Degraded voices through mobile phones and their neural effects: A possible risk of using mobile phones during driving

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Transportation Research Part F 8 (2005) 331–340

Degraded voices through mobile phones and their neuraleffects: A possible risk of using mobile phones during driving

Tsuneo Kawano a, Sunao Iwaki b, Yoshitaka Azuma c,Toshimichi Moriwaki c, Takashi Hamada b,*

a Faculty of Engineering, Setsunan University, Neyagawa, Osaka 572-8508, Japanb National Institute of Advanced Industrial Science and Technology (AIST),

Kansai, 1-8-31, Midoriga-oka, Ikeda, Osaka 563-8577, Japanc Graduate School of Science and Technology, Kobe University, Kobe, Hyogo 657-8501, Japan

Received 6 September 2004; received in revised form 4 March 2005; accepted 28 April 2005

Abstract

We firstly studied qualities of voices transmitted from a mobile phone in a building to another in the

same building or in a car. The voices were found to be often degraded and the degradations were classified

in one of the three types: delay of transmission, spectral distraction (distractions in the spectral structure of

the voices) and silent interruptions. The interruptions occurred more frequently and longer if the car with

the phone for receiving was moving than at rest. Secondly, brain responses to the interruptions were mea-

sured with magnetoencephalography (MEG). It was found that the cortex was bilaterally activated both at

starts and ends of the interruptions. Our another study [Hamada, T., Iwaki, S., & Kawano, T. (2004).Speech offsets activate the right parietal cortex. Hearing Research, 195, 75–78] had shown that these activi-

ties are reduced to sources in the brain for auditory perception and auditory attention. This suggests that

listening to voices through a mobile phone during driving would allocate less resources for auditory percep-

tion and attention at moments of the interruptions.

� 2005 Elsevier Ltd. All rights reserved.

Keywords: Mobile (cellular) phone; Degraded voice; Interruption; Brain; A risk for driving; Auditory attention

1369-8478/$ - see front matter � 2005 Elsevier Ltd. All rights reserved.

doi:10.1016/j.trf.2005.04.016

* Corresponding author. Tel.: +81 727 51 8794; fax: +81 727 51 8416.

E-mail address: [email protected] (T. Hamada).

mailto:[email protected]

332 T. Kawano et al. / Transportation Research Part F 8 (2005) 331–340

1. Introduction

Mobile (cellular) phones are now widely used. As an example, the number of Japanese subscrib-ers of mobile phones exceeded 88 millions in July 2004 (Japanese Telecommunications CarriersAssociation), which corresponds to 69.1% of the total population. As the numbers of mobilephones increased, traffic accidents supposed to be due to uses of mobile phones during driving alsoincreased accordingly up to 1998 (Fig. 1). Although the number of accidents decreased in 2000 dueto an enforcement of the law for prohibiting uses of mobile phones during driving, the numberstarted to increase again thereafter. The law was thereby strengthened in November 2004, althoughit applies only to hand-held phones and still allowed uses of hands-free phones during driving.

Goodman, Tijerina, Bents, andWierwille (1999) have statistically described the risk of using mo-bile phones during driving. The risk was also experimentally testedwith the dual-task paradigm, oneconversation through mobile phones and the other driving a car (Alm & Nilsson, 1995; Barkana,Zadok, Morad, & Avini, 2004; Brookhuis, de Varies, & de Waard, 1991; Brown, Tickner, &Simmonds, 1969; Consiglio, Driscoll, Witte, & Berg, 2003; Kawano, Nishida, Hashimoto, &Moriwaki, 1998; Laberge-Nadeau et al., 2003; Lamble, Kauranen, Laakso, & Summala, 1999;McKnight & McKnight, 1993; Nelson & Nilsson, 1990; Nunes & Recarte, 2002; Patten, Kircher,Ostlund,&Niosson, 2004; Richard et al., 2002; Stein, Parseghian, &Allen, 1987; Treffner&Barrett,2004). All of these studies proved unfavorable interference between the two tasks. The interferencewas composed ofmanual, ocular and cognitive factors. Namely, if the hand is used formanipulatingamobile phone, it cannot be used for driving, and if the eyes gaze at the phone, they cannot be simu-ltaneously used to look at the scene in front of the car. The cognitive factors include attention, butstill remain to be rather vague.Haigney andWesterman (2001) summarized that these factors shouldbe studied more analytically in more realistic situations. We here asked specific questions: Whether

