The intensity-time relation of a stimulus in simple visual reaction time

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1 The intensity-time relation of a stimulus in simple visual reaction time Item Type text; Thesis-Reproduction (electronic) Authors Pease, Victor Phillip, Publisher The University of Arizona. Rights Copyright is held by the author. Digital access to this material is made possible by the University Libraries, University of Arizona. Further transmission, reproduction or presentation (such as public display or performance) of protected items is prohibited except with permission of the author. Download date 26/04/ :47:45 Link to Item

2 THE INTENSITY - TIME RELATION OF A STIMULUS IN SIMPLE VISUAL REACTION TIME by. V icto r Po P ease A T hesis Subm itted to th e F a c u lty of th e DEPARTMENT OF PSYCHOLOGY In P a r t i a l F u lfillm e n t o f th e Requirem ents : i For th e Degree o f MASTER OF ARTS In th e Graduate C ollege THE UNIVERSITY OF ARIZONA

3 STATEMENT BY AUTHOR This th e s is has been subm itted in p a r t i a l f u lf illm e n t of r e quirem ents fo r an advanced degree a t The U n iv e rsity o f A rizona and i s d e p o sited in The U n iv e rsity L ib rary to be made a v a ila b le to borrow ers under r u le s of th e L ib ra ry. B rie f q u o ta tio n s from t h i s th e s i s a re allo w ab le w ithout s p e c ia l p erm issio n, provided th a t a ccu ra te acknowledgment of source i s made. R equests fo r perm issio n fo r extended q u o ta tio n from o r rep ro d u c tio n of t h i s m anuscript in whole or in p a r t may be g ran ted by th e head of th e m ajor departm ent or th e Dean of th e Graduate C ollege when in t h e i r judgment th e proposed use of th e m a te ria l i s in th e in te r e s t s o f sch o la rs h ip. In a l l o th e r in s ta n c e s, however, perm issio n must be o b tained from th e a u th o r. SIGNED: APPROVAL BY THESIS DIRECTOR This th e s is has been approved on th e d ate shown below: I]/ N. R, BARTLETT P ro fe sso r of Psychology

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5 LIST OF FIGURES FIGURE ' ' - ' ' ; : F,. PAGE 1= V isu al D iscrinl inator» = e s t,.,»<,6 600»»<,0 =«,»<, o,,»»c oo., o»»»»<,»»» 10 Zo R eaction lim e as a F u n ction of lo g D u ration f o r S u b je c t IS 3* R eaction Time as a F unction of Log D u ra tio n f o r S u b ject # * * * 1 9 4> R eaction Time, a s a. F u n ction o f lo g D u ratio n fo r \ S u b ject.tys**#*###'#**-**#» *-#(* *ik*»>*»* *4' S'.20 5» R eaction Time a s a F unction of lo g (S tim ulus lum inance Times Stim ulus D uration) f o r S tibieet»»*«23 60 R eaction Time as a F unction o f Log (S tim ulus Luminance Times Stim ulus D uration) f o r S ubject L<,H» =o, <, =6,»»o 24 7o R eaction Time as a F u n ction of Log (S tim ulus Luminance Times Stim ulus D uration) f o r S u bject ToSo,.**...,, 25. 8= Uumulative P ercen tag e Curves of Four- Stim ulus - Durations for Subject 27

6 LIST OF TABLES TABLE ; V \ ; ' ' I ' ' ', ' : TAGE I* The ExperTmeHhal D esign o f E xperim ent 14 IIo. The E xperim ental D esign of Experim ent IIo«oo? < > <,» 16 I I I, The A nalysis o f V ariance f o r th e Data o f Experim ent I, =6o.<, 22 IF, ' Means, Medians, and Standard D ev iatio n s in M illiseco n d s f o r each S u b ject f o r each Dui*atlon-Luminance C ondition* <,» 28

7 THE IHTENSITr^TIME DELATION OF A STMJLUS H SIMPIE VISUAL.EEACTION TIME VICTOR VP EEASE In Experim ent I, vi.sual s tin ru li were p re sen te d a t vary in g le v e ls o f stim u lu s d u ra tio n and stim u lu s lum inance* The d u ra tio n s ranged from 3 to 500 m illise c o n d s # and th e lum inances from 2,670 to. OW+Z m lllila m b e rts* The area o f th e v is u a l stim u lu s was h e ld co n sta n t a t 20? thro u g h o u t th e experim ents» In th e second e x p e rim ent, f iv e d u ra tio n s from 30 to 120 m illise c o n d s, and two lum inances from and 1*07 m illila m b e rts were p re sen te d to s u b je c t 1*3* R eaction tim e was m easured as th e dependent variable*. The. su b je c t made h is re a c tio n s by re le a s in g a le v e r a tta c h e d to a m lc ro -sw itc h *. In Experim ent I,, curves were p lo tte d fo r a l l th re e su b jects* One s e t o f curves p lo tte d median r e a c t i o n tim es a g a in s t lo g stim ulus d u ration* These curves show th a t re a ctio n, tim e d ecreases as stim ulus d u ra tio n in c re a s e s fo r th e two low est lum inances* th a t r e a c tio n tim e approaches a c o n sta n t a t th e h ig h e st lum inance a t a l l stim u lu s dura*- t i o n s, and th a t re a c tio n tim e appears to d ecrease most a p p re c ia b ly to in c re a s e s o f stim u lu s d u ra tio n a t th re s h o ld le v els* A nother se t o f Curves p lo tte d median re a c tio n tim es f o r a l l th re e s u b je c ts a g a in st f la s h energy, These curves in d ic a te th a t as th e t o t a l f la s h energy in c r e a s e s, th e re a c tio n tim e decreases^ in s o f a r as th e d a ta f o r th e two low er lum inances a re concerned*

8 The r e s u lts o f Experim ent I I where f iv e stim u lu s d u ra tio n s were p a ire d w ith th re e lum inances were th a t re a c tio n tim e was h ig h e r to energy v alu es o f le s s energy and in c re a s e d d u ra tio n and t h a t an in c re a s e o f t o t a l stim u lu s energy produces a d ecrease in re a c tio n tim e. - ', I t i s m entioned i n th e d iscu ssio n of t h i s stu d y t h a t stim ulus d u ra tio n has a g re a t e f f e c t upon r e a c tio n tim e p a r tic u la r ly a t th r e s h o ld.. I t i s p o in te d o u t th a t c r i t i c a l d u ra tio n seems to depend upon fla s h lum inance and t h a t as h ig h er lum inance le v e ls a re reach ed, in c re ases in d u ra tio n (beyond some sh o rt c r i t i c a l ' p erio d ) do n o t a f f e c t th e re d u c ib le m argin o f th e re a c tio n tim e*

9 AOMOIIEDCEENTS This re searc h ^r&s conducted tinder a. g ra n t ( n atio n al. Science Form dation to th e U n iv e rsity of.arizona* from th e The a u th o r ex p resses h is g r a titu d e t o th e p r o je c t d ir e c to r and t h e s i s d ir e c to r,.ur* H ell E* B a r t l e t t y vrithout xhose c o n trib u tio n s t h i s re s e a rc h could n o t have been com pleted.

