How hearing guides action

Question 1

small bats - the echolocating predators (Alcock, 2007)

Answer 1

Bats (Chiroptera):
Megachiroptera (150 species): large eyes, simple ears, non-echolocating (except Rousettus - clicking (HF, short, frequent pulses, in roosting caves)
Microchiroptera (800 species): small-sized, small eyes, complex ears, echolocation
○ Spallanzani (1794) and Jurin (1795) found that hearing essential for bats to avoid obstacles in flight
○ Griffin and Pierce (1938) discovered emission of high-freq ultrasonic pulses in flying bats
○ Ultrasound attenuates quickly - useful for short-distance object detection and tracking
○ Higher pitch = shorter sound travels
○ Sense vibrations - air movement v. close to body

Moths have tympanum on each side of body - compare input from each side - is sound louder on one side or other or behind - hear where bat is - respond to change in sound depending on wing

see notes

Question 2

Small bats - the echolocating predators (Alcock, 2007) research

Answer 2

Mann et al. (2011)

Kalko (1995)

Götze et al. (2016)

Denzinger and Schnitzlet (2013)

Neuweiler (2003)

Question 3

Mann et al. (2011)

Answer 3

Individual recognition via olfactory, auditory, or visual cues is crucial for animals to form and maintain stable social groups, particularly in large colonies such as those of Egyptian fruit bats (Rousettus acuptiacus). We tested whether Egyptian fruit bats are able to distinguish between familiar and unfamiliar conspecifics, using two captive groups of male bats. We recorded the behavioural and auditory responses of focal animals in a binary choice experiment in which they could approach either members of their own social group or unfamiliar individuals. In general, bats preferred to stay close to other bats, familiar or unfamiliar, over resting alone and spent more time in close proximity to members of their own group than to unfamiliar conspecifics. The majority of bats interacted more with the unfamiliar individuals, although this result did not reach significance. We conclude that Egyptian fruit bats are able to distinguish between familiar and unfamiliar conspecifies. Since only one individual emitted social calls and bats never producedecholocationcalls during the experiment, we infer that individual recognition was most likely mediated via olfactory and/or visual cues. The ability to identify familiar individuals may indicate that males of Egyptian fruit bats form stable groups within their large colonies.

Question 4

Kalko (1995)

Answer 4

The foraging and echolocation behaviour of three European pipistrelles (Pipistrellus pipistrellus, P. nithusiiandP. kuhlii) was studied under natural conitions. The pipistrelles were photographed with two 35 mm cameras under stroboscopic illumination, and their echolocation signals were recorded simultaneously. This permits a three-dimensional reconstruction of the flight paths of bat and prey, and allows the details of echolocation behaviour to be studied in the context of natureal foraging behaviour. The general relationships between foraging and echolocation behaviour were consistent among the three species. Foraging behaviour consisted of four stages: search flight (before detection of prey), approach flight (pursuit after detection of prey), capture and retrieval of prey. These stages correlated with phases in echolocation behaviour: search, approach, and terminal phase followed by a pause. Detection of prey occurred at distances of 1·14−2·20 m. The search cone extending from the bat’s mouth was up to 150° wide. The pipistrelles caught prey in mid-air, either with the tail membrane alone or by funnelling it with a wing onto the tail membrane. Except for some intra- and interspecific differences in sound duration, pulse interval, bandwidth and terminal frequency in search phase, the structure and pattern of the echolocation signals were similar in the three pipistrelles. In the approach and terminal phases, pulse duration and pulse interval decreased with the approach to the target, while bandwidth and sweeprate increased. While pursuing insects, the pipistrelles precisely avoided an overlap between outgoing signal and the echo returning from the prey. Furthermore, the bats stopped emitting signals several centimeters before they reached the insect.

Question 5

Götze et al. (2016)

Answer 5

Frequency shifts in signals of bats flying near conspecifics have been interpreted as a spectral jamming avoidance response (JAR). However, several prerequisites supporting a JAR hypothesis have not been controlled for in previous studies. We recorded flight and echolocation behavior of foragingPipistrellus pipistrelluswhile flying alone and with a conspecific and tested whether frequency changes were due to a spectral JAR with an increased frequency difference, or whether changes could be explained by other reactions.P. pipistrellusreacted to conspecifics with a reduction of sound duration and often also pulse interval, accompanied by an increase in terminal frequency. This reaction is typical of behavioral situations where targets of interest have captured the bat’s attention and initiated a more detailed exploration. All observed frequency changes were predicted by the attention reaction alone, and do not support the JAR hypothesis of increased frequency separation. Reaction distances of 1–11 m suggest that the attention response may be elicited either by detection of the conspecific by short range active echolocation or by long range passive acoustic detection of echolocation calls.

Question 6

Denzinger and Schnitzler (2013)

Answer 6

Throughout evolution the foraging and echolocation behaviors as well as the motor systems of bats have been adapted to the tasks they have to perform while searching and acquiring food. When bats exploit the same class of environmental resources in a similar way, they perform comparable tasks and thus share similar adaptations independent of their phylogeny. Species with similar adaptations are assigned to guilds or functional groups. Habitat type and foraging mode mainly determine the foraging tasks and thus the adaptations of bats. Therefore, we use habitat type and foraging mode to define seven guilds. The habitat types open, edge and narrow space are defined according to the bats’ echolocation behavior in relation to the distance between bat and background or food item and background. Bats foraging in the aerial, trawling, flutter detecting, or active gleaning mode use only echolocation to acquire their food. When foraging in the passive gleaning mode bats do not use echolocation but rely on sensory cues from the food item to find it. Bat communities often comprise large numbers of species with a high diversity in foraging areas, foraging modes, and diets. The assignment of species living under similar constraints into guilds identifies patterns of community structure and helps to understand the factors that underlie the organization of highly diverse bat communities. Bat species from different guilds do not compete for food as they differ in their foraging behavior and in the environmental resources they use. However, sympatric living species belonging to the same guild often exploit the same class of resources. To avoid competition they should differ in their niche dimensions. The fine grain structure of bat communities below the rather coarse classification into guilds is determined by mechanisms that result in niche partitioning

Question 7

Neuweiler (2003)

