Note: Descriptions are shown in the official language in which they were submitted.
W091/13584 PCT/US91/01260
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FIELD OF T~E lNVENT~ON
The pre~ent invention relates generally to
appar~tus for the rapid plac~ment of electrodes on and
acquisition of ~ignals fro~ ~he human body
BAC~GROUlND . OF T~ INVENTION
Many ~edical t~t- requirs th~ ~cquisition of
bioelectric signal- fro~ th~ brain, eyes, mu~cles or
nerv~s or ~ro~ a co~bin~tion of th abovem~ntioned body
parts Other biosignal-, such a- elQctroder~al signals,
heart pulse, voice signal~, tc , are often ~180
required
U S Patent 3,882,8~6 de~cribe~ a capacitive
electrode for acquiring el-ctroc~rdiographic (ECG)
signal~ which do~ not n~c~--itato the U8~ of conductive
gel~ or thQ pr~paration of thQ ~kin of ~ subject before
~cquirlng th EC~ ~lgnal~ While a ma~or lmprove~ent in
the practicality of EoG ~1gnal acquisition, the
~ap~citi~ electrode still r-quir~ u~e of a
co m ntional conducti~e electrodo as a reference ground
In ~ddit~on, ther~ i~ no convonient way to sterilize the
capacitlv~ lec*ro~o bstw ~n pati~nt~
urthQr~or~, wh~n pair~ of the capacitive
electrod~ are utilized to obtain differen~ial voltage
2S ~e~ure~onts o~ bio~lectr~c sisnal~, the robustness o~
the sign~l acquisition in th~ face of v~rious move~ent-
rel~ted arti~act~ i8 low Noi~e p~ckup fro~ extraneous
electromagnetic ~ource~ due to cabling is sub~tantial
It i~ known in th~ art that pr~paring the skin
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and the electrodes, placing the electrodes in their
correct location on the body, and fastenin~ them to the
body is a time-consuming process requiring much skill
Many devices have been cr-ated to ensure correct
S placement of the electrod-s on the body
on- such d-vice i~ describ d ln U S Patent
4,800,888 It compri--- a h l- t onto which is mounted
an electrode a~--mbly Each el-ctrod- of the as~embly
flo~t~ in ~ cylinder which i- mountQd on a pressure
lo responsive drive When the pre~sure responsive drive is
under pressure, it carrie- the lectrode to the scalp of
a subject
SUMMARy QF THE INVENTIQ~
It i~ therefore an ob~-ct of th- present
inv-ntion to provid an apparatu- for mounting
electrodQs on th- hu~an body and for acquiring
bioelQctric ignal- ther ~rom without skin preparation
and with mini al Qxp~rti~e
It i- al~o an ob~ect of the present invention
to provide practical mean- for ~terile use of capacitive
electrodes
Th r- i~ th-r-fore provided, in accordance
with a pref-rr d abodim nt of the pr~s-nt invention,
apparatus for mounting l-ctrode~ on a hu~an body which
~ 25 apparatus is op rative to obtain hu~an biosignals and
; compri~-s clo-e fitting clothing apparatus, a plurality
of electrode- mounted to the close fitting clothing
apparatu~, re o~able cov-r sheet ~pparatus for providing
a ~teril- intarface b4tw en the ~kin and at least one of
the electrode- and joining apparatu~ for joining the
cover sheet apparatu~ to at least one of t~e plurality
of lectrode~
Additionally, in accordance with a preferred
embodi~ent of the present invention, the apparatus for
mounting electrodes on a hu~an body also comprises
signal processing appar~tus uounted on the close fitting
clothing apparatus for preamplifying, transient
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protecting and filtering at least one differential
signal obtained betw en two of the el~ctrodes
Moreover, in accordance with a preferred
embodiment of the prQsent invention, the cover sheet
apparatus includes r-f-r ne- apparatus for providing a
refer-nc- signal for at l-a-t on- of the plurality of
eleetrodes Alternatively, the eover sheet apparatus
inelude~ eonduetiv apparatu- for providing a conductive
path between at least on of the plurality of electrodes
and the hu~an body
Still furth-r, in aeeordanee with a preferred
embod$~cnt of th- pr-sent inv-ntion, at l-ast one of the
plurality of leetrode~ i~ a e~paeitive electrode
Addltionally, in accordance with a preferred
embodiment of the present invention, the elose fitting
clothing apparatus ean be a glove, a faee mas~, goggles,
a h-adband, gla~--J, a eap or a pilot flight hælmet If
the elo~- fitting apparatus i~ a glove, a
photopl~thys~ographie en or ~ay b- ineluded
Ther i- al~o provide~, in aeeordanee with an
embodi~ nt of th pr-s-nt invention, a referenced
eapaeitive leetrode assQobly for ~ounting on human skin
eo~pri-ing a eapaeitiv~ etrode ~ounted in a
sub~trat-, ~t-rilizabl- re~ovabl- eov-r apparatus
separat- tro~ th eapaeitive eleetrode for providing an
~l-etrieal r fer-ne- ~ignal and for providing a
s parabl- int-rfaee betw -n the hu an skin and at least
on of th l-etrodes and ~oining apparatus for joining
the covQr apparatu~ to the eapaeitive eleetrode
Th-re i~ additionally provided, in accordance
with an embodi~ent of the present invention, a
ref~reneed eap~eitive sensor ehannel assembly for
mounting on hu~an skin for the purpose of measuring
bioelectrie signals The sensor ehannel comprises a set
of at least two capacitive eleetrodes mounted in a
subfitrate, removable cover apparatus separate from the
set of capaeitive electrode~ for providing a separable
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interface between the human skin and at least one of the
capaeitive electrode~ and including refer-nce apparatus
for providing an electrical referenco signal for the
sensor cbannel, joining apparatus for joining the cover
apparatus to the capacitive electrode~ and signal
proce~sinq apparatus for proee-sing th- bioelectric
~ignals
Further ore, there i~ provided, in accordance
with an embodiment of the pre~-nt in~ention, a
capacitive electrode for mounting on hu~an skin and
compri~ing a housing having a ~kin-faeing side in which
ther is an op ning, a eonduetive l-ment placed in the
op-ning and lying along the ~kin-faeing side, and a
dielectrie eov r eovering th op ning and touching the
eonduetive l~cent
Th-r i~ further provid d, in aecordanee with
a preferr d e bodi ent of th- pr-~ent invention,
apparatus for al-rting a drow~ing sub~eet eomprising a
elos- fitting fr~o mount-d on th sub~eet~s head, a
plurality of l-etrode~ ~ounted to the elose fitting
fra~e for mQa~uring bio~ignal aetivity oecurring
generally in th- ar a of the face and h-ad of the
sub~-et, data proe-s~ing apparatu~ for proee~sing the
biosignal aetivity into ba~eline eurves and for
d t-roining when th- bio~ignal activity crosses a
thre-hold related to the baseline eurves for longer than
a pr d-tQr~ined ~m~unt of tim- indicating an increased
ri~k of drow~ine~, and al-rting apparatus for alerting
the drow~ing ub~-ct upon deteroination by the data
proees~ing apparatu~ that an inereased risk of
drowsiness has oeeurred
Additionally, in accordanc- with a preferred
embodiment of the inv-ntion, the biosignals ean be of
high and/or low frequency and the apparatus includes
respon~e detection means for detecting the subject's
response to an alert is~ued by the alerting apparatus
Moreover, in accordanee with a preferred
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embodiment of the pres-nt invention, th- alerting
apparatus includes apparatu- for produclng a variety of
audible sound~ The al-rting appar~tus al~o includes
apparatus for varying th- int-nsity of the audi~le
sounds
Further, in accordance with a proferred
embodiment of the pres-nt invention, a head motion
sensor for detecting head motion i- also optionally
included in the apparatu~ for alerting a drowsing
subject
Still further, in accordance with an
embodiment of th- pre~ent invention, the close fitting
frame is a frame of a pair of eyegl~sses, a set of
goggles, a headband or a fra e of a face mask
lS There i8 further provided, in accordance with
an embodi~ent of the pr~sent invention, a ~ethod of
al-rting a drow ing sub~-ct including th- steps of
r-ceiving bio-ignal- from l-ctrod-s placed on and near
the fac- of the sub~ect, processing the biosignals into
b~s-lin- curv-s, and d-t-roining whon amplltudes of the
biosignalfi cross the baseline cur~es for longer than a
predetQrmined ~ount of tim indicating an increased
risk of drowsiness, alerting th- subject via an alerting
action every ti~e the increasQd risk of drowsiness is
indicat d, and dotecting a response to the alerting
action
Further, in accordance with an embodiment of
th pres-nt inv-ntion, the al-rting action differs each
ti~e th- increa~ed ri~k of drowsinQss is indicated The
alerting action is an audible sound who~e intensity is
initially low and intensifie~ until the subject gives a
confirmatory response indicating that the subject is
alert
There is further provided, in accordance with
an embodim~nt of the present invention, apparatus for
rapidly preparing to obtain biosignals from a human body
and comprising close fitting clothing apparatus, a
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plurality of electrode~ ~ounted to the close fitting
clothing apparatus, wherein at lea-t one of the
electrodes i~ a capacitive lectrod- and r-ference
apparatus mounted to the clo~e fitting clothing
apparatus for providing a r ference signal for use
together with the at l-ast one capacitive electrode
Moreover, th re i- provided, in accordance
with an embodi~ent of the present invention, eye
tracking apparatus for tracking the direction of a
sub~ect's gaze comprising, close fitting clothing
apparatus ~ounted close to th face of the sub~ect, at
least fir~t and second pairs of capacit$ve electrodes
for obtaining biosignals relating to the gaze mounted
onto the close fitting clothing apparatus, wherein the
first pair i~ mounted 80 as to be above and below one of
the subject'~ eye~ and wherein th- second pair is
~ounted 80 as to b- on oppo~lte ~idQs of one of the
~ub~-ct's y s, and apparatus for converting the
biosignals into position infor ation
Additionally, there is provided, in accordance
with an embodiment of the present invention, a fetal
biosignal probe for rapidly obtaining bio~ignals of a
fetus, typically during labor, compri~ing at least one
capacitive electrode apparatus ~ounted on a flexible
body for obtaining fetal biosignal~ and referencing
apparatu~ for providing a reference signal for the
capacitive electrode apparatu~
Furthermore, in accordancc with an embodiment
of the pr-s-nt im ntion, ther i~ provid-d a system for
rapidly obtaining f-tal bio~ignals comprising at least
two fetal biosignal probes to be temporarily attached to
a fetus scalp and signal processing apparatus for
processing fetal electroencephalographic signals
Finally, there is provided in accordance with
an embodiment of the present invention, apparatus and a
method for measuring a critical flicker fusion frequency
of a subject and comprisinq a plurality of light sources
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arranged in a predetermined pattern, typically familiar
to a sub~ect, comprising a first multiplicity of
background light source- ~nd a second multiplicity of
flicker group light source~, driving circuitry apparatus
for illuminating the background light ~ources so as to
appear non-flickering, for o~cillating the flicker group
light sources at a gradually decreas~ng oscillation
frequency and for maintaining the background and flicker
group light ~ources vi-u~lly indistinguishabl~, and
input apparatu~ oper~ted by the sub~Qct for indicating
to the driving circuitry apparatu~ at which frequency
fllcker is first ob~erved in the ~licker group and which
of the plurality of light sources belongs to the flicker
group.
