Perception Flashcards
difference between sensation and perception
- Sensation - very “biological”; not much psychology involved
- Perception - integration of stimulation from the senses; very active process (automatic); involves inferences; involves top-down processes.
what is top-down processes?
the involvement of memory, expectations, mood, current context and beliefs on the interpretation of information from the senses
allows sensation to become perception
examples of inference in perception
perceptual constancy
brightness contrast
what is perceptual constancy?
despite variation in the “raw data” received by the brain from the senses, our perception of the world remains remarkably constant.
- size (unaffected by distance)
- shape (door opening)
- colour (colour of friend’s face is the same whether it is day or night)
- brightness (white wall remains bright despite the fact that it is night time)
what is brightness contrast?
our perception of brightness is not solely dependent on the absolute amount of light reflected from surface of an object, but also on the amount of light reflected from other objects in the vicinity.
in contrast to brightness constancy
examples of top-down processes in perception
“Filling in the gaps” if an auditory or visual signal is missing then the brain will fill in the gaps
1) Phonemic restoration – removal of phonemes within a sentence will result in the brain filling in the gaps (Masking – audio can be masked by other audios – it is useful for compression)
2) Illusory contours – even when boundaries are not present, we can be fooled into seeing them
3) Degraded figures – pieces missing from a picture will be filled in
what is a perceptual set?
readiness to interpret stimuli in a certain way depending on expectations, experience and psychological state
what are perceptually ambiguous figures?
figures that can be perceived in two different ways.
same “raw material” from the senses but two different “interpretations” of it.
can bias interpretation of figure by manipulating a person’s perceptual set
perception and reality
- If we are imposing our own interpretation on the world, do we ever objectively experience reality?
- Descartes’ malevolent demon
- Virtual Reality
- A lot of objective reality is out of the range of either sensation or perception (dog whistles; infrared rays)
- Stratton - wore goggles that inverted the world and adjusted well he certainly isn’t seeing reality; have we also just “adjusted well” to a distorted perception?
types of visual perception
depth perception
binocular depth cues
monocular depth cues
depth perception
ability to judge distance
i. Absolute distance – distance between observer and object
ii. Relative distance – distance between objects
binocular depth cues
need two eyes
i. Convergence – eyes move together as object gets closer; muscle tension is a cue to how far away object is
ii. Binocular disparity – slightly different views of world presented to each eye are interpreted by brain to give depth information – the further an object is from he observer, the less the disparity between the images projected on the retinas of the two eyes
monocular depth cues
only one eye necessary
i. Motion parallax: objects closer to observer appear to move faster e.g. driving in car
ii. Relative size – size of an object relative to others around it
Must have prior knowledge of size of object
Drawing of two people, one large on small: attribute difference in size of retinal image to distance rather than size
Moon illusion: moon on horizon seems larger – we assume that objects on horizon are farther away; automatically scale size according to distance
iii. Linear perspective: apparent convergence of parallel lines on the horizon (railway lines) – converge at vanishing point
iv. Texture gradient: objects at a distance are denser, less detailed and closer together e.g. view of houses from an elevated perspective of a city
v. Aerial perspective: distant objects are fuzzy due to moisture and particles in the air
vi. Occlusion: objects that occlude others are perceived to be closer
visual illusions
1) Muller-Lyer illusion - depth cues suggest the “long” line is closer, the principle
of size constancy causes us to see same size retina image as larger (similar to
moon illusion)
2) Ponzo illusion - linear perspective suggests that object is further away;
perceptual system makes same size retinal image seem larger (size constancy).
3) The Ames room illusion - all depth cues suggest these people are the same
distance from the observer; however, they are not;
how do we locate objects using auditory perception?
1) Difference in the intensity of sound at the two ears; somewhat like binocular
disparity with vision
2) Overall intensity of sound; if louder, it is closer
3) Difference in the time it takes sound to reach different ears (wouldn’t work
for vision since the wave form is too fast)
motion perception
when motion isnt perceived
When we examine a stable object, we move our eyes but see a
stable image. Why is image stable since retinal images are
changing?
