Sensation and Perception
Sensation
Sensation and Perception
Sensation
The process through which the senses pick up visual,
auditory, and other sensory stimuli and transmit them to
the brain; sensory information that has registered in the
brain but has not been interpreted
Perception
The process by which sensory information is actively
organized and interpreted by the brain
Three parts of the psychology of
sensation
Psychophysics: What is the relationship between the
physical characteristics of a stimulus and the
psychological experience of it? Is it the connection
between body and mind, as Fechner thought?
Sensory physiology: How do sense organs, receptor
cells, and neural circuits respond to physical stimuli,
to tell our brains what is out there?
Transduction
Stimulus is converted into neural impulses
Sensation….imp. concepts
Stimulus: A source of physical energy that produces
a response in a sense organ.
Sensation: A process by which an organism
responds to a stimulus.
Intensity: The strength of a stimulus.
Psychophysics: The study of the relationship
between the physical nature of stimuli and a person’s
sensory responses to them.
Cont.
Sensory receptors:
Specialized cells in the sense organs that detect
and respond to sensory stimuli—light, sound,
odors—and transduce (convert) the stimuli into
neural impulses
Provide the essential link between the physical
sensory world and the brain
Cont.
We do not detect all of the stimuli that are present.
Senses are limited or restricted.
Absolute Threshold: The smallest amount of
physical intensity by which a stimulus can be
detected.
Noise: Background stimulation that interferes with
the perception of other stimuli.
Cont.
Sensing the difference between 2 stimuli:
Difference threshold (just noticeable difference):
The smallest detectable difference between two
stimuli.
OR “The minimum difference a person can detect
between any two stimuli (50% of the time)”
Can we ever detect stimuli that are below threshold?
Subliminal: Below one’s absolute threshold for
conscious awareness.
The JND increases with the magnitude of the stimulus.
Cont.
Sensory Adaptation: diminishing sensitivity
to an unchanged stimulus.
- after constant exposure to a stimulus, our
nerve cells fire less frequently.
But...
Process of Sensation
Sensory adaptation
The process of becoming less sensitive to an
unchanging sensory stimulus over time
Allows you to shift your attention to what is most
important at any given moment
Selective Attention
focusing of conscious awareness on a particular
stimulus
The Five Senses
Humans are credited with
five basic senses:
Seeing
Hearing
Smelling
Tasting
Touching
Vision
Stimulus for Vision-----Light waves
(Electromagnetic waves to which our eyes are
sensitive & capable of responding.
Electromagnetic waves are measured in
wavelengths.
Every wave length refers to different level of energy.
Range of wave lengths to which humans are
sensitive →Visual Spectrum
Visual Spectrum
Visual System
Human visual system consist of the Eyes,
several parts of the brain, and the pathways
connecting them.
The Eye : consist of two systems
Image forming system
Image transduction System
1.
2.
Eye
Image forming System: consist of following
structures:
Cornea .…front surface of eye: light enters here.
Its a transparent protective window into eyeball,
constantly being washed by tears, keeping it moist
and clean.
Pupil …. A circular opening which changes size in
response to the incoming amount of light.
Size of pupil opening depends on the amount of
light in the surroundings
1.
2.
Vision
Eye
3. Iris ….The colored part of the eye, ranges from light
blue to dark brown.
4. Sclera…. The sclera is commonly known as "the
white of the eye." It is the tough, opaque tissue that
serves as the eye's protective outer coat.
5. Lens …. Located behind the pupil, focuses the light
by changing its own thickness, through a process
called Accommodation.
Accommodation: The ability of the lens to vary its
shape in order to focus incoming images on the
retina.
Eye
Kind of accommodation depends on the location of
the object
distant objects → relatively flat lens
Close objects → Thick, rounder lens
Having traveled through pupil and lens ,light waves
reach its ultimate destination in the eye.
6. Retina : Part of the eye that converts the electro
magnetic energy of into useful information for the
brain.
It is actually a thin layer of nerve cells at the back of
the eye ball.
Cont.
Two types of light
sensitive receptor cells in
Retina
Rods → long &
cylindrical ( perform well poor
light, insensitive to color & small
details, used for peripheral vision &
night vision)
Cones → short, thick,
cone shaped (responsible for
sharp focus and color perception,
particularly in bright light)
Peripheral Vision: The ability to
see objects outside the eye’s main
center of focus.
Eye
7. Fovea : part of retina, where concentration of
cones are greatest.
Best at seeing details.
It helps in focusing on something of particular
interest.
No rods in Fovea.
Cont.
Optic Nerve: Nerve at the back of the eyeball
that carries neural impulses (visual
information) from the eye to the brain.
Cont.
Blind Spot: point at which
the optic nerve leaves the
eye, creating a “blind spot”
because there are no
receptor cells located there
Optic Chiasm: A point
between and behind the
eyes at which nerve
impulses from the optic
nerves are reversed and
“righted” in the brain.
Cont.
Light Adaptation: The eye’s temporary
insensitivity to light dimmer than that to
which it has most recently been exposed.
Dark Adaptation: A heightened sensitivity to
light resulting from being in low level light.
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