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A road to a better understanding of rhythms in speech 1
using a comparative approach 2
Lara S. Burchardt and Susanne Fuchs 3
4
Leibniz-Zentrum Allgemeine Sprachwissenschaft, Berlin 5
Emails: burchardt@leibniz-zas.de, fuchs@leibniz-zas.de 6
1. Introduction 7
The production and perception of acoustic communication signals in different species, 8
including humans have intrigued scientists all over the world and from diverse research fields 9
such as linguistics, biology, and psychology. Whilst having completely different foci, some 10
questions are important to answer in all fields. One of these topics is the temporal structure of 11
acoustic communication, and how it is used to convey information. These temporal structures 12
or rhythms can act on different levels, within a phrase or between phrases, they can also help 13
in determining phrase boundaries. Perspectives on these connected questions are manifold 14
and cross-talk between the three disciplines is often limited. In this chapter, we are advocating 15
for more cross-talk using two prosodic markers connected to rhythms as examples to 16
showcase the advantages of combining linguists’ and biologists’ knowledge about the 17
respective phenomena. 18
Rhythms can be defined in various ways (for an overview see (Turk and Shattuck-Hufnagel, 19
2013)). One example is given by Patel, where rhythm is the “systematic patterning of sounds 20
in terms of timing, accent and grouping” (Patel, 2008:96). Building on this, we consider rhythm 21
as a non-random, ordered, predictable, and repeated alternation of different elements in a 22
sequence. The motivation to use this definition is to be relatively independent of theoretical 23
concepts in one or the other research domain. We think that a broader perspective including 24
humans and non-human animals alike is important because it allows us to better understand 25
the underlying principles and may root rhythms of human language in evolution. 26
According to this definition, the building blocks of rhythm are elements in a sequence. 27
Determining these elements in a known human language, i.e. linguistic units like syllables, 28
words, and prosodic phrases, even though a challenge on its own (Fletcher, 2010:524), might 29
be more straightforward than determining the building blocks of rhythm in non-human 30
vocalizations. Amongst other approaches, rhythmic markers might be a way to tackle this 31
issue in non-human animals. In the current chapter, we will focus on two prosodic markers of 32
rhythm, fundamental frequency (f0) declination and final lengthening. Both are frequently 33
found in human communication and have also been reported for specific species in non-34
human communication. 35
Final lengthening refers to a phenomenon where a final or penultimate syllable of an utterance 36
or prosodic phrase is produced for a longer duration than when the same is uttered within an 37
utterance or prosodic phrase (Fletcher, 2010:540)(Figure 1A). Thus, the lengthening of an 38
element can signal the end of a unit which varies nonlinearly with the strength of a boundary 39
(Kentner et al., 2023). It can co-occur with pauses and fundamental frequency (f0) lowering 40
(Petrone et al., 2017). From a perceptual side, it is a phonetic signature that might help to 41
mark the end of a unit (Schel et al., 2009). 42
F0 declination has been widely discussed in phonological (Ladd, 2008, 1988) and phonetic 43
terms (Strik and Boves, 1995). We broadly define f0 declination as “the gradual decrease of 44
f0 over the course of an utterance” ((Fuchs et al., 2015:35) in order to be as inclusive as 45
possible concerning non-human animal communication (Figure 1 A-D). F0 declination is 46
common in statements as opposed to questions. From a phonetic perspective, it is calculated 47
as a linear regression through f0 values in a given temporal window (e.g., 1-4s in (Yuan and 48
Liberman, 2014:69) that often corresponds to interpausal units or annotated prosodic phrases. 49
The linear regression slope is by definition (f0 decline) negative and varies with utterance 50
length. Various studies (among others (Cooper and Sorensen, 1981; Swerts et al., 1996; 51
Fuchs et al., 2015)); have shown that the longer the utterance, the shallower the slope, and 52
the shorter the utterance, the steeper the slope. 53
Together, f0 declination and final lengthening can be used to create a sense of units in a 54
rhythmic sequence, helping to signal boundaries between units and convey information about 55
the length of a unit in the sequence itself that may be repeated over time to produce structured 56
time events. 57
There is a lot of potential in studying the described phenomena in a more comparative way 58
between species. Linguistics could help to answer long-standing questions in animal 59
communication. The other way around we can also use knowledge about animal 60
communication and the opportunities we might have when studying a wide variety of animal 61
species with different cognitive abilities or physical constraints to solve debates in linguistics. 62
We can observe variations in pitch and timing in non-human animal communication similar to 63
prosodic features in human speech ((Briefer, 2012; Hotchkin and Parks, 2013; Filippi, 2016). 64
Oftentimes the reason for these changes is caused by physiological changes (for example the 65