10 HISTORY Simple r e a c tio n tim e as used in t h i s paper i s d e fin e d as th e le n g th of tim e between th e onset of a stim u lu s and th e com pletion of th e response* R arely^ i t has been used to mean th e tim e between th e te rm in a tio n of a stim u lu s and th e o n set o f th e response* However<> in t h i s second s itu a tio n, th e o ffse t of th e stim u lu s i s a. change o f energy and can be regard ed as a stim u lu s i t s e l f * response la te n c y a r e used in terch an g eab ly * The term s r e a c tio n tim e and The term*, r e a c tio n speed, r e f e r s to th e re c ip ro c a l o f th e l a t e n t p e rio d and has been used as an in d ex of th e in t e n s i t y of sen sa tio n ( P ie ro n # 1920). PieTon ( l 920) has s ta te d th a t r e a c tio n speed i s n o t th e la te n c y of se n s a tio n, b u t th e la te n c y of a t o t a l re a c tio n.. The t o t a l re a c tio n tim e can be d iv id ed in to two components th e ir r e d u c ib le minimum and th e re d u c ib le margin* The ir r e d u c ib le minimum c o n sis ts. o f th e tim e o f re c e p to r p ro cesses and n e u ra l Conduction^ and i s somewhat v a ria b le depending upon th e le v e l o f e ffic ie n c y o f th e v ario u s n e u ra l u n its involved* Therefore^ in v is u a l e x c ita tio n,, th e compon e n ts o f th e ir r e d u c ib le minimum a re th e a ffe re n t and e f f e r e n t tr a n s m issio n d elay s and th e tim e re q u ire d f o r th e com pletion o f C en tral p r o c e s s e s,. The ir r e d u c ib le minimum changes from experim ent to experiment depending upon th e v a ria b le s which a re h eld constant* The re d u c ib le m argin of re a c tio n tim e i s t h a t p o rtio n which f a l l s above th e ir r e d u c ib le v a lu e i t s d u ra tio n i s governed la r g e ly by th e independent v a ria b le s in th e stim u lu s s itu a tio n * This re d u c ib le ' 1 : ' - '

11 . ' 2: m argin may T?e determ ined q u ite a c c u ra te ly by s u b tra c tin g th e maximum re@ dtion tim e f o r th r# sh o ld. s tim u li from th e minimum re a c tio n tim e to maximum stim u lu s in te n s itie s The re d u c ib le m argin may be re la te d in sy stem atic ways to a stim u lu s v a r ia b le, fu n c tio n was suggested by F iero n (1920)» in example o f such a He s ta te d t h a t th e hypers b e l i e fu n c tio n, -.. ;. f = i / ( l 4- C) -I- K, d e sc rib e s ts e d e c lin e of re a c tio n tim e w ith in c re a s in g f la s h lum inance^ In t h i s e q u atio n T r e a c tio n time# A th e re d u c ib le laten cy # I fla s h in te n s ity # and K = an irre d u c ib le lim itin g la te n c y. The v a ria b le s of lum inance and d u ra tio n of a v is u a l stim u lu s a f f e c t th e redu& lbie m argin* V arious s tu d ie s w ill be c ite d to demons t r a t e th e v a r ie ty of r e la tio n s h ip s th a t have a r is e n out of re a c tio n tim e d a ta,.. The v a ria b le o f stim u lu s in t e n s i t y or lum inance and i t s e f f e c ts upon sim ple v is u a l r e a c tio n tim e w ill be d iscu ssed f i r s t, fro e b e rg (1907) s tu d ie d th e e f f e c ts o f th e in t e n s i t y o f a v is u a l stim u lu s upon human r e a c tio n t i n e. His stu d y was a ls o concerned w ith th e e f f e c ts o f d u ra tio n upon r e a c tio n tim e# but th e s e r e s u lts w ill be d iscu ssed l a t e r in t h i s p a p er. The method f o r both experim ents was e s s e n tia l ly th e same# and i t w ill be d e sc rib e d th o ro u g h ly h e re. The source o f illu m in an ce was d a y lig h t r e f le c te d o f f M3.lton B radley w hite b a ry ta paper and B ering^s g ra y s. The illu m in an ce from th e M ilton B radley pap er was d e sig n a te d a s.100 and th e o th e r I n t e n s i t i e s were o btain ed from B ering^s g ra y s. They were compared w ith th e w h ite b a ry ta paper by p la c in g them on a c o lo r w heel. The degree o f b rig h tn e s s was determ ined by th e s iz e of th e w hite secto r# expressed in term s o f

12 ' / ".., 3 p e rcen tage of th e whole c i r c l e t h a t ' produced th e same shade o f g ray as th e p ap er to be te ste d * The lo w est i n t e n s i t y used was d a y lig h t r e f le c te d o f f v e lv e t b la c k, and th e o th e r i n t e n s i t i e s were d esig n ated as 56, 25, 16, 10, 6 2/ 3, 3 1 /2, 2 l / 4 and 3/4 The stim u lu s d u ra tio n s were o b tain ed by moving paper of a d e sire d a b so rp tio n v alu e acro ss an a p e rtu re v ary in g in s iz e from 3 to 48 m illim e te rs* The paper was r o ta te d a t a r a te of one m illim e te r p er m illise c o n d, th e r e f o r e, each a d d itio n a l m illim e te r would add one m illise c o n d to th e d u ra tio n o f th e stim u lu s. The d u ra tio n ' f o r th is, experim ent were 3, 6, 12, 24, and 48 m illise c o n d s., Two su b je c ts were Used and 400 r e a c tio n s were tak en f o r each co n d itio n * Mean re a c tio n ' tim es and mean v a r ia tio n s were computed fo r each of th e s e ts of d a ta. I t was s ta te d th a t th e lo w est i n te n s ity used was w e ll above th re s h o ld due to th e lim ita tio n of th e apparatus*; The r e s u lts showed t h a t re a c tio n tim e in c re a s e s as th e in t e n s i t y of th e stim u lu s d e c re a se s. More e x p l i c i t l y, th e tim e o f ' re a c tio n ten d s to in c re a s e a r ith m e tic a lly,as She' in te n s ity ; of th e stim u lu s d ecreases g e o m e tric a lly. R eaction tim e was p lo tte d a g a in s t th e lo g a rith m o f th e stim u lu s i n te n s ity and a l i n e a r curve Was o b tain ed. Hecht?s (1918) work on Mva a r e n a r ia has shown a s im ila r r e la tio n o f lum inance and re a c tio n tim e, Mva, when exposed to l i g h t, r e t r a c t s i t s siphon. Hecht used th e.tim e from th e beg in n in g of th e exposure to th e beginning o f th e r e tr a c tio n to c a lc u la te th e veloc i t y of l i g h t a d a p ta tio n. He showed t h a t re a c tio n tim e i s a r e lia b le method o f-fin d in g v a lu e s /o f the- increm ent o f i n te n s ity which give th e same degree o f d is c rim in a tio n a t d if f e r e n t a d a p ta tio n l e v e l s, In a s im ila r stu d y (1928), he found th a t r e a c tio n tim e appears to in c re a se.'

