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|What Is an Affordance?
Jones, Keith S.
- Evolution of Gibson's affordance term
- 2 categories:
- Objects and events have no inherent
everything created in animals mind.
- Objects and events have inherent
by animal, without any mental calculation, direct perception view.
- (1938) Valence term,
motion perception, field of safe travel+minimum stopping zone.
Connection with affordance, ratio
of, Warren. Ratio of stair-riser height and leg length ->
control of climbing behavior
- (1947) Inherent meanings of optical
retinal motion pattern, optic flow
- (1950) Possibility of perceiving spacial meanings
- meanings and spacial properties not
(color, texture etc.)
- symbolic meaning separable and learned
- meaning is inherent in something ->
- immediate awareness of the
by environmental objects.
- (1966) Relation between perception and
- "When constant properties of constant
perceived, the observer can go on to detect their affordances"
- (1979) The
Ecological Approach to Visual Perception
- Gives fundamental components of
- Environment offers
affordances to animals,
affordances to animals
- Imply complementarity of animal and
- Psychologists assume that objects are
quantities. What we perceive when we look at the objects are their
affordances, not their quantities -> Special combination of
quantities are not noticed.
- Perceiving an objects properties and
is quite different.
- Affordance: The
affordance of anything is a specific combination of properties of its
substance and its surfaces taken with respect to an animal.
theory of affordances
affordances with events
- At 2002, Ecological Psychology, North American Meeting:
- Stoffregen critiques Turvey's definition and gives
- Claire Micheals discussed:
- ontological status of affordances
- their relations with actions
- their relations with effectiveness
- question of what level of description
- Chemero: Affordance is relation between
animals and features of the environment.
|Affordances as Properties
of the Animal-Environment System.
Stoffregen, Thomas A.
- Affordances are emergent properties of the
- A critique of Turvey's formal definition of
affordances (dispositional properties)
- Properties of animal-environment system:
- do not rely on dispositional properties (I think
they rely on, but not completely)
- should be consistent with direct perception.
- Affodances are central to ecological approach
to perception and action, lots of references.
in the exact meaning complicate attempts to use affordances.
- In this article, a formal definition of affordances is
- Definitions in prose:
- What kind of things are afforded? Behaviors... ex:
- Gap affords passage,
- Stair with a certain propotion to leg length
- Rigid surface with respect to the weight of animal
- Ball falls with respect to person's velocity
- Time gap on traffic, safe crossing is afforded.
- Affordances are relations between animal and
environment with consequences in behavior
- Affordances are properties of environment of an
animal that have consequences for animals behavior.
- Turvey: Affordance
is property of environment, effectivity is property of animal ->
Behaviors are actualized. However dispositional properties should be
actualized whenever conditions are sufficient.
- Formal Definition of
- Wpq = (Xp,Zq) ie person-climbing stairs system
- p is property of X, q is property of Z
- relation between p&q, p/q, defines a higher
order property h.
- h is said to be an affordance of Wpq iff
- Wpq posses h
- Neither X nor Z possesses h (exists only in
- The dynamics of
animal locomotion is influenced by the dynamics of surface support.
- Not only leg length, but also strength, flexibility,
- Relations between the size and mass of the objects and
the reach, grasp and displacement capabilities of the person combine
not only whether prehension is possible but also how it should proceed.
(compare this view with Michaels)
- Definition of Behavior: Behavior
is what happens at the conjunction of complementary affordances and
intentions or goals. A given behavior will occur if and only if an
affordance and its complementary intention co-occur at the same point
in the space-time continium. From unlimited set of intentions, set of
affordances determines those that can be satisfied at any given place
and time. Architecture representation discussion!
psychological choice function, m(h,i),
this discussion is more central to behavior not affordances.
- Perceiving that a given intention is not satisfied
here, can motivate an animal to seek out conditions under which the
intention can be satisfied. Motivates:
- Exploration of the
- the acquisition of new
modification of the environment.
- Implications on specification:
- Identifying information that specifies affordances
is a critical challenge. Gibson :
"The central question..."
- Describing the physical relations and showing that
participants detect them does not explain how they are detected.. A lot
|An Outline of a
Theory of Affordances.
- Affordances are real and perceivable.
- Affordances are not properties of either environment
or animal but relation between environment and abilities
- Meaning of perceptions?
theories: Meaning arise inside animal, based on interactions
Meaning is inside the environment. Not depend on meaning conferring
inferences, simply gather information from a meaning-laden environment.
If world contains not only physical appearance but also some more (in
our case affordances), then it may include meanings.
- Gibson: Affordance is a resource, environment
offers any animal that has the capabilities to perceive and use it.
- What kind of animal-relative properties?
