Chapter 10: Hearing in the Real World

Hearing in the Real World begins by detailing how sound localization is achieved through binaural cues, specifically interaural time differences (ITD) processed in the medial superior olive and interaural level differences (ILD) processed in the lateral superior olive. These mechanisms allow the brain to calculate the horizontal angle of a source, known as the azimuth, though they face challenges like the cones of confusion where certain spatial locations produce ambiguous timing and intensity data. To resolve these ambiguities and determine the elevation of a sound, the auditory system relies on the directional transfer function (DTF), which utilizes the unique physical filtering provided by the shape of the pinnae, head, and torso. Perception of auditory distance is further informed by the inverse square law regarding sound intensity, the dampening of high-frequency spectral components over long ranges, and the ratio of direct energy to reverberant energy reflecting off environmental surfaces. The text highlights how complex sounds are defined by their harmonic spectra, where the fundamental frequency typically dictates the perceived pitch and overtones contribute to the unique quality of timbre. A remarkable phenomenon known as the missing fundamental effect demonstrates the brain's ability to perceive a pitch based on temporal patterns even when the lowest frequency is physically absent. Beyond individual sounds, auditory scene analysis explains how the brain segregates overlapping acoustic signals into distinct "streams" using principles of similarity in frequency or timbre, common onset times (common fate), and spatial consistency. Perceptual restoration effects, an auditory analog to visual occlusion, allow the brain to seamlessly fill in missing acoustic information through the principle of good continuation when a signal is briefly masked by loud noise. Finally, the chapter addresses auditory attention, distinguishing between the rapid, unselective acoustic startle reflex and selective attention, which allows for focused listening in busy environments but can also lead to inattentional deafness for unexpected background stimuli.