Anatomy and Function of the Cochlea

Auditory System

• Cochlea: a snail-like structure with two fluid-filled chambers, containing hair cells that bend to transduce sound
• Hair cells code for different frequencies, with those closest to the oval window coding for high frequencies and those near the end of the cochlea coding for low frequencies
• Hair cells do not regenerate, leading to hearing loss over time

Organ of Corti

• Located in the cochlea, where hair cells are habituated and the solid membrane hits them back and forth

Piano and Cochlea

• Piano works similarly to the cochlea, with strings vibrating at different frequencies when pressed

Cochlear Implants

• External speaker picks up sound, and an electrode stimulates the area of the cochlea associated with the frequency picked up
• Typically, high pitches are lost first, as high frequencies only shake the cochlea in a specific area, whereas low frequencies shake the whole cochlea

Phenomenology

• Process of figuring out which frequencies belong to which object or auditory stream
• Frequencies are grouped into streams by proximity, similarity, and common fate
• Proximity refers to frequencies that are close together being grouped together
• Tamber (tone envelope) refers to how fast the onset/offset of the tone is, and how our perceptual system makes sense of different amplitudes

Speech and Perception

• Perceiving speech involves lungs pumping air into the mouth, and the lack of segmentation between words and the auditory signal
• Our perceptual system puts silences between words, which is why foreign languages can sound like a continuous stream
• Inter- and intra-speaker variation refers to differences in pronunciation and acoustic signals between individuals

Cues to Disambiguate Speech

• Context and experience are used to disambiguate speech
• Phonemic restoration effect: our perceptual system can fill in missing phonemes using context and experience
• Categorical boundaries: our perceptual system groups similar acoustic signals into categories

Olfactory System

• Olfactory epithelium: a big hole in the head with olfactory receptor cells that are like strings that dangle down
• Method of transduction: occurs on the olfactory epithelium by olfactory receptor/sensory neurons
• Olfactory receptor cells work like a puzzle, where the molecule has a specific shape and fits into the receptor
• We are actually touching the molecules we smell

Smell and Maternal Relationships

• Fetuses can smell in the womb and make attachments and connections
• Newborns can identify their mother's amniotic fluid and breast milk
• Mothers' brain reward centers are activated by their baby's scent

Multisensory Integration

• We need to piece all the senses together to experience the world
• The binding problem: how do we combine information from different sensory systems?
• Different specializations depending on space and time: audition for time, vision for space, touch for shape and temperature, and smell for identification
• Our brain combines and correlates information between sensory systems when they converge

Proprioception

• First person perspective: our sense of our own body and how it moves
• Perceptual metosychrony: as we give proprioceptor motor command, we get proprioceptive feedback, and see our hand move in a given way
• Babies learn to balance by constantly moving and getting visual feedback

Synesthesia

• Lack of sensory information can lead to hallucinations and combining of sensory systems
• Synesthesia: the bleeding of sensory systems into others, e.g., seeing letters and numbers as different colors
• Neuroimaging shows that the color area of the brain is activated when seeing black and white numbers

Perceptual Disorders

• Visual disorders: brain processes visual fields differently depending on the side of the brain