8 Auditory perception
We have learned so far that physical energy from the environment is transduced into electrochemical messages that affect the nervous system and give rise to psychological experiences, that is, produce sensations and perceptions. Sensation refers to the initial process of detecting and encoding environmental energy. The first step in sensing the world is performed by receptor cells, which in the case of hearing are the hair cells in the cochlea. Perception on the other hand, generally refers to the result of psychological processes in which meaning, relationships, context, judgement, past experience and memory all play a role. In many meaningful environmental encounters however, it is difficult to make such a clear distinction between sensation and perception. For example, when we hear a tune are we aware of any isolated tonal qualities of the notes, such as pitch and loudness, distinct from the melody? In most instances, perception and sensation are unified, inseparable psychological processes. In the next section we will now look at an essential tool that has been used to study the quantitative relationship between environmental stimulation (the physical dimension) and sensory experience (the psychological dimension). We will then go on to examine the sensory or psychological effects produced by simple sounds and finally, look briefly at the reception of sound as meaningful information that allows us to perceive spatial features such as localisation.