Saturday, January 28, 2012



The process of receiving information from the outside world, translating it, and transmitting it to the brain is called Sensation.


The process of interpreting that information and forming images of the world is called perception.


Virtually anything that can excite receptor cells can be a stimulus.

Transduction is translating messages for the brain. To be useful to the brain, sensory messages must be translated into neural impulses that the neurons carry and the brain understands. The translation of one form of energy into another is called transduction

Sensory limits determine how strong the messages must be for sensation to take place. 

Sensory adaptation: When a stimuli is continuously present or repeated at short intervals, the sensation that the same amount of sensory energy causes becomes gradually weaker, probably because the receptor cells become fatigued.

Psychophysics: The specialty area within the field of psychology that studies sensory limits, sensory adaptation and related topics is called psychophysics.

Brain is not in direct with the outside world. The world is known to us only indirectly because our brains are not in direct with the outside world. The sensory receptor cells have the ability to transduce physical energy into coded neural messages that are sent to the brain (sensation) where they are interpreted (perception).  Not all forms of physical energy can become part of our perception. We must have the sensory receptor cells that can transduce that form of energy. The stimulus must be strong enough to exceed the sensory threshold.


Both the eye and a camera are instruments that use a lens to focus light onto a light sensitive surface on which the visual image is registered

Light: Light is one small part of the form of energy known as electromagnetic radiation that also includes radio waves and X rays.

The eye: The eye is an almost perfect sphere composed of two fluid filled chambers. Light passes through the clear cornea into the first chamber. At the back of this chamber, the colored iris opens and closes to regulate how much will pass through the pupil into the lens. The lens is held in place by ligaments that attached to the ciliary muscle. Eye has rods and cones.

Dark and Light Adaptation: In lighted room, the rods and cones of the eye are being used frequently, so they are not very sensitive. When we enter darkness, the rods and cones are not sensitive enough to be stimulated by the low-intensity light and they stop firing almost completely. This gives the receptors a rest so they being regain their sensitivity by making a fresh supply of the chemicals used in light reception that have been literally bleached out by the intense light.

Color Vision

It has taken psychologists and other scientists more than a hundred years to reach our current understanding of the complex mechanisms of color vision.

There are two major theoretical explanations of how the visual system transduces color.
Young and Helmholz guessed that there are three kinds of cones in the retina that respond mostly to light in either the red, green, or blue range of wavelengths. Their theory is referred to as the trichromatic theory of color vision.
The opponent-process theory was developed to explain the three phenomena listed above that could not be explained just by the existence of three kinds of cones.


The sense of hearing depends on the ear, a complex sensory instrument that transduces the physical properties of sound waves into neural messages that can be sent to the brain.

Sound: Hearing or audition is the sense that detects the vibratory changes in the air known as sound waves. Not all sound waves are alike. For one thing, sound waves differ in the frequency of cycles of compression and rarefaction of the air. The frequency of a sound wave largely determines its pitch or how high or low it sounds to us.  The loudness of sound is largely determined by its intensity.

The Ear: The external part of the year or pinna is useful as a sound collector.
The sound wave is transduced into mechanical energy in the middle ear.


The body senses tell us how the body is oriented, where it moves, and what it touches, and so on.

Orientation and Movement: A complicated set of sensory structures called the vestibular organ is located in the inner section of the ear where it provides the cerebral cortex with information about movement. Individual sensory receptors called kinesthetic receptors located in the muscles, joints, and skin provide additional messages about movement, posture and orientation.

Kinesthetic Sense
Skin Senses
The skin can detect pressure, temperature, and pain.
Phantom Limbs

CHEMICAL SENSES: Taste and Smell

The sense of gestation (taste) or olfaction (smell) differs from the other senses in that they respond to chemicals rather than to energy in the environment. The chemical senses tell us about the things we eat, drink, and breathe.


Sensations that are transmitted to the brain have little meaning of their own. They are in the form of raw neural energy that must be organized and interpreted in the process we call perception.

Visual Perception
Perceptual Organization

Gestalt principles of perception

Figure ground

There are individual and Cultural Influences on Perception. Perception is strongly influenced by other factors as well. For example, a number of studies tell us that motivation influences perception. Hungry college students are more likely to interpret ambiguous pictures as being of food. Anxious persons are more likely to interpret ambiguous sentences as being threatening.

Web References



Psychology - Related Knols

Psychology Article Series (KVSSNRao) - Directory

Introduction to Psychology


Article originally posted on Knol (Knol number 83)
Knol not available for public access after 30 April 2012

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