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Fig. 1. Temporal evolutions of the number of subscribers of mobile phones (circle and the right scale) and of the traffic

accidents supposed to be due to uses of mobile phones during driving (columns and the left scale) in Japan. A law for

inhibiting uses of mobile phones during driving was firstly enforced in November 1999. Redrawn from the report by

Japanese Telecommunications Carriers Association, 2003.

T. Kawano et al. / Transportation Research Part F 8 (2005) 331–340 333

voices through mobile phones were degraded more seriously in a moving car than in a parked car?;How such degradations would burden the listener�s brain?We firstly studied degradations of voicesbetween twomobile phones in Section 2, and then neural activities to one type of the degradations inSection 3. Finally, possible effects of these degradations on driving are discussed in Section 4.

2. Degradations of voices through mobile phones

2.1. Methods

We studied voices between two mobile phones of the TDMA (time division multiple access) sys-tem. One of the phones, with the carrier frequency at 1.5 GHz, was placed in a room on the 6thfloor of a university building and used for sending voices. The other phone, with the frequency at800 MHz, was positioned either in the same room or in a car and used for receiving the voices.The car was either moving at about 40 km/h or at rest within a zone of radio-wave transmission(cell) different from that for the other phone. Either short vowel [u] or longer one [u:] was pro-nounced repeatedly at a rate of approximately once a minute by a male for transmissions. Thevoices both before and after the transmissions were recorded in personal computers for later pro-cessing. The measurements were carried out at around 2:00 p.m.

2.2. Results

Voices after the transmissions were found to be degraded and the degradations were classifiedinto one of the three types.

The first type was delay of transmissions. The upper trace of Fig. 2(a) shows the voice [u] fed tothe phone for sending, and the lower trace shows the voice received by the other phone. Thephone for receiving was not placed in a car, but in the same room as the other phone for preciselymeasuring the delay. The delay was about 370 ms in the figure and its average ± SD was317 ± 34 ms.

The second type of the degradations was spectral distractions or distractions in the spectralstructure of the voices. When a long vowel [u:] was sent from one of the phones in the building,voice received by the other phone in the moving car had the sonogram (power spectrum vs. time)shown in Fig. 2(b). Although the formant structure of the vowel was first apparent, it was sud-denly distracted after the time marked by ., which made the voice hard to be recognized as[u:]. The distractions started and ended abruptly along time. Total length of the distractionsamounted 2.3% to of the time of measurement when the car was at rest, but it increased up to5.5% of the measurement time when the car was moving.

The third type of degradations was silent interruptions. When a long vowel [u:] was sent fromone of the phones (upper trace of Fig. 2(c)), the voice in the other phone within the moving carwas suddenly interrupted and kept to be silent for 300 ms (the lower trace of the subfigure). Thevoices during the interrupted periods were thereby missed. Fig. 3 shows the frequency of occur-rences of the interruptions as a function of their duration: The interruptions were longer andmore frequent when the phone for receiving was placed in the moving car (gray columns) thanit was in the car at rest (black columns). Numerically, the average frequency of occurrences of

Fig. 2. Three types of degradations in voice quality through mobile phones. (a) Transmission delay. Brief sounds [u] fed

to one of the phones (upper trace) were transmitted to the other phone after delays of 370 ms (lower trace). Ordinate,

sound pressure (arbitrary unit). Abscissa, time. (b) Spectral distraction. The sonogram of long and constant vowel [u-:]

was suddenly distracted after the time indicated by .. Ordinate, frequency. Abscissa, time. (c) Silent interruption. Long

vowel [u:] fed to one of the phone (upper trace) was suddenly interrupted and made to be silent for 300 ms in the other

phone (lower trace). Ordinate, sound pressure (arbitrary unit). Abscissa, time.


the interruptions was 4.8 times per minute when the car was at rest, but it increased to 6.4 whenthe car was moving. Besides, medians and averages ± SD of their duration were 236.5 ms and232.1 ms ± 114.2, respectively when the car was at rest, but these numbers increased up to325.0 ms and 424.4 ms ± 336.6 when the car was moving.

