- Email: [email protected]
Orientation and spatial frequency channels in peripheral vision
Vision Rcs. Vol.
13. pp.
2IOWll2.
ORIENTATION
Pergamon Press 1973. Printed in Great Britain.
AND SPATIAL FREQUENCY IN PERIPHERAL VISION
CHANNELS
C. R. SEURPE’and D. J. TOLI-KJRST* Physiological
Laboratory,
Cambridge CB2 3EG, England
(Received 14 July 1972; in revisedform
13 January, 1973)
INTRODUCTION
abundant psychophysical evidence for the existence of systems of channels in the visual system of man seIectively sensitive to limited ranges of spatial frequency and orientation of periodic patterns (SACHS, NACHMIAS and ROBSON,1971; BLAKEWORE and CAMPBELL, 1969 ; CAMPBELLand KULIKOWSKI,1966; BLAKEMORE and NACHMIAS,1971). These studies have all been concerned with central vision. One naturally asks whether peripheral vision utilizes similar channels. Preliminary evidence (SHARPE,1972), showing width and orientation specific fading of the moving entopic shadows of the retinal blood vessels, suggests that this may be so; these blood vessels lie only on the peripheral retina. It is known that subjects are more sensitive to temporally modulated patterns than to stationary patterns in the periphery (see TROXLER,1804). A similar effect is seen in central vision but only at low spatial frequencies (ROBSON,1966). Perhaps, as would be expected from the inability of the periphery to detect fine detail, the high spatial frequency channels are simply absent in the periphery. In other words, is the periphery organized in the same way as the fovea, but with a relative absence of high spatial frequency channels? An attempt is made to answer this question by using spatial adaptation to define channels. BLAKEMORE and CAMPBELL (1969) showed that prolonged viewing of a sinusoidal grating of high contrast elevated the contrast threshold to gratings over only a limited range of spatial frequency, the elevation being maximal at the adapting frequency. Subsequently, BLAKEMORE and NACHMIAS(1971) showed that adaptation is also orientation-specific, and they develcped the method of equivalent contrast to determine the orientation specificity of the effects of adaptation. These techniques have been used in this study to show the existence of spatial frequency and orientation channels in peripheral vision, and to examine the effects of various types of temporal modulation on the properties of these channels. The experiments to be reported here were carried out under photopic conditions. THERE IS
METHODS Gratings, whose luminance was sinusoidally modulated along one axis. were generated on the face of a cathode ray tube (P31 phosphor) by the method described by CAMPBELL and ROEWN (1968). The screen subtended 3.8” of visual angle. Its space-averaged mean luminance was estimated as 140 cd/m2 using an SE1 spot-photometer. The retinal illumination was thus about 2500 td. The screen was brighter than the background (the white wall of a well-lit room). The contrast of the stimuli was defined as (L,.. -&,,)/ I Recipient of a studentship from the MRC of Canada. Present address: Unit, Dept. of Physiology, McGill University, Montreal, Canada. * Recipient of a Scholarship from the MRC of Great Britain. 2103
Aviation Medical Research
C. R. SHARE
‘104
ASD D.J.
TOLHURST
f&n,, f Li,)
where L,,, is the luminance of the peak of the sinusoidal grating and Lmin the iuminance Contrast thus varies between 0 and 1. The voltage required to give a contrast of 03 was determined exactly and, thereafter, the contrast of the stimulus was calculated from the amplitude of the electrical signal fed to the Z-asis of the CRT. The gratings could be caused to drift laterally, could be switched on and off repetitively or could be held stationary. The orientation of the grating could be changed by rotating the deflection coils of the CRT, The subject set his threshold by changing the amplitude of the signal fed to the Z-axis of the CRT (and hence the contrast) using a logarithmic attenuator having steps of 0.025 log units. The results are expressed as contrast semiticity, the reciprocal of the threshold contrast. The mean luminance of the screen was unaffected by changes in the contrast, spatial frequency or temporal frequency. In experiments involving central vision, the subject either viewed a small spot in the centrz of the screen when the stimuli were moving or allowed his eyes to roam randomly when the stimulus was stationary; in rhis way after images of the adapting grating were not generated. Both eyes were used for fovea1 experiments. The peripheral experiments, however, were carried out with monocular vision. The subject fixated a small spot IO” to the left of the centre of the screen, using his left eye alone; his right eye was closed. Thus, the temporal resion of one retina was used. Two subjects, both experienced observers, were used. DJT was an emmetrope; CRS was a well-corrected myope. of the trough.
