PROCEEDINGS of the
23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Directional selectivity of auditory spatial attention in multi-talker
environment
Ryo TERAOKA1; Shuichi SAKAMOTO1; Zhenglie CUI1;
Yôiti SUZUKI1,2; Satoshi SHIOIRI1
1
2

Tohoku University, Japan,

National Institute of Information and Communication Technology (NICT), Japan

ABSTRACT
When people direct their auditory selective attention in a specific direction, the information from that
direction can be perceived easily, even in a noisy environment. Understanding how this effect is distributed
spatially is important. The extent of spatial distribution may depend on the direction of the attention focus,
and thus may differ between the frontal and oblique directions. In the present study, we investigated thedependence of the spatial extent of auditory selective attention on the focus azimuthal direction. To
examine the spatial extent, speech intelligibility was measured in a multi-talker environment. In theexperiment, a target sound and multiple distracting speech sounds were presented simultaneously fromloudspeakers surrounding observers. By manipulating the probability of the target presentation directions,the listener’s auditory spatial attention was directed to a specific loudspeaker. The attracted direction was
one of three directions: –30, 0, or +30 degrees. The results showed that the greatest improvement in
intelligibility was observed at the attracted direction, for all attracted directions. The spatial extent of theauditory selective attention seems identical for all attracted directions. This means that the attention
spotlight is not modulated by the direction of the attention.
Keywords: auditory spatial attention, cocktail-party effect, auditory scene analysis, psychoacoustics

1. INTRODUCTION
In real-world listening environments, various sounds are mixed acoustically before reaching ourears. Nevertheless, even in the environment, most normal-hearing listeners can extract a sound ofinterest from the mixed sounds. This remarkable ability, called the “cocktail-party effect” (1, 2), hasbeen studied for over half a century. Despite its essential importance for both communication andorientation in space, a number of important questions remain.
Among the questions regarding the cocktail-party effect for which we are lacking a satisfactory
answer is how human listeners highlight one sound (voice) from background noises. Numerous
previous studies have addressed what kind of physical characteristics contributed to the soundsource segregation in a “cocktail-party” situation (for review, see (3–6)). Bregman (3) proposed atheory known as "auditory scene analysis". In this theory, a stream segregation involves thegrouping together of sounds according to frequency, spatial, and temporal aspects, following Gestalt
principles (e.g., sounds that start at the same time are more likely to be coming from the same
source). Indeed, several studies have demonstrated that such acoustical characteristics can facilitate
segregation of the target sound from background noises. For example, Ebata and his colleagues (7)demonstrated that when a listener hears a target sound in the presence of masker sounds that are
spatially separated from the target, the detection threshold of the target sound is lower than in asituation when they are co-located.
Although the physical characteristics of the sounds themselves affect the performance of thesegregation, it is also necessary for listeners to actively focus on to the target sounds, which is
known as selective attention. Indeed, recent studies have reported that auditory attention in thespatial domain (hereafter “auditory spatial attention”) plays a critical role in this ability under acomplex listening environment (8–10). Kidd and his colleagues (9) demonstrated that the1

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terar@dc.tohoku.ac.jp

performance of perceiving the target sound is relatively high when the listener knows a priori where
the target sound will be presented in multi-source listening environments. Furthermore, we also
demonstrated that speech intelligibility in a multi-talker environment is improved when the auditory
spatial attention is directed to a specific direction where the target sounds are presented (10). Thesestudies suggest that auditory spatial attention contributes to the occurrence of the cocktail-party
effect.
When a human listener directs their spatial selective attention to a specific location, the effects ofthe spatial attention spread over a range around the focal point, in accordance with the “spotlight”
metaphor (11–12). This phenomenon has been well-documented in the visual domain. Indeed, arecent electrophysiological study demonstrated the spatial spread of visual spatial attention (13). In
the auditory domain, there are a few pieces of evidence suggesting that auditory spatial attention
operates in the manner of a spotlight of attention (10, 14). Our study has demonstrated that listening
performance (i.e., speech intelligibility) decreases as the angular distance from the center ofattentional focus increases (10). However, previous studies have investigated the spatial spread ofauditory spatial attention only in regards to the frontal direction. It is still unclear whether the shapeof the spatial spread is identical between the frontal and oblique directions.
In general, the spatial acuity of hearing is particularly good when the sound source is locatednear 0 degrees azimuth. This performance generally deteriorates as the angular distance moves off
the front, and then, this performance is the worst at 90 degrees. Mills (15) measured the resolutionof an auditory location with broadband or low-frequency sources by the threshold angle fordiscriminating the position, called the minimum audible angle (MAA). This study showed that the
MAA is always more than 40 degrees at an azimuth of 90 degrees, although the MAA isapproximately 1 degree at the front of the listener. These studies suggest that the auditory spatial
resolution is not constant, and differs depending on the angle. This tendency may also influence thespatial extent of auditory selective attention, because a human listener must first localize the soundof interest to then direct auditory spatial attention to the specific direction. However, it has still
unclear whether the shape of the auditory selective attention is different between the frontal andoblique directions. To investigate this question, we examined the respective widths the spatial extent
of auditory selective attention when the listener's attention is attracted to –30, 0, or +30 degrees, andcompared these spatial extents.

