Definition
Sensation – Sensing the external or
internal stimuli.
Sensory Process - The process of detection
of external or internal stimuli through the activation of sense organs (Eyes,
ear, nose, skin and tongue).
Visual Sensory Process
The visual sensory process means transducing the visual stimuli
into neural impulse. Human eye is a specialized sense organ that detects light
and transduce it into neural impulse. In fact eye converts light rays into
images.
Structure of
Human Eye
1. The
outermost layer of an eye contains a transparent membrane known as Cornea.
2. The
second layer is made up of watery fluid known as Aqueous Humor (nourishment channel).
3. Then
there is a circular hole known as Pupil found in Iris, a muscle (Colourful
part).
4. Lens
is the next part suspended by muscles behind the iris.
5. Open
space filled with jelly like substance known as Vitreous Humor (Nourishes the
eye and responsible for the shape of eye).
6. The last part where light stops is Retina that contains photoreceptors known as
Rods and Cones.
Function of
Each Part
1. Cornea
– Refracts light.
2. Pupil
– Ensure entry of optimal light.
3. Iris
– Maintains and regulate (Constrict & Dilate) the opening of pupil.
4. Aqueous
Humor – Nourishes and give shape to the eye.
5. Lens
– Refracts the light.
6. Vitreous
Humor – Nourishes and give shape to the eye.
7.
Retina – Converts light energy into neural impulse with the help of rods and
cones.
8. Optic
Nerve – Carries neural impulse to the brain.
Function of
Human Eye
In
its first encounter light rays meets the cornea and then enters the round door
i.e. pupil whose diameter is regulated by a pair of sentinels known as Iris.
After meeting through the pupil the light rays pass through the Aqueous Humor
and falls on the transparent suspended (by ciliary muscles) fellow popularly
known as Lens. The light then passes through a jelly like substance called
Vitreous Humor to focus it on the receiving platform placed at the back of the
eyeball known as Retina. Len refract the light rays in a way that places the
image of the object upside down. At this point the rods and cones are
stimulated that converts the light rays into neural impulse which then passes
to brain via optic nerve.
Some
Important Terms
1. Rods
– Sensory receptors and responsible for vision in low intensity of light
(Scotopic vision or night vision), 100 million (10 crore) rods are found in
each eye.
2. Cones
– Sensory receptors and responsible for chromatic vision or colour vision
(Photopic vision or day vision), 60 lakh cones found in each eye.
3. Fovea
– The central part of retina which have highest concentration of cones. It is
also known as Yellow spot.
4. Blind
Spot – The area of retina that have no photoreceptors and where optic
nerve leaves the retina.
5. Nearsightedness
– Nearer object are clearly visible and distant objects are out of focus.
Visual image is focussed slightly in front of the retina.
6. Farsightedness
– Distant objects are seen clearly and near objects are out of focus. Visual
image is focussed slightly behind the retina.
7. Optic
Nerve – A bundle of axons of ganglion cells found behind the retina.
8. Visual
Adaptation – The process of getting adjusted to
different intensities of light.
9. Light
Adaptation – Process of adjusting to bright light after exposure low
intensity light (Time – 1 or 2 min).
10. Dark
Adaptation – Process of adjusting to low intensity light after exposure
to bright light (Time – 30 min or
more).
11. After
Images – The persistence of effect of visual stimulus even after it has
been removed from the visual field.
Reference:
1. NCERT,
XI Psychology Text book.
2. Ciccarelli,
S. K. & Meyer, G. E. (2016). Psychology. Noida: Pearson India.
3. Baron,
R. (1993). Psychology.
4. https://www.thepoke.co.uk/2011/06/16/
colour-mind-trick/
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