the dead region that is being stimulated can be used. This means that the threshold of the responding area is sufficiently raised, so that it cannot detect the spread of excitation from the tone. This technique has led to the suggestion that a low frequency dead region may be related to a loss of 40-50 dB. However, as one of the aims of PTA is to determine whether or not there is a dead region, it may be difficult to assess which frequencies to mask without the use of other tests. Based on research it has been suggested that a low frequency dead region may produce a relatively flat loss, or a very gradually sloping loss towards the higher frequencies. As the dead region will be less detectable due to the upward spread of excitation. Whereas, there may be a more obvious steeply sloping loss at high frequencies for a high frequency dead region. Although it is likely that the slope represents the less pronounced downward spread of excitation, rather than accurate thresholds for those frequencies with non-functioning hair cells. Mid-frequency dead regions, with a small range, appear to have less effect on the patient's ability to hear in everyday life, and may produce a notch in the PTA thresholds. Although it is clear that PTA is not the best test to identify a dead region. Psychoacoustic tuning curves (PTC) and threshold equalizing noise (TEN) tests Although some debate continues regarding the reliability of such tests, 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). In the case of dead regions, when the test signal