The chief dimensions of auditory experience are pitch, correlated with the frequency of vibration of the sound waves that constitute the stimulus, and loudness, correlated with the amplitude of these waves. The absolute threshold for hearing depends on the frequency of the tone. Very low or very high-pitched tones must be more intense to be heard than tones in the middle range of frequencies.
Most tones are not pure, that is composed of only a single frequency. Musical instruments may be differentiated by the timber of their tones, a quality that depends on the overtones and other impurities differing from one instrument to another. Complex sounds composed of many frequencies not in harmonious relation to one another are called noise.
The auditory apparatus consists of the external ear, leading by way of the auditory canal to the eardrum, giving access to the middle ear. The bones of the middle ear transmit the sound waves to the oval window, leading to the inner ear.
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The coehlea houses the receptors of the inner ear, sensitive hair cells buried in the basilar membrane. Wave motion in the fluid of the inner ear agitates these hair cells, which in turn, activate the auditory nerve.
Theories attempting to give a physiological explanation of pitch are the place theory, which emphasizes the place on the basilar membrane where a particular frequency produces its maximum effect, and the frequency theory, which assumes that pitch, is determined by the frequency of impulses travelling up the auditory nerve.
Evidence indicates that the place theory applies to high frequencies, while synchronous discharge is important for the lower frequencies.
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It is noted that the judgements made by people depend both on sensory and non-sensory, or bias, factors. Signal detection theory provides a way of separating sensitivity from bias by making an analysis of Receiver Operating Characteristics (ROC) curves. There are a number of special methods that have been developed for measuring detection thresholds.
They are the Method of limits (also known and the method of minimal change; method of serial exploration; and method of just noticeable difference), Method of constant stimuli, and the Method of average error (also known as the method of adjustment and the method of reproduction and it is used relatively infrequently).
The classical psychophysical methods are tools for gaining knowledge about the operation of a perceptual system. Use of classical psychophysical methods has led to the discovery that the human observer is strikingly sensitive to certain forms of energy variations.
Weber’s Law:
Webers law states that the differential limen is a constant fraction of the standard stimulus i.e. the size of the DL, other things constant, depends on the magnitude of the standard stimulus.(DL = cSt, or equivalently, DL/St = c, where, c is a constant. The relation DL = cSt, is, of course, a linear function in which the additive constant k is zero.)
Fechner’s Law:
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Starting with Weber’s law, Fechner derived a mathematical equation which presumably described the relationship between the intensity of a physical stimulus and the magnitude of the corresponding sensory response (Rs). The equation, known as Fechner’s law, stated that the magnitude of a sensation grows with the logarithm of the initiating stimulus, i.e., Rs = c (log S).