Transcript Sensation & Perception

Sensation & Perception
• What is the difference?
Sensation
• Detection of physical energy emitted or
reflected by physical objects
• Sense organs
– eyes, ears, tongue, nose, skin, internal body
tissues
• Without sensations, we would not
experience reality
Perception
• A set of mental operations that organize
sensory input into meaningful patterns
• Perception allows us to interpret our
sensations and thus reality
How many Senses?
• Five?
• Actual many more
The Riddle of Separate
Sensations
• Sense receptors
– specialized cells in the sense organs that
convert physical energy from the environment
into electrical energy to be transmitted as nerve
impulses to the brain
Johannes Muller
• doctrine of specific nerve energies
– Different sensory modalities exist b/c signals
received by the sense organs stimulate nerve
pathways leading to different brain areas
– Because different brain areas are stimulated,
different sensations are experienced
– Synesthesia
• Stimulation of one sense evokes sensation of another
Functional Codes
• Doctrine doesn’t account for variations
within a sense
– Seeing gold versus yellow
• Functional code account for this
– Within a sense certain neurons fire or don’t, fire
fast or slowly, or in a pattern to create different
sensations
Measuring the Senses
• Psychophysics
– How the physical properties of stimuli are
related to our psychological experience of them
Absolute thresholds
• Smallest quantity of energy that can be
reliably detected 50% of time
• Very sharp senses
– candle flame on a clear, dark night from 30 miles
away!)
Difference thresholds
• just noticeable differences (jnds)
• Smallest difference in sensory stimulation
that can be detected reliably between two
stimuli
jnds
• The larger, or more intense, stimulus 1 is,
the greater the jnd needs to be
Signal-detection theory
• Theory that accounts for response biases in
absolute threshold and difference threshold
measurements
• An observer’s response in a detection task
is divided into a sensory process (which
depends on the stimulus’s intensity) and a
decision process (which is influenced by the
participant’s response bias)
Signal-detection theory
• A mathematical formula separates estimates
of a person’s sensory process and decision
process, yielding a predicted value for one’s
true sensitivity to a particular stimulus
Sensory Adaptation
• When stimulation is unchanging or
repetitious, sensory receptors “tire” and fire
less frequently, resulting in a decline in
sensory responsiveness
• Sensory adaptation to touch/pressure
– (the feel of the clothes on your body)
– smell (of one’s perfume or cologne)
We rarely adapt to visual stimuli
• because our eyes are constantly moving
back and forth
We never completely adapt
• to very intense stimuli (e.g., noxious fumes,
intense pain)
Sensory deprivation
• Absence of normal sensory stimulation
– Heron (1957)—visual, auditory, an tactile
stimulation was deprived, resulting in
disorientation, feelings of edginess and
confusion, and many reports of hallucinogenic
visions
Don’t oversimplify!!—
• sensory deprivation may be a form of
relaxation for some, but torture for others
• it all depends upon the context
– meditation/relaxation versus solitary
confinement in prison
Sensory without Perceiving
• Selective attention is necessary to focus on
and filter out numerous sensory stimuli
from being consciously perceived all at
once
• “Cocktail party phenomenon”