Answer 7

This review is yet another attempt to explain how echolocation in bats or bat-like mammals came into existence. Attention is focused on neuronal specializations in the ascending auditory pathway of echolocating bats. Three different mechanisms are considered that may create a specific auditory sensitivity to echos: (1) time-windows of enhanced echo-processing opened by a corollary discharge of neuronal vocalization commands; (2) differentiation and expansion of ensembles of combination-sensitive neurons in the midbrain; and (3) corticofugal top-down modulations. The second part of the review interprets three different types of echolocation as adaptations to ecological niches, and presents the sophisticated cochlear specializations in constantfrequency/frequency-modulated bats as a case study of finely tuned differentiation. It is briefly discussed how a resonant mechanism in the inner ear of constantfrequency/frequency-modulated bats may have evolved in common mammalian cochlea

Question 8

The echo

Answer 8

• Echo variation: direction, delay, amplitude, freq
  
  • Factors: physical (wave propagation, diffraction), object range, object size, object distance, object velocity
  • Bat produces sound - then listens to echo - sound hits surface in sufficient distance and echo returns - knows there’s an object there - change in shape and freq - properties analysed to define whether large or small object

Calculate diffs between cry and echo returned - direction, speed, size of object - diff variables

see notes

Neuweiler (2003)
- See notes

Question 9

The echo research

Answer 9

Thiagavel et al. (2018)

Question 10

Thiagavel et al. (2018)

Answer 10

Substantial evidence now supports the hypothesis that the common ancestor of bats was nocturnal and capable of both powered flight and laryngeal echolocation. This scenario entails a parallel sensory and biomechanical transition from a nonvolant, vision-reliant mammal to one capable of sonar and flight. Here we consider anatomical constraints and opportunities that led to a sonar rather than vision-based solution. We show that bats’ common ancestor had eyes too small to allow for successful aerial hawking of flying insects at night, but an auditory brain design sufficient to afford echolocation. Further, we find that among extant predatory bats (all of which use laryngeal echolocation), those with putatively less sophisticated biosonar have relatively larger eyes than do more sophisticated echolocators. We contend that signs of ancient trade-offs between vision and echolocation persist today, and that non-echolocating, phytophagous pteropodid bats may retain some of the necessary foundations for biosonar.

Question 11

deflection of basilar membrane

Answer 11

Voldrich (2009)

Frank and Kossl (1995)

Question 12

Voldrich (2009)

Answer 12

A fresh basilar membrane has different mechanical properties in the radial and in the longitudinal directions. When pressure with a needle is exerted on the basilar membrane, a narrow radially oriented strip is deflected. The form of the deflection can be deduced from the pathological consequences of the acoustic trauma as well. The observed anisotrophy is a property of the vital membrane and is disturbed by chemical and physical influences and is lost post mortem. The post-mortem changes can explain the results obtained by von Bekesy which differ from ours. The physiological meaning of the mechanical properties of the basilar membrane is discussed here.

Question 13

Frank and Kossl (1995)

Answer 13

so-suppression tuning curves (STCs) of the 2f(1)-f(2) distortion product (dp) were measured over a primary frequency range of 20 to 93 kHz in mustached bats, Pteronotus pamellii pamellii. Primary levels were chosen to produce dp levels between 0 and 7 dB SPL. At frequencies outside the ranges of 60 - 72 kHz and 90 - 93 kHz the shapes of the STCs were symmetrical or asymmetrical with a steep high frequency slope. In the vicinity of 61 kHz where a strong stimulus frequency otoacoustic emission (SFOAE) is present, the asymmetry of the STCs was inverted with a very steep low frequency slope(max. -89 dB/kHz) and a shallow high frequency slope. The inverted STCs resemble neuronal tuning curves of the same species with best frequencies at about 61 kHz. Close to 61 kHz the STCs were sharply tuned with Q(10dB) values up to 177. The STC-thresholds were about 20 dB above the neuronal thresholds. Thickenings of the basilar membrane located just basal to the cochlear place of the SFOAE frequency are probably involved in creating the asymmetric STCs. Cochlear resonance at the SFOAE frequency and an increased longitudinal coupling within the thickened basilar membrane region are thought to contribute to the specialized STC shape. In the range of 40 - 93 kHz, the STCs are also sharply tuned with inverted asymmetry which is probably not due to an harmonic effect of the specialized cochlear mechanics in the 60 kHz region but may be caused by an independent mechanism.

Question 14

Harmonics in the vocalisations of bats

Answer 14

• Natural sounds are not pure tones - besides noise, there can be harmonics and overtones

Sounds produced by instruments, singing birds and vocalising bats contain harmonics - harmonic freqs multiples of fundamental freq

see notes

* Greater horseshoe bat Rhinopholus ferrmequinum: broadcast freq is 2nd harmonic (loudest freq band, preferred freq is around 83 kHz)
* Reduce octaves by changing length of string 

Broadcast in frequency

Neuweiler (2003)
• FM signals (broadband) - excellent for distance and texture analysis

CF signals (constant freq, narrow band) - excellent for analysis of object movement and object detection over very large range (long pulses, higher energy) - distorts sound when object moves through it - Doppler effect 
- See notes

Question 15

Harmonics in the vocalisations of bats research

Answer 15

Motamedi and Muller (2014)

Bates et al. (2011)

Question 16

Motamedi and Muller (2014)

Answer 16

The biosonar beampatterns found across different bat species are highly diverse in terms of global and local shape properties such as overall beamwidth or the presence, location, and shape of multiple lobes. It may be hypothesized that some of this variability reflects evolutionary adaptation. To investigate this hypothesis, the present work has searched for patterns in the variability across a set of 283 numerical predictions of emission and reception beampatterns from 88 bat species belonging to four major families (Rhinolophidae, Hipposideridae, Phyllostomidae, Vespertilionidae). This was done using a lossy compression of the beampatterns that utilized real spherical harmonics as basis functions. The resulting vector representations showed differences between the families as well as between emission and reception. These differences existed in the means of the power spectra as well as in their distribution. The distributions were characterized in a low dimensional space found through principal component analysis. The distinctiveness of the beampatterns across the groups was corroborated by pairwise classification experiments that yielded correct classification rates between similar to 85% and similar to 98%. Beamwidth was a major factor but not the sole distinguishing feature in these classification experiments. These differences could be seen as an indication of adaptive trends at the beampattern level.

Question 17

Bates et al. (2011)

Answer 17

When echolocating big brown bats fly in complex surroundings, echoes arriving from irrelevant objects (clutter) located to the sides of their sonar beam can mask perception of relevant objects located to the front (targets), causing “blind spots.” Because the second harmonic is beamed more weakly to the sides than the first harmonic, these clutter echoes have a weaker second harmonic. In psychophysical experiments, we found that electronically misaligning first and second harmonics in echoes (to mimic the misalignment of corresponding neural responses to harmonics in clutter echoes) disrupts the bat’s echo-delay perception but also prevents clutter masking. Electronically offsetting harmonics to realign their neural responses restores delay perception but also clutter interference. Thus, bats exploit harmonics to distinguish clutter echoes from target echoes, sacrificing delay acuity to suppress masking.

