biological foundations of the reactive paradigm
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Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 1
3 Biological Foundations of the Reactive Paradigm
ReviewWhy?-comp. theoryIRMPerception-Summary
• Describe the three levels in a Computational Theory.
• Explain in one or two sentences each of the following terms: reflexes, taxes, fixed-action patterns, schema, affordance.
• Be able to write pseudo-code of an animal’s behaviors in terms of innate releasing mechanisms, identifying the releasers for the behavior.
• Given a description of an animal's sensing abilities, its task, and environment, identify an affordance for each behavior.
• Given a description of an animal's sensing abilities, its task, and environment, define a set of behaviors using schema theory to accomplish the task.
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 2
3 Robots In the Hierarchical Paradigm
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 3
3 Timeline of Influences
1980 19901970
Braitenberg’sVehicles
Arbib’sSchemas
Tinbergen &Lorenz & von Frisch
Marr’s ComputationalTheory
J.J. Gibson
Neisser
Middlestat
Arkin’s Schemas
Brook’s Insects
Payton
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 4
3 Marr’s Computational Theory
Level 1:What is the phenomena
we’re trying to represent?
for (i=nCol..Level 2:How it be represented as
a process with inputs/outputs?
Level 3:How is it implemented?
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 5
3 Level 1: Existence Proof
Level 1:What is the phenomena
we’re trying to represent?
Goal: how to make line drawings of objects?
people can do this by age 10, computers should
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 6
3Level 2: Inputs, Outputs, Transforms
for (i=nCol..Level 2:How it be represented as
a process with inputs/outputs?
light drawing
retina(gradient)
light lines (edges) drawing
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 7
3 Level 3: Implementation
Level 3:How is it implemented?
+-
-
-
--
- -
-
Center Surround Cellin retinal ganglion
Sobel Edge Detectorin computer vision
0 +2
+10-1
-2
-1 0 +1
0 0
-1-2-1
0
+1 +2 +1
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 8
3 Class Discussion
• Give three examples of how biology has informed modern technology?
– ex. Wright Brothers- control flaps on airplane wings
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 9
3 Behavior Definition (graphical)
BEHAVIOR
SensoryInput
Patternof MotorActions
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 10
3 Types of Behaviors
• Reflexive – stimulus-response, often abbreviated S-R
• Reactive – learned or “muscle memory”
• Conscious – deliberately stringing together
WARNING Overloaded terms:Roboticists often use “reactive behavior” to mean purely reflexive,
And refer to reactive behaviors as “skills”
WARNING Overloaded terms:Roboticists often use “reactive behavior” to mean purely reflexive,
And refer to reactive behaviors as “skills”
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 11
3 Ethology: Coordination and Control of Behaviors
Nobel 1973 in physiology or medicine•von Frisch•Lorenz•Tinbergen
www.nobel.se
INNATE RELEASING MECHANISMSINNATE RELEASING MECHANISMS
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 12
3 Arctic Terns
• Arctic terns live in Arctic (black, white, gray environment, some grass) but adults have a red spot on beak
• When hungry, baby pecks at parent’s beak, who regurgitates food for baby to eat
• How does it know its parent?– It doesn’t, it just goes for the largest red spot in its field of
view (e.g., ethology grad student with construction paper)
– Only red thing should be an adult tern
– Closer = large red
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 13
3 behavior template
BEHAVIOR
SensoryInput
Patternof MotorActions
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 14
3 “the feeding behavior”
FeedingBEHAVIOR
SensoryInput
Patternof MotorActions
RED PECK AT RED
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 15
3 the releaser template
Releaser
present? N
Y
/dev/null
Sensory inputand/or
internal state
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 16
3 “the feeding releaser”
FeedingBEHAVIOR
RED PECK AT RED
Releaser
present? N
Y
/dev/null
internal state
RED &HUNGRY
sensory input
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 17
3 Innate Releasing Mechanisms
BEHAVIOR
SensoryInput
Patternof MotorActions
Releaser
present? N
Y
/dev/null
Sensory inputand/or
internal state
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 18
3 Example: Hide Behavior
• Programmed in C++, << 100 LOC
• shows – taxis (oriented relative to light, wall, niche)– fixed action pattern (persisted after light was
off)– reflexive (stimulus, response)– impliciting sequencing– use of internal state
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 19
3 Example: Cockroach Hide
• light goes on, the cockroach turns and runs
• when it gets to a wall, it follows it
• when it finds a hiding place (thigmotrophic), goes in and faces outward
• waits until not scared, then comes out
• even if the lights are turned back off earlier
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 20
3 Reflexive Behaviors S-R
• light goes on, the cockroach turns and runs
• when it gets to a wall, it follows it
• when it finds a hiding place (thigmotrophic), goes in and faces outward
• waits until not scared, then comes out
• even if the lights are turned back off earlier
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 21
3 Fixed Pattern Actions
