Psychol. Forsch. 36, 145-161 (1973)
© by Springer-Yerlag 1973
Light-Difference Threshold and Subjective Brightness
in the Periphery of the Visual Field*
.
Ernst P6ppel** and Lewis O. Harvey, Jr.**
Department of Psychology, Massachusetts Institute of Technology, Cambridge,
:Massachusetts
and
Massachusetts Coilcge of Optometry, Boston, l\Iassachusetts
•
Received December 30, 1972/April2, 1973
Summary. Light-difference thresholds were measured in the center and peri-
phcry of the visual field at photopic and scotopic levels. Under photopic conditions
the fo· , a has the lowest light-difference threshold. From the fovea to 10 degrees
eccont"fity threshold gradually incre:~qns. It relllains constant up to approximately 35·degrees eccentricity in the temporal visual field (nasal retina). Beyond the
edge of this plateau of constant Iight.difference threshold, it again increases to the
limit of the visual field. Under scotopic conditions the extent of the plateau of
constant light-difference threshold remains the same as under photopic conditions.
" The fovea itself" however, and its immediate environment are less sensitive than the
plateau area.
Subjective brightness of a supra-threshold target is not dependent on its position in the visual field. A target with a given luminance will elicit the same brightness sensation at all retinal positions. As a consequence of this brightness constancy
throughout the visual field, peripheral targets at threshold appear brighter than
foveal targets at threshold because a peripheral target at threshold has more luminance than a foveal target at threshold.
'.
•
ZusammenfatJaung. Die Inkrementalsehwelle wurde in der Fovea und in der
:>eripherie des Gesichtsfeldes bei photopischen und skotopischen Adaptationsbedingungen gemesson. Bei plwtopischen Bedingungen ist die Schwelle in der Fovea
am geringsten (groBte Sensitivitiit). Yon der Fovea bis etwllo 10 Grad in die Peripherie nimmt die Inkremelltalsehwelle allmii.hlich zu. Die Sehwelle bleibt dann konstant bis etwa 35 Grad imi temporalen Gesichtsfeld (nasale Retina) und bis etwa
20 Grad iII1 nasalen GeHichtsfcld (temporale Retina). Jenseits dieses Plateaus
konstanter Sensitivitat nimmt die Schwelle wieder zu, bis schlieBlieh das Enue des
Gesichtsfeldcs erreicht wird. Bei skotopischen Adaptationsbedingungen wurde die·
* For Jiirgen Aschoff'll 60th ~irthday.
,
, ** E.P. was supported by Deutsche Forschungsgemeinschaft, L. O. H. by the
Slorm Foundation. ~,. O. H. is Assistant Profcssor of Physiology and Ph)'siologica\
Optics at t~ Massachusett!l College of Optomctry and Rcsearch Associate at the
Department:of Psychology., MaRsachllscttR InRtitllte of Technology.
This paper is based on pnJscntations by both authors at the mecting ofthe Eaetern
Psychologiea.l Assoclation in Boston, April 27 -29, 1972.
,
10·
,
146
E. Poppel and L. O. Harvey, Jr.:
selbo A\JRdehnl1n~ des Plateaus lconstariter fiehwelIe iml temporalen und nasa.len
Gesichtsfeld beobachtet. Die Fovea und die unmittelbare Umgebung der Fovea
ha.ben bei skotopischen Bedingungen eine geringere SensitivitKt.
Die subjektive Helligkeit iiberschwelliger Reize ist nieht abhiingig von der Lage
cles Lichtreizes im Gesichtsfeld. Ein liberschwelIiger Reiz mit gegebener Intcnsitiit
hat iiberall im Gesichtsfeld dieselbe subjektive Helligkeit. AIs Konscquenz der Konstanz del' Helli!:(kcit im Gesiehtsfcld crscheillen Schwcllenreize in del' Peripherie
heller als Sehwellenreize iin Fovea-nahen Bereich, da die Lichtintensita.t fUr Schwel·
lenreize in del'
Peripherie
grof3er
ist
als
im
Fovea-nahcn
Bereich.