~gI~E~E~CRIP~QN OF THE D~AwIN~s
The pre~ent invention will be understood and
appreciatod more fully fro~ th following detailed
de~cription taken in con~unction with the drawings in
which:
Fig. lA is an i~ometric illu~tr~tion of an
electrode a~seibly and a cover sheet assembly covering
the lectrode as~embly constructed and operative in
accordance with an e~bodi~ent of the present invention;
Fig. 1~ is a side view sectional illustration
of the electrode and cover sheet assemblies of Fig. lA;
Fig~. lC and lD are side view sectional
illu~trations of alternative e~bodiments of the
el~ctrode of Fig. lA;
Fig. 2 is a side view sectional illustration
of ~n electrode ~ssembly and an alternative embodiment
of the cover ~heet assembly of Fig. lB useful for
incorporating conductive lubrication means;
Fig. 3A is a schematic illustration of a face
mask having any one of the electrode assemblies of Fig.
1 and two sterile integrated electrode covers
constructed and operative in accordance with an
embodiment of the present invention:
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Fig. 3B is a detalled schematic illustration
of one of the sterile integrated electrode covers of
Fig. 3A;
Fig. 4 i8 a sche~atic illu~tration of an
alternat~ embodiment of the face n~k of Fig. 3 in
conjunction with a flexible printed circuit;
Fig. 5 iB a d-tall-d sch-n~tic illustration of
the flexible printed circuit o~ Fig. 4:
Fig. 6 i~ an l-ctronic ~ch ~atic diagram of a
circuit for prea~plification, transiQnt protection and
filtering of bioelectric ~ignals:
Fig. 7A i~ a pictorial illu~tration of a c~p
in which ar- incorporated the electrode assemblies of
Fig. 2;
Figs. 7B and 7C ~re pictorial illustrations of
a pilot flight h-ln t into which are incorporated
capacitiv- electrode-;
Fig. 8 is a pictorial illustration of a glove
in which are incorporated any one of the electrode
assemblies o~ F~g. l;
Fig~. 9A, 9B and 9C are pictori~l
illu~trations of an apparatu~ for detecting drowsiness
of a ~ub~ect and for ~ub~-gu-ntly ~lerting ~aid sub~ect;
Flgs. lOA and lOB are graphic illustrations of
RMS ~plitude curv~ of low and high frequency ~ignals
produced by the apparatus of Figs. 9A - 9C;
Fig. ll ~8 a block diagra~ illustration of
proc~-~ing apparatus useful in th~ appar~tus of
Fig~. 9A - 9C;
Fi~. 12 i~ a ~chem~tic circuit diagram of a
signal conditionin~ ~odule useful in the processing
mQans of Fig. 11;
Fig. 13 ic a ~ch~matic illustr~tion of
fl~xible circuit board appara~ug us~ful in the apparatus
of Figs. 9A - 9C;
Fig~. 14A, 14~ and 14C are front, back and
side view illustr~tions of ~ fetal biosignal probe
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utilizing the electrode~ of Fig
Figs 15A, 15B and 15C are front, back and
sid~ view illustrations of an alternative embodiment of
a fetal biosignal probe utilizing the electrodes of
Fig 1 ~
Fig 16 i~ a part pictorial, part block
diagr~o illu~tration of a y teo for obtaining fetal
bioQignal~ during d-liv-ry u-ing one or both of the
fetal biosignal prob- of ~lg- 14 and 15
Fig 17 is a part pictorial, part block
diagra~ illu~tration of apparatus for ~easuring Critical
Flicker Fu~ion and
Fig 18 is an lectronic sche~atic of
circuitry for~ing part of th apparatu~ of Fig 17
DETAIL~ DESCRIPTION OF PRESENT INVENTION
Refer nc- i~ now uade to Fig~ lA and lB which
illustrat- an el-ctrod- aa-- bly 10 and a cover sheet
as~ mbly 12 El-ctrod- a--- bly 10 typically co~prises
a capacitive electrod- 14, such a~ thOSQ available from
Heart Rate Inc of Costa ~esa, Ca
Electrod a~e bly 10 additionally comprises a
flexible non-conducting substrate 16, such as silicone
rubber or o~t pla-tlc, in which i~ ~ounted capacitive
electrode 14 Al~o ~ounted in substrate 16, near
l-ctrod 14, i~ at l-a~t one electrical contact site,
shown in Fig lB as two contact sites 18 and 20
Attach d to electrical contact sites 18 and 20
and to electrode 14, and pa~ing through or residing
within sub~trat- 16, are electrical conductors 22
El-ctrical conductor~ 22 ter~inate at an electrical
connector 24
Cover ~heet a~s mbly 12 is typically a thin
sheet which i~ typically dispo~ablQ but may
alternatively be permanent It typically comprises at
least one electrical contact ~ediu~, shown in Fig lB as
contact media 26 and 28, ~or touching human skin and for
providing an electrical reference signal to electrode
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14 Media 26 and 28 are typically eonduetive silver
impregnated eloth el~ctrod 8, ~ueh ac th E301 or E331
electrodes anufaetured by In-Vivo ~etrie of Healdsburq,
Ca , and are typically ~ounted on a non-eonduetive
substrate 30, ~ueh as a thin plastie sh~et Through
openings in substrate 30, m dia 26 and 28 are
electrieally eonn-ct-d to m tallie contaet~ 32 and 34
~he ~etallic contacts 3Z and 34 ar designed to easily
and re~ovably attach but rlruly to cont~ct sites 18 and
20, thereby providing a reference signal for ~lectrode
14 In the pr f-rred obodimQnt hown hereinabove, a
p~ir of one contact site 18 or 20 and one metallic
contact 32 or 34 creat-- both a m chanical and an
eleetrieal eonneetion betw -n the eov~r sheet assembly
12 and the ~leetrode assembly 10 An appropriate pair
is a male-f4rale press eontaet pair such as the Dot
eontaet ~anufaetur-d by TRW Corpor~tion of the USA
Alternativ-ly, th pair ean b- ~orned of silver
impregnated eloth fa~t-ner~ for ed of Velero (registered
trademar~)
In an alt-rnate embodiment, th- mechanical
~oining and tho lectrical ~oining c~n be produced
separat~ly by two separat- eonneetion assemblies An
exa~plo of sueh a dual joining ass~hly is an adhesive
band around th~ border of cover 12 on th- side of
substr~te 30 whleh i~ not in contact with the skin for
m ehanieal ~oining and a separate Dot contact pair
insid the border for electrical ~oining
An alt-rnate Qmbodinent of olectrode assembly,
labeled 40, is shown in Fig 2 and i~ intended for use,
in conjunction with a cover sheet assembly 42, on areas
covered by body~hair Cover sheet assembly 42 comprises
a substrat- 44, preierably made of a thin plastic film,
and a multiplicity of ~ponges 46 f~lled with a moist
conductive gQl or similar conductive m~dium and attached
to the sub~trate 44 A prot-ctive, sealing cover film
48, such ~s is used in commercial disposable ECG
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electrode~ ~uch as the Red Dot electrode manufactured by
3M Corporation of Minnesota, USA, maintains the gel in
sponge 46 in a wetted statQ and i5 typically peeled from
the cover 42 after the cover 42 iB attached to electrode
14
As in cover sheet assembly 12, cover sheet
assembly 42 additionally compriseJ contact media 26 and
28 and ~etallic contacts 32 and 34 for providing a
reference signal for el-ctrode 14
Si~ilar to electrode assembly 10, electrode
assembly 40 comprises a sub~trate 50, sîmilar to
flexible ~ubstrate 16, in which are mounted electrode
14, contacts 18 and 20 and any neces~ary wires Cover
sheet ~88~bly 42 is attached to sub~trate so via
adhesive pads 52 suc~ that sponges 46 lie on top of
electrode 14 and ~edia 26 and 28 Alternatively,
adhesiv- pad~ 52 can be nad- of Velcro (registered
trademark)
It will be appreciated that sponge 46 provides
a moi~t lectrical connection between the sk~n and
sub~tr~te 4~ Substrate 44 may optionally have pores
under spongQ 46 to establi~h electrical contact with
electrode 14 and media 26 and 28 ~he sealing cover
film 48 i8 made to hermetically se~l off all sides of
cover 42 80 ~8 to preserve the ~oistness of sponges 46
Sealing cov-r film 4~ is s~milar to those used for
dispo~able ECG electrodes
It will further be appreciated that the
electrode apparatu~ 10 or 40 is fir~t covered by its
respective cov-r ~heet assembly 12 or 42 and then the
combination i~ placed onto the ekin of a subject, with
tha cover assembly ~ide located against the s~in Via
the electrode and cover sheet asse~bly combination,
reference ~nd bioelectric signal~ are gathered, without
the nece~sity of skin preparation Due to the
replaceability of cover a~se~blies 12 and 42, electrode
as~emblie~ 10 and 40 are hygienic and suitable for
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sterile u~ with a multiplicity of subjects
Reference i~ now madQ to Fig6 lC and lD which
illustrate alternative e~bodiments of electrode assembly
40 in which a single diQlectric layer sepArates the
skin from the conductive ele~ent of the capacitive
electrode 14
In accordance with thi~ Q bodi~ nt of the
pre~-nt inv-ntion, the capaclti~e electrode, here
denoted 60, co~pri~-- a conducti~ le~ent 62, such as a
lo piece of metal, a di-l-ctric ~aterial 64, such as a thin
plastic sh~t, ~orming a cov~r to a thre--sided housing
66, and a buff-r amplifi-r 68
Capacitive QlectrodQ 60 performs as a
capacitor after being mounted, dielectric material 64
side down, onto th~ hu an skin Buffer amplifier 68
operatQs in a manner sinilar to thQ buffer amplifier in
U S Pat-nt 3,882,8~6 It is op~rative on the signal
d~tected by th~ co bination of th- conductive element 62
and th- di~lectric nat-rial 64
Th~ conductiv~ ent 62 and the buffer
amplifi-r 68 ar~ encloaed within hou~ing 66 which is
covered by dielectric material 64 Conductive element
62 i~ placed inaid- hou-ing 66 in a location close to
the ~id~ of hou-ing 66 which is covered by dielectric
mat-rial 64 In thi- anner, conductive element 62
touchs~ di~l-ctric natQrial 64 The diel-ctric material
64 c~n b- for- d as an int gral part of housing 66, as
~hown in Fig lC, or a~ a detachable element, as shown
in Fig lD In the embodiment of Fig. lD,. the