Question 18

What does a bat need to know to locate prey? (Carew, 2000)

Answer 18

• Distance to object - orient towards and whether close enough to catch
• Size of object (loudness/amplitude of echo = subtended angle - size and distance correlated) - how much weaker is echo than amplitude of initial sound
• Location of object
• Moving (Doppler shift - shift in the pitch) or stationary object (no Doppler effect)
- Texture of object
- See notes

Question 19

What does a bat need to know to locate prey? (Carew, 2000) research

Answer 19

Griffin et al. (1960)

Webster and Griffin (1962)

Question 20

Griffin et al. (1960)

Answer 20

○ 1 . Bats of the genus Myotis (M. lucifugus, M. subulatus leibii and M. keenii septentrionalis) have been studied while pursuing and capturing small insects under laboratory conditions . It is apparently important to provide fairly large numbers of such insects in order to elicit insect catching behaviour indoors .
○ 2 . Insect catches are individually directed pursuit manoeuvres ; each insect is detected, located, and intercepted in flight within about half a second .
○ 3 . Certain individual bats caught mosquitos (Culex quinquefaciatus) and fruit flies (Drosophila robusta and D. melanogaster) at remarkably high rates which could be measured conservatively by the gain in weight of the bat . Sometimes a bat would average as many as 10 mosquitos or 14 fruit flies per minute during a period of several minutes. In four cases motion pictures showed two separate Drosophila catches within half a second .
○ 4. The orientation sounds of the hunting bat are adjusted in a manner that seems appropriate for the echolocation of single insects one at a time . There is a search phase before the occurrence of any apparent reaction to the insect . In this phase the frequency drops from about 100 to 50 kilocycles during each pulse of sound, and the pulses are emitted by M. lucifugus at intervals of 50 to 100 milliseconds .
○ 5 . When an insect is detected the search phase gives way to an approach phase characterized by a progressive shortening of the pulse-to-pulse interval and, if necessary, a sharp turn towards the insect . In this phase the pulse duration may shorten somewhat, but the frequencies remain approximately the same as in the search phase or drop slightly .
○ 6 . When the bat is within a few centimetres of the insect there is a terminal phase in which the pulse duration and interval between pulses shorten to about 0 . 5 millisecond and 5 or 6 milliseconds respectively . Contrary to a conclusion reached earlier on the basis of much less adequate data (Griffin, 1953), the frequency drops in the terminal phase, sometimes to 25 or 30 kilocycles . This is the buzz, which also occurs in many cases when the bat is dodging wires or landing.
○ 7 . The distance from the insect at which detection occurs can be judged by the shift from search to approach patterns . This distance of detection is commonly about 50 cm. for Drosophila, and it occasionally may be as much as a 153 metre with fruit flies or mosquitos.
8 . Two M. lucifugus which had become adept at catching Drosophila in the laboratory were exposed to broad band thermal noise either at low frequencies (0 . 1-15 kilocycles) or high (20- 100 kilocycles). The low frequency noise had an approximately uniform spectrum level of about 50 decibels per cycle band width (re 0 . 0002 dyne/cm2) from 0. 1 to 8 kilocycles . It was thus very loud compared to the flight sounds of Drosophila which have a fundamental frequency of a few hundred cycles/second and a maximum sound pressure level of 20-25 decibels at the distances of detection by these bats . The high frequency noise was of low and varying intensity, but it discouraged or prevented insect catching . The low frequency noise, on the other hand, had no effect on insect catching ; the bats gained weight in this noise (and in the dark) just as rapidly as in the quiet. Although bats sometimes detect insect prey by passive listening to sounds emanating from the insects themselves, these experiments appear to us to establish conclusively that small and relatively silent insects are often detected by echolocation .

Question 21

Webster and Griffin (1962)

Answer 21

○ 1. A large series of electronic flash photographs of bats catching insects on the wing has demonstrated several common techniques employed
○ 2. A small and slow-flying insect such as a fruit fly may be sometimes seized directly with the mouth. In most cases, however, the interfemoral membrane is formed into a pouch by forward flexion of the hind legs and tail just before an insect is intercepted. Immediately after contact with the insect, the head is enclosed within the pouched tail membrane while the insect is seized in the jaws. Examples of this technique occur when aMyotis lucifuguscatches mealworms tossed into the air, and whenLasiurus borealiscatches flying moths.
○ 3. When the insect is not directly in front of the approaching bat one wing is often extended so as to intercept it. Sometimes the terminal joints of the 3rd and 4th fingers are flexed to form a scoop in which the insect is rapidly conveyed to the mouth, usually by way of the pouched tail membrane. This technique has been photographed inMyotis lucifuguscatching fruit flies and also mealworms that had been tossed into the air. The wing was also employed in this manner during a single case where a greater horseshoe bat,Rhinolphus ferrum-equinum, was photographed catching a flying moth.
○ 4. In a few cases the photographs show that the wing is used either deliberately or accidentally to flick an insect into a position where it is seized in the mouth or pouched tail membrane a fraction of a second later. This technique has been clearly photographed only withMyotis lucifuguscatching tossed mealworms.
○ 5. While the use of tail and wing membranes greatly increases the potential area of contact with insect prey over the area of the opened mouth alone, the photographs almost invariably show that the bat’s head is pointed at the insect well before contact with it. Preparatory movements such as cupping the tail membrane, flexing the terminal joints of the fingers, and reaching the wing toward the moving insect, all show that the insect is located quite accurately before it touches any part of the bat. These photographs strongly indicate that each insect is individually located and intercepted.
6. The wing of these bats thus retains some of the prehensile functions of the hand in non-flying mammals.

