Pure Tone Audiometry - Psychoacoustic Tuning Curves

Psychoacoustic Tuning Curves

Although some debate continues regarding the reliability of such tests,Summers V, Molis MR, Musch H, Walden BE, Surr RK, Cord, MT. Identifying Dead Regions in the Cochlea: Psychophysical Tuning Curves and Tone Detection in Threshold-Equalizing Noise. Ear Hear. 2003;24:133-42. it has been suggested that psychoacoustic tuning curves (PTCs) and threshold-equalising noise (TEN) results may be useful in detecting dead regions, rather than PTA. PTCs are similar to neural tuning curves. They illustrate the level of a masker (dB SPL) tone at threshold, as a function of deviation from center frequency (Hz). They are measured by presenting a fixed low intensity pure tone while also presenting a narrow-band masker, with a varying center frequency. The masker level is varied, so that the level of masker needed to just mask the test signal is found for the masker at each center frequency. The tip of the PTC is where the masker level needed to just mask the test signal is the lowest. For normal hearing people this is when the masker center frequency is closest to the frequency of the test signal (See Figure 9).Sek A, Alcantara J, Moore BC, Kluk K, Wicher A. Development of a fast method for determining psychophysical tuning curves. Int J Audiol. 2005;44:408-20.

In the case of dead regions, when the test signal lies within the boundaries of a dead region, the tip of the PTC will be shifted to the edge of the dead region, to the area that is still functioning and detecting the spread of excitation from the signal. In the case of a low frequency dead region, the tip is shifted upwards indicating a low frequency dead region starting at the tip of the curve. For a high frequency dead region, the tip is shifted downwards from the signal frequency to the functioning area below the dead region. However, the traditional method of obtaining PTCs is not practical for clinical use, and it has been argued that TEN’s are not accurate enough. A fast method for finding PTCs has been developed and it may provide the solution. However, more research to validate this method is required, before it can be accepted clinically. Although it is clear that PTA is not the best test to identify a dead region.