Effect of signal duration on detection for gated and continuous nois

Jeffress, L. A.

Tucker, A.

Williams, P. I.

English

NASA Technical Reports Server

8 
E F F E C T  OF S I G N A L  D U R A T I O N  ON D E T E C T I O N  
FOR GATED A N D  FOR C O N T I N U O U S  NOISE 
A n n  Tucker Department of P s y c h o l o g y  a n d  
Paul I Wil l iams D e f e n s e  R e s e a r c h  L a b c r a t o r y  
Lloyd A J e f f r e s r  T h e  U n i v e r s i t y  o f  T e x a s  a t  4 u r t i n  
https://ntrs.nasa.gov/search.jsp?R=19680015199 2020-03-12T10:32:41+00:00Z
E F F E C T  OF S I G N A L  D U R A T I O N  ON D E T E C T I O N  
FOR GATED A N D  FOR C O N T I N U O U S  NOISE 
Department o f  Psychology a n d  
A n n  Tucker  
Paul I. Wi l l i  oms D e f e n s e  R e s e a r c h  L a b o r a t o r y  
Lloyd A .  J e f f r e s s  T h e  U n i v e r s i t y  o f  T e x a s  a t  A u s t i n  
This work was supported by a grant  from t h e  
Nat ional  Aeronautics and Space Administrat  i o n  
(Grant R-129) through t h e  Office o f  Naval 
Research Contract  Nonr-3579(04), and by 
Naval Ship Systems Command Contract 
NOOO24-68-C -1117. 
L 
DEFENSE RESEARCH LABORATORY 
THE UNIVERSITY OF TEXAS AT AUSTIN 
AUSTIN, TEXAS 78712 
Effec t  of S igna l  DuraLion 011 Detrctiorl fo r  Gat4 m d  for Continuous Noise 
Ann Tucker, Paul I .  W i l l i a m s ,  and Lloyd A .  J e f f r e s s  
* 
Depr tment  of  Psychology and Defense Research Laboratory 
The Uxivers i ty  of  Texas a t  Aust in ,  Aust in ,  Texas 78712 
ABSTRACT 
A series of  two-a l te rna t ive ,  forced-choice experiments showed t h a t  
f o r  s h o r t  du ra t ions ,  t h e  de t ec t ion  o f  a t o n a l  s i g n a l  i n  noise  when t h e  two 
a r e  ga ted  synchronously i s  superior  t o  t h e  d e t e c t i o n  of  t h e  s i g n a l  i n  a 
background o f  cmt inuous  noise .  The experiments a l s o  showed t h a t  f o r  
ga t ed  s i g n a l  and noise ,  t h e r e  i s  a s t eady  improvement i n  d e t e c t i o n  as t h e  
d u r a t i o n  i s  shortened,  provided tha t  h ighly-prac t iced  observers  a r e  employed 
i n  t h e  t a s k .  Naive observers  exh ib i t  a similar t r e n d  b u t  t h e i r  performance 
drops a t  t h e  s h o r t  du ra t ions  ( 5  and 1 0  msec) where t h e  l i s t e n i n g  t a s k  be- 
comes ve ry  d i f f i c u l t .  
. 
Tucker, W i l l i a m s ,  and J e f f r e s s  
JASA - 2 
INTRODUCTION 
The r o l e  of dura t ion  i n  s i g n a l  d e t e c t i o n  is  of v i t a l  importance t o  
t h e  theory  of s i g n a l  d e t e c t a b i l i t y  (TSD), 
t h e  s i g n a l  i s  unknown, Peterson, B i r d s a l l ,  and Fox (1954) have shown t h a t  
opt imal  de t ec t ion  should occur a t  a du ra t ion  t h a t  i s  t h e  r e c i p r o c a l  of t h e  
For t h e  case where t he  phase of 
bandwidth of  the f i l t e r  involved.  Since i n  t h e  d e t e c t i o n  of  s i g n a l s  by 
human observers,  t h e  f i l t e r  o f  concern i s  t h e  c r i t i c a l  band of  t h e  ear, t h e  
theo ry  p red ic t s  t h a t  s u b j e c t s  should show a pronounced peak of d e t e c t i o n  
a t  du ra t ions  t h a t  are t h e  r e c i p r o c a l  of  t h e  c r i t i c a l  bandwidth. Such a 
f ind ing  has not been observed i n  experiments wi th  human l i s t e n e r s .  Green, 
Birdsal l ,  and Tanner (1957) found almost uniform d e t e c t i o n  over  a consider-  
able range of dura t ions  when t h e  energy of  t h e  s i g n a l  was kept  cons t an t .  