- Reed: The fundamental
hypothesis of ecological psychology is that affordances and only
relative availability of affordances create selection pressure on
animals; hense behavior is regulated with respect to the affordances of
the environment for a given animal. Resources in environment ->
develop perceptual systems to perceive resources -> resources exist
prior to animals. Tie evolution by natural selection and affordances
- Turvey: Affordances are
dispositional properties of environment. Dispositions depend on
possible actualizing circumstances, an object canbe edible only if
there are animals that can eat and digest it. Affordances, in Turvey's
preferred language, must be complemented by properties of animals. No selection pressure on animals.
For example, body scale is the property of animals to which affordances
of the environment related.
- Affordances are animal-relative
properties of the
- Are these properties exist without
- Affordances are resources that guide
- Dispositional properties of
should be complemented by properties of animals.
- Relevant properties of animals?
- Chemero: Affordances
are not properties! Affordances are relations between particular
aspects of animals and particular aspects of situations.
- Definition: Affords-Q (environment,
organism), where Q is a behavior.
- The relation affords-Q holds between
- The environment affords behavior Q to
- Chemero: Perceiving
affordances is placing features, seeing that the situation allows a
certain activity. Environmental relata in affordances should be features not properties!!
(stepping ability, riser height) - Affords-Q(feature,
- Effectivity: Effectivities
are defined as organismal complement to affordances qua properties of
the environment. Dispositions are guaranteed to become manifest :
soluble solid sugar will always dissolve in water in suitable
- Turvey: effectivity
- Ability: Functional
properties of animals.
- Chemero: affordance
has connections with evolution, but not in a selectionalist view.
Selectionalist view is inconsistent with animal-environment mutuality.
- Niche: a set of affordances
for a particular animal. An animals abilities imply an ecological
niche. All abilities depend on basic
Points of Debate.
Michaels, Claire F.
- 4 points:
- ontological status of affordances ,
exists without animals etc.
- affordances are related to one others
- relation between affordances and
- nesting of affordances, level of
- affordance: what environment offers to animals.
- Affordances are not created in the act of perception.
- Many scientists use term affordances to
refer mental states regarding
- Affordances do not arise as a
consequence of mental
operations. They are action-referential properties of the
environment that may or not may be perceived.
- Action relatedness?
- Ground affords walking, stair-climbing,
gap-step over, a nearby- object reaching
- Cliff affords danger, air affords visual
auditory perception. etc..
is tied to intentions. dynamics of intention.
- Visually guided action has two component
For example some situations affords swinging a bat but that the details
of when and exactly how to swing are solved by organization that is
assembled when on perceives the affordance.
- Definition of
- Affordances are actions permitted an animal by
environment objects, events, places...
- Action: goal-directed
- entails intention
- detection of information
- relation between information and
- Affordance is a
multi-dimensional compound of properties.
- Affordance exist independent of being perceived.
- Perceiving an action -> some action can be
engaged in himself.
|What Events Are.
- The aim of the article is to oppose Stoffregen's argument
on events such that we do not perceive events, thus there
is no motivation for an event research in ecological psychology.
- Events are defined as static
and dynamic properties of objects and surfaces defined without
reference to behavior and not scaled relative to action-relevant
properties of animals. However, Chemero try to make some events
defining the term as changes in the
layout of affordances of the animal-environment system, in the
examples of rising stair and
widening gap, we perceive the critical point where
affordance of the layout changes (we can climb/jump or not. This shows
that we can perceive the events. In such a convention, events are
perceived since they are action-related, personally scaled changes in
- From my point of view, this is a direct consequence of a somewhat threshold based approach, where
thresholds are directly known..
|Where Is the Information for
Gibson, Eleanor J.
- Focuses on the significance of the perception of events on
the perception of affordances in an ecological approach. Account of the
development of the perception of
events and affordances.
- Not relevant to the discussion of information extraction
from objects for affordances, but relevant to discussions on events..
- Members of air force, importance of being in high speed
- Gibson: Information for perceiving
the layout in motion and events
occuring over time, Gibson interested in the case of a moving
observer finding a safe path and avoiding
- Information for an affordance is to be found in events that
include the relevant environmental features, the activity of the
organism, and the consequences that ensue as well as the relations
- James Gibson in 1966, putting them into categories and
subcategories, noticing their similarities and dissimilarities.
- Minimal exploration behavior of babies, such as sucking and
looking, that enable them to their education. Learn their own abilities to control events,
and outcome... Eppler, 1993
|Perceptual Learning in
Development: Some Basic Concepts.
Gibson, Eleanor J
- This paper is a rare one, in which
learning of affordances are discussed. Eleanor Gibson based her
perception learning theory on differentiation,
instead of a process called association. She defines affordance
learning as the learning of relation between "organism's power of
control" and "some offering of the environment". Learning is a process
of selection, not construction from smaller pieces.
- She asserts that this relation is
learnt during development, and gives examples from infant studies.