Question 22

How well can bats discriminate different sources? (Carew, 2005)

Answer 22

• Determining the limits of distance resolution (Simmons, 1973)
• Training: near platform contains reward, the far one not - sides swapped regularly
• Tests: sound-reflective targets removed from platforms and replaced with speakers - phantom targets presented via loudspeakers when pulse-echo delays modified and simulate smaller and smaller distanced between targets until choice perf breaks down (random choices around 50%)
- Train to find prey relative to something that I couldn’t understand her saying
- See notes

Question 23

How well can bats discriminate different sources? (Carew, 2005) research

Answer 23

Simmons (1973)

Schnitzler et al. (2003)

Question 24

Simmons (1973)

Answer 24

Using simultaneous discrimination procedures the acuity of resolution of differences in target range has been determined on four species of echolocating bats (Eptesicus fuscus, Phyllostomus hastams, Pteronotus suapurensis, and Rhinolophus ferrumequinum ). All can discriminate range differences as small as 1 to 3 cm and, for the first three species, the acuity of range resolution appears to be independent of absolute range, at least at short distances. In Eptesicus range discrimination is mediated in terms of the arrival times of echoes returning from different targets. Comparisons between discrimination performance and autocorrelation functions of echolocation sounds used in the discriminations suggesthat these bats possess some neural equivalent of a matched-filter, ideal sonar receiver which functionally cross-correlates a replica of the outgoing signal with the returning echo to detect the echo and determine its arrival time. Eptesicus and Phyllostomus both use the entire FM signal for target ranging. Pteronoms uses its entire compound, short-duration CF/FM signal for ranging, while Rhinolophus separates the FM component from its compound, long-duration CF/FM sound and uses the FM part for target ranging. The results indicate different functions for the CF and FM components of bat sonar cries, and they suggest that the matched-filter or cross-correlation approach to echolocation is appropriate.

Question 25

Schnitzler et al. (2003)

Answer 25

Field research on echolocation behavior in bats has emphasized studies of food acquisition, and the adaptive value of sonar signal design as been considered largely in the context of foraging. However, echolocation tasks related to spatial orientation also differ among bats and are relevant to understanding signal structure. Here, we argue that the evolution of echolocation in bats is characterized by two key innovations: first, the evolution of echolocation for spatial orientation and, second, a later transition for prey acquisition. This conceptual framework calls for a new view on field data from bats orienting and foraging in different types of habitats. According to the ecological constraints in which foraging bats operate, four distinct functional groups or guilds can be defined. Within each group, signal design and echolocation behavior are rather similar

Question 26

Distance estimation from delay between pulse and echo (Simmons, 1971, 1973; Altringham, 1996; Carew, 2000)

Answer 26

see notes

• Smallest distance between targets can distinguish - how much echo is delayed after sound produced - delay between sound and echo returning to bat - equiv to distance range
• 20ms echo delay - short delay
- CF - range resolution not as good as those with many freqs

Question 27

Distance estimation from delay between pulse and echo (Simmons, 1971, 1973; Altringham, 1996; Carew, 2000) research

Answer 27

Simmons et al. (2019)

Question 28

Simmons et al. (2019)

Answer 28

In complex biosonar scenes, the delay of echoes represents the spatial distribution of objects in depth. To avoid overlap of echo streams from successive broadcasts, individual echolocation sounds should only be emitted after all echoes of previous sounds have returned. However, close proximity of obstacles demands rapid pulse updates for steering to avoid collisions, which often means emitting a new sound before all of the previous echoes have returned. When two echo streams overlap, there is ambiguity about assigning echoes to the corresponding broadcasts. In laboratory tests of flight in dense, cluttered scenes, four species of echolocating bats exhibited different patterns of pulse emissions to accommodate potential pulse-echo ambiguity. Miniopterus fuliginosus emitted individual FM pulses only after all echoes of previous pulses had returned, with no alternating between long and short intervals. Pipistrellus abramus and Eptesicus fuscus alternated between emitting long FM pulse intervals to receive all echoes before the next pulse, and short intervals to update the rapidly changing scene while accepting partial overlap of successive echo streams. Rhinolophus ferrumequinum nippon transmitted CF/FM pulses in alternating short and long intervals, usually two to four closely spaced sounds that produced overlapping echo streams, followed by a longer interval that separated echo streams. Rhinolophus f. nippon is a statistical outlier from the three FM species, which are more similar to each other. The repeated overlap of CF/FM echo streams suggests that CF components have a distinct role in rejection of clutter and mitigation of ambiguity.

Question 29

Echolocation phases during an approach

Answer 29

• Myotis lucifugus (little brown bat) capturing a mealworm tossed into the air (Webster and Griffin, 1962)
• Species specific call
• Calls shorter over time and in faster succession - hone in on prey or coming closer to obstacle
• Active component/active control
- Can also go silent - eavesdrop on others - conceal what honing in on

see notes

• Heffner (2004)

see notes

• R'ship between max functional interaural distance (as measured by time in microseconds required for sound in air or water to travel from one auditory meatus to other) and high-freq hearing limit (highest freq audible at 60 dB SPL)
• Primates indicated by filled circles and named, along with some other fam species for comparison
• Stat analysis and regression line don’t include 3 subterranean species, indicated by triangles, for reasons described in text
• Regression line determined by minimising sum of square residuals  - Need to be small in size - small distance between ears

Question 30

Echolocation phases during an approach research

Answer 30

Johnson et al. (2006)

Valero et al. (2017)

Question 31

Johnson et al. (2006)

Answer 31

Blainville’s beaked whales (Mesoplodon densirostris Blainville) echolocate for prey during deep foraging dives. Here we use acoustic tags to demonstrate that these whales, in contrast to other toothed whales studied, produce two distinct types of click sounds during different phases in biosonar-based foraging. Search clicks are emitted during foraging dives with inter-click intervals typically between 0.2 and 0.4 s. They have the distinctive form of an FM upsweep (modulation rate of about 110 kHz ms(-1)) with a-10 dB bandwidth from 26 to 51 kHz and a pulse length of 270 mu s, somewhat similar to chirp signals in bats and Cuvier’s beaked whales (Ziphius cavirostris Cuvier), but quite different from clicks of other toothed whales studied. In comparison, the buzz clicks, produced in short bursts during the final stage of prey capture, are short (105 mu s) transients with no FM structure and a -10 dB bandwidth from 25 to 80 kHz or higher. Buzz clicks have properties similar to clicks reported from large delphinids and hold the potential for higher temporal resolution than the FM clicks. It is suggested that the two click types are adapted to the separate problems of target detection and classification versus capture of low target strength prey in a cluttered acoustic environment.

