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An example of absolute threshold of hearing would be hearing a watch ticking twenty feet (six metres) away from a subject in a quiet room. [14] The threshold of hearing is generally reported as the RMS sound pressure of 20 μPa (micropascals) = 2×10 −5 pascal (Pa).
The absolute threshold of hearing (ATH), also known as the absolute hearing threshold or auditory threshold, is the minimum sound level of a pure tone that an average human ear with normal hearing can hear with no other sound present. The absolute threshold relates to the sound that can just be heard by the organism.
In measuring sensory threshold, noise must be accounted for. Signal noise is defined as the presence of extra, unwanted energy in the observational system which obscures the information of interest. As the measurements come closer to the absolute threshold, the variability of the noise increases, causing the threshold to be obscured. [5]
In 1962, Eugene Galanter, a psychologist, tested stimuli till people were able to feel them approximately 50% of the time, then used the following as examples of absolute threshold: [9] Visual – On a clear, dark night a candle can be seen from approximately 30 miles away. [10]
A basic measure of hearing is afforded by an audiogram, a graph of the absolute threshold of hearing (minimum discernible sound level) at various frequencies throughout an organism's nominal hearing range. [4] Behavioural hearing tests or physiological tests can be used to find the hearing thresholds of humans and other animals.
An absolute threshold is the level of intensity at which a subject can detect the presence of a stimulus a certain proportion of the time; a p level of 50% is commonly used. [16] For example, consider the absolute threshold for tactile sensation on the back of one's hand.
The odor detection threshold and the odor recognition threshold are absolute thresholds; the first is the minimum concentration at which an odor can be detected without any requirements to identify or recognize the stimulus, while the second is the minimum concentration at which a stimulus can be identified or recognized. [2]
By measuring this minimum intensity for testing tones of various frequencies, a frequency-dependent absolute threshold of hearing (ATH) curve may be derived. Typically, the ear shows a peak of sensitivity (i.e., its lowest ATH) between 1–5 kHz, though the threshold changes with age, with older ears showing decreased sensitivity above 2 kHz. [9]