Sensory Adaptation

• Our diminishing sensitivity to an unchanged stimulus

• Do you feel your underwear all day?

• Do you feel your shoes all day?

Perception

The process of organizing and interpreting information, enabling us to recognize meaningful objects and

events.

We see not how the world is but how it is useful to us

Top-Down Processing• We identify something b/c

our brain tells us what the object is (prior knowledge)

• We perceive by filling the gaps in what we sense.

• I _ant ch_co_ate ic_ cr_am.• Based on our experiences

and schemas.• If you see many old men

in glasses, you are more apt to process a picture of an old man (even when you may be in error).

Bottom-Up Processing• Also called feature

analysis• We use the features on

the object itself to build a perception

• No prior knowledge• Takes longer than top-

down but is more accurate Kids.exe

Click to see an example of bottom –up processing.

Cocktail-party phenomenon• The cocktail party

effect describes the ability to focus one's listening attention on a single talker among a mixture of conversations and background noises, ignoring other conversations

• Form of selective attention

Selective Attention• The focusing of conscious

awareness on a particular stimuli• You didn’t notice consciously feel

your shirt until you read this • Inattentional Blindness: failing to

see visible objects when our attention is directed elsewhere

• Change Blindness: failing to notice changes in the environment

Click on the mouse to see an example of change blindness.

Thresholds• Absolute Threshold: the minimum amount of

stimulation needed to detect a light, sound, pressure, taste, odor… 50% of the time– Psychophysics: the study of relationships between

physical characteristics of stimuli (like intensity) and our psychological experience of them (look for absolute thresholds)

– Ex: mtn on dark night, see light miles away– Ex: vision & hearing tests – Ex: mosquito ring tones– Ex: shopkeeper

Signal Detection Theory• Theory that predicts when we

detect weak signals amid background stimulation– Says absolute thresholds are

not really absolute• So many factors affect what we

can sense– time of day? did you eat

breakfast? do they exercise? Did you get enough sleep? …

• 4 possibilities:– Hit-signal present & sensed– Miss-signal present but not

sensed– False Alarm-signal not present

but sensed– Correct Rejection-signal absent

& not sensed

(Just Noticeable Difference) Difference Threshold

• The smallest amount of change needed to detect in a stimulus before we detect a change

• Why would you need this?• Ex: hearing your

friend’s voice over other voices in the hallway

• Ex: My mom’s whistle• Ex: Musician detecting

differences when tuning an instrument

Weber’s Law• The greater the

magnitude of the stimulus, the larger the differences must be to be noticed• Ex: if you are listening to

the tv at volume 40, the JND occurs when you decrease the volume by 4

• If you are listening to tv volume at 20, the JND occurs when you decrease the volume by 2

Perceptual Ideas

Figure Ground Relationship

• We organize what we see into objects (the figures) that stand out from their surroundings (the background)

• We always organize stimulus into a figure seen against the ground

Gestalt Psychology• Gestalt psychologists focused on how we

GROUP objects together• We innately look at things in groups or as

a WHOLE, not as isolated elements (we want to see the forest, not the trees)

• Proximity (group objects that are close together as being part of same group- 3 sets of 2 lines, not 6)

• Similarity (objects similar in appearance are perceived as being part of same group- vertical columns of similar shapes not horizontal of different)

• Continuity (objects that form a continuous form are perceived as same group- 1 wavy, 1 straight line)

• Connectedness (b/c they are uniform & linked we think of the 2 dots and line as one unit)

• Closure (like top-down processing…we fill gaps in if we can recognize it)

CLOSURE

Depth Cues• Depth Perception: allows us to

judge distance– Our retinas pick up 2D but we

see 3D• Eleanor Gibson and her Visual

Cliff Experiment.• If you are old enough to crawl,

you are old enough to see depth perception.

• We see depth by using two cues that researchers have put in two categories: – Monocular Cues– Binocular Cues

Binocular Cues• We need both of our

eyes to use these cues.• Retinal Disparity: as

an object comes closer to us, the differences in images between our eyes becomes greater

• Convergence (as an object comes closer our eyes have to come together to keep focused on the object)

Monocular Cues• You really only need

one eye to use these (used in art classes to show depth).

• Linear Perspective: parallel lines appear to converge w/ distance

• Interposition: if one object partially block our view of another we think it’s closer

• Relative Height: we perceive objects higher in our field of vision as farther away

• Relative Size: the smaller the object the farther away we think it is

• Light and Shadow: given 2 identical objects the dimmer one seems farther away

Constancy• Objects change in

our eyes constantly as we or they move….but we are able to maintain content perception

• Shape Constancy• Size Constancy• Brightness

Constancy

Perceived Motion• Stroboscopic effect

(flip book effect, cartoons)

• Phi phenomenon: movement illusion when 2 or more adjacent lights are blink on and off in quick succession

• Autokinetic Effect (if people stare at a white spotlight in a dark room, it appears to move)

Perceptual Constancy• Size Constancy• Lightness Constancy • Color Constancy• You saw all of these

in the “Brain Games” video

Perceptual Set• What do these letters spell? FOLK• How about these? CROAK• And these? SOAK• What do we call the white of an egg? – NO!!! IT’S AN EGG WHITE!!!

• Perceptual Set: a mental predisposition to perceive one thing and not another