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Title

Study on detectability of target signal byutilizing differences between movements in
temporal envelopes of target and backgroundsignals

Author(s)Yano, Yuta; Miyauchi, Ryota; Unoki, Masashi;
Akagi, Masato

Citation

2011 International Workshop on Nonlinear
Circuits, Communication and Signal Processing(NCSP'11): 231‑234

Issue Date

2011‑03‑02

Type

Conference Paper

Text version

publisher

URL

http://hdl.handle.net/10119/9975

RightsThis material is posted here with permission of
the Research Institute of Signal Processing
Japan. Yuta Yano, Ryota Miyauchi, Masashi Unoki,
and Masato Akagi, 2011 International Workshop on
Nonlinear Circuits, Communication and Signal
Processing (NCSP'11), 2011, pp.231‑234.

Description

Japan Advanced Institute of Science and Technology

2011 International Workshop on Nonlinear Circuits,
Communication and Signal Processing
NCSP'11, Tianjin, China, March 1-3, 2011

Study on detectability of target signal by utilizing differences between movements
in temporal envelopes of target and background signals
Yuta Yano, Ryota Miyauchi, Masashi Unoki, and Masato Akagi
School of Information Science, Japan Advanced Institute of Science and Technology
1-1 Asahidai, Nomi, Ishikawa, 923-1292 Japan
Phone/FAX:+81-761-51-1391/+81-761-51-1149
Email: {s0810064, ryota, unoki, akagi}@jaist.ac.jp

Abstract
In this paper, we investigated whether difference between
movements in temporal envelopes of the target and background signals can improve the detectability of target signal
against background signals. The movement of the signal was
defined as the mean value of slopes as the first-order approximation of temporal envelope. Stimuli were generated by multiplying one of three processed temporal envelopes (movements of 88, 700, and 1313 mV/s) with one of three different
noise carriers (1/2-octave bandwidth at the center frequencies (CFs) of 200, 525, and 1380 Hz). The auditory search experiment was carried out. Results showed that the detectability of target signal, that is, d0 , is improved as the differenceof the movements increases, in which the CF of target signal
was the same as that of the background signal. This tendency
constantly appeared when the movement of the target signal
was faster than that of the background signal. These results
suggest that greater difference of the movements improves thedetectability of the target signal.
1. Introduction
Audible alarm signals are used to attract the attention of
persons in many everyday activities, for example, the beeps
and melodic sounds of electronic products for providing starting and ending, and fire alarm sounds for emergency [1].
Therefore, these signals must be perceived accurately and efficiently by everyone. For this purpose, alarm signals withmany different stimulus shapes have been studied to checkif they are perceived adequately, e.g., by Mizunami et al.
[2]. There are, however, cases where alarm signals cannot
be correctly perceived in real environments because they aremasked or partially masked by background noise, so that theintended person knows when and what events have occurred.
Therefore, it is important to present alarm signals in such a
way that they can be correctly detected in any environment.
It is well known that the detectability of a signal in thepresence of noise could be improved by utilizing directional
information [3]. Saberi et al. also reported that the detectabil-

ity of a pulse train signal against white noise in the free field
could be improved when the signal and masker were spatiallyseparated [4]. This means that the detectability can be improved by using spatial cues in binaural hearing. Therefore,
this is referred to as “spatial release from masking (SRM)”[4]. If SRM occurs for alarm signals in noisy environments,
it can suppress the influence of the masking effect produced
by noise on alarm signals, which facilitate the perception of
their existence and directions, so it can help us in designing
the way in which alarm signals are presented.
On the other hand, a human can easily selectively listen toa target sound in real noisy environments that simultaneously
contains various kind of sound such as conversation speechand environmental sounds. It has been considered that weare not attend to listen all signals in real environments but weare attend to listen a specific signal such as alarm signal inas the all signals. In the related study, there is what is called
the “cocktail party effect” that is ability of human auditory
system [5]. This ability is what we can perceive one soundin complex sounds. Consequently, it may be considered thathuman can perceive a specific alarm signal easily in noisy
environments, by utilizing this ability.
In the most related study, there is, for example, auditory
search tasks, studied by Asemi et al. [6]. They studied
whether the detectability of the target against background signal can be improved, by carrying out auditory search experiments. In their experiments, narrow-band noise and pure tone
were used and temporal fluctuations of the target was controlled as a cue to investigate improvement of the detectabilityof the target signal. Their results conducted that the temporal fluctuation of the target against background signals plays
a role of the improvement in the detectability.
Based on their results, Kusaba et al. have investigated how
much the temporal fluctuation between the target and background signal can improve the detectability of the target signal in auditory search experiments [7]. Their results suggestthat lower similarity of temporal fluctuations between target
and background signals can improve the detectability of thetarget in noisy environments. However, In their experiments,- 231 -

