Hearing in Time

In Brief This article reviews the temporal aspects of human hearing as measured using the auditory evoked potentials. Interaural timing cues are essential to the detection and localization of sound sources. The temporal envelope of a sound—how it changes in amplitude over time—is crucially important for speech perception. Time is taken to integrate, identify, and dissolve auditory streams. These temporal aspects of human hearing can be examined using the auditory evoked potentials, which measure the millisecond-by-millisecond activity of populations of neurons as they form an auditory percept. Important measurements are the time taken to localize sounds on the basis of their interaural time differences as measured by the cortical N1 wave, the contribution of the vocal cord frequency and phonemic frequency to the perception of speech sounds as indicated by the envelope-following responses, the temporal integration of sound as assessed using the steady state responses, and the duration of auditory memory as shown in the refractory periods of the slow auditory evoked potentials. Disorders of temporal processing are a characteristic feature of auditory neuropathy, a significant component of the hearing problems that occur in the elderly, and a possible etiological factor in developmental dyslexia and central auditory processing disorders. Auditory evoked potentials may help in the diagnosis and monitoring of these disorders. The auditory evoked potentials can be used to evaluate the temporal processing of sounds in the human brain. The N1 wave of the transient response to changes in interaural timing can measure binaural interaction; envelope-following responses can evaluate the processing of speech; and the auditory steady state responses can track temporal integration in both brain stem and cortex. The evoked potentials can thus provide objective information that might help in the diagnosis and monitoring of disorders of temporal processing.