- In her own words, perceptual
learning entails discovering "distinctive
features" and "invariant
properties of things and events".
- She underlines that even new born
infants are ready for active probing for i)gathering external
information, and ii)exploring body's own capabilities. James Gibson
locates information in ambient array of energy, and Eleanor Gibson says
"this array must be searched by the
appropriate perceptual systems to extract invariants".
Exploratory activity is crucial in her theory, as an example, infants
selects novel information instead of old/repeated experience. By the
means of this activity, organisms gradually.
- Perceptual learning is a selective
process, and selection process
rests on two principles:
- for an Affordance Fit: Fit between
ctions performed by an infant and the consequences at the end. Learning
to grasp, and carrying to the mouth for further exploration. In order
to grasp, first infant should learn if it is reachable, therefore,
learn its own arm length, the optimal or maximal size for grasping etc.
Additionally, in order to reach an object, it should learn the
affordance of locomotion.
- for Unity, Order, and Economy: "Economy of action and reduction of
perceptual information stand out as principles of selection for
increasing specificity." .. " Perceiving an object as a unit is a case
of detecting order and reducing information..." Talks about intermodal redundancy.
Approach to Perceptual Learning and Development: Commentary on
Michaels and Beek. By: Eppler, Marion A.; Adolph, Karen E.
- list of papers on ecological psychology, perception
learning, and perception especially in infants:
|Development of knowledge
of visual tactual affordances of substance.
Gibson. E. J., &
- Experiments on infants for study of affordance of rigid and
elastic objects, and establish connection between haptic and visual systems.
- In first experiments, infants are given identical rigid and elastic objects to play with, in a dark room. After the exploration
phase, objects are taken and motion pictures of not identical but
similar rigid and elastic objects. Infants pay more attention to the
objects that they did not see but handle before.
- In experiment 2, the objects are given in a lighted room.
The results are similar to the first experiment. The question is that
in first experiment, is it experience or direct detection of intermodal
invariants that drive affordance?
- Experiment 3 was performed on very young, 1 month infants.
The objects was concealed by hand while babies mouthing the objects. It is seen
that babies pay attention to the novel
- In all experiments, there is a tendency to look either novel or handled objects. This shows the
existence of the detection of
intermodal invariance on objects.
- Infants while handling, handle elastic objects and strike
rigid objects to ground, and while mouthing chew elastic objects. However, no real
discussion is performed on affordances, detection of affordances,
learning of affordances...
|The World Is So Full of
a Number of Things: On Specification and Perceptual Learning.
Gibson, Eleanor J.
- Main emphasis is on the discovery of information that
specifies affordances, in perceptual
learning. The aim of the paper is to discuss the importance of perceptual learning: The process of discovering information
that specifies an affordance is
- Differentiation is
the key term.
- Perceptual learning is not properly
defined as association or as
and addition of any kind, as
a response to a stilmulus, or as a "representation" of anything. An
active perceiver has the tasks of extracting the information that
specifies relevant events and especially, of detecting the information
that specifies an affordance of the environment relevant to the
perceiver's species, needs, and powers. Learning to detect the
information that specifies such a relationship is perceptual learning. Narrowing
down from vast manifold information to minimal,
optimal information for the affordance of an event or object or
- Infant learning and
infant labratory Discover
invariants of things
- Learning about communication,
learning about objects,
and learning about locomotion.
(most exciting comes with the advent of locomotion)
- Perception learning is not a matter of enriching the input but of
differentiating the information.
- Reference: An Ecological Approach to
Perceptual Learning and Development.
- The baby (after learning) learns how to use its perceptual systems
for obtaining information about what is going on nearby.
- Exploratory systems that are available very early are mouthing, listening and looking. Exploratory strategies are
greatly extended by increasing abilities to reach, grasp and engage.
|An Interview with
- Learning development of affordances.
- Not only static perception.
- Experiments with baby animals.
- Only Bob Shaw does research in cognition in the context of
- Visual Cliff Experiments
|Notes from Introduction to
Robin R. Murphy (Section 3.4.3)
- Affordance may be viewed as a percept that
behavior. Presence of red to a hungry baby arctic tern releases the
feeding behavior. Red: guide as well
as release an action.
- High object and ramp? object height
- poppy color evolution for bee bandwidth (evolution of environment-agent system...?)
- Why attractive from robotics point of
- Affordance is directly viewable, not
- Ball thrown, optic flow->
- Time to
- Not form or structure BUT function...
Stark and Bawyer
- GRUFF identifies chairs by function
form, chair is ... which serves functionality of sittability, no
memory, no inference, no interpretation?
- seat size, height etc. should be
- Direct perception
- When solving a problem, it should be determined if
affordances are sufficient or not for the problem. If not, one should
'certainly' employ more sophisticated methods.