emotional state can influence muscle tension (Briefer, 2012)). Different kinds of information 66
can be conveyed by those changes, may it be individual identity in birds (and many other 67
species) (i.e. (Linhart et al., 2022) or context in primates (Crockford et al., 2018). There are 68
many other examples of such changes that are species-specific and can have very different 69
functions. 70
With the variety of functions, production mechanisms, and environmental constraints, the 71
specific mechanisms and functions of prosodic communication in animals are still not fully 72
understood. An interdisciplinary exchange will enrich linguistics and biology in a 73
complementary fashion. Linguists may consider language and communication as less 74
uniquely human when taking results on other species into account. There have been many 75
recently published papers finding more and more similarities in human and non-human animal 76
communication (Favaro et al., 2020; Huang et al., 2020; Valente et al., 2021). In biology, more 77
research is needed to explore the extent and complexity of prosodic features in non-human 78
communication. Animal communication may resemble human prosody, but there are 79
important differences as far as we know by now: many animal vocalizations are innate, not 80
learned through acquisition and they may also be less flexible and expressive than human 81
speech. At the same time, the spectrum between innate, adjusted and learned vocalizations 82
gives interesting options to study the prerequisites for prosodic phenomena. 83
The aim of the paper is to once again point out the advantages of a comparative approach 84
between human and non-human animals as a road to a better understanding of the origin of 85
rhythms in language evolution. To illustrate another field that would highly benefit from the 86
comparative approach, we focus on acoustic signals of human and non-human animals using 87
two concrete phenomena: final lengthening and f0 declination. These two phonetic markers 88
have been chosen, because they are involved in determining the units that can form a rhythmic 89
sequence. Final lengthening is a phonetic signature of the end of a phrase and signals a 90
boundary, while the slope of f0 declination can signal the length of an entire phrase. Both are 91
relatively frequent in human communication, they have been considered as being universal 92
even if language-specific modifications may be found. There have been several debates about 93
the origin of prosodic phenomena in general, e.g. whether they rely on linguistic 94
representations or general physical properties. Similar to other scientists ((Pika et al., 2018; 95
Matzinger and Fitch, 2021; Pouw and Fuchs, 2022; Hersh et al., 2023; Hoeschele et al., 2023), 96
we strongly believe that more interdisciplinary cross-fertilization is needed to better understand 97
what properties are shared among human and non-human animals in their rhythm 98
communication. The road towards such interdisciplinary exchange is clearly not without 99
obstacles, but the joint venture, in our case between a biologist and a linguist, can enhance 100
the collection of species producing selected phenomena, can initiate new recording and open 101
source databases (Hersh et al., 2023), may reduce the human-centric view on the evolution 102
of complex acoustic communication and the insider bias when doing comparative work 103
(Hoeschele et al., 2023). 104
2. F0 declination in acoustic signals: Humans vs. 105
animals 106
2.1 Characteristics of f0 declination in human speech 107
F0 declination, the gradual decrease of f0 over the course of an utterance, is spanning several 108
words in human language and is a macro rhythm (rhythms in longer time units) in human 109
speech. Strik and Boves among others proposed to start at 1 second, otherwise, the 110
calculation of the declination slope might be heavily affected by local f0 variations (Strik and 111
Boves, 1995). F0 declination is not a rhythm in itself, but similar to final lengthening, it is a 112
prosodic signature of a unit that can be repeated over time and form a rhythm. 113
While more cross-linguistic work on f0 declination using the same methodology is missing, it 114
has been reported for various languages, such as Danish, Dutch, English, French, German, 115
Greek, Japanese, and Spanish (see (Fuchs et al., 2015) for an overview) so that there is 116
reason to believe it is a relatively robust phenomenon (Hauser and Fowler, 1992), at least in 117
Indo-European languages. However, it is not mandatory and can be modulated, e.g. f0 can 118
rise at the end of a phrase (called continuation rise) to signal the speaker’s motivation to 119
continue talking or f0 can raise signaling question intonation. There are also language 120
specificities as well as other factors that may shape the declination slope. For example, 121
Lieberman et al. found more negative slopes in reading than in spontaneous speech 122
(Lieberman et al., 1985). 123
Since at least the end of the 60s of the last century, a potential physiological origin of this 124
phenomenon has been postulated. Lieberman measured subglottal pressure and f0 125
declination in three human participants reading declarative sentences and found a positive 126
correlation between the two variables (Lieberman, 1967). He, therefore, suggested a potential 127