When t h e  de t ec t ion  index, d ' ,  f o r  t h e i r  fou r  observers  was averaged, t h e  
h ighes t  va lue  occurred a t  a du ra t ion  of  50 msec, wi th  only  s l i g h t l y  i n f e r i o r  
d e t e c t i o n  a t  dura t ions  of 20 msec and 100 msec. The suggested bandwidths, 
ranging from 1 0  Hz t o  50 Hz, are much narrower than  t h e  u s u a l  estimates. 
The sharp  peak predic ted  by TSD d i d  not  occur .  
"A r a t i o n a l  theory i s  s t i l l  bad ly  needed which w i l l  exp la in  why t h e s e  o r  
Green e t  a1 concluded, -- 
similar r e l a t i o n s h i p s  e x i s t  . t '  
The p red ic t ions  of TSD are based on t ak ing  similar samples of  no i se  ( N ) ,  - 
and of s i g n a l  Flus noise  ( S N ) .  This sampling procedure was probably not  - 
satisfied by the  s u b j e c t s  i n  t h e  experiment by  Green e t  a l ,  s i n c e  t h e y  were -- 
furn ished  a continuous noise ,  and only t h e  s i g n a l  was g a t e d .  A four -  
a l t e r n a t i v e ,  forced-choice procedure was employed, w i th  t h e  onse t  of t h e  
s i g n a l  indicated by a f l a s h  of  l i g h t .  The Sub jec t s  were, t h e r e f o r e ,  not  
-
Tucker, W i l l ; a m s ,  and Je f f ress  
JASA - 3 
furnished information about how long t o  sample t h e  no i se .  Even i f  t h e  
su3 jec t s  had been given a v i s u a l  s igna l  t o  i n d i c a t e  the  onset  and termina- 
t i o n  o f  t h e  sampling i n t e r v a l ,  i t  is  doubt fu l  whether t hey  could have used 
t h e  information t o  ob ta in  t h ?  similar samples of N and S N  requi red  by TSD 
assumptions.  The present  experiment w a s  undertakeri, Usiiig noise  t h a t  vas  
gated i n  t h e  same way as t h e  s igne l ,  i n  o rde r  more nea r ly  t o  f u l f i l l  t h e  
requirements of TSD. 
- -
EXPERIMENT I 
Experiment i was conducted' t o  s tudy  t h e  d e t e c t i o n  of gated s i g n a l s  
of va r ious  du ra t ions  when t h e  noise was ga ted  synchronously. 
a two-a l te rna t ive ,  forced-choice procedure, w i th  no feedback suppl ied t o  
t h e  s u b j e c t .  
of about 50 dB r e  0.0002 microbars. The energy of  a 500 Hz s i g n a l  was kep t  
cons tan t  a t  an E/No of 8.  
and 500 msec, wi th  a 0.5 msec r i s e - f a l l  t i m e .  Three naive observers  served 
f o r  an hour twice  a day, w i t h  the s i t t i n g s  separa ted  by a t  l e a s t  two hours .  
The f irst  600 t r ia ls  f o r  each dura t ion  were discarded,  and t h e  d a t a  po in t s  
based upon 1800 a d d i t i o n a l  t r i a l s .  
t h e  a p r i o r i  p r o b a b i l i t y  of a s igna l  ( 0 . 5 0 ) .  
