Consequently, how much is an audiometric threshold affected by a tone with its frequency within a dead region? This depends on the location of the dead region. Thresholds at low frequency dead regions, are more inaccurate than those at higher frequency dead regions. This has been attributed to the fact that excitation due to vibration of the basilar membrane spreads upwards from the apical regions of the basilar membrane, more than excitation spreads downwards from higher frequency basal regions of the cochlea. This pattern of the spread of excitation is similar to the ‘upward spread of masking’ phenomenon. If the tone is sufficiently loud to produce enough excitation at the normally functioning area of the cochlea, so that it is above that areas threshold. The tone will be detected, due to off-frequency listening which results in a misleading threshold.