ABBOTTABAD UNIVERSITY OF
SCIENCE AND TECHNOLOGY
Submitted to:Maam Anum
Submitted by: Tayyaba Haroon
Department:Psychology
Semester:1st
VISION:
Definition:Vision is the process by which eyes detect
light,colour,and other visual information from the
environment,and the brain interprets this information to
create a meaningful representation of world.
Stimulus for vision:Stimulus for vision is a waveform of radiant
energy that is light radiated from its source in waves ,called
light waves.
Light has three major characteristic that are related to
psychological experience.
1) Wave amplitude:The psychological experience of wave
amplitude or intensity is brightness.
2) Wavelenght:Wavelenght determines colour.
3) Wavepurity:The wave purity determines psychological
experience that we called Saturation.
STRUCTURE OF EYE:
Human eye is nearly spherical,with diameter of approximately
24mm.
LAYERS: Human eye consist of three layers .
i. The outermost layer (Cornea,Sclera)
ii. Middle layer (Choroids)
iii. Inner most layer (Retina)
CHAMBERS: Eye is partioned into two chambers.
i. The small Anterior Chamber
ii. The large Vitreous Chamber
LAYERS:
1) THE OUTERMOST LAYER:
Sclera: Except the cornea ,the eye is covered by strange
protective tissue called sclera .In Greek sclera means hard,
usually 1mm thick and give protection to the eye.
Cornea: It is curved, transparent outer shell of the eye .It
bends the incoming light waves so the image can be focused
on retina.
2) THE MIDDLE LAYER:
Choroids: Heavily pigmented, spongy structure called
choroids .About 0.2mm in thickness an contain network of
blood vessels, including capillaries. Blood from these
capillaries will nourish cells in the retina.
CHAMBERS:
THE ANTERIOR CHAMBER: It is a small chamber that contai
aqueous humor.
Aqueous Humor: it is a clear liquid that shape and nourish eye,
transports oxygen and nutrients, the cornea and lens rely on it
for nourishmnet.
Iris: It is a circular patch of tissue that give eye colour. The iris
comes from Greek word for (rainbow).
Pupil: At the center of iris ,is a round black region called Pupil.
Pupil size change in response to psychological factor. Positive
emotional reactions dilate the pupil, whereas negative one
constrict it. Pupil size also reflects mental effort, dilate when
concentration is intense.
Lens: A very important optical element of the eye is crystalline
lens that lies right behind the iris.
Visual accomodation: A process through which lens changes
its shape to focus on near or far objects.this process is
regulated by ciliary muscles .
THE VITREOUS CHAMBER: The larger chamber is bounded
by the lens in front and retina on the sides. It is filled with
transparent jelly like fluid called vitreous.
Retina: The inner most layer lies just below the vitreous.The
most critical function of eye is to convert information ,carried
by light waves into neural signals ,that brain can process.
The retina divided into three layers: Photoreceptors ,Bipolar
cells and Ganglion cells.
•Photoreceptors.
The basic conversion from light energy to neural responses is
performed in the retina by photoreceptors.
There are two distinct types of these receptors called Rods and
Cones.
Rods: Rods contain Rhodospin.Light sensitive receptor cell that
handle low illumination vision.
Cons:Cons cotain iodopsins, responsible for coloured vision.
Fovea:It is the center of retina that contain densly packed
cones.It is the area of high Visual activity.
Blind Spot:It is the area where optic nerve leaves the eye, having
no photo receptors. Therefore, insensitive to light.
• Bipolar cell: The nerve cells that combine impulses from many
receptors and the result to ganglion cells.
•Ganglion cell: The axons of the ganglion cell make up the optic
nerve ,which carries the visual information out of the eye and
back towards the brain.
• Optic nerve: The nerve fibers make the optic nerve that
directly lead to brain.
PATHWAY TO BRAIN:
Eyes → Optic Nerves → Optic Chiasma → Optic Tracts →
Lateral Geniculate Nucleus → Visual Cortex.
LIGHT AND DARK ADAPTATION:
Light adaptation, also known as visual adaptation, is the
process by which the eye adjusts to changes in light intensity
maintain optimal visual performance.
Types of Light Adaptation:
1. Dark Adaptation: Adjusting to decreasing light levels.
2. Light Adaptation: Adjusting to increasing light levels.
SENSORY ADAPTATION: Sensory adaptation is
the process by which the nervous system adjusts to repeated
or continuous sensory stimuli, reducing the intensity or
frequency of the sensation.
Types:
1. Sensory accommodation: Gradual decrease in sensitivity.
2. Sensory habituation: Decreased response to familiar stimuli.
COLOUR VISION:
The ability to perceive and distinguish different wavelengths of
light, enabling the recognition of various colors.
There are three different aspect of colour sensation.
1. Hue: essential colour determined by the dominant
wavelength in the mixture of light.
2. Saturation: related to purity of colour.
3. Brightness: refers to overall intensity of all the wavelengths
making up light.
Colour blindness:
Colour blindness is the inability to distinguish two or more
shades in the colour spectrum.
Monochromats: colour blindness occur in people who have only
one rods ,but also in people who are born with one kind of
functioning cone instead of threee.Such people are
monochromatas.
Dichromates: The people havej ust two kinds of cones,mostly
males are called dichromate.
COLOUR VISION THEORIES:
THE TRICHOMATIC THEORY OF COLOUR VISION:
Early in 19th century ,Thomas Young and later,Herman von
Helmholtz established that any colour could be matched by
mixing pure lights of just three wavelengths.For example:By
mixig blue light,green light,and red light in different ratios any
other colour can be produced.
THE OPPONENT PROCESS THEORY OF COLOUR VISION:
Proposed by Ewald Hering in 1878, the theory complements
the trichromatic theory and is widely accepted in explaining
color vision.
The theory suggests that color perception is controlled by
three opposing color pairs: (Red vs. Green) (Blue vs. Yellow )
(Black vs. White ) (for brightness perception)
Mechanism and after images:
Specific neurons in the retina and the visual pathways are
excited by one color of the pair and inhibited by the opposing
colour.
A red-green opponent cell is activated by red and suppressed
by green. A blue-yellow opponent cell is activated by blue and
suppressed by yellow.
When you stare at a color (e.g., red) for an extended period
and then look at a white background, you see the opposing
color (green). This occurs because the overstimulated neurons
for red become fatigued, and the opposing process (green)
dominates momentarily.
