Book review

Review The reality of the artificial: nature, technology and naturoids. In the midst of pervasive and embedded intelligent systems, in seeking frontiers around biological systems, neurological cognition, emotional intelligence and ecological complexity, 'The Reality of the Artificial' is an inspiring and reflective contribution to the study of the culture and technology of the artificial. The book takes the reader on a journey of the methodology of artificial reality that involves discovering Naturoids as a metaphor of the artificial and becoming familiar with the associated concepts , principles and analytical insights underlying the technology of the artificial. Throughout the book, we are reminded of the centrality of the observation level, the exemplar and essential performance, within the historical motivation of designing the machine of the artificial. We are asked to note that when we observe reality, the level of our observation is not only affected by the relationship between our perception and representation of reality, but may also be impacted by our culture, and thus, the design of Naturoids is much more than a rational scientific process. Through this exploration of the Naturoid, the author guides the reader to appreciate the classical tradition of scientific enquiry into the reality of the artificial, the methodological approach to the study of an emerging innovation, and the analytical yet reflective mind in conceiving and designing technologies of the artificial, such as the 'artificial heart' and 'artificial limb'. We are asked to not only be incisive in our enquiry but to also be critical observers of the reality and actuality of the technological process, the selection of observation level, the choice of an exemplar, and in determining the essential performance. Here, the author cautions us about the blind faith in scientific analysis of the natural world, as the term analysis which is derived from the Ancient Greek 'to break down' always has some costs in terms of the effectiveness of the scientific explanation and prediction, and hence for the design of the Naturoid. On this journey, we meet Icarus of Greek mythology, Leonardo da Vinci, Francois Bight a French scientist, the Heisenberg and the indetermination principle, Kuhn's scientific paradigm, C. Morris's 'objec-tive relativism', Oscar Wild on art as exaggeration of reality, Niels Bohr on representation of the atom, Coper-nican representation, Keplar's Machina mundi artificialis, Marvin Minsky on 'making ourselves into machines', Joseph Needam recounting the story of the inventor Shih' s automation, and the Chinese …

While including the other phyllostomids may have substantially taxed the project's resources, it would have been useful to have them included. Although phyllostomids can be notoriously difficult to distinguish acoustically, their calls do fall into groups of acoustically similar species. Including that information along with the predicted distributions would have been very helpful in trying to move acoustic understanding of the family forward.
The potential distribution maps are an excellent feature of the book and will make it worth having for that alone. These were based on the previous work of Zamora-Gutierrez et al. (2018) when possible, or adapted from the IUCN. The authors do warn that some species may have been detected outside the predicted ranges, but this is to be expected with any distribution maps. Since acoustic recordings can provide distributional data which may not be easy to obtain otherwise (personal observation), it would be interesting to know if any acoustic data was used in generating these maps.
All the sonograms are full spectrum and uncompressed, so spaces between bat calls are shown at the same magnification as the pulses themselves, generating a lot of white space and showing little detail in the pulses themselves. The horizontal (time axis) varies depending on species, from a coverage of just 70 ms for Thyroptera tricolor up to 17 seconds for Eumops underwoodi. This means T. tricolor pulses are magnified 240 times as much as for E. underwoodi, which illustrates the wide range of phenomena included within bat echolocation.
The vertical (frequency) axis is linear and mostly covers from 0 to 150 kHz, except for a few species where the maximum frequency is 80, 120 or 250 kHz. Given the wide range used for the time axis, it seems a little odd that more use was not made of varying the frequency axis to better show detail in some species, especially those at low frequencies which are poorly resolved by a linear scale. A logarithmic scale would provide a more meaningful magnification across the whole spectrum without having to vary the scale.
In most respects these sonograms follow a standard approach commonly used to illustrate bat calls since the 1980s. Unfortunately, this dated approach fails to convey many important aspects of echolocation signals. Technological advances have made it relatively easy to use compressed displays and a logarithmic frequency scale. One way this book does a much better job than most is by providing horizontal 'Y-bars' across the display. This makes it much easier for the user to appreciate what frequencies are being displayed. This could help shift the emphasis from tables of figures to visual displays which convey acoustic distinctions much more easily.
The second page of each species account includes four acoustic parameters showing measurements made from the recorded call sequences. These parameters are the means of Duration, Maximum Frequency, Minimum Frequency and what is called 'Characteristic Frequency'. The range is not explained and we assume it refers to one standard deviation each side of the mean, but this should have been made clear.