2.3. Discussion

Degradations of voices through mobile phones were classified in one of the three types: spectraldistraction, transmission delay and silent interruption. As far as we know, the last two types of the

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Fig. 3. Frequency histogram of the silent interruptions as a function of their lengths. Ordinate, the frequency of

occurrences of the interruptions (times per minute). Abscissa, length of the interruptions grouped into classes for

200 ms. Filled columns, during the car was parked. Gray columns, during the car was moving.


degradations have been already described qualitatively, and attributed to the highly complicatedsignal processing for reducing resources for the transmission (Janssen, De Vleeschauwer, Buchli,& Petit, 2002; Robinson, 2003). We found that these degradations were more serious, i.e., longerin the interruptions and the spectral distractions and more frequent in the interruptions, when thephone for receiving was placed in a moving car than in a car at rest. A consequence of this findingwill be discussed in Section 4. Although these degradations are known to decrease subjective quali-ties of the voices (Enderes, Khoo, Somerville, & Samaras, 2002; Markopoulou, Tobagi, &Karam, 2003), it is not known how such degradations affect the neural processing in the humanbrain. In the next section, we will study neural responses to one of the degradations, i.e., theinterruptions.

3. Neural responses to the interruptions

3.1. Methods

3.1.1. Auditory stimuli

Among the three types of degradations, the interruptions were chosen as stimuli for neuralexperiments, because they were easy to be produced experimentally. Eleven subjects (right-handed, Japanese) participated in this study. During an experimental session, the subject listenedto stories spoken in their native language for 6 min. The stories were interrupted 60 times at tim-ings chosen randomly, only if the interruptions did not overlap with silent periods. The timingswhen the interruptions started, i.e., offsets of the voices, were marked with triggers for later pro-cessing. While the stories were interrupted, the subjects generally had to make cognitive leapsfrom the offsets to the onsets (i.e., restarts) of the voices. Within a session, the ear of stimulationwas either left or right and lengths of the interruptions were either 1000, 500 or 200 ms. Each sub-ject participated in 3.7 sessions on an average.


3.1.2. Measurements and analyses of neural activity

Brain activities were measured with magnetoencephalography (MEG; NeuroMag-122,Finland). Informed consents were obtained from the subjects before experiments. MEG signalswithin a session were averaged with respect to the triggers, where the numbers of averagingwas more than 50. The averaged responses to interruptions with one of the lengths were essentiallythe same irrespective of stimulated ear and subjects. Thus, the responses with each length of inter-ruptions were further grand-averaged across the ears of stimulation and the subjects. Peakresponses at offsets and onsets of the voices have previously been reduced to three equivalent cur-rent dipoles (Hamada, Iwaki, & Kawano, 2004) with the use of multi-dipole model (Hamalainen,Hari, Ilmoniemi, Knuutila, & Lounasmaa, 1993). Positions of the dipoles in one of the sessionswere represented on the brain surface of the subject.