•
I. Introduction
In a recent revil'v Aulhorn a1)d Harms (1912) proposed ~ha.t the
Rpecial perimeter constructed by Harms should make it possible to
determine various "functions in any part of the visual field and for
any state of adaptation." One of the functions they mention is the
"light-difference threshold". We have attempted to measure the
light-difference threshold throughout the entire visual field. Prcvious
I
'
measurements of the light-difference threshold in the visual field
eit,llCr were made exclusively a.long the horizontal meridian (e.g.,
\
Aulhorn, 1964), or were confuied to an area close to the fovea (e.g.,
'
Kishto, 1970).
There are various reasons, in addition to mere curiosity, for
\V;shing ·to learn more about the Hght-difference Ithreshold in the peri.
phery I)f thc visual field. In a great nUUlucr of neurophysiological
experiments, properties of receptive fields in the retina (e.g., Kuffler,
1953; Hubel and Wiesel, 1960), the lateml geniculate nucleus (e.g.,
Hubel and Wiesel, 1(61), and the visual cortex (e.g., Hubel and Wiesel,
1968) have been described. One general observation ha.s been that the
diameter of receptive fields in all these structures increasl,ls 'with increasing
distance from the visual axis. In order to relate this obsel'vat,iun to the
light-difference tlucshold in man, as Aulhorn and H~l'ms ('1072) have
suggested, the light.difference threshold throughout the visual field
I
needs to be defined.
Visual information from the periphery of the visual field determines
to a great extent orientation in space. If the light-difference threshold
varies differentia.lly along different meridians, there may be preferences
in oculomotor reactions along the more sensitive meridians. ~ye movements I to targets appearing in m9re sensitive a,reas may be ~ifferent
than movements to target8 in less ~ensitive areas. Thus, information is
needed about the sensitivity of the peripheral visual field, if onc wishes to
study oculomotor performance (Frost and Poppel, '1(73).
~
.In addition, ithere ~re a number of practical reasons for mea.suring
the sensitivity of the peripheral visua.l field. On any task involving
surveillance of severa.l control instrUments, the observer - for instance
,
•
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Differential Threshold an d Subjective Brightness in tll c Pe rip he ry
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LUMINANCE ABOVE BACKGROUND (m U
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Ol alo nce fro m IlIe Fo ve a In Ot v re ..
Fi g. 3. Light.difference thresholds (L1LfL) as a fu nc tio n of re tin
al locus an d
ad ap ta tio n level. MrJ\surements ob.~ined from th~ rig ht cye of.
E. P. alo~.th~
ho riz on tal m er id ian un de r five different adaptatIOn levels: a.
8.5 x 10 , b.
8.5 x 10 -2 ; c: 8.5 x 10 -3 ; d: 8.5 x 10 -·; e: 8.5 x 10 -5 ~illilambert
. Tar~et size:
10 m in ar c of visual angle. Du ra tio n of ta rg et pr es en ta tio n: 200
msec. No te ~he
decrease of foveal se ns iti vi ty compared to th e pe rip he ry un de r. da
rk a~aptatlO~
(o) an d th e remaining constancy of light.difference th~cshold III
th c pla_tean
ar ea irrespective of th e level of ad ap ta tio n. (D at a ta ke n from Ha rv
ey an d Po pp cl,
1972)
I
Fig. 4. Su bj ec tiv e br ig ht ne ss of different su pr a.t hr es ho ld ta rg et
s pr es en te d at
tw o positions in th e pe rip he ry of th e visual field at 5° a.nd 30°.
Ta rg et 10 m in
ar c, pr es en ted for 200 msec. Ba ck gr ou nd : 0.83 millilambert. M
easurements for
th e rig ht eye of E. P. along th e horizontal meridian. Ea.ch po in t
or circle is th e
geometric m ea n of 10 individual m ag ni tu de es tim ate s. No te
th e increase of
m ag ni tu de es tim at es wi th increasing luminance. Fo r fu rth er de
tai ls see te xt
fit te d to th e da ta fo r ea ch re tin al lo ca tio n us in g t,he le as t·s qu ar es cr
ite rio n.
Th is fu nc tio n ha s th e fo rm :
1Jl= K(<p- <PoY]
re m ai n fa irl y co ns ta nt bo th on th e te m po ra l an d ?~ th e na sa l si
d~. In
th e mesopic re gi on (Fig. 3, eurve d, 8.5 X 10 -4 ml1ltlambert) th e
hghi...
difference th re sh ol ds for fovea, pe rif ov ea an d pl at ea u ar e th e sam
c.