dielectric mat-rial 64 operate~ both as a dielectric and
as the cubstrate of cover sheet asse~bly 12 of Fig lB
It will be approciated that the capacitive
electrodes 60 of Figs lC and lD can be utilized in
place of capacitive electrode 14 in the assembly of Fig
lB Capacitiv- electrode 60 is advantageous over
capacitive electrode 1~ in that capacitive electrode 14
typically has two dielectric l~yers, one inside the
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electrode housing and one defining substrate 30, while
cap~citive el-ctrode 60 has only one dielectric layer 64
which serves both a6 a di-l-ctric and as a cover sheet
assQmbly.
Reference is now ~ade to Figs 3A, 3~, 4 and 5
which illustrate apparatua 70, constructed and operative
in accordanc- with a pr-f-rr d e~bodi~ent of the present
invention, for rapidly applying ~l~ctrode~, such as any
of the l-ctrode~ of Fig 1, to tho fac- of a subject
Appar~tus 70 require~ no ~kin or lectrod preparation,
nor do-~ it r~quire ~uch knowl dg- on the part of the
operator as to the corr ct plac-~nt of the electrodes
It i~ design-d to be ea~y for an un~killed operator to
use and to b- comfortabl- and hygi-nic for a subject to
wear
Accordingly, apparatus 68 i~ typically
eibodied in a face nask 70, including a p~ir of frames
71, ~i ilar to th fra~ ~ of wi~ r's goggle~ and
typically nanufactured of _ oft ~aterial such as
silicone rubber or a soft pla~tic, an adjustable bridge
~2 for on_bling the Sac- ~a~k 70 to adapt to the
particular int-rocular di-tance of a ~ubject and an
adju-tabl- band 74, typically ~n lastic band, for
fir ly ~aintaining the fac- ~a~k 70 again~t the face of
a ~ubj-ct - Th adju~tability of th adju table band 74
acco-oodate- subject~ with differ-nt head sizes
Mounted onto fac- ~ask 70 are a multiplicity
of l-ctrod- asse~blie~, ~uch a~ apparatu~ 10 (Figs lA
and lB), label-d lOa - 10~, ~or r cei~ing facial
bio~ignal~ The electrod- a~emblie~ lOa - lOj are
- located in predetermined locations around the eyes so as
to measure ~io~ignals relating to eye ~ovement and eye
position Sp cifically, electrodes lOa and lOb are
located in fra~e 71 so as to be above a subject's pupils
and electrodes lOg and lOh ar~ arranged so as to be
located below the subject's pupils Electrodes lOe and
lOf are loc~ted ~o a~ to be placed in the inner canthus
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of the eyes and electrode~ 10~ and lOi are located so as
to be placed in th- outer canthi of the eyes
El-ctrodes lOc and lOd ar arrang d to b- located at the
temples and are therefor- plac d on ad~ustable band 72
Typical bio~ignal- to b m-asured are as
follows l-ctrod- pair- lOa and lOg and lOb and lOh
measur l-ctrooculogran (EOGs) relatlng to the
vertic~l ~otion and po-ltion of th- l-ft and right eyes,
respectively, and el-ctrod- pairs 10~ and lOe and lof
and lOi ~ asur- EOGs r lating to the horizontal motion
and position of the l-ft and right y-~, respectively
alternatlv~ly, el-ctrode~ 10- and lOf ~ay b- replaced by
a single l-ctrode at 10-, at lOf, on the nose bridge,
or betwQen the eyebrow~ The horizontal and vertical
motion neasurenents are us-ful for detecting nystagmus
and for ~ a~uring a sub~ect's blink response and the
converg-nc- capablllty of a ubj-ct's y-s
El-ctrod - lOa and lOb, located above the
pupils, are al~o u~-~ul ~or m a~urlng the electromyogram
(EMG) of facial nuscle~ and l-ctrodes lOc and lOd are
use~ul for ~ea~uring EMG- o~ ~uscles associated with eye
lids and ey- nove~ nt~ or with facial relaxation
In accordance with a preferred embodiment of
the pre~Qnt inv ntion, th cover ~h et asse~blies 12
corre~ponding to th- nultlpllclty of electrodes lOa -
10~ ar for~ed in two integrated cover sheet assemblies
76 and 78 Cov r~ 76 and 78 ar- de~igned so as to cover
all of th- portions o~ fac- na~k 70 which come into
contact with the skin of a sub~ect, including the
templo- and the area- n-ar the inner oanthi of the eyes
They are r-placeable ~o 3s to ensure that apparatus 70
i~ hygienic and can be u~od with a multiplicity of
sub~ect~ without concern o~ spreading disQase from one
subject to the next
3~ Cover sheet ass-~bly 78 is shown in detail in
Fig 3B and co~er shQet as-e~blie~ 76 and 78 are both
shown in Fig 4 Cover sheQt a~se~bly 78 includes
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substrate 30 onto which ar placed one or more media 26
and 28, where, for clarity'- sake, only one pair of
media 26 and 28 are shown Media 26 and 28 are arranged
on substrate 30 such that they will mate with the
S corregponding electrode a--eibly 10 located on face
mask 70
Th~ entirety o~ ctrod a---mblies 10 are
connected to ~ignal proc---ing equipm nt via electrical
connection- 80 ~Fig S), typically co~pris-d of wires
In accordance with a pref~rred bodi~ent of the present
invention, l~ctrode as~bli-~ 10 and th~r respective
el~ctrical connections 80 are eib-dded in flexible
printed circuit~ 82 (Figs 4 and 5) which are fixedly or
removably attach-d to face mask 70 and extend along
ad~ustable band 74 The electrical connections 80
typically ter inate at a ~ingle connector 84 located on
the face ~ask 70 or within a cable 86 which extends from
the face ask 70
Flexibl- print-d circuits 82 can be molded
directly onto fac- mask 70 Alternatively, they can be
formed into a soft plastic ribbon or otherwi~e
surrounded with electrical and mechanical insulation
The soft pla~tic ribbon can then b- removably mounted to
face ~-k 70 u-ing renewable adhesive pads or other
renewable bind$ng mean-
Additionally, in accordance with a preferred~bodiment of th- pre~ent invention, preamplification,
trans$-nt prot-ction and bandpass ~iltering circuits,
d~scribed in ~or detail her-inbelow with reference to
Fig 6, ar~ a~sociated with face ma~k 70 for each pair
- of electrod- assemblies 10 attached to face mask 70
The circuit~ for the entirety o~ the pairs of electrode
asseiblie~ 10 corresponding to each eye are preferably
incorporated a~ a hybrid circuit in signal processors 88
and 90 attach-d to frame 71 ~y attaching signal
processors 88 and 90 to the frame 71, noise pickup
caused by cabling is reduced
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Moreover, sine- the majority of the biosignals
to be mea~ur-d will b~ m a-ured a~ diff-r-ntial signals,
a ref-rene- ~ignal i8 provid-d for co~ on ~ode
rejection This is provided by a reference electrode 92
preferably eonprised of a silver impregnated cloth
eleetrode, sueh as the E301 or E331 eleetrode
manufaetured by In-Vivo ~ trie
A~ m ntioned her-in~bove, ~ignal proeessing
equipment l- typieally provided with f~ee mask 70 It
typieally compri~es a power ~upply 94 for supplying the
required voltage~ to the leetrode a-~emblies 10 of the
faee mask 70 and ~plifier- 96 for further conditioning
and proee~sing of the pr aoplified biosignals received
from ~ignal proee~sors 88 and 90 Specifically, the
electrod- a~enbly 10 and th- ignal proce~sors 88 and
90 normally reguire power in th- 10 - 500 milliwatt
rang-
Further digital signal proee~sing, such asfrequency analy~i~, ~ay oeeur in digital eireuitry 98
It will b- appreeiated that power ~upply 94, amplifiers
96 and digital eircuitry 98 are typically located
separately rrom fae- ~a~k 70 It will al~o be
appr-eiat d that ~ingl- eonn etor 84 enables face mask
70 to b- readily and ea~ily s-paratable from the signal
proe-~ing equipment
Speeifie referenee is now made to Fig 5 which
d-tail- eleuent~ of one of the flexible printed circuit
bo~rd~ 82 Shown are the leetrieal connections 80
whieh bring th voltage from power ~upply 94 to the
eleetrod as--~bly 10 and bring to the amplifiers 96 the
deoired differ-ntial biooignal~ fro~ signal processor
88 Speeifieally, eonneetions 80a and 80b provide r
voltage to the eleetrodo asse~bly 10 and to the signal
proee~sor 88, conneetion 80e eonneets to reference
eleetrode 92, and eonneetions 80d and 80e provide
preamplified, filtered signals from the two pairs of
eleetrode assemblies 10
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In order to obtaln a diff~rential signal
between the pair of electrodes lOc and lOd on the
temples, the two connections 80f are both connected to
connector 84 Connections 80f are connected to
electrodes lOc and lOd and are located on the respective
flexible printed circuit boards 82 The differential
signal i8 then typically cr ated in one of signal
processors 88 and 90
The -ction of flexible circu~t board 82 on
which lies electrode lOe is preferably bent in order to
match the curvature of the area between the eye and the
nose bridge
Reference i5 now ~ade to Fig 6 which
illustràtes a typical circuit for preamplification,
transient protection and bandpass filtering Or a single
differential signal acguired from a pair of electrodes
and a reference electrode Th- circuit is beiieved to
be self-explanatory and therefore, in the interest of
concisQness, a full description will not be given It
will be noted that the couponents are selected to
provide low and high frequency cutoffs at predetermined
frequQnciQs, such a8 0 5 and 200 Hz
The circuit of Fig 6 is replic~ted for each
differential voltage signal to be measured and is
implemented a8 ~ single hybrid circuit Signal
processors 88 and 90 typically contain at least one
circuit such as i8 shown in Fig 6
Referring back to Figs l - 5, ~ace mask 70 is
utilized a8 follows Preparatory to placing the face
ma~k 70 on a sub~ect's face, an operator attaches cover
sheet assemblies 76 and 78 to face mask 70 by snapping
together the contact pairs 18 and 32 and 20 and 34
