Binaural fusion or binaural integration is a cognitive process that involves the combination of different auditory information presented binaurally, or to each ear. In humans, this process is essential in understanding speech in noisy and reverberent environments.
The process of binaural fusion is important for perceiving the locations of sound sources, especially along the horizontal or azimuth direction, and it is important for sound segregation.[1] Sound segregation refers to the ability to identify acoustic components from one or more sound sources.[2] The binaural auditory system is highly dynamic and capable of rapidly adjusting tuning properties depending on the context in which sounds are heard. Each eardrum moves one-dimensionally; the auditory brain analyzes and compares movements of the two eardrums to extract physical cues and perceive auditory objects.[3]
When stimulation from a sound reaches the ear, the eardrum deflects in a mechanical fashion, and the three middle ear bones (ossicles) transmit the mechanical signal to the cochlea, where hair cells transform the mechanical signal into an electrical signal. The auditory nerve, also called the cochlear nerve, then transmits action potentials to the central auditory nervous system.[3]
In binaural fusion, inputs from both ears integrate and fuse to create a complete auditory picture in the brainstem. Therefore, the signals sent to the higher auditory nervous system are representative of this complete picture, integrated information from both ears instead of a single ear.
The binaural squelch effect is a result of nuclei of the brainstem processing timing, amplitude, and spectral differences between the two ears. Sounds are integrated and then separated into auditory objects. For this effect to take place, neural integration from both sides is required.[4]