13 . - ' V ', - : ; ; V - 4 lin e a r l y to th e logarithm : o f th e stin m ltis in te n s ity * Hovland (1936) in v e s tig a tin g re a c tio n, tim es to f i e l d lum inances and stim u lu s lum inances in humans found a d ecrease in r e a c tio n tim e as th e d iffe re n c e between th e stim ulus and a d a p ta tio n f i e l d increased* Here re a c tio n tim e i s to a stim ulus p re se n te d upon a v a r ia b le f i e l d. lum inance r a th e r th a n a fix e d background* I n a s im ila r study,, although u sin g more com prehensive stim ulus ra n g e s> B a r tle tt and Macleod (1954) stu d ie d th e e f f e c ts o f f la s h and f i e l d lum inance upon human re a c tio n time* They found t h a t re a c tio n tim e shows l i t t l e in c re a s e where th e stim u lu s lum inance i s c le a r ly d is tin g u is h a b le from th e f i e l d lum inance* There was,: however, a la rg e in c re a s e i n r e a c tio n tim e as th e f i e l d and f la s h lum inances approached equal le v e ls * u sin g h ig h e r f i e l d lum inances* The re a c tio n tim e was f a s t e r f o r th e fo v e a l p o s itio n th a n i t was f o r th e p e rip h e ra l p o s itio n, but w ith dim lum inances th e re v e rse was tru e* The fu n c tio n a l r e l a t i o n of lum inance to r e a c tio n tim e was dem onstrated by f i t t i n g th e fo llo w in g eq u atio n t o th e d a ta : T - ' l ' " + K». B lo g I / I 6.. where- B i s a slo p e c o n sta n t, I is. f la s h lum inances,. I Q i s a lim itin g f la s h in t e n s i t y dependent on th e f i e l d lum inances, a t which re a c tio n tim e approaches in f in ity,, and K i s a lim itin g la te n c y which re a c tio n tim e approaches as I becomes v e ry larg e* The e s s e n tia l d iffe re n c e be-. tw een t h i s fo rm u latio n and th a t o f P ie ro n ^ s, m entioned e a r l i e r in t h i s p ap er, i s th a t B a r tle tt and Macleod employed lo g a rith m ic u n its in s te a d of a rith m e tic units*. This lo g a rith m ic u n it s u b s titu tio n has more ad eq u a te ly d escrib ed th e ex ten siv e B a r t l e t t and Macleod?s d a ta th an

14 ... ' : th e fonm tl ation of P iero ru This study* h is sh o w th a t th e re d u c ib le mai-gin o f re a c tio n tim e can be d ir e c tly re la te d ' to stim u lu s changes# in t h i s case- lum inance l e v e l s. - Temporal c o n d itio n s Of a v is u a l s tim u lu s. a lso determ ine th e m agnitude o f r e a c tio n tim e although not a l l in v e s tig a to r s ag ree on th e amount or d ire c tio n s o f th e e f f e c t& The f i r s t sy stem atic in v e s tig a tio n in to th e e f f e c ts o f d tiratio ti o f a v i s u a l. stim u lu s upon re a c tio n tim e was made by Froeberg (1907)» The method has been d e sc rib e d e a r l i e r in t h i s p a p e r0 From th e se re su lts*. Froeberg s ta te d t h a t r e a c tio n tim e in c re a s e s a r ith m e tic a lly as d u ra tio n d e crease s g e o m e tric a lly, o r th a t,. r e a c tio n tim e in creases, as d u ra tio n d e c re a se s «W eighing th e e ffe c ts o f th e d u ra tio n of stim u lu s a g a in s t th e e f f e c ts o f illu m in a n c e, he found th a t r e a c tio n tim e decreased w ith an in c re a s e in e ith e r v a ria ble,: b u t t h a t th e increm ent produced by an in c re a s e in illu m in an ce was tw ice t h a t of th e same in c re a s e in d u ra tio n. W ells (1913) stu d y in g th e e f f e c ts of th e d u ra tio n o f a v is u a l stim u lu s on re a c tio n time, d id not fin d any evidence th a t re a c tio n tim e in c re a s e s as d u ra tio n d ecreases* W ells o b tain ed re a c tio n s from th e onset of a stim u lu s l i g h t 12y 25# 61, 144* and 1,000 m illise c o n d s in d u ra tio n. A p la s t ic d isc form ing a r e t i n a l image of m illim e te rs was illu m in a te d by a N ernst fila m e n t. The illu m in a tio n a t th e d isc was 3' candle power a t a d is ta n c e o f c e n tim e te rs. From th e se r e s u lts,, i t was s ta te d th a t i f th e re was any r e la tio n between re a c tio n. tim e and th e d u ra tio n of stim u lu s, i t was t h a t th e lo n g e r th e d u ra tio n o f th e stim u lu s th e lo n g e r was th e re a c tio n * The probable re la tio n s h ip between th e r e a c tio n tim e and d u ra tio n o f stim u lu s would be a. d ir e c t one, t h a t is,.f o r every u n it in c re a se in stim u lu s d u ra tio n th e r e would

15 ' :. ' ' : ;. - 6 be an. in c re a s e in re a c tio n tim e although n e t in th e same p ro p o rtio n. Thus i, th e in v e rse r e la tio n t h a t Pro eh erg found was n e t substan t i a t e d in V e ils r d a ta. V e ils m inim ized th e e f f e c ts o f d u ra tio n in both h i s experim ent and P ro eb erg s experim ent because of th e sm all d iffe re n c e s in re a c tio n tim e produced by su ccessiv e in c re a se s in d u ra tio n, Froeberg and V e ils used a wide range of d u ra tio n s which a t th e th re s h o ld le v e l would l i e w ith in th e c r i t i c a l d u ra tio n, b u t t h e i r illu m in an ces were to o high to allo w d u ra tio n to determ ine much o f th e resp o n se. In o rd er to dem onstrate th e e f f e c ts of d u ra tio n upon re a c tio n tim e^ n ear th re s h o ld lum inances should be employed. According to Graham and Eatoosh (1962) a lum inance of high i n t e n s i t y may ta k e somewhat le s s d u ra tio n to be seen th a n an other f la s h of low er lum inance and th e same d u ra tio n, and any l i g h t coming in a f t e r th e i n i t i a l p a rt of th e f la s h has been seen w ill be w asted f o r t h i s re sp o n se,, - : ' - ' ' * ' The re c ip ro c a l re la tio n s h ip o f stim u lu s in t e n s i t y and stim ulus d u ra tio n, m entioned above, has been e s ta b lis h e d f o r th re s h o ld s tim u li, B loch s law (1851) s ta te s t h i s r e c ip r o c ity as I t C, where I = lum i nances, t = time,; and G ^ a co n stant w ith th e proper dim ensions, Bloch has a p p lie d t h i s law to v is u a l s e n sa tio n s s ta tin g th a t th e re c ip ro c a l r e la tio n s h ip of tim e and in t e n s i t y e x ip ts w ith in c e r ta in l i m i t s, namely f o r sh o rt fla s h e s,, tcs th e v i s u a l. process# Graham and M argaria (1935) in v e s tig a tin g a r e a, in te n s ity, and " tim e r e la tio n s in v is u a l th re s h o ld in th e p e rip h e ra l r e t i n a found th a t w ith sh o rt d u ra tio n s, th e energy of a f la s h. I t, i s c o n sta n t f o r a given a re a, b u t w ith long d u ra tio n s a l l a re a s r e q u ire an in c re a s e in