~ypically, the mask 70 is then placed onto the subject's
face, and the ad~ustable bridge 71 is ad~usted, if
neces~ary Finally, connector 84 is attached to cables
connected to the signal processing equipment The
electrode assemblies lO are in their proper location and
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are now ready to obtain m a-urem nts No further
ad~ust~ent- ar- required In thi~ manner, the
eleetrode~ are plae-d on a ub~eet with ease
It i- a f-atur- of the pr---nt invention that
an operator do-~ not n- d to be skill-d in s~in or
electrod~ preparation or in l-ctrode plae-~ent to
utiliz- th- fae- nask 70 of th- pr ~ent invention With
littl- work on the part of th op rator and little
discomfort to th ub~-et, the apparatus 70 is ready to
obtain the de~ired biosignals
It will b- appr ciated that th- apparatus 70
can be utiliz-d for det-rmining a vertical and/or
horizontal gaz- po-ition r-latlv- to the position of the
head A- i- known in th- art, th horizontal and
vertical components of th- thre--dimensional gaze angle,
deflned here as the horizontal and ~ertical gaze
po~ition~, incr a~e monotonieally with th amplitude of
th EOG signal obtain d from v-rtieal and horizontal
pair- of el-etrod -, r ~p etiv ly The r-lationship
b-tw ~n th- gaz- po~ition and th- a~plitud- of the EOG
signal i~ obtain d by having th- sub~ect observe targets
at known angular position~ r-lative to ~straight ahead"
a~ is eom on praetiee in n urological test~ of EOG and
eye ~ov-~ nt~
A~ m ntion d her inabove, the vertical EOG is
obtain~d from a pair of l-etrod-~, illustrat~d in Fig
S a~ lOa and lOg or lOb and lOh, whieh are typically
loeat d abov- and below one eye, r -peetively The
horizontal EQG i~ obtained from th- pair of electrodes
lOg and lOi whieh are typieally plaeed near the outer
eanthus of eaeh eye
The gaze position can be utilized in an eye
mouse, an apparatus for providing one or two-dimensional
po~itional input to a eomputer, providing much the same
information as that provided by a m ehanical mouse
The eye mouse is utilized a~ follows while
keeping his head fixed, a subj-ct calibrates the eye
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mouse by looking at a predetermined calibration position
on the computer scre-n or within his field of view and
by confirming through ~om tandard input route, such as
via a keyboard or a m chanlcal mouse button, that he is
S looking at the calibration position known to the
computer
Co~puter softwar , i~ple -ntlng equations 1 -
6 hereinb-low, rec-iv - th horizontal and vertical EOG
a~plitud-s, after low pa-- f~ltering by digital
circuitry 98 to re~ov- transients and sudden jerks or
other high fr-guency noises or artifacts, and associates
them with th- pr det-rain d calibration position
While maintaining hi- h-ad in a fixed
pocition, th- ~ùb~-ct then loo~ at a s-cond
pred-termin-d calibration point at a location
significantly horizontally and v-rtically far from the
fir~t pr d-t-r ined calibration polnt and confirms his
gaze as de~crib4d hereinabove Th- computer software
r-ceiv-- th- EOG a~plitud - for th- ~econd point and
co~put-~ fro~ th~ , fro~ th first EOG amplitudes, and
fro~ the coordinatcs of th two calibration points, a
r lationship b tween th- s~b~ect's horizontal and
vertical EOG aaplitude~, EX and EY rospectively, and the
po~ition X, Y of a point at which th- sub~ect is gazing
for a giv n distanc- and ori-ntation of th head
rel~tiv- to th- computer scr -n
Th- X, Y po~ition of the point is typically a
lin-~r function of th EOC a~plitudes EX and EY as
follow~
X - AX~EX + BX (1)
Y - AY~EY I BY (2)
where AX, AY, BX and 8Y are defined a~ follows
AX - (X2 - Xl)/(EX2 - EXl) (3)
BX - Xl - AX~EXl (4)
~ AY ~ (Y2 - Yl)/(EY2 - EYl) (5)
BY - Yl - AY~EYl (6)
and wh~re (Xl, Yl) and (X2, Y2) are the computer
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coordinates of the respective calibration points X2 is
different from Xl and Y2 i~ d$fferent from Yl EXl and
EX2 are the horizontal EOG amplitud-~ received when the
subject looked at point- (Xl, Yl) and (X2, Y2) and EYl
and EY2 are the vertical EOG amplitudes received when
the sub~ect looked at point- (Xl, Yl) and (X2, Y2)
Alternatlvely, in a second calibration method,
the sub~-ct can look sequ ntially at the points of a
grid or oth r -t (Xl, Yl), (X2, Y2), , (Xn, Yn),
known to th- computer, with each point having an
a~sociated m a~ured (EXn, EYn~ a two-dimensional
mathematical function relating true (Xi, Yi) to measured
(EXi, EYi) i- thu~ ~ampled
By fitting the sampl-d lattice Or points
(xi~ Yi) for given value~ (EXi, EYi) with linear,
polynominal or other math~catical ~odels known in the
art, any po~ition (X, Y) can be e~ti~ted fro~ the
mea-ured (EX, EY) of an arbitrary point a~ long as the
~ub~-ct's head maintain~ a fix~d orientation and
di~tance r lativ to th calibration points
In ither of th- abovementioned calibration
methods, upon moving hi~ h-ad, the ub~ect indicates to
th computer by k ypad or similar input means that his
head is b-ing rQpositioned When a new position is
taken, th ~ub~-ct indicate~ via the above mean~ that he
i8 r ady for the computer to redefine the new position
The co~puter sequentially di~play~ one or more points,
g n rally f w r than in the original calibration set,
and the ~ub~-ct ~-quentially ~ov-~ only his eyes to
focu~ on the mo~t recent point thereby to indicate to
the computer when each point i8 in view If the subject
has not rotated his head or mov-d it sub~tantially (i e
the mapping of the eye position to the computer position
i8 baQically the ~ame but the offset BX, BY has
changed), then typically a ~ingle calibration point can
be u~ed to identify the new position of his eye
In this manner, the eye mouse can be utilized
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for indieating position lnformation to the computer
It will be appr-eiat-d that the eye mouse
remains ealibr~ted only as long a8 th sub~ect's head
remains in a eonstant po-itlon relative to the sereen
-~ 5 Refer-nee i8 now ~ade to Figs 7A - 7C which
illustrate alternativ- e bodi~ents of the present
in~ ntion for us- in a-ily aequiring brain, eye, scalp
musele and faeial aetivity ignal~ In Fig 7A,
~leetrod- apparatu~, sueh a~ leetrod- assemblies 40,
are ~ount-d onto a eap or hat shap d element lOO,
siJilar to a hat eo~ionly ~old to sport~ fans, in
appropriat- loeations for aequiring electro-
ene-phalograph (EEG) ~ignal~
In one preferr d bodiment, the eleetrode
ass- blio- ~0 ar- loeat-d along the ~idline of the skull
wherein el-etrode as~eobli-~ 40d and ~Oe are at the
eentral and oeeipital r gion~, r-sp etiv 1y, and
el-etrode a~-- bli-~ 40a, ~Ob and ~Oe are on the
~or h ad El-etrod- as-~ bli-~ 40i and 40~ are held
against th- ~kin in th ar a- b-hind the ears via
xtension- of th- eap el-ment lOO
A ref-r nee el-etrode 41, such as described
hereinabov-, ia pr-ferably loeated on th- forehead
Alt~rnativ-ly, el-etrod- a--- bly ~0 are plaeed at a
multiplieity of points on the skull eorr-sponding to the
int-rnational lO - 20 sy~t-a of EEC eleetrode placement
In thi- alternativ- eobodlu nt, the output of the
l-etrod- as-- bly 40, after appropriate amplification,
ean b utiliz-d, for exampl-, in standard commercial
polygraphie ~tripehart or brain mapping analysis
sy~t-~s
Either electrod- plaee~ent eonfiguration,
ineorporated alternativ-ly into a elo~e-fitting pilot
flight h-l~et a~ shown in Fig 7B and de~eribed in more
detail hereinbelow, ean be used to deteet the pilot~s
EEG, EOG and EMG signals Sueh an apparatus can be
utilized for d~t-cting change~ in pilot status such as
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1088 of consciousness
As in the previous embodiment of the present
invention, the electrode as-enbly 40 are typically
mounted to the cap el~- nt 100 via an appropriately
S shaped flexible printed eireuit (not ~hown) As in the
previous enbodiment, an int grated eover sheet asse~bly,
of the typ- shown in F~g 2, ean be utilized; the
integrat-d eov r she-t ~-senbly in this embodi~ent would
be a singl- kull eap eo~po-ed of a ~ultiplicity of
cover sheet a~se~blies 42 Cap 100 is adjustable to
ensure that it firnly fits to any size head
Fig 7B illustrates th- apparatus of the
prQs nt invention ~bedded in a pilot flight hel~et 102
Th- apparatu- co~pri--- a plurality of eapacitive
elQetrodQs 14 ranged about the face of a sub~ect, with
or without th- U8- of a co~-r sheet ass-~bly A
refer nc- l-etrod- 10~, sueh as a silv-r i~pregnated
eloth eleetrod-, provid-- a r-f-r-ne- signal for the
apparatus and is typieally loeated n-ar th sub~ect's
forehead
Flexible wire~ 106 extend fron the electrodes
to an int-rnal wiring conneetor 108, typieally placed
inside the h l~ t 102 A pre-anplirier can be included
in wiring eonn-etor 108 and the output of the eonnector
108 is typically eonn ct-d to circuitry (not shown) such
a~ that hown in Fig 4 A ~icrophone outlet 110 is
typieally ineluded in sueh flight hel~ets and is
operativo, in thi~ e~bodin-nt, to provide a convenient
acees- fro~ th- eonnector 108 to the circuitry
Typically, a standard pilot flight helmet is
retrofitt-d to produce the apparatus shown in Fig 7
Fig 7C illu~trates this operation A pilot flight
hel~et typieally eonprises a hel~et and padding (not
shown) eovored by a typically leather liner 112 A
plurality of acee~s holes 114 are cut into the liner 112
of the helmet 102 and capacitive electrodes 14 are
placed into the~ Reference electrode 104 is attached
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W091/13584 PCT/~S91/01260
