This experiment tested the hypothesis that the occlusion effect is accompanied by an increase in sound pressure level in the external auditory canal. Pure tone bone conduction thresholds and sound pressure levels were measured, first with the ear canal open, then with the ear canal closed, at two positions of the bone vibrator and at five frequencies in 28 normal listeners. Statistical analyses revealed a significant difference between measures at 250, 500, and 1 000 cps but not at 2 000 and 4 000 cps. Average sound pressure level shifts tended to be larger than their threshold measure counterparts. The two measures, nevertheless, yielded positive correlations.

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Basic assumptions and inferences underlying hearing aid evaluation procedures are discussed. A model of hearing aid e valuation incorporating these assumptions and inferences is presented. Problems associated with obtaining valid electroacoustical measurements of hearing aids as well as valid psychoacoustic measurements, aided and unaided, are discussed. Implications for the future study of aided listening are included.

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