Introduction to Cognitive RoboticsTypes of Memory Episodic •Episodic memory is a constructive...

Artificial Cognitive Systems 3 1 Introduction to Cognitive Robotics

Introduction to Cognitive Robotics

Module 6: Artificial Cognitive SystemsLecture 3: Memory and prospection; internal simulation, the symbol grounding problem

www.cognitiverobotics.net


Memory

• Memory plays a crucial and sometimes unexpected role in cognition

• Strong parallel between memory and knowledge

• Memory and knowledge are equivalent: they both encapsulate the experience that arises from interaction with the world

• Memory is not just as a passive mechanism for storing knowledge about the past


Types of Memory

• Declarative

• Procedural

• Semantic

• Episodic

• Long-term

• Short-term

• Working

• Modal

• Amodal

• Symbolic

• Sub-symbolic

• Hetero-associative

• Auto-associative


Types of Memory

Declarative memory

• Knowledge of things / facts

• “Knowing that” • Propositional memory (true or false)

• Can be communicated from one agent to another through language

• Can be acquired in a single act of perception or cognition

• Accessible to conscious recall

• Explicit memory


Types of Memory

Procedural memory

• Skill-oriented memory of actions

• “Knowing how”• Can only be demonstrated

• Acquired progressively and may require an element of practice

• Not accessible to conscious recall

• Implicit memory

• Non-declarative memory


Types of Memory

Episodic memory

• Specific instances in the agent’s experience: autobiographical

• Explicit spatial and temporal context– what happened, where it happened, and when it happened

– This temporal sequencing is the only element of structure in episodic memory

• Sub-symbolic


Types of Memory

Episodic memory

• Episodic memory is a constructive process

– Each time an event is assimilated into episodic memory, past episodes are reconstructed a little differently each time

– Related to the role that episodic memory plays in the process of internal simulation that forms the basis of prospection


Types of Memory

Semantic memory

• General knowledge about the agent’s world: facts, ideas, and concepts

• May be independent of the agent’s specific experiences

• Memory necessary for the use of language

• Derived from episodic memory through a process of generalization and consolidation • Symbolic


Types of Memory

Modal memory

• Tied directly to a particular sensory modality such as vision, audition, or touch

• Episodic memory though is more likely to be modal since it is closely tied to an agents’s specific experiences

Amodal memory

• Amodal memory has no necessary association with the sensorimotor experiences

• Semantic declarative facts, represented symbolically, are typically amodal


Types of Memory

Associative memory

• An element of information or some pattern is linked to another

• The first element or pattern is used to recall the second, by association

AssociativeMemory

Pattern A Pattern B


Types of Memory

Hetero-associative memory

• Recalls a memory that is different in character from the input

• A particular smell or sound, for example, might evoke a visual memory of some past event

AssociativeMemory

Sound Image


Types of Memory

Auto-associative memory

• Recalls a memory of the same modality as the one that evoked it

• A picture of a favourite object might evoke a mental image of that object in vivid detail

AssociativeMemory

Image A Image B


Role of Memory

The role of memory – why do we remember things?

– To recognize objects, events, and people we’ve encountered before

– To act towards them in some appropriate way (attraction/avoidance)

– Memory is what makes it possible for the changes that occur as a result of learning and development to persist

– Memory also is what makes it possibleto project forwards into the future


Role of Memory

One of the central pillars of cognitive capacity:

– the ability to simulate internally the outcomes of possible actions and select the most appropriate one for the current situation

– Memory can be seen as a mechanism that allows a cognitive agent to prepare to act,overcoming through anticipation the inherent “here-and-now” limitations of its perceptual capabilities

– a cognitive system doesn’t operate just on the basis of its current sensory data but readies itself for what it expects and adjusts to the unexpected


Role of Memory

Memory is an active & constructive process, and it is fundamentally associative

– Memories are recalled by associated triggers, possibly other memories

– If you have a network of associative memories, you can run through this network backwards or forwards

– Running through it forwards provides the anticipatory predictive element of memory suggesting possible sequence of events leading to a desired goal

– Running through it backwards provides a way of explaining how some event or other might have occurred or imagining ways in which it might have turned out differently


“It’s a poor sort of memory that only works backwards”

Remarks of the White Queen to Alicein Lewis Carroll’s Through the Looking Glass

Memory is Prospective


“It’s a poor sort of memory that only remembers what has actually happened”