origin in respiratory behavior, because respiration is a driving force of phonation. Others have 128
argued that muscular tension in the vocal folds may rather be at the origin of f0 declination 129
(e.g., (Ohala, 1978)) and that tensioning of the vocal folds is independent of respiration 130
because the primary function of the larynx is to save lives and protect the lungs from foreign 131
bodies, hence it must be independent and quick (Ohala, 1990). The challenge for or against 132
one or the other argument or a mix of the two is that measuring subglottal pressure and 133
laryngeal tension is very invasive so empirical data is limited so far. 134
Apart from the physiological origin of f0 declination, cognitive processes seem plausible as 135
well. Since the slope of the f0 declination is correlated with the length of the upcoming 136
utterance, some anticipatory planning may be involved (Yuan and Liberman, 2014). 137
2.2 F0 declination in animal communication with a focus on bird 138
species and primates 139
We scarcely find descriptions hinting at f0 declination in monkeys. For example, in a 140
description of the vocalizations of the Black and White Colobus monkey, we find the following 141
“The final phrase is often deeper pitched than the others [...]” (Marler, 1972:181). This refers 142
to the alarm call “roar”. This leads Schel et al. to hypothesize that this phenomenon is 143
perceptually conspicuous and marks the end of the sequence (Schel et al., 2009). In Colobus 144
monkeys a roaring sequence consists of one or more roaring phrases, where a phrase is a 145
basic unit, made up of ~ 15 “pulses”, each with an average duration of 0.7 seconds, which 146
makes a whole phrase to be around 10 seconds (Marler, 1972). 147
Confusingly, in the same species in a different study, the exact opposite was reported at least 148
for the Black colobus monkey (Colobus satanas): “Initial phrases all decreased in pitch during 149
delivery, the terminal phrases all increased” in pitch (Oates and Trocco, 1983:100). This could 150
have different explanations: in this species the phenomenon could be dependent on unknown 151
parameters that have differed between the studies, or that coincidentally the decline in final 152
phrases was observed in a different colobus monkey species. 153
The most detailed study on f0 declination in non-human animals was conducted in vervet 154
monkeys (Cercopithecus aethiops) and rhesus macaques (Macaca mulatta), two very 155
common model species (Hauser and Fowler, 1992). For both species, vocal production also 156
shows f0 declination, which is suggested to serve a similar communicative function as in 157
human language (Hauser and Fowler, 1992). Under investigation were vocalizations uttered 158
during aggressive interaction for vervet monkeys in the wild and for an affiliative vocalization 159
of wild rhesus macaques. For both species – rhesus macaques and vervet monkeys – an 160
almost linear decline in f0 could be shown over call bouts of two calls and for call bouts of 161
three calls. Furthermore, for two call bouts of vervet monkeys, a correlation between the 162
duration of the bout and the magnitude of the f0 decline could be shown, as expected from 163
human language literature (e.g., (Yuan and Liberman, 2014). No correlation could be found 164
between the duration of the bout and the magnitude of the f0 decline in rhesus macaques. 165
Another interesting thing to note is, that the structured decline of f0 in vervet monkeys could 166
only be seen in adults, not in juveniles, which could be explained by the fact, that inter-call 167
intervals in juveniles are generally longer, indicating juveniles might take a breath between 168
calls, in contrast to adults. This makes it even more interesting to study the phenomenon 169
further in this species, to study the exact mechanism in more depth. 170
Another instance of f0 declination being reported in monkeys stems from Baboons, where f0 171
is also reported to decline within bouts of calling. This is here described to be independent of 172
rank and age, in a species, where f0 generally is highly correlated to these two parameters 173
(Fischer et al., 2004), making it a more general phenomenon, worthy to be investigated further. 174
In birds, f0 decline was found in the vocalizations of the budgerigar (Melopsittacus undulatus). 175
Here “mean F0 measurements were lower for segments in syllable-final position when 176
compared to medial segments” (Mann et al., 2021:6, fig. 4 caption). This makes the budgerigar 177
the only non-human species so far, where both final lengthening and f0 declination were 178
observed. This is very likely not representative of the abundance of the phenomena, but of a 179
sampling bias, where those phenomena have not been studied in many species. 180
181
Figure 1: Explanation of f0 declination and final lengthening on two examples. A) Oscillogram 182
of human language. The spoken text is: Always there had been war between the giants and 183
the gods. The duration of the ‘s’ of giants and gods is annotated, the final ‘s’ is much longer, 184
demonstrating final lengthening. B) The Spectrogram for the same human sentence is shown 185
with a solid line indicating the fundamental frequency . A clear f0 decline is visible. C) An 186
oscillogram of budgerigar twittering. D) The corresponding spectrogram of the twittering, the 187
