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TheEcologicalApproachtoVisualPerception
WhyGibson'sparadigmaticshift(still)matters
VincenzoSantarcangeloIEDMilano
May 11th 2017ONTOLOGIADELPROGETTO
PolitecnicodiTorino
There is considerable variation in the style and language of theories of visual perception
The reason for this is essentially that none of them deals with exactly the same arena of perception
The greater the number of regions to be included in a theory the more that theory tends to be general in form...
Brain
receptors
stimuli
effectors
ENVIRONMENT
ENVIRONMENT
ENVIRONMENT
ENVIRONMENT
Knowledge of the important properties of stimuli has come mainly from physics
Brain
receptors
stimuli
effectors
ENVIRONMENT
ENVIRONMENT
ENVIRONMENT
ENVIRONMENT
The environment is the physical world of surfaces and objects - the ecology of the organism
Incoming stimuli fromobjects in the world giverise to events some ofwhich can be detectedby perceivers
Sensory surfaces take incoming stimuli and translatethem into a neural code: of course, it is fundamental toknow the nature of this transduction, how light isabsorbed by the eye
Important questions concernthe pathways taken by neuralmessages, the codes which areused to represent differences inquality, intensity and duration
The brain obviously has a role to play, but...
Brain
receptors
stimuli
effectors
ENVIRONMENT
ENVIRONMENT
ENVIRONMENT
ENVIRONMENT
Most behaviourdepends upon brainprocesses but theseare commonly notavailable to directstudy and must beexplored indirectly
...organisms taken as wholesmake explicit responses to stimuli in the environment
We move around in the world and in this way strongly determine the stimulation we receive
Brain
receptors
stimuli
effectors
ENVIRONMENT
ENVIRONMENT
ENVIRONMENT
ENVIRONMENT
Modern Psychology (1950s - ∞ )
• Origins in developments during WW II• Influenced by development of – Information theory– Artificial Intelligence (computers)
• Emphasis is on the notion of information (as it is studied by informatics):– information available to organism
• e.g., via incoming light
– information processing needed to produce percept, carry out task• e.g., sense light, detect edges, group edges, …
Modern PsychologyMajor Assumptions
• Human and animal evolved in a particular environment for specific purposes– e.g. survival, reproduction, communication
• Uses computer models and simulations to gain insight into how biological brains work
• Focuses on information sensing and processing– ecological optics– cognitive psychology
Cognitive Psychology(Helmholtz, Marr)
• Perception is like scientific inference:–Information helps us decide between different
possible hypotheses• Internal model created by reweaving perceived
information–Hypotheses chosen using best guess based on
experience and information available to observer
Cognitive PsychologyAssumptions
• Information given is usually not enough to recover the “true nature” of objects– need to use knowledge and guesses– final result is hypothesis (with certainty)
• Hypothesis formation involves– processes that operate on symbolic representations of
the incoming information– processing is done unconsciously– similar to a computer
Cognitive PsychologyProblems
• It is still not clear that brain is and acts like a computer–we certainly know computers are not like
brains–brains may not use symbolic representations to
create an internal “copy” of the world• It is not applicable to conscious experience–computers are never conscious?
David Marr (1945-1980)The computational theory of perception
His work on artificial intelligence led tonumerous papers on perception and finally tohis book Vision which was publishedposthumously (he died aged 35 in 1980)
Important developments which contributedto his theories: - information theory- cybernetics - construction of large digital computers
MARR Contributing studies used in developing his theory
This suggests that the visualsystem analyses visualinputs into specificcomponents, and that themechanisms which do thisare "wired into" thenervous system
It is therefore possible that the perception of certain basic features of the world is unlearned
In cat visual cortex
Cells respond differentially to lines and edges according to the orientation of these stimuli
MARR
Vision must start with the image on the retinathe end point is our awareness of the world
There seems to be a picture of the worldavailable to us whenever we open our eyesand look around. But the fact is that lightstops at the retina.
There can be no actual pictures in our heads,only neural activity. It follows that thisneural activity is representing the worldsymbolically, and we must therefore strive tounderstand this symbolic process.
Marr argues that symbolic representations of various aspects of the world, initially obtained from the retinal image, are combined into the descriptions which we call seeing.
MARR
He also used his knowledge of computer science to formulate a guiding principle - modular design
In solving computationalproblems generally, it iswise to break down thecomputation intocomponent parts whichshould proceed asindependently as possible.