Remarks by Tom Ziemke

at a talk in Linköping University

Memory is Constructive


Self-Projection, Prospection, & Internal Simulation

Memory plays at least four roles in cognition

1. Remember past events

2. Anticipate future ones

3. Imagine the viewpoint of other people

4. Navigate around our world



All four roles involve self-projection

– Ability of an agent to shift perspective from itself in the here-and-now

– It does this by internal simulation,

i.e. the mental construction of an imagined alternative perspective


There are four forms of internal simulation

1. Recalling episodic memories (remembering the past)

2. Navigation (orienting yourself topographically, i.e. in relation to your present surroundings)

3. Theory of mind (taking someone else’s perspective on matters)

4. Prospection (anticipating possible future events)



• All four forms of simulation are constructive

– They involve a form of imagination

• Fine for prospection, theory of mind, or navigation

• but remembering the past? ... more on this in a moment




• There is a difference between knowing about the future and projecting ourselves into the future

• Projection is experiential, knowing is not

• Episodic memory (experiences) and semantic memory (facts) facilitate different types of prospection



• Episodic memory

– Re-experience your past

– Pre-experience your future

• Projecting yourself forward in time is important when you form a goal

– Creating a mental image of yourself acting out the event

– Episodically pre-experiencing the unfolding of a plan to achieve that goal

– Episodic Future Thinking [Atance and O’Neill 2001]



Episodic memory is inherently constructive

– Old episodic memories are reconstructed slightly differently every time a new episodic memory is assimilated or remembered

– The constructive episodic simulation hypothesis [Schacter and Addis 2007]

• Episodic memory allows the simulation of multiple possible futures

• This imposes an even greater need for a constructive capacity because of the need to extrapolate beyond past experiences


The Past

Past events arereconstructed ...

Episodic MemorySpecific instances of

the agents experience


The Past


Episodic Memory

To allow the agent to pre-experience the future

The Future


The Past


Episodic Future Thinking


The Future

C. M. Atance and D. K. O’Neill, “Episodic future thinking,” Trends in Cognitive Sciences, vol. 5, no. 12, pp. 533–539, 2001.


The Past


The constructive episodic simulation hypothesis


Future B

D. L. Schacter and D. R. Addis, “The cognitive neuroscience of constructive memory: Remembering the past and imagining the future,” Philosophical Transactions of the Royal Society B, vol. 362, pp. 773–786, 2007.

Future A

Future C...


The Future

SemanticEpisodic

K. K. Szpunar, R. N. Spreng, and D. L. Schacter, A taxonomy of prospection: introducing anorganizational framework for future-oriented cognition, PNAS 111(52), 18414–18421, 2014.

General knowledge about the agent's world


The Future

SemanticEpisodic

Procedural

K. K. Szpunar, R. N. Spreng, and D. L. Schacter, A taxonomy of prospection: introducing anorganizational framework for future-oriented cognition, PNAS 111(52), 18414–18421, 2014.

Action knowledge and motor skills


AnticipationProspectionPredictionIntentionPlanningSimulationEpisodic future thinking


Schulkin J. (2011). Social allostasis: anticipatory regulation of the internal milieu. Frontiers in evolutionary neuroscience, 2, 111.




• Episodic memory is not an exact and perfect record of experience

• It captures the essence of an event and is open to re-combination



• When humans imagine the future

– They anticipate an event

– They anticipate how they feel about that event

• Knowing how you feel about something is a very good way of telling whether or notthat event is safe or dangerous

• We call these the hedonic consequences of the event

• Pre-experience of prospection also involves pre-feeling


Internal Simulation and Action

• So far, internal simulation considered entirely in terms of memory-based self-projection

Using re-assembled combinations of episodic memory to

• Pre-experience possible futures

• Re-experience (and possibly adjust past experiences)

• Project ourselves into the experiences of others

• However, action plays a significant role in our perceptions so does action play a role in internal simulation?

