate at which the user could have sent messages, given her speed and accuracy for given target properties. Selecting targets with the mouse, for instance, yields throughputs of 3.7–4.9 bps [17]. Although the metric has been contested, no better alternatives exist for comparing performance across tasks, conditions, and devices.

This paper extends the measurement of throughput from aimed movement to full-body movement—that is, multiple contributing limbs in continuous movement that does not need to be aimed at targets prescribed by an experimenter. In so-called configural movements, the goal is to produce a shape or pattern in movement.

We calculate throughput from mutual information of two or more deliberately repeated movement sequences. Our definition of mutual information captures the intuition that a skilled actor can produce complex (surprising) movements and reenact them precisely at will.

Analyzing precision in repeated efforts allows us to distinguish the controlled from uncontrolled aspects of movement. A newborn, for example, while able to produce complex-looking movements, does not have the capacity to reproduce them.

Since our I(x; y) excludes most of the uncontrolled movements and inaccuracies due to the actor’s inability to repeat the movement precisely, it provides a measure of the controlled information in x and y.

Extensions of Fitts’ law models to continuous aimed movements [1] covered only path width and length originally but were later extended to curvature [11]. However, to our understanding, these models have no interpretation in information theory.

Sometimes imposing constraints may lead to underestimation or overestimation of capacity, as in the case of sliding movements on a physical surface.

In handling of p-dimensional sequences, p > 1, where each time frame xt is composed of p measured movement features, it would be invalid simply to add up the information throughput of all of the features. For us to calculate the “genuine” capacity of the leg, any correlation in the movement of the knee and the calf must first be removed.

One drawback of the second-order autoregressive model is its short “memory”: a human observer can easily detect repeats in a movement, but the model considers each repetition as surprising as the first instance. However, when CTW was removed, TP fell by a factor of 6.7, to 43 bps. The actor’s high TP was achieved at the expense of accuracy in timing.

Furthermore, to understand which limbs are the best candidates for controlling an interface, we estimated limbs’ contribution to the capacity. We averaged raw TPs per movement feature across the dances. As the adjacent figure shows, the two hands and the right foot had the largest throughputs, all above 12 bps. Markers for the torso, head, and distal parts of the feet had far lower values. This analysis reveals a laterality effect (left vs. right hand) and that torso and leg movements may be less well-rehearsed and important aspects of the teacher’s dancing. An interface designer could use such information when mapping human movements to virtual controls.



Net-Surfers Don’t Ride Alone: Virtual Communities and Communities

March 16, 2014 by

Wellman and Gulia

Net-Surfers Don’t Ride Alone: Virtual Communities and Communities

List of questions answered, seems obvious now.
Are relationships on the Net Narrow and specialized or are they broadly based? (both) What kinds of support can one expect to find in a virtual community? (most any type found in a “real” community)


The one thing you should know: social groups online are a thing, a functional and useful thing which resembles physical social groups in many ways.

Social Translucence: An Approach to Designing Systems that Support Social Processes

March 16, 2014 by

Erickson and Kellogg

Social Translucence: An Approach to Designing Systems that Support Social Processes

“What properties of the physical world support graceful” face to face interactions and what are the design recommendations? Visibility, Awareness, accountability for actions, this is related to social translucence; where participants are aware of the rules of the environment and held accountable by public knowledge of their actions. In virtual environments these social cues can be represented in three ways, realistic, memetic (as literal as possible within he bandwidth of the system) and abstract. Memetic has the problems that a relatively unconscious social act (smirk command in a MUD for instance) is consciously produced through an avatar, cutting into user cognitive load and making for a less natural communication. Babble (MIT Q&A program) gives an abstract graphical feedback about interrelated conversations. Dots are placed and move according to activity of the conversation.

The one thing you should know: This is early Reddit, the value of questions and answers are impacted by the group. This is also Batman: Arkham video game, social cues presented by avatars.

Doing Virtually Nothing: Awareness and Accountability in Massively Multiplayer Online Worlds.

March 16, 2014 by

Moore et al

Doing Virtually Nothing: Awareness and Accountability in Massively Multiplayer Online Worlds.

MMORPGs lack realistic social cues from (avatar) face to face interactions, especially in light of recent advances in the realism of the environment. Using video-based conversational analysis and sampling the video stream to the monitor, the study focused on the persona projected into the virtual environment, not the person on the keyboard. Phenomena of interest included the mechanics of avatar interaction, grouping sequences, coordinated travel and combat, player hosted events role plays techniques, etc. With that said, avatars do not provide the high level of situational messages observing a human in the environment and conversations are far slower, due not only to the speed of inputting text versus speaking but also the lack of physical conversational cues to let the other speaker get ready. This can result in an interesting phenomenon, a simultaneous-multiple subject conversation with the same person or more multiple people. Observation lead to design recommendations, entirely private player actions shouldn’t be allowed, they lack social realism, if text chat is going to be be the primary mode of communication it should present word by word or even character by character. Autonomic (and possibly situationally aware) responses of avatars when still, such as breathing, looking around or even fidgeting are important, finally keeping the environment window as clear as possible from game cues is recommended.

The one thing you should know: This is Batman: Arkham video games, social cues presented by avatars, layout of game information, etc are all vital.

