Human evoked cortical responses to acoustic stimuli occurring within 150-170 msec after stimulus onset yielded input-output functions fairly comparable with Stevens' power functions from psychophysical experiments. The objective threshold and equal-loudness contours thus obtained were both in fair agreementwith the well-known subjective measurements.

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Although noise in general can induce hearing loss, environmental noise represents an important risk for children, teenagers and young adults. Epidemiological investigations now support the occurrence of an increasing number of irreversible hearing losses in these groups. Major causes of hearing loss are toys (guns), explosives and electroacoustically amplified music delivered by head sets or heard in discotheques and open air concerts. Clinical indications are discussed.

The slow component of the auditory evoked potential in man was investigated under various conditions which produced an increase in stimulus repetition rate. The left ear received a 1000 Hz tone once each 5 sec. Intervening stimuli, also of 1000 Hz, were presented to (1) the right ear, (2) both ears, and (3) the left ear. Their relative influence on response amplitude to periodic left ear stimulation was evaluated. The results indicated that: (1) intervening right ear stimulation reduced significantly response amplitude to left ear stimulation; (2) presenting the intervening stimuli to both ears simultaneously caused no further decrement in response amplitude; (3) presenting the intervening stimuli to the left ear alone brought about a further and significant decrease in response amplitude to left ear stimulation. These findings imply that habituation of the auditory evoked potential is greatest when the same pattern of neural activity is repeatedly initiated. When the intervening stimuli elicit a different pattern of neural excitation, habituation is less, even though stimulation rate remains unchanged.