A confusing aspect of this work is how the term 'Characteristic Frequency' has been used. Use of Characteristic Frequency (Fc) originated with the development of Zero-Crossings (ZC) methods in the 1980s. Because ZC does not directly deal with sound amplitude, the commonly used parameter Frequency of Peak Energy (Fp) is not accessible for ZC methods. Instead, Fc was defined as a feature of pulse shape, so it can be used by either Full-Spectrum (FS) or ZC methods. Fc is most easily thought of as the frequency at the right hand end of the least steep part of a call (C. Corben, personal observation) (Fig.  1). To avoid confusion, we will hereafter use 'Character istic Frequen cy' including the double quotes for values tabulated in this book and Fc to mean actual values measured as ex plained above, or inferred from viewing the sonograms. The diagram in the methods on p. 21 shows 'Characteristic Frequency' as a typical measure of Fp, derived from a power spectrum display. While Fc and Fp often agree quite closely, they may be very different, especially in pulses showing little change of slope. It is unfortunate that the term is misused in this context in a way which contradicts its usage elsewhere and may confound comparisons to other works.
To illustrate a case where it makes a large difference whether Fc or Fp is being measured, we refer to p. 155 for the sonogram and acoustic parameters for Myotis melanorhinus 'Characteristic Frequency' is given as 56.5 ± 8.1 kHz. However, the pulses shown in the sonogram clearly show an Fc of about 40 kHz -a very large discrepancy.
The Methods section states that "Spectrograms were analyzed with BatSound Pro" and the sonograms certainly seem to have been created using that software. However, according to the Metadata table provided after the species accounts, the software Sonobat was used for 45 of the 90 species, and it isn't at all clear what roles the two software suites played or how that might have affected the measurements presented. Effectively then, the values for 'Characteristic Frequency' are completely meaningless, as we cannot tell how they were really measured.
Some inconsistencies were noted in how call parameters are presented for different species. For example, separate measurements are provided for the paired higher and lower frequency FIG. 1. Graphic representations of Fc as applied to several different pulse shapes. In A, this also shows Sc, the Characteristic Slope, which is the slope of the part of the call with the lowest absolute slope. Fc is the frequency at the right hand end of that portion. In the case of B, a call type typically seen in Pteronotus, Fc is chosen as the maximum frequency of the call, because this is the most consistent feature pules of species in the genus Molossus (Molossidae) but not for Promops centralis or species of Saccopteryx (Emballo nuridae) for which the alternating pulses are diagnostic and just as important.

How Useful Will This Book Be?
Given the stated aim of the book, how effective will it be for meeting its objectives? Unfortunately, the very conciseness and brevity which aid the attractiveness of this work, will make it difficult to use it in practice for many species. Someone trying to use this book to acoustically identify Mexican bats would soon find it frustrating on two levels. First, there is no discussion at all about what features are actually useful for identifying a particular species. Second, there is no attempt to convey the range of call types to be expected from any species, just a single sonogram depicting calls from a single sequence.
In practice, there are three aspects to echolocation pulses which are essential for understanding how to use them for species identification. These are: 1) The shape of a pulse, which is how the frequency changes in time throughout a pulse. The shape usually varies over a wide range depending on what the bat is doing and under what conditions. It isn't as if 'search phase' defines a narrow part of a bat's repertoire. Rather, it covers a broad spectrum of phenomena which typically can overlap broadly with other species; 2) The frequency of the call, which typically varies depending on the call shape being produced. This often differs, at least on average, between closely related species giving similar call shapes, but it can also be that even bats in different families can share calls of similar shapes at similar frequencies; 3) How the shapes vary within a species and in particular, how often different shapes are encountered, which is a way in which species can often be distinguished even if there is broad overlap in their repertoires.
Calls of two species which are easy to distinguish under most conditions, can overlap enough to be confusing under some conditions. So, an essential requirement is to understand which types of calls are useful for discrimination and which are not. We illustrate these points with some examples.
Diclidurus albus is a very distinctive species mostly easy to identify. Yet in the account presented, there is no useful information to help distinguish it from Tadarida brasiliensis, Nyctinomops laticaudatus or Eumops nanus and possibly some other species. There will be much overlap between the calls of these species, all of which can make a wide range of call types much more diverse than is depicted here for any of them. Diclidurus albus is distinctive as it is an emballonurid and as such has a very different harmonic structure than the other species (Fig.  2) and a very different way of changing its calls when it goes into an attack or changes how close it flies to other objects (Fig.  3). The lack of any mention of these very distinctive features makes it impossible to use this book as a stand-alone reference for identifying Diclidurus.