The top five reasons for lurking: improving community experiences for everyone

March 16, 2014 by

Preece et al

The top five reasons for lurking: improving community experiences for everyone

There are many reasons people lurk, including understanding the norms of a community, to see if their concerns are valid, obtain vicarious support. Most lurkers are not selfish free riders as with the largest reason for not participating being they did not feel the need to but other concerns include difficulty in posting or becoming accepted in the community, language or knowledge deficits to overcome. Since an inactive space is unlikely to succeed, design recommendations are: encouragement to post (such as a explicitly telling the community posting is encouraged), encouragement by moderators, reward both quality & quantity of posts and make sure your site supports the methods is user interaction. Accelerating the process for people to get to know the community: such as with a greeter, guided tours, mentoring or discussion summary pages. Reducing the clutter so people can better gauge the value of their contribution, such as up voting on Reddit as well as other usability issues. Social issues that apply to being new in a group also apply to these virtual groups.

The one thing you should know: Design recommendations for building a successful online community.

Using Social Psychology to Motivate Contribution to Online Communities

March 16, 2014 by

Ling et al

Using Social Psychology to Motivate Contribution to Online Communities

Field testing four design principals derived from Social Loafing. Aim, stronger link between social science theory and CSCW. Identified the abstract mental state the theories propose should lead to contribution, then translated into specific mental state participants likely to have, then designed persuasive message or other stimuli to promote these mental states.

Test 1 Paired like and unlike groups, because uniqueness can stimulate participation (as the antitheses of the reliance of social loafing) and uniques contributed more (confounded by messages to participants which acted as prodding to participate).

Test 2 reached out to members who has reviewed rarely reviewed movies, promoted with message focusing on their uniqueness with variable in benefit, no benefit, only benefit to self, only benefit to others and benefit to self and others. Only uniqueness of individual contributed to increased effort.

Test 3 determining if the act of receiving the message increased the salience (mental prominence) of intrinsic motivation. It was concerning that in test 2, mentioning self or other benefit decreased participation but mentioning both did not. Presented identical verbiage but added “they tell us they rate because it is fun” caused an increase but not a statistically significant.

Test 4, motivating through goal setting. Hypotheses tested member who have a goal will rate more and members with an individual assigned goal will rate more still. Specific goals work more than general (just do your best), group goals more than individuals. difficulty of goal has a convex effect on contributions (weakly supported). Researchers felt where social science theories didn’t match up, it was the case of poor implementation and incomplete theories.

The one think you should know: Movie rating website, researchers attempted to link social science theory with CSCW. Good for study design.

The Social-Technical Design Circle

March 16, 2014 by

Can use social practices to simplify technical implementation. Social systems are in flux, even great design can’t simply address it statically. Intertwined social and technical aspects of design. Activity theory characterize tools as representations of cultural history, mediators of cultural understanding and learning, and ways of extending human capability to accomplish shared objectives.

1. Using social practices to simplify a technical implementation. In the example of a shared editor applet, the designers chose a quick, easy technical solution, with an assumption that users would learn and practice explicit social controls to manage their collaborations.
2. Designing technical mechanisms to achieve a social objective. The gag command was redesigned to encourage the use of social mechanisms for conflict resolution.
3. Similar tools with different social effects. Places and channels are two facilities for organizing group communication which have some similar technical features. Channels were developed in addition to (and some would argue in violation of) the already existing place metaphor. Subtle differences between the two mechanisms were magnified in their social effects.
4. Co-evolution of social and technical mechanisms. The roles played by MOO wizards have co-evolved with new social policies and new tools that give technical powers to teachers and other design team members.

The one thing you should know: What I did as an IMM to players in MUDs were wrong and right, as exampled in the paper. The online community is a “real” world, our ‘arbitrary’ rules can and do have social impact.

Blogging as a Social Activity, or, Would You Let 900 Million People Read Your Diary?

March 16, 2014 by

Nardi et al

Blogging as a Social Activity, or, Would You Let 900 Million People Read Your Diary?

Ethnographic look at Blogging. despite the title, blogging has many social uses beyond diary: updating others on activities, expressing opinion/influencing others, seeking opinions, as a writing tool, releasing emotion. Yes, it is two way communication but it is mostly unidirectional. Design recommendations, text based media and tools, integration of photos, browsing and search, audience specify and privacy, ability to collaborate and use of use.

The one thing you should know: Did the people Zuckerberg stole Facebook from read this paper and then make it?

HutchWorld: Clinical Study of Computer-Mediated Social Support for Cancer Patients and their Caregivers

March 16, 2014 by

Farnham et al

HutchWorld: Clinical Study of Computer-Mediated Social Support for Cancer Patients and their Caregivers

Computer mediated information and social support, deployed to bone marrow cancer and caregivers. Studied usage patterns (which patterns), impact on quality of life and access issues in building the community. Those that used the community found an improvement in quality of life, though it was potentially slightly masked by what was perceived as improvement of quality of life from internet access.

The one thing you need to know: Can a technology based social group “work” for helping people cope with tragedy? Yes.

HomeNet: A Field Trial of Residential Internet Services

March 16, 2014 by

Kraut et al

HomeNet: A Field Trial of Residential Internet Services

Nice empirical study, 48 families (157 participants) got the internet in 1995, 25% poor, 25% minority, over half female, over half children. After five months half were regular users, teenagers had the deepest saturation, teens modeled as early adopters. Half checked out porn, but 20% looked at it more than three times. Three created content.


The one thing you need to know: At home internet is a good idea, teenagers use it more.