COGNITION
Cognition 73 (1999) B55±B66
www.elsevier.com/locate/cognit

Temporal cortex activation during speech
recognition: an optical topography study
Hiroki Sato a, Tatsuya Takeuchi a, Kuniyoshi L. Sakai a,b,*a

Department of Cognitive and Behavioral Science, Graduate School of Arts and Sciences,
The University of Tokyo, Komaba, Tokyo 153-8902, Japanb
CREST, Japan Science and Technology Corporation (JST), Tokyo, Japan
Received 9 August 1999; accepted 14 September 1999

Abstract
Cortical activity during speech recognition was examined using optical topography (OT), a
recently developed non-invasive technique. To assess relative changes in hemoglobin oxygenation, local changes in near-infrared light absorption were measured simultaneously from 44
points in both hemispheres. A dichotic listening paradigm was used in this experiment, inwhich target stimuli and non-target stimuli were presented to different ears. Subjects wereasked to track targets and to press a button when targets shifted from one ear to the other. We
compared three tasks: (i) a control task, in which a tone was used as the target; (ii) a repeat
task, in which the target was one repeated sentence; (iii) a story task, in which the targets were
continuous sentences of a story. The activity for the story task, compared with the repeat task,
was localized in the left superior temporal cortex. Relative to the control task, we observed inthis region a larger increase in oxyhemoglobin concentration and a decrease in deoxyhemoglobin concentration in the story task than those in the repeat task. These results suggest thatthe activity in the left temporal association area re¯ects the load of auditory, memory, andlanguage information processing. q 1999 Elsevier Science B.V. All rights reserved.
Keywords: Speech recognition; Temporal association area; Hemoglobin oxygenation

1. Introduction
Optical topography (OT) is a recently developed non-invasive technique of functional mapping, which measures temporal changes in hemoglobin oxygenation
simultaneously from multiple regions (Koizumi et al., 1999; Maki et al., 1995;* Corresponding author. Tel.: 181-3-5454-6261; fax: 181-3-5454-6261.
E-mail address: sakai@mind.c.u-tokyo.ac.jp (K.L. Sakai)
0010-0277/99/$ - see front matter q 1999 Elsevier Science B.V. All rights reserved.
PII: S 0010-027 7(99)00060-8

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Yamashita, Maki & Koizumi, 1996; Yamashita, Maki & Koizumi, 1999). OT is a new
extension of near-infrared spectroscopy (NIRS) used to acquire a topographicalimage, whereas NIRS measures spectroscopic re¯ection and scattering from a single
region with a light emitter and a detector (Chance, Zhuang, Unah, Alter & Lipton,
1993; Hoshi & Tamura, 1993; Kato, Kamei, Takashima & Ozaki, 1993; Villringer,
Planck, Hock, Schleinkofer & Dirnagl, 1993). The technological development fromNIRS to OT is conceptually similar to that from nuclear magnetic resonance (NMR)
spectroscopy to magnetic resonance imaging (MRI). Measurement from multiple
regions is achieved by independently modulating the intensities of each radiatedlaser beam, that is, by frequency encoding of spatial information (Yamashita, Maki
& Koizumi, 1999). The minimum distance between measurement points of thecurrent OT system is 21 mm, and minimum sampling interval is 100 ms.
There are several advantages of using OT over other functional mapping techniques. First, it is possible to independently measure the temporal changes in theconcentrations of oxyhemoglobin and deoxyhemoglobin. Secondly, there is no
scanning noise interfering with any auditory stimuli. Thirdly, its signal-to-noise
ratio is relatively high, allowing for the observation of cortical activity even witha single trial. Finally, OT does not require a head constraint; thus its safe application
to infants may make developmental mapping studies possible. One major disadvantage of OT is that its measurement is restricted to the cortical surface. Nevertheless,
OT has a potential to open a new dimension for mapping human cognitive functions.
Here we report the ®rst successful application of this technique to the study ofcortical responses during speech recognition. We have devised a dichotic listening
task that requires intensive tracking of speech sounds and have compared a task withsuccessive sentences of a story and that with repeated sentences. A portion of thisstudy has been reported in abstract form (Sakai, Sato & Takeuchi, 1999).
2. Methods
2.1. Subjects
Seven male native Japanese speakers (ages: 21±32 years) participated in thepresent study. They showed right-handedness (laterality quotients: 81±100) by the
Edinburgh inventory (Old®eld, 1971). The subjects' consent was obtained according
to the declaration of Helsinki. Approval for the human experiments was obtained
from the institutional review board of the University of Tokyo, Graduate School ofArts and Sciences.
2.2. Auditory stimuli
The auditory stimuli used in this study were speech sounds and non-speechsounds that were presented in speech-recognition tasks and a control task, respectively. All speech sounds were digitized (16 bit, 11 025 Hz) using speech synthesis
software (Oshaberi-mate, Fujitsu, Tokyo, Japan) that converts Japanese written text
into sound waveforms. Sine-wave tone and white noise used in the control task wereH. Sato et al. / Cognition 73 (1999) B55±B66