Unknown Structured Environments.
Diaz, J., Stoytchev, A., and
- In this article, affordance
is not applied explicitly, and mentioned very
abstractly. Perceptual algorithms may be related to affordance
discussions, but they are very general and straightforward techniques.
- The aim of the paper is the exploration of structured
environments, whose inherent structures are statically embedded to the
control of the robot, which is a severe restriction for studies whose
aim is to develop systems for search, rescue missions.
- Literature on docking motor schema, which seems
nice. Arkin and Murphy (90), according to some endpoints, construct
vector fields, where robot make smooth moves.
- In corridor detection, based on laser range sensor
readings, hallway angle and width is calculated in order to navigate
robot in the middle line of the corridor. In door detection, again
absolute values, end points of door openings and width is calculated. Box filters with robot-based length
and width is used for detection of appropriate openings.
- Usage of laser range
scanner in perception of corridor
and doors may be used...
- Doorway endpoints repels
robot and hallway attracts, a potential field
is created... POTENTIAL FIELDS!
|Case studies of
applying Gibson's ecological approach to
Murphy R. R.
- Main emphasis is on the application of affordances in robotics as direct perception, where is can be
alternative to model-based approaches. It says it is an art rather than
science, as noted in all reactive implementations, and affordances are
compatible with reactive robotics.
- Literature on use
of optic flow in robotics is
- Literature on functionality of objects in the
context of affordances is represented.
- Neisser is
important since depending on this neurological and cognitive studies,
he suggests two perceptual systems, for direct perception and for recognition, where second one
accounts for semantic content (ie. your coffee cup). This in turn
suggests that affordances are not applicable for all behaviors.
- Murphy developed four step methodology for identifying
Three case studies:
- Define the task in
order to establish whether the behavior is a suitable candidate for
- Define the ecological
niche for the robot.
- Isolate potential
affordances either by examining biological processes or by extensive
consideration of the perceptual context.
- Implement the
perceptual process for each affordance and test over the range of
In discussion, the information on color of cans or color of
line or textures are innate and
no requirement for explicit perceptual models.
My result is the article
is on direct perception
but could hardly be used in affordance based robotics.
But it gives clues on the difficulties of designing of affordances,
importance of complexity of tasks, Neisser's division of perception
system, and the importance of ecological niche.
- Fine positioning: The
problem is to dock with a workstation. First robot uses coarse
ballistic movement to get in the range, then use affordances for
fine-positioning. The inverse
perspective tranform, which is based on distortions in size and
shape of landmarks might be used, but it is very sensitive to
segmentation errors. Inspired from fish
schooling behavior and employment of number of activated cones
that plays important role in fish perception, following method used:
Surface with a uniform texture appears differently from different
orientations. Therefore, the region is divided into two, and the ratio
between two halves give directions.
- Path Following: A
winner white line path following algorithm is given. The algorithm is
solely based on majority of the
brightness pixels. Sonars are used to differentiate white
objects from white line. In the discussion, direct perception is good
for predictable environments,
and affordances should be carefully designed, that the system should
not be brittle. (Ecological niche)
- Pick up the Trash: There
are red, white cans, and trashes that should be put in. Colors serves
as affordances. There is no need to model because colors are
distinctive, and there was no reason to label cans, only approach to
the closest can. However, system is again brittle, in different
lighting conditions, brown surrounding boxes are similar to red cans,
and attract robot.
Duchon A. P., Warren W. H.
- This article mainly emphasizes the striking parallels
between ecological psychology and new trends in robotics in terms of
interaction with environment. Mainly optical
flow is employed in obstacle
avoidance and game of tag
on two different robots. (Louie &
- Robotic research mostly employs sensors other than vision
because vision problems are usually ill-posed. However, they allege,
instead, by active vision,
these problems would become well-posed. He suggest vision as the most
promising sense relating robotics and ecological psychology. Following
Ballard's (1991) question, 'what is vision for? ' they concluded
animals may not need to model their environment in order to perceive
the relationship for survival.
- direct perception: 'the
animal has direct knowledge of, and a relationship to, its environment
as a result of natural laws. Direct perception is usually applied to
motor behaviors, BUT animals not respond stimuli, choice among many
possibilities is done.
- They gave a introductory description of optic flow and
motion control laws, and present related work on control rules, like control of balance, steering, baking in
humans, and control of flight in flies. Control laws are mostly
referred to Warren. Authors
additionally give emphasize on the importance of action mode, when governing
different control laws, and relate this to affordances.
- Authors define the term ecological
robotics as the field which applies principles of ecological
psychology to mobile robot design. They gave some principles of
- Animal-environment system should be treated together
- Dynamics of the system has main role on animal's behavior.
- Task is to map available information to control
parameters in order to achieve a desired state.
