Sensation & Perception

Sensation: Process by which our sensory receptors and nervous system receive stimuli from the environment

Perception: Process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events

What’s the Difference?

Sensation vs. Perception

Psychologists distinguish between two types of processes in perception:

1.Bottom-up processing: perception begins with the stimulus itself

2. Top-down processing: refers to the use of contextual information in pattern recognition

Richard Gregory, 1970sTop-down Processing

Perception involves a lot of hypothesis testing to make sense of the information presented to the sense organs.

Our perceptions of the world are hypotheses based on past experiences and stored information.

The formation of incorrect hypotheses will lead to errors of perception.

This object appears to flip between orientations because the brain develops two equally plausible hypotheses and is unable to decide between them.

Let’s Take a Look at Charlie Chaplin

Charlie Chaplin's Face

What's Up?!

Psychophysics

• Study of the relationship between the physical characteristics of stimuli and our psychological experience of them.

Absolute Threshold

• Minimum stimulation necessary to detect a particular stimulus 50% of the time

• Absolute thresholds vary with:– Our age– Our psychological state

Signal Detection Theory• Tries to predict when we will react to a weak

signal (stimulus)• Whether we will detect a weak stimulus

depends on motivation, expectations, and experience

• Examples– Mom of a newborn– Soldier in combat– Someone who plays video games

What is a “subliminal” stimulus?

• A stimulus that is detectable LESS than 50% of the time.

• They are below absolute threshold.

• Helps account for those times when we “feel” what we can’t put words to (intuition?)

An Advertising Campaign

Who eats Skittles Anyways?

Are Your Thirsty?

A Nice Picture in a Children’s Book

The Big Message

• Much of our information processing occurs automatically, out of sight, off the radar screen of our conscious mind.

Difference Thresholds

• Just Noticeable Difference

• Minimum difference a person can detect between any to stimuli 50% the time

• The detectable difference increases with the size of the stimulus

Weber-Fechner’s Law

• For people to really perceive a difference, the stimuli must differ by a constant "proportion" not a constant "amount"

Sensory Adaptation

Is There Visual Adaptation?

Sensory Adaptation Activity