1
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2. Definition and control of the movement of signal

PN−1

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Amplitude envelope

they used similarity of temporal fluctuations between target
and background signals to account for the improvement ofdetectability. Thus, it is still unclear what characteristics ofthe movements that can contribute to the improvement are.
In this study, we have the same approach that Kusaba et
al. had, to investigate the detectability of the target against
background signal as the auditory search problem. Instead of
the use of similarity between target and background signals,
we reconsidered whether difference between movements in
temporal envelopes of the target and background signals canimprove the detectability of the target signal. This study aims
to reveal what movements in temporal envelopes of the target
signal can improve the detectability of the target signal.

0.5
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Time, t (s)

2

2.5

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N

Figure 1: Example of the movement in the temporal envelope
We defined the movement in temporal envelope of a signal (176 mV/s).
as the mean value of slopes as the first-order approximationof temporal envelope.
To control the movements in temporal envelopes, we sysNA0 ∑ |Pn − Pn−1 |tematicallycontrol envelopes shown in Fig. 2(f) by using thev=(1)
N − 1 n=2 Tn − Tn−1
Eq. (1). The movements tend to increase as the CF of filter
increases and/or bandwidth of them widens. As the above,
where Pn is the values of peak/dip in temporal envelopes, the three types of movements were generated by systematiTn is the time, and N is the number of peaks/dips. A0 is cally controlling the modulation spectrum of them using BP
output reference-voltage (through the TDT SystemIII and the filter.
SANSUI AU-α 907MR Integrated Amplifier). The output
reference-voltage to computerize amplitude value of 1.0 is 88
3. Experiment
mV. Therefore, v is in mV/s.
Figure 1 shows an example of the temporal envelopes toderive their movements. Red line indicates a temporal en- 3.1. Apparatus
velope of a signal. Green line indicates the mean value of
Figure 3 shows the diagram of the apparatus used in theslopes of the temporal envelope. In this case, the number of experiment. The experiment was carried out in a sound-proof
peaks/dips is seven. Therefore, this movement in temporal room. Stimuli were generated by Tucker-Davis Technoloenvelope is 176 (= 88/(7 − 1) × 12) mV/s.
gies (TDT) System III and presented to each subject throughWe systematically controlled the movements, defined in an amplifier (SANSUI, AU-α) and headphones (Sennheiser
the above by bandpass (BP) filtering on the modulation spec- HDA200). A subject’s response was recorded through the retrum as follows. We assumed that signal can be expressed by sponse box.
multiplying temporal envelope with carrier. Here, band-noise
was used as the carrier.
Figure 2 shows an example of stimulus generation, used in 3.2. Stimuli
auditory search experiment. White noise is used to generate
The movements in temporal envelopes we used in the exstimulus, as shown in Fig. 2(a). Figure 2(b) shows the mod- periment were 88, 700, and 1313 mV/s. The carrier was 1/2ulation spectrum of (a). Figure 2(c) shows characteristics of octave band-noise. The CF of the carrier were 200, 525, andthe BP filter in the modulation frequency. This filter has the 1380 Hz. Stimuli were composed of the three temporal enbandwidth of 2.5 Hz at the CF of 2 Hz. By BP filtering on the velopes with the three noise carriers. All stimuli have ninemodulation spectrum, the processed modulation spectrum of conditions.
them was obtained as shown in Fig. 2(d). The processed amplitude envelope was then obtained from the inverse Fourier 3.3. Proceduretransform of them as shown in Fig. 2(e). This was normalized by the averaged value of amplitude to be ±0.5. Stimuli
In auditory search experiment, there were two kinds ofwere generated by multiplying the temporal envelopes with judgments: positive and negative judgments. In the positive
the carriers. The rising and falling edge of the stimuli were judgments, two of the nine stimuli as the target and backcreated as 30-ms raised-cosine.
ground signals were simultaneously presented to the partici-- 232 -

Amplitude(a)White noise

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Time, t (s)(b)Modulation spectrum of white noise

Filter gain (dB) Spectrum (dB)Spectrum (dB)