- "The environment provides enough information to make
adaptive behavior possible"
- No central model is need, but memory for specific tasks
may be employed.
- Detailed formulas of control
laws on obstacle avoidance,
wandering, fixating the target, escaping, and chasing
are given, and described. Some triggering mechanisms for activation of
these behaviors are determined according to optic flow. Additionally segmentation from optic flow is used
for escaping and chasing. Results showed that there are some drawbacks
in usage of segmentation, and it requires careful design.
- Centering response: bees
fly to equate optic flow in the lateral positions of each eye.
- Balance strategy is
used in obstacle avoidance from the motivation, closer objects give rise to faster motion
across retina than farther objects. It is found to be
resistance to noise. However it is inept when robot is encountered with
corners since it has
same properties with hallway.
- 2 reflexes for emergency : 1- intensity reflex (when no optic
flow available) 2- eta-reflex (when
too close to an object).
- If FOE (focus of
expansion) is false due to imperfect alignment of camera with wheels,
is could be adapted.
- Some literature on
robotic implementations of similar
ideas are given, and an additional one for insect literature is given.
- The behavior when robot passing
through apertures, is obtained and discussed in terms of optic
flow and speed of the robot.
- Some literature on
- Subsumption architecture
- Simultaneous acting of
controls with varying thresholds
- Simultaneous acting with
- dynamics (Schoner
- schemas (Arkin
- When Wanderer moves at an angle to Watcher's heading,
because of the resulting flows, target is misinterpreted to expand and
thought it is close. One possible explanation for prey's zigzag
- Literature and
references on action-perception
robotic research and planning.
- Aloimos, Brooks, Coombs, Horswill, Pfeifer,and Sandini
- Mataric and Meeden
- One conclusion or motivation 'know that' first requires one to 'know how'.
First avoid, then know what is it..? BUT both are required.
|Ecological Perspectives on the New
Effken, Judith A.; Shaw, Robert E.
- In this article authors make reviews of two books, which
study robotic problems in ecological perspectives. Both Connell's and
Beer's books criticizes traditional AI approach, and opposes of its
deliberative reasoning approach, symbolic representations and
restricted application domains. Beer says domain-specific intelligence is
often totally inept outside that domain, and could not form a basis for
- They oppose the view of deliberative reasoning and instead
they propose adaptive behavior,
which implies animal's short term survival. From traditional AI view,
internal models should be constructed as world maps, however Connell
suggests an environmental consequence of an action taken by the robot
is perceived and used to modify and coordinate behavior directly
without intervening mental models or plans.
- In explaining reciprocal fine-tuning relation of detection
and control (action), authors compare European and Trukese navigators
in their exploration patterns.
- As a last word Beer in his book explores encoding
intelligence as adaptive behavior, and Connell demonstrates goal-based
robot "behavior without representation".
Review: Intelligence as
Adaptive Behavior: An Experiment in Computational Neuroethology.
Randall D. Beer.
- He designed a cockroach who is mainly governed by its
perceptual sensitivity, by mimicking reflexes, taxes, fixed-action
patterns, and motivational control.
- Beer is influenced from
- Maturana and Varela's (1980) structural congruence theory
which is about animal-environment relationship.
- Schoner and Kelso's (1988) dynamic patterns
- Brook's ideas (1986)
- Braitenberg's synthetic approach, which dictates the law
of uphill analysis and downhill invention. Synthetic approach is
reminiscent of Grey Walter's Elmer and Elsie electronic tortoises
(1940), which seeks light, charge, explore, become hungry, and seek
- One of the main emphasis is on the modeling of the simple whole animal in their environment,
instead of modeling a subsystem of a complicated
animal in a restricted domain. This would give better insight on
natural systems. Beer defines this approach as computational neuroethology.
- Shaw and Bransford (1977) evolution tunes perception
systems to be most sensitive to the invariants (is one of the greatest
adaptive significance to the animal).
- Control is established through a number of mechanisms
- A central pattern generator for rhythmic movements of leg
- Stance and swing motor neurons for swinging when eating
- 6 individual leg controllers for avoid walking when moving
- Control of the gaits cannot be designed statically, but
should be made dynamically, heavily depending on the stimuli
- There is no mechanism for compensation of a lost leg,
Effken et. al. suggests a mechanism where reflex detectors perceive
absence of contacts, and make use of another gait control. Beer
suggests redundant structures that could be recruited in case of
- Effken et. al. suggests directions for future work on
robotics, where he gave termite nest building mechanism.
Minimalist Mobile Robotics: A colony-Style Architecture for an
Artificial Creature. Jonathan H. Connell.