100 msec, then  a t  2@0 and 500, at 100 again,  and then  a t  50, 20, and 10. 
Resul ts  
It employed 
The noise  (100 Hz to 3000 Hz i n  wid th)  had a s p e c t r a l  l e v e l  
Tlie dura t ions  used were 10, 20, 50, 100, 200, 
The observers  were t o l d  t h e  va lue  of 
Data were co l l ec t ed  f irst  a t  - 
The r e su l t s  of Experiment I are presented i n  F ig .  1. Observer RDB 
showed his b e s t  d e t e c t i o n  a t  a durat ion of 20 msec, JAB a t  50 msec, and 
DFH a t  100. Detect ion a t  t h e  two s h o r t e s t  du ra t ions  was gene ra l ly  supe r io r  
t o  d e t e c t i o n  a t  t h e  two l o n g e s t .  I f  we i n f e r  widths of t h e  c r i t i c a l  band 
Tucker, W i l l i a m s ,  and J e f f r e s s  
JASA - 4 
from t h e  dura t ions  a t  which b e s t  d e t e c t i o n  occurred, w e  ob ta in  50 Hz f o r  
RDB, 20 Hz f o r  JAB, and 10 Hz f o r  DFH, gene ra l ly  much narrower than  t h e  
u s u a l  es t imates .  
t o  be similar f o r  dura t ions  from 20 msec t o  100 msec as i n  t h e  experiment 
The average d e t e c t i o n  ind ices  f o r  t h e  t h r e e  sub jec t s  tended 
by Green e t  a l .  -- 
EXPERIMENT I1 
Experiment I1 was undertaken t o  compare d e t e c t i o n  f o r  gated - N and - SN 
wi th  de t ec t ion  f o r  continuous noise  and ga ted  s i g n a l .  It w a s  motivated i n  
part by an observat ion by Jeffress and Gaston (1966) (see Jeffress, 1967), 
t h a t  an  e l e c t r i c a l  model, which c l o s e l y  approximated t h e  f ind ings  of Green 
e t  a1 wi th  continuous noise  and gated s igna l ,  showed d e t e c t i o n  f o r  ga ted  -- 
N and S N  t h a t  was supe r io r  a t  s h q r t  du ra t ions .  It w a s  supe r io r  not  only 
' 7  + I .  . - - 
t o  d e t e c t i o n  fo r  continuous N and S, bu t  a l s o  t o  d e t e c t i o n  for gated - N and 
S N  a t  longer  du ra t ions .  
improved cons i s t en t ly  as t h e  d u r a t i o n  was shortened t o  5 msec. 
- n -  
For a cons tan t  energy s i g n a l ,  t h e  model 's  d e t e c t i o n  -
Experiment I1 used e s s e n t i a l l y  t h e  same procedure as Experiment I, 
except t h a t  t he  data po in t s  were based on 1,200 observa t ions  in s t ead  of 
1,800. A s  i n  Experiment I, the  onset  and t e rmina t ion  of  an i n t e r v a l  was 
ind ica t ed  by a lamp adjacent  t o  the response bu t ton  f o r  that i n t e r v a l .  A 
new group o f  three naive observers  was employed. 
Resu l t s  
The r e s u l t s  of Experiment I1 are shown i n  F i g s .  2, 3, and 4. 
each observer  showed h i s  b e s t  performance a t  a d i f f e r e n t  d u r a t i o n  from 
t h e  o t h e r s .  
Again 
F igure  4 shows t h e  s u p e r i o r i t y  of gated N and c S N  over  ga ted  - 
Tuckpr ,  W i I . l i a m s ,  and Jeffress 
JASA - 5 
S and continuous N, as p red ic t ed  b y  t h e  e l e c t r i c a l  model. It does not; - - 
show, however, t h e  p red ic t ed  s u p e r i o r i t y  o f  d e t e c t i o n  w i t h  ga ted  N and 
SN f o r  sho r t  du ra t ions  over de t ec t ion  f o r  l onge r .  
