The Intricacies of Audition: A Psychological Research Perspective
Audition, the sense of hearing, is a fundamental aspect of human cognition and communication. While often considered a 'secondary' sensory system compared to vision, audition plays a crucial role in our daily lives. This article delves into the complexities of auditory processing, highlighting its significance in cognitive science research.
The Fundamentals of Sound and Neural Encoding
Where our vision sense is designed to transduce light information, our hearing sense is designed to extract information from vibrations in the air (sound waves). People are capable of getting a large amount of information from the basic qualities of sound waves. The amplitude (or intensity) of a sound wave codes for the loudness of a stimulus; higher amplitude sound waves result in louder sounds. The pitch of a stimulus is coded in the frequency of a sound wave; higher frequency sounds are higher pitched. Pitch variations over time provide the basis of melody for most music, and pitch contours provide language cues (and meaning in the case of tone languages). We can also gauge the quality, or timbre, of a sound by the complexity of the sound wave - this often relies on the onset, decay, and overtones (layers of harmonics/frequencies) present.
For us to sense sound waves from our environment they must reach our inner ear. Lucky for us, we have evolved tools that allow those waves to be funneled and amplified during this journey. Initially, sound waves are funneled by your pinna (the external part of your ear that you can actually see) into your auditory canal (the hole you stick Q-tips into despite the box advising against it). During their journey, sound waves eventually reach a thin, stretched membrane called the tympanic membrane (eardrum), which vibrates against the three smallest bones in the body-the malleus (hammer), the incus (anvil), and the stapes (stirrup)-collectively called the ossicles. Both the tympanic membrane and the ossicles amplify the sound waves before they enter the fluid-filled cochlea, a snail-shell-like bone structure containing cilia (auditory hair cells) arranged on the basilar membrane according to the frequency to which they respond (called tonotopic organization). Young humans can normally detect sounds between 20 Hz and 20 kHz, though as we age, we lose the ability to detect the higher frequencies.
After being processed by auditory hair cells, electrical signals are sent through the cochlear nerve (a division of the vestibulocochlear nerve) to the thalamus, and then the primary auditory cortex of the temporal lobe. Interestingly, the tonotopic organization of the cochlea is maintained in this area of the cortex (Merzenich, Knight, & Roth, 1975; Romani, Williamson, & Kaufman, 1982).
Perceptual Tasks in Audition
In this review, we focus on three seemingly simple perceptual tasks to demonstrate the complexity of perceptual-cognitive processing involved in everyday audition. We present a description of the perceptual task of segregating multiple sound events that are mixed together in the signal reaching the ears. Then, we discuss the ability to localize the sound source in the environment. Finally, we provide some data and theory on how listeners categorize complex sounds, such as speech. In particular, we present research on how listeners weigh multiple acoustic cues in making a categorization decision.
Sound Segregation
One of the primary tasks our auditory system performs is the segregation of multiple sound events that are mixed together in the signal reaching the ears. This is a complex process that allows us to distinguish individual sounds in a noisy environment.
Sound Localization
Another crucial ability is to localize the sound source in the environment. This involves processing information about the timing and intensity of sounds reaching each ear, allowing us to determine the direction and distance of the sound source.
Categorization of Complex Sounds
Listeners are able to categorize complex sounds, such as speech. Research shows how listeners weigh multiple acoustic cues in making a categorization decision. Pitch is crucial to our perception and understanding of music and language.
| Sound Property | Neural Encoding | Perceptual Effect |
|---|---|---|
| Amplitude | Firing rate of auditory neurons | Loudness |
| Frequency | Position of activated hair cells on basilar membrane | Pitch |
| Complexity | Combination of different frequencies and their intensities | Timbre |
The Need for Auditory Cognitive Science Development
One conclusion of this review is that it is time for auditory cognitive science to be developed to match what has been done in vision in order for us to better understand how humans communicate with speech and music. Audition is often treated as a 'secondary' sensory system behind vision in the study of cognitive science.