- Email: [email protected]
Convergence in the human newborn
Convergence
in the
Human
Newborn’
Recent studies of ocular orientation iTI newborn infants hnvc usecl human ob~crrtw to judge direction of orientation (Fantz, 1963, 19661. A reflection of any part. of the stimulus owr the npproxiiwtc~ I)upil ccntcr in either eye: has been used as the operational definition of orientation toward the at~imulus. Such judgment.s of orient’ntion may hc innwurate it t,hc newbow’:: cyw arc not directed toward the same pl:w~ at. a given moment (Inc~l; of co~~wrgc~~c~i or if t,hc eyes do not mox~ together (lack of conjug:~tioni .? It is porsil)lc for the two eyes to move together in colljngation without c>onxwging on the same spot while resting. Dayton, Joucs, Stccl(a, and How ( 1964’1 hnvc rlemonst~ratcd electro-oculogrnphic‘:llly that ~~cd~ornr (xii look at :~ncI follow a series of targets with relntivcly clw;ti c*oltjug:ition of cyc mowments. Hershenson (1964) obeerretl some tlc:grcc of newborn conjugation and convcrgencc, while White (1963) did IIO~ fintl (‘onvc~‘-
’ Fantz (1963) has wcognized the problem of dcttsrminiug ~~s:tctly ~vheria a nelvhoru is lnoking. Hf, stat4 that eye movements and fixations are not as clrar in newborns as in older infants and that photographic techniques might, hc superior lo t,hP usual human observer-juclgt71
genc*c>ill th(l newborn. Thus, although evidence indicates that conjugate eye mov(~mcnts occur in newborn infants, the evidenrr for cnnvergence is less fl(%l,. The present study consisted of two esperiments. The first experiment n-:W designed to assess color-brightness preference in newborns. In large l)nrt the Ss’ tmo eyes were not directed toward the s:mle stimulus at a given moment, and therefore preference could not be determined un:mbiguously. Consequently, a second experiment was designed el~ecifically to stutly convergence. As previous experiments have shown preferences for pnt,tc~rns in newborns (Fantz, Ordy, and Udelf, 1962; Fant8z, 1963)) Esp. 2A paired :L distinctive striped stimulus with a neutr:il gray one. Esperimerit 2B used a single center stimulus to test the pos4bility that stimulus competition with the pairocl st,imuli might have accounted for t,he lack of c+onr’crgence in Exp. 1.
Subjects Subject’s for the espcrimcnts were 28 awake newborn infants from 2 to :i clays of age in the nursery of the ‘I’nlc-Kcw Haven Community Hospital. In Esp. I Tvcre 16 XY, 9 males and 7 females. In Exp. 2 were 12 S$, 8 males rind 4 females. An additional 34 babies were seen, but observations of these bxbies could not be usccl either because they fell asleep during the olwenxtion or because their film records were unscorablc.
The rspc~riments w’ere conducted in R small room on t’hc maternity ward of the hospital. Figure 1 shows a diagram of the app;uxtus. The> S was placed facing upward in a head-restraining crib on 3 tnblc. Two grounclglass et,imulus screenswere mounted 14 inches above S’s head, oIle to each Fi(le of midlinr. The screenswere G-inch squares anal were 6 inches apart. The total stimulus ficl(l, from the left edge of t#heleft scre(ln to the right c~lgc of the right, screen, subtended npprosimnt,ely 60” of visual angle. TWO .500-w slide projectors were mounted so as to project, st,imullusimngcs from slides onto the screens when the projector bcnms wrre bent 90’ by t’wo front surface mirrors above t,ltc screens. Four Bausch and Lomb Nicholas illuminators fitted with Kodak Wrat,tcn 87C :mtl Corning 7.69 filters were used as marker lights for the stimulus panels. The filters eliminated all visible light csrept, a barely visible reddish bc:im nborc 800 m/~.