3.2. Results

Fig. 4(a) shows grand-averaged responses above the whole cortex to interruptions which lastedfor 1000 ms. Peaks are evident in several channels above the both hemispheres. Two tracessurrounded by small circles are enlarged in Fig. 4(b). Traces in Fig. 4(c) and (d) represent grand-averaged responses in the same channels, but in different sessions where lengths of the interrup-tions were 500 ms in c and 200 ms in d. Two peaks are evident in each of the traces. The earlierpeaks marked with • always had latency about 120 ms after the triggers, while the later peaksmarked with � are separated from the first by 1000 ms in b, 500 ms in c and 200 ms in d. Sincethese are averages with respect to offsets of the voices, the earlier peaks represent off responsesand latter�s on responses of the voices. Our previous study analyzed the peaked activities in eachof the averaged responses in a session. The activities were then reduced in three dipoles in thebrain, two in each of the left and the right temporal cortex and one in the right parietal cortex,irrespectively of the ear of stimulation and lengths of interruptions. As an example, interruptionsfor 200 ms given to the right ear of one of the subjects yielded three dipoles, whose positions wereplotted on the brain surface of the subject (Fig. 5). Note that the dipole in the parietal cortex waswithin the right hemisphere.

3.3. Discussions

Interrupted voices elicited peaked activities both at offsets and onsets of the voices within theboth hemispheres. The peaked activities had been reduced to two dipoles in each of the temporalcortices and one in the right parietal cortex (Hamada et al., 2004). The former two are due tochanges in acoustic energy of the sounds, because they were also activated by simple transientstimuli such as tone bursts. Previous studies have attributed the latter to auditory attention, be-cause the right parietal was activated when subjects pay attention to auditory events, such aschanges in frequency (Levanen, Ahonen, Hari, McEvoy, & Sams, 1996; Zatorre, Mondor, &Evans, 1999), in intensity (Belin et al., 1998; Paus et al., 1997), in location (Zatorre et al.,1999), in stimulated ear (Alho et al., 2003), in duration (Kasai et al., 1999; Levanen et al.,1996) and in ISI (inter-stimulus-interval) of repetitive brief sounds (Levanen et al., 1996). This evi-dence thereby suggests that the interruptions of voices activated neural systems for auditory per-ception and auditory attention.

Fig. 4. (a) Grand-averaged neural responses above the whole cortex to interruptions for 1000 ms. Responses to the left

ear and to the right ear were assembled and the number of subjects was 11. Vertical bars represent offsets of the voices

and 100 fT/cm and horizontal bars 500 ms. (b) Responses in two of the channels marked by small circles in (a). Others

are the same as in (a). Responses at offsets and onsets of the voices are represented by d and�, respectively. (c) and (d)

Same as (b), except that lengths of the interruptions were 500 ms in (c) and 200 ms in (d). Others are the same as in (a).


4. General discussion

Voices between two mobile phones were degraded in one of the three types: spectral distortions,delay and interruptions. Neuromagnetic studies then showed that the interruptions activate the

Fig. 5. Positions of the dipoles above the cortical surfaces. One dipole was positioned on the left temporal cortex.

Within the right hemisphere, one was on the temporal cortex and another on the parietal cortex.


bilateral temporal cortices and the right parietal cortex. The activities in the right parietal cortexwere considered to be due to auditory attention. The other types of degradations should also acti-vate this part of the cortex, because previous studies have shown that this part of the cortex isactivated by attention to auditory changes in frequency (Levanen et al., 1996; Zatorre et al.,1999) and in timings of occurrence of sounds among their repetitions (Levanen et al., 1996).

Although vision is essential for driving, audition is also required for driving. As an example, thein-vehicle information systems often utilize auditory cues for navigation and alerting (Liu, 2001;Wiese & Lee, 2004). Audition also provides information for the drivers to estimate the vehiclespeed (Evans, 1970) and to detect events outside the car where visual cues are not feasible. If adriver listens to voices through a mobile phone during driving, his resources (Kramer & Spinks,1991) for auditory perception and auditory attention should already be used even if voicesthrough the phones were not degraded. The resources should be further used when the voicesthrough the mobile phone are degraded, which implies further risks of using mobile phones duringdriving. The risks during driving should be more frequent than during parking, because the degra-dations occur more frequently in a moving car than in a parked car.

Acknowledgement

The authors appreciate Prof. A. Muzet�s comments.

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Degraded voices through mobile phones and their neural effects: A possible risk of using mobile phones during driving