Sensation & Perception Intro

Unit 4 – Chapters 5 & 6

Sensation & Perception

How do we construct our representations of the external world?

Sensation vs. PerceptionSensation: detecting physical energy from the environment and encoding it as neural signals

**associated with bottom-up processing

Perception: selecting, organizing, and interpreting our sensations as meaningful objects and events

**associated with top-down processing

Sensation vs. PerceptionExamples: • Hearing – you “sense” the noises the vocal tract

makes when a person speaks, you “perceive” the meaning of what those noises represent

• Health Problem – you “sense” sudden pain in your heart, you “perceive” by recognizing you are suffering a heart attack

Bottom-Up Processing:•analysis that begins with the sensory receptors and works up to the brain’s integration of sensory information

Letter “A” is sensed as a black blotch decomposed into features by the brain and perceived as an “A” by our mind .

“Thinking comes last”

 

A A

Top-Down Processing

• guided by higher-level mental processes, such as experience, motivation, and expectations, we interpret what we see using context clues

Describe this picture (colors? How many men? Trees? Horses? Where is this?:

Title: “The Forest Has Eyes”Now what do you see?

Processing

Bottom-Up Processing: Top-Down Processing:

– detecting lines, angles, and colors that form the horses, riders, and surroundings

– considering the painting’s title, you noticed the apprehensive expressions, and attended to aspects that gave meaning

 

Absolute Threshold • Psychophysics: the study of how physical energy

relates to our psychological experience

– **What stimuli can we detect? At what intensity? How sensitive are we to changing situations?

• Absolute Threshold: the minimum stimulation needed to detect a particular stimulus 50 percent of the time– candle flicker at 30 miles away on a clear night – Ticking watch in a quiet room

Difference Threshold• Difference Threshold: the minimum difference a person can

detect between any two stimuli half the time– also called just noticeable difference (or jnd)– Example: slight flavor distance between two wines, child’s voice

among other kids

• Weber’s Law: difference thresholds differ by a constant percentage rather than amount

– Example: Adding 1 pound to a 50 pound weight is enough to be a difference threshold; adding 1 pound to a 500 pound weight is not• Exact proportion varies by stimulus: weight must differ by 2%; light

intensity by 8%

Signal Detection• Signal detection theory: predicts when we will

detect weak stimuli amid background noise– Detection partly depends on experience, expectations,

motivation, and fatigue level– Example: new parents detect faint noise from baby’s

room despite loud TV blasting– Example: guard on duty – may hear faint noises due to

alertness

• Subliminal messages: stimuli below one’s absolute threshold– for a stimuli to be subliminal, we are not aware of it (it is

unconsciously sensed)

Subliminal Messages FAQs• Do subliminal messages work? – To an extent: invisible words or images can prime your

response to a later question

• Can advertisers manipulate us with subliminal persuasion? – No. Subliminal messages have subtle, fleeting effects;

they do not have powerful, enduring effects on behavior

• People who KNOW they are receiving subliminal messages THINK it affects them, but it really doesn’t

Adaptation• Sensory Adaptation: diminished sensitivity as a

consequence of constant stimulation– Examples: water’s cold at first but you get used to it• Moving your watch up an inch on your arm- bugs you at first,

then no problem

– Our eyes constantly flutter which prevents what we “see” from diminishing

– sensory adaptation helps us focus on informative changes in the environment • As opposed to getting confused with too much stimuli

Senses – Where are we going…?

• Vision• Hearing• Touch• Taste• Smell