L C W Pols

M E H Schouten

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Identification of deleted plosives: the effect of adding noise or applying a time window: a reply
to Ohde and Sharf
Pols, L.C.W.; Schouten, M.E.H.
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The Journal of the Acoustical Society of America
DOI:
10.1121/1.385312
Link to publication
Citation for published version (APA):
Pols, L. C. W., & Schouten, M. E. H. (1981). Identification of deleted plosives: the effect of adding noise or
applying a time window: a reply to Ohde and Sharf. The Journal of the Acoustical Society of America, 69(1),
301-304. https://doi.org/10.1121/1.385312
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Download date: 02 Jul 2019
Identification of deleted plosives: The effect of adding 
noise or applying a time window (A reply to Ohde and 
Sharf) 
L. C. W. Pols and M. E. H. Schouten 
Institute for Perception TNO, Soesterberg, The Netherlands 
(Received 5June 1980; accepted for publication 8September 1980} 
A Letter in this Journal [Ohde, R. N. and Shaft, D. J., J. Acoust. Soc. Am. 69, 297-300 {1981)] deals with the 
identification ofvoiced and voiceless tops from vocalic transition + vowel stimuli edited from CV and VC 
syllables. The segmentation points were smoothed by applying a time window. With respect to an earlier 
study, in which straightforward segmentation without ime window was applied, final plosives were still 
identified better than initial plosives. The present Letter shows that there is, however, one major difference 
between the with-window and the no-window condition, namely a substantial improvement in identification 
for initial voiced plosives. This improvement is similar to that found by the present authors in identification 
experiments with a noise burst adjacent to the segmentation point versus no-noise listening conditions. 
Instead of a controversy reported by Ohde and Shaft, this Letter suggests a unifying interpretation. 
PACS numbers: 43.70.Dn, 43.70.Ve, 43.66.De 
INTRODUCTION 
Several recent papers (&hurl and Hemeyer, 1972; 
Sharf and Beiter, 1974; LaRiviere e! al., 1975; Ohde 
and Sharg, 1977; Pols and Schouten, 1978; Pols, 1979; 
Ohde and Sharf, 1980) deal with the identification of ini- 
tial and/or final plosives in monosyliables from which 
the initial or final plosive burst + aspiration has been 
deleted. The stimuli for plosive identification, partic- 
nlarly identification oI place of consonant articulation, 
then consist only of the consonant-vowel- (CV) vocalic 
transition + vowel segment for initial plosives, or of the 
vowel segment + vowel-consonant'(¾C) vocalic transi- 
tion for final plosives. Ohde and Sharf (1977) and La- 
Riviere et al. (1975) also studied the vocalic transition 
alone. Pols and Schouten (1978) and Pols (1979) used 
various segmentation points. 
The two discussion points we want to focus on in this 
Letter are: 
(1) Is there a substantial difference between initial 
and final plosive identification? 
(2) Does the deletion procedure itself introduce arti- 
facts or lower the correct score, and if so are there 
ways of overcoming this? 
In Pols and Schouten (1978) we, somewhat provoca- 
tively, claimed that there is no inherent difference in 
information content between CV and VC transitions. We 
contended that any such differences found (Sha_• and 
Hemeyer, 1972; Ohde and Sharf, 1977) were due to the 
abrupt onset of the CV transitions after deletion of the 
initial burst + aspiration. As a result, deleted initial 
stop consonants were identified much worse than de- 
letsd final consonants. We demonstrated that for Dutch 
piesives the advantage of final over initial consonant 
identification could be reduced considerably by replac- 
ing the deleted consonants with noise, thus smoothing 
the abrupt onsets. As a result, identification of initial 
consonants improved, whereas that of final consonants 
remained unchanged. 
In their recent Letter to the Editor, Ohde and Sharf 
(1980) set out to cOUnter our claim that there is no in- 
herent difference in information content between con- 
sonant-vowel (CV) and vowel-consonant (VC) transi- 
tions. They describe a new experiment, in which they 
eliminate a possible "click sensation" by smoothing the 
onsets of CV transitions and the offsets of VC transi- 
tions by means of an amplitude-smoothing time window. 
