By exploiting the frequency-based sensitivity of the basilar membrane, the brain effectively has access to a spectral decomposition of the incoming sound waves. It is similar to, but not exactly the same as, the Fourier decomposition which discussed in Section 11.1. Several differences are mentioned in Chapter 4 of . If pure tones at two different frequencies are simultaneously presented to the ear, then the basilar membrane produces a third tone, which is sometimes audible . Also, the neural impulses that result from mechanoreceptor output are not linearly proportional to the frequency amplitude. Furthermore, the detection one of tone may cause detections of nearby tones (in terms of frequency) to be inhibited , much like lateral inhibition in horizontal cells (recall from Section 5.2). Section 11.4.1 will clarify how these differences make the ear more complex in terms of filtering.