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synthesized by sound-editing software (Sound Forge XP, Sonic Foundry Inc.).
Speech sounds and non-speech sounds were presented with a stereophonic headphone at the peak of 60- and 58-dB sound pressure levels, respectively.
2.3. Task paradigm
A dichotic listening paradigm was used for all tasks in this study. Target stimuli
and non-target stimuli were simultaneously presented to different ears every 2 s, anda target was alternatively presented to either the left ear or the right ear at random
intervals. The frequency of presentation of targets was balanced between the left andright ears. Subjects were asked to track targets and to press a button when a target
was shifted to the other side.
In the control task, a tone (sine wave: 1000 Hz) and white noise (low-pass cut-off
frequency: 1000 or 10 000 Hz) were presented as targets and non-targets, respectively (duration: 1000 ms). In order to con®rm that subjects performed tasks byrecognizing targets, a tone of different pitch (sine wave: 300 Hz) was presented as a
non-target at a lower rate. These probe stimuli prevented subjects from performing
the tasks by tracking non-targets only.
We used two speech-recognition tasks: (1) a repeat task, in which the targets
consisted of one repeated sentence, and (2) a story task, in which the targets weresuccessive different sentences of a continuous story. In the repeat task, one sentence(duration: 1000±1530 ms, mean: 1270 ms) was repeated for a 36-s period, anddifferent sentences were used in each period. Successive sentences for the story
task were divided into phrases at natural break-points (duration: 590±1650 ms,
mean: 1150 ms) for the presentation. In both tasks, a non-target was obtained byscrambling the sequence of syllables of the correspondent target. These jumbled
stimuli conformed to the rules of Japanese phonotactics but had no meaning. A
sentence different from the target for the repeat task and contextually anomalous
phrases for the story task were used as probe stimuli. These tasks, therefore, cannot
be completed appropriately by identifying speech sounds without paying attention totheir meanings.
2.4. Experimental procedures
During the experiments, the subject sat in a chair with his eyes closed in a darkroom. A pair of head shells with probe sockets was attached on both sides of thesubject's head. In a single run with the repeat tasks (R), a 36-s period for the control
task and the repeat task alternated three times, with one more control period at theend of a run. A single run with the story tasks (S) had the same alternation. Twelve
runs were performed in the order of alternating S-R-R-S and R-S-S-R in one
imaging session. Each subject was tested in at least two sessions. The ®rst run ofeither S or R was counterbalanced by subsequent sessions.
After the experiment, a three-dimensional (3D) magnetic resonance (MR) image
was taken of the subject to reconstruct a cortical surface image. Alfacalcidol beads(0.25 mg) buried in a head shell were used as MR markers, which can be identi®edon the MR image as spheres (diameter: 3 mm).