The case of D. albus clearly illustrates how more information is needed to make this book really useful, for what is one of the easier identification issues. This issue is further confounded by misleading values for the call parameters. For D. albus the pulse durations are given as 4.7 ± 1.4 ms. Such a short duration could only apply to the attack phase calls or calls given in very high clutter. When flying in the open, which is typical for this species, pulse durations are usually between 10 to 15 ms. (personal observation). Abnormally short durations are also given for T. brasiliensis and N. laticaudatus, but not for E. nanus. The metadata table shows the first two were recorded as hand releases and E. nanus as a free flying bat which might explain these differences.
The second problem with this book is the lack of information about the variability of call types. Most of the species included produce a wide range of call types so that in many cases, the overlap between species will largely mask the differences illustrated between them. To make this clear, Fig. 4 shows a composite image of ZC calls all from one species, Lasiurus borealis. Lasiurus is an especially variable genus, and the six species found in Mexico will produce, between them, a range of calls with an Fc between 15 and 60 kHz. While many sequences from Lasiurus are distinctive, because of the way the calls rapidly fluctuate in frequency and shape in commonly found conditions, this is neither displayed nor mentioned. Species of this one genus will overlap acoustically with many other genera.
A consequence of this variability is that hardly any of the vespertilionids could be identified using the limited information in this book. Calls of Euderma maculatum reaching down below 10 kHz could be identified, but many of their calls can also be confused with Idionycteris phyllotis. Some other species might be distinguishable, such as Corynorhinus outside the range of C. mexicanus. Even for species which should be easy in some situations, like Myotis thysanodes, M. vivesi and L. cinereus, there just isn't enough information provided for differentiation.  (upper, Mismaloya, Mexico) and T. brasiliensis (lower, northern Florida, USA). Truetime plots on the left, showing the true temporal patterns and compressed views on the right, to clearly show pulse shapes. D. albus shows much less tendency to increase maximum frequency into the attack, and even the pulses of the feeding buzz are more similar to the preceding search-phase calls, but shorter in duration and with a much higher Pulse Repetition Rate (PRR). The differences seen here are typical distinctions between emballonurids and molossids The phyllostomids included are hypothetically the easiest of the family to identify acoustically and they were selected for that reason. Unfortunately, the usefulness of most of the sonograms is greatly reduced because individual pulses are shown with too little horizontal magnification to clarify which harmonic is dominant -an important criterion for interpreting calls from this family. For example, in the sonogram of Chrotopterus auritus, three different harmonics can be seen but it isn't clear which parts of them coincide in time. The lower two would be the fourth (H4) and fifth (H5) if the higher one reaches 100 kHz at the same time as the lower reaches 80, but they might be H3 and H4, if the higher reaches 107 as that moment or H2 and H3 if it reaches 120. There just isn't enough detail to be sure. This ambiguity could have been avoided by stretching the pulses in the time scale.
Species in the families Emballonuridae, Noctilionidae and Mormoopidae would be readily distinguishable with this level of information if the distinctive call shapes are recognized, but with some exceptions. Additional information would be really useful, e.g., how to distinguish Saccopteryx bilineata from Centronycteris centralis or Balantiopteryx plicata from Peropteryx macrotis.
Of the molossids, only the lowest calls of Eumops perotis will be readily identifiable, along with the very distinctive calls of Promops centralis. The latter case is particularly interesting because these calls look typical of social calls and if Promops make sequences without those distinctive pulse shapes, they could be hard to tell from a number of other species.

Conclusions
This book is a beautiful production, and despite the limitations we have noted, most of the emballonurids, mormoopids and both species of Noctilio will be easily distinguishable from the information therein. For many other species, there will be challenges and additional information will be required. However, this is to be expected in a volume covering so many species and there will always be some, such as most of the Myo tis and Phyllostomidae, which will be very difficult to identify to spe cies acoustically.
The importance of this book will come by encouraging more bat researchers to take an interest in acoustic sampling by providing a useful starting point. It represents a very important step in the development of this field by providing the most comprehensive coverage of bat acoustics for any country in the Americas. The project deserves congratulations for taking on this task and doing it so well.