2. METHODS
2.1 Listeners
Twenty listeners (fifteen males and five females, aged 20–24 years, mean age 21.6) participatedin the experiment. All listeners were naïve to purpose of the experiment. All listeners were native
Japanese speakers with normal hearing acuity. Informed consent was obtained from each listener
before the experiment. The procedure was approved by the Ethics Committee of the ResearchInstitute of Electrical Communication of Tohoku University.
2.2 Apparatus and stimuli
The experiment was conducted in an anechoic room at the Research Institute of ElectricalCommunication, Tohoku University. Figure 1 shows the experimental setup. In the anechoic room,
five loudspeakers were set circularly on a horizontal plane centered on the listener, in intervals of
30 degrees: – 60, – 30, 0, + 30 and + 60 degrees (a positive value represents the right-hand side ofthe listener). The radius of the loudspeaker array was 1.6 m.
The speech sounds, comprised of four Japanese moras uttered by male and female speakers, wereselected from the “Familiarity-controlled Word lists 2003” (FW03 (16–17)). The target words wereselected from the one thousand entries of the FW03 ranked as the highest familiarity. These words
were entries of the “Familiarity-controlled Word lists 2007” (FW07 (18–19)), which is a shrunken
version of FW03 for clinical use. The total number of the target words was 400 (20 lists, with 20
words per list). The other 600 words were used as distractors. In this study, one female (fhi) and one
male (mya) voice were assigned as the target and distractor, respectively.
The A-weighted sound pressure level (L Aeq) of each target and distractor speech was 65 dB at theposition of the center of the listener’s head. The target and four distractors were simultaneously
presented from five loudspeakers.

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Figure 1 – Schema of the experimental setup. The listener sits on a chair at the center of the loudspeakerarray, facing the front (0 degrees).
2.3 Procedure
In the experiment, data was collected for two conditions: cue and probability-control. The orderof the two conditions was counterbalanced across the listeners. For both conditions, the listeners
were instructed to focus on the target speaker (i.e., female speaker) , and to write down the uttered
words on a response sheet as soon as they heard the words. Moreover, the listeners were asked tokeep their head stationary and straight ahead at 0 degrees during the entire session. One target word,uttered by the female speaker, was presented from one of the five loudspeakers, while four
distractors, uttered by the male speaker, were presented from the other four loudspeakers.
In the cue condition, the loudspeaker where the target speech sound would be presented wasindicated beforehand. To indicate the direction of this loudspeaker, a burst of 500 ms of white noise(including a 10 ms rise/fall, sound pressure level: 65 dB) was delivered via the loudspeaker,
1000 ms prior to the presentation of the speech sounds. The listeners were asked to direct theirattention to the loudspeaker from which the cue was presented. This condition consisted of
100 trials; five lists (i.e., 100 words) were assigned as the target speech sounds, and 400 words wereselected from the 600 distractor candidates and assigned as distractors. In one session, the fivetarget lists were separately assigned to five target loudspeakers in the directions of – 60, – 30, 0,+ 30, and + 60 degrees. Consequently, 20 target speech sounds were presented from each
loudspeaker. The order of the words and the loudspeakers where the target speech sounds were
presented were randomized.
In the probability-control condition, the direction was not explicitly indicated to the listeners. In
contrast, to implicitly attract attention to a specific loudspeaker, the probe-signal method wasapplied (20). Among the 400 trials, the target speech sound was presented from the loudspeakers at+ 30 degrees (or – 30 degrees) in 80% of the trials (hereafter the “primary angle”). In the remaining
20%, the target speech sound was presented from one of other four loudspeakers , chosen randomly(hereafter the “probe angle”). That is, 16 lists (i.e., 320 words) were presented from the primary
angle, whereas four lists (i.e., 80 words) were presented from one of the other four loudspeakers .
For half of the listeners, the loudspeaker at – 30 degrees was assigned as the primary angle. For theremaining listeners, the primary angle was + 30 degrees. With this procedure, we could expect that
listeners could be aware that most target speech sounds were presented from the loudspeaker at + 30
degrees (or – 30 degrees), resulting in attention directed at the primary angle. 

