Endowing Agents with a Personal Sense of Time

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Endowing Agents with a Personal Sense of Time

• Haythem O. Ismail Stuart C. Shapiro
• Department of Computer Science and Engineering
• and Center for Cognitive Science
• State University of New York at Buffalo
• hismail shapiro_at_cse.buffalo.edu

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Outline

• Introduction
• Subjective Time
• Time and Bodily Knowledge
• Time and External States
• Summary

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Uses of Timeby a Cognitive Agent

• Reason about time
• Talk about time
• Reason and act in time
• Decide to act in timely fashion
• Remember acts and when done
• Sense current states
• Be informed of current states
• Be informed of past/future states
• Understand generate NL with correct tense
  aspect.

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Cassie

• A Computational Cognitive Agent
• Based on SNePS
• Logic-based
• Network-based
• Knowledge representation, reasoning, and acting.

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Embodied Cassie

• A Cognitive Robot
• Hardware
• or Software-Simulated
• Separate, but aligned
• Body
• Mind.

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GLAIR Architecture
Grounded Layered Architecture with Integrated
Reasoning
Knowledge Level
NL
SNePS
Perceptuo-Motor Level
Sensory-Actuator Level
Vision
Sonar
Motion
Proprioception
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Symbol Grounding Alignment
lex
lex
classhead
classmod
class
!
member
lex
B6
action
object
Find the green robot.
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Outline

• Introduction
• Subjective Time
• Time and Bodily Knowledge
• Time and External States
• Summary

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Deictic Center

• ltI, YOU, NOWgt
• Variables whose values are SNePS terms
• Aspects of embodiedness
• I SNePS term representing Cassie
• YOU person Cassie is talking with
• NOW current time.

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Subjective Time

• NOW contains SNePS term representing current
  time.
• NOW moves when Cassie acts or perceives a change
  of state.

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Representation of Time
before
after
before
after
!
!
!
?????????????
state
time
agent
act
B1
action
object
B6
I
lex
NOW
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Movement of Time v.1
t1
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The Pacemaker

• PML process periodically increments variable
  COUNT.
• COUNT some PML integer.
• Reset to 0 when NOW moves.
• Provides bodily feel of passing time.

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Quantizing Time

• Cannot conceptualize fine distinctions in time
  intervals.
• So quantize, e.g. into half orders of magnitude
  (Hobbs, 2000).

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Movement of Time with Pacemaker
q
t1
t2
KL
PML
hom
COUNT
n
NOW
0
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Outline

• Introduction
• Subjective Time
• Time and Bodily Knowledge
• Time and External States
• Summary

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Modality Variables

• Similar to Deictic Center.
• E.g. VISION, AUDITION, WHEELS, ARMS
• VISION Holds(Lookat(Cassie, Stu), t3)
• if vision currently occupied by looking at Stu
• t3 denotes the time during which Cassie will be
  looking at Stu
• NOW is during t3
• Set at PML when bodily state starts/ceases.
• One state may occupy multiple modalities.

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Knowing What Youre Doing

• When NOW moves
• For each modality variable v
• s.t. v Holds(s, t)
• Make NOW a subinterval of t
• So the agent believes it is now doing everything
  it is, in fact, doing.

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When you stop

• When state s ceases
• For each modality variable vi
• s.t. vi Holds(s, ti)
• Set vi to nil
• Move NOW
• Believe each ti is before NOW.

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When you start

• When state s starts
• For each modality v that s occupies
• set v to Holds(s, ti)
• Move NOW.

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Outline

• Introduction
• Subjective Time
• Time and Bodily Knowledge
• Time and External States
• Summary

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The Problem of the Fleeting Now

• How can you reason about now
• if it never stands still?

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Motivating Joke

• 93000 AM (Door-to-Door Salesman)
  May I interest you in a brush?
• 93002 AM (Homeowner) Not now.
• 93003 AM (Salesman) Now?

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Fleeting Now Example 1

• 91500 If the walk light is on now, cross the
  street.
• If the walk light is on at 91500,
• cross the street.
• 91501 Turn to look at walk light.
• 91502 The walk light is on at 91502.
• Should you cross the street?
• Yes, but why?

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Fleeting Now Example 2

• 121500 Is John having lunch now?
• 121502 Agent walks to Johns office.
• 121700 Agent sees John at his desk, eating.
• 121900 Agent reports yes.
• Appropriate granularity.

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Fleeting Now Example 3

• 121500 Is John having lunch now?
• Agent knows John is at home without a phone.
• Agent contemplates driving to Johns home.
• Dont bother---inappropriate granularity.

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The Vagueness of now

• Im now giving a talk.
• Im now teaching a course.
• Im now visiting Houston.
• Im now living in Buffalo.
• The agent is now walking to Johns office.
• The agent is now seeing if John is eating lunch.
• Multiple nows at different granularities.

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NOW-MTF
Maximal Temporal Frame based on NOW
NOW
Semi-lattice of times, all of which contain
NOW, any of which could be meant by
now Finite---only conceptualized times of
conceptualized states
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Moving NOW with MTF
NOW
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Typical Durations

• If the walk light is on now, cross the street.
• Relevant duration is typical duration of walk
  lights.
• Is John having lunch now?
• Relevant duration is typical duration of lunch.
• Use quantized typical durations when updating
  NOW-MTFs.

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Using Appropriate Granularity
Lunch time
Lunch?
Lunch!
NOW
Yes!
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Outline

• Introduction
• Subjective Time
• Time and Bodily Knowledge
• Time and External States
• Summary

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Summary

• Distinguish body mind, but align them.
• Body (PML)
• What people and things look like.
• Primitive and routine actions.
• Time intervals.
• Pacemaker Feel for elapsing time.
• Deictic Center variables.
• Modality variables.
• Mind
• Conceptualized people, things, actions, times,
  states.

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When Inquire about States

• Put them into MTF
• According to their typical duration.

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When NOW Moves

• Use Pacemaker to measure old NOW.
• Include current actions in MTF.
• Include other states according to their typical
  durations.

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For More Information

• http//www.cse.buffalo.edu/sneps/