Th es e ob se rv at io ns suggest th at th e pl at ea u of co ns ta nt lig ht .differen
ce
th re sh ol d ca n also be found un de r mesopic an d scotopic ad ap
ta tio n
co nd iti on s. Th e ex te nt of th is pe cu lia r ar ea ap pe ar s to be ra th
er un ·
affected by th e level of ad ap ta tio n. W ha t is affected is th e se ns
iti vi ty
of th e foveal re gi on re la tiv e to th e re st of th e vi su al field.
3. Subjective Brightness in the Periphery of the Vi su al Fi el d
Fi g. 4 pr es en ts th e geometric m ea n of ma~nitude es tim at es
. for
su bj ec tiv e br ig ht ne ss as a fu nc tio n of target. lu m m an ce for tw o
rc tm al
lo ca tio ns (5 D.nd 30 degrees, te m po ra l vi su al field). Ea ch po in t is th
c m ea n
of te n judgment.s. It ca n he seen in Fi g. 4 th at ~here is a mono
~onjc
re la tio ns hi p be tw ee n stimulus luminanl:o (ll.USClSS:1) :1nu m ag
lll tu ue
estim:1tes (o rd in at e) . Th e ne xt st ep w as to describe th es e da ta
m at hc ·
m at ic al ly . To th is en d, a modified po w er fu nc tio n (Marks, 1966
) was
•
,
w he re 1p = su bj ec tiv e m ag ni tu de ; <p = st im ul us lu m in an ce ; <Po = th re
sh ol d
co rr ec tio n fa ct or ; f3 = slope of cu rv e in log.log co or di na te s; K = co
ns ta nt .
W e at ta ch no th eo re tic al significance to ou r us e of th e po w er fu
nc tio n.
It serves to de sc rib e th e da ta well by ac co un tin g fo r ov er 95
% of th e
v:1riance in ea ch se t of da ta .
Th e solid lines in Fi g. 4 re pr es en t th e be st .fi tti ng cu rv es for th e
tw o
se ts of da ta . Th es e tw o were se le ct ed to sh ow th e ra ng e of slopes
fo un d.
Th e be st ·fi tti ng fu nc tio n ha d th e st ee pe st slope at 5 degrees ec ce
nt ric ity
(f3 = 0.62) an d th o shallowest slope at 30 de gr ee s (f3 = 0.42). Th is
sm al l
ra ng e of slopes su gg es ts th at th e su bj ec t is capable of di sc rim
in at in g
am on g lu m in an ce s eq ua lly well a.t all pe rip he ra l positions. Th er e
w as no
sy st em at ic re la tio ns hi p be tw ee n slope of th e be st -f itt in g fu nc tio
n a.nd
re tin al po si tio n.
Since th e da ta re pr es en te d in Fi g. 4 ar e m ag ni tu de ju dg m en ts m
ad e
re la tiv e to a foveal co m pa ris on ta rg et whose br ig ht ne ss was as si
gn ed a
va lu e of 50, th e da ta Cllon be us ed to de riv e th e lu m in an ce at ea ch
re tin al
locus w hi ch would eq ua l th e br ig ht ne ss of th e fovea I ta rg et . To th
is en d,
th e le as t.s qu ar es po w er ftUletion for ea ch re tin al ec ce nt ric ity was
us ed
to ca lc ul at e th e luminn.nce va lu e of th e ta rg et w hi ch would ha ve el
ic ite d
Differential Threshold and Subjective Brightness in the Periphery
155
.
156
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10
20
30
40
50
60
DISTANCE FROM FOVEA IN DEGREES
(TEMPORAL VISUAL FIELD)
)
Fig. 5. Subjecti,e brightness as a function of retinal eccentricity: Those luminances of the targets at various eccentricities are shown (black dots)' which
~ITespond to the apparent brightness of the foveally presented stimulus (cf.
FI~. 4): The curve connecting the open circles would be obtained, if apparent
brlg~tness of threshold targets were the same for all peripheral positions; more
lu~mance would be neede~ in the periphery to obtain a sensation of eqnal
brIghtness because of the hIgher threshold, or a target with constant luminance
would ~ppcar dimmer in more peripheral areas. The actual measurements (black
?otsl, I~tead, sugg~st that app.a:ent. brightness is related to light intensity
lITe~pectlve of the stImulated pOSItIOn m the visual field. Targets with the same
lummance appear to have approximn.tely the smIle subjective brightness whell
they are presented in different areas of t.he visun.l field, as long as both are
supra-threshold
a judged magnitude of 50. In Fig. 4, the dashed lines represent this
process. It can be seen that the criterion luminance for the target at 5°
is 21 millilambert above background and the criterion luminance for
retinal eccentricity of 30° is 23 millilambert.