16 / ; " ' ' V ' ;. 7 th e I t product n e c e ssa ry to reach th re s h o ld. In t h i s same study# i t was. found th a t r e c ip r o c ity e x iste d for- sh o rt exposures and sm all a re a s b u t i f th e exposure tim e was in c re a se d beyond 0,05 seconds# e v id e n tly th e c r i t i c a l d u ra tio n fo r p e rip h e ra l th resh o ld # th e c o n d itio n 1 = 0 p revailed * Above c r i t i c a l duration# i n t e n s i t y alone seens to be e f f e c tiv e in determ ining th e re sp o n se,. Graham and Kemp'X 1938) stu d ie d b rig h tn e s s d is c rim in a tio n and found t h a t th e i n t e n s i t y re q u ire d to produce a J u st n o tic e a b le in c re a se.in ap p aren t b rig h tn e s s d e crease s w ith an in c re a s e in d u ra tio n up to a c r i t i c a l d u ra tio n. Beyond c r i t i c a l d u ra tio n th e re q u ire d in te n s ity to ' produce an in c re a s e in ap p aren t b rig h tn e s s of a stim u lu s f i e l d o f a given i n t e n s i t y i s c o n sta n t. In a stu d y t o fo llo w up th a t by Graham and Kemp# K e lle r (1941) supported t h e i r fin d in g s# She found t h a t ACt = 0 holds f o r exposures of A 1 up to th e lim it of a c r i t i c a l d u ra tio n a t a l l le v e ls o f th e' b a sic in te n sity *. Beyond th e c r i t i c a l duration#.a I eq u als a constant# and i n te n s ity d is c rim in a tio n i s independent of duration* K e lle r in te n s iv e ly explored a sm aller range o f d u ra tio n s th an d id Graham and Kemp i n o rd er to ex p lo re th e e f f e c t o f sm all d u rations# th e re b y in s u rin g a more, a c c u ra te d e term in a tio n o f th e c r i t i c a l d u ra tio n v a lu e s. From both Graham and Kemp? s and K eller% stu d ie s# i t i s c le a r t h a t th e c r i t i c a l d u ra tio n i s a fu n c tio n of th e b a sic a d a p ta tio n in te n s ity *. The above m entioned th re s h o ld s tu d ie s along w ith H a r tlin e s (1934) stu d y o f th re s h o ld e f f e c ts in th e S in g le f ib e r in th e eye of ' Limulus polyphemus in d ic a te th a t th e re i s a f a i r l y sharp break from th e I t = 0 r e la tio n to I G# in d ic a tin g a c r i t i c a l d u ra tio n a f t e r which i n te n s ity alone determ ines th e re sp o n se.

17 Although th re s h o ld s tu d ie s have c le a r ly p o in ted out t h i s r e c i p ro c a l r e la tio n s h ip, re a c tio n tim e s tu d ie s h a w not* Most studies,,. such as th o se of F roeberg and W ellsy have employed i n t e n s i t i e s of v is u a l - stim u lu s w ell above th resh o ld,,. The th re s h o ld re g io n, howevery a ffo rd s a lo n g er d u ra tio n, one in which stim u lu s energy may c o n trib u te to a sen so ry e f f e c t 0 I t i s reasonable,, th e re fo re,, to look in th e th re sh o ld re g io n of lum inances fo r th e r e a c tio n tim e to show th e e f f e c ts o f - stim u lu s duratio n * ' - I f p revio u s s tu d ie s have not found much e f f e c t o f d u ra tio n upon r e a c tio n tim ey - i t may be. because o f th e high stim u lu s in t e n s i t i e s t h a t were used* I t i s th e purpose.o f t h i s study to m easure th e r e la t io n o f stim u lu s i n t e n s i t y and stim u lu s d u ra tio n upon sim ple human v is u a l re a c tio n tim e over a wide stim ulus range* I t i s reasoned t h a t i f low lum inances, approxim ating th re s h o ld, a re used re a c tio n tim e w ill e x h ib it th e in te n s ity -tim e re la tio n s h ip th a t has been shown in th re s h o ld studi.es* D u ratio n, then,, would be expected to determ ine p a rt of th e re a c tio n up to a c e r ta in v a lu e, th e c r i t i c a l d u ra tio n, a f t e r which lum inance alo n e would determ ine th e m agnitude of th e response* As in th re s h o ld s tu d ie s, re a c tio n tim es m easures should show t h a t c r i t i c a l d u ratio n ' i s a fu n c tio n ' of th e le v e l o f lum inance employed,.

18 ' METHOD, i ' : A pparatus ' - ' The VisuaA P is c rim in a to r c o n sis te d o f a covered tu n n e l. x 3gn x A-g, a s shown i n f ig u r e which provided th e stim u lu s and f ix a tio n so u rces. The l i g h t source was a S jlv a n ia Glow M odulator (ty p e H1131C) tu b e (A) w ith a ri.se and decay tim e l e s s th a n 0*0001 seconds o The lig h t from t h i s source, p assed through a. c o llim a tin g le n s (B) 22mm in diam eter w ith a fo c a l le n g th of l62mm«s lo ts in th e tu n n e l w a lls ( 0) h e ld W rather n e u tr a l d e n sity f i l t e r s which could be in s e r te d to o b ta in a p p ro p ria te lum inances. The f i e l d sto p h o ld er (D) enabled th e s e le c tio n of stim u lu s a re a by th e in s e r tio n of a r e a s lid e s.0 A fte r p assin g through th e a re a s l i d e, th e l i g h t tra v e rs e d a beam s p l i t t e r (E% a converging le n s 35 in diam eter w ith a fo c a l le n g th of 9Gmm (f)> and th e n converged a t an a r t i f i c i a l p u p il 3mm i n diam eter (H)= The f ix a tio n p o in t was r e t i e c t e d o ff a 45 in c lin e d s l i d e g la s s cover in s e r te d between th e converging le n d and th e a r t i f i c i a l p u p il (g)* An opening above th e g la s s re c e iv e d th e l i g h t from a neon bulb (ty p e KE51) mounted in a clo sed m etal c y lin d e r» The c y lin d e r was covered w ith aluminum f o i l through which th r e e pin-si% e h o le s were d r i l l e d 3*5mm a p a r t? th u s allo w in g a tria n g u l a r f ix a tio n d is p la y which subtended 3 51tf a t th e eye to be proje c te d to th e in c lin e d g lass* The f ix a tio n source was p o sitio n e d 9

