block 4-barn owls Flashcards
what behavioural abilities should barn owls have?
-Must be able to locate prey accurately in both the:
- Horizontal plane (azimuth)
- Vertical plane (elevation)
what did Roger Payne find?
- late 1950s
-Sound is the cue that owls use. not body heat or odour
how accurate are barn owls
- 1-2 degrees in both azimuth and elevation.
- Similar to humans in azimuth but 3-fold better in elevation!
- Needs both ears…
how sensitive are barn owls?
- Most sensitive to sounds coming from the front.
- Most sensitive to high frequencies (think mouse in rustling leaves!)
- Can DETECT sounds ranging from 100 Hz - 12 KHz. similar to humans
- Can LOCALISE prey well between 1 - 9 KHz (for azimuth) and 3 - 9
KHz (for elevation).
What physical features enable an owl to pinpoint sound?
Face shape= channels sounds into the facial area e.g. like a satellite dish
-ears stick out but there’s a asymmetry.= one ear higher than the other and sounds can go in from the ear higher up and lower down too
-the facial ruff:stiff feathers in tightly packed rows funnel sound into the ears
-facial dish= the whole face
why might the barn owl evolved to use sounds cue?
- catch camolague/hidden prey
-They are nocturnal = an animal that is active at night and sleeps during the day.
ears of barn owls?
Asymmetric Ears
Left ear higher, points down,
Right ear lower, points up,
-therefore, blocking one ear createsan error in elevation and not in azimuth as expected .e.g. if we bloack the left ear the sound would seem to be coming hgher up.
If one ear of a barn owl is plugged so that the
sound intensity on that side is reduced, what
will happen sound localisation ability?
- barn owl has errors in elevation but there is also a small influence on localisation in azimuth.
.because of the ears point in different directions. right ear =up left ear= down e.g. if you block the left ear sounds seems to be coming from lower down and right higher up. - Experiments demonstrate that barn owls use Interaural
Intensity Differences IID (also known as Interaural Level
Difference (ILD) to determine the Elevation of a sound
source.
-
what do owls use to determine the azimuth(horizontal location)
-interaural Time Difference (ITD)
-Transient disparity= time taken for a sound to start/stop
-both ears receive the sound frequency at the same time but one ar hears it first before the other . the time difference from when the one ear hears the sound waves and then the next ear does the gap is called the onset temporal disparity. the first one
-after that the gap would be called the ongoing disparity which determines the azimuth
-ongoing temporal disparity is what determines Azimuth
-see lecture for picture
what did the experiments show about azimuth?
-In experiments using earphones implanted in the owls’ ears, where
they could control transient and ongoing disparities and sound
level, Moiseff and Konishi
(1981) demonstrated that the head-turns in azimuth were guided by ongoing disparities of as little as a 10 μs.
How does the owl analyse Interaural Intensity
and Interaural Time differences?
From behaviour to brain
1. The inner ear:
- Frequency analysis done by basilar membrane.
- Attached to the basilar membrane are neuronal cell bodies with axons that feed into the auditory nerve: Each neuron
encodes a different frequency.
-hair cells in a region of the basilar membrane are tuned to specific frequency
what about ILD and ITD?
Level (ILD) and timing (ITD) are not segregated within the
auditory nerve. Each sensory neuron contains both timing and
intensity information
what is the elevaltion and azimuth encoded by?
Intensity (elevation) is encoded by changing rate of action
potentials.
– Higher intensity = more action potentials (spikes)=higher the sound was
Timing (azimuth) is encoded by phase locking of action
potentials. =each hearing neuron fires at a specific point in the sound wave’s cycle — like always firing at the “peak” of a wave.
This helps the brain track when the sound hits each ear.
-The pattern of timing between both ears = helps figure out direction (left or right).
why is phase locking important?
-For a particular sensory neuron, each spike occurs at
the same instant during each sound cycle.
* Phase locking ensures accuracy of the timing
information from each ear:
– Comparing between the ears gives interaural timing
differences. [We will come back to this in the second lecture]
– Allows location in horizontal plane (azimuth).
* Works very precisely for all but the highest sound
frequencies an owl can hear.
* So each sensory neuron encodes information about
both sound intensity (firing rate) and timing (phase
locking)!
what does each auditory neuron carry?