fundamental frequency is shown as an extra solid line and an f0 decline is visible. 188
189
2.3 Comparing the use of f0 declination in human and animal 190
communication 191
The amount and detail of papers published on f0 declination is clearly more substantial in the 192
linguistic domain which shouldn’t imply that this is an exclusively human phenomenon. Papers 193
published on f0 declination in animal communication include primates and birds. They often 194
lack empirical work on the underlying mechanisms (note, however, this is different for final 195
lengthening, see below). While papers on animal communication are a stepping stone toward 196
a broader perspective, they are mostly descriptive. 197
Whether or not f0 declination is primarily the result of a decrease in subglottal pressure, a 198
reduction in laryngeal tension over the course of an utterance, a marker of anticipatory 199
planning of an utterance, or a mixture of these is still unclear. The invasiveness of recording 200
data in favor of the first two explanations also limits the empirical evidence in humans. 201
There may also be some challenges when comparing human and non-human animals. The 202
minimum length of an utterance that can be considered for calculating the f0 declination slope 203
may have to be adjusted for various animal species, similar to the terminology used. For an 204
untrained linguist, the term “syllable” that is used in animal communication may have a very 205
different connotation than for a biologist, for whom it may be clear that this is an utterance 206
between pauses. Joint venture investigations on human and non-human animals might also 207
reveal deeper insights because they differ in their respiratory, vocal, and cognitive repertoire. 208
3. Final lengthening: Humans vs. animals 209
3.1 Final lengthening in human speech 210
Over the last 50 years phonetic studies that investigated temporal properties in a variety of 211
languages found that final lengthening is a reliable phonetic marker determining the end of a 212
speech chunk and is very pronounced next to a following pause (e.g.(Klatt, 1976; Edwards et 213
al., 1991), for a review on languages, see (Paschen et al., 2022)). There have also been 214
considerations that the lengthening of the final segment is part of the pause (e.g., (Krivokapić 215
et al., 2022)) or can, in extreme cases, be produced instead of a pause in fast speech rate. 216
Indeed, pause is an important determiner of rhythm. 217
Final lengthening has been claimed to be universal in human language (Fletcher, 2010) with 218
additional language specificities (e.g., (Nakai et al., 2009). Since the term “universal” can be 219
ambiguous in meaning (Bickel, 2011), we refer to statistically universal here, which relies on 220
robust statistical evidence across languages but also allows for exceptions. There is only 221
recent empirical evidence using the same methodology for 25 mostly understudied languages 222
that the lengthening of vowels is a statistically robust cross-linguistic phenomenon (Paschen 223
et al., 2022). Language-specific variations, driven by phonological vowel length, were found 224
as well. Sound-specific variations have also been reported, for example in Berkovits for 225
Hebrew, who reported stronger lengthening effects for final fricatives than stops (Berkovits, 226
1993) . Paschen provided evidence for Lower Sorbian that lengthening occurs in vowels, 227
sonorants, and fricatives, but not in stops (Paschen, in press). While these latter segmental 228
influences may be specific to human language, they may also give some hints that continuous 229
airstream mechanisms make final lengthening more likely. 230
The degree (how long) of lengthening has been extensively discussed in the linguistic 231
literature. For example, the pi-gesture model (Byrd and Saltzman, 2003) proposes that the 232
longer the segments, the closer they are to the boundary. Moreover, the degree of lengthening 233
varies with the boundary type. Without going too deeply into theoretical proposals such as the 234
Prosodic Hierarchy (Jun, 1998), it is fair to say that final segments at major boundaries, for 235
example at the end of a sentence, may be longer than segments at phrase boundaries within 236
a sentence. While language-specific variants exist, this does not exclude the assumption that 237
the underlying principles are physical in nature but have been shaped in various ways by the 238
properties of the sounds and the users of individual languages. 239
The puzzling question is - what are the underlying mechanisms that may cause final 240
lengthening? Do we also find it in other behavior or other species? 241
3.2 Final lengthening in animal communication with a focus on 242
bird species and primates 243
Final lengthening is getting increased attention in animal acoustic studies. Final lengthening 244
was found in birds and primates. We can find final lengthening as well as we found f0 245
declination in the budgerigar, a vocal learning parrot species. It was reported that segments 246
at the end of vocalizations were more likely to be longer. In 14 adult budgerigars, it was found 247
that segments in syllable-final positions are on average longer than medial segments (Mann 248
et al., 2021). In another study on 80 different song snippets from 80 different songbirds, the 249
same could be shown: song-final notes were on average significantly longer than non-final 250