They claim that, although there are now no abrupt on- 
sets anymore, the original advantage of final over ini- 
tial transitions remains, and that the difference be- 
tween the two is consequently an inherent one. The pur- 
pose of our present reply is, firsfly, to indicate that we 
think that Ohde and $harf's (1980) data do not differ es- 
sentially from ours, and secondly, to discuss some con- 
siderations they raise in their discussion. 
I. INTERPRETATION OF THE DATA 
In Table I, we present a summary of the figures on 
which Ohde and Sharf (1980) base their claim, and on 
which we base ours. We include the results of an ex- 
periment on American English plosives, recently con- 
ducted by one of us and described in Pols (1979). 
A few things should first be said about differences be- 
tween stimuli, experimental designs, and languages. 
Ohde and Shari (1980) used CV-type syliables and sep- 
arate subsets for voiced/b, d, g/and voiceless/p, t, k] 
stimuli, whereas we used CVC syllables and mixed 
voiced-voiceless presentations and response sets. 
Moreover, Dutch differs from English in that Dutch 
plosives are unaspirated and do not have initial/g/or 
'final voiced plosives. Dutch voiced plosives are usually 
prevoiced, and it is not uncommon for a Dutch/t/to be 
mistaken for a/d/ by a native speaker of English. So 
identification results will only be comparable in a rela- 
tive sense. 
Ohde and Sharf (1980) conclude from their new iden- 
tiffcation experiment with a time window that "the re- 
liability and direction of the results ... ," with respect 
301 J. Acoust. Soc. Am. 69(1), Jan. 1981 0001-4966/81/010301-02500.80 ¸ 1981 Acoustical Society of America 301 
TABLE I. This table contains the identification scores for deleted plosive consonants from aH the studies mentioned in this Letter. 
The deletion procedure resulted in stimuli consisting of vocalic transition + vowel for initial plosive identification or vowel + vo- 
calic transition for final plosive identification. The first five columns specify the experimental conditions, namely: Segmentation 
procedure; whether voiced or voiceless ubsets were used, or a full set; the syllable type (CV and VC or CVC); the language used 
(AE =American English, D=Dutch); and whether or not a time window or noise were applied. The next four columns give the de- 
tailed scores; the last two columns give combined scores. 
Initial Final 
Segment Stimulus Window (CV) 0/C) 
Study procedure response Syllable Language noise /b,d,g/ /p,t,k/ /b,d,g/ /p,t,k/ CV VC 
Shad and Better (1974) splicing subset Cz AE ß-. 64 39 79 83 52 81 
Shad and Hemeyer (1972) splicing subset C• AE - ß ß 66 26 91 91 46 91 
Ohde and Shad (1977) erasure subset CV AE --- 44 35 73 58 39 65 
Ohde and Sharf (1980) digital subset CV AE window 72 40 78 57 56 67 
Pols (1979) digital full set CVC AE ß-- 54 17 63 82 35 73 
Pols (1979) digital full set CVC AE noise 82 26 67 69 54 68 
lb. dl 
Pols and Schouten (1978) digital full set CVC D --- 74 34 ß ø ß 77 ....... 
noise 73 66 ß ß ß 77 ...... 
to earlier studies (where other deletion techniques with- 
out time window were employed) "... were similar." 
In other words, final stop identification is still superior 
to initial stop identification. They, furthermore, reject 
our noise paradigm because of the "risk of not being 
able to explain the effect obtained." 
Table I shows that for the new experiments with a 
time window (Ohde and Shad, 1980), the VC score (67%) 
is indeed still higher than the CV score (56%). The dif- 
ference, however, is substantially reduced with respect 
to the no-window condition (Ohde and Sharf, 1977), 
where the VC and CV scores are 65% and 39%, respec- ' 
tively. Moreover, if one looks more carefully at the 
data, it is clear that there is a major difference be- 
tween the no-window versus window conditions, namely 
for the initial voiced plosives (44% versus 72%). In- 
terestingly enough, this improvement is comparable to 
that found by Pols (1979) for inittat American English 
voiced plosives in the no-noise versus noise conditions 
(54% versus 82%), and to that found by Pols and Schout- 
eu (1978) for initial Dutch voiceless plosives in the no- 
noise versus noise conditions (34% versus 66%). In 
English, the vocalic transitions of the voiced stops are 
more consonant-specific than those of the voiceless 
stops, where most coarticuhg•ion takes place during 
aspiration. Dutch voiceless stops are unaspirated, 
which makes their vocalic transitions more consonant- 
specific. 
