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Perception is the cognitive awareness of the sensory stimulus that is received by the brain. Typically, initial sensory input is received by sensory nerves specific to the modality (such as vision or audition), and the receptor cells convert stimulus into electrical nerve signals that can be transmitted to the brain (Gazzaniga et al., 2019). In hearing, for example, hair cells in the ear are stimulated by sound waves and are converted into electrical impulses (Gazzaniga et al., 2019). These impulses travel through the synapses of the cochlear nerve which then sends input to the cochlear nuclei in the medulla (Gazzaniga et al., 2019). From there, information is sent to the thalamus, where sensory integration happens, and then onto the primary cortex in the temporal lobe (Gazzaniga et al., 2019). At the higher level of processing, information about the environment is integrated to help determine where the sounds are coming from and identify the details of the sound (Gazzaniga et al., 2019).
The ability to collect stimulus could impact perception; those with hearing loss may have damaged hair cells that do not respond to soundwaves (Gazzaniga et al., 2019). In situations involving disruption of sensory perception it may be necessary to use technology like cochlear implants to bypass damaged components and send electrical stimuli directly to the cochlear nerve (Gazzaniga et al., 2019). However, sometimes the stimulus collection is intact, but the perception process is dysfunctional.
An important part of sensory perception is integration of multiple senses in areas of the brain such as the thalamus (Gazzaniga et al., 2019). An example of a multimodal perception is speech; the brain combines auditory information with visual information (such as a person’s lip movement) to gain the perception and understanding of words spoken (Gazzaniga et al., 2019). Sometimes, these perceptions can become scrambled as a result of irregularity in the cross-activation of one cortical area with another (Gazzaniga et al., 2019). fMRI’s and structural imaging in individuals with synesthesia show abnormal activation and connectivity patterns in the brain (Gazzaniga et al., 2019).
Synesthesia is believed to be a result of this dysfunctional synthesis of information from multiple senses, but it may also result from hypersensitive sensory systems (Gazzaniga et al., 2019). A fun example of synesthesia is when individuals mix up their olfactory senses with auditory senses; some people experience different tastes when they hear specific words (Gazzaniga et al., 2019). Similarly, some individuals perceive colors when hearing music or words. While there is no specific association across individuals, the perceived associations stay consistent within the individual over time (Gazzaniga et al., 2019).
