page_title: Binaural fusion
section_title: Anatomy
hierarchical_section_title: Binaural fusion / Anatomy
caption_attribution_description: English: Lateral lemniscus in red, as it connects the cochlear nucleus, superior olivary nucleus and the inferior colliculus. Seen from behind.
context_page_description: Binaural fusion or binaural integration is a cognitive process that involves the "fusion" of different auditory information presented binaurally, or to each ear. In humans, this process is essential in understanding speech as one ear may pick up more information about the speech stimuli than the other.
  The process of binaural fusion is important for computing the location of sound sources in the horizontal plane, and it is important for sound segregation. Sound segregation refers the ability to identify acoustic components from one or more sound sources. 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 both eardrums to extract physical cues and synthesize auditory objects.
  When stimulation from a sound reaches the ear, the eardrum deflects in a mechanical fashion, and the three middle ear bones transmit the mechanical signal to the cochlea, where hair cells transform the mechanical signal into an electrical signal.
context_section_description: As sound travels into the inner eardrum of vertebrate mammals, it encounters the hair cells that line the basilar membrane of the cochlea in the inner ear. The cochlea receives auditory information to be binaurally integrated. At the cochlea, this information is converted into electrical impulses that travel by means of the cochlear nerve, which spans from the cochlea to the ventral cochlear nucleus, which is located in the pons of the brainstem. The lateral lemniscus projects from the cochlear nucleus to the superior olivary complex (SOC), a set of brainstem nuclei that consists primarily of two nuclei, the medial superior olive (MSO) and the lateral superior olive (LSO), and is the major site of binaural fusion. The subdivision of the ventral cochlear nucleus that concerns binaural fusion is the anterior ventral cochlear nucleus (AVCN). The AVCN consists of spherical bushy cells and globular bushy cells and can also transmit signals to the medial nucleus of the trapezoid body (MNTB), whose neuron projects to the MSO. Transmissions from the SOC travel to the inferior colliculus (IC) via the lateral lemniscus. At the level of the IC, binaural fusion is complete. The signal ascends to the thalamocortical system, and sensory inputs to the thalamus are then relayed to the primary auditory cortex.
caption: Transmissions from the SOC, in the pons of the brainstem, travel along the lateral lemniscus to the IC, located in the midbrain. Signals are then relayed to the thalamus and further ascending auditory pathway.
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