19 A 10 B E C D E F H FIGURE 1. Apparatus as described in text.,

20 so th a t S would re c e iv e th e stirau ln s 15 from th e fovea on th e tempo ra l re g io n of th e r e tin a *.S m ain tain ed a stead y p o s itio n by holding a b i t e p la te ( l ) in h is te e th * The b i t e p la te vas made from "F astray",. a, s e lf - c u r in g d e n ta l p la s t ic and "was clamped between two p ieces of p ly fo cd a ffix e d to th e booth "wall* An in d iv id u a l b i t e p la te was made f o r each 5* S s a t in a lig h t-e e c u re ^ v e n tila te d booth 65n x 36". The end of th e v is u a l d is c rim in a to r c o n tain in g th e f ix a tio n cover g la s s and th e a r t i f i c i a l p u p il extended th re e in ch es in to th e booth through th e back panel* As S s a t in th e f ix a tio n p o s itio n, he re s te d h is r ig h t arm on a s ix -in c h s h e lf a tta c h e d to th e s id e o f th e booth*. A m icro-s'w itdh (BZ-2RW80) vjas mounted in a s lo t in th e sh elf* A le v e r was a tta c h e d to t h i s sw itch arid b ent so th a t th e le v e r was p a r a l l e l w ith th e base o f th e s w itc h. and. was stopped by a m etal p la te which lim ite d th e d is ta n c e to which i t would be d ep ressed to 2mm* To execute a r e a c tio n, S h e ld th e le v e r a g a in s t th e sto p u n t i l th e Onset o f th e stim ulus^ and l i f t e d h is fo re fin g e r as r a p id ly as p o s s ib le The E le c tro n ic R e sp o n se-ln d icato r System (model R-2) manufa c tu re d by th e P sy cholo g ical Instrum ent and R esearch L aboratory of Rome, New York, contain ed both th e stim u lu s source power supply and a B erkeley E le c tro n ic Counter which m easured re a c tio n s to seconds», H unter Decade I n te r v a l Timers (model 100C) c o n tro lle d both. th e stim ulus d u ra tio n and th e d u ra tio n of th e fo re p e rio d * S i n i t i a t e d th e fo re p e rio d by d ep ressin g a fo o t sw itch which c lo sed th e tim er c i r c u i t * At th e end o f th e fo re p e rio d, th e tim er d ev ice trig g e re d th e counter and stim ulus' l i g h t sim u lta n eo u sly, and th e co u n ter was stopped when S re le a s e d th e r e a c tio n le v e r, opening th e co u n ter c ir c u it

21 Twelve d u ra tio n s, covering a -wide span of tim e, were used in t h i s study* They were 3s 6$ 12, 30> 40, 48, 60, 80, 96, 120, and 500 m illise c o n d s* Area was h e ld co n stan t by th e u se o f & *083 in ch f i e l d s to p which subtended a v is u a l a n g le o f 20?c The f i e l d sto p was- c o n stru c te d by d r i l l i n g opaque film sprayed w ith f l a t b lack. p a in t to e lim in a te any l i g h t leaks* The film izvas mounted i n an aluminum, fram e which was in s e r te d in to th e v is u a l d isc rim in a to r* Five lum inances were, u se d, ra n g in g from n e a r th re s h o ld to v e ry b rig h t* They were determ ined by in s e r tin g W ratten n e u tr a l dens i t y f i l t e r s in f r o n t o f e ith e r a 26,700 m illila m b e rt (m l*) source ( source A) o r a 34,200 m l, so u rce..(source B)» These lum inances were c a lib r a te d w ith a EacBeth lllum inom eter* A ll th re e s u b je c ts re c eiv e d th e lum inances from source A which were (a ) 0*42 ml* (d e n s ity value 4 * 8 ) (b) 0,84 ml*, (d e n s ity v a lu e 4 * 5 )I and (c ) 2,670 ml* (d e n s ity v alu e l*0)o S u b ject T0S0 re c e iv e d, in a d d itio n to th e so u rce A v a lu e s, th e two so u rce B v a lu es which were (a ) 0*54 ml* (d e n s ity v a lu e 5*8) and (b) 1*07 m l* '(d e n s ity v a lu e 5*5)» SUBJECTS S u b jects were th r e e male g ra d u a te stu d en ts in t h e Department o f Psychology Each s u b je c t p ra c tic e d t h i s re a c tio n tim e ta s k f i f t e e n hours p r io r to th e t e s t t r i a l s * PROCEDURE This stu d y encompassed.two s im ila r experim ents which w ill be r e fe rre d to in th e te x t as Experim ent I and Experim ent IT*

22 P r io r to aoh s^ebsion^ eaoh dark adapted 30 m inutes in th e r e a c tio n 'booth* A fte r t h i s p e rio d o f tim e^ S was re a d y to re a c t t e th e s tim u li j. each of - which was preceded by a variak Le fo rep erio d * The le n g th o f th e fo re p e rio d ranged in ste p s of te n th s o f a second from two to fo u r seconds* The fo re p e rio d le n g th was. predeterm ined by u se of a ta b le o f random numbers» P a irs of numbers w ere s e le c te d from t h i s ta b le, th e f i r s t d i g i t corresponding to seconds and th e second d i g it to te n th s of seconds# E s e t th e fo re p e rio d on th e H unter Timer, and th e n s a id, "Ready"* This was th e s ig n a l f o r S to depress th e resp o n se key and th e fo o t sw itch to s ig n a l he was p rep ared to r e a c t * The fo o t sw itch i n i t i a t e d th e fo re p e rio d and was f i e l d down u n t i l th e r e a c tio n had been executed# By l i f t i n g h is fo re fin g e r from th e le v e r, S, stopped th e counter* E would th e n read th e re a c tio n tim e aloud to S and' re c o rd i t on th e d a ta sheet* This p ro cess was re p e a te d u n t i l a l l th e d a ta were reco rd ed fo r each block* A r e s t p e rio d o f 10 m inutes se p a ra te d one block from another* When a low energy fla s h follow ed a h igh one in th e t r i a l s, a r e s t p erio d was in s e r te d to allo w S to re a d ap t to p rev io u s le v e ls * Each sessio n la s te d from 1 to 2 hours* ' '. In Experim ent I, t r i a l s were ad m in istered in b lo ck s o f 35* Each blo ck was id e n tif ie d by one of th e th re e lum inance v alu es which was p a ire d w ith each of th e seven d u ra tio n s g iv in g a t o t a l o f 7 condh- tio n s fo r each one of th e th re e blocks* The o rd er of each d u ra tio n as i t was p a ire d w ith each I n te n s ity i s giv en in Table 1*.Five r e a c tio n tim es were c o lle c te d f o r each d u ra tio n in any one block every session* F i f t y re a c tio n s were c o lle c te d fo r each dtira&lott lum inance c o n d itio n over te n sessio n s* The S s a t f o r one se s sio n p e r day*

23 TABLE I The E xperim ental D esign of 'Experim ent I Luminances a re re p re se n te d by c a p ita l l e t t e r s, and d u ra tio n s a re re p re se n te d by t h e i r v alu e i n m illise c o n d s* Each d u ra tio n - lum inance conditio n, was re p e a te d 5 tim e s, as ex p lain ed in th e te x t Day C onditions 1 A3>96,6,.24*12,48,500 B6,24>12*48,500,96, B3, 9 6,6,2 4,1 2,4 8, , 2 4,1 2,4 8,5 0 0,9 6,3 A12, 48, 500, 96, 3, 24,6 3 c3, 9 6,6, 24, 12,4 8,500 A6, 2 4,1 2,4 8,5 0 0,96, A3, 9 6,6,2 4,1 2,4 8,5 0 0 c12,4 8,5 0 0,9 6,3,.2 4,6 B6*24,12,48*500,96,3 3 B3, 9 6,6, 24, 12, 48,500 A12, 48, 500, 96, 3, 24,6 B6, 24, 12*4.8, 500, 96*3 6 C3, 9 6,6, 24, 12, 48,500 b1 2,4 8,500, 96, 3,2 4,6 A6,2 4,12, 48*500*96,.3 7 A9 6,2 4,5 0 0,6,3,1 2,4 8 E500,.6,3,12*48,24,96 03, 12, 48, 24, 96, 6,500 8 B9 6,2 4,500,6*3,12,48 C5 0 0,6,3,12*48,24,96 A3*12,48* 2 4,9 6,. 6, G96*24*500*6*3*12,48 A500,6,3,1 2,4 8,2 4,9 6 B3,1 2,4 8,2 4,9 6,6, A6, 500*12,48,24*96,3 G2 4,9 6,3,5 0 0,6,4 8,1 2 B12, 4 8,24*96*3 *500*6