Question 32

Valero et al. (2017)

Answer 32

Cochlear synaptopathy can result from various insults, including acoustic trauma, aging, ototoxicity, or chronic conductive hearing loss. For example, moderate noise exposure in mice can destroy up to ∼50% of synapses between auditory nerve fibers (ANFs) and inner hair cells (IHCs) without affecting outer hair cells (OHCs) or thresholds, because the synaptopathy occurs first in high-threshold ANFs. However, the fiber loss likely impairs temporal processing and hearing-in-noise, a classic complaint of those with sensorineural hearing loss. Non-human primates appear to be less vulnerable to noise-induced hair-cell loss than rodents, but their susceptibility to synaptopathy has not been studied. Because establishing a non-human primate model may be important in the development of diagnostics and therapeutics, we examined cochlear innervation and the damaging effects of acoustic overexposure in young adult rhesus macaques. Anesthetized animals were exposed bilaterally to narrow-band noise centered at 2kHzat various sound-pressure levels for 4h. Cochlear function was assayed for up to 8 weeks following exposure viaauditory brainstem responses(ABRs) and otoacoustic emissions (OAEs). A moderate loss of synaptic connections (mean of 12–27% in the basal half of the cochlea) followed temporary threshold shifts (TTS), despite minimal hair-cell loss. A dramatic loss of synapses (mean of 50–75% in the basal half of the cochlea) was seen on IHCs surviving noise exposures that produced permanent threshold shifts (PTS) and widespread hair-cell loss. Higher noise levels were required to produce PTS in macaques compared to rodents, suggesting that primates are less vulnerable to hair-cell loss. However, the phenomenon of noise-induced cochlear synaptopathy in primates is similar to that seen in rodents.

Question 33

Echolocation is used by some blind human individuals (Thaler et al., 2018)

Answer 33

• Blind and sighted indvs can learn to echolocate
• Human echolocators (N=8, blind) adjusted loudness and number of clicks for detection of reflectors at various azimuth angles
• Task: click and report presence/absence of objects (chance level 50%)
- Increasing intensity and no’s of clicks improves signal-to-noise ratio (imp for weak echoes)

see notes

Question 34

Echolocation is used by some blind human individuals (Thaler et al., 2018) research

Answer 34

Thaler and Goodale (2016)

Question 35

Thaler and Goodale (2016)

Answer 35

Bats and dolphins are known for their ability to use echolocation. They emit bursts of sounds and listen to the echoes that bounce back to detect the objects in their environment. What is not as well‐known is that some blind people have learned to do the same thing, making mouth clicks, for example, and using the returning echoes from those clicks to sense obstacles and objects of interest in their surroundings. The current review explores some of the research that has examined human echolocation and the changes that have been observed in the brains of echolocation experts. We also discuss potential applications and assistive technology based on echolocation. Blind echolocation experts can sense small differences in the location of objects, differentiate between objects of various sizes and shapes, and even between objects made of different materials, just by listening to the reflected echoes from mouth clicks. It is clear that echolocation may enable some blind people to do things that are otherwise thought to be impossible without vision, potentially providing them with a high degree of independence in their daily lives and demonstrating that echolocation can serve as an effective mobility strategy in the blind. Neuroimaging has shown that the processing of echoes activates brain regions in blind echolocators that would normally support vision in the sighted brain, and that the patterns of these activations are modulated by the information carried by the echoes. This work is shedding new light on just how plastic the human brain is.

Question 36

Neural basis of listening to echoes (Jarvis, 2009)

Answer 36

see notes

see notes

• Evolution of Pallium in birds and reptiles
• Example sensory (auditory) and motor (vocal) pathways in songbirds, in comparison with other vertebrates
• (a) auditory pathway in songbird showing ascending and descending input
• (b) similar auditory pathways, but sometimes with diff nomenclature used for indv nuclei, can be found for all amniotes examined
• Only sub-pathway through cochlea and lateral leminiscal nuclei shown
• Once in telencephalon, parallels found in cell type connectivity, although pallial organisations diff and projections in amphibians mostly to striatum
- Cochlear nuclei and ganglion imp to compare info in both ears

Question 37

Neural basis of listening to echoes (Jarvis, 2009) research

Answer 37

Borina et al. (2011)

Wada et al. (2017)

Question 38

Borina et al. (2011)

Answer 38

The effective use of echolocation requires not only measuring the delay between the emitted call and returning echo to estimate the distance of an ensonified object. To locate an object in azimuth and elevation, thebat’s auditory system must analyze the returning echoes in terms of their binaural properties, i.e., the echoes’ interaural intensity and time differences (IIDs and ITDs). The effectiveness of IIDs for echolocation is undisputed, but when bats ensonify complex objects, the temporal structure of echoes may facilitate the analysis of the echo envelope in terms of envelope ITDs. Using extracellular recordings from the auditory midbrain of thebat, Phyllostomus discolor, we found a population of neurons that are sensitive to envelope ITDs of echoes of their sonar calls. Moreover, the envelope-ITD sensitivity improved with increasing temporal fluctuations in the echo envelopes, a sonar parameter related to the spatial statistics of complex natural reflectors like vegetation. The data show that in bats envelope ITDs may be used not only to locate external, prey-generated rustling sounds but also in the context of echolocation. Specifically, the temporal fluctuations in the echo envelope, which are created when the sonar emission is reflected from a complex natural target, support ITD-mediated echolocation.

Question 39

Wada et al. (2017)

Answer 39

The avian cerebrum has pallial functions similar to those of the mammalian cortex. Although the avian pallium is organized as nuclear structures, and the mammalian cortex as layers, the avian pallium supports cognitive abilities similar to those of many mammals. We recently presented a global view of the pallial organization of birds, based on quantitative analyses of constitutively expressed or behaviorally regulated genes in different pallial cell populations (Jarvis et al. J Comp Neurol 521:3614–3665, 2013; Chen et al. J Comp Neurol 521:3666–3701, 2013). Here we present a shortened synopsis of these articles. The findings of the constitutively expressed genes and known neural connectivity reveal four major cell populations: (1) a primary sensory input population, (2) a secondary intrapallial population, (3) a tertiary intrapallial population, and (4) a quaternary output population. These populations have greater similarities to cell layers of the mammalian cortex than to the amygdala. The patterns of behaviorally regulated genes revealed functional columns of activation across boundaries of these cell populations, reminiscent of columns through layers of the mammalian cortex. Each neural cell population contributes portions to columns that control different sensory or motor systems. These findings influence hypotheses on homologies of the avian pallium with other vertebrates.