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to the skin-~ide of liner 112 and lts connecting wiring
is passed through a small hole (not shown) in liner 112
towards internal wiring connectox 108
An individual co~-r sheet assembly 116 can be
placed over each capacitiv- lectrod 14, or a single
cover sh-et a~sQ~bly 118 can be plac-d over a plurality
of capacitive electrodes l~ The cover~ 116 and 118 are
operative to keep sweat ~nd dirt ~way from the
capacitive electrodQ~ 14 and are typically non-
conductive If cover 118 i8 utilized, then referenceelectrode 104 is located on th~ pilot's skin side of
cover 118
Alternatively, th- padding which is covered by
liner 112 can be augment-d by, or replaced by, padding
of appropriate shape and thic~ness which already
contains the aforementioned electrodes and wiring
circuitry
Reference i~ now made to Fig 8 which
illu~trate~ another alternate embodiment of the present
inv-ntion for us- in ea~ily acquirlng spontaneous or
evoked mU8Cle activity signal~, a~ w ll as
photopletheysmographic mea~urements of blood flow and
h-art rate
In thi~ embodiment, the apparatus for rapidly
applying lQctrodes compri~e~ a modified glove 120 onto
which are ~ounted, via the elements described
h-reinabove, two standard conductive electrodes 122,
~uch a~ th- ~ilver impregnated cloth electrode
manufactured by In-Vi~o Metric, ~or providing electrical
stimuli to th- hand, two capacitivo electrode as~emblies
lO for acquiring EMG signals in response to the signals
providQd by the electrode3 122, and a photo-
plethey~ographic sensor ~24, such a~ a light source and
photodiode combination found in the Model 6390 Omni-Sat
ear ~ensor by Critikon of Tampa, Fl of the USA, for
providing blood flow data This apparatus is useful for
m~asuring neuromu~cular tr2n~mission across the wrist,
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W091/13584 PCT/US91/012
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in order to determine deliberate muscle relaxation
during surgery or inten~iv- eare, while si~ultaneously
monitoring relative blood flow in the finger
As in the pr-viou- two ~ bodiments of the
present invention, glov- 120 is ela~tic and has an
adjustable band on the baek to en~ur~ that it fits
firmly to any ~ze hand
It i~ a feature of the pr~--nt invention that
common artiel~- of clothing arQ u--d to ~ount the
various leetrode a~semblies to the ~ubject's body
This helps to nake th sub~ect eomfortable with the
testing to be perfor ed by the apparatu- of the present
invention and it ensur - th~t th both the sub~ect and
the op~rator know how to plaee the artiele of clothing
on the body
A further e~bodim~nt of the present invention,
shown in Fig- 9a, 9B and 9C, is us-ful for detecting
and r~sponding to drow~in --, or pre-alQQp b~havior, of
a sub~eet In thia ~obodi~ nt of th~ inv-ntion, labeled
130, el~etrod- aa~Qoblies 10 are typieally mounted on a
frame 131 who~e funetion i~ ~imilar to that of frame 71
Tho eleetrod- a~Q bliQ- lOq - lOt are loeated near the
outer eanthi of the ey~s, templQs and/or below the eyes
for ~easuring th- EOC and other ye-related signals
The el-etrod a~-e~blies lOg - lOt are typieally located
a- cloae to the yea as co~fortably pos~ible, preferably
without re~tricting the subj~ct' 8 visual field A
r-ferenee l-etrod- 132, such as ~ silver impregnated
eloth ~lectrode ~anufactured by In-Vivo M~tric, is also
mounted onto fr~e 131 By placing the electrode
assembli-s 10 close to the eyes, the efficiency of the
signal aequisition i~ maximized and spurious pickup of
brainwavec (the electroencephalogram or EEG) is
minimized
3S Alternatively, electrode lOq can be located
behind the ear of the side of the head opposite to
electrode lOt, which may be located anywhere around the
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eye or forehead
Frano 131 can be any clos- fitting frame or
clothing which can place a plurality of electrode
assemblies near the eyes A minimal set of electrode
assenblies includes one above one eye, one at a
reference location and another near an eye or behind the
ear, contralateral to the lectrod- assemblie~ above the
eye Examples of such fr~oe- ar an yeglass frame, a
face mask, a cap, goggl--, a headband or ~eadphones
Apparatus 130 optionally comprises head ~otion
sensors 134a and 134b Thes- can b~ electrodes such as
the E220 silver/silvQr-chloriao electrodes manufactured
by In-Vivo Metric or any standard metallic electrode
type, and ar u~ed in con~unction with signal
conditioning equipment for detecting low frequency
signal~ Alternatively, head motion ~ensors 134a and
i34b can be accelorometric motion detectors, used in
conjunction with appropriato signal conditioning
equipment ~ead sensors 134a and 134b are mounted on
frane 131 in a location which ensures that they are not
in contact with the ~ubject'~ skin, thereby ensuring
that they do not pick up any bioelectric signals but
instead, ~ a~ure only head motion
Th- biosignals and optional head motion
signal~ are collect~d via flexible circuit boards 136,
one of which i~ shown in Fig 13, which are similar to
the ones de~cribed hereinabove with reference to Fig 5
Flexibl- circuit boards 136 can be fixedly or removably
attached to the frame 131, as described hereinabove
Typically, i~ frame 131 is the ~ubject's eyeglasses, the
flexible circuit boards 136 are removably attached
The signals are sent, via a cable 138, to
processing ~eans 140, described in more detail
hereinbelow An integrated cover sheet assembly (not
shown) is also optionally included
Apparatus 130 is typically utilized for
passively and non-obtrusively monitoring a subject for
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signs of drowsiness. Such an appar~tu~ can be used for
monitoring truck drivers or other pQrsonnel in jobs in
which they must not fall asleep. To ensure that the
subjects do not fall asleep, the processing means 140
S comprise a detQctor modul- 142 for detecting behavior
associated with an incrQ~-d risk of falling asleep,
known hereinafter as th- drowsines- condition, and an
alerting ~odul- 144 for ~lerting th- 8ub~ect upon the
detection of drow~iness. Processing ~Qans 140 are
typically powcred by a power supply 146.
In accordance with a preferred embodiment of
the present invention, the alerting module 144 typically
activates a loudspeaker 148, such as an earphone, a
hearinq-aid type spQaker, or a small speakQr
incorporated into alerting module 144, located near the
sub~ect, to produce an audibl~ alerting sound. Upon
detection of th~ drow~in~ condition, the alerting
module 144 produce~ the alerting ~ound at a low
intensity and increa-e~ the intensity until the subject
responds, typically by blinking or by moving the head.
In one e~bodiment, to prevent accommodation by the
subject, the ~lerting sound is alternatively selected by
the alerting ~odule 144 fron among a multiplicity of
different r-cordQd or progr~ed sounds such that the
g~n sound i~ never used to alert the subject twice in a
row. Alternativ~ly, the same sound m~y be used two or
mor~ t~e~ in a row.
Pr~-~leep behavior, typically occurring for
many sQconds before the onset of sleep, tends to be
characterizQd by quiescent behavior and the relaxation
of facial musclQs. Conv~rsely, awake behavior is
characterized at least in part by eye, facial and head
movements, bl$nking, ~nd or talking. The bioelectric
signals to be obtained from the vicinity of the eyes
while a sub~ct is awake have substantial signal
amplitudes in a high frequency range of typically
30 - 1500 Hz. and in a low frequency range of typically
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wosl/l3ss4 PCT/US91/01260
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1 - 10 Hz Conversely, the average amplitudes of the
biosignals obtained at the on6et of drowsine~s are ~uch
smaller than those obtain-d from an awake subject The
high frequency range typically characterizes muscle
activity and the low fr qu ncy rang- typically
characterizes eye moveu nt~, blinks and motion
artifacts
In a preferred ~ bodi~ent of the present
invention, the alerting odule 144 i- to be activated
lo whenever the amplitud-s of the biosignals in the low
and/or high frequency r~nge~ drop substantially below
baselin value~, ~ea6ured when the subject is awake, for
more than a selectable nu~ber of seconds The baseline
values nay b- record-d during a s-t-up period occurring
at the beginning of th- use of the apparatus 130 or
they may be updated periodically during use of the
apparatu~ 130
Typical RMS a~plitude curves of biosignals
representing a ~everal ~inut- period in which a typical
sub~Qct fall- a-leep ar- ~hown in Fig~ lOA and lOB
The biosignal~ are fro~ electrode a~semblies 10 located
near the ey 8 Th- aboci~sa- of the graphs in Figs lOA
and lOB are in ~inute~ and the ordinates are in
arbitrary a~plitude units proportional to an integrated
average RNS a~plitude of the signal in its pass band
The pa~- band for the low frequency signal is 0 5 - lo
~z and the paa~ band for the high freguency signal is
30 - 1500 Hz
In Fig lOA, curve 150 is the actual RMS
amplitude of the high frequency portion of the
biosig~al, averaged using a moving window of a duration
of typically a few ~econds Curve 152 is a typical
baseline curve calculated by averaging the RMS values of
the biosignal using a moving 1 - 2 ~inute window ending
30 - 60 seconds before the current time
It will be appreciated that at a point 154 in
ti~e, the high frequency activity drops below a
8UBSTITUTE SHEET
:
WO91/13584 PCT/US9liOl260
.