notes (Tierney et al., 2011). This is especially impressive, as the analysis wasn’t conducted 251
for individual species, but across all 80 species, indicating this to be a generally observable 252
phenomenon in songbirds. A more detailed analysis of these 80 songs, to find possible 253
differences between families would nevertheless be interesting, to get a better understanding 254
of how widespread final lengthening in songbirds really is. Both papers argue that final 255
lengthening can be observed in these songbirds as well as in humans, because of similar 256
motor constraints. Both humans and songbirds show a high control of their vocal articulators 257
with the possibility to rapidly adjust them during vocal production. Nevertheless, abrupt 258
termination of these movements might be difficult, as opposed to a gradual relaxation and 259
therefore slowing of articulators, resulting in final lengthening. This argument is further 260
strengthened by the fact that especially budgerigar segments are produced within a single 261
breath (Mann et al., 2021; Tierney et al., 2011). It would be interesting to investigate respiratory 262
kinematics and final lengthening in human speech production. 263
Final lengthening was also investigated in at least three different primate species: two crested 264
gibbon species and the indri. For all three species, an elongation of unit duration near the end 265
of a phrase was found (Huang et al., 2020; Valente et al., 2021). In the gibbons, this effect 266
was found on two different structural levels, in vocal sequences and in vocal bouts (where a 267
vocal sequence is a short unit and a bout is made up of several vocal sequences). The 268
suggested reasons for this form of final lengthening differ from those discussed in humans. 269
The authors suggest a connection to the performance hypothesis. Gibbons might be 270
modulating the frequency of their calls rapidly at the end of sequences, to advertise their 271
individual quality to females as potential mating partners. An increase in frequency 272
modulations, even though fast, would potentially lead to an increase in the duration of notes 273
(Huang et al., 2020). If this is true, the observed phenomenon of final lengthening in crested 274
gibbons would only be a byproduct of other processes. 275
3.3. Comparing the use of final lengthening in human and animal 276
communication 277
There have been different explanations for final lengthening in the literature which may not be 278
exclusive. It has been understood as a general motor property rather than being innate. 279
Tierney et al. attribute it to energy efficiency of the underlying motor actions in humans and 280
singing birds (Tierney et al., 2011). As mentioned above, Huang et al. explain it as a byproduct 281
rather than a phenomenon on its own (Huang et al., 2020). Matzinger and Fitch mention the 282
possibility that the slowing down of articulators could be a result of a change from exhalation 283
to inhalation, i.e., respiratory dynamics and the occurrence of a breathing pause cause final 284
lengthening(Matzinger and Fitch, 2021). We think that it could be a plausible explanation for 285
those species that produce segments within one breath, but in humans, final lengthening can 286
also be found without a change from exhalation to inhalation. Nevertheless, the relation of one 287
breath to one segment (or one phrase in human communication) may have been at the origin 288
of human language evolution. In spontaneous interactive dialogues, more than 50% of all turns 289
consisted of only one breathing cycle (Rochet-Capellan and Fuchs, 2014). Linguistic studies 290
have mostly focused on language- and segment-specific properties in the implementation of 291
final lengthening. Because the number of published papers on these specificities is so much 292
more than in animal communication, one may implicitly assume that it is a phenomenon of 293
human language. 294
Even if language variations exist, it does not exclude the possibility of an underlying motor 295
principle. Human and non-human animals clearly have motor constraints, but these may not 296
be persistent under each, and every situation and all animals may also be able to compensate 297
for it if needed. Monocausalities are rather rare in biological systems. For example, the 298
available exhalation air in human speech may be physically constrained by the lung volume 299
(vital capacity) of a speaker. In human and non-human acquisition, a high positive correlation 300
between lung volume and utterance/vocalization length has been found (see review in (Fuchs 301
and Rochet-Capellan, 2021). Evidence for a similarly strong correlation between utterance 302
length and vital capacity in adults is missing, because humans with smaller lung capacities 303
may adjust their laryngeal resistance and lose less expiratory air to compensate for their 304
physical constraints. 305
All in all, evidence for final lengthening in non-human animals has changed the perspective 306
that the phenomenon is a purely linguistic phenomenon to the notion, that it might be grounded 307
in general motor constraints. There is clearly an advantage when human and non-human 308
animals are taken into account. 309
4. Future directions for research 310
4.1 A roadmap 311
312