Question 40

Auditory interneurons are selectively tuned to preferred frequencies

Answer 40

• Little brown bat - FM, therefore no preferred freq
• Horseshoe and moustached bat - CF/FM
- More interneurons connecting to hair cells to basilar membrane in preferred freq

see notes

Question 41

Auditory interneurons are selectively tuned to preferred frequencies research

Answer 41

Moore and Wehr (2013)

Question 42

Moore and Wehr (2013)

Answer 42

In the auditory cortex, synaptic inhibition is known to be involved in shaping receptive fields, enhancing temporal precision, and regulating gain. Cortical inhibition is provided by local GABAergic interneurons, which comprise 10-20% of the cortical population and can be separated into numerous subclasses. The morphological and physiological diversity of interneurons suggests that these different subclasses have unique roles in sound processing; however, these roles are yet unknown. Understanding the receptive field properties of distinct inhibitory cell types will be critical to elucidating their computational function in cortical circuits. Here we characterized the tuning and response properties of parvalbumin-positive (PV+) interneurons, the largest inhibitory subclass. We used channelrhodopsin-2 (ChR2) as an optogenetic tag to identify PV+ and PV- neurons in vivo in transgenic mice. In contrast to PV+ neurons in mouse visual cortex, which are broadly tuned for orientation, we found that auditory cortical PV+ neurons were well tuned for frequency, although very tightly tuned PV+ cells were uncommon. This suggests that PV+ neurons play a minor role in shaping frequency tuning, and is consistent with the idea that PV+ neurons nonselectively pool input from the local network. PV+ interneurons had shallower response gain and were less intensity-tuned than PV- neurons, suggesting that PV+ neurons provide dynamic gain control and shape intensity tuning in auditory cortex. PV+ neurons also had markedly faster response latencies than PV- neurons, consistent with a computational role in enhancing the temporal precision of cortical responses

Question 43

Acoustic fovea in CF bats

Answer 43

see notes

lots of interneurons

Question 44

Acoustic fovea in CF bats research

Answer 44

Bruns and Schmieszek (1980)

Question 45

Bruns and Schmieszek (1980)

Answer 45

• The innervation of the cochlea of the greater horseshoe bat was investigated by different methods. The regional densities of the spiral ganglion neurons and of the inner and outer receptors were determined from surface specimens and histological sections. The pattern of the unmyelinated fibers was reconstructed in EM serial sections and the efferent pattern separately by localization of cholinesterase activity.
• The study reveals three regions each adapted to different auditory functions:
(1) The region 1.3–5.4 mm from the basal end where the constant frequency segment of the orientation signal (around 83 kHz) is analysed. The neuronal structures of this region are similar to other mammals studied. Since, however, this region has widely expanded frequency mapping, the innervation density per octave is very high. In the region of this ‘acoustic fovea’ 25% of the receptors and 21% of the spiral ganglion neurons of the cochlea represent 10% of a single octave.
(2) The region from 5.4 to 8 mm with frequencies from 40–80 kHz encompasses the frequency modulated segment of the orientation signal. This region is characterized by a high density of spiral ganglion neurons together with a short spiral course of the afferent fibers to the outer receptors.
(3) The region from 8 mm to the apex (16 mm) represents frequencies lower than 40 kHz. Here neuronal elements, except for the efferents, are comparable to those of other mammalian cochleae. An important and surprising finding was that there is no efferent fiber to the outer hair cells in any part of the cochlea.

Question 46

Parallel pathways process different features of biosonar information in CF/FM bats (Suga, 1990)

Answer 46

• Early on info processing segregated and coded in parallel pathways
• Target velocity computed from comparison of freq shifts in CF component between pulse and echo (due to Doppler effect) - comparison involves diff freq bands (fundamental and up to 3 harmonics)
• FM component allows to compute distance from time delay between pulse and echo - also done across diff freq bands
• 2 pathways - go through same stages
- Auditory interneurons that sit in same place in basilar membrane pick up same sound info but project to diff areas

see notes

Question 47

Parallel pathways process different features of biosonar information in CF/FM bats (Suga, 1990) research

Answer 47

Chiu et al. (2009)

Question 48

Chiu et al. (2009)

Answer 48

Although it has been recognized that echolocating bats may experience jamming from the signals of conspecifics, research on this problem has focused exclusively on time-frequency adjustments in the emitted signals to minimize interference. Here, we report a surprising new strategy used by bats to avoid interference, namely silence. In a quantitative study of flight and vocal behavior of the big brown bat (Eptesicus fuscus), we discovered that the bat spends considerable time in silence when flying with conspecifics. Silent behavior, defined here as at least one bat in a pair ceasing vocalization for more than 0.2 s (200 ms), occurred as much as 76% of the time (mean of 40% across 7 pairs) when their separation was shorter than 1 m, but only 0.08% when a single bat flew alone. Spatial separation, heading direction, and similarity in call design of paired bats were related to the prevalence of this silent behavior. Our data suggest that the bat uses silence as a strategy to avoid interference from sonar vocalizations of its neighbor, while listening to conspecific-generated acoustic signals to guide orientation. Based on previous neurophysiological studies of the bat’s auditory midbrain, we hypothesize that environmental sounds (including vocalizations produced by other bats) and active echolocation evoke neural activity in different populations of neurons. Our findings offer compelling evidence that the echolocating bat switches between active and passive sensing to cope with a complex acoustic environment, and these results hold broad implications for research on navigation and communication throughout the animal kingdom.

Question 49

Organisation of the auditory cortex in the moustached bat (Pteronotus parnellii) (Suga, 1990)

Answer 49

see notes

Question 50

Organisation of the auditory cortex in the moustached bat (Pteronotus parnellii) (Suga, 1990) research

Answer 50

Bottier et al. (2019)

Question 51

Bottier et al. (2019)

Answer 51

The caudomedial nidopallium (NCM) is a higher level region of auditory cortex in songbirds that has been implicated in encoding learned vocalizations and mediating perception of complex sounds. We made cell-attached recordings in awake adult male zebra finches (Taeniopygia guttata) to characterize responses of single NCM neurons to playback of tones and songs. Neurons fell into two broad classes: narrow fast-spiking cells and broad sparsely firing cells. Virtually all narrow-spiking cells responded to playback of pure tones, compared with approximately half of broad-spiking cells. In addition, narrow-spiking cells tended to have lower thresholds and faster, less variable spike onset latencies than did broad-spiking cells, as well as higher firing rates. Tonal responses of narrow-spiking cells also showed broader ranges for both frequency and amplitude compared with broad-spiking neurons and were more apt to have V-shaped tuning curves compared with broad-spiking neurons, which tended to have complex (discontinuous), columnar, or O-shaped frequency response areas. In response to playback of conspecific songs, narrow-spiking neurons showed high firing rates and low levels of selectivity whereas broad-spiking neurons responded sparsely and selectively. Broad-spiking neurons in which tones failed to evoke a response showed greater song selectivity compared with those with a clear tuning curve. These results are consistent with the idea that narrow-spiking neurons represent putative fast-spiking interneurons, which may provide a source of intrinsic inhibition that contributes to the more selective tuning in broad-spiking cells.