- 
There was a decided drop -
a t  10 msec. 
EXPERlMENT I11 
Whitmore (1967) suggested,  on t h e  b a s i s  of cons iderable  experience as 
a l i s t e n e r  i n  experiments involving shor t -dura t ion  s t i m u l i ,  t h a t  t h e  t a s k  
of t h e  observer  i n  dec id ing  which o f  t h e  two br ie f  i n t e r v a l s  conta ins  t h e  
s i g n a l  i s  a very  d i f f i c u l t  one, and t h a t  p rac t i ced  observers  might g ive  
d i f f e r e n t  responses  t o  t h e  very  s h o r t  s t imuli  than  na ive  observers .  Accord- 
i n g l y  Experiment XI1 was undertaken. 
wi th  shor t -dura t ion  s t i m u l i  f o r  same t i m e  were given p r a c t i c e  on t h e  present  
experiment, a long  wi th  p r a c t i c e  with o the r  sho r t  s t imuli  i n  a s tudy  
be ing  conducted by Whitmore (see Whitmore, 1968). The ses s ions  continued 
over  a per iod  of  about four months, a t  t h e  end of which time t h e  observers  
had reached p l a t eau  i n  t h e  present  experiment.  
employed i n  t h e  f i n a l  summary co l l ec t ed .  
Three observers  who had been working 
Only then  were t h e  d a t a  
Seven d i f f e r e n t  s i g n a l  l e v e l s  ( i n  random sequence) were used i n  2AFC 
experiment,  a l though d a t a  for only one s i g n a l  l e v e l  (E/No = 10) a r e  repor ted  
h e r e .  To avoid t h e  sha rp  t r a n s i e n t s  r e s u l t i n g  from abrupt  g a t i n g  o f  t h e  
noise ,  which may have been a d i s t u r b i n g  f a c t o r  i n  Experiments I and 11, 
t h e  ga ted  N and S N  was passed through a Krohnhite f i l t e r  having a passband 
of about  400 Hz (centered  a t  t h e  s i g n a l  frequency, 500 H z ) .  Three hundred 
o r  more observat ions were obtained f o r  each  data p o i n t .  Yne r e s u i t s  are 
presented  i n  F ig .  5 .  
- - 
Tucker, W i l l i a m s ,  and J e f f r e s s  
JASA - 6 
It w i l l  be seen t h a t  f o r  a l l  t h r e e  observers ,  t h e r e  i s  a cons i s t en t  
improvement i n  d e t e c t i o n  as t h e  du ra t ion  i s  decreased.  
shown i n  t h e  d a t a  f o r  t h e  o t h e r  s i g n a l  l e v e l s  employed. 
t h e  d i f f e rence  between ga ted  and continuous noise  shown i n  F ig .  4 continued 
t o  hold f o r  experienced observers ,  data were gathered a t  10 msec and a t  5 
f o r  JW. 
N and SN and f o r  continuous noise  than  t h e  naive observers  had shown. 
The same t r e n d  was 
To determine whether 
H e  showed an  even g r e a t e r  d iyference  between de tec t ion  fbr ga ted  
- - 
DISCUSSION 
A s  J e f f r e s s  (1968) pointed out ,  t h e  results of Experiment I11 are t o  
be expected not only on t h e  b a s i s  of t h e  e l e c t r i c a l  model, b u t  from t h e  
very  na ture  of t h e  f i l tering process .  If w e  accept  t h e  idea  t h a t  i n  d e t e c t -  
ing  a t o n a l  s i g n a l  i n  noise ,  t h e  a u d i t o r y  system serves  i n  some fa sh ion  
(no  mat te r  how) as a f a i r l y  narrow bandpass f i l t e r ,  we Etre forced  t o  p r e d i c t  
t h a t  when w e  employ ga ted  N and - SN and keep the s i g n a l  energy cons tan t ,  we 
w i l l  eventua l ly  reach  a du ra t ion  where d e t e c t i o n  w i l l  improve wi th  f u r t h e r  
reduct ion  of  the d u r a t i o n .  When it i s  less  than  t h e  r e c i p r o c a l  o f  t h e  
f i l t e r ' s  bandwidth, bo th  s i g m l  energy and n o i s e  energy w i l l  be l o s t  due 
t o  frequency spreading-- Af l / h t .  Now, i f ,  as w e  sho r t en  t h e  du ra t ion ,  
we inc rease  the s i g n a l  power, bu t  do not  i n c r e a s e  t h e  noise  ( t h u s  keeping 
E/No cons t an t )  w e  are c e r t a i n  t o  reach a p o i n t  where t h e  l o s s  of  n o i s e  
power due t o  frequency spreading is  s u f f i c i e n t  t o  a l low t h e  s i g n a l  ( o f  in -  
creased power) t o  be de t ec t ed  more e a s i l y .  