RESULTS
Infruence of temporal modulation on contrast sensitivity
The peripheral contrast sensitivity to sinusoidal gratings as a function of spatial frequency is shown in Fig. 1. The open squares show the sensitivity to stationary gratings, the filled circles for patterns flashed on and off at 5 Hz, and the open circles for gratings drifting laterally at 5 Hz. This temporal frequency was chosen because it was the one to which the subjects were most sensitive, at ail spatial frequencies. For comparison, similar data are presented in Fig. 2 for fovea1 viewing. Strictly speaking, the two sets of data are not directly comparable as the peripheral data were obtained
Spatial
frequency,
c/deg
FIG. 1. Contrast sensitivity for vertical sinusoidal gratings in the periphery of the visual field. The gratings were viewed with the left eye 10” into the temporal hem~etina. The aatings were either stationary (a), switched on and off at 5 Hz (Of or drifted away from the fovea at 5 Hz (0). Subject CRS.
Orientation
and Spatial Frequency Channels
2105
monocularly and the fovea1 data bin~larIy. CAMPBELLand GREW (1965) have shown that, in the fovea, the binocular sensitivity is about t/2 times the monocular sensitivity. However, the sensitivity to gratings in the periphery is considerably less than would be expected by simply closing one eye; the sensitivity to both stationary and drifting gratings is reduced by about the same factor. The sensitivity curves are shifted towards lower spatial frequencies in the periphery. The frequency at which the sensitivity is greatest is about 4 c/deg in the fovea but only about 2 c/deg in the periphery. Further, the high frequency fall-off in sensitivity is considerably steeper in the periphery, the curve extrapolating to about 9 c/deg compared to the fovea1 value of about 40 c/deg. This shift to low spatial frequencies presumably reflects the difficulty with which fine detail is seen by the periphery.
Spatial frequency,
c/deg
Fro. 2. Contrast sensitivity for vertical sinusoidal gratings viewed with the fovea; both eyes were used. The gratings were either stationary (El), switched on and off at 5 Hz (0) or drifted laterally at the same rate (0). Subject CRS. When the grating is temporally modulated, the low spatial frequency fall-off in sensitivity becomes less severe in both regions of the visual field. The sensitivity for on-off stimuli begins to differ from that for stationary stimuli only at low spatial frequencies. At these frequencies, it was noted that the on-off stimuli appeared to move to and fro in steps, the size of half a period of the grating. At higher spatial frequencies, no such movement was apparent at the detection threshold: the stimuli appeared to be stationary. Similarly, in the periphery, drifting gratings appeared to be stationary at threshold when their spatial frequency was greater than about 4 c/deg (cf. LICHTWSTEIN,1963). Spatial freqtdency selective channels
B~KE~o~ and CAMPBELL(1969) found that prolonged viewing of a high contrast sinusoidal grating elevated the contrast threshold over a spectrum of spatial frequency V.R.13/Il-H
2106
c.
