On the Relation between the Acoustic Reflex and Loudness

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Abstract
For each of 4 subjects, a set of equal-loudness contours constructed from obtained loudness balances was compared to contours of contra- or ipsilateral sinusoidal stimulations that activate the acoustic reflex to the same degree, as indicated by a constant change in acoustic impedance at the eardrum. Two subjects produced "normal" equal-loudness contours, showing close coincidence with the respective equal-reflex contours; the remaining 2 subjects produced "abnormal" equal-loudness contours, exhibiting significant departures from the respective equal-reflex contours. Results indicate no systematic difference in the sensitivity of the acoustic reflex to ipsi- and to contralateral stimulation. Middle-ear attenuations calculated from the magnitude of the acoustic impedance at the eardrum, together with estimates of the reflex-generated attenuations, were employed to transform the sound-pressure levels (SPL''s) of the equal-reflex contours to relative values of volume velocity of the cochlear fluid. The transformed contours support the hypothesis that the acoustic reflex is activated to the same degree by sinusoidal stimulations producing the same total number of neural impulses within about 200 msec. For some subjects, equality of loudness between 2 sinusoidal stimulations appears to be attained under this same condition.

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