Page 2 - Sensory, Attentional and Perceptual Processes

as “hard”, “warm”, “loud”, and “blue”, which result from appropriate stimulation of a
sensory organ. Different sense organs deal with different forms of stimuli and serve
different purposes. Each sense organ is highly specialised for dealing with a particular
kind of information. Hence, each one of them is known as a sense modality.

FUNCTIONAL LIMITATIONS OF SENSE ORGANS

Our sense organs function with certain limitations. As human beings, we function within
a limited range of stimulation. For being noticed by a sensory receptor, a stimulus has to
be of an optimal intensity or magnitude. The relationship between stimuli and the
sensations they evoke has been studied in a discipline, called psychophysics.

1. A stimulus in order to be noticed has to carry a minimum value or weight. The
minimum value of a stimulus required to activate a given sensory system is called
absolute threshold or absolute limen (AL). The AL is not a fixed point; instead it
varies considerably across individuals and situations depending on the people’s
organic conditions and their motivational states.
2. It is also not possible to differentiate between all stimuli. In order to notice two
stimuli as different from each other, there has to be some minimum difference
between the value of those stimuli. The smallest difference in the value of two
stimuli that is necessary to notice them as different is called difference threshold
or difference limen (DL).

3. Sensory processes do not depend only on the stimulus characteristics. Sense
organs and the neural pathways connecting them to various brain centers also play
a vital role in this process.

4. A sense organ receives the stimulus and encodes it as an electrical impulse. For
being noticed this electrical impulse must reach the higher brain centers. Any
structural or functional defect or damage in the receptor organ, its neural
pathway, or the concerned brain area may lead to a partial or complete loss of
sensation.