SUSS PSY 305 STUDY UNIT 2 PERCEPTION (CONCEPTIONS OF OBJECT PERCEPTION…
SUSS PSY 305 STUDY UNIT 2 PERCEPTION
Perceiving a Scene
to determine what is “out there,” it is necessary to
go beyond the pattern of light and dark
that a scene creates on the retina
—the structure that lines the back of the eye and contains the receptors for seeing
Top-down and Bottom-Up processing
Factors that influenc top-down or bottom-up processing
The multiple personalities of a blob
of different pictures appear to be identical, they are
perceived as different objects depending on their orientation
and the context within which they are seen
We perceive it as different objects because of our knowledge of the kinds of objects that are likely to be found in different types of scenes. The human advantage over computers is therefore due, in part, to the additiona
l top-down knowledge available to humans
coded in the form of memory can
Hearing Words in a Sentence
Because of our knowledge of the language, we are able to tell when one word ends and the next one begin.
Otherwise, it will be percevied as an unbroken string of sound
if a listener understands the language, that knowledge (top-down processing) creates the perception of individual words.
The continuous sound signal enters the ears and triggers signals that are sent toward the speech areas of the brain (bottom-up processing)
direct pathway model .
According to this model, pain occurs when receptors in the skin called nociceptors are stimulated and send their signals in a direct pathway from the skin to the brain
It is a bottom up processing.
refers to a decrease in pain from a substance that has no pharmacological effect
It is a top down effect
Top-down and Bottom-up
The brain is constantly bombarded by sensations or raw signals/information coming from various
stimulus detected by sense organs (bottom-up processing)
and subsequently, the
attempts to make sense of these incoming signals
The signals are not always easy to decipher and are at times, ambiguous.
This sequence of events from stimulus to receptor to brain is called bottom-up processing , because it starts at the beginning of the system (i.e stimulus), when
environmen stimulates the receptors.
originates in the brain
, at the “top” of the perceptual system, which influences the receptors to interprete stimulus in a certain manner.
Some Basic Characteristics of Perception
change based on added information
Something that looks unfamiliar may be more clear when we get closer and have more information.
involve a process similar to reasoning
or problem solving
(Figuring out what a perceived object is based on recalling information which mirrors features associated with the present perceived object)
perception can be
based on a perceptual rule
(when objects overlap, the one underneath usually continues behind the one on top), which may be based on the persons' past experiences.
involve a process
(i.e information gathering, processing and recognition)
occurs in conjunction with action
(i.e. you percevie teh presence of an object eitehr through the act of seeing, heaering or feeling, etc)
Perceptual errors and illusions
Our brain constantly strives to resolve visual ambiguities in our environment and we often
rely on our past experience and existing knowledge to help make sense of ambiguous stimuli.
We use heuristics (rule of thumb) or shortcuts to make quick decisions and this sometimes leads to errors in perception.
For example, mistaking a coil of garden hose in the garden for a snake. If one did not have any knowledge about snakes or snakes in the garden, one may not mistake a garden hose for a snake
WHY IS IT SO DIFFICULT TO DESIGN
A PERCEIVING MACHINE?
Objects Can Be Hidden or Blurred
problem of hidden objects occurs any time one object obscures part of another object.
Problem can easily be overcom by humans who understands that
part of an object that is covered continues to exist,
. Not easily recognised by computers
Objects Look Different From Different Viewpoints
This means that the
images of objects are continually changing
, depending on the angle from which they are viewed.
Thus, although humans continue to perceive the object as the same chair viewed from different angles, this isn’t so obvious to a computer.
The Stimulus on the Receptors Is Ambiguous
inverse projection problem
Object perception starts with the image on the retina, and its job is to determine the object “out there” that created the image.
The task of determining the object responsible for a particular image on the retina is called the inverse projection problem , because it
involves starting with the retinal image and extending rays out from the eye
extending rays out from the retina could result in a number of ambiguos image.
Although the inverse projection problem can be countered by the human eye, it may not be easily countered by a computer
CONCEPTIONS OF OBJECT
Helmholtz’s Theory of Unconscious Inference
Helmholtz’s question was,
How does the perceptual system “decide”
what pattern is displayed on the retina
Helmholtz suggested the likelihood principle, which states that
we perceive the object that is most likely to have caused
the pattern of stimuli we have received
through the process of unconcious inference
it is a process in which our perceptions are the
result of unconscious assumptions
, or inferences, that we make about the environment. Thus, we infer what is likely to be the pattern
rapidly and unconsciously
These unconscious assumptions, which are based on the likelihood principle, result in perceptions that seem “automatic,” even though they are the outcome of a rapid process.
Thus, although you might have been able to “automatically” solve the perceptual puzzles, this ability, according to Helmholtz, is the
outcome of a rapid process that we are unaware of
The Gestalt Principles of Organization
The Gestalt psychologists rejected the idea that perceptions were formed by “adding up” sensations. (i.e. rejects structuralism)
According to gestalt we don't learn such laws but it is in built in us.
Wertheimer's observation on 'moving lights'
The conditions for creating the perception of movement between flashing lights.
(a) One light flashes, followed by
(b) a short period of darkness, followed by
(c) another light flashing at a different position.
The resulting perception (d), is a light moving from initial point, to its present point.
Movement is seen between the two lights even though there is only darkness in the space between them
from the phenomenon of apparent movement
movement cannot be explained by sensations
, because there is nothing in the dark space between the flashing lights
His second conclusion became one of the basic principles of Gestalt psychology:
The whole is different than the sum of its parts
. This conclusion follows from the fact that the perceptual system creates the perception of movement from stationary images (led to the principles of percetual organisation)
Principle of good continuation
The principle of good continuation states the following:
Points that, when connected, result in straight or smoothly curving lines are seen as belonging together, and the
tend to be seen in
such a way
follow the smoothest path.
Also, objects that are
overlapped by other objects are perceived as continuing
behind the overlapping object
principle of good figure, simplicity/ law of pragnanz
Every stimulus pattern is seen in such a way that the resulting structure is as simple as possible
principle of similarity
Similar things appear to be grouped together.
can occur because of similarity of colour, size, shape, or orientation
Taking Regularities of the Environment Into Account
Modern perceptual psychologists have introduced the idea that
perception is influenced by our knowledge of regularities in the environment
—characteristics of the environment that occur frequently.
For example, blue is associated with open sky, landscapes are often green and smooth, and verticals and horizontals are often associated with buildings.
We can distinguish
two types of regularities
: physical regularities and semantic regularities
two types of regularities
Physical regularities are
regularly occurring physical properties
of the environment.
For example, there are more vertical and horizontal orientations in the environment than oblique (angled) orientations.
We usually assume that light is coming from above, because light in our environment, including the sun and most artificial light, usually comes from above.
influence our perception of depth and texture.
Semantic regularities are the characteristics
associated with the functions
carried out in different types of scenes.
I.e. When asked to imagine an office, people would normally percive or assocaite images of office-related peripherals and furniture. It is not likely for a person to evok an image of a toilet in an office scene for instance.
This knowledge of what a given scene typically contains is called a
Bayesian inference was named after Thomas Bayes (1701–1761), who proposed that our
estimate of the probability
of an outcome is determined by
likelihood of the outcome
What Bayesian inference does is to restate Helmholtz’s idea—that we perceive what is most likely to have created the stimulation we have received—in terms of probabilities
the prior probability , or simply the prior , which is our
about the probability of an outcome
the extent to which the available evidence is consistent with the outcome
Comparing the Four Approaches