negative after images appear in complementary colours. These images appear when a person stares at the patch of a particular colour for at least seconds, and then transfers the gaze to a neutral background (e.g., a white or grey surface). If the person looks at the blue colour, the negative after image will appear in yellow. Similarly, a red stimulus will yield a negative after image of green colour.
Auditory Sensation Audition or hearing is also an important sense modality that carries great value for us. It provides us with reliable spatial information. Besides orienting us to certain objects or individuals, it plays a vital role in spoken communication also. Auditory sensation begins when sound enters our ear and stimulates the chief organs of hearing.
The Human Ear Ear is the primary receptor of auditory stimuli. While its well-known function is hearing, it also helps us in maintaining our body balance. The structure of an ear is divided into three segments, called the external ear, the middle ear, and the inner ear (Fig. .
). External Ear : It contains two main structures, namely pinna and auditory meatus . Pinna is a cartilaginous funnel-shaped structure that collects sound waves from the surroundings. Auditory meatus is a canal protected by hair and wax that carries sound waves from pinna to the tympanum or ear drum .
Middle Ear : The middle ear starts with tympanum , a thin membrane highly sensitive to sound vibrations. This is followed by the tympanic cavity . It is connected to the pharynx with the help of Eustachian tube , which maintains the air pressure in tympanic cavity. From the cavity the vibrations pass to three ossicles known as malleus (hammer), incus (anvil), and stapes (stirrup).
They increase the intensity of sound vibrations about times, and send them to the inner ear. Inner Ear : The inner ear has a complicated structure known as membranous labyrinth , which is encapsulated in a bony shell called bony labyrinth . A lymph-like fluid is found in the space between bony labyrinth and membranous labyrinth. This is called perilymph