- 28 ~ 7 ~
predetermined threshold l-v-l, mark d 156 In Fig lOA,
threshold l-v l 156 i8 50~ of the current baseline
value A~ ~hown in Fig lOA, point 154 stays below
threshold level 156 for longer than a predetermined
period Tl, typically 10 - 20 aecond~ The end of period
Tl marks the achievQ~Qnt of the drow~iness condition and
is the activation point of the alertlng ~odule 144 The
actual ons-t of ~1QeP~ characteriz-d by very low
amplitud- l-v-l- and lndlcated by r f-r-nce numeral 158,
typically occurs after the activation point of the
alertinq module 144, assu~ing that the alertinq module
144 h~ not been activat d Fig- lOA and lOB
illustrate the typical b havior of th~ biosignals in
which the alerting module 144 i~ not activated
Fig lOB illustr~tes the low frequency
behavior o~ a typical biosignal fro~ electrodes placed
near th- eye~ where curv- 160 i~ th- low freguency RMS
amplitud~ curv- similar to curv~ 150 Curve 162 is a
typical ba~-line curv- c~lculated a~ described
herein~bov- In Fig lOB, the predetermined threshold
level, marked 166, is typically 50~ and the
pr-deter~ined period is marked ~2 At point 168, the
onset of ~leep occurs
It will be appreciatQd that the alerting
modul- 1~ can be activat-d when one of the two curves
150 or 160 achi-ve~ the drow6in ~8 condition or when
both i~ultan~ou~ly indicate the drowsines~ condition,
or when ono achieve~ the drow~iness condit$on and the
other achieve~ it within a predetermined period of time
Additionally, alerting module 144 can be
periodically activated to check that th~ subject is
still alert In such an embodi~ent, the ti~e from the
alert until the subject respond6, herein denoted the
re~ponse time, is m~asured Alerting module 144 can
also be activated in relation to the length of the
response time or the length of time a subject remains
active or guiescent after previously being alerted
8UBSTITUTE SHEET
W09t~13~ PCT/US9t/01260
~ t
- 29 -
Head ~otion- ar optionally d-t-cted by head
~otion sensors 134a and 13~b for tho-- applieations
whieh involv sub~tantlal h ad otlon Their signals
ar- proee-- d in a ~ann r i~ilar to that of the low
frequeney r~nge signal- d -eribed h r inabove The head
motion aetivity i- th n r nov d fron the low and high
fregu~ney blosignal~ by ~anJ of r~ ti adaptive
filt~ring ~oftwar ~ueh a~ that d- er~b d in chapter 9,
"Adaptiv Fllt-ring,~ of ~ L~o~C:~L~CC:2~
Vol 1, written by Arnon Cohen, publi-hed by CRC Press,
~oea Raton, Fl in 1986 and incorporat d herein by
r-f~rene-
Sub~-et r ~pon~e to the al-rt i~ detected by
~ an~ of th aegui-ition l-ctronic a- d-~eribed
her~inabov R ~pon~- d teetion i~ achieved by
eo~paring the pre~ent a~plltud- to that whieh
iY diately pr c d d tb- al-rt A ~ub~tantial inerease
i- eon~tru d a~ a ~ub~-ct r ~pon~-
Alt-rnatlv ly, tb pr --nt a~plitud- is
co~pared to tbat r eord~d wb n tb ~ub~-ct is known to
be aware and alert Alt-rnatively, the present
a~plitud i- co~pared to a p ak a~plitude obtained when
tb- ~ub~-et i~ blinking but i~ otberwi~- quie~eent, or
tb- ~ignal i- eo~par d to a wavefor~ of r presentative
blink~ r eord d wh-n tb- ~ub~ et i~ otherwi~e guieseent,
u~ing ~ateh~d filter or cro-~ eorr lation ~ethods
~ueh a- tho~- pre~-nt~d in the abov refarenee by
Arnon Coh-n
Eaeh ti~ th alerting ~odule 144 i~
activated, th r~spon~- detection ~eans are aetivated
and th- r ~pons- ti~e i~ ~ a~ured The re~pon~e time is
additionally co~par-d to the pr-~iou~ response time If
th- r--pon~e ti~ has iner-ased, typieally indieating an
incr-a~e in drow~ine~, the time between periodic
alerting i~ d-er-a~ed
Further~ore, the alerting module 144 is
operative to gradually inerea~e the intensity of the
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- 30 - ~7
audible sound until the r -pon~e dotection means
indicate that a respon-- ha- been u asured
The proc-~sing ans 140 are d~tailed in Fig
11 to which reference i8 now ad Detector module 144
comprises two prea~plifi-r- 172, of t~ type described
with refer nce to Fig 6, for a plifying by a gain
of typically 500 to 1000, dlff-r ntial bio~ignals
r~ceiv-d fro~ two pair- of l-ctrod- a~ blies lo
Pr uuplifi-ra 172 ar~ not lncorporat d into the
proce-sing ~ ans 140 if th- inco~ing signal6 are
r-ceived fro~ ignal proc-a-or~ 88 on fr~oQ 131 Each
prea~plifier 172 receivos ~ignal- fro~ one pair of
electrode aaae~blies 10
Th two a~plifi-d aignal- are ~nt to a pair
of identical low frequency band pa~a filters 174 for
filt-ring frequoncie~ in a pa~ band of typically 1 - 10
Hz and to a pair of id-ntical high fr-qu-ncy band pass
filt~r- 176 for filtering fr qu nci-a in a pas~ band of
typlcally 100 - lSOO Hz Fllt-r- 174 and 176 attenuate
fregu-nci-- out~ld th ir r ap ctiv- pa~a band~ by at
lea~t 12 dB p r octav
Signal proce~aora 178 typically receive the
filt-r-d high fr qu ncy ignal- fro filters 176 and
r ctify, p ak n~- and int grate the~, producing
2s r lativoly auooth ~ignala Th re~ultant ~ignals are
proportional to the poak-to-p ak a~plitude o~ the
filt-r d high fr quency aignal- and have a limited
bandwidth of typically o - 100 Hz A typical ~ignal
proc-a-or 178 i8 shown in Fig 12 where integrated
circuit~ Vl aro the TL06~ chipo ~anufacturQd by Motorola
and integratod circuit~ V2 are the LM393 chip~,
~anufactured by National S-~iconductor
Amplifi-r pair~ 180 and 182 amplify the
ro~p ctive~filtered low and high freguency signals
receivod, ro~p ctively, fro~ filters 174 And processors
178, to an amplitude in the range of a few, typically
1 - 5, volt~
SUB8TITUTE SHEET
~W091/13S84 PCT/US91/012~
: .
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An A/D converter 184, typically a multichannel
A/D convert-r having on- channel for each electrode
assembly pa~r input, converts the amplified signals from
amplifiers 180 and 182 to four digltal signals of at
least 2Ni ~a~ple~ per second, where Ni is the bandwidth
of th ith channel The resolution of th- samples is
typically ight bit- A/D converter 184 can optionally
be a coubination of an A/D convert-r and a multiplexer