R. SHARPE
AND
D. J. TOLHURST
with a bandwidth of about an octave at half-amplitude, centered on the adapting spatial frequency. This phenomenon is termed “spatial adaptation”. We have used this effect to show the existence of channeis selectively sensitive to limited ranges of spatial frequency in peripheral vision, for stationary and drifting gratings. The procedure was as follows. The subject determined his contrast thresholds over a range of spatial frequencies, five readings being taken at each point; the standard error of these readings was about 15 per cent. He then viewed a high contrast grating of one particular spatial frequency for 3 min before redetermining his threshold for each of the test stimuli. Between each threshold reading, the subject re-adapted for about 20 sec. The change in threshold caused by the adaptation was expressed as relative threshold elevation which is defined as Rel. elev. =
sensitivity before adapting - 1. sensitivity after adapting
Figure 3 (filed circles) shows the adaptation curve after adapting to and testing stationary gratings in the periphery. The threshold was affected only over a narrow range of spatial frequency with the maximum effect at the adapting frequency. The shape of the curve drawn through the points is very similar to that used by BLAKEMORE and CAMPBELL (1969) to describe their results on the fovea. When the subject adapted to and tested moving gratings in the periphery, the threshofd elevation was spread over a slightly narrower range of spatial frequency {Fig. 3, open circles). The adapting grating drifted backwards and forwards, changing its direction every le.5 set; in this way, the waterfall aftereffect was eliminated (WOHLGEMUTH,1911).
Test spatial frequency,
c/deg
FIG. 3. Spatial frequency speciticity of the relative elevation of threshoId for sinusoidal gratings after adapting to a high contrast grating of 2 c/deg (arrow). Ah gratings were vertical and were viewed with the peripheral visual field. The filled circles show the effects of adapting to and testing stationary gratings; the adapting grating had a contrast of 055. The open circles show the effects of adapting to and testing gratings which drifted at 5 Hz; the adapting grating had a contrast of O-1. Subject CRS.
Orientation and Spatial Frequency Channels
2107
The slight narrowing of the etevation curve was also found when the gratings were flashed on and off repetitively rather than being made to drift. Onfy a small number of experiments were carried out and the proposed effects of temporal modulation must be confirmed. Orientcition-specific
channels
BLAKEMORE and NACHMIAS(1971) have developed a method for determining the orientation-specificity of threshold elevation from adaptation experiments; simple non-linearities in the adaptation process can be overcome. Prolonged viewing of a grating raises the threshold for that grating to an extent dependent on the contrast of the adapting pattern; the lower the adapting contrast, the less the threshold is elevated. The threshold can also be elevated by adapting to gratings of different orientations. At any one adapting contrast, the more different are the adapting and testing orientations, the less the amount of threshold elevation. Thus, it is possible “to express the decfine [of the effect] with increasing discrepancy between adapting and testing orientations as an equivalent reduction in contrast of an adapting grating of the same orientation as the test pattern” (BLAKEMORE and NACHMIAS,1971). We have used this method to examine the effects of temporal modulation on the orientation specificity of peripheral channels and to compare these channels to those in the fovea (SHARPEand TOLHURST,1973). The specificity was determined from two experiments. in the first, the subject adapted to gratings of one orientation (the same as that of the test grating) and several different contrasts; and, in the second, he adapted to gratings of one contrast but several different orientations. The test grating was the same throughout. The contrast chosen for the latter experiment was generally the highest contrast which did not produce saturation of the threshold elevation effect. Figure 4 shows the threshoId elevation (in log units) of a 0” (i.e. vertical, moving to the left) sinusoidal grating after adapting to gratings of different orientations and directions of drift. All gratings had a spatial frequency of 2 c/deg and drifted steadily at 5 Hz (2_5”/sec); the adapting gratings had a contrast of 0.1. The convention for labelling the orientation and direction of drift was as follows: 0” refers to a vertical grating drifting to the left, while 180” refers to a vertical grating drifting to the right. A horizontal grating drifting downwards is considered to be 90”. The stimulus was presented 10’ into the temporal retina of the left eye, and so a grating drifting to the left would move away from the fovea. Figure 4 shows that the threshold for a drifting grating can be elevated by adapting to gratings that drift either in the same or opposite directions, but not in directions differing by more than about 60” from these two directions. It wilf be noticed that the grating moving in the same direction is the most effective adapting stimulus. Thus, adaptation in the periphery is both orientationand direction-specific, as it is in the fovea (SEKULERand GANZ, 1963). Figure 5 illustrates the equivalent contrast transformation: the data for the peak centred on 0” are replotted, together with a graph of threshold elevation as a function of the adapting contrast of a 0” grating. This and other elevation vs contrast functions were well fitted by a straight line on log-log co-ordinates over much of the contrast range; at higher contrasts the curve flattened off. From this figure, the adapting effect of a non-vertical grating can be expressed in terms of the adapting contrast of a vertical grating required to produce the same elevation of threshold. For example, adapting to a 20” off-vertical grating with a contrast of 0.1 produced the same elevation of threshold as adapting to a 0” grating with a contrast of about O-04; the equivalent contrast of the 20” grating is thus 044. Figure 6 (solid curve) plots the equivalent contrast against the orientation of the adapting grating,
2108
C.