- Problem in traditional robotics stems from the centralized nature of world models
and path planners since all sensory inputs should be condensed for the
model. Connell relies heavily on vertical
decomposition of tasks and distributed
perception and control of independent
agents for tasks, which may in turn limit the overall
- Control is solely depend on local information, no mental or world models involved. This
approach may be enriched with incorporation of global intentional
constraints for future development. Independent agents work with local
info but these agents should monitor the plan along the way.
- Use of world as its own
- There is no overall plan and representation, but embedded
partial representations and sketching plans.
- Decend, Bounce, Surface and
Over behaviors for
control of hand to pick-up can above a table. The robot's plan is
actually derived from the sequence in which the environment allows
behaviors to be triggered:
- raise hand, extend hand, hand down, search for can, when
approach -> local proximity sensor allignment
- The trajectory is guided by environmental constraint, very
flexible in case of changes.
- Six independent behaviors are included into a sort of subsumption architecture. Insert new
levels.. With such a mechanism, complexity of behavior of arm
- A Gibsonian view on object retrieval. When robot perceive a
can, it approaches to the can. If can's image is greater than a
predefined patch, robot loses interest to the object.
- Direct coupling of
perception-action, robot concentrates only on that part of the
environment directly relevant to current activities.
- For future:
- Local minima problem can be overcome by acting on no
showing of progress.
- Detection of invariants (exploitation
of Gibson's affordance concept). Structural invariants are those
properties that remain unchanged under transformation. Gibson: When the constant properties of constant
objects are perceived (the shape, size, color, texture, composition, motion, animation, and position relative to other objects), the observer can go on to detect their affordances. The
design trade-off: determining invariant structure that specifies
affordance and building robot with the capability to detect the
invariants in its world. Critical
preliminary for learning. Which
affordance requires which invariant?
- If usual path is blocked, develop alternatives
- No adaptation... An alternative: priority setting
procedure, theta-space summation alternative
where behaviors are rated in all possible directions.
- Effker and Shaw emphasizes the importance of dual work
performed by ecological psychologists and robotic researchers.
|Human wayfinding in
unfamiliar buildings: A simulation with cognizing agents.
- Afffordances : 1- pyhsical, 2- social-intitutional, 3-
- interested in immediate
sensing of information presented
- no ability to
learn, everything is explicitly given
- transition graph and commonsense reasoning on decision
- extracting meaning of features directly
- "Gibson describes the process of perception as the
extraction of invariants from the stimulus flux. Surfaces absorb or
reflect light and Gibson's radical hypothesis is that the composition
and layout of surfaces constitute what they afford"
- Gibson is criticized
by neglecting process of cognition.
- Gaver "a person's culture
and experience and intentions
also determine her perception of affordances".
- path's affordance: 'go-to' affordance, sign: 'reflect
light, match', decision point: 'search'
intelligence from artificial reality: building
stupid agents in smart environments.
- This article is devoted to the development of intelligent agents in virtual
worlds, especially for online games. The aim is to increase the
believability of the agents, giving adaptation abilities to agents in
changing worlds, equipping agent with learning abilities, enabling
agent to direct perception and means of usage of environmental
features, and enabling agents to have completely different
characteristics when encountered with different situations.
- Affordance, is only
used as an abstract concept, author described affordances and nice
features that it provide. The world is
its own best model , from Brooks, construct a basis for the
ideas in the paper. For example agents would learn from
experiences through direct queries rather than pure reasoning, but this
point of view has loose relation with Gibsonian perception approach.
- Initially, the characters only know the world's basic
dynamics, by using the annotations given, they will become believable
and living characters. They will naturally evolve as unique individuals.
- Additionally updating [world] annotations is easier than
reprogramming each agent.
|Events as Changes in the
Layout of Affordances.
Chemero A., Klein C., Cordeiro W.
- The motivation is to show that event as changes in the
layout of affordances are perceived.
The question is on the value of event perception research.
- Change in the layout of affordances: Appearance and disappearance of
- 2 types of events:
- Ecological events changes
in action-neural physical magnitudes
- Physical events static
or dynamic properties of objects.
- Judge the critical point where gap not affords passing over
(gap crossing affordances disappear)
- 3 main experiments:
- step-across judgment task with a platform moving away
- step-across judgment task with static platforms
- and actual stepping task to measure stepping length.
- Results show that there is a high correlation between
critical points of first two experiments, and real stepping length.
- The discussion is on the notion of event, should changes in the layout
of affordances regarded as events or not.
Kinsella-Shaw, J. M., Shaw, B.,
& Turvey, M.T.
- The main emphasis of the paper is on the distinction of visual and geographical slant study. The
previous slant perception has limitations, later one has implications
on affordance study since it
underscores the importance of action-relevant
- In geographical slant, the focus is on a surface's
inclination relative to the surface of the earth where in optical
slant, absolute measures are considered, ie with respect to another
- In the first experiment, the slope of the surfaces are
incremented and decremented by a participant in order to determine the critical walk-on-able point. It is
observed that independent of the distance of the participant, he can
judge the critical point correctly.