24 I n Experim ent I I # t r i a l s v e re ad m in istered In fo ttr b lo c k s. F ive d u ra tio n s were used,, and each d u ra tio n was p a ire d >rith each luminance re p re se n te d in every b lo ck. Every luminancej, th e n, was re p re sen te d in two b lo c k s. T able I I shows th e design f o r Experim ent I I, F iv e r e a c tio n tim es were c o lle c te d fo r each d u ratio n -lu m in an ce c o rd l- t i o n in every block y ie ld in g a t o t a l o f 10 re a c tio n s p e r day p er ; c o n d itio n. Five days w ere re q u ire d to c o lle c t a t o t a l o l 50 re a c tio n s f o r every c o n d itio n. The rem aining p ro ced u re for Experim ent I I was th e same as th a t fo r Experim ent I,

25 16 TABLE I I The E xperim ental Design of Experim ent I I Luminances a re re p re se n te d by c a p ita l l e t t e r s, and d u ra tio n s t a re re p re se n te d by t h e i r v alu e in m ille se c o n d s«each lum inance appears tw ice in each se ssio n p a ire d w ith each o f 5 d u ratio n so Day. C onditions 1 A3 0,4 0,60,80,120 B4 0,60,80,120,30 ' A6 0,8 0,120,30,40 B8 0,120,30,40,60 2 B4 0,6 0,80,120,30 A6 0,80,120,30,40 B8 0,1 2 0,3 0,4 0,6 0 ' A1 2 0,3 0,4 0,60,80 3 A J; '. '. b 60, 80, 120,30,40 80,120,30,40,60 B1 2 0,3 0,4 0,60,80. A3 0,4 0,6 0,8 0,1 2 0 A B8 0,1 2 0,3 0,4 0,6 0 '. A120,3 0,4 0,6 0,8 0 A3 0,4 0,60,80,120 ^ B4 0,60,80,120,30 5 A1 2 0,3 0,4 0,60,80 A3 0,4 0,60,80,120 B 1 ' -p '' ' 40, 60, 80, 120,30 / 60, 80,120,30,40

26 RESULTS E xperim ent I The d esig n of t h i s experim ent was c o n stru c te d so th a t a. lum inance-by-duration-by*-subj e c ts a n a ly s is of v a ria n c e m ight be perform ed oti th e d a ta * The a n a ly s is was perform ed on median r e a c tio n tim e sco res and n o t mean r e a c tio n tim e scores* This was done because in some c o n d itio n s, some f la s h e s were n o t seen b y th e su b ject* Thus a f la s h a t th re s h o ld le v e ls m ight n o t be seen and th u s would be counted a s an i n f i n i t e r e a c tio n tim e, hence th e median i s th e only m eaningful m easure o f c e n tr a l ten d en cy. The F r a t i o f o r th e. a n a ly s is o f v a ria n c e was te s te d a t t h e. 0.1 p ercen t le v e l of c o n fiv dence.. The e f f e c ts o f d u ra tio n, lum inance, and d u ra tio n by lu m i- nance wer e te ste d *. - In t h i s experim ent, seven d u ra tio n s w e r e a d m in istered to. th e s u b je c t a t th r e e lum inances* The lum inances ranged from n ear th re s h o ld to in te n s e v alu es * F ig u res 2, 5, and 4 p re s e n t th e median re a c tio n tim es of a l l th r e e su b je c ts p lo tte d a g a in s t th e d u ra tio n o f th e stim u lu s a t each o f th e th re e lum inance le v e ls * In sp e c tio n bf th e s e curves' re v e a l t h a t, g e n e ra lly, re a c tio n tim e i s in v e rs e ly r e la te d to an in c re a s e in d u ra tio n f o r th e two low est lum inances (0*42 ml* and 0*84 m l* ), and t h a t fo r th e h ig h e st lum inance (2,670 ml*) th e r e seems to be l i t t l e e f f e c t o f d u ra tio n Upon re a c tio n 'tim e * F u rth e r in s p e c tio n re v e a ls th a t f o r a l l th re e. s u b je c ts - f o r th e two low est lum inances, r e a c tio n tim e d ecreases w ith a d d itio n a l In creases, i n d u ra tio n to a p o in t a f t e r which re a c tio n ' ' ' ' 17 - ;.

27 18 S U B J E C T J. B m. L m L - 2, m L L O G T I N M I L L I S E C O N D S FIGURE 2. Median reaction times plotted as a function of log stimulus duration for subject J.B. '

28 19 S U B J E C T L. H m L m L 2, m L L O G T I N M I L L I S E C O N D S FIGURE 3. Median reaction times plotted as a function of log stimulus duration for subject L.H.

29 20 S U B J E C T T. S m L m L - 2, m L L O G T I N M I L L I S E C O N D S FIGURE 4. Median reaction times plotted as a function of log stimulus duration for subject T.S.

30 tim e no lo n g e r decreases* This p o in t seems to l i e ne&r 48 m i l l i seconds' f o r a l l subjects.*. The g r e a te s t d iffe re n c e between any two co n secutiv e p o in ts on th e curve i s between th e th re s h o ld f la s h (3 m illise c o n d s a t 0*45' m illila m b e rts ) and th e n ex t h ig h e st f la s h (6 m illise c o n d s at. 0*45 m illila m b e rts )» R eaction tim es fo r th e f i r s t fla s h o f th e low th re s h o ld curve a re 100 or more m illise c o n d s h ig h e r th a n th e re a c tio n tim es f o r th e second f la s h on t h a t curve* R eaction tim e ap p ears, th e n, to d ecrease most a p p re c ia b ly to in c re a s e s o f stim u lu s d u ra tio n a t. th re s h o ld l e v e l s The doubling o f stim u lu s d u ra tio n from 3 m i l l i seconds to 6 m illise c o n d s enabled th e s u b je c ts to see t h i s second fla s h 100 p ercen t o f th e tim e, whereas th e f i r s t f la s h was seen around 50 p ercen t of th e tim e» In th e next curve f o r a lum inance o f 0*84 m illila m b e rts, th e d iffe re n c e between th e 3 m illise c o n d f la s h and th e 6 m illise c o n d fla s h i s not as g re a t as in th e th re s h o ld f la s h * Table I I I shows th e r e s u lts o f th e a n a ly s is o f v a ria n ce p e r formed upon th e se data* The e f f e c ts o f d u ra tio n a re h ig h ly s i g n i f i cant as a re th e e f f e c ts o f lum inance. The e f f e c ts o f th e in te r a c tio n o f d u ra tio n and lum inance, however, f o r t h i s s t a t i s t i c a l t e s t a re n ot s ig n if ic a n t» This would in d ic a te th a t th e e f f o r ts o f d u ra tio n and th e e f f e c ts o f lum inance may be a c tin g in d ep en d en tly o f each o th e r» F ig u res 5, 6, and 7 p re se n t th e curves fo r median re a c tio n tim es p lo tte d a g a in s t lo g ( stim u lu s lum inance tim e stim u lu s duratio n ), o r th e t o t a l f la s h energy.. These curves show t h a t as th e t o t a l f la s h energy in c re a s e s, th e r e a c tio n tim e d e crease s, in s o fa r as th e d a ta f o r th e two low er lum inances a re concerned. T h e o re tic a lly