R.
SHARPE
AFiT)
D. J. Tomms-r
2-O ce’deg
5Hz
I
f
300
11 0
I 60
I
I 120
T
drift
I!
I! 240
I80
Orientation of adapting grating,
de9
FIG. 4. Elevation of the contrast threshoId of a vertical drifting grating after adapting to gratings drifting at other orientations and directions. All gratings had a spatial frequency of 2 c/deg and drifted at 5 Hz; the adapting gratings had a contrast of O-1. The test grating had an orientation defined as 0” (vertical, drifting to the left). 180” refers to a vertical grating drifting to the right, while 90” refers to a horizontal grating drifting downwards. The threshold elevation is orientation specific; adapting gratings were effective only when their orientation was within 60’ of the vertical. Further, the effect was directionally speczfic: compare the effects of adapting to a grating at 0” and 180”. Each point is the mean of five threshold settings and the standard error is indicated. The dashed horizontal lines show the range of threshold elevation which,
statistically, was not significant. Subject DJT.
for those adapting gratings determining the orjentation
centred around 0”. The width of the channel was specified by which was equivalent to a vertical grating of half the contrast.
This quantity (termed the half-width at half amplitude) is indicated by the f3Ied arrow and is about 6-Y. Figure 6 (broken curve) also shows the results of the equivalent contrast transformation for the reverse direction, centred around adapting gratings of 180”. The adapting effect
2-O 5Ht 0.50
0.25 0~
0
20
Orient&ion.
40
60
deg
Adaptingcontrost
FIG. 5.The equivaient contrast transfo~ation. On the left, the decline of threshold elevation with increasing discrepancy between test and adapting orientations is plotted. The data are taken from Fig. 4; the test grating had an orientation of 0’ and the adapting gratings had a contrast of @l. On the right is plotted the decline of adapting effect of a vertical grating as its contrast is decreased. A change in the adapting orientation with constant contrast is equivalent to a decrease in the contrast at one orientation.
Orientation
2109
and Spatial Frequency Channels
0.1
z-
-
z e
0.03
0 E 4 0 .g w”
I
I
I
I
20
30
40
50
I
0.01
IO
Orientation.
deg
FIG. 6. Contrast of vertical grating to which gratings of one contrast but various orientations are equivalent. The solid curve shows the transformed data of Figs. 4 and 5, while the dashed curve shows the transform of the data centred on the reverse direction (180’). The arro*s indicate the orientations which were equivalent to a vertical grating with half the contrast. The half-widths at half-amplitude of the two curves are about 6.5”.
of an off-180” grating was expressed as the contrast of 180’ grating that gave identical elevation of the threshold for the 0” test grating. The dashed arrow indicates the half-width of this channel; it is 6-S’. Table 1 summarizes the results of this and similar experiments. In general, when the gratings were moving, the half-widths were in the range of 6-8’. The results of adapting to and testing stationary gratings in the periphery are also illustrated in Table I. The half-widths were considerably broader, being about 12-20”. Thus, in the periphery, temporal modulation causes a large difference in the half-widths of the elevation curves. TABLE 1. PERIPHERAL VIEWING--MONOCULAR
Stationary
Drifting at 5 Hz
Spatial frequency (c/deg)
Subject
4.9 1.8 4.4 2-o 1.8
C.R.S. C.R.S. D.J.T. D.J.T. C.R.S.