In the venture of finding the biological underpinnings of prosodic phenomena like f0 declination 313
and final lengthening through a comparative approach combining knowledge and advantages 314
from studying human and non-human communication, there are several issues to overcome 315
and steps to take. We will lay out a possible roadmap to achieve this here, with concrete steps. 316
1) Establishing a common vocabulary and conceptual framework 317
To ensure effective communication between researchers from different disciplines, it 318
is essential to establish a common vocabulary and conceptual framework for 319
discussing prosodic features like f0 declination and final lengthening. This touches on 320
issues mentioned earlier, where terms like “syllable” might be understood differently 321
between linguists and biologists, but also within biology. Clear terminology, glossaries, 322
and clear, but adjustable definitions and criteria for measuring and analyzing features 323
are important steps. 324
2) Establishing the necessary data basis 325
We would need to develop a comprehensive database of vocalizations from a wide 326
range of species to study these and other phenomena comparatively. A database 327
should include both natural or spontaneous and elicited vocalizations. Most 328
importantly, meta-information about the social or ecological contexts is important to 329
know, as well as potential age and sex. 330
3) Identifying universal and species-specific patterns 331
Once established, researchers can begin to identify robust patterns in the use of 332
prosodic features like f0 declination and final lengthening across species, as well as 333
species-specific variations by means of the database. Eventually, this can help to shed 334
light on the evolutionary and ecological factors that shape the use of these features in 335
different species with different needs and skills. 336
4) Integrating insights from different disciplines 337
To fully understand the mechanisms and functions of prosodic features in speech and 338
animal communication, researchers need to integrate insights from different 339
disciplines, including linguistics, biology, psychology, and neuroscience. With a 340
comprehensive knowledge of theories, mechanisms, and constraints in all these fields 341
from interdisciplinary collaborations we can identify new research questions and can 342
generate novel insights into the biological and cognitive foundations of communication. 343
4.2 Prosodic rhythm markers and respiration 344
A future endeavor towards a better understanding of prosodic markers of rhythm could be to 345
investigate the interaction between respiration, phonation (voice quality) and anticipatory 346
planning in human and non-human animals. Respiration itself is a biological rhythm and the 347
duration of breathing cycles can constrain how long an animal can phonate. At the end of long 348
sequences when lung volume is reduced, laryngeal adjustments may be required to continue 349
phonation. While this has been modelled for humans (Zhang, 2016), it may also exist in non-350
human animals. The amount of air inhaled may further shape acoustic properties like intensity 351
and to some extent f0 (Watson et al., 2003). 352
Vocalizations in nonhuman primates such as screams or grunts may have specific prosodic 353
features such as f0 declination and final lengthening which can be shaped by respiratory 354
control. Birds have more complex respiratory and laryngeal systems than humans, including 355
not only lungs but several additional air sacs that are necessary during avian flight. Phonation 356
is produced with a syrinx which is much closer to the lungs than in humans, at the place where 357
the trachea forks into the lungs. These physiological differences and control mechanisms are 358
on the one hand a big challenge for comparative work, on the other hand, they may give us 359
insights into which physiological or cognitive systems is able to produce these patterns and 360
which features does it have. Recent technological developments in the area of thermography 361
allows us to record breathing and acoustics even in free ranging animals (Demartsev et al., 362
2022). 363
4.3. The potential for interdisciplinary collaborations between 364
linguistics, psychology, and biology 365
The potential for interdisciplinary collaborations was already discussed throughout this paper 366
from different angles but shall be summarized here again. Opportunities arise on different 367
levels and for different questions. There is a strong potential of gaining evolutionary insights 368
into any phenomenon when studied comparatively, as is the case for prosodic phenomena 369
such as f0 declination and final lengthening. By comparing the use of prosodic features in 370
human and non-human animal communication, we can get insights into their evolutionary 371
origins and development of speech rhythms. We can also light on the cognitive and biological 372
underpinnings of human language and communication. On a different level, the comparative 373
approach can provide valuable perspective on the diversity of prosodic features used across 374
different languages and language families and therefore might raise new questions in more 375
specific research areas. We will be able to identify universal patterns and language-specific 376
variations better. 377
378
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