14n Automas 1Iodel G-2 35-mm variable-speed soundproofed camera was mounted above the st,imulus panels behind a wire screen. The camera
E.rperimrnt I. ‘1%~~I’our stimuli were ec~u:trc~ of utliL’oml light ~~ro~ittecl by filters plnct~l between Koclnk B351 glx, ic: slitlc ~ov(~r~. Two red st~imuli. bright and clim, and two gray stimuli, bri& :md tlim, Ivel’c uwd. The bright rctl stimulus was a Wratten 25 filter. The dim rccI stkn~lus was :I Wratten 25 filter plus R M7ratteu ND 1.30 filter. The bright gray stimulus, equated with the bright red for physical intmsit,y, tvus :I Wratten XII .70 filter. The dim gray> equated for physical intensity nith the dim red Anulus, w:ts a Wratt,en ND 2.00 filter. The tlim stimuli were calearly visible, and the bright ones tlirl not, wuse Ss to c~low their c~ycs. Tht, stimuli were grouped into four I)niw: bright rchtl v,<;.(linl ~~(1. l)right red VS.
I,YS
\\‘.
WICKELGREN
plane was measured and subtracted from each S’s mean interpupillnry clistnncc. The resulting difference score was converted into its correrponding rlist.nnce at the stimulus plane, which indicated how far apart at, the stimulus plane each S’s pupil centers were, i.e., the cstent of pupil tlivrrgcnce. The mean disttmce between pupil centers at tli(b stimulus plant :tnd the mean within-subject standard deviation in i~ltcl~l,ul)ill:trp distance wre computed for cnch experiment.
Wxtn proportions Ijrightness st(imuli)
for joint orientations of the two eyes in Esp. 1 (colorare given in Table 1. The matrix shows that, in no
Hight I,Cf ( .~.
eye orientation (!e111 Cl‘
I :ight
.-
LeE L Center
1 (i .(I0
I -1 .OI
.-..‘,a, .-I‘1’)
Kg111
.oo
.oo
.2
5
V:ISCSdid the two eyes cross between panels; all instances of hctwwn-panel nonconvcrgen~~ were in the direction of flare. For example, the right, eye looltetl at the right st~iniulus while the left eye looked at the l(bft Aimulus 22% of the time. The most frequent oriclkation was for both eyes to look right,. Proportions rcprcsenting convergence on a stimulus psnel or on the cemer are along the left-left to right-right, diagonal of the matrir. These proportions are not n true indication of convergcncc; they include instnncw in which 8s cycs were in fact looking at different parts of the same lx~nel :md t,hus did not converge on one l’oint. 1Ic:ui proportions for *joint oricntntions of the two eyes in Esp. 2-4 (stripc,s vs. gray stimulus pair) arc given in Table 2. As in Esp 1 there n-ctre no r:iws of t’lie two eyes crossing between panels? and tlicx most freqwiit orientation was for hot,h eyes to look right. Table 3 gives the mean proportions for joint oricnt~ation~ of t.1~ cyw in Esl). 2B (single center stimulus). In this situation the most frcrluent, orientation was for the right eye to look right and the left eye to look left; there were again no instances of tlic eyes crossing. The mean proportion of convergence (left-left, center-center! nncl right-
clistauce wliicll represented exact convergence on the centkr point was subtractetl from S’s actual intcrpupillnry distnnccs. The resulting differ(‘ncc ~corc:: were conwrted into rorrcsponclin, v dihnccs at t,hc stimulus plane of the figure. ‘I% out,w :ln(l inner lines iron) S 19’:: 13,vw to tlw
STIMULUS PLANE
STRIPED-GRAY
PAIR
STIMULUS PLANE
CENTER
STIMULUS
l;lc,. 3. 1
and the lower tliagram Frc~ll~~‘n~.y distributions
represents his kmge of thr interpupillary
when hr. distanree
,STIMULUS PLANE
( ADULT
”
!,