Apparently, for those situations where a lot of con- 
sonant-specific information is present in the vocalic 
transition directly following the segmentabort point, the 
abrupt voc'aiic onset ("click sensation") produces con- 
fiicting information and reduces the ideniJ.fication score. 
The perceptual effect of this abrupt onset can be avoided 
by xpplying a time window to smooth the segmentation, 
or by a noise burst preceding the segmentation point; 
both procedures cause a considerable improvement in 
identification of deleted plosives, especially initial 
American English voiced ones. 
We find it difficult to include in this discussion the 
data from similar experiments by Sharf and Hemeyer 
(1972) and Sharf and Better (1974). As can be seen in 
the first three rows of Table I, there is considerable 
inconsistency among these scores and those found by 
Ohde and Sharf (1977), whereas the experimental condi- 
tions were quite similar. There were two differences, 
however, which may have influenced the results: (1) 
Sharf and Hemeyer (1972) and Sharf and Beiter (1974) 
used only the vowel/o/, whereas Ohde and Sharf (1977) 
used a larger vowel set; (2) the segmentation procedure 
used in the two earlier papers was tape splicing, re- 
placed in 1977 by tape erasure. We consider the more 
recent data of Ohde and Sharf (1977) to be the more re- 
liable ones; moreover, in that study, the set of vowels 
is more similar to the one used by Ohde and Sharf 
(1980). 
II. IMPLICATIONS 
In our 1978 paper, we used the term "click sensation" 
for want of a better term. What we meant by it was the 
effect produced by the inevitable spectral consequences 
of an abrupt onset. We felt that this effect differed only 
in degree, but not in principle, from the clearly audible 
click produced by cutting and splicing at a high ampli- 
tude point on a waveform. Combining Ohde and Sharf's 
(1980) and our own results, we think it may be said that 
the addition of noise or of a time window reduces, per- 
haps even cancels, the unwanted onset spectrum. Such 
an effect is to be expected if a time window is used, 
provided not too much information is smoothed away. 
With noise, however, the effects are perhaps less pre- 
dictable, although the net results appear to be at least 
as effective. In addition to supplying the required spec- 
tral continuity, added noise could also (1) serve as an 
alerting signal to subjects (this could be investigated by 
having noise bursts of various durations); (2) mask the 
no-signal situation, with unpredictable effects. If no 
noise is applied there is silence instead, with the con- 
302 J. Acoust. Sec. Am., Vol. 69, No. 1, January 1981 Letters tothe Editor 302 
sequence that no information is present at all; (3) al- 
low subjects to suppose that the original information 
could be present but has been made inaudible ("hear 
through the noise") (Plomp, 1980). 
The third possibility is the one we briefly hinted at in 
our paper, where we said that this "possibility must 
not be excluded." The truth is, however, that we do not 
really know exactly what happens when noise is added to 
a signal; how, for example, would it provide "spectral 
continuity?" The fact that Ohde and Sharf's (1980) and 
our results are of the same magaitude could indicate 
that the effects caused by a time window or noise are 
the same, but it is too early to say that. 
LaRiviere, C., Winitz, H., and Herriman, E. (1975). "Vocal- 
ic transitions in the perception of voiceless inithi stops," J. 
Acoust. Soc. Am. 57, 470-475. 
Ohde, R. N., and Sbarf, D. J. (1977). "Order effect of acous- 
tic segments of VC and CV syllables on stop and vowel iden- 
tification,,' J. Speech Hear. Res. 20, 543-554. 