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2.5. Optical topography procedures
We used two OT systems with the same calibration (ETG-100 and ETG-A1;
Hitachi Medical Corporation, Tokyo, Japan), one for each hemisphere. Near-infrared laser diodes with two wavelengths (ranges: 782±793 and 823±832 nm) wereused as the light sources (maximum intensity: 2 mW/mm 2: intensity modulation: 1±
10 kHz). The re¯ected lights were detected with avalanche photodiodes located 30
mm from an incident position. Using lock-in ampli®ers, the detected signal was
separated into individual light sources with each wavelength (Yamashita et al.,1999). The transmittance data ln T(l ,t) for a wavelength (l ) at measurement time(t) were obtained for each run.
The position of each MR marker was a midpoint between an incident point and a
detection point. Each measurement point was de®ned as an intersection of thecortical surface and a perpendicular line from a marker point (Maki et al., 1996).
Twenty-two points in each hemisphere were simultaneously measured at minimum
spatial intervals of 21 mm, and each point was sampled every 500 ms. The measured
region in each hemisphere centered on the Sylvian ®ssure and covered an area of
6 £ 12 cm 2 (Fig. 1a).
2.6. Data analyses
Time-series data of ln T(l ,t) in a single run were baseline-corrected with a curveof the third degree, which was ®tted for time points during the control task (Fig. 2).
Either intrasubject data or intersubject data of multiple runs (R or S) were thenaveraged for each wavelength before calculating the relative hemoglobin changes.
In the case of calculating the hemodynamics in the story run (S) relative to that in therepeat run (R), averaged runs under the two conditions were directly compared. We
also compared R or S with the baseline curve in a similar manner. Because hemodynamic signals are relative changes from the baseline in the latter case, a longrange ®tting, which spans more than one cycle of control-stimulation-control, should
be used to estimate a baseline level throughout a single run (Fig. 2). By comparing ln
T(l ,t) under two conditions, the relative changes in oxyhemoglobin concentration(Coxy) and deoxyhemoglobin concentration (Cdeoxy) were calculated (Maki et al.,
1995; Yamashita et al., 1996).
Relative hemodynamic changes were assumed to be delayed 6 s from the task
periods in this study, and each shifted period of the story and repeat tasks wasde®ned as an activation period. A correlation coef®cient (r) of hemoglobin time
points with a box-car waveform (each period: 36 s, delay: 6 s) was calculated foreach measurement point (Bandettini, Jesmanowicz, Wong & Hyde, 1993; Watanabe
et al., 1998), and we created an r-map from the r-values. As a threshold for the rvalues, 0.73 or 20.73 was chosen for statistical signi®cance (P  0:05). This levelof signi®cance was determined from an equation
P  2Q TH £ N 1=2 
where Q(u) represents the upper probability of normal distribution above u, TH is a

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Fig. 2. Representative time courses of transmittance data at CH16 for one subject. (a) Data for awavelength of 790 nm. (b) Data for a wavelength of 832 nm. Thick solid lines show the averagedtransmittance data ln T(l ,t) for each wavelength (l ) at time (t) in an arbitrary unit (a.u.). Note theprominent signal changes, which synchronize with each onset and end of three periods of the repeat
task (R). For baseline correction, the data are ®tted for time points during the control task with a curve ofthe third degree (thin solid lines). The relative difference between data for the two wavelengths is notaffected when only linear interpolation is applied (broken lines), but we found that ®tting with a thirddegree curve was better than linear ®tting for a long-range ®tting, which resulted in a better signal-to-noise
ratio.

Fig. 1. Superior temporal cortex activation in the story task. (a) The measurement points in the left
hemisphere. The numbers represent channel numbers (CH) for the measurement points. The right hemisphere has the same arrangement of measurement points (CH 1 at the superior-anterior corner). Corticalsurface images were reconstructed from 3D MR images of a representative subject. (b) The r-map of Coxyin the story task relative to the repeat task. Circles at CH 16 (r  0:73) and CH 21 (r  0:84) are shown as
activation points. The relative size of each circle represents the r-value. (c) The r-map of Cdeoxy in the story
task relative to the repeat task. Activation at CH 21 (r  20:73) is shown. The r-maps for the righthemisphere are not shown here because there was no signi®cant activation in this comparison (r , 0:5).