111 I;\-(x The coiwspoiitlirig mean pupil diwrgcncc :rt the stimulus pl:lne xv:Ls 5.22 inche,q.The mwii within-subject, skuitlnrtl cleviat,ion of intcrpupikwy tlibt:liiw n-as ,025. In Exp. 2A (stripw VS. gra;r stirnullw 1xGk.I the mean ~list:Hiw hctcve~li die pupil centers w:ts 1.47 inch(5, .03 inch grcxtcr tlinli 1lit il~tc~q~upillw~ clistnncc representing wnct conw~‘pcnw ot’ llw oyw. 1’11~8 cwriwpoucliug mean pupil tlivcrgence nt the stimulus pl:t~ir~ nxs 2.61 incli(x Tllc m(?:111 within-subject rtnndnrd cleviat,ion of illt~c’l~l~ul)illnrydiut:mw was .037. In Esp. 2B (center light) the mean distanw hetmecn the pupil centers was 1.49 inchw, .05 inch greater thnn the i~ltc~rpul~illnr~ rlis-tanre rrpre-
senting exact, conwxgence of the cyw. The corresponding mean pupil divergence nt the stimulus plane ww 4.35 inches. The man withinsubject standard deri:itjion of intcrpupill:~ry distance was .014. There was no eignifir:mt tliffercnc*c among the espcriments in the mean distnncc betmcen lwpil centcw. The me;111~~ithin-Puhject slantlad clwiat,ioli for Xs seeing tlicx strilx$S \Y. gray ,stimulus pair was significantly gre:tkr both than that ~~-hcn the Fame SS ~xrf scxeiiig the center stimulus ( t --= 2.14, df = 11, p < .03‘1 and than that for & weing color-1)rightness st,imnli (t = 1.85, (/,j T 26, p < .ri.Yi The differencxe Iwtweeli the menn lecithin-~;uhjcct st:mdarrl tltG1tioii for cclntor :m(l color-brightnws stimuli ww riot significant. h single :i;:( +- wnicnt. of x11 diffcrcnces roll111 llot 1x5 made t;incc tlic 1 s::mw SS w(~rc run iti Fkp~. 2A1 :llld 2R. I)TS(‘PSSTOS , ,
St.iniuliw prcfcrcncw n-crc’ iii:~.~ktrl in niort in&uiccs by dominant posit,ioll prcfcrcnces, whirli nia~le the m:yJCt~utlc of indix-itlual stimulus prefercnrrs negligibly sm:~ll. Wlicn 1)r~f~w~ii~(~ ww :tkgnchtl t,o in(liridii:rl 85. c~st~remc iiidiviclu:cl flificrciic*c~~ ill the orrlcr of &muhls prcfcwnce prec+lutletl t,he c~~;t:ll,li~lirnc~lit of :1.11o\-c&1x11or(lcr of 5~iriliihw prcferwlcc. Alorc’over, stimulus prcfcrc~iice t(xli(l(‘llci( ‘S coulcl not 1)~ i~itc~rlxc’tccl me:tningfull~ ,kicc tlicy wcw bawd on (‘;ww in 1rliic*h 8~:’ P~-CYoftclli wwc’ not looking at upon caws of the sarnc p:m(~l. Fkminntioll 01 tlloSc! tl:Lt:l Ixkwl only convergence upon oi1t’ p:u1(~1 clifl ilot yicsltl :m> consistent prefcwnccs in eit,lier espcrimciit. Tn both csperimcnts newborns somehcs (lit1 converge on a sir&~ stimulus; that is, both eyes wcrc tlircctcd ton-arll one stimulus at a part,icular momcnt. Such nomin:kl coiivcrg(‘Iice on :I stimulus panel oft8ell occurred, l~owcvcr, v;hen the two clyc~ ww :tctunlly tlirect,ed to di.ferent pcwfs of t11nt p:\11c1. Ful~tlleJ~lnoYc. ,Ss’ ryes often did not cwn converge upon tlic .amc stimulus lxtnchl. Convc~rgenw upon n xtimulus panel w-as Agnificmitl-y greater with the +.ilws vh. gray stimulus pair than with c,olor-hriglit,iicse st,imuli. l.:i(~l; of (‘on\.(‘r~(‘ncc’ might, inrlicatc: lack of :I well-perccivetl stimulus on n-liich to conr-crgc, L Qtiinulw compct~itioii, physi..,. cnl inability to coiix~~rge~or ~omcbcombin:~tioli of t,liew powbllitlw. The diffcrciiws bckccn the cqc~rimc~lits in :mioiiiit of Iio~i(‘o~l~-crgcI~ccma> ha\-e rcflccte(l in p:trt, some kincl of tliffclx~ntinl Ftimulw pcrc’Cptibility. Stimulii:: conipctition (lit1 not complet,ely account for nolic~oll~c~~(‘Ilc(’sills nxrrlwcl clirergcnce occurred Iv-it11tl~c xinglcx ~t~imulus.The ctructur(~ of th(, ~rc~wborn’aeye may niukc c~iiwi~g~~iif~difficult. During emblyonic clcwlopment the eyes swing inwnrd from the side of the head toward the front (Mann, 1964). It may be that further growth is necessary before newborns ran hrinr the cpes inw-nrd enough to converge consistently on a stimulus