31 2 2 TABLE I I I A nalysis of v a ria n ce fo r th e d a ta of Experim ent I SOURCE OF VARIATION SUM OF SQUARES DEGREES OF FREEDOM MEAN SQUARES F RATIO SIGNIFICANCE AT 0,1 PERCENT D uration $1, ,656,86 fl = 279,79 61,25 Luminance 133, , 692,97 S u b jects 3, ^652,21 DXS 1, 103, fb = ,38 DIE ,36 ' LXD 35, , fld - 1, SXLXD 40, ,

32 23 R E A C T I O N T I M E IN M I L L I S E C O N D S S U B J E C T J. B m L m L " 2, m L 4. 0 L O G I ( M I L L I L A M B E R T S ) T ( M I L L I S E C O N D S ) FIGURE 5* Median reaction times plotted as a function of log ( stimulus luminance times stimulus duration) for subject J.B.

33 R E A C T I O N T I M E IN M I L L I S E C O N D S S U B J E C T L. H m L m L " 2, m L ' Q _ Q _ ( y - 0 O L O G I ( M I L L I L A M B E R T S ) T ( M I L L I S E C O N D S ) FIGURE 6. Median reaction times plotted as a function of log (stim ulus luminance times stimulus duration) for subject L.H;

34 25 R E A C T I O N T I M E IN M I L L I S E C O N D S S U B J E C T T. S m L m L " m L 2, m L " ''0 0-.q 0 o L O G I ( M I L L I L A M B E R T S ) T ( M I L L I S E C O N D S ) FIGURE 7 * Median r e a c t i o n t i m e s p l o t t e d as a f u n c t i o n o f log (stim u lu s luminance tim es stim ulu s duration) for su b je ct T.S.

35 26 the. re a c tio n tim e to a f la s h of 6 m illise c o n d s a t 0,4 2 m illila m b e rts should be equal to th e r e a c tio n tim e to a f la s h o f y m illise c o n d s a t 0*84 m illila m b e rtsg b u t as th e c u rre s show, t h i s does n o t seem to be tr u e in d ic a tin g th a t lum inance, has more e f f e c t upon d eterm in in g th e tim e o f r e a c tio n th a n does, duration* The h ig h e st lum inance curve (2*670 m l.) does n o t f o r any of th e th r e e su b jects- show any apprec ia b le d e c lin e of re a c tio n tim e w ith f u r th e r in c re a se in energy due to in c re a s in g f la s h d u ra tio n. For t h i s high lum inance, over th e range o f d u ra tio n s te s t e d, r e a c tio n tim e i s probably dependent upon lum inance alo n e, and not d u ra tio n.. - F igure 8 p re s e n ts cum ulative p ercen tag e frequency curves p lo tte d fo r fo u r d u ra tio n s a t 0.84 m l. f o r su b je c t T«S. The stim u lu s d u ra tio n s shown a re a sam ple' of th e e ig h t te s te d. This fig u re shows th a t th e b r ie f f la s h (3 m illise c o n d s a t 0.84 m illila m b e rts ) produces an in c re a se d v a r i a b i l i t y of resp o n se as w ell as lo n g e r. r e a c tio n tim e s. - In c re a se s in fla s h d u ra tio n decrease v a r i a b i l i t y and d ecrease th e b a s e lin e p o s itio n of each curve in t h i s grap h. E v id e n tly changing th e d u ra tio n changes th e p o p u la tio n o f responses being sam pled. Table IV p re s e n ts th e re a c tio n tim e d ata f o r Experiment- I in th e forms of Median, means and stan d a rd d e v ia tio n s. Means and stan d ard d e v ia tio n s were computed only where 50 re a c tio n s were c o lle c t ed f o r each condxtion. I t w ill be n o tic e d th a t where means were computed th e y do n o t d i f f e r in any g re a t degree from th e.medians th a t have been computed. S tandard d e v ia tio n s were f a i r l y low due to th e u se of w ell p ra c tic e d s u b je c ts.

36 S U B J E C T T. S. C U M U L A T I V E P E R C E N T A G E OA o e M S E C. 4 8 M S E C. 6 M S E C. 3 M S E C R E A C T I O N T I M E I N M I L L I S E C O N D S FIGURE 8. Cumulative percentage curves of fo u r stim ulus d u ra tio n s a t 0.84 m illila n fc e rts fo r su b ject T.S*

37 TABUS JLV R eaction tim e in m illise c o n d s fo r a l l th re e su b je c ts tak en under th e co n d itio n s of Experiment I STIMULUS ' M E D I A N~ S' LUMHfflCE (m l.) SUBJECT J4B* SUBJECT L0H0 SUBJECT ToSo- STMJLUS DURATIONS IN MILLISECONDS ^ » M E A 1 S # * OOS S T A N D A R D D E V I A T I 0 I S T -. *

38 29 Experim ent I I This experim ent was s im ila r to Experim ent I*, tm t i t s purpose was to in v e s tig a te ^ in d e t a i l f o r one tr a in e d s u b je c t,, th e e ffe c t of an in c re a s e in d u ra tio n in a th re s h o ld f la s h 0 S u b ject T«S» was. given f iv e d u ra tio n s, 30, 40, 60, 80, and 120 m illise c o n d s a t two lum inances of 0,054 ml* and 1,0? m l. F ig u re 7 shows th e curves fo r t h i s d a ta, th e p lo ts b ein g re p re se n te d by th e so lid, sym bols. The t o t a l energy fo r th e 30 m illise c o n d and 0,054 m illila m b e rts fla s h and f o r th e 3 m illise c o n d and 0,42 m illila m b e rts f la s h o f Experim ent I i s ap p roxim ately th e same. The r e a c tio n tim e to both o f th e se fla s h e s would be th e same i f th e e f f e c ts of d u ra tio n were equal to th o se o f lum inance. These curves show th a t r e a c tio n t ime i s h ig h e r to 30 m illise c o n d - 0,42 m illila m b e rt com bination th a n to th e one of equal energy in v o lv in g h ig h er lum inances and s h o rte r d u ra tio n s. As in a l l of th e o th e r curves fo r n ear th re s h o ld c o n d itio n s, in c re a s e of t o t a l stim u lu s energy produces a d ecrease in re a c tio n tim e.

