Sensation and Perception
Types of Processing
Bottom-up
Data-driven
Build up from features to more complex
shapes
Sensation
Sensation involves
stimulation of the sensory organs
Top-down
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
Threshold
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
Paradigms
Dichotic listening
Different messages played into each ear
Pay attention to one message (attended ear)
Ignore other message (unattended ear)
Shadowing
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
Expectations
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
Movement
Draws attention to stimuli
Involuntary
Vision
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
Retina
- 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