The criterion luminance (that luminance which would be judcred
equal in brightness to the foveal stimulus) as a function of retinallo~us
is presented in Fig. 5. The dashed line in Fig. 5 represents the lunlinance
of the foveal comparison target (19 millilambert). It can be seen that in
order t,o appear equally bright a peripheral target must have a luminance
which is approximately equal to 19 millilambert. Fig. 5 shows that the lu.
minance for equal brightness does not change as 11. function ofretinal locul'.
The upper curve in Fig. 5 represent,s the result to be expected if, in
order to appear equally bright, peripheral stimuli had to have luminances
equally elevated at any given location above the local tlu·eshold. Put
in another way, under test conditions given, a 19 millilambert target has
about 210 times its threshold luminance at 2 degrees eccentricity but
only 9 times its threshold luminance at 60 degrees. Yet the results shown
E. Poppel and L. O. Harvey, Jr.:
in Fig. 5 indicate that these two stimuli are equally bright. ,+hese data
suggest that stimuli of equal luminance appear equally bright ~t different
retinal loci.
The present data do not agree with those of Marks (1968). This
conflict is probably due to the following factors: 1) We were interested
in relative brightness judgments which simultaneously compared the
periphery with the fovea whereas Marks was interested in absolute
brightness judgments made for different retinal locations 2) Our range
oftarget luminances was only 1.3 log units, varying around the luminance
of the foveal comparison target since the purpose was to derive luminances
of equal brightness. Marks used a range of luminances of 4 log units, a
very wide ra.nge which falls outside the operating range of the adapted
retina; 3) Our data Were collected with the entire retina maintained at a
constant level of light adaptation. Marks extinguished the adaptation
field one second before the presentatio?- of the test target which remained
on for one second. The judged:magnitudes were undoubtedly influenced by
the rapidly changing state of the darkened retina.
,,-
PREDICTED, FROM
THRESHOLD DATA,-I
E
·'t·~
"
IV. Discussion
1. Distribution ot Sensitivity in the Visual Field
•
The data on light-difference thresholds obtained from 14 subjects
afford a generalized picture regarding the distribution of sensitivity in
center and periphery of the human visual field. This picture is schematically represented in Fig. 6. Under photopic conditions, the fovea has the
highest sensitivity (Fig. 6, A). The perifoveal area (B) has a decreasing
sensitivity beginning at the fovea and ending where the plateau starts.
The radius of the perifoveal area is approximately 10 degrees. If the
data on sensitivity from both eyes are superimposed, the plateau of
constant sensitivity (C) extends from the perifoveal area. to approximately
35 degrees along the horizontal meridian and to approximately 20
degrees along the vertical meridian. The stippled circle outlines the limits
of the plateau from the nasal sides of both eyes. The plateau areas peripheral to the stippled circle are provided by the larger extent of the
temporal plateaus for both eyes. Beyond the peripheral edge ofthe plateau,
sensitivity again decreases until the end of the visual field is reached.
This peripheral area of decreasing sensitivity is over its larger part
binocular (D). The areas marked E in Fig. 6 indicate the monocular
crescents, i.e., those peripheral parts of the temporal visual fields that
fall beyond the edge of the nasal visual fields in both eyes.
The data obtained under scotopic conditions (Fig. 3) and the measurements reported by Crozier and Holway (1939) suggest that the plateau
is rather stable and presumably uninfluenced in its extent when the
Differential Threshold and Subjective Brightness in the Periphery
,/
f
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e'le
,
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"-
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)
Fig. 6. Schematic representation of the human visual field obtained from meas.