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threshold of r, and N is the number of samples. N should be the number of independent samples, and here we assumed N  7, which was the number of alternatedperiods in each run.

3. Results and discussion
3.1. Task performance
The behavioral accuracy and reaction times are shown in Table 1. Analysis ofvariance (ANOVA) indicated no main effect of tasks in the total performance(F 2; 18  2:7, P . 0:05), or in the probe performance (F 2; 18  3:3,
P . 0:05). On the other hand, there was a main effect of tasks in the reaction
time (F 2; 18  7:5, P , 0:005). Post-hoc tests (Fisher's PLSD) revealed a difference between control and repeat tasks (P , 0:05), and a difference between
control and story tasks (P , 0:005). The difference between repeat and story
tasks, however, was not signi®cant (P . 0:1). These results suggest that the repeat
and story tasks were equally balanced in terms of behavioral control for task
dif®culty.
3.2. Mapping the difference between the story and repeat tasks
The r-map for the hemodynamics in the story run relative to that in the repeat run
shows a focal activation in the left superior temporal cortex (Fig. 1b,c). In these®gures, r-maps for averaged data among subjects were superimposed on a representative cortical surface image of one subject. Two measurement points at channel
16 (CH 16) and channel 21 (CH 21) showed signi®cant activation in Coxy (Fig. 1b).
These two measurement points were on the superior and middle temporal gyri.
Comparing the individual mean hemoglobin changes during the story and repeat
tasks (at a plateau level, from 10 s after the onset to the end of the task period) of CH
16 and those of CH 21, ANOVA (subjects £ channels £ periods) indicated themain effect of channels (F 1; 32  4:2, P , 0:05) and no other main effects. The
increase in Coxy at CH 21 was signi®cantly larger than that at CH 16. Moreover, ther-map in Cdeoxy (Fig. 1c) showed CH 21 as a signi®cant activation point. These

Table 1
Behavioral performance for tasks aTask

Total accuracy (%)

Probe accuracy (%)

Reaction time (ms)Control
RepeatStory

97 ^ 1.0
97 ^ 1.2
93 ^ 1.6

98 ^ 0.8
96 ^ 1.3
94 ^ 1.1

660 ^ 59
870 ^ 73990 ^ 49aMean and standard errors are shown (N  7).

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results showed that the activation in the story task relative to the repeat task was
more prominent in the mid-lateral part (CH 21) of the left temporal cortex.
3.3. Spatial registration
We carefully assessed the measured areas among subjects using their 3D MR
images. Based on Talairach coordinates (Talairach & Tournoux, 1988), the positions of measurement points were determined for each subject. The largest distancein the positions of the same measurement point among subjects was less than
18 mm in both hemispheres. The activated measurement points shown in Fig.
1b were con®rmed to be on the superior and middle temporal gyri in all subjects(CH 16: x  265 ^ 2:0, y  236 ^ 6:3, z  16 ^ 5:0; CH 21: x  264 ^ 1:9,
y 248 ^ 6.5, z  5:9 ^ 5:5).
3.4. Hemodynamic differences between the story and repeat runs
The hemodynamics in the story and repeat runs relative to the baseline were
further examined. The temporal changes at CH 16 and CH 21 are shown in Fig.
3. With a delay of 6 s, an increase in Coxy synchronized with each onset of the storytask, and after reaching a plateau, Coxy returned to the baseline level at the end of thetask (Fig. 3a,b). Although a decrease in Cdeoxy also synchronized with each period of
the story task, Cdeoxy did not exactly mirror the temporal dynamics of Coxy. Similar,
but smaller, changes in both Coxy and Cdeoxy were observed in the repeat run (Fig.