3. RESULTS
Word intelligibility scores are shown in Fig. 2. The scores are plotted as a function of theloudspeaker direction from which the target speech sound is presented. Data points and error bars
represent the mean and standard error, respectively, across listeners. Solid squares and open
triangles represent the results of the cue and probability-control conditions, respectively. To match

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the number of trials in each data point, the results of the probability-control condition at 0 degrees(or ±30 degrees) are the results of the last 20 trials among the 320 trials.
From this figure, it appears that the mean intelligibility score s in the probability-control condition
are approximately 15–20% lower than those in the cue condition, in all primary angle conditions. A
two-way repeated-measures analysis of variance (ANOVA) was performed on the mean data acrossall listeners with the condition (cue/probability-control) and target speech sound directions (– 60, –Figure 2 – Word intelligibility score as a function of the direction of target speech sound (a. the primary
angle is – 30 degrees, b. the primary angle is 0 degrees (Adapted from Teraoka et al. (10)), c. the primary
angle is + 30 degrees). Solid squares and open triangles represent the results of the cue and probabilitycontrol conditions, respectively. Error bars denote the standard error of the mean.
30, 0, + 30 and + 60 degrees) as the factors to each primary angle condition. In the – 30 degrees
condition, the main effect of conditions is close to significant (conditions: F 1,9 = 4.13, p = .073, η2G= .107, target speech directions: F4,36 = 5.31, p = .002, η2 G = .187, conditions × target speech sounddirections: F 4,32 = 1.66, p = .180, η2 G = .034). The post hoc test (Ryan’s method, p < .05) revealed
there are no significant differences. In the 0 degrees condition, only the main effects are significant(conditions: F 1,17 = 6.20, p = .023, η2 G = .070, target speech directions: F 4,68 = 6.03, p = .003, η 2G
= .082, conditions × target speech sound directions: F 4,68 = 2.24, p = .073, η2G = .040). The post hoc
test (Ryan’s method, p < .05) revealed significant differences in direction between + 30 and+ 60 degrees, – 60 and + 30 degrees, 0 and + 60 degrees, and – 30 and + 60 degrees. In the+ 30 degrees condition, the main effect of conditions is insignificant (conditions: F 1,9 = 0.91, p= .365, η2 G = .001, target speech directions: F 4,36 = 7.95, p < .001, η 2G = .219, conditions × target
speech sound directions: F 4,32 = 1.24, p = .031, η2 G = .040). The post hoc test (Ryan’s method, p< .05) revealed significant differences in direction between 0 and + 60 degrees, – 30 and+ 30 degrees, – 30 and + 60 degrees, and – 60 and 0 degrees. The results show the word
intelligibility in the cue condition is higher than that in the probability-control condition, thoughthese differences are not statistically significant.

4. DISCUSSION
In the present study, we investigated whether the spatial extent of auditory selective attention isdifferent between the frontal and oblique directions. In the cue condition, the word intelligibility
score was measured when the auditory spatial attention was explicitly directed to the loudspeakerfrom which the target speech sound was presented. In contrast, in the probability-control condition,
the word intelligibility score was measured when attention was implicitly directed to the primary
angles (i.e., + 30 or – 30 degrees) using the probe-signal method. Therefore, when the target speech
direction was not the primary angle, the auditory attention in the probability-control condition was
not directed to the target speech direction. The results show that the word intelligibility scores in thecue condition are higher (mean=15%) than those of the probability-control condition when the target
speech direction is not the primary angle. These results reveal that an improvement of speech
intelligibility by auditory spatial attention is observed regardless of the angle of attentional focus.
Notably, the results shown in Fig. 2 represent not only the effect of auditory spatial attention, but

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Figure 3 – Difference of word intelligibility score as a function of the direction of target speech sound(a. the primary angle = – 30 degrees, b. the primary angle = 0 degrees (Adapted from Teraoka et al. (10)),c. the primary angle = + 30 degrees). Solid squares represent the results of the difference these conditions.
Error bars denote the standard error of the mean.