Ohde, R. N., and Sb.,•rf, D. J. (1981). "Stop identification 
from vocallc transition plus vowel segments of CV and VC 
Syllables: A follow-up study," J. Acoust. Soc. Am. 69, 
297-300. 
Plomp, R. (1980). ,Perception of sound sigmaIs at low signal- 
to-noise ratios," in Proceedings of Symposium on the Recog- 
nition and Classification of Aural Signals, June 1978, Cam- 
bridge, MA. 
Pols, L. C. W. (1979). "Coarticulation and the identification 
of initial and final plosives," ASA 50 Speech Communication 
Papers, edited by J. J. Wolff and D. H. Klatt (Acoustical 
Society of America, New York ), pp. 459-562. 
Pols, L. C. w., and Schouten, M. E. H. (1978). "Identifica- 
tion of deleted consonants," J. Acoust. 8oc. Am. 64, 1333- 
1337. 
Sharf, D. J., and Belief, R. C. (1974). "Identification of con- 
sonants from formant transitions presented forward and 
backward,,, Lang. Speech 17, 110-118. 
Sharf, D. J., and Heineyet, T. (1972). "Identification of place 
of consonant articulation from vowel formant transitions," J. 
Acoust. Soc. Am. 51, 652-658. 
Absorption of acoustic energy by plant leaves 
Maurice J. M. Martens 
Section Experimental Ecology, Department of Botany, Catholic University, 6525 ED Nijmegen, 
The Netherlands 
Axel Michelsen 
Institute of Biology, Odense University, DK 5230 Odense M, Denmark 
IReeeived 6 May 1980; accepted for publication 22 July 1980} 
We investigated the vibration of leaves of four plant species in a sound field using a laser-Doppler-vibrometer 
system. All leaves behave as linear mechanical systems when driven by sound and noise at sound pressure 
levels (SPL} of up to 100 dB re 20 p Pa. The modes of vibration are complex in the investigated frequencies 
(0.5-5.5 kHz), and change with the orientation of the leaf in the sound field. The vibration velocities of the 
leaves varicd between 10 -s and 3 X 10 -4 m/s, while the vibration velocity of the air particles i 5 X 10 -a m/s at 
100 dB SPL. Although the amount of sound energy absorbed in this way by a single leaf is very small, this 
mechanism ay anyhow contribute to sound attenuation by plants and plant communities, since the number 
of leaves Of one fullgrown tree equals 2X l0 s. 
PACS numbers: 43.80.Gx, 43.28.Hr 
INTRODUCTION 
The acoustic properties of the environment are im- 
portant with regard to noise pollution problems and 
noise abatement, H and for the understanding of sound 
communication by animals. 9't2 Vegetation is a complex 
medium consisting of air, soil, and the stems, trunks, 
branches, and foliage of herbs, shrubs, and trees. 
Despite both theoretical t3't4 and experimental 
work, 1'9't4'•6 the mechanisms of sound attenuation in 
various types of plant communities remain obscure. 
Among the mechanisms which have been suggested are 
the ground effect, the thermoviscous absorption of 
sound at the soil and in the boundary layer of air at the 
surface of the leaves, scattering from trunks, branches, 
and leaves, and the vibration of thin branches •tnd 
leaves. •I'he aim of this paper is to investigate the vi- 
bration of plant leaves in a sound field using a laser- 
Doppler-vibrometer system. iv 
The acoustic force acting upon a leaf is determined 
by the vectorial difference between the sound pressures 
at its two surfaces, cf. a ribbon microphone and other 
pressure gradient receiversJ s A part of the sound 
energy received by a leaf may be lost by friction and 
thus absorbed, and some of the energy may be re-emit- 
ted. At low frequencies the force acting on the leaf is 
small, and the re-emission of sound is likely to be in- 
efficient? At higher frequencies the driving force is 
larger, and a considerable part of the energy received 
303 J. Acoust. Soc. Am. 69(1), Jan. 1981 0001-4966/81/010303-04500.80 ¸ 1981 Acoustical Society of America 303 


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UvA-DARE (Digital Academic Repository) Identification of deleted plosives: The effect of adding noise or applying a time window (A reply to Ohde and Sharf)

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