Fig. 3. Hemodynamics in speech-recognition tasks relative to the control task. (a) The story run at CH 16.
(b) The story run at CH 21. (c) The repeat run at CH 16. (d) The repeat run at CH 21. Thick lines show themostly positive temporal changes of Coxy, whereas thin lines show the mostly negative temporal changesof Cdeoxy. These temporal changes were calculated from averaged data among subjects. There are three
periods of either the story task (S) or the repeat task (R) in each run.

H. Sato et al. / Cognition 73 (1999) B55±B66

B633c,d). These results suggest that the hemodynamics re¯ects the processing ofcomplex temporal and spectral features related to speech sounds.
These two measurement points (CH 16 and CH 21) showed similar hemodynamics, which was con®rmed by signi®cant temporal correlations (P , 0:0001)
in the story task (Coxy: 0.97, Cdeoxy: 0.80) and in the repeat task (Coxy: 0.88, Cdeoxy:0.65). Although CH 16 did not show signi®cant activation for Cdeoxy in the directcomparison (Fig. 1c), the hemodynamics at both measurement points were parallel
when compared with the baseline.
After the two measurement points were averaged, the individual mean hemoglobin changes in the activation periods were statistically compared between the story
and repeat runs (Fig. 4). Both the increase in Coxy and decrease in Cdeoxy during thestory task were two times larger than those during the repeat task. ANOVA (subjects£ tasks £ periods) was performed separately for Coxy and Cdeoxy. This analysis
indicated a signi®cant main effect of tasks (Coxy: F 1; 12  36, Cdeoxy:
F 1; 12  36, P , 0:0001) without any interactions.
3.5. Relationships between oxyhemoglobin and deoxyhemoglobin dynamics
We further examined two types of correlations between Coxy and Cdeoxy dynamics.
Firstly, mean changes of either Coxy or Cdeoxy in each activation period were compared

Fig. 4. Mean hemoglobin changes in the activation periods relative to the baseline. Each sample isintrasubject-averaged data of mean hemoglobin changes during each activation period, averaging CH
16 and CH 21. Error bars indicate the standard errors (n  21). The ®lled bars denote mean hemoglobinchanges in the story task, and the open bars denote changes in the repeat task. According to post-hoc tests(Fisher's PLSD), the differences between the story and repeat tasks were signi®cant in both Coxy and Cdeoxy(*P , 0:01).

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among subjects (CH 16 and CH 21 averaged). The intersubject correlation coef®cient
between mean Coxy changes and mean Cdeoxy changes was signi®cantly negative in thestory task (20.71, P  0:0001) and in the repeat task (20.86, P , 0:0001). In bothtasks, the more the mean Coxy changes increased, the more the mean Cdeoxy changes
decreased. This result suggests that mean changes of both Coxy and Cdeoxy are usefulindices of task activation that can be used for functional mapping.
Secondly, we compared each corresponding time point of Coxy and Cdeoxy in theactivation periods of the story run for intersubject-averaged data. As indicatedabove, the exact temporal dynamics of Cdeoxy did not mirror those of Coxy. Accordingly, the temporal correlation coef®cient between Coxy and Cdeoxy was not signi®cant(0.11, P . 0:1, CH 16 and CH 21 averaged). These results indicate that the temporalchanges of Coxy and Cdeoxy may re¯ect different physiological processes whose
temporal dynamics are dependent over the long term (,30 s) but are different in
the short term (,10 s).
3.6. Laterality
Hemispheric differences were examined by separately analyzing the temporal
dynamics of Coxy in the story and repeat runs. Channels (CH) for the measurement
points with signi®cant r-values are listed in Table 2. CH 16, 20, and 21 were locatedon the superior temporal cortex, and CH 15 and 19 were found on the Sylvian ®ssurein almost all hemispheres. Some of these measurement points showed activation inboth hemispheres. It is clear that wider regions with more measurement points wereactivated in the story task than the repeat task in both hemispheres.
After the measurement points shown in Table 2 were averaged within eachsubject, the mean Coxy changes in each activation period were examined among
subjects. ANOVA (subjects £ hemispheres £ tasks £ periods) indicated nomain effect of hemispheres (F 1; 44  0:10, P . 0:1), but there was a signi®cantinteraction between hemispheres and tasks (F 1; 44  5:5, P , 0:05). Separate
ANOVA for hemispheres indicated a main effect for tasks only in the left hemisphere (left, F 1; 12  12, P , 0:01; right, F 1; 12  0:68, P . 0:1). This result is
consistent with the r-map of direct comparison between the story and repeat runs
(Fig. 1).
Table 2Comparison of measurement points with activation
Hemisphere