in the
Human
Newborn’
Recent studies of ocular orientation iTI newborn infants hnvc usecl human ob~crrtw to judge direction of orientation (Fantz, 1963, 19661. A reflection of any part. of the stimulus owr the npproxiiwtc~ I)upil ccntcr in either eye: has been used as the operational definition of orientation toward the at~imulus. Such judgment.s of orient’ntion may hc innwurate it t,hc newbow’:: cyw arc not directed toward the same pl:w~ at. a given moment (Inc~l; of co~~wrgc~~c~i or if t,hc eyes do not mox~ together (lack of conjug:~tioni .? It is porsil)lc for the two eyes to move together in colljngation without c>onxwging on the same spot while resting. Dayton, Joucs, Stccl(a, and How ( 1964’1 hnvc rlemonst~ratcd electro-oculogrnphic‘:llly that ~~cd~ornr (xii look at :~ncI follow a series of targets with relntivcly clw;ti c*oltjug:ition of cyc mowments. Hershenson (1964) obeerretl some tlc:grcc of newborn conjugation and convcrgencc, while White (1963) did IIO~ fintl (‘onvc~‘-
’ Fantz (1963) has wcognized the problem of dcttsrminiug ~~s:tctly ~vheria a nelvhoru is lnoking. Hf, stat4 that eye movements and fixations are not as clrar in newborns as in older infants and that photographic techniques might, hc superior lo t,hP usual human observer-juclgt71
genc*c>ill th(l newborn. Thus, although evidence indicates that conjugate eye mov(~mcnts occur in newborn infants, the evidenrr for cnnvergence is less fl(%l,. The present study consisted of two esperiments. The first experiment n-:W designed to assess color-brightness preference in newborns. In large l)nrt the Ss’ tmo eyes were not directed toward the s:mle stimulus at a given moment, and therefore preference could not be determined un:mbiguously. Consequently, a second experiment was designed el~ecifically to stutly convergence. As previous experiments have shown preferences for pnt,tc~rns in newborns (Fantz, Ordy, and Udelf, 1962; Fant8z, 1963)) Esp. 2A paired :L distinctive striped stimulus with a neutr:il gray one. Esperimerit 2B used a single center stimulus to test the pos4bility that stimulus competition with the pairocl st,imuli might have accounted for t,he lack of c+onr’crgence in Exp. 1.
Subjects Subject’s for the espcrimcnts were 28 awake newborn infants from 2 to :i clays of age in the nursery of the ‘I’nlc-Kcw Haven Community Hospital. In Esp. I Tvcre 16 XY, 9 males and 7 females. In Exp. 2 were 12 S$, 8 males rind 4 females. An additional 34 babies were seen, but observations of these bxbies could not be usccl either because they fell asleep during the olwenxtion or because their film records were unscorablc.
The rspc~riments w’ere conducted in R small room on t’hc maternity ward of the hospital. Figure 1 shows a diagram of the app;uxtus. The> S was placed facing upward in a head-restraining crib on 3 tnblc. Two grounclglass et,imulus screenswere mounted 14 inches above S’s head, oIle to each Fi(le of midlinr. The screenswere G-inch squares anal were 6 inches apart. The total stimulus ficl(l, from the left edge of t#heleft scre(ln to the right c~lgc of the right, screen, subtended npprosimnt,ely 60” of visual angle. TWO .500-w slide projectors were mounted so as to project, st,imullusimngcs from slides onto the screens when the projector bcnms wrre bent 90’ by t’wo front surface mirrors above t,ltc screens. Four Bausch and Lomb Nicholas illuminators fitted with Kodak Wrat,tcn 87C :mtl Corning 7.69 filters were used as marker lights for the stimulus panels. The filters eliminated all visible light csrept, a barely visible reddish bc:im nborc 800 m/~.