-each is specific for different frequency
-sound intensity is encoded by rate of action potentials
-sound timing is encoded by phase locking of action potential firing
what is parrallel processing of neuronal pathways in barn owls ?
Barn owls use both Interaural Time Differences (ITDs) and Interaural Level Differences (ILDs) to locate sounds in space. ILDs refer to the difference in sound intensity between the two ears, which helps the owl determine if a sound is coming from the left or right.
Parallel processing means that different neural pathways handle ILD and ITD information separately but simultaneously. This allows the barn owl to process spatial sound information quickly and efficiently.
where does the neuronal pathways occur in the barn owl
-on both sides of the brain=2 copies
describe the intensity pathway of prcessing ILDs ?
Sound Input Begins at the Angular Nucleus (NA):
Auditory nerve fibers (afferents) send sound intensity (loudness) information to the Nucleus Angularis (NA).
This nucleus processes how loud a sound is but does not track sound timing (not phase-locked).
Information Flows to the Posterior Lateral Lemniscal Nucleus (PLLN):
The PLLN receives two types of inputs:
Excitatory input from the contralateral Angular Nucleus (the opposite side of the brain).
Inhibitory input from the contralateral PLLN (the corresponding nucleus on the opposite side).
This arrangement allows the PLLN to compare the intensity difference (ILD) between both ears.
Since the Angular Nucleus does not track timing, the ILD pathway only processes loudness, not timing.
Neurons in the PLLN Are Organized to Detect Sound Intensity Differences:
Neurons in the PLLN are arranged in a structured way according to sound frequency.
Ventral neurons (lower in the nucleus) fire strongly when the sound is louder in the same-side ear.
Dorsal neurons (higher in the nucleus) fire when the opposite-side ear hears the sound more loudly.
describe the Time pathway for processing ITDs?
- The laminar nucleus receives bilateral inputs from both the magnocellular nuclei which is phase-locked information so provides the timing of info.
-also form delay lines that synapse onto coincidence detector neurons in the laminar nucleus
-neurons in the laminar nucleus provide the mechanism (coincidence detection) for comparing spike timing from the left and right ears
-
coincidence detector in laminar nucleus
- Barn owls use Interaural Time Differences (ITDs) to locate sounds based on the slight difference in arrival time between the two ears.
-Nucleus Magnocellularis (NM) receives sound signals and sends phase-locked (timing-preserved) inputs to the Nucleus Laminaris (NL) on both sides of the brain.
-Delay lines in NL create systematic time delays so that signals from each ear take different routes before reaching coincidence detector neurons.
-Coincidence detector neurons in NL fire only when signals from both ears arrive at the same time.
The position of the active neuron in NL represents a specific ITD, meaning it tells the brain exactly where the sound is coming from.
NL is topographically organized, so different neurons respond to different ITDs, forming a map of sound location in the owl’s brain. - This allows the owl to instantly and precisely determine sound direction, which is critical for hunting in darkness.
how do we turn timing information into place codes?
-– Each coincidence detector differs in its place in the laminar nucleus
giving an array for a given frequency band.
– Laminar neurons at the right end respond best to sounds from the owl’s left.
– Laminar neurons at the left end respond best to sounds coming from the
right of the owl.
– Laminar neurons in the middle will respond best to sounds coming from
the front (or the back) of the owl.
– They send signals up to the higher brain (ICX) where signals combine with
information on ILDs and from different frequencies to enable the owl to
pinpoint the sounds source
phase ambiguity
Coincidence detector neurons in the Nucleus Laminaris (NL) fire maximally when signals from both ears arrive at the same time.
However, sound waves are periodic—they repeat every full wavelength.
If the signal from one ear is delayed or advanced by exactly one full wavelength (or any whole number multiple of a wavelength), the coincidence detector still fires maximally.
The problem: The brain cannot tell whether the right ear signal is actually ahead or behind the left ear signal by one or more full cycles.
This creates ambiguity in interpreting ITDs because multiple possible sound source locations could produce the same neural response.
-phase ambiguity=Can’t tell if the
soundwave in the right ear is delayed or advanced with respect to the left ear
Phase ambiguity is frequency-specific
Because each frequency has a different wavelength, a delay
that causes ambiguity at one frequency will not cause an
ambiguity for other frequencies
