Consolidated by
Abhishek Singh Chauhan, 1630201, I CEP B
Christ University, Bangalore, Karnataka
As defined by
APA Glossary of Psychological Terms, sensation is the process by which
stimulation of a sensory receptor gives rise to neural impulses that result in
an experience, or awareness of, conditions inside or outside the body.
In simpler words
sensation can be explained as the process by which our sense organs receive
inputs from our environment. Hence, the classical human senses – sight, sound,
taste, smell and touch– register the sensory inputs that evoke our respective
sense organs. But it is important to note that the scope of sensory experience
is much wider than the basic functions of these five senses, as sensory
information can also be in the form of light, pressure, vibration, heat and pain.
These are the stimuli to which our nervous system reacts through sensory
receptors.
A stimulus
is a physical influence that initiates and provokes a reaction. It can be
specific information that is received by the sensory organs, and the resulted
experience is a sensation. Stimuli can vary in type and intensity. Different
sense organs respond to different stimuli, and the intensity of the stimulus
decides whether it can be deducted by the sensory receptors. This is the core
subject matter of the branch of psychology called psychophysics, which studies the physical characteristics of stimuli
in relation with our psychological reaction to them.
Sensory
receptors are the specialized structures that
react to a physical stimulus. A group of receptor cells is called a sense
organ. These receptors vary in classification –taste, gustatory, odour,
olfactory, etc. – but perform the same basic function of being in contact with
the physical stimulus to receive information, decode this information into
creating neural impulses or signals, and transmit these impulses to sensory
cortices of the brain for it to interpret them. This interpretation is called perception.
Sensation and perception are often explained
as one unit. These are two interrelated but distinct parts of a continuous
process. Sensation is a physical response of detecting and translating the
sensory information into signals going up to the brain (bottom-up processing),
while perception is a psychological
response that follows it by analysing and interpreting these signals and makes
sense of them based on our experiences and expectation (top-down processing).
A stimulus has
to be strong enough to be detected by the sense organs. For that, it has to
have the smallest level of intensity to be registered by our senses, which is
called an absolute threshold. However, at such low levels, it may
be difficult to detect a stimulus if noise (any disturbance or distraction in
the form of background stimulation that interferes with other senses) is present
in the environment. Therefore, an absolute threshold is defined as a level of
stimulus that is detectable 50 percent of the time. These thresholds may vary
with age.
The minimum
change in stimulus intensity required to detect the difference in sensory
experience 50 percent of the time is called difference
threshold or a just noticeable
difference. Ernest Weber observed that the size of difference threshold is
a constant proportion of the original stimulus magnitude. This relation is
called Weber’s Law and is expressed
as ∆I / I = K, where ∆I represents the difference threshold, I represents the
initial stimulus intensity and K signifies the proportion that remains constant
despite changes in I. For examples, if two cell-phones are playing music with
the intensity of 100 units, and one’s volume is increased just enough for it to
be noticeably louder, the increased volume would have the intensity of 110
units, and the just noticeable difference would be 10. The Weber fraction in
this would be 10/100 = 0.1. This being a constant proportion, a person’s
difference threshold can be predicted for any level of intensity using the law.
Due to repeated
exposure to a stimulus, our sensitivity to it decreases. This happens through sensory adaptation, which is an adjustment our brain makes to accustom
itself to an unchanging stimulus. This happens when a strong odour in a room
can no longer be smelled after a while. It is not because the smell vanishes,
but our nerve cells fire less frequently in response to the continuous
exposure, and we adapt to it.
BIBLIOGRAPHY:
· Feldman, Robert S.
(1986) Essentials of Understanding Psychology. New York City, NY, USA:
McGraw-Hill Education. (pp. 91-96)
· Myers, David G. (2009)
Psychology – 9th edition in modules. New York City, NY, USA: Worth Publishers.
(pp. 225-231)
Glossary of
Psychological Terms – American Psychological Association.
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