A ~icroproc---or 186, typically a low power
consu~ing microprocessor such as the Motorola 68HCll,
proco~s~ th- four digital ignals in accordance with
the ~ethod de~cribed hereinabove with refcrence to Figs
lOA and lOB At the appropriate ~o~ents, the
microproce~or 186 activat-~ alerting ~odule 144,
describ d in ~ore detail her inb-low Software
pseudocode outlining th~ op ration of the microprocessor
186 is incorporat-d her-in in Annex A
Al-rting module 1~ co~prises an audio
genQrator 188, such as a ton or voice synthesizer,
which i~ controlled by ~icroprocessor 186, for producing
on- of a ~ultitud~ of preprogrammed tone ~ignals or
sounds stor d in ~icroproc-ssor 186, and an audio
a~plifier 190, such as a Walkuan audio amplifier
~anufactur d by Sony of Japan, for amplifying the tone
~ignals produc d by the audio generator 188 Audio
a~pliti-r 190 is al~o controlled by microprocessor 186
to n~ble the alerting module 144 to vary the amplitude
of th al-rting sound according to the subject's res-
pons- or lack thereof Th~ tone signals emanating from
audio ~ plifier 190 are made audible by loudspeaker 148
Refer-nce is now made to Figs 14A - 14C which
re~pectively illustrate front, back and side views of an
s~bodi~ent of a ~etal biosignal probe 200 using any of
the electrode assemblies of Fig
The probe 200 typically comprises a capacitive
electrode a~embly 202, such as described hereinabove
particularly with respect to Fig 1, and a wiring cable
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W09l/l3584 PCT~US9t/01260
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- 32 -
204 for connecting the electrode 202 to a data
processing syste~, described in ~ore detail hereinbelow
with respect to Fig 16
The electrode 202 and wiring cable 204 are
typically e~bedded in a r~latively flat probe body 206
which i~ typically couprl-~d of a stiff but flexible
~aterial, such a- nylon or oth-r co~ on plastic, and is
Or suf~icient l~ngth to r-ach fro~ a tetal scalp to
completely outside the ~oth~r'~ cervlx A typical
lenqth i8 between 40 - 50 cm
The probe 200 additionally comprises a
referenc- el-ctrode 208 for providing an lectrical
reference signal, sinilar to those described hereinabove
in Fig 1 The refer nc electrod 208 i~ ~ounted on an
outer surfac- 210 of body 206 facing the fet~l scalp and
its wiring 212 is onbeddQd in body 206
Th wirinq cablea 20~ and 212 ~ay comprise a
flexible print-d circuit- whos- wir~s s-rve to provide
thQ wiring to l-ctrod - 202 and 208, in a manner
si~ilar to that illustrat d in Fig 5
On th outer scalp-sid- surface 210 of probe
200 is a frictionous or adh r nt ar-a 214 for enabling
the prob- 200 to adher to th ~calp of the fetus,
ther by pr~venting th- probe 200 fro~ slipping relative
to the surrac- of th- ~calp Frictionous area 214 is
typic~lly co~prisQd of a layer of ribbed, soft rubber
such ~8 that u~ed for dishwashing gloves, ~uch as
ranu~actured by Playt-x, Inc of the USA A surface
216, on th- oppo~ite side of the probe fro~ surface 210,
includQs a ~ooth ~urface 218, on the opposite side of
the probe 200 from area 214, for enabling generally easy
slippag- of the probe 200 against the uterine wall
The probe 200 i5 typically operated a~
follows During labor, the probe 200 is inserted into
the uterus of the mother and i8 positioned in a desired
po~ition on the scalp of a fetus Area 214 and surface
218 enable the probe 200 to travel with the fetal head
8UBSTITUTE SHEET
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'' '' ' ,. ,, `', .,. : :. ,
~O91/13~ PCT~US91/01260
2 ~ 7 ~ ~ 9 ~
- 33 -
as it emerges during delivery
R f-renc- is now ~ade to Fig~ lSA - lSC which
resp-ctively illustrate front, back and side views of an
alternative e~bodinent of fetal biosignal probe 200
using the electrode of Fig l Si~ilar reference
numerals refQr to si~ilar leuents
In thi- e~bodin nt, the prob 200 is
optionally u--d in conjunct~on with a cover shQath 220
which cov~r- th ntlr~ l-ngth or prob- 200 and is
prof-rably ~ad- of a thin pla~tic, such a~ polyethylene
or ~ther co on plastic Sh ~th 220 is preferably
~t~rile and is prefer~bly di~po~abl-
Th r-Sorence lectrod- 208 i~ ~ounted on an
outer surfac- 222 oS sh~ath 220 facing tho fetal scalp
The electrode wiring, h-r- al~o l~beled 212, passes
through th wall of shQath 220 and runs down its length
to wh-r it xit~ th h-ath 220 In thi~ e~bodiment,
th frictionou- or adher nt ar a, h r- label-d 224, is
si~ilar to that d--crib d abov , and i~ on the outer
sur~ac- 222 of sh ath 220 Th uooth surface, here
labeled 226, is on an outer surfac- 228 of Rheath 220
ReferencQ is now ~ad- to Fig 16 which
illustrate~ a ~yst-n for obtaining fotal biosiqnals
during dolivory usinq at l-ast two probes 200 of either
of th abov aentionod embodi~ nts
Th ~y-t-4 typ~cally couprises at least two
prob-- 200 for obtaining dirf-rential fetal signals
typically plac-d on oppo~ito ido~ of the fetus~s head
Th- ~y~t-u al~o co~prise~ ~ignal processing equipment
si~ilar to tho~- doscribed herein~bove with reference to
Fig 4
Spocifically, the signal processing equipment
compriaes a~plifiors 230, connected to probe 200 via
electrode wiring 212 and wiring cable 204, digital
3s circuitry 240 and a power supply 245 In this
configuration, however, the probes 200 will acquire
fetal ECG signal~ in addition to fetal EEG ~ignals
8U8STITUTE SHEET
WO 91/13584 PCT/US91/01260
- 34 -
This complicates tha EEG analysis. Therefore, to remove
the fetal ECG signal from the total acquired signal, an
ECG amplifier 250, such as a Hewlett Packard fetal
monitor model 8030 or 840, is included in the signal
processing equipment. The output of amplifiers 230 and
the ECG signal from amplifier 250 are typically input to
digital circuitry 240 containing real-time adaptive
filter software 260, such as described in Chapter 9 of
the book Biomedical Signal Processing: Vol. 1 of Aronon
Cohen. Software 260 removes the fetal ECG signal from
the differential biosignal free of ECG signal from
providing the EEG and EMG signals free of ECG artifact.