® image® primal sketch® 2½-D sketch® 3-D model
James Jerome Gibson (1906 – 1979)
The Perception of the Visual World (1950)
The Senses Considered as Perceptual Systems (1966)
The Ecological Approach to Visual Perception (1979)
[Trad. it. 1999 (Il Mulino); 2014 (Mimesis)]
James Jerome Gibson is one of theleading theoretical pshychologist othe XXth century. He was a sort oflone genius working away ondifferent ideas that lastly leaded toth so-called ecological revolution inpsychology of perception.
The ecological approach is atheoretical standpoint according towhich psychologists have to workin the context of an intermediate levelof reality, that is in between theelementaristic psychology andmore abstract disciplines such asbiology, etology, physics, etc.
Inverse projection problemBottom-up information is not enough to create 3D perception.
Perception reconsidered
J. J. Gibson’s ecological approach– All the studies we have seen so far are conducted
in laboratory settings, in which stationary stimuli were given.
– Perception is not a stationary experience.
– Perception should be studied as it occurs in the natural environment.
The animals’ Environment, asdistinguished by the physicalambient is made by 1) amedium which contains 2)substances 3) surfaces,characterized by specifictextures, that separate thesubstances from the medium,and 4) information that theanimal can directly pick-up fromthe environment.
Ecological Psychology: some keyword
For terrestrial animals the specific medium is air. Being notinsubstantial it makes possible locomotion, that is, animalsare able to move in the environment.
Locomotion is controlled by the available information in themedium, and the information availability vary dipending animalspecies' ecological niches.
Information
Question:• What information do perceivers use as they
move through the environment?
• One type of information is:– Optic flow• E.g., expansion/contraction of a scene (an optic array that
reaches the retina).– We naturally notice the ratio of
expansion/contraction (what Gibson define a agradient of flow).
Some important characteristics of optic flow
• Invariant information– Gradient information remains constant under
different conditions.– E.g., texture gradient
Optic flow and a gradient of flow• A gradient of flow gives a strong cue for motion
and depth perception.– How much the scene expands on your retina gives you
enough information to capture depth perception
Optic flow and a gradient of flow• A gradient of flow gives a strong cue for motion
and depth perception.– How much the scene expands on your retina gives you
enough information to capture depth perception
An important consequence of James J. and EleanorGibson's theories is for example the assumption thatinfants can directly perceive information that exists inthe environment.
A famous example: Gibson and Walk (1960)
Depth perception in human childs
According to this perspective, infants actively explore for invariant features of the environment – that is, features that remain stable in a constantly changing perceptual
world.
Affordances
A key part of this strong assertion is the introduction of the well-known concept of affordances (see Gibson 1977, Gibson 1979; for its use in context of design Norman 1988, Gaver 1991).
The notion of affordances emphasizes there is an ecological fitbetween the individual and the situation (the environment), but...
What is an affordance?
"The affordances of the environment are what it offers the animal, what it provides or furnishes, either for good or evil." (Gibson 1979)
Affordances
• "The verb to afford is found in the dictionary, but affordance is not. I have made it up."
• "I mean by it something that refers both to the animal and the environment in a way that no existing term does."
• "It implies the complementarity of the animal and the environment." (p. 127)
Ontology
• Ontology studies the constituents of reality• An ontology of a given domain describes in
formal terms the constituents of reality within that domain
• The ontology also describes the relations between these constituents, and also the relations between constituents of one domain and others
(Smith, Mark)
What exists?
James J. Gibson's flat ontology“New Reasons for Realism,” Synthese, 17, 2, 1969
Objects. The earth and its fixtures: physical objects with theirperduring properties – as opposed, to objects (say, clouds), weesee in the sky, where this kind of properties do not exist.Events. Moving objects in the environment. Events can happenindividually or can be nested in sequences of singles events (e.g.speech, music). Anyway, events are part of the availabeinformation we can directly pick-up from the environment.Images. A particolar kind of non-direct information. Gibsondedicated the last two chapters of The Ecological approach to staticand moving images - to pictorial representation and to cinema.
Geographic Affordances(Smith, Mark)
• Conjecture: Parts of the environment gain meaning, become things, mainly according to the activities that they afford.
• Parts of the Earth's surface that afford more or less the same activities may be considered to belong to the same category.
For example...
• Mountains afford climbing• Mountains also afford navigation when they
serve as landmarks • Lakes afford fishing, the obtaining of drinking
water, swimming, travel by boat• Forests afford wood gathering, hunting, hiding
from enemies• Etc.
The Truth about Earth
• Earth is a roughly spherical planet with a rocky mantle and crust.
• In more detail, Earth is somewhat flattened pole to pole into an oblate spheroid.
