Sensation and Perception

Types of Processing



Build up from features to more complex shapes


Sensation involves stimulation of the sensory organs


Conceptually driven

Knowledge interacts with sensation to yield perception

Perception involves the processing and interpretation of sensory input

Sensing the world/ basic principles

- Sensory systems have developed to enable organisms information needed for survival

- Adaptive sensitivity (humans)

- Hearing

- Color perception

- Face perception

- Brain regions and cells respond specifically to faces


Absolute threshold – the minimum stimulation necessary to detect a particular stimulus

-  Record the stimulation needed for detection 50% of the time

-  Absolute thresholds vary

Subliminal Stimulation

-  First time controversy

- Movie audiences exposed to subliminal suggestions

- "Drink Coke" and "Eat Popcorn"

-  In advertising

- In music

-  As a Self-help device

-  Two assumptions

    We can unconsciously sense subliminal (below threshold) stimuli
    These stimuli have extraordinary suggestive powers

- Evidence in support of assumptions

- Sensing below threshold
- Effect on behavior
-  Krosnick, Betz, Jussim, & Lynn (1992)

-Priming studies

- Deciding whether a target is a word is faster when preceeded by a subliminal related word

-  Conclusion (be sure to write conclusion here)

- Proof

- Canadian Broadcasting Corporation study

Sensory adaptation

- Adaptation occurs is because everything we consciously experience is the result of neurons sending signals

- It requires energy for neurons to fire .

- Energy for pumping sodium ions out of the cell to allow for another action potential.

- Energy for creating neurotransmitters to send messages from cell to cell.

- Constant neuron stimulation causes the neuron to fatigue.

- It slows down the rate of firing or stops altogether.

Visual system fatigue

- It is impossible to keep our eyes totally still and fixated on one object

- Our eyes are always quivering and moving.
-  This is involuntary

Stabilized retinal images

- Fading is the result of retinal neurons becoming fatigued
- Fade occurs in meaningful chunks

Fatigue of cortical neurons

- Spiral aftereffect demo (if we have an internet connection)

Selective Attention

Selective attention: choosing to attend to one stimulus and ignoring others

Cocktail party phenomena


Dichotic listening

Different messages played into each ear

Pay attention to one message (attended ear)

Ignore other message (unattended ear)


Repeat message heard in attented ear

Unattended stimuli

Only certain types of information enter system when not attended to

Indicated by perception of information in unattended channel

Physical sensory changes

One's own name


Affect our ability to perceive stimuli

Signal in expected location

Faster response

More accurate response

Selective attention acts like a spotlight

Sudden Appearance

Draws attention to stimuli

Visual or auditory

Possible adaptive value


Draws attention to stimuli



Response to electromagnetic radiation

Perception of color

Response to wavelength

Perception of brightness

Response to amplitude of wave

Eye converts electromagnetic radiation into neural impulses

Structure of the Eye (make sure to add notes when appropriate)

-  Cornea

-  Pupil

-  Iris

-  Lens


-  Processes information

-  Part of the central nervous system

-  Rods/cones

-  Located in the innermost layer of the retina
-  Sensitive to light
-  Rods outnumber  cones

- Cones
-  Stubbier than rods
- 6.4 million
-  Play a key role in daylight vision
-  Do not respond well to dim light
-  Play a key role in color vision
-  Provide better visual acuity (sharpness and precise detail) than rods
-  Concentrated most heavily in the center of the retina
-  Fovea
-  A tiny spot in the center of the retina that contains only cones
-  Visual acuity is greatest at this spot
-  Rods
-  Enable black and white vision
-  Dazzled by bright light
-  Rods remain sensitive in dim light
-  Greatly outnumber cones in the periphery
-  Density greatest just outside the fovea
Optic nerve
-  Bipolar cells
-  Ganglion cells
-  Axons converge to form an optic nerve
- Carries information to the brain
-  The optic nerves leave the eye and go to the brain through a hole in the retina called the optic disk
Blind spot

Visual pathway to the brain

Optic chiasm

- Axons from the inside half of each eye cross over and then project to the opposite half of the brain

-  Info from right half of right eye and left half of left eye goes to same hemisphere

-  Info from left half of right eye and right half of left eye crosses over to the opposite part of the brain

- Optic nerve fibers diverge along two pathways

-  Both pathways terminate at occipital lobe

Visual Cortex

In occipital lobe

Contains cells that respond to specific features

Discovered by Hubel & Wiesel (1962)

Organized in layers

Layers respond to different stimuli

Simple cells

Process lines and edges

Very selective

Cells respond to specific orientations of lines

Complex cells

Respond to more complex stimuli

Moving lines

Cortical architecture

Series of columns

Cells within column respond to same orientation

Adjoining column

10 degree difference

Visual processing is computationally intensive

Many components working in parallel

Integration into single percept is still a mystery

Top-down processing

· Conceptually driven

· Knowledge interacts with sensations

Affects perception

Facilitates object identification

Effects of prior experience/ memories

Effects of  Context

· Context refers to the surroundings in which a stimulus is embedded

·  Context also influences perception

· Biederman

· Pattern recognition in scenes
· The variable of interest was the length of time it took a person to recognize a particular object
·  People are much quicker to identify objects in the unscrambled scenes even though those objects remained in the same place for both groups.

Effects of expectations

Proofreading errors

· Our expectations of what we are going to perceive in our environment heavily influence what we actually perceive in the environment