Question 52

Sensory maps exist in both vertebrate and invertebrate brains

Answer 52

3 somatosensory maps in cortex of star-nosed mole with subdivided areas for diff tips of star-shaped nose (touch organ; Catania and Kaas, 1996)

see notes

Nose with 22 fleshy rays and large no’s Eimer’s organs, Ray nr 11 on each side of nose short and more sensitive and has largest projection area in somatosensory map

Question 53

Sensory maps exist in both vertebrate and invertebrate brains research

Answer 53

Catania (1999)

Catania and Remple (2005)

Catania and Kaas (1995)

Question 54

Catania (1999)

Answer 54

The star-nosed mole (Condylura cristata) has a snout surrounded by 22 ¯eshy and mobile appendages. This unusual structure is not an olfactory organ, as might be assumed from its location, nor is it used to manipulate objects as might be guessed from its appearance. Rather, the star is devoted to the sense of touch, and for this purpose the appendages are covered with thousands of small mechanoreceptive Eimer’s organs. Recent behavioral studies ®nd that the star acts much like a tactile eye, having a small behavioral focus, or ``fovea’’ at the center ± used for detailed explorations of objects of interest. The peripheral and central nervous systems of the mole re¯ect these behavioral specializations, such that the small behavioral focus on the nose is more densely innervated in the periphery, and has a greatly enlarged representation in the somatosensory cortex. This somatosensory representation of the tactile fovea is not correlated with anatomical parameters (innervation density) as found in other species, but rather is highly correlated with patterns of behavior. The many surprising parallels between the somatosensory system of the mole, and the visual systems of other mammals, suggest a convergent and perhaps common organization for highly developed sensory systems.

Question 55

Catania and Remple (2005)

Answer 55

oraging theory provides models for predicting predator diet choices assuming natural selection has favoured predators that maximize their rate of energy intake during foraging1,2,3,4,5,6. Prey profitability (energy gained divided by prey handling time) is an essential variable for estimating the optimal diet. Time constraints of capturing and consuming prey generally result in handling times ranging from minutes to seconds, yet profitability increases dramatically as handling time approaches zero, providing the potential for strong directional selection for increasing predator speed at high encounter rates (tiny increments in speed increase profitability markedly, allowing expanded diets of smaller prey). We provide evidence that the unusual anatomical and behavioural specializations characterizing star-nosed moles resulted from progressively stronger selection for speed, allowing the progressive addition of small prey to their diet. Here we report handling times as short as 120 ms (mean 227 ms) for moles identifying and eating prey. ‘Double takes’ during prey identification suggest that star-nosed moles have reached the speed limit for processing tactile information. The exceptional speed of star-nosed moles, coupled with unusual specializations for finding and eating tiny prey, provide new support for optimal foraging theory.

Question 56

Catania and Kaas (1995)

Answer 56

The nose of the star-nosed mole consists of a star-like array of 22 fleshy appendages that radiate from the nostrils and are moved about to explore the environment. The surface of each appendage, or ray, is densely packed with bulbous receptor organs (Eimer’s organs) that are highly responsive to tactile stimulation. Here, we report that these rays have corresponding morphological specializations in somatosensory cortex. Using a stain for the metabolic enzyme, cytochrome oxidase (CO), to reveal subdivisions of cortex, we disclosed a complex pattern of CO-dense stripes or bands separated by sharp lines or septa of low CO staining. Multiunit microelectrode recordings of neural activity evoked by light tactile stimuli in somatosensory cortex of anesthetized moles allowed us to mark some of the bands and other CO-dark regions with small electrolytic lesions and later relate recording results to the CO pattern. The results suggest that the primary somatosensory cortex, S1, has an unusual ventrolateral location and orientation with representations of mouth, nose rays, facial vibrissae, forepaw, and trunk in a rostrocaudal sequence. Within this presumptive S1, the 11 rays of the contralateral nose are represented as a rostral-to-caudal cortical pinwheel of 11 stripes. Cortex ventral to the primary set of stripes contains a second rostrocaudal representation of the rays as a mirror image of the first. This second set of stripes may be part of the second somatosensory area, S2. A third pattern of CO stripes appears to merge partially with caudal stripes of the first two patterns, so that a full pattern of 11 stripes is not obvious. This representation may correspond to the ventral somatosensory area, VS, of other mammals. An extensive area of cortex separated from the nose by a large septum was responsive to stimulation of the forelimb. Auditory cortex is unusually caudal in this mole, and the presumptive primary visual area is relatively small. These specializations of somatosensory cortex in star-nosed moles may be more patent examples of the consequences of more general factors in brain development. The observations are consistent with the general rule that the terminations of sensory projections with discorrelated activity segregate

Question 57

Cortical encoding in form of somatotopic maps

Answer 57

Adjacent regions on body generally encoded in adjacent regions in cortex (with some curious exceptions)

see notes

Question 58

Cortical encoding in form of somatotopic maps research

Answer 58

Bartoli et al. (2016)

Question 59

Bartoli et al. (2016)

Answer 59

During speech listening motor regions are somatotopically activated, resembling the activity that subtends actual speech production, suggesting that motor commands can be retrieved from sensory inputs. Crucially, the efficient motor control of the articulators relies on the accurate anticipation of the somatosensory reafference. Nevertheless, evidence about somatosensory activities elicited by auditory speech processing is sparse. The present work looked for specific interactions between auditory speech presentation and somatosensory cortical information processing. We used an auditory speech identification task with sounds having different place of articulation (bilabials and dentals). We tested whether coupling the auditory task with a peripheral electrical stimulation of the lips would affect the pattern of sensorimotor electroencephalographic rhythms. Peripheral electrical stimulation elicits a series of spectral perturbations of which the beta rebound reflects the return-to-baseline stage of somatosensory processing. We show a left-lateralized and selective reduction in the beta rebound following lip somatosensory stimulation when listening to speech sounds produced with the lips (i.e. bilabials). Thus, the somatosensory processing could not return to baseline due to the recruitment of the same neural resources by speech stimuli. Our results are a clear demonstration that heard speech sounds are somatotopically mapped onto somatosensory cortices, according to place of articulation

Question 60

Summary

Answer 60

• Sensory info filtered, modified and amplified at diff stages of serial sensory processing
• Parallel processing implemented in sensory pathways
• Preservation of spatial locations of sensory sources in outer world through topological sensory maps in brain
Highly ordered organisation of feature-extracting interneurons as sensory maps (found in mammals, birds, insects)

