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 Frequency(kHz) Time (msec) -- Because of Doppler shift delayed in time -- Doppler shifted echo frequency  target (moth) velocity -- Shifted in frequency Because speed of sound  information on target (e.g., moth) distance

CF-CF neurons show selectivity form pulse echo pairs Frequency (kHz) Response (spikes/sec) Pulse aloneEcho alonePulse + Echo Weak or no response Strong response Weak or no response time You have seen neurons whose responses are selective for specific pulse echo combos

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? The same neurons that encode echolocation respond to these social calls But not selectively 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

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

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 But there auditory systems do not show the degree of specialization of bats Evolution and selection has had a large influence on primate auditory processing

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 leopard they must get to high ground (but beware of eagles) For eagle get low to ground (but that would get you eaten by a snake or leopard) 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 Affiliative Coo Grunt

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 CochleaMultiple brain stem areasInferior colliculusMGB Various parallel and hierarchical auditory pathways not shown 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_