03/23/08 15-494 Cognitive Robotics 1Affordances15-494 Cognitive RoboticsDavid S. Touretzky &Ethan Tira-ThompsonCarnegie MellonSpring 200803/23/08 15-494 Cognitive Robotics 2J J Gibson●American psychologist (1904-1979)who worked in the area of visualperception.●Coined the term “affordance”.●“The affordances of the environment are what it offers the animal, what it provides or furnishes, either for good or ill.”●In Gibson's formulation, affordances are properties of the environment, independent of the animal's perception.03/23/08 15-494 Cognitive Robotics 3Don Norman●Cognitive scientist at UC San Diego who studied under Gibson.●Replaced Gibson's objective affordanceswith the notion of perceived affordances.●“... the term affordance refers to the perceived and actual properties of the thing, primarily those fundamental properties that determine just how the thing could possibly be used... Affordances provide strong cues to the operation of things.”03/23/08 15-494 Cognitive Robotics 4The Design of Everyday Things●Norman's book “The Psychology of Everyday Things” helped popularize the notion of affordances.●Later reissued with updated frontmatter as “The Design of Everyday Things”.●Looked at examples of physical objects such as door handles and light switches.03/23/08 15-494 Cognitive Robotics 5Affordance Examples from Norman●Plates (on doors) are for pushing.●Knobs are for turning.●Slots are for inserting things into.●Balls are for throwing or bouncing.“When affordances are taken advantage of, the user knows what to do just by looking; no picture, label, or instruction needed.”03/23/08 15-494 Cognitive Robotics 6How To Open a DoorShape determines grasp strategy:03/23/08 15-494 Cognitive Robotics 7How (Not) ToOpen a Door“Emergency Exit OnlyPush Until Alarm Sounds Door Can BeOpened In 15 SecondsFurniture illegally blocking exit03/23/08 15-494 Cognitive Robotics 8Changing An AffordanceRubber handle fits on doorknob to allow easier opening by people with gripping difficulties.03/23/08 15-494 Cognitive Robotics 9Learning by Observation?03/23/08 15-494 Cognitive Robotics 10Is This Really Necessary?03/23/08 15-494 Cognitive Robotics 11Kodak DC-290 CameraRight hand fingers curl around gripLeft thumb goes hereExample from Joel Spolsky's “User Interface Design for Programmers”, ch. 4.● Encourages users to hold camera with both hands.● Keeps fingers away from the lens and viewfinder.03/23/08 15-494 Cognitive Robotics 12Affordances Are An Important Concept in GUI Design● Buttons drawn as 3D shapes appear to “stick out” and hence afford pushing.● Sliders and scroll bars afford dragging.03/23/08 15-494 Cognitive Robotics 13Window Controls: Resize TabLines look like the ridges on a slider switch that increase friction(Spolsky)03/23/08 15-494 Cognitive Robotics 14Tabbed Dialogs1980s-style Mac control panel: major mode shown by icon on left. That mode's choices appear on the right.1990s-style Mac control panel using tabbed dialogs was much easier for users to understand.Tabs are affordances.03/23/08 15-494 Cognitive Robotics 15What Does This Have ToDo with Robotics?1. Robots must be able to deal with unfamiliar objects.–Recognizing affordances can lead them to effective strategies for interacting with objects.●2. Humans needs ways of instructing robots.–Language for describing object interactions would be helpful.–This is the language in which affordances are described.03/23/08 15-494 Cognitive Robotics 16Stoytchev (2005):Recognizing Tool Affordances●Robot experiments randomly to learn the effect of actions using various tool shapes to move an orange puck.03/23/08 15-494 Cognitive Robotics 17Robert St. Amant:Tool Use With the AIBO●“Some tools seem to have the property that one can tell how they should be used just by looking and experimenting – no instruction or specialized knowledge is needed. Affordances are part of the explanation why, as is general tool-using ability.”(movie)03/23/08 15-494 Cognitive Robotics 18Recognizing Affordances●Physical properties of the object●Understanding how the robot's body could interface with that object.PLUS03/23/08 15-494 Cognitive Robotics 19Affordances of Known Objects●For familiar objects such as balls, we already know a variety of strategies for interacting with them.●Which ones are applicable depend on factors such as size and position.03/23/08 15-494 Cognitive Robotics 20Ball Affordances●Can build a library of ball affordances.●Write code to detect when particular ones are applicable.–push with paw–push with chest–push with head–kick ball ...03/23/08 15-494 Cognitive Robotics 21Line Affordances●Lines afford a variety of actions.–Visually trace line–Walk to line–Cross line–Touch point on line03/23/08 15-494 Cognitive Robotics 22Brick Affordances●Brick affordances include:–Push brick to location x–Rotate brick to orientation –Flip brick over–Stand on brick03/23/08 15-494 Cognitive Robotics 23Problems of Action Representation●Preconditions for feasibility: is this action possible?●Parameterization: How far? What direction?●Interactions between affordances●Recognizing failures03/23/08 15-494 Cognitive Robotics 24Preconditions for Actions●When is an action feasible?●Example: when can we push a ball?–Must be close enough to touch the ball–Must be oriented properly to push in desired direction–Must have freedom of motion–Ball must not be obstructed●What if we're not close enough to push?–Balls could afford “moving into position to push” actions.03/23/08 15-494 Cognitive Robotics 25Parameterized Actions●We don't usually want to just push at random.–“Push ball in direction ”●Do we recognize an infinite number of affordances?●Special cases?–Push ball toward object/landmark x03/23/08 15-494 Cognitive Robotics 26Interactions Among Affordances●A wad of paper affords tossing.●A wastebasket affords receiving tossed objects.–Potential for combinatorial explosion?●Interactions can supply parameter values.–Where to push03/23/08 15-494 Cognitive Robotics 27Recognizing Failures●Trace line affordance fails:–Neck pan limits exceeded.●Need to understand whythe action failed.●Failure explanations:–positioning problem–lost sight of object–lost contact with object (dropped it)–etc.03/23/08 15-494 Cognitive Robotics 28Dealing with Novel ObjectsHow do you turn on the