Download But not selectively

Why vocal communication is hard to study physiologically
Categorical components
Complex signals vary along multiple parameters
For example, frequency, duration, temporal envelope, etc.
Therefore hard to map onto continuous variables like most sensory
studies
You have seen song selective neurons in pre-motor HVc of birds
Anesthetics?
You have seen song selective neurons in frontal forebrain
This displays idea of Song Selectivity
Neurons specialized for song
Neurons don’t respond well to any other sounds
You have seen bat echolocation
-- Shifted in frequency
-- Because of Doppler shift
Frequency(kHz)
delayed in time
Because speed of sound
 information on target (e.g., moth) distance
120
90
60
-- Doppler shifted echo frequency
 target (moth) velocity
30
Time (msec)
You have seen neurons whose responses are selective for specific pulse echo combos
CF-CF neurons show selectivity form pulse echo pairs
Echo alone
Pulse + Echo
120
Response
(spikes/sec)
Frequency (kHz)
Pulse alone
90
60
30
Weak or no response Weak or no response
time
time
Strong response
time
This reinforces idea of combination selectivity
Neurons specialized for specific Doppler shifts or delays
Different brain areas organized to analyze Doppler shift and delay
How are species specific communications sounds analyzed by
mustached bats?
These responses seen in
DSCF, CF-CF, FM-FM
But that’s not all
Neurons responding to both
echolocation and social calls
found in frontal cortex
The same neurons that encode echolocation respond to these social calls
But not selectively
So we need a different way (not selective neurons) to account for brain
encoding
Population code:
- neurons respond to subset of of vocalizations
- partial selectivity
- combined activity pattern tells you which vocalization
Temporal code
- not just how many spikes but when they fire
- using a population
- combined with temporal pattern  much better reliability
Monkey representation of species specific calls similar to bats
Foreshadow
Monkey representation of species specific calls similar to bats
Primates: Generalist or Specialist
A Generalist would analyze all sounds of which vocalizations are just 1
A specialist would have a specialized auditory system
What not to do as a scientist
Chapter 1 of Primate Audition: “The species –general view of primate
audition is incorrect …”
Primates are not pure generalist
They have some specialization for important sounds like social calls
Evolution and selection has had a large influence on primate auditory
processing
But there auditory systems do not show the degree of specialization of
bats
How primates use vocal communication
To avoid predators
For example in vervet monkeys predation accounts for ~ 70% of deaths
Alarm calls help to prevent predation
But be careful some predators can detect alarm calls
Vervets have different predators
Eagles, leopards and snakes
Each predator type needs to evoke a different behavioral response
For eagle get low to ground (but that would get you eaten by a
snake or leopard)
For leopard they must get to high ground (but beware of eagles)
Therefore vervets have developed different calls for each predator
type
Some primate species can detect and respond to alarm calls of different species of
animals (e.g birds or deer) hunted by a common predator
How primates use vocal communication
To find food
Calls convey information about
Location and
Characteristics of food source
Can convey quantity and quality
Failure to call when food is encountered  punihsment
To find a mate
Aggression
Grunt
Affiliative
Coo
Primate Song
Primates that string together multiple different notes in song a rare
In general they just call
Song/Call distinction
Also important because bird song is acoustically closer to human
speech than primate calls
Some primates like the Gibbon siamong sing.
However no relationship between the few singers and closeness to
humans.
Anatomy
Cochlea
Multiple brain stem areas
Inferior colliculus
Various parallel and hierarchical auditory pathways not shown
MGB
cortex
Neural coding of primate vocalizations
Population code:
Temporal code
In some species they have shown preference for (but not selectivity)
forward over reverse calls
Preference – responds stronger to forward but responds to both
Selectivity – almost no response to reverse
This is still unresolved though as in some species very contradictory
results exist (in macaques one study shows forward preference, one
shows slight reverse preference_