Question 61

Simmons and Young (2010)

Answer 61

• Animal behaviour
○ Aim of ethology, the scientific study of animal behav, is to analyse behav into basic elements such as: sign stim; innate releasing mechanisms; and fixed action patterns. These elements can be perf by neuronal processes such as sensory filtering and pattern generation
• Neurons and nervous systems
○ Electrical signals carried and processed in 2 types of process in neuron: dendrites, which receive signals; and axons, which carry output signals
○ Aim of neuroethology is to trace neuronal routes by which info collected, transformed and transmitted to control animal behav
○ In many invertebrates, neurons aggregated into ganglia. Axons connect ganglia w/ each other, with sense organs and with muscles
○ In vertebrates, surface of brain in many regions consists of 5-7 layers of cells - large in cerebral cortex of mammals, which is divided into various sensory, motor and association regions
○ One approach to identify neurons involved in particular behav is to study animal with clear anatomical and behav specialisation - another is to use genetic mutants to correlate behav with neurons or parts of nervous system
• Star-nosed mole
○ Eats many pieces of food per second and identified food by touch with nose that inc. 22 motile rays
○ Ray 11 is fovea and always used to examine food in detail before bite - smallest ray, but has greatest no. of sensory axons
○ Large proportion of somatosensory cortex dedicated to nose, esp. ray 11 - 3 distinct maps of nose
• Drosophila courtship
○ Sequence of events, inc. male singing by vibrating one wing
○ Males with fruitless gene mutation court indiscrim but never finish
○ Fruitless gene can be tagged to allow neurons that express it to be seen - expressed in 2% of neurons in pupa, spliced to code for 4 diff reg proteins
○ Frum protein associated with male courtship - interfering with it alters normal courtship: experimentally exciting frum neurons switches on courtship
○ Female thoracic ganglia contain neuronal networks that can create courtship behav, but normal activation probably requires male-specific frum brain neurons
• Owls
○ Locate sounds by comparing signals between the 2 ears: intensity for elevation and timing for azimuth
○ Space-specific neurons in the external auditory nucleus of the midbrain respond to sounds from particular locations - arranged in orderly way, forming map of space
○ Sensory neurons from ear encode info about sound freq, time and intensity - brain uses info to compute receptive field for each space-specific neuron
○ Info about relative intensity and timing of sounds at 2 ears processed in separate pathway on either side of brain
○ Sound intensity compared in angular and then posterior leminiscal nuclei
○ Sound time is compared in laminar nucleus, in which neurons act as coincidence detectors receiving inputs from axons of left and right magnocellular nuclei, which act as delay lines
○ Auditory map of space is calibrated by reference to visual map in optic tectum
• Bats
○ Most insectivorous bats use echolocation, monitoring echoes of own cries to navigate and find insect prey
○ In FM cry, sound freq alters to give broadband signal, suitable for target ranging and description - in CF cry, sound freq constant, useful for detecting relative velocity and for hunting in woodland
○ As bat detects and then intercepts prey, rate of echolocation pulses increases dramatically
○ Bat’s auditory system specialised to detect faint echoes that follow loud cries: most sensitive to freqs near that of cry; highly directional; and shows reduced sensitivity to loud cry compared with flowing soft echo, both in ear and brain - bat auditory neurons quick to recover responsiveness following each sound
○ Some neurons in inferior colliculus act as accurate time markers, signalling exact time of cry and then of echo
○ In cerebral cortex, time-marking neurons provide inputs to neurons that are sensitive to particular cy-echo delays - in some bats, neurons arranged in organised map in which neuron’s location related to distance between bat and sound-reflecting target
○ Bats that use CF cried have acoustic fovea in ears, and large no. of brain neurons dedicated to analyse echoes of CF cry
In auditory cortex of CF bat are neurons that detect flying insects by responding to small modulations in freq of echoes from CF cries

Question 62

Hill et al. (2016)

Answer 62

• Neural circuits of the vertebrate retina integrate the responses of retinal photoreceptors to excite and inhib retinal ganglion cells - ganglion cell receptive fields may be excited or inhib by light at centre of field, whereas light in surround antagonises effect of light in centre
• Straight-through pathways (photoreceptor –> bipolar cell –> ganglion cell) produce centre (on-/off-centre) of ganglion cell’s receptive field - lateral pathways through horizontal cells and amacrine cells produce antagonistic surround
• Axons of ganglion cells make up optic nerve, relaying visual info to several brain areas - geniculostriate pathway projects to lateral geniculate nucleus (LGN) and from there to primary visual cortex
• Simple and complex cells in V1 respond to light or dark bars or edges oriented at particular angles
• Parallel pathways in the visual cortex convey info about diff aspects of visual stim such as details of visual form, movement, colour and binocular determination of object distance
Colour vision depends on the ratio of activation of 3 classes of cone photoreceptors sensitive to diff wavelengths of light - retinal circuitry integrates colour contrasts based on red-green and blue-yellow opponencies

Question 63

Zupanc (2019)

Answer 63

• Echolocation as an active orientation mechanism involves the emission of high-intensity sound, followed by perception and analysis of the returning echo, to negotiate the animal’s surrounding
• Although some animals use sound in the freq range of human hearing, most bats produce ultrasound for echolocation
• Due to short wavelength, ultrasound better suited than lower-freq sound for detection of small objects, although disadv is stronger atmospheric attenuation
• Based on freq spectrum, sound produced by bats can be divided into 2 major categorised - freq-modulated (FM) signals and constant-freq (CF) signals
• FM signals are used to estimate distance of bat from object - achieved by measuring time delay between emitted signal and returning echo
• In inferior colliculus of bats, neurons have been identified that serve as time markers by encoding time interval between emitted pulse and returning echo - in auditory cortex, neurons exist that respond best to particular pulse-echo time delay
• CF signal of bat ultrasound particularly well suited for so-called Doppler shift analysis, which is perf during flight and when localising flying insects - during flight movements of bat, analysis forms basis for Doppler shift compensation to keep freq of returning echo in range of max sensitivity of auditory system - during prey hunting, Doppler shift analysis used to detect fluttering of wings of flying insects
• Sensory structures in ear and neural structures in brain of bat both specialised to max sensitivity to freqs in range of CF component of returning echo - inc. over-representation of such freqs in cochlea and auditory cortex
To counteract bat echolocation, several groups of insects developed no. of adaptations - inc. development of ears sensitive in ultrasound range and, in some tiger moths, production of high-freq clicks