cell depends on the relative strengths of the two inputs, which in turn, depends on the sound intensities at the ears. In the auditory midbrain nucleus, the inferior colliculus (IC), many ILD sensitive neurons have response functions that decline steeply from maximum to zero spikes as a function of ILD. However, there are also many neurons with much more shallow response functions that do not decline to zero spikes. The cone of confusion Most mammals are adept at resolving the location of a sound source using interaural time differences and interaural level differences. However, no such time or level differences exist for sounds originating along the circumference of circular conical slices, where the cone's axis lies along the line between the two ears. Consequently, sound waves originating at any point along a given circumference slant height will have ambiguous perceptual coordinates. That is to say, the listener will be incapable of determining whether the sound originated from the back, front, top, bottom or anywhere else along the circumference at the base of a cone at any given distance from the ear. Of course, the importance of these ambiguities are vanishingly small for sound sources very close to or very far away from the subject, but it is these intermediate distances that are most important in terms of fitness. These ambiguities can be removed by tilting the head, which can introduce a shift in both the amplitude and phase of sound waves arriving at each ear. This translates the vertical orientation of the interaural axis horizontally, thereby leveraging the mechanism of localization on the horizontal plane. Moreover, even with no alternation in the angle of the interaural axis (i.e. without tilting one's head) the hearing system can capitalize on interference patterns generated by pinnae, the torso, and even the temporary re-purposing of a hand as extension of the pinna (e.g., cupping one's hand around the ear). As with other sensory stimuli, perceptual disambiguation is also accomplished through integration of multiple sensory inputs, especially visual cues. Having localized a sound within the circumference of a circle at some perceived distance, visual cues serve to fix the location of the sound. Moreover, prior knowledge of the location of the sound generating agent will assist in resolving its current location. Sound localization by the human auditory system Sound localization is the process of determining the location of a sound source. The brain utilizes subtle