• YES



• Internal simulation – extends beyond episodic memory

– includes simulated interaction, particularly embodied interaction

• Terms– Simulation

– Internal simulation

– Mental simulation

– Emulation • approach tries to model the mechanism by which the simulation is produced



• Several simulation theories, but perhaps the most influential is known as the Simulation Hypothesis [Hesslow 2002, Hesslow 2012]

• Three core assumptions

1. The regions in the brain that are responsible for motor control can be activated without causing bodily movement

2. Perceptions can be caused by internal brain activity and not just by external stimuli

3. The brain has associative mechanisms that allow motor behaviour or perceptual activity to evoke other perceptual activity

Covert action / covert behaviour

Simulation of perceptions

Simulated actions elicit perceptions



Internal Simulation Hypothesis [Hesslow 2002, 2012]

S1

S2 s2

r1s1 R1

r2 R2

No internal simulation




S1

S2 s2

r1s1 R1

A motor response to an input stimulus causes the internal simulation of an associated perception …




S1S2 s2

r1s1 R1r2 R2

S3 R3s3 r3

This elicits a covert action which in turn elicits a simulated perception and a consequent covert action



HAMMER accomplishes internal simulation using forward and inverse models

– The inverse model

• Takes as input the current state of the system and the desired goal, and it outputs the motor commands necessary to achieve that goal

– The forward model

• Acts as a predictor

• Takes as input the motor commands and simulates the perception that would arise if this motor command were to be executed

(just as the simulation hypothesis envisages)

ActionPercept

Goal

PerceptAction


Y. Demiris and B. Khadhouri. Hierarchical attentive multiple models for execution and recognition (HAMMER). Robotics and Autonomous Systems, 54:361– 369, 2006.

Inverse Model Forward ModelInverse Model Forward Model

Perception Action Perception


HAMMERArchitecture


Inverse Model Forward ModelInverse Model Forward Model

Perception Action Perception


HAMMERArchitecture


The HAMMER Architecture[Demiris and Khadhouri 2006]




The HAMMER Architecture[Demiris and Khadhouri 2006]

The choice of inverse/forward model pair is made by an internal attention process based on how close the predicted outcome is to the desired one




D. Wolpert, R. C. Miall, and M. Kawato. Internal models in the cerebellum. Trends in Cognitive Sciences, 2(9):338–347, 1998.

Cognitive Behavior of Humans, Animals, and Machines: Situation Model Perspectives 49 Center for Interdisciplinary Research, University of Bielefeld, Germany.

Multiple pairs of inverse & forward models




• HAMMER provides for the hierarchical composition of primitive actions into more complex sequences

• It has been implemented both in robot simulations and on physical robotic platforms



• HAMMER goes beyond the scope of episodic memory in effecting internal simulation by invoking actions and behaviours

• The sensorimotor associations involved in internal simulations, for forward and inverse models, requires both episodic memory and procedural memory

• Episodic memory is needed for visual imagery, including proprioceptive imagery

• Procedural memory is needed for motor imagery


The Symbol Grounding Problem

• Assuming a cognitive system has some form of symbolic representation of the world around it

– i.e. some set of tokens that denote objects in the agent’s world

• How does the representation, i.e. the symbols, acquire meaning?

How do purely symbolic representations acquire semantic content?

• These apparently innocent questions are made difficult by the fact that (physical) symbol systems are governed by purely syntactic processes



• Physical symbol systems

– Atomic symbols

– Strings of symbols

– Symbol-based rules that define the manipulation and recombination of symbols and strings of symbols

• Defined in terms that make no reference to what these symbols mean



• But they are all “semantically interpretable”

– the syntax can be assigned a semantic meaning so that symbols and strings of symbols can represent objects, events, or concepts, and describe them or stand in for them

• The problem is how to assign this meaning

• This is the symbol grounding problem [Harnad 1990]



• Symbolic representations have to be grounded bottom-up in non-symbolic representations of two kinds:

• Iconic representations– Derived directly from sensory data (e.g. visual imagery, motor imagery)

– Allow you to discriminate between different objects

• Categorical representations– Based on the output of both learned and innate processes that detect invariant features of

object & event categories from these sensory data(e.g. object affordances, repeated behaviours ... food is nice; dogs bite)



• Higher-order symbolic representations can then be derived from these elementary symbols

• Both types of representation are non-symbolic

• A non-symbolic process is required to learn the invariances and thereby form the categories



• Usually, we use some form of connectionist approach

– Create the mapping

– Form the categorical representation

• As a consequence, according to this argument, a grounded symbol system is a hybrid system: a combination of symbolic and emergent approaches (h not H)



• A restricted form is the symbol anchoring problem[Coradeschi and Saffiotti 2003]

• Concerned only with artificial systems



• Establish a relationship between a symbolic label denoting some object and the sensory perception of that object

• Maintaining that relationship over extended periods of time, even when that object cannot be seen

• Only concerned only with grounding physical objects

– Doesn’t address the grounding of abstract concepts (war or peace)

Introduction to Cognitive RoboticsTypes of Memory Episodic •Episodic memory is a constructive...

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