In the hearing process, multiple sounds are absorbed simultaneously. Distinguished scientist and musician James Beament puts it into perspective when he writes, “The cortex is so complex that the most we may ever hope for is to understand it in principle, since the evidence we already have suggests that no two cortices work in precisely the same way." When the sound pulses pass into the cortex, the specifics of what exactly takes place are unclear. The auditory cortex is an important yet ambiguous part of the hearing process. Individual cells consistently get excited by sounds at specific frequencies, or multiples of that frequency. Human brain scans have indicated that a peripheral bit of this brain region is active when trying to identify musical pitch. The auditory cortex is involved in tasks such as identifying and segregating auditory "objects" and identifying the location of a sound in space. There are multiple auditory areas (much like the multiple areas in the visual cortex), which can be distinguished anatomically and on the basis that they contain a complete "frequency map." The purpose of this frequency map (known as a tonotopic map) is unknown, and is likely to reflect the fact that the cochlea is arranged according to sound frequency. Neurons at one end of the auditory cortex respond best to low frequencies neurons at the other respond best to high frequencies. Neurons in the auditory cortex are organized according to the frequency of sound to which they respond best. Damage to the Primary Auditory Cortex in humans leads to a loss of any awareness of sound, but an ability to react reflexively to sounds remains as there is a great deal of subcortical processing in the auditory brainstem and midbrain. Evidence for this comes from lesion studies in human patients who have sustained damage to cortical areas through tumors or strokes, or from animal experiments in which cortical areas were deactivated by surgical lesions or other methods. As with other primary sensory cortical areas, auditory sensations reach perception only if received and processed by a cortical area.
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