Alteration in loudness perception during auditory rehabilitation.

Figure 3 illustrates loudness matching results for each frequency and the various test times. On 2-way repeated-measures ANOVA, a significant effect was found for frequency (F(9,216)=18.318; p<0.001), with less intensity being necessary for high frequency tones to be perceived as being as loud as the reference frequency. No effect was found for rehabilitation time-course (F(3,216)=2.491, p=0.084), but a significant interaction was observed (F(27,216)=1.623, p=0.032). Post-hoc tests revealed that this effect was only observable at Fc and at Fc+1/8 octave, with a modification in loudness perception between 1 month and 6 months post-rehabilitation (at Fc, p<0.001; at Fc+1/8, p<0.001): 6 months after the auditory rehabilitation, the intensity needed to match the reference frequency tone at 30 dBSL was clearly weaker than 1 month after the auditory rehabilitation.

Figure 3: Mean equal-loudness contours for the 9 subjects with high-frequency hearing loss.

The loudness cues were measured at intervals of 1/8 octave around the Fc, except for Fref which was measured at 1 octave before dFc and was set at 30 dBSL.

Pearson’s correlation was used to assess the relationship between the alteration in loudness perception observed between 1 and 6 months at Fc+1/8 octave and the degradation in auditory threshold over the same period (Figure 4). A significant positive correlation emerged between the difference in auditory threshold between 1 month and 6 months on the one hand and the difference in loudness perception between 1 month and 6 months on the other hand (r= 0.837, p=0.003): i.e., the increase in loudness perception at 6 months was correlated with the degradation in auditory threshold.

Figure 4: correlation between the alteration in auditory threshold and loudness perception at 1 month versus 6 months after auditory rehabilitation at Fc+1/8 octave. Each cross represents one of the nine subjects.