- In the second experiment, the relation between haptic and visual contacts with slanted
surfaces are compared, participants were able to judge the correct
visual slant, with respect to a haptic slant applied to one of his foot.
- My own
notes: The application to the robotics would be to learn the
critical slant of robot, and than robot's weight may be changed (robot
may carry a heavy object), and affordance critical slant should be
|To Cross or
Not to Cross: The Effect of Locomotion on Street-Crossing Behavior.
Oudejans, R., Michaels, C., van Dort, B., &
- Main emphasis of the paper is on the comparison of
crossability affordance of a street between in a stationary state or
- For some affordances, body scaling is not sufficient, and
scaling of environment to action capabilities is required.
- In the end of the experiments (observations), it is seen
that moving people judge the critical
value of crossing much better than in stationary because affordance entails a relation
between time gap and walking speed, and perception of the walking speed is clearly
not accurately available in stationary state.
- Gibson : We must
perceive in order to move, but we must also move in order to perceive.
Clearly while walking we perceive our ability about walking.
Additionally while walking we possess enhanced perception of distance and
enhanced perception of time to arrival because of the optic flow.
affordances: Visual guidance of stair climbing. Warren, W.H.
- Main emphasis of the paper is the affordance
of objects or features, where constant critical points (phase
transition to a new action) and optimal
points are perceived, and these points are body-scaled metrics with respect to
environment and experiments
are performed for stair climbing case.
Optimal points are searched in terms of minimum energy consumption.
- The motivation is to understand how animals and humans
could efficiently visually guide in a cluttered
- In a work of Gibson (1983), infants exploration of traversable and non-traversable surfaces.
- A path affords locomotion?
- surface rigidity in relation to body mass,
- surface contours in relation to gait,
- passage width in relation to body dimensions, and so on.
- Perception of relationship between environmental properties
and properties of its own action system: Intrinsic or 'body scaled' metric for
analysis of visual information.
- Affordance studies for animals:
- Frog detects
apertures that afford passage
for its specific size.
- Praying mantis
attacks according to prey radius and it's forelimb.
- East-coast limpets:
the affordance of attack and retreat are determined by relative size of
predator and prey.
- Affordances do not depend on solely geometric variables but also kinetic and dynamic variables such
as mass, force, friction, elasticity.
- In stair climbing case: the
functionally relevant variables are: step frequency, riser height,
stair diagonal, leg length, and body weight.
- The intrinsic unit, the dimensionless ratio, pi is defined to be the ratio of
environment related properties and animal related properties. Through
experiments this pi ratio is
taken to be R/L where R is
riser height and L is leg length. If this ratio is too high, it is very
difficult to climb the stair; if too low, the time and energy
will be large in order to reach a certain height.
- 3 experiments are performed:
- In first experiment, visual perception of critical
riser height is first estimated in pi ratio, then experimented, and at
last observers are asked to judge
whether each stairway looked climbable or not. Both short and tall
observers judge critical height, in a constant pi.
- In second experiment, energetic
of optimal riser height, the height of the riser is tuned, and
participants are asked to walk on the stairs. According to the total oxygen consumption, a pi value is again computed. This
constant is found to be same for tall and short participants.
- In third experiment, visual
perception of optimal riser height is studied, and visual
preferences of tall and short observers are found to be compatible with
the pi number of second
- The intrinsic optical
information is underlined in the discussion part, since it is
available in natural viewing conditions.
|Visual guidance of
walking through apertures: body-scaled information for affordances.
Warren WH Jr and Whang S.
- The previous work, which was devoted to understand the perception of constant optimal and critical points on climbability affordances, is
extended to the analysis to visual guidance of walking through apertures. Passability judgments are studied
under static and moving viewing conditions. Aperture-to-shoulder width ratio is
found to be the body-scaled constant
which results in shift in behavior (transition from frontal walking to
- Affordance problem: visually
controlling body rotation when walking through narrow apertures.
- Evidence for body-scaled
perception: Hallford (1984) Observers are more accurate and had
higher confidence when judging whether they could grasp rectangular
objects with one hand than when judging their widths relative to a
standard object that was first viewed and then held during the
- Other works:
- Optimal and maximal sitting
height (Mark and Volene)
- Maximal reaching distance
- Infant climbing
stairs (Ulrich, Thelen, and Niles, 1986)
- Infant traverability
of surfaces (gibson, Riccio, Stoffregern..)
- Experiment 1: Critical
Aperture Width is analyzed for rotation of body, done with narrow and
broad shoulders. Aperture width and
significant, and there was also a main effect of speed. The result is intrinsic
scaling eliminates group differences. and critical point is a constant
for the ecosystem, regardless of scale changes in the size of the actor.