Task

Measurement points a

Left

Story
Repeat15, 16, 19, 20, 21
16, 20

Right

Story
Repeat15, 16, 19, 20
15, 19, 20

aNumbers shown are channels (CH) for the measurement points whose r-values were above thethreshold of r  0:73. These r-values were obtained by using Coxy time courses, which were calculated
from averaged data among subjects. These CH numbers correspond to positions in Fig. 1a.

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4. General discussion
There are two major ®ndings in the present OT studies. First, focal activation was
found in the left superior temporal cortex, preferentially for the story task over the
repeat task. Compared with the baseline, we con®rmed that an increase in Coxy changes
and a decrease in Cdeoxy changes synchronized with each period of the story run.
Although similar changes were observed in the repeat run, the signal changes in therepeat run were half those in the story run. Secondly, we found a correspondence anddissociation between oxyhemoglobin and deoxyhemoglobin dynamics. The meanchanges of Coxy and Cdeoxy in each activation period were negatively correlated,while the exact temporal dynamics of Coxy and Cdeoxy did not mirror each other.
There are some possible cognitive factors that are differentially involved in thestory and repeat tasks. Repeating one sentence in the repeat task may cause a
habituation of cortical responses. However, Cdeoxy in the repeat task did not show
an apparent decrease in signals after reaching the plateau level. A sustained habituation effect in the repeat task, if present, might result in a lack of Cdeoxy change during
the activation period, in contrast to Cdeoxy in the story task (Fig. 3). But Coxy in therepeat task showed signal changes parallel to those of Coxy in the story task.
Although we cannot exclude the involvement of transient habituation before reaching the plateau level, such a general repetition effect would have in¯uenced many
cortical regions, which was not the case in our observations.
Critical differences in cognitive factors between the story and repeat tasks would
be the load of processing speech stimuli. Recognition of successive different
sentences of a story demands more auditory, memory, and language information
processing than the recognition of repeated sentences. The selective activation in the
superior and middle temporal gyri reported here is consistent with the role of the
primate temporal association area in memory storage and memory retrieval (Sakai &Miyashita, 1993). Further, our ®nding is consistent with a previous PET study thatclearly showed an activation of the left superior and middle temporal gyri whensubjects listened to continuous speech in their native language (Mazoyer et al.,1993). Moreover, the left middle temporal gyrus was activated only in that story
condition among other conditions such as distorted stories, matching with the prominent activation of CH 21 in the present OT study.
From the current study, it is clear that the OT technique can be successfully
applied to map the functional localization of cognitive factors, as well as to measure
the temporal dynamics of cognitive activity. Because we found a correspondence
and dissociation between oxyhemoglobin and deoxyhemoglobin dynamics, OT has
the potential to provide novel information not previously obtained with otherimaging techniques. Thus OT will open up new possibilities for studying cognitive
function in the human cerebral cortex.
Acknowledgements
We would like to thank Dr Juro Kawachi for his encouragement; Dr Hideaki

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H. Sato et al. / Cognition 73 (1999) B55±B66