- 
A similar conclusion fol lows from t h e  energy-de tec tor  model of  Green 
and McGill (Green and McGill, 1968, and McGill, 1968). Thei r  mathematical  
. 
Tucker, Williams, and Jeffress 
JASA - 7 
model predicts tha t  as duration is decreased,there will be a corresponding 
decrease in the number of degrees of freedom of the underlying non-central, 
chi-square distribution finction, with a consequent improvement in detection 
for any constant value o f  E/N . 
discussion of this point.) 
(See Jeffress, 1968 f o r  a more detailed 
0 
Tucker, W i l l i a m s ,  and Jeffress 
JASA - 8 
ACKNOWLEDGMENTS 
This work was supported by a g ran t  from t h e  Nat ional  Aeronaut ics  and 
Space Adminis t ra t ion (Grant R-129) through t h e  Off ice  of  Naval Research 
Contract Nonr 3579(04) and by t h e  Naval Ship Systems Command Contract  
NOOO24-68-C-1117. The w r i t e r s  are g r a t e f u l  t o  Rand B.  Evans for se rv ing  
as coexperimenter dur ing  Experiment I, and to John K .  Whitmore, bo th  f o r  
suggest ing Experiment 111 and for serv ing  long hours as one of t h e  observers .  
They are a l s o  g r a t e f u l  t o  Earold L .  Emey  for  h i s  s e r v i c e  as an  observer  i n  
Experiment 111. 
c 
Tucker, WiL.? i a m s ,  arid j r f f r c s s  
JASA - 9 
FOOTNOTES 
* 
Present  address:  Department of Psychiatry,  Neurology, and Behavioral  
Sciences,  The Univers i ty  of Oklahoma Medical Center,  800 Northeast  
Th i r t een th  S t r e e t ,  Oklahoma City, Oklahoma 73104. 
hxper i rnents  I and I1 were cocducted by  Tucker (1967). 
Experiment I were presented by  Tucker, Evans, and J e f f r e s s  (1966) a t  t h e  
72nd meeting o f  t h e  Acous t i ca l  Society of America. 
conducted by W i l l i a m s  for purposes o f  t l ie present  a r t i c l e .  
The results of 
Experiment I11 was 
I .  
. 
Tucker, W i l l i a m s ,  and Jeffress 
JASA - 1 0  
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(1966). "Ef fec t  of S igna l  Duration on 
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JEFFRESS, L.  A (1967). "Stimulus-Oriented Approach t o  Detec t ion  Re-examined," 
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JEFF'RESS, L. A .  (1968). "Mathematical and E l e c t r i c a l  Models of Auditory 
Detect ion,  " J. Acoust . SOC. Am. 
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WCI(ER, Ann, WmS, R .  B., and JEFFRESS, L .  A .  (1966). "Effec t  of  Durat ion 
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Am. 40, G 5 O ( A ) .  - 
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and Continuous Noise and Signal , "  
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Ph. D .  D i s se r t a t ion ,  The Univers i ty  of 
WHI!BIORE, J. K .  ( 1967). Personal  communication. 
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"Some Resul t s  
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Effect of signal duration on detection for gated and for continuous noise

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