**1. Introduction**

Until recently, electrophysiological evaluations were performed exclusively with nonverbal stimuli such as clicks and tone bursts which allow rapid and synchronous stimulation of neurons. However, the use of verbal stimuli, such as speech sounds, allows a more accurate analysis of the auditory system, especially if the aim is to investigate how the system decodes speech sounds involved in daily communication. Verbal and nonverbal stimuli are decoded in different ways and follow different trajectories through the central auditory nervous system.

Human communication consists predominantly of verbal stimuli, and it is important to understand how verbal sounds are coded at various levels of the auditory system. The need to develop research methods that are objective and accurately represent daily listening led to the development early this century of electrophysiological tests for measuring how speech sounds are perceived [1, 2]. Subsequently, a number of research groups have focused their efforts on using complex stimuli such as speech for diagnostic purposes [3–10].

The initial studies were performed in animal models [11] aiming to evaluate how the temporal and spectral properties of verbal stimuli were coded, and later human responses were also analyzed [12]. Among the electrophysiological procedures for investigating the processing and coding of verbal sounds, we highlight the frequency following response (FFR).
