New lecture for students

1. Sensation

2. 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

3. • Sensation: your window to the world
• Perception: interpreting what comes in your
window

5. • Sensation is a process that makes
possible, and facilitates our contact with
reality
• ‘To sense’ means to become aware of
something
• All living organisms have sense organs.
• Sensation is the process by which our
sense organs respond to different stimuli.

6. • It is the mechanism through which stimuli
from outside or inside the body are received
and felt by different faculties e.g., hearing,
sight, smell, touch, taste.
• In the process of sensation the incoming nerve
impulse is registered in that part of the brain,
which has a potential of such reception. The
awareness of a stimulus results from the
perception of the sensory receptors

7. Three parts of the psychology of
sensation
• Psychophysics: The study of the relationship
between the physical nature of stimuli and a
person’s sensory responses to them
• Sensory physiology: The Study of how
sensory stimulus is transferred by sensory
receptors and processed by the nervous
system.
• Transduction: The action or process of
converting something and especially energy or
a message into another form. It is that in which
Stimulus is converted into neural impulses

8. Sensation….important 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.

9. • Sensory receptors:
– Specialized cells in the
sense organs that detect
and respond to sensory
stimuli—light, sound,
odors. It transduce
(convert) the stimuli into
neural impulses
– Provide the essential link
between the physical
sensory world and the
brain

10. Sensory Thresholds
• 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. The absolute threshold is the point
where something becomes noticeable to our
senses. It is the softest sound we can hear or the
slightest touch we can feel. Anything less than
this goes unnoticed

11. Sensing the difference between 2 stimuli:
Once a stimulus becomes detectable to us, how do we
recognize if this stimulus changes. When we notice
the sound of the radio in the other room, how do we
notice when it becomes louder
• Difference threshold (just noticeable difference):
The smallest detectable difference between two
stimuli.
The difference threshold is the amount of change
needed for us to recognize that a change has occurred.
This change is referred to as the just noticeable
difference.
– The JND increases with the amount of the
stimulus.

12. Subliminal:
• Can we ever detect stimuli that are below
threshold? As humans, we have great abilities
to perceive things (e.g., to see things
happening far away, to hear sounds at a
distance, etc.). However, we also have
limitations
• Subliminal: Below one’s absolute threshold
for conscious awareness.

13. • When we are presented with some
information that is just below our conscious
awareness but still reaches our brains, it is a
subliminal message.
• You may be familiar with the idea of
subliminal messages is advertising in which a
message is flashed so quickly that we don't
"think" we saw it (containing the message the
advertiser wants us to get) but our brains
actually processed it. The idea being that we
will still respond to that message even though
we didn't realize we saw it.

14. Sensory adaptation
– The process of becoming less sensitive to an
unchanging sensory stimulus over time
– Sensory Adaptation occurs when sensory
receptors change their sensitivity to the stimulus.
– An example of sensory adaption is dark
adaptation, when the pupil of the eye gets bigger
when exposed to a dark environment
 Selective Attention
 focusing of conscious awareness on a particular
stimulus

16. Vision/ The visual sensation
• The sensation that takes place through the
function of eyes; eyes receive the visual
messages or stimulation, that is carried by
nerves to the concerned part of the brain that
processes the received information.

17. The Eye
• The eye is a very complex, delicate, and vital
structure, that is responsible for an organism’s
interaction with the external world. It is the
most important and influential sense organ.
• It receives information from the outside world
in the form of light, and sends loads of
information to the brain all the time
• The human eye is a little less than one inch in
diameter and almost spherical

18. • The eye has a very specific design or form,
which captures and processes light coming
from outside…light reflected by the stimuli
• Eyes function like a camera, which has its
opening, and a lens through which the light
enters and cells present in it process the
received light just as do the involved internal
parts of the camera

19. Structure of the Eye
• The anatomy/ structure of the eye is broadly divided
into three parts
i. The external structure of the eye
ii. The immediate structure of the eye
iii. The internal structure of the eye

20. The external structure
The external structure consist of following
structures:
1. 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.

21. 2. Sclera: Outer walls of the eye are formed by a
hard, white substance called ‘sclera’, sclerotic
coat covers 5/6th of the surface of the eye. 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.

22. The immediate structure
1. Pupil: A dark, adjustable opening in the center of
the eye through which the light enters. It changes its
size as the amount of light entering the eye varies
2. Iris: Around the pupil of the eye, there is a ring of
muscle tissue that controls the size of the pupil
opening, through its contraction and expansion.
• It contains the color pigments and thus gives color to
the eye__ the color which the eyes possess such as
brown, black, green, blue etc are due to the iris
muscles

23. 3. Lens: The transparent part of the eye that is located
behind the pupil that changes it shape in order to focus
images on the retina
Accommodation: The lens changes its own thickness in
order to focus image properly on retina, this ability of
the lens is called “accommodation”
 Kind of accommodation depends on the location of
the object
distant objects → relatively flat lens
close objects → Thick, rounder lens

25. The internal structure
• Retina: Retina is the light- sensitive inner
surface or chamber of the eye that converts the
electromagnetic energy of the light into useful
information for the brain.
• It contains about 130 million nerve cells.

26. • It contains the receptors rods and cones plus
the neurons; these cells are very important as
they initiate the processing of visual
information.
• The retina has an area of 5 square centimeters
located at the back of the eye, which is a
location where all light detection takes place.

27. 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.

28. Important Regions of Retina
• Fovea: The very sensitive and important part
of the retina that helps in focusing; it is the
area of best vision.
The largest concentration of cones is present
in fovea
There are no rods present in fovea
• Blind Spot: The area/ point where the optic
nerve leaves the eye; no receptor cells are
located here, thus creating a “ blind” spot__
area of no vision

29. Cont.
• Optic Nerve: Nerve at the back of the eyeball
that carries neural impulses (visual
information) from the eye to the brain.

30. Optic Chiasm: A point
between and behind the eyes at
which nerve impulses from the
optic nerves are reversed and
“righted” in the brain.
• When the optic nerves split at
this point, the nerve impulses
from the right half of each
retina go to the right side of
the brain and those from the
left half to the left side of the
brain

31. Adaptation
• The process of the eye becoming used to a
certain amount of light is called adaptation.
What will happen when you enter into a dark
room and hardly see anything? The other
people, or your seat. And what happens after a
few moments? It is an example of adaptation to
darkness

32. 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 for
some duration. On the contrary, you can see
quite well in light after coming from the
darkness__ dark adaptation