Olfactory Perception – Smell.
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“…We have five senses, but only two that go beyond the boundaries of ourselves. When you look at someone, it’s just bouncing light, or when you hear them, it’s just sound waves, vibrating air, or touch is just nerve endings tingling. Know what smell is?... It’s made up of the molecules of what you’re smelling.”
Angels in America, p. 17
What is smell?
The substance that you’re “smelling” has been emitted from that source as gas molecules, which in turn you take into your body
Different from light, sound & cutaneous stimulation, which involves transformations of receptors
We have not yet defined the physical parameters the way we have in other senses (i.e., frequency, spatial contrast)
We have not yet defined the perceptual experiences like in other senses such as vision (brightness, color) or hearing (loudness, pitch)
Very difficult to manipulate the stimulus-medium (i.e., how do you control the concentration of airborne molecules?)
General alarm system (smoke, disease)
Component of flavor (quality of food)
Part of communication (pheromones)
Discrimination of social context (family, gender, attractiveness…)
Already stated, we do not have the yardsticks of frequency or spatial measurement
Largely done by description of examples
“Soap smells like lavender”
Human receptors work as good as dogs even though the dog’s ability to smell is 300 to 10,000 times more sensitive then humans
Difference? Number of receptors.
Humans = 10 million
Dogs = 1 billion
Olfactory system fun facts: human recognize their own odor and can distinguish between male v. female odors
Russell (1976) had subjects where a shirt for 24-hours consecutively, then sealed the shirts in plastic bags
Subjects could recognize there own shirt (from a set of 3) 75% of the time (chance: 33%)
Subjects could recognize the strangers (male and female) also 75% of the time
Six primary (independent) odor qualities: fragrant, etheral, resinous, spicy, burned, putrid
This corresponds to 6 types of receptors, which are reflected by specific anosmias (\'smell blindness\') – though the actual number of receptors are still disputed
Can we localize smell? Comparisons to other senses, we are very poor at this
Experimentally, this problem is less easy to approach than in vision or hearing?!
Some researchers invented some ingenious sniffo-meters…
NOTE: other animals seem to perform much better (dogs)
10 Million Olfactory Receptor Neurons (ORN) synapse on 1-to-2,000 Glomeruli
Translation: 5-to-10,000 ORN’s per Glomerulus lots of transduction at Olfactory Bulb
Central Nervous System anatomy of smell: starting with the Olfactory Bulbs (in Brain) to…
Sites in the Cortex for Olfactory Processing: a work in progress (Zatorre, et al., 1992)