39 DISCUSSION The p r in c ip le purpose of t h i s stu d y was to determ ine th e e f f e c ts o f d u ra tio n o f a v is u a l stim u lu s upon sim ple human r e a c tio n tim e. Since p rev io u s s tu d ie s have employed a lim ite d ' range Of stim u lu s d u ra tio n s ' a t high lum inances8 t h i s stu d y has used a la rg e range of d u ra tio n s from 3 to 500 m illise c o n d s a t lum inances t h a t ranged from th re s h o ld to v ery b rig h t v a lu e s. The f i r s t experim ent showed th a t re a c tio n tim e i s in v e rs e ly r e la te d to an in c re a s e in d u ra tio n fop th e two low est lum inances te s te d, and th e r e a c tio n tim e i s.f a i r l y co n stan t to th e rem aining v e ry high lum inance. Furtherm ore- f o r th e two low lum inance curves,, re a c tio n tim e d ecreases as stim u lu s d u ra tio n in c re a s e s up to a c e r ta in d u ra tio n a f t e r which 're a c tio n tim e i s a co n stan t* These fin d in g s a re in accord w ith th e study by Graham and M argaria (1935) n th e a r e a, in te n s ity, and tim e r e la tio n s in v is u a l th re s h o ld in th e p e rip h e ra l re tin a * The p r in c ip le fin d in g h e re was th a t ap p roxim ately r e c ip r o c ity e x is ts f o r s h o rt exposures and sm all a re a s, but i f th e exposure tim e i s in c re ase d beyond a c e r ta in c r i t i c a l d u ra tio n th e n lum inance alo n e determ ines th e re sp o n se. This i s p r e c is e ly th e e ffe c t, th a t i s expected. P revious re a c tio n tim e s tu d ie s have n o t c le a r ly shown t h i s r e la tio n s h ip, and in deed a t l e a s t one stu d y has in d ic a te d t h a t d u ra tio n o f a V isual stim u lu s has no e f f e c t upon re a c tio n tim e. To summarize some fin d in g s' of e a r ly in v e s tig a tio n s in to th e d u ra tio n o f a v is u a l stim u lu s and re a c tio n tim e m entioned in a previous s e c tio n of t h i s p a p er, two c o n tra ry r e la tio n s h ip s have been

40 r e p o r t e d F r o e b e r g (1907) found th a t re a c tio n tim e in c re a s e s a r i t h m e tic a lly.as d u ra tio n d ecreases g e o m e tric a lly, or th a t r e a c tio n tim e 31 in c re a s e s as d u ra tio n d e c re a se s. This fin d in g seems to f i t in w ith th e r e s u l t s of t h i s p re sen t experim ents but as W ells has p o in t out (1913) F ro eb erg 1s d a ta were n o t v ery convincing sin ce th e d iffe re n c e s produced by th e a d d itio n of d u ra tio n were l i g h t and p ro b ab ly not above th e in flu e n c e s of chance o r e r r o r. W ells (1913) in an attem p t to c le a r up many of th e d i f f i c u l t i e s th a t a ro se out of F ro eb erg r s d ata in v e s tig a te d th e e f f e c ts of d u ra tio n o f a v is u a l stim u lu s upon re a c tio n timej. b u t re p o rte d le s s p o s itiv e, r e s u lts th a n F ro eb erg, W ells found th a t r e a c tio n tim e d id n o t d ecrease as d u ra tio n in c re a se d, and i t was s ta te d th a t i f th e re was any r e la tio n between re a c tio n tim e and th e d u ra tio n o f stim u lu ss i t was th a t th e lo n g e r th e d u ra tio n of th e stim u lu s th e lo n g er was th e re a c tio n. This in d ic a te s a d ir e c t r e la tio n s h ip between d u ra tio n and re a c tio n tim e. According to t h i s, then# i f d u ra tio n in c re a se s re a c tio n tim e would in c re a s e. In th e l i g h t o f th e th re s h o ld s tu d ie s m entioned p re v io u sly in t h i s p aper, th e se fin d in g s do not make good sen se. In th re s h o ld s tu d ie s I t = 0 hold s up to a c r i t i c a l d u ra tio n a f t e r which 1=0, I t was th e purpose of t h i s stu d y to employ i n t e n s i t i e s o f v is u a l s tim u li in th e th re s h o ld re g io n where a lo n g er d u ra tio n i s a ffo rd e d and stim ulus energy m ight c o n trib u te to th e sensory e f f e c t. The d iscrep ancy of th e d ata of W ells and Froeberg i s probably due to th e high stim u lu s i n t e n s i t i e s th a t were used, and i f c r i t i c a l d u ra tio n depends upon f la s h lum inance th e n t h e i r i n t e n s i t i e s determ ined th e resp o n se and d u ra tio n had l i t t l e in flu e n c e. The r e s u l t s of t h is

41 . - ' '. 32 p re se n t stu d y in d ic a te th a t c r i t i c a l d u ra tio n seems to depend upon fla s h luminancej, and th a t as h ig h e r lum inance le v e ls a re reached in c re a s e s \. - ' ' in duration; (beyond some sh o rt c r i t i c a l p e rio d ) do n o t a f f e c t th e re d u cib le m argin o f th e re a c tio n tim e» I t i s th e r e f o r e in c o rre c t to s t a t e, as d id W ells, th a t stim u lu s d u ra tio n has no e f f e c t on re a c tio n tim e,. The a n a ly s is o f v a ria n ce perform ed on th e d a ta o f t h i s stu d y re v e a ls th a t th e e f f e c ts of d u ra tio n a re h ig h ly s ig n if ic a n t as a re th e e f f e c ts o f 'lum inance.

42 SUMMARY - Reaction; tim es have been reco rd ed f o r v a rio u s com binations of stim u lu s d u ra tio n s and stim u lu s lum inances f o r the. p e rip h e ra l r e tin a of th e human, The r e s u l t s o f Experim ent I where seven d u ra tio n s were p a ire d w ith th r e e lum inances a r e summarized as fo llo w s: lo R eaction tim e d ecreases as stim u lu s d u ra tio n in c re a se s fo r th e two low est lum inances, 2a R eaction tim e approaches a co n stan t a t th e h ig h e st luminance a t a l l stim u lu s d u ra tio n s, 3, In th e low lum inance curv es? r e a c tio n d ecreases w ith a d d itio n a l in c re a s e s in d u ra tio n to a p o in t a f t e r which r e a c tio n tim e no lo n g e r d e c re a se s, 4» R eaction tim e appears to d ecrease most a p p re c ia b ly to in c re a s e s o f stim ulus d u ra tio n a t th re s h o ld le v e ls, 5= As th e t o t a l f la s h energy in c re ase s^ th e re a c tio n tim e d e c re a se s, in s o f a r as th e d a ta f o r th e two low er lum inances a re concerned, 6, The h ig h e st lum inance curve (2,670 m l,) does n o t fo r any o f th e th r e e s u b je c ts show any a p p re c ia b le d e c lin e of r e a c tio n tim e w ith' f u r th e r in c re a s e in energy due to in c re a s in g f la s h d u ra tio n over th e range of d u * atio n s te s t e d. These r e s u lts a re in te r p r e te d as in d ic a tin g th a t up u n t i l a c r i t i c a l d u ratio n ^ th e tem poral le n g th of a v is u a l stim u lu s a f f e c ts r e a c tio n tim e, f u r th e r c r i t i c a l d u ra tio n i t s e l f i s dependent on fla s h lum inance, ', ' 33 ' /. '