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Figure 3: Environment for auditory search experiment.
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Modulation Frequency (Hz)(e)Amplitude envelope
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Time, t (s)(f)Amplitude envelope (normalization)
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Time, t (s)Figure 2: Examples of stimulus generation: (a) white noise,(b) modulation spectrum of (a), (c) bandpass (BP) filter on themodulation spectrum, (d) modulation spectrum of BP-filtered Figure 4: Detectability of target signal by the difference benoise, (e) amplitude envelope of (d), and (f) normalized am- tween movements in the temporal envelopes of target andplitude envelope of (e).
background signals. Movement of target signal is 88 mV/s,
the center frequency of target signal is 1380 Hz, and the center frequencies of background signal are 200, 525, and 1380
pants via headphone. In the negative judgments, background Hz.
signal was separately presented to the participants. The participants were required to judge whether there was the target signal with the background signal and to press “true” or tected.
“false” button on the response box. Before the participant
Figure 4 shows d0 as a function of the movements of thestarted to run the session in this experiment, a target signal background signals in which the CF and the movement of thewas repetitively presented to the participant to learn the target target signal were 1380 Hz and 88 mV/s, respectively.
signal that would be presented in the session. All trials in the
When the CF of target signal differed from the backgroundsession were 720 (= nine target signals × eight background signal (see blue and red bars in Fig. 4), the value of d0
signals × two judgments (positive and negative judgments) was constantly great regardless of the movement of the back× five repetitions). These trials were randomly presented.
ground signal. These results indicate that the target signal iseasily detected. In the current experiment, three kinds of the
CF of the target signal and background signals were set to be
4. Results
200, 525, and 1380 Hz. Under such conditions, the target and0
We obtained the detectability of target signal, i.e., d , from background signals that have different CFs are resolved in thethe results of the judgments of the participants. The classi- auditory periphery systems. Thus, the signal detection is very
fications of the results of the judgments were the four types: easy and the effect of the movement to detect the target signal
Hit (they pressed “true” when there was a target), Miss (they is very small.
pressed “false” though there was a target), False Alarm (theyOn the other hand, when the CF of target signal was thepressed “true” though there was not a target), Correct Rejec- same as that of the background signal (see green bar in Fig.
tion ((they pressed “false” when there was not a target). The 4), the value of d0 varied with the movement of the backgreater value of d0 indicates that the target signal is easily de- ground signal, whereas the value of d0 was small. Under this- 233 -

stantly appeared when the movement of the target signal was
faster than that of the background signal. This means that wecan perceptually separate the target and background signals
and detect the target signals by increasing the difference ofthe movements between the target and background signals.
Therefore, the results of the auditory search experiment suggest that the target signal is easily detected as the differenceof the movements between the target and background signals
increases when the CF of target signal was the same as thatof the background signal.
Figure 5: Detectability (d0 ) of target signal by the difference 5. Conclusionof the movements. Movement of target is 88 mV/s and the
We investigated what movements in temporal envelopes ofcenter frequency of target is the same as that of background.
the target and background signals can improve the detectability of the target against the background signals. We found thatthe detectability of target signal is improved as the differenceof the movements increases in which the CF of target signal
was the same as that of the background signal. This tendency
constantly appeared when the movement of the target signal
was faster than that of the background signal. These results
suggest that greater difference of the movements plays a roleof improving the detectability of the target in auditory searchtasks.

Acknowledgments

Figure 6: Detectability (d0 ) of target signal by the differenceof the movements. Movement of target is 1313 mV/s and the This work was partially supported by Ono Acoustics Recenter frequency of target is the same as that of background. search Fund.
condition, the target and background signals pass through thesame auditory filter. This indicates that these two signals aredecomposed into one component as one sound. Thus, it isbasically difficult to separate two signals. Our study aims to
improve the detectability of the target signal in such difficult
situation by controlling the movement in temporal envelopesof the target and background signals. The results showed thatthe value of d0 varied with the movement of the backgroundsignal. It suggests that the detectability of the target signal
might be improved by the relationship between the movements of the target and background signals. To discussing
this tendency in detail, we analyzed the experiment data inwhich the CFs of the target and background signals were thesame.
Figure 5 shows d0 as a function of the movement of the
background signal when the movement of the target signal
was 88 mV/s. Figure 6 shows d0 as a function of the movement of the background signal when the movement of thetarget signal was 1313 mV/s.
These results show that the detectability (d0 ) of the target signal is improved as the difference of the movements
between the target and background signals increases on anyof three kinds of CF of target signals. This tendency con-

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