Koizumi, Dr Atsushi Maki and Mr Yuichi Yamashita for their technical advice; Dr
Eiju Watanabe and Dr David Embick for their helpful discussion; Mr Ryuichiro
Hashimoto, Mr Fumitaka Homae and Dr Kyoichi Nakajima for their technicalassistance; and Ms Hiromi Matsuda for her administrative assistance. This research
was supported by a CREST grant from JST to KLS.
References
Bandettini, P. A., Jesmanowicz, A., Wong, E. C., & Hyde, J. S. (1993). Processing strategies for timecourse data sets in functional MRI of the human brain. Magnetic Resonance in Medicine, 30, 161±173.
Chance, B., Zhuang, Z., Unah, C., Alter, C., & Lipton, L. (1993). Cognition-activated low-frequency
modulation of light absorption in human brain. Proceedings of the National Academy of Sciences of
the United States of America, 90, 3770±3774.
Hoshi, Y., & Tamura, M. (1993). Detection of dynamic changes in cerebral oxygenation coupled toneuronal function during mental work in man. Neuroscience Letters, 150, 5±8.
Kato, T., Kamei, A., Takashima, S., & Ozaki, T. (1993). Human visual cortical function during photic
stimulation monitoring by means of near-infrared spectroscopy. Journal of Cerebral Blood Flow andMetabolism, 13, 516±520.
Koizumi, H., Yamashita, Y., Maki, A., Yamamoto, T., Ito, Y., Itagaki, H., & Kennan, R. (1999). Higher-orderbrain function analysis by trans-cranial dynamic NIRS imaging. Journal of Biomedical Optics, 4, 403±
413.
Maki, A., Yamashita, Y., Ito, Y., Watanabe, E., Mayanagi, Y., & Koizumi, H. (1995). Spatial andtemporal analysis of human motor activity using non-invasive NIR topography. Medical Physics,
22, 1997±2005.
Maki, A., Yamashita, Y., Ito, Y., Watanabe, E., & Koizumi, H. (1996). Spatial and temporal analysis ofhuman motor activity using non-invasive optical topography. In R. R. Alfano, & J. G. Fujimoto, OSA
trends in optics and photonics on advances in optical imaging and photon migration, (pp. 357±362).
Washington, DC: Optical Society of America.
Mazoyer, B. M., Tzourio, N., Frak, V., Syrota, A., Murayama, N., Levrier, O., Salamon, G., Dehaene, S.,
Cohen, L., & Mehler, J. (1993). The cortical representation of speech. Journal of Cognitive
Neuroscience, 5, 467±479.
Old®eld, R. C. (1971). The assessment and analysis of handedness: the Edinburgh inventory. Neuropsychologia, 9, 97±113.
Sakai, K., & Miyashita, Y. (1993). Memory and imagery in the temporal lobe. Current Opinion in
Neurobiology, 3, 166±170.
Sakai, K. L., Sato, H., & Takeuchi, T. (1999). Hemodynamic changes in auditory association cortex
during speech recognition: functional mapping with optical topography. Society for Neuroscience
Abstracts 25, part 2, 1813.
Talairach, J., & Tournoux, P. (1988). Co-planar stereotaxic atlas of the human brain. 3-dimensional proportional system: an approach to cerebral imaging. Thieme, Stuttgart.
Villringer, A., Planck, J., Hock, C., Schleinkofer, L., & Dirnagl, U. (1993). Near infrared spectroscopy(NIRS): a new tool to study hemodynamic changes during activation of brain function in humanadults. Neuroscience Letters, 154, 101±104.
Watanabe, E., Maki, A., Kawaguchi, F., Takashiro, K., Yamashita, Y., Koizumi, H., & Mayanagi, Y.
(1998). Non-invasive assessment of language dominance with near-infrared spectroscopic mapping.
Neuroscience Letters, 256, 49±52.
Yamashita, Y., Maki, A., & Koizumi, H. (1996). Near-infrared topographic measurement system:
imaging of absorbers localized in a scattering medium. Review of Scienti®c Instruments, 67, 730±732.
Yamashita, Y., Maki, A., & Koizumi, H. (1999). A measurement system for non-invasive dynamic optical
topography. Journal of Biomedical Optics 4, 414−417.