14n Automas 1Iodel G-2 35-mm variable-speed soundproofed camera was mounted above the st,imulus panels behind a wire screen. The camera
E.rperimrnt I. ‘1%~~I’our stimuli were ec~u:trc~ of utliL’oml light ~~ro~ittecl by filters plnct~l between Koclnk B351 glx, ic: slitlc ~ov(~r~. Two red st~imuli. bright and clim, and two gray stimuli, bri& :md tlim, Ivel’c uwd. The bright rctl stimulus was a Wratten 25 filter. The dim rccI stkn~lus was :I Wratten 25 filter plus R M7ratteu ND 1.30 filter. The bright gray stimulus, equated with the bright red for physical intmsit,y, tvus :I Wratten XII .70 filter. The dim gray> equated for physical intensity nith the dim red Anulus, w:ts a Wratt,en ND 2.00 filter. The tlim stimuli were calearly visible, and the bright ones tlirl not, wuse Ss to c~low their c~ycs. Tht, stimuli were grouped into four I)niw: bright rchtl v,<;.(linl ~~(1. l)right red VS.
I,YS
\\‘.
WICKELGREN
plane was measured and subtracted from each S’s mean interpupillnry clistnncc. The resulting difference score was converted into its correrponding rlist.nnce at the stimulus plane, which indicated how far apart at, the stimulus plane each S’s pupil centers were, i.e., the cstent of pupil tlivrrgcnce. The mean disttmce between pupil centers at tli(b stimulus plant :tnd the mean within-subject standard deviation in i~ltcl~l,ul)ill:trp distance wre computed for cnch experiment.
Wxtn proportions Ijrightness st(imuli)
for joint orientations of the two eyes in Esp. 1 (colorare given in Table 1. The matrix shows that, in no
Hight I,Cf ( .~.
eye orientation (!e111 Cl‘
I :ight
.-
LeE L Center
1 (i .(I0
I -1 .OI
.-..‘,a, .-I‘1’)
Kg111
.oo
.oo
.2
5
V:ISCSdid the two eyes cross between panels; all instances of hctwwn-panel nonconvcrgen~~ were in the direction of flare. For example, the right, eye looltetl at the right st~iniulus while the left eye looked at the l(bft Aimulus 22% of the time. The most frequent oriclkation was for both eyes to look right,. Proportions rcprcsenting convergence on a stimulus psnel or on the cemer are along the left-left to right-right, diagonal of the matrir. These proportions are not n true indication of convergcncc; they include instnncw in which 8s cycs were in fact looking at different parts of the same lx~nel :md t,hus did not converge on one l’oint. 1Ic:ui proportions for *joint oricntntions of the two eyes in Esp. 2-4 (stripc,s vs. gray stimulus pair) arc given in Table 2. As in Esp 1 there n-ctre no r:iws of t’lie two eyes crossing between panels? and tlicx most freqwiit orientation was for hot,h eyes to look right. Table 3 gives the mean proportions for joint oricnt~ation~ of t.1~ cyw in Esl). 2B (single center stimulus). In this situation the most frcrluent, orientation was for the right eye to look right and the left eye to look left; there were again no instances of tlic eyes crossing. The mean proportion of convergence (left-left, center-center! nncl right-
clistauce wliicll represented exact convergence on the centkr point was subtractetl from S’s actual intcrpupillnry distnnccs. The resulting differ(‘ncc ~corc:: were conwrted into rorrcsponclin, v dihnccs at t,hc stimulus plane of the figure. ‘I% out,w :ln(l inner lines iron) S 19’:: 13,vw to tlw
