Unit 3 - Sensation & Perception

Chapter 4 Part 1: Intro. to S & P

Today’s Goals

●Can you:

○Define sensation and perception

○Discuss basic principles of sensory

transduction, including absolute threshold,

difference threshold, signal detection, and

sensory adaptation.

○Explain the role of top-down processing in

producing vulnerability to illusion.

Sensation & Perception

How do we construct our representations of the

external world?

To represent the world, we must detect physical

energy (stimulus) from the environment and convert it

into neural signals, a process called sensation.

When we select, organize, and interpret our

sensations, the process is called perception.

What do you sense? In this

case, what do you see?

What do you perceive?

Bottom-up Processing

Analysis of the stimulus begins with the sense receptors

and works up to the level of the brain and mind.

Knowing that the bottom middle flag is the American flag is due to bottom-up

processing…your senses break down the flags into colors, shapes and

lines…which you then process and organize to figure out which is the

American flag.

Which of the following is the American flag?

Top-Down Processing

Information processing guided by higher-level mental

processes as we construct perceptions drawing on our

experience and expectations.

Y-u c-n r-ad -hi- se-te-ce -it-

ev-ry -hi-d l-tt-r m-ss-ng.

The reason you can…is top-down processing! Your expectations

and experiences let you fill in the blanks by making inferences on

what you think “should” be there!

Bottom-up and top-down processing work

together to help us sort out complex images.

Making Sense of Complexity

“The Forest Has Eyes,” Bev Doolittle

Thresholds

Absolute Threshold: Minimum stimulation needed

to detect a particular stimulus 50% of the time.

Difference Threshold: Minimum difference between

two stimuli required for detection 50% of the time,

also called just noticeable difference (JND).

Weber’s Law

The size of the JND is proportional to the intensity of the

stimulus

●if the stimulus intensity is high, the JND will be large

(or it will take a bigger increase to notice the difference)

●if the stimulus intensity is low, the JND will be smaller

(or it will take less of an increase to notice the difference)

Subliminal Threshold

When stimuli are below

one’s absolute threshold for

conscious awareness.

In other words…for most

people these items are not

consciously detected.

HOWEVER…it is possible

that some will notice these

items!

Examples of “subliminal” messages in

advertisements…

In the spring/summer of 1990, Pepsi

distributed a line of “Cool Cans” as

part of a promotional campaign.

All 4 of them are shown below…

…the 2nd “NEON” can apparently

had an “embedded” message if you

stacked two cans together..http://www.snopes.com/business/hidden/coolcans.as

p

http://www.tombihn.com

/

Info from…http://www.snopes.com/business/hidden/tombihn.asp

An embedded “subliminal”

message was found in 2004 on the

french translation portion of a care

tag on Tom Bihn backpacks/laptop

cases/briefcases…

What does it say????

“We’re sorry our president

is an idiot. We didn’t vote

for him.”

Many people viewed this

as a slam against

President Bush…the

company maintains that it

is a joke between a

seamstress and the CEO.

During the 2000 Presidential campaign…the following ad

was run nationally on TV by the Republican party…

Bush campaign ad controversy…

The Democratic party claimed that

the Republicans were trying to use

“subliminal” messages to influence

the national public…so they asked

the FCC to investigate the TV ad!

The ad's creator calls the word's appearance a "visual

drumbeat" meant to grab viewers' attention and not an

intentional message. It was supposed to be an abbreviated

version of “bureaucrats”… Bush also said “rats” ad not

meant to be a subliminal message

Subliminal Messages…Backmasking?It is recording technique in which a sound or message is recorded

backward onto a track that is meant to be played forward.

This is a deliberate process…currently the technique is being used to

censor words or phrases for "clean" releases of songs.

Backmasking was popularized by The Beatles, who used backward

vocals and instrumentation on their 1966 album Revolver.

The Backmasking has been a controversial topic in the US since the

1980s, when allegations from Christian groups of its use for Satanic

purposes were made against prominent rock musicians, leading to

record-burning protests and proposed anti-backmasking legislation by

state and federal governments.

Whether backmasked messages exist is a debate, as is whether

backmasking can be used subliminally to affect listeners.

Background…

● initially gained worldwide fame in the early 80s as “backmasking” in

music

●the pioneer of this field is Australian, David John Oates

What is reverse speech?

● idea that if human speech is recorded and played backwards, mixed

amongst the gibberish at regular intervals can be heard very clear

statements

●statements are usually short and relate to the content of the

forward speech

●believed to be a natural part of our speech processes

●Oates believes that the reverse speech is our unconscious mind

finding a “voice”

○for example…if telling a lie in forward speech, in reverse the

truth may come out

Subliminal Messages…Reverse Speech?

Some examples of reverse speech….

“I surely would fit in”

You will hear the “forward” message 1st…followed by 3 “reverse”

messages (1 at regular speed and 2 at slowed speeds).

Can you figure out what is being said???

“See the dream” “Soon I’ll beat the law”

For more examples visit…http://www.reversespeech.com/home.htm

Studies have found that subliminal words

flashed briefly on a screen can “prime” a

person’s later responses…but will not impact a

large group’s buying habits!

Do the previous items really constitute

subliminal messages?

Do subliminal messages really influence

our behaviors?

Signal Detection Theory (SDT)

Predicts how and when we detect the presence

of a faint stimulus (signal) amid background

noise (other stimulation). Assumes that there is

no single absolute threshold and detection

depends on:

●Person’s experience

●Expectations

●Motivation

●Level of fatigue

JOE!

Signal Detection Theory (SDT)

Presence of Stimulus

Yes No

De

tectio

n o

f S

tim

ulu

s

Ye

sN

o

Sensory Adaptation

Diminished sensitivity as a consequence of

constant stimulation.

Put a band aid on your arm and

after a while you don’t sense it.

After you initially get into a pool,

it no longer feels cold.

Let’s test the idea of sensory adaptation…

Sensory Adaptation – Marker Test

Number your paper to 12…

Each time I tell you to “SMELL”,

please quickly sniff your marker and

quickly rate the

INTENSITY OF THE AROMA

on a scale of 1 – 20(1 = very slight smell 20 = very strong smell)

What happened over the various trials?

Quickly switch markers with your neighbor and rate the

intensity of the aroma of their marker…