心理物理的同調曲線（ｐｓｙｃｈｏｐｈｙｓｉｃａｌ　ｔｕｎｉｎｇ　ｃｕｒｖｅ）による周波数選択能の臨床的評価：　第一報

The frequency selectivity evaluated by psychophysical tuning curve (PTC) was investigated in 12 cases of unilateral cochlear deafness (CD) of unknown cause and 13 cases of surgically proven unilateral acoustic neuroma (AN).<BR>Test tones were pure-tones of 1-2 seconds duration with the intensity of 5dB above the hearing threshold at 1000Hz and 4000Hz which were produced from a pure-tone audiometer (RION AA-67N). Masking tones were continuous pure-tones at 500Hz, 800Hz, 1500Hz and 2000Hz for 1000Hz testing, and at 2000Hz, 3000Hz, 6000Hz and 8000Hz for 4000Hz testing. These masking tones were produced from a pure-tone audiometer (RION AA-61BN) and were presented by the simultaneous masking method. The PTC in each ear was drawn from the minimal masking levels at 4 masking frequencies and test tone's level. The angle at tip region (tip angle) of PTC was adopted to be the quantitative parameter to investigate the frequency selectivity in this study.<BR>The results obtained were as follows;<BR>1) The tip region of PTC was sharp and the slope of PTC in high frequency side was steeper than that in low frequency side in normal-hearing ears (unimpaired ears of the subjects).<BR>2) The intersubject variance of tip angle of PTC was relatively small in normal-hearing ears.<BR>3) The tip angle of PTC slightly widened as the elevation of hearing threshold at test frequency even in normal-hearing ears. This result suggested that the frequency selectivity could slightly be deteriorated as the elevation of hearing threshold even in normal-hearing ears.<BR>4) When the relationship between the hearing threshold at test frequency and the tip angle of PTC was analyzed, the slope of the regression line in CD and AN ears was steeper than that in normal-hearing ears. This result suggested that the frequency selectivity in CD and AN ears could more apparently be deteriorated as the elevation of hearing threshold than that in normal-hearing ears.<BR>5) Based upon these results, it was concluded that the analysis of the tip angle of PTC enabled us to quantitatively evaluate the frequency selectivity in the individual ear.