STIMULUS PLANE
STRIPED-GRAY
PAIR
STIMULUS PLANE
CENTER
STIMULUS
l;lc,. 3. 1
and the lower tliagram Frc~ll~~‘n~.y distributions
represents his kmge of thr interpupillary
when hr. distanree
,STIMULUS PLANE
( ADULT
”
!,
111 I
senting exact, conwxgence of the cyw. The corresponding mean pupil divergence nt the stimulus plane ww 4.35 inches. The man withinsubject standard deri:itjion of intcrpupill:~ry distance was .014. There was no eignifir:mt tliffercnc*c among the espcriments in the mean distnncc betmcen lwpil centcw. The me;111~~ithin-Puhject slantlad clwiat,ioli for Xs seeing tlicx strilx$S \Y. gray ,stimulus pair was significantly gre:tkr both than that ~~-hcn the Fame SS ~xrf scxeiiig the center stimulus ( t --= 2.14, df = 11, p < .03‘1 and than that for & weing color-1)rightness st,imnli (t = 1.85, (/,j T 26, p < .ri.Yi The differencxe Iwtweeli the menn lecithin-~;uhjcct st:mdarrl tltG1tioii for cclntor :m(l color-brightnws stimuli ww riot significant. h single :i;:( +- wnicnt. of x11 diffcrcnces roll111 llot 1x5 made t;incc tlic 1 s::mw SS w(~rc run iti Fkp~. 2A1 :llld 2R. I)TS(‘PSSTOS , ,
St.iniuliw prcfcrcncw n-crc’ iii:~.~ktrl in niort in&uiccs by dominant posit,ioll prcfcrcnces, whirli nia~le the m:yJCt~utlc of indix-itlual stimulus prefercnrrs negligibly sm:~ll. Wlicn 1)r~f~w~ii~(~ ww :tkgnchtl t,o in(liridii:rl 85. c~st~remc iiidiviclu:cl flificrciic*c~~ ill the orrlcr of &muhls prcfcwnce prec+lutletl t,he c~~;t:ll,li~lirnc~lit of :1.11o\-c&1x11or(lcr of 5~iriliihw prcferwlcc. Alorc’over, stimulus prcfcrc~iice t(xli(l(‘llci( ‘S coulcl not 1)~ i~itc~rlxc’tccl me:tningfull~ ,kicc tlicy wcw bawd on (‘;ww in 1rliic*h 8~:’ P~-CYoftclli wwc’ not looking at upon caws of the sarnc p:m(~l. Fkminntioll 01 tlloSc! tl:Lt:l Ixkwl only convergence upon oi1t’ p:u1(~1 clifl ilot yicsltl :m> consistent prefcwnccs in eit,lier espcrimciit. Tn both csperimcnts newborns somehcs (lit1 converge on a sir&~ stimulus; that is, both eyes wcrc tlircctcd ton-arll one stimulus at a part,icular momcnt. Such nomin:kl coiivcrg(‘Iice on :I stimulus panel oft8ell occurred, l~owcvcr, v;hen the two clyc~ ww :tctunlly tlirect,ed to di.ferent pcwfs of t11nt p:\11c1. Ful~tlleJ~lnoYc. ,Ss’ ryes often did not cwn converge upon tlic .amc stimulus lxtnchl. Convc~rgenw upon n xtimulus panel w-as Agnificmitl-y greater with the +.ilws vh. gray stimulus pair than with c,olor-hriglit,iicse st,imuli. l.:i(~l; of (‘on\.(‘r~(‘ncc’ might, inrlicatc: lack of :I well-perccivetl stimulus on n-liich to conr-crgc, L Qtiinulw compct~itioii, physi..,. cnl inability to coiix~~rge~or ~omcbcombin:~tioli of t,liew powbllitlw. The diffcrciiws bckccn the cqc~rimc~lits in :mioiiiit of Iio~i(‘o~l~-crgcI~ccma> ha\-e rcflccte(l in p:trt, some kincl of tliffclx~ntinl Ftimulw pcrc’Cptibility. Stimulii:: conipctition (lit1 not complet,ely account for nolic~oll~c~~(‘Ilc(’sills nxrrlwcl clirergcnce occurred Iv-it11tl~c xinglcx ~t~imulus.The ctructur(~ of th(, ~rc~wborn’aeye may niukc c~iiwi~g~~iif~difficult. During emblyonic clcwlopment the eyes swing inwnrd from the side of the head toward the front (Mann, 1964). It may be that further growth is necessary before newborns ran hrinr the cpes inw-nrd enough to converge consistently on a stimulus