• light goes on, the cockroach turns and runs
• when it gets to a wall, it follows it
• when it finds a hiding place (thigmotrophic), goes in and faces outward
• waits until not scared, then comes out
• even if the lights are turned back off earlier
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 22
3 Exhibits Taxis
• light goes on, the cockroach turns and runs
• when it gets to a wall, it follows it
• when it finds a hiding place (thigmotrophic), goes in and faces outward
• waits until not scared, then comes out
• even if the lights are turned back off earlier
to light
to wall
to niche
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 23
3 Class Exercise
• Draw flowchart of how this works
• light goes on, the cockroach turns and runs
• when it gets to a wall, it follows it
• when it finds a hiding place (thigmotrophic), goes in and faces outward
• waits until not scared, then comes out
• even if the lights are turned back off earlier
• light goes on, the cockroach turns and runs
• when it gets to a wall, it follows it
• when it finds a hiding place (thigmotrophic), goes in and faces outward
• waits until not scared, then comes out
• even if the lights are turned back off earlier
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 24
3 Break into Behaviors
• light goes on, the cockroach turns and runs
• when it gets to a wall, it follows it
• when it finds a hiding place (thigmotrophic), goes in and faces outward
• waits until not scared, then comes out
Flee
Follow-wall
hide
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 25
3 Find Releasers
• light goes on, the cockroach turns and runs
• when it gets to a wall, it follows it
• when it finds a hiding place (thigmotrophic), goes in and faces outward
• waits until not scared, then comes out
Flee
Follow-wall
hide
LIGHT
present?N
Y
SCARED &SURROUNDED
present?N
LIGHT
present?N Ooops, need internal state:
ScaredOoops, need internal state:
Scared
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 26
3 Internal State Set
• light goes on, the cockroach turns and runs
• when it gets to a wall, it follows it
• when it finds a hiding place (thigmotrophic), goes in and faces outward
• waits until not scared, then comes out
Flee
Follow-wall
hide
LIGHT
present?N
Y
SCARED &SURROUNDED
present?N
BLOCKED &SCARED
present?N
SCARED
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 27
3 Action
• light goes on, the cockroach turns and runs
• when it gets to a wall, it follows it
• when it finds a hiding place (thigmotrophic), goes in and faces outward
• waits until not scared, then comes out
Flee
Follow-wall
hide
LIGHT
present?N
Y
SCARED &SURROUNDED
present?N
BLOCKED &SCARED
present?N
SCARED
steer 360,drive forward
steer =F(dist to wall)drive forward const.
steer =F(dist to wall)drive forward const.
stop
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 28
3 Sensory Input
• light goes on, the cockroach turns and runs
• when it gets to a wall, it follows it
• when it finds a hiding place (thigmotrophic), goes in and faces outward
• waits until not scared, then comes out
Flee
Follow-wall
hide
LIGHT
present?N
Y
SCARED &SURROUNDED
present?N
BLOCKED &SCARED
present?N
SCARED
steer 360,drive forward
steer =F(dist to wall)drive forward const.
steer =F(dist to wall)drive forward const.
stop
encoders
IR
IR
IR
IR
IR
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 29
3 How Do You Link Them?
• light goes on, the cockroach turns and runs
• when it gets to a wall, it follows it
• when it finds a hiding place (thigmotrophic), goes in and faces outward
• waits until not scared, then comes out
Flee
Follow-wall
hide
LIGHT
present?N
Y
SCARED &SURROUNDED
present?N
BLOCKED &SCARED
present?N
SCARED
steer 360,drive forward
steer =F(dist to wall)drive forward const.
steer =F(dist to wall)drive forward const.
stop
encoders
IR
IR
IR
IR
IR
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 30
3 Analogy:IRMs work on THREADS,not sequential processing!
• Very simple modules
• Nice building blocks since not directly linked
• If one module (part of brain) fails, what happens?
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 31
3 What happens when there’s a conflict from concurrent
behaviors?
• Equilbrium– Feeding squirrels-feed,
flee: hesitate in-between
• Dominance– Sleepy, hungry: either
sleep or eat
• Cancellation– Sticklebacks defend,
attack: build a nest
?
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 32
3 Perception
• Two uses of perception (can be the same percept)– Release a behavior– Guide a behavior
• Action-oriented perception (Neisser)– Planning is not needed to act – Perception is selective
CognitiveActivity
World
Perceptionof
Environment
Samples, FindsPotential Actions
Acts &ModifiesWorld
Directs whatto look for
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 33
3 Gibson’s Ecological Approach
• Acting and sensing co-evolved as agent survived in a particular environment. The environment affords the agent what it needs to survive.
• The perception needed to release or guide the “right action” is directly in the environment, not inferred or memorized – Ex. Red on Artic Terns== food
– Ex. Sound of filling container==full
• Percepts are called affordances or said to be obtained through direct perception
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 34
3 Gibsonian Affordances• How do you know you’re going fast in a car? Or in a
space movie?
• How do animals know when to mate?
• How do mosquitoes know to bite in the most tender areas?
• What should you do when you think you’re being stalked by a mountain lion?
• What’s your favorite fishing lure?
