Attractions and Repulsions
A Gravity-based Animated Microworld
for Exploration of Dynamical Systems
Jeffrey Ventrella
Visible Language Workshop
The Media Lab, MIT
December 9, 1993
This paper is about an animated exploration tool. It can be described in three ways:
1) It is a toy
2) It is a simple animated cartoon with many possible stories
3) It is a microworld for learning about motion
How is it like a toy?
Well, what makes it NOT like a toy in the traditional sense is that it runs on a Silicon Graphics IRIS workstation - the kind that can cost as much as a small house. What makes it LIKE a toy is that it is fun to play with.
How is it like an animated cartoon?
It features a set of characters (three shapes and a deformable box, analogous to a room) which move around and interact in a variety of ways, giving rise to a number of scenarios. These shapes are easily personified due to the nature of their motions. Names can be attached to the shapes to "customize" them to represent personal friends and foes (or even abstract concepts which relate to one another).
How is it a microworld?
First, what is a microworld? A microworld is a tool with which one can learn about some aspect of the world and also about him or herself. An effective microworld encourages exploration, manipulation, and some degree of designing. Microworlds can model scenes from the real world in simple form - like animals, people, things - or they can even model collections of ideas, which can be manipulated and explored. In any case, a microworld is a tool which lets one enter into a place - visual or cyber - and to learn things in a bricolage fashion.
The microworld I am describing was designed so as to motivate one to step in, to explore, play, and learn about motion styles and the way physical bodies can interact. This motivation is through a syntonic relation to the characters - they seem to exhibit a psychology all their own, and a way of moving around reminiscent of our own (even though the components of their behaviors are very simple - thus they are tractable). This brings to mind Braitenberg's "Vehicles" [Braitenberg], simple robots with wheels which, through primitive sensors and actuators, can exhibit psychological states. Braitenberg calls this phenomenon, "synthetic psychology".
Creatures of Habit
This microworld can be compared to the "Creatures of Habit" [Pea], (also influenced by Braitenberg), which was designed to enhance scientific thinking in students about system dynamics. In this system, as well as the one I have developed, triangles, squares, and circles interact according to attracting and repelling forces in controllable ways to comprise a simple "ecosystem". This ecosystem may have biological analogies, or references to physical laws, molecular affinities, and other domains. Creatures of Habit is a more extensive system in that it allows the user to specify many creatures to interact and be displayed at once. It also allows a number of different rule-settings to be initiated, for exploration of different domains.Origins
This microworld was developed over a short period (about a month) and began as an exploration in how dynamics from computer algorithms used for modeling gravity could be applied to modeling simple psychological states and dynamics. The original version, consisting of only two shapes (a male and female symbol) was the result of a computer bug. I had originally attempted to show two "planets" orbiting a "sun", but with repulsions from each other. An accidental "-" where a "+" should have been caused the two planets to chase each other around the solar system like a pair of cartoon characters. The effect of this simple program, and this serendipitous bug, was so amusing, and depicted so much "character", that I decided to develop it into a microworld, where a user could tweak the "+", and "-" values. These variables constitute the fear and desire knobs in the present system.The Basic Scene
Here I will describe the computer interface to the scene. The illustration below shows the components of this microworld.
The three shapes (shown in the middle, blurred from motion) have attracting and repelling forces between each other and also with the box (the double-lined rectangle in the middle). These forces can be altered by adjusting the controls on the lower left of the screen. As one adjusts the forces, one sees immediately the results on the screen. This immediate feedback enables one to "tune" the behaviors of each shape rather quickly to develop a scenario. Sometimes these scenarios are regular and periodic. At other times, they can be very unpredictable and complex, and in most cases, they tend to tell "micro-stories" - little tales of interactions which tend to repeat themselves over a short period of time.
Some stories have already been pre-designed as force-interaction settings and initial positions of the shapes and of the room-object. These stories (there are four) can be run by selecting one of the story buttons. This feature allows one to observe the variety of scenarios possible with this system, and to inspire ideas for novel settings.
Styles of Motion
Force is determined by the inverse square law - familiar to students of the analysis and modeling of electromagnetic phenomena. For shape A's relation to shape B, the following is done for each frame in the animation:1) calculate the distance between A and B
2) square it
3) take the "emotion" of shape A, and divide it by the squared distance
4) this is used to accelerate A
Other styles of motion have not been implemented in a systematic way so as to allow one to switch from one to the other, as in the Creatures of Habit System. The addition of this feature would be useful in a future version my system.
Giving Names
Any sympathy one may have for a shape is multiplied a hundred times when that person's name appears beneath the shape. Another feature of this system is the ability to attach names (words, numbers, etc..) to each shape, so that they can symbolize something other than "I am a shape that likes another shape", for instance. The use of text can be very effective for turning an otherwise bland object into an icon of a concept or of intentionality.Party Planner
This microworld has been compared to the Party Planner [Dewdney], a game-like system by Richard Goldstein, in which one can explore a simple model of social dynamics by setting up the components of a party, and letting it run. In my system, the room-object can be used to represent a place where a shape can feel safe, a place where it does not want to go, it can be expanded to a large proportion, or shrunk down. A shape can be designed to exhibit ambivalence by making it desire another shape which occupies the room, yet it is afraid to go near the room. Many varieties of scenarios, some quite amusing, are possible with the inclusion of the room-object.Questions and Problems
Some questions arising from this system have to do with interface design. How, for instance, how should the control panels (lower left of the illustration) be designed to maximize user understanding of what can be controlled? Should the controls be consolidated into one panel? And, more importantly, how should the panel look when more shapes are added to the scene, like fifty or a hundred? The Visible Language Workshop is dedicated to such questions, and other design problems of this sort. This would be explored in depth, if and when the system is developed further.Other questions have to do with the educational value of the system. Currently, there is a button in the interface which opens up a window with a short explanation of the microworld, and some suggestions for scenarios to try to generate, starting with simple ones, and becoming more complex. This is presented as a list of "tests". Each test describes the behavior to achieve, but not the way to achieve it. The idea is that the user of the system is encouraged to try out settings and initial states to generate the desired behaviors. But questions exist in terms of how effective this can be as an educational tool. Would the user be too tempted to just play with the story buttons? These give one the option to watch the pre-designed scenarios and may discourage one from tweaking things and designing one's own settings Could this encourage something analogous to "channel-surfing"? Certainly, bringing subjects in to explore the system, and reporting on their reactions and motivations would contribute to how I would approach further development, and to develop this as a more effective educational tool.
References
Braitenberg, V. Vehicles 1984 MIT Press, Cambridge.Dewdney, A. K. Computer Recreations - Diverse personalities search for social equilibrium at a computer party. Scientific American (issue and date not available)
Pea, Roy (New York University), Michael Eisenberg, Franklyn Turbak (MIT). Creatures of Habit - A Computational System to Enhance and Illuminate the Development of Scientific Thinking