INTRODUCTION TO PSYCHOLOGY
Chapter 5
Perception
At the end of this Chapter you should be able to:
Understand what Distance Perception is
Understand what Motion Perception is
Understand what Form Perception is
Learn about Attention
Learn about Visual Illusions
Distance Perception: Where is it?
Living in the world requires us to manage our sensations: and to answer these
questions once we sense an object in the environment:
Where is it?
What is it doing – is it moving, still?
What is it?
Binocular cues
We compare the retinal image in one eye to the retinal image in the other;
they differ: each eye is a slightly different distance from an object in the
world
Monocular cues
Interposition
Linear perspective
Texture Gradients
Perception of Depth through Motion
When we are still:
Objects further away will “move” across the retina a shorter distance that
objects closer to us; this provides a cue for depth
Optic flow information changes as we move either closer or farther away from
an object
Motion Perception
When you ride in a moving vehicle and look at the side window, the objects you see
appear outside move in opposite direction
Objects seem to be moving in different speeds-the ones that are closer to you seem
to move faster, whereas objects far behind seem to move slower
Perception of an event -motion- rather than an object
Motion tells us what the object is doing.
• Apparent movement
• Eye movement
Apparent motion
When intervals between images occur at correct timing (not too far apart in time)
we perceive motion
This principle used to create ‘motion’ from stills
In movies, when still pictures are put together, it produces the sensation of
movement for the viewer (audience). Even though there is no ACTUAL movement.
We do not only detect motion but we also interpret it.
Eye Movements
Problem: Our eyes and bodies are moving too…
But we do not routinely perceive “motion” in the world when our eyes move… only
when the object moves. How is this possible?
Our nervous system “compensates” for motion in head/eyes
Nothing around the object has moved, therefore the brain interprets that scene as
static. The two cancel each other out.
Form Perception
We can find differences among features effortlessly
Finding a circle in a field of squares is easy regardless of how many squares
there are
We need more than features or a simple checklist to be able to recognize
objects
Detecting object features (parts)
The importance of organization
Perceptual parsing
Separating the figure from the ground
How do we recognize what we see?
We need to be able to organize all the visual input we get, in our brains!
There are too many features around us: colors, lines, edges, textures etc…
How do we group together features that belong with each other?
What about the variability in objects that we see?
The same animal but the features look different. So how can we classify all of them
as a giraffe?
What about the variability in objects that we see?
We recognize giraffes as being giraffes whether we see them from the side, or the
front, or close up, or from far away.
Our brains can deal with the complexity in real world scenes.
Do we actually pay attention to every detail (feature)?
We only interpret crucial information. We don’t have time in the real-world to pay
attention to every little detail. Otherwise we cannot survive!
Organization’s role in perception
Features: some we ignore, some we attend to
How do we decide whether to ignore or attend?
We interpret some features as being part of the object, other features as irrelevant
Gestalt psychology
Important: Is the object figure or ground?
Our interpretation of figure / ground will influence how we perceive an object
The full pattern – the “gestalt” – is what determines our perception
Sense of shape: derived from the whole, not the sum of its parts (feature +
feature + feature)
Gestalt principles of organization
Perceptual parsing:
Segregating the “scene” into its constituent objects
The first step to organizing
Gestalt principles of organization:
Issues of figure/ground
Similarity
Proximity
Good continuation
“subjective contours”
The classical approach to perception
Emphasis on the active, constructive role of the perceiver, who routinely:
Resolves ambiguous figures
Determines identity of objects based on contextual clues and previous
knowledge
Maintains perceptual constancy: Shape, brightness, position
Illusions: How could we make such mistakes?
Cues sometimes cause an over-estimate or under-estimate;
Slight over/under interpretations can cause us to misinterpret the information we
receive
Usually:
perceptions are accurate
are based on relevant experience
reflect the world we live in
Perceptual selection: Attention
What starts the synchrony? One possible mechanisms: ATTENTION
Selective control of orientation
Selective looking
Difficult when target represents multiple, rather than a single, feature
Unless “binding” occurs, “illusory conjunctions” result – a feature from one object
assigned to another object instead
Some final thoughts: Seeing, knowing, and the perceiver’s active role
Perception is not knowledge
Perception frequently contradicts what we know is “possible”
Knowledge and perception are mutually influenced, but are not the same thing: the
perceiver and the knower are distinct in many instances
