Taste

• Humans vary in how many taste buds they have and hence their sensitivity to taste

– About 25% have less than 1000 (“nontasters”), 25% have 10,000+ (“supertasters”), and about 50% of us are in the middle (“tasters”)

– Supertasters are oversensitive to sweet, bitter, and capsaicin (hot pepper).

• Taste buds are located around edges of tongue and down throat and are only sensitive to sweet, sour, salty and bitter.

Olfaction (Smell)

• 6-10 million olfactory receptors located in 1 sq. inch of olfactory epithelium at the top of each nostril

• Although we can’t sense smell like a dog (~10-20 times as many receptors and olfactory epithelium), we are still pretty sensitive

• We seem to have hundreds of different types of olfactory receptors to detect different shaped molecules

Olfaction

• Axons of olfactory receptors pass directly thru skull to brain olfactory bulbs

• Olfactory input is then sent to emotion and memory areas

• About 1 in 100 suffer serious anosmia; many more partial anosmias

• 75-90% of those with Alzheimer’s have decreased olfactory sensitivity (may be useful in diagnosis)

Rods

• ~120 million/eye

• more in periphery

• very sensitive – respond in dim light

• show convergence

• night vision (scotopic vision)

vs Cones

• ~6 million/eye

• most in fovea region

• need bright light (photopic vision)

• have 1-to-1 lines to brain – good for detail vision or “acuity”

• 3 different types - provide color vision

Optic Nerve (image)

Audition (Hearing)

• We have about 15,000 auditory receptors called hair cells lined up on the long membrane inside the cochlea (basilar membrane)

• For all but the deepest tones, different pitches maximally stimulate different places along the basilar membrane

Cochlear Implants (image)

Pain - a “gated” sense

• Pain receptors are activated by irritating chemicals released by injured cells (example: prostaglandins)

• They send their messages to the CNS using transmitter called Substance P

• Built-in “gate” determines whether the pain message gets to brain full force or whether the gate will close and dampen the pain messages

• Both psychological factors (motivation, laughter, feelings of control) and physical factors (other sensory stimulation, endorphins, narcotic pain relievers) can help close the gate

Our Perceptual System

Organizes the input from millions of receptors

Interprets input in terms of your past experience, expectancies, context

Perception, thus, is individual

Perceptual Organization

• Tries to pick out the figure or foreground from the background

• Identifies patterns, continuous lines, what things go together, “wholes”

• Tries to recognize or match input to your memories of past sensory experiences

• Maintains that recognition even if angle of view, lighting, distance, etc. changes

• Distinguishes depth, 3-dimensions