The ECG amplifier 250 preferably obtains the
unamplified biosignal from one of probes 200 via the
input connections to amplifiers 230. A maternal
electrical reference electrode 270, such as the standard
silver/silver-chloride gel disposed type disclosed
hereinabove, typically placed on the mother's thigh.
Alternatively, ECG amplifier 250 can be incorpated
into amplifiers 230.
If only the fetal ECG signal is desired, a
single fetal probe 200 and the maternal reference
electrode 270, can be used in conjunction with ECG
amplifier 250.
Reference is now made to Figs. 17 and 18 which
respectively illustrate apparatus for accurately
measuring a true Critical Flicker Fusion Test (CFFT)
frequency score of a subject constructed and operative
in accordance with a preferred embodiment of the present
application and electronics to drive the apparatus.
One psychological test of particular
importance for the detection of impaired cognitive
function is the CFFT. Numerous clinical studies have
documented the effects of various drugs, fatigue and
other factors on the CFFT. Many clinical studies have
the article "Critical Flicker Frequency and Psychotropic
W091/13S84 PCT/US91/Ot260
~ ~ ~ 7 ~
- 3s -
Drugs in Nor~al Human Sub~-cts - A Revi-wn, by Smith and
Misiak, published in ~ C~ Y~ Y~ Vol 47, pp
175 - 182, l976 These ~tudies have shown that a
reduced CFFT frequency scor can be indicative of
impairment of cognitive functions, uch as reaction
time, visual p rception and decision ~aking
In th CFFT, a ub~-ct ob~erv ~ a light source
who~- int-n-ity ~ari-~ ~ccording to an o-cillation
frequency Th ub~ect i- requir-d to peci~y the
highest oscillation frequency, known as the critical
flicker fu~ion frequency, at which the liqht source
appears to flicker For frQquenci~6 greater than the
critical fr quency, the light ~ourc- i~ p rcei~ed by the
sub~ect to b- con~tantly lit, d-noted her in a~
lS supercritical non-flick r; for frequenc~e~ less than the
critical froqu ncy, th- light source appears to flicker
The purpose of the pr-sont invention i$ to
provid- a r liabl- CFFT ~cor ~en for sub~ects who may
have an inter-~t in trying to avoid providing an
accurat- ~ti~at- of th- CFPT Such action by a subject
i8 lik-ly if a low or reduced CFFT frequency score
indicate- that th sub~ect has an l~pair~ent
The apparatus of the pre-Qnt invention, an
embodi~ent of which is ~hown in Fig 17, makes it highly
i~probable for a sub~ect to clai~ a higher CFFT
fr-quency than hi~ true CPP~ frequency This is
achi-v d by r-quiring the sub~ect to ~dentify a pattern
of flick ring light aource6 e~beddQd or a~sociated with
surrounding non-flickering light source~ which are
either constant (DC) in the~r intensity or
supercritically non-flickering The non-flickering
sources are otherwise identical in appearance to the
flickering sources In the following discussion, the
light sources are LEDs it being under~tood that any
light source capable of rapid intensity modulation is
suitable
A preferred e~bodiment of the apparatus
8UB8TITU~ SHEET
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. . . .. . : . ~, . , ; . . .
wogl/l3s84 PCT/USgl/01260
36 ;~ 7 o ~ ~ i
_
comprises a ~et of 12 id-ntical LED~ 300 capable of
rapid inten~ity oscillation, arranged in a circular
pattern similar to a clock face O~her patterns of
multiple light source~, uch as l~near arrays, matrices
S or dot array~ can alternativ~ly be e~ployed Driving
electronic circuitry 302, hown in d tail in Fig 18,
under th- control of a co puter 304 uppli-8 oscillating
electric ~ignal- to th LED~ 300, thereby causing their
inten~iti-~ to vary accordingly Th ~ubj-ct
communicat-~ with the computer 304 via an input keyboard
306 or similar input means
The LED~ 300 are dlvided into two groups, a
background group 308 and a flick r group 310 The
flicker group 310 comprise~ at l-a~t one LED The LEDs
of the background group 308 ~re osc~llated at a
fr-quency far great-r than any known CFFT frequency,
typically 250 ~z, or ar- h-ld at a constant (DC)
int-nsity Any fr quency can b- us-d to dr$ve the LEDs
of th- flicker group 310 ~he o~cillation~ ~re
generally ~inu~oidal although other alternating patterns
can be used
Th- op-ration of the apparatus is as follows
LED~ of th- flicker group 310 ar- initially oscillated
at a fregu ncy of approximat-ly 60 Hz, a frequency known
2s to b~ above th~ critical flicker fr quency The
oscillation fr-qu-ncy of the flicker group 310 is
r duc-d, typically at a rat- of 1 Hz per second, until
the ub~-ct id-ntifi-~ to th computer 304 via the
k-ybo~rd 306 that he d~t~ct~ ~t lea~t one of the LEDs
300 flickering Th co~puter 304 th~n ~tops reducing
the o~cillation fr-quency of the flicker group 310
The recording of the ~ub~ect~s CFFT frequency
score i~ d-pendent on hi~ identifying the correct
flicker group Incorrect identification of the flicker
35 group can be indicative of a deliberate attempt to gain
a fraudulent ~core
For example, assu~ing that just the LED in the
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W09l/l3~ PCT/US91/01260
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- 37 -
6 o'clock position belongs to the flicker group 310, the
ubject has only a 1 in 12 chance of gues~ing correctly
the flickering LED b-for- hi- tru- CFFT i~ reached If
two LEDs aro used, the sub~ect has le~8 than a 1~ chance
of correctly pinpointing which LEDs are flickering
before hi~ true CFFT is reached
Not only doe- the proposQd appar~tu~ prevent a
sub~ect fro~ deliber~tely raising hi- tru- CFFT, but the
subj-ct i~ al~o unlik ly to r-port a CFFT below his true
lo readout This is bec~use th- ~ub~ect, after detecting
flick ring of on Or th LED , i- not lik ly to wa~te
ti~ in trying to r cogniz- th- entir flicker group
whil- th- o~c$11ation fr qu-ncy continue~ to drop,
th-reby giving a CFFT scorQ bolow his tr~- score
Instead, the sub~ect i8 ~ore likely to first notify the
computer 304 that he has detected flickering in at least
on- of th- LED~ H c~n then identify the other
flickoring LED~ without low ring hi- ~coro
It will b appr-clat-d by porsons skilled in
the art that th- pre~-nt invention 18 not limited to
what has been particularly shown and described
her~inabovo Rather the 8cope of the present invention
is defined only by th clai~ which follow
8U8STlTlJTE SHEET
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