- Experiment 2: Visual
Perception of Critical Aperture Width is analyzed. Two different
conditions, first one is static condition
with monocularly preferred
eye, and second condition is moving condition
with binocular view. In both
conditions, for varying aperture sizes, participants are asked whether
the gap is passable or not. In this experiment group and aperture width are found to have a
main effect but viewing condition
effect is found to be insignificant.
The aperture-shoulder width ratio
is found to be a bit smaller than first experiment, most probably
because of the setting of the experiments.
- One main results is that, despite
the fact that more visual information is available in the moving than
in the static condition, there was no main effect, and perceptual
category boundary values are nearly identical. Experiment 3 are
conducted in order to understand this unexpected result, is prior
exposure the main effect?
- Experiment 3: is on
the available information (perception) nature, is it intrinsic or
extrinsic? In the first paragraphs of this experiment, the importance
of eyeheight information and
what clues it may provide to us about height/width/distance
of surrounding objects is discussed. After this discussion, in
experiment environment, the eyeheight of participants are changed and
this modification with its known observable results is conceived from
participants. The aim is to try to change intrinsic information (eyeheight
ratio) without changing absolute values (absolute width of apertures).
Since most probably people use this intrinsic information (eyeheight
ratio) when perceiving the width of the aperture, their estimation of
the size of aperture in terms of passability
affordance, is altered; observers overestimates the size of the
apertures in the raised floor
- Although observer make false judgments on width of the
apertures, distance values remain invariant independent of the
- There are some work on animals:
- Ingle and Cook (1977) found similar cues on frogs jumping through apertures.
- Lock and Collett (1980) found similar cues on toad move through apertures.
- The general results are:
- Static monocular vision seems sufficient for judgments of
- Animals use intrinsic information (perceive aperture
width as ratio of eyeheight).
Information About Affordances: A Study of Sitting and Stair Climbing.
Mark L. S.
- The main emphasis is on the intrinsic or body-scaled
information (scaling with reference to eye-height).
- The extrinsic traditional approach says that for example
distance is scaled in meters, and we make a re-scaling according to our
demands and body-size. However, in intrinsic view, there is no such
metric absolute information that we obtain, but instead we perceive
them either far or close to reach.
- Climbing on case,
Warren find constant proportion.
- Sitting Mark and
Vogele constant wrt. person's leg length.
Solomon et. al.
- Grasping Hallford.
- Passing through
aperture, Warren and Wang.
- Children's climbing Ulrich,
Thalen and Niles.
- Style of contact Lee.
- Catching behaviors Micheals,
Prindle and Turvey.
- Experiment 1: Observers
utilize eye-height scaled information about surface height in
determining whether surface can be sat
on and climbed on.
For each subject, judgments of perceived eyeheight, in terms of max sit and climb cases, decreased
monotonically with viewing distance. In contrast to these, estimates of
object size did not decline as a function of viewing distance. Changes
in judgment of two action boundaries are closely correlated with
- The motivation between the relation of eye-height and
viewing distance is a suggestion that observers
tend to underestimate their eyeheight as a function of their distance
from surface at which they are looking???
- Experiment 2-3: A
block is wore by observers, therefore, they were aware of the change in
their body-abilities and eye-height dimensions. Results show that
observers use intrinsic eyeheight-scaled information in determining..
|Detection of the
traversability of surfaces by crawling and walking infants.
Gibson, E. J., Riccio, G., Schmuckler, M. A., Stoffregen, T. A.,
Rosenberg, D., Taromina, J.
- The main objective of the experiments is to study affordance of surfaces, via rigid and deforming surfaces. The experiments
are performed on both crawling and walking infants, and effect of visual
and haptic information is tried
to be understood.
- In order to perceive the affordance of sth, we should also
detect the constraints imposed by own statures (ie. Warren's stair
height, observer's height experiment).
- The importance of visual and haptic information, and any
dominance of visual or haptic information is looked for.
- The rigidity of surface is defined as its resistance to
- Experiment 1: Two
textured surfaces, deforming one is agitated by an unseen experimenter,
giving a wavy appearance. In the results section, rigid surface tended
to have a shorter tendency for initiation of traversal for walkers.
There is no differentiation between surface latencies for crawlers. The
next experiment used dual way, and infants are asked to select rigid or
deformable surfaces. Again the behavior and latency of walkers and
- Other 3 experiments are performed in order to understand
the importance of visual and haptic information, by means of
contradicting the optical information for deformability, giving
surfaces which does not give any visual clue on its deformability.
- The details of the experiments are not relevant to
affordance based robotic research for the time, since there are very
detailed discussions on other factors like age, effect of novelty, etc.
- BUT on conclusion
for is may be agents employ both haptic and visual information when
deciding the affordance of traversability of surfaces.