Perceptual system compensates for voluntary eye movements.
If we move our eyes with something other than eye muscles,
perceptual system can’t compensate; see object as moving
More evidence of activity in perception
motion perception
when motion is perceived
i) If we do sense motion, necessary to distinguish between the object moving and
observer moving
we do so by noticing how the background changes relative to object. Moving
object occludes objects as it moves; if we are moving, objects appears more
stable relative to background.
ii) Ears tell us about motion also; the discrepancy in the intensity of sound to
each ear (and how it changes over time) gives information about movement
movies with stereo or surround sound take advantage of this fact
illusions of motion
1) Apparent motion: perceptual system fills in the gaps on successive, motionless images
- motion pictures
- animation
i] Phi-phenomenon - apparent motion produced by a
succession of flashing lights
e.g., railway station signs showing train times
1) Apparent motion (cont.)
ii] Induced motion - if objects near a stationary one are moving, the
stationary one appears also to be moving
- clouds in front of the moon on a windy night
- objects under the water in a stream.
related idea is the experience of feeling like your moving in a train
station, whereas in fact it’s the train immediately outside window that
has started to move.
iii] Motion after-effect - after moving forward for some time and then
stop, scenery outside seems like it is moving backward slightly.
perception of form
Controversy about whether we perceive the object as a whole first, and the
analyse the parts (Gestalt), or vice versa (feature analysis)
feature analysis
bottom-up processes
We have different feature detectors that are activated when a stimulus
is presented (ganglion cells)
Activated feature detector cells in turn activate different stored
representations of letters in memory
The memory representation that is most activated wins
Gestalt
top-down process
“the whole is greater than the sum of the parts”
believed we couldn’t understand perception by trying to look at the whole built up
from the parts; must try to examine the system at a higher level.
“Filling in the gaps” - the perceptual system wants to make a complete, holistic interpretation, so if pieces are missing, it fills them in (using memory) to complete it.
Perceptually Ambiguous Figures - the Gestalt or organisation can “flip” on you
such that suddenly a brand new interpretation is obtained
Can’t see both Gestalts at once; they “flip back and forth” from one
organisation to the next
how are gestalts formed?
Organising Principles
i] Figure/ground distinction - the distinction b/t that which stands out
(figure) and that which is background (ground)
interesting if it is ambiguous
ii] Grouping Principles
a) proximity
b) good continuation
c) closure
how can gestalt principle be applied to sound perception?
i] Figure-ground - in a lecture, the speaker is figure and the sound of the audience in ground
ii] Grouping Principles
a) proximity of notes in a song allow you to hear successive notes as
belonging to a melody
b) Good continuation allows you to pick out the melody in the presence of
other background harmonies
c) closure allows you to fill in the gaps of a radio announcer who is competing with a lot of static that cuts out several of his words
perceptual ambiguity
Perceptual ambiguity in audition is also like visual perception:
only one organisation of sound can occur at once
Nudist play
New display
gestalt principles and problem solving
AHA! type problems can be organised into a particular Gestalt, but suddenly
“flip” such that a new interpretation is obtained This is often necessary to solve the problem.
Often people are fixated on one organisation of the problem (often as a result of prior experience).
Solving the problem involves a sudden flip to a new Gestalt that is often accompanied by a feeling of enlightenment or an AHA! experience.
nature/ nurture and perceptual organisation: evidence for nature
Evidence for Nature (inborn)
i] at 6 months, infants will not go to beckoning mother if there is a
visual cliff
shows that infants at 6 months respond to depth cues
ii] Newborns show preference for shapes that resemble human face
nature/ nurture and perceptual organisation: evidence for nurture
Evidence for Nurture (learning)
i] Feature detectors cells - can be trained to be sensitive to particular orientations
Blakemore and Cooper: kitten experiments
ii] Perceptual Adaptation and Differentiation
Adaptation - Stratton example
Differentiation - experience refines perception
trained musicians can hear subtleties in harmony that others would miss.
our ability to read - very subtle differences (e.g., difference b/t B and 8; P and R; I and 1)