Figure 4 – Difference of word intelligibility score as a function of the relative angular distance from theprimary angle. Thickest line, mid-thickness line, and thinnest line represent – 30, 0, and + 30 degrees ofthe primary angle condition, respectively. Solid squares represent the results of the difference these
conditions. Error bars denote the standard error of the mean.
also the effect of other factors, such as the release from masking. Therefore, to analyze the effect of
the auditory spatial attention, we extracted the effect of the attention by subtracting the scores of theprobability-control condition from those of the cue condition. Figure 3 shows the results as afunction of the target speech direction. Figure 4 shows the relative angular distance from theprimary angle when all three primary angles are aligned at 0 degrees. Figure 3 shows that thedifference at the primary angles is lower than those at any other probe angles. Furthermore, thisscore monotonically increases as the direction deviates from the primary angle, up to ± 60 degrees.
The spatial pattern may represent a spatial spread of auditory selective atte ntion. A one-way
repeated-measures ANOVA was performed on the mean data across all listeners, with the target
speech directions as a factor to each primary angle condition. In the – 30 degrees condition, there isno significance (conditions: F4,36 = 1.66, p = .180, η2 G = .072). In the 0 degrees condition, the main
effect is significant (conditions: F 4,36 = 1.24, p = .312, η2 G = .092). The post hoc test (Ryan’s method,p < .05) revealed a significant difference in direction between 0 and + 60 degrees. In the+ 30 degrees condition, there is no significance (conditions: F 4,36 = 1.19, p = .330, η 2 G = .090).
These results indicate that the spatial spread of the auditory selective attention is flat in all three
primary angle conditions except for the 0 degrees condition, as shown in Fig.4. However, theseresults seem to suggest that there is a peak of the function at each primary angle. Thus, if theexperiment were conducted with a larger number of listeners, we could expect that a significant
notch might appear at the primary angle, as in the 0 degrees condition.
In Fig. 2, as the distance from the target speech direction increases from 0 degrees, the observed
score also increases in all three primary angle conditions, in the two presentation conditions. This5768

result is inconsistent with the results of the previous study (8). The reason for the difference is theeffect of a spatial release from masking (4, 6, 21–23). In this experiment, the target speech soundand distractors were presented by five loudspeakers (– 60, – 30, 0, + 30, and + 60 degrees). Whenthe target speech sound was presented from 0 degrees, the numbers of distractors to left and right of
the listener were the same. In contrast, when the target was presented from other directions, thenumbers of distractors on the listener’s left and right were different. For example, when the target
sound was presented from the peripheral direction (e.g., ± 60 degrees), compared with to present
from the center ones, the distance between the target and distractor is relatively longer. Then, due tothe effect of the spatial release from masking, the effect of masking is reduced as the distance from
distractor to target sound. The results of the present study may reflect the above factor.
As mentioned in the introduction, the MAA broadens as the angular distance from the front (i.e.,
0 degrees) increases. This means that the auditory spatial resolution is not constant , and differs
depending on the angle. Thus, sound source localization is necessary when the auditory spatialattention is directed to a specific location. We expected that the spatial extent of the auditory
selective attention is affected by such factors (e.g., the spatial extent becomes broader as the
distance from 0 degrees increases). However, Fig. 3 and Fig. 4 indicate that the spatial extent of theauditory selective attention is similar in all three primary angle conditions. The results suggest that
there is no directional selectivity in the spatial extent of auditory selective attention. Thus, thepresent result is not consistent with our expectations. This seems to us to lead to an interesting
future study.

5. CONCLUSIONSIn the present study, we investigated whether the spatial extent of auditory selective attention isdifferent between the frontal and oblique directions. The results show that the spatial extent ofauditory selective attention is similar in all three primary angle conditions, which suggests that thesame factor determines spatial extent independently of attention directions.

ACKNOWLEDGEMENTS
This research was partly supported by JSPS KAKENHI Grant-in-Aid for Challenging
Exploratory Research (No. 17K19990) and Grant-in-Aid for JSPS Research Fellow (No.18J13203).

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