AP Psychology Outline
Chapter 4: Sensation and Perception
Red – Definition
Blue - Important Points
Green - Important People & Contributions
1. Sensation – The Stimulation of Sense Organs.
2. Perception – the Selection, Organization, and interpretation of Sensory Input.
3. Psychophysics: Basic Concepts & Issues
a. Psychophysics - Study of how physical stimuli are translated into Psychological
b. Gustav Fechner
i. Psychophysics Psychologists in 1860’s at University of Leipzig.
ii. Wilhelm Wundt based lots of research upon Fechner.
iii. Question: For any Given Sense, what is the weakest detectable Stimulus?
iv. Absolute Threshold – Minimum Stimulus Intensity that an Organism can detect.
v. As Stimulus Intensity Increases, the Subject’s probability to responding to
Stimuli Gradually increases.
vi. The Absolute Threshold is the Stimulus Intensity detected 50% of the time.
vii. Just Noticeable Difference (JND) – The smallest difference in stimulus intensity
that a specific sense can detect.
viii. Weber’s Law – The size of a Just Noticeable Difference is a constant proportion
of the size of the initial Stimulus.
1. Weber’s Fraction – The Fractions that apply to different Sensory Inputs
until a Difference is noted. Increases constantly proportionately.
c. Signal-Detection Theory – The detection of stimuli involves Decision Processes, along as
Sensory Processes, which are both influenced by a variety of factors besides Stimulus
i. Noise – Background distractions that lower the chance of detection of a
d. Subliminal Perception – The registration of Sensory Input without conscious awareness.
i. Such as Subliminal Messages in movies, advertisements, etc.
John Krosnick – Experimented and found that “Subliminal stimulation generally
produces weak effects.
e. Sensory Adaptation – The Gradual Decline in Sensitivity to prolonged Stimulation.
i. Ex. You jump in Cold Water; it is very cold at first, But You Get Used to It.
ii. Process that keeps people tuned into the changes rather than constants in
a. The Stimulus: Light
i. People need Light to See
ii. Light – Form of Electromagnetic Radiation that travels as a wave at the Speed of
iii. Amplitude – Affects perception of brightness (Height).
iv. Wavelength – Affects perception of Color (Distance between Peaks).
b. The Eye
i. Two Purposes: Channel light to the Neural Tissue that receives it (Retina). And
they House the Retina. ii. Lens – Transparent eye Structure that focuses the light rays falling on the
iii. Nearsightedness – Caused by Retina, Close objects are seen clearly, but distant
objects appear blurry.
iv. Farsightedness – Distant objects are seen clearly, but close objects appear
v. Pupil – The opening into the center of the Iris that permits light to pass into the
rear chamber of the eye.
vi. Iris – Regulates the amount of Light entering the Pupil by controlling the size of
c. The Retina
i. Retina – Neural Tissue lining the inside back surface of the eye; it absorbs light,
processes images, and sends visual information to the brain.
1. The Retina is a part of the Central Nervous System.
ii. Optic Disk – A hole in the Retina where the Optic Nerve Fibers exit the eye.
d. Visual Receptors: Rods & Cones
i. Rods Outnumber Cones.
ii. Located in the Retina.
iii. Cones – Play a key role in Daylight Vision and Color Vision.
iv. Fovea – Tiny spot in the center of the Retina that contains only Cones; visual
clarity is best here.
v. Rods – Play a key role in Night Vision and Peripheral Vision.
1. When you want to see an object in the dark, look slightly above or
below where it should be to find it easier.
e. Dark and Light Adaptation
i. Dark Adaptation – The process in which the eye becomes more sensitive to light
in low illumination.
ii. Light Adaptation – Process in which the eye becomes less sensitive to light in
f. Information Processing in the Retina
i. Receptive Field of a Visual Cell – The Retina area that when stimulated, affects
the firing of that Cell.
1. Light in the Center of the Receptive Field Increases firing Rate.
2. Light in the Outside of the Receptive Field Decreases Firing Rate.
ii. Lateral Antagonism – Occurs when Neural Activity in a cell opposes activity in
1. Allows viewing Contrast in sight. From light falling on center or
outside of Receptive Field.
g. Vision & The Brain
i. Imaging is processed in the Brain.
ii. Visual Pathways to the Brain
1. Optic Chiasm – The point at which the optic Nerves from the Inside
half of each eye cross over and then project to the opposite half of the
a. Leads to Thalamus 90% of the Time. Then to Occipital Lobe.
b. 10% Leads to the Superior Colliculus, Then Thalamus, then
i. Belongs to the perception of Motion and
Coordination of Visual input with other Sensory
c. Main Visual Pathway leads to Magnocellular and
d. Parallel Processing – 2 Channels simultaneously extract
different kinds of Information from the same input.
h. Information Processing in the Visual Cortex
i. Hubel & Wiesel 1. Feature Detectors – Neurons that respond selectively to very specific
Features of more Complex Stimuli.
a. Gets more specific as Moving along the Visual Processing
5. Viewing the World in Color
a. Color is viewed by Wavelength (Hue) Amplitude (Brightness) and Purity (Saturation).
b. Subtractive Color Mixing – Works by removing some Wavelength of light, leaving less
light than originally there.
c. Additive Color Mixing – Works by Superimposing Lights, putting more light in the
mixture than exists in any one light by itself.
d. Trichromatic Theory - Color Vision holds that the Human eye has 3 types of Receptors
with differing sensitivities to different light wavelengths.