This document summarizes key concepts about sensation and perception from Chapter 3 of Sensation & Perception. It discusses: 1) The difference between sensation (sensory input) and perception (interpretation of sensory input by the brain). 2) Gestalt principles of perceptual organization including figure-ground, similarity, proximity, continuity, and closure. 3) Depth cues for monocular and binocular vision like linear perspective, relative size, and binocular disparity. 4) Top-down and bottom-up processing in perception and how perceptual set and inattentional blindness can influence perception.

1. Sensation & Perception
Chapter 3
Part II
William G. Huitt
Last revised: May 2005

2. Sensation and Perception
• Sensation
– The process through which the senses pick up
visual, auditory, and other sensory stimuli and
transmit them to the brain; sensory information that
has registered in the brain but has not been
interpreted
• Perception
– The process by which sensory information is
actively organized and interpreted by the brain

3. Perception
Gestalt principles of perceptual organization
• Figure-ground
– Organization depends on what we see as figure (object) and
what we perceive a ground (context).
• Similarity
– Objects that have similar characteristics are perceived as unit.
• Proximity
– Objects close together in space or time perceived as
belonging together.
• Continuity
– We tend to perceive figures or objects as belonging together if
they appear to form a continuous pattern.
• Closure
– We perceive figures with gaps in them to be complete.

4. Perception
• You can see a white vase as figure against a
black background, or two black faces in profile
on a white background

5. Perception

6. Perception
• Perceptual constancy
– The tendency to perceive objects as maintaining
stable properties (e.g., size, shape, brightness, and
color) despite differences in distance, viewing angle,
and lighting
– Size constancy
• Perceiving objects as being about the same size when
they move farther away
– Shape constancy
• Perceiving objects as having a stable or unchanging shape
regardless of changes in the retinal image resulting from
differences in viewing angle

7. Perception

8. Perception
• Monocular depth cues
– Depth cues that can be perceived by only one eye
– Types of cues
• Interposition
– When one object partly blocks your view of another,
you perceive the partially blocked object as farther
away
• Linear perspective
– Parallel lines that are known to be the same distance
apart appear to grow closer together, or converge, as
they recede into the distance

9. Perception
• Monocular depth cues
– Types of cues
• Relative size
– Larger objects are perceived as being closer to the
viewer, and smaller objects as being farther away
• Texture gradient
– Near objects appear to have sharply defined textures,
while similar objects appear progressively smoother
and fuzzier as they recede into the distance
• Atmospheric perspective
– Objects in the distance have a bluish tint and appear
more blurred than objects close at hand

10. Perception
• Monocular depth cues
– Types of cues
• Motion parallax
– When you ride in a moving vehicle and look out the
side window, the objects you see outside appear to be
moving in the opposite direction
– Objects seem to be moving at different speeds – those
closest to you appear to be moving faster than those in
the distance
– Objects very far away, such as the moon and the sun,
appear to move in the same direction as the viewer

11. Perception
• James Gibson
– Pointed out that our perceptions of motion appear to
be based on fundamental, but frequently changing,
assumptions about stability
– Our brains search for some stimulus in the
environment to serve as the assumed reference
point for stability
– When you’re driving a car, you sense the car to be
in motion relative to the outside environment

12. Perception
• Depth perception
– The ability to see in three dimensions and to
estimate distance
• Binocular depth cues
– Depth cues that depend on two eyes working
together
– Convergence
• Occurs when the eyes turn inward to focus on nearby
objects – the closer the object, the greater the
convergence
– Binocular disparity (or retinal disparity)
• Difference between the two retinal images formed by the
eyes’ slightly different views of the objects focused on

13. Perception
• Ambiguous figures
– Can be seen in different ways to make different
images
– Best known ambiguous figure is “Old Woman/Young
Woman,” by E. G. Boring

14. What do you see?
Now what do you see?
Copyright © Allyn & Bacon 2005

15. Perception
• Impossible figures
– Do not seem unusual at first
– Figures that cannot be built

16. Perception

17. Perception
• Illusion
– A false perception of actual stimuli involving a
misperception of size, shape, or the relationship of
one element to another

18. Perception
 Müller-Lyer Illusion
– The two lines above are the same length, but the diagonals
extending outward from both ends of the lower line make it look
longer than the upper line

19. Influences on Perception
• Bottom-up processing
– Information processing in which individual
components or bits of data are combined until a
complete perception is formed
• Top-down processing
– Application of previous experience and conceptual
knowledge to recognize the whole of a perception
and thus easily identify the simpler elements of that
whole

20. Influences on Perception

21. Influences on Perception

22. Influences on Perception
• Perceptual set
– An expectation of what will be perceived, which can
affect what actually is perceived
• David Rosenhan
– David Rosenhan and some of his colleagues were
admitted as patients to various mental hospitals with
“diagnoses” of schizophrenia
– Once inside, they acted normal but the staff
members only saw what they expected to see and
not what was actually occurring
– The real patients were the first to realize that the
psychologists were not really mentally ill

23. Influences on Perception
• Inattentional blindness
– The phenomenon in which we miss an object in our
field of vision because we are attending to another

24. Influences on Perception
• Simons and his colleagues
– Showed participants a videotape of a basketball
game in which one team is uniformed in white and
the other in black
– Instructed them to count how many times the ball
was passed from one player to another either on the
white or black team
– About a third of participants typically fail to later
recall the presence on the screen of even extremely
incongruent stimuli (e.g., a man dressed in a gorilla
costume) under such conditions

25. Influences on Perception
• Social perception
– Facial expressions, the visual cues for emotional
perception, often take priority over the auditory cues
associated with a person’s speech intonation and
volume, as well as the actual words spoken