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 35
3 Sittability
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 36
3 But does this really hold for everything?
• “my car” versus “your car”?– Difference is
• where I parked it (memory)
• Semantic meaning (cars aren’t generic like nuts to a squirrel)
• Neisser’s Two Systems– Direct Perception: older, behavioral
– Recognition: evolved later, deliberative
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 37
3 Review Questions• What are the levels of a computational theory?
• Existence proof, inputs-outputs-transformations, implementation
• What is a behavior?
• A behavior is a mapping of sensory inputs to a pattern of motor actions
• Is sequencing normally implicit or explicit in IRM?
• implicit
• What is an affordance?
• A potentiality in the environment for an action
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 38
3 Schema Theory
schema- is used in cognitive science and ethology to refer to a particular organized way of perceiving cognitively and responding to a complex situation or set of stimuli
• is generic, equivalent to an object in OOP– schema specific knowledge (local data)
– procedural knowledge (methods)
• schema instantation is specific to a situation, equivalent to an instance in OOP
• a behavior is a schema, consists of– perceptual schema
– motor schema
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 39
3 Behavioral Schema
MotorSchema
(MS)
PerceptualSchema
(PS)
percept,gain
action,intensity
alternative PS, MSsequencing logic for reactive skills
(judgment value function)
Reflexive behaviors usually just have “methods”, not data
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 40
3 Ex. Fly Snapping Behavior IRM
snap(blob)track(blob)
x,y,z,100%
snap,100%
Releaser:small moving dark blob
present? N
Y
/dev/null
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 41
3 Schema Instantiation (SI)
snap(blob)track(blob)
x,y,z,100%
snap,100%
Releaser:small moving dark blob
present? N
Y
/dev/null
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 42
3 Schema/Schema Instantiation
behaviorschema
releaser
present?N
1.
snap(blob)track(blob)track(blob) snap(blob)snap(blob)track(blob)
PerceptualSchema Library
MotorSchema Library
2.
snap(blob)track(blob)
x,y,z,100%
3.
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 43
3 Advantages
• modular
• can assemble new behaviors from existing schemas– learning by experimentation
• can substitute alternatives– reroute nerves
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 44
3 Instantiation for each eye
snap,100%
snap(blob)track(blob)
x,y,z,100%
Releaser:small moving dark blob
present?N
Y
/dev/null
snap,100%
snap(blob)track(blob)
x,y,z,100%
Releaser:small moving dark blob
present?N
Y
/dev/null
Left eye
Right eye
Snap atvector sum(middle)
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 45
3 Where’s the MS and PS?
• light goes on, the cockroach turns and runs
• when it gets to a wall, it follows it
• when it finds a hiding place (thigmotrophic), goes in and faces outward
• waits until not scared, then comes out
Flee
Follow-wall
hide
LIGHT
present?N
Y
SCARED &SURROUNDED
present?N
BLOCKED &SCARED
present?N
SCARED
steer 180,drive forward
steer =F(dist to wall)drive forward const.
steer =F(dist to wall)drive forward const.
stop
encoders
IR
IR
IR
IR
IR
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 46
3 General Principles
• All animals possess a set of behaviors
• Releasers for these behaviors rely on both internal state and external stimulus
• Perception is filtered; perceive what is relevant to the task
• Some behaviors and associated perception do not require explicit knowledge representation (e.g., rely on affordances)
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 47
3 Silicon v. Carbon
• Individual robots must survive, not species– detection of non-productive behaviors
– graceful degradation
• Must be able to predict emergent behaviors
• Not clear how to learn quickly
• Robots need more alternative perceptual schemas since poorer understanding of the environment
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 48
3 Unresolved Issues
• How to resolve conflicts?– behavioral arbitration/combination
• When is explicit representations, memory needed?
• How to set up or learn new sequences of behaviors
• What are the affordances for a particular ecology?
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 49
3 Take Home Thoughts…• Ideas bubbling up for robotics
– Maybe programming in terms of behaviors is better than STRIPS or trying to set up a complex hierarchy
– Intelligence has something to do with agent’s ecological niche: its abilities, its tasks (survival), and environment
– Perception is going to be critical because it releases and guides actions
– IRMs, Schemas are nice ways to start thinking about the computational structure of programming a robot
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 50
3 Review Questions• Think about the robots at the WTC. What are affordances of
victims?
• color, motion, sound, heat
• Can schema theory represent behaviors in both biological and computational systems?
• yes
• A behavior schema is composed of at least the following:
• motor schema and a perceptual schema
• What is an example of behavior-specific knowledge?
• sequencing in a skill, alternative PS or MS
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 51
3
BEHAVIOR
SensoryInput
Patternof MotorActions
Releaser
present? N
Y
/dev/null
Introduction to AI Robotics (MIT Press) Chapter 3: Biological Foundations 52
3 Inhibition
while (TRUE) { predator = sensePredator(); //has a time delay if (predator==PRESENT) //as long as predator persists flee(); else { food = senseFood(); hungry = checkStateHunger(); ... }}
Could also be done as an interrupt
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