. uremcnts of the light-difference threshold throughout the visual field of the
ri~ht and left eye. A: Foveal region with highest sensitivity (lowest light.
difference threshold) under photopic conditions.B: Perifovea.l area. with a
r~dius ap'p~ximately 10° with. increasing light·difference threshold under photo.
plC conditIOns. 0: Plateau With constant light.difference threshold extending
from approximately 10° to 20° both below and above the fixation point and
£:om approximately 10° to 35° along the horizontal meridian. The stippled
Circle on the left (ri~ht~ side indicates the limits of the plateau for the right
(I~ft) eye; the nasal limits do not extend as far as the plateau in the temporal
. V:lsual field. The dark. dot on the right (left) represents the blind spot of the
right (left) eye. D: PerIpheral area of increa.sing light·difference threshold extend·
ing from the lateral edge of the temporal plateau of each eye to the border of the
binocular visual field. E: Monocular crescents, i.e., E on the right (left) signifies the
area. which is only seen by the right (left) eye
adaptation level is changed. Since under scotopic conditions fovea and
pcrifovcal area are less sensitive than the "periphery", the plateau is
the most sensitive part of the visual field in night vision. It is interesting
to note that early measurements of acuity by Aubert and Foerster (1857)
and Dobrowolsky and Gaine (1867) already showed such a horizontally
extended plateau.
The plateau is not concentric with the fovea but with a point approximately seven degrees lateral of the fovea in the temporal visual
field. The optical axis of the eye does not coincide with the visual axis
(fovea) either but, with a point between fovea and blind spot; both
axes are roughly in the same horizontal plane but the optical axis lies
approximat{:ly five degre,es more towards ~he tempora.l side (Le Grand,
1957). The geometric center of the plateau and the optical axis of the
eye thus roughly coincide.
We a.re not aware of any statement ~hich in a satisfactory way
explains why visual and optical are displa.ced from one another. The
E. Poppcl and L. O. Harver. Jr.:
proximity between geometric center of the plateau and optical axis
suggests, however, a speculation why there is such a diRplacement. The
reason may be historic. .Eyes with tl. fovea have dev?lopcd rather late in
evolution; many mammals still lack a fovea. Perhaps the plateau
corresponds to an "early" fovea, iiimilar to the visual streak in rabbits,
and the fovea itself has developed later. For some reason the fovea did
not develop in the geometric center of the plateau which also coincided
with the optical axis, but slightly shifted to the temporal side ofthe retina.
\
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157
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158
2. Relationship between Belzavioml and A.natomical Data
.
The distribution of receptors in the human ret,ina (0sterberg, 1935)
shows a. peak for the cones in the fovea and a peak for the rods at approxi.
mately 20 degrees eeeentriL:ity. A plateau in the distribution of receptors
is not found even if one takes the sum of rods and cones for each retinal
position. If one looks, however, at the distribution of the ganglion cells in
the retina, one finds a pattern which cor:;-esponds closely to the sensitivity
distribution in the visual field.
Van Euren (1963) has determined the distribution of ganglion cells
throughout the retina. He observed that the ganglion cells arc arranged
in layers with one to five ganglion cells in thickness. Tn the most central
part of the retina one finds a ganglion cell layer of five cells in thickness;
this layer is surrounded by a layer of four cells in thickness, which in
turn is surrounded by a layer of three cells in thickness, and'so on. There
are two different kinds of layers with only one ganglion cell in thickness,
a more central one with no intercellular gaps, and 1\ more peripheral one
with intercellular gaps.
It is very interesting to note that the ganglion cell layer with one cell
in thickness and no intercellular gaps has the same asymmetric distribu·
tion and also approximately the same extent as the plateau of sensitivity.
The layer of one cell in thickness and with no intercellular gaps extends
from 12.14 to 32.45 degrees in the nasal retina (temporal visual field) and
from 12.23 to 19.05 degrees in the temporal retina (average data for
14 human retinae). These numbers coincide fairly well with those ob·
tained from the tlu'eshold measurements (Table 1).
One would like to know whether the distribution of receptive fields
in the retina shows a pattern which would agree with the distribution of
sensitivity. In particular, one would expect that the size of receptive
fields in the retina remains constant throughout the plateau. Such data
on the human retina are of course not available, but even for the monkey
retina. there is a lack of information. The only measurements available
indicate that the receptive field size increases with increasing distance
from the fovea (Hubel and Wicscl, 1960), but in order to make the in·
.
Differential Threshold and Subjective Brightness in the Periphery
161
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~
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Dr. Ernst P6ppcl
Dr. Lewis O. Harvey, Jr.
Depn.rtment of Psychology
Massachusetts Institute of Technology
Cambridge, Massachusetts 02139
USA
11·