• Geodesists have defined a reference surface known as the geoid which approximates the shape of planet Earth and which provide a datum for measuring surface irregularities.
More Truths: Water and Life
• Some 70 percent of the surface of Earth is covered by liquid water, and the planet is surrounded by a gaseous envelope called the atmosphere.
• Plants cover most parts of the land surface, and animals (including humans) move about among those plants.
Ontology for Science?
• A complete ontology of geographic phenomena will have to incorporate all of these scientific facts and more, but are they relevant to our current effort to describe primary geographic theory, naive geography, that is a geography relevant to action in environmental situations?
Land Forms
• Forces from above and below have shaped the form of the surface of Earth and other rock planets.
• The influence of gravity is a dominant factor—loose material tends to move away from high areas toward lower ones in a process generally termed erosion.
Land Forms
• Steeper slopes are less stable than gentle ones and so over time there is a tendency toward leveling unless other forces act against that.
• Overhanging cliffs are extremely rare, so the elevation of the Earth's surface can be conceptualized as a single-valued function of horizontal position, that is, as a continuous field.
Land Forms (generally speaking...)
• Generally speaking, this is how science hasmodeled the geometry of the Earth's surface.
• Scientists who attempt to account for or modelhydrology and sediment transport conceptualizethe Earth's surface as composed of slopegradients and orientations over a field ofelevations.
Topography Experienced
• The topographic environment as experienced by people is very different from this
• It is the same environment, of course, but experienced through human senses in the context of human activities and needs.
Topography Experienced
• When viewed from the surface of the Earth by a creature between 1 and 2 meters tall, variations of surface elevation of tens, hundreds, or thousands of meters dominate the experienced landscape, while at the same time, the curvature of the geoid, of the horizontal, is almost imperceptible.
Topography Experienced
• When people see, learn, and describe a landscape, they do not think of it as a field or surface.
• Rather, they consider it to be composed of objects or things, presumably based on some combination of gestalt visual perception and the perception of affordances.
Topography Experienced
• Visual perception tends to identify convexsurfaces are forming objects, and Gibson wroteof detached objects as having completely closedsurfaces making them moveable, or as attachedobjects that forms parts of the surfaces oflarger things.
Topography Experienced
• The perceived surface of the Earth appears tofollow this principle and to be dominated byconvex rather than concave parts.
Topography Experienced
• In an experiment which subjects were asked to list examples of geographic features, objects, or things, mountain was the most frequent example, listed by 151 of 263 subjects.
• A secondary form of land convexity, hill, was listed somewhat more often (by 43 subjects) than was the most frequent concave form, valley (39 subjects).
Topography Experienced
• Evidently, mountains are the quintessential geographic things to everyday people, yet they hardly appear in the scientific models. Nor do they appear as objects in our geographic databases.
Topography Experienced
• Mountains and the like also have been neglectedin philosophers' ontologies (e.g. Aristotle),which have taken as their paradigm for objectscomplete moveable things with their ownboundaries (such as people, or atoms, orplanets), what Gibson called "detatchedobjects".
Summary
• Geographic things are special• Some phenomena are more like fields• People apparently conceptualize most phenomena
as objects• Formalizing geographic ontologies should be
difficult, and fun!
Out of our heads: the enactive approach
Alva Noë, Out of our heads. Why youare not your brain, 2010.
“Enter art as a tool for phenomenological exploration. Consider the way a Richard Serra sculpture presents a surprising environmental occasion for phenomenological self-reflection. The pieces overpower and overwhelm, induce giddy disorientation,
and generally make us aware of what it is like to be a perceiver, an enactor of perceptual content. When we explore a Serra sculpture we actively explore an environment and the sculpture provides a context in which we are enabled to
catch ourselves in the act of exploring the world”.
“According to this approach to perceptual experience, the content of anexperience is not given all at once, as is the content of a picture given all atonce. Rather, the content is given only thanks to the perceiver’s exercise ofknowledge of sensorimotor contingencies. The content of experience isn’treally given at all – it is enacted”.
“It is not pictures as objects of perception, that can teach us about perceiving; rather, it is making pictures — that is, the skillful
construction of pictures — that can illuminate experience. Making pictures is a way of enacting experience. Picture-making, like
experience itself, is an activity. It is at once an activity of careful looking to the world, and an activity of reflection on what you see and what you have to do to see. The painter literally enacts the content of a
possible experience”. .
The artist, then, is a kind of experience engineer.
L’artista:uningegneredell’esperienza
L’artista:uningegneredell’esperienza