4.4 2.0
D.J.T. D.J.T.
2.0
D.J.T.
1 In these cases testing was done at 45”.
Half width at half amplitude (deg) 15.0 20.0 15.5 12.0 11.5 5.5 8.5 6.5 6.5 7.0 5.0
for for for for for for for
adapting adapting adapting adapting adapting adapting adapting
same direction opposite direction same direction same direction opposite direction same direction’ opposite direction’
2110
C.
R.
SHARPE
AND
D.J.
TOLHLXST
DISCUSSION
At any one background luminance, peripheral vision is far less acute than is fovea1 vision (MENDELBAUM and SLOAN,1947). This is reelected in our Fig, I: the highest spatial frequency of sinusoidal grating detectable 10” into the periphery is only about 9 c/deg. This should be compared with the equivalent fovea1 parameter of 40-50 c’deg. This finding has an immediate neurophysiological correlate. WIESEL (1960) and EXROTH-CUGELLand ROBSOK(1966) found that retinal ganglion cells in the cat tended to have much larger receptive fields when in the periphery of the visual field. We have also confirmed the observation of DNTCH and GREEN(1969) that the sensitivity to gratings is less in the periphery than it is in the fovea. Our data shows that the sensitivity at the optimum spatial frequency falls by a factor of about four when viewed 10” into the periphery. GREEN(1970) showed that this fall in sensitivity was not due to optical factors, and it is more likely that the sensitivity is lower because there are fewer neurones subserving the peripheral retina. STONE (1965) found that the number of ganglion cells per square millimetre on the cat’s retina decreased with increasing distance from the c:ntre of the visual field. D.-ZMELand WHITTERIDGE (1961) and ROLLSand COWEY (1970) found a corresponding decrease in the cortical “magnification factor” (millimetres along the surface of the visual cortex per degree of visual angle). A third reported difference between the periphery and the fovea is that, in the periphery, one is much more sensitive to moving than to stationary patterns (e.g. TROXLER,18M). Our data provide little obvious support for this proposition. There is a fall in sensitivity to both moving and stationary gratings in the periphery, the scaling factor being much the same for the two types of stimulus. However, the sensitivity curves in the periphery are biased towards low spatial frequencies where movement does cause an increase in sensitivity in the fovea as well as the periphery. It is only at high and medium spatial frequencies, which are poorly served in the periphery, that movement does not cause an increase in sensitivity (e.g. ROBSON,1966). There appear to be fewer neurones in the periphery and these tend to have larger receptive fields than those in the fovea. The results of this paper suggest that the remaining neurones are utilized in much the same way as those in the fovea. By the method of spatial adaptation, we have shown that the peripheral retina possesses channels which each respond to limited ranges of stimulus orientation and spatial frequency; there are also directionally specific units. In the spatial frequency domain, our results differ little from similar experiments in the fovea. But, the orientation specificities of the elevation curves are different (cf. fovea1 results of SHARPEand TOLHURST,1973). In the periphery, we found that adaptation was much more specific when the stimuli were temporally modulated; just the reverse is true in the fovea. This might support the notion that the periphery is concerned with the analysis of temporal changes, while the fovea is capable of acute spatial vision. But, this conclusion requires confirmation with other experimental techniques. Other methods have been used to demonstrate the existence of channels in fovea1 vision (e.g. CAMPBELL and KULIKOWSKI,1966; SACHS et al., 1971). Under identical viewing conditions, two different methods do not give the same quantitative results; KULIKOWSKI (1972) found that the half-width of orientation “channels” was twice as great using the technique of simultaneous masking as when adaptation was used. Similarly, estimates of the specificity of spatial frequency channels in the fovea differ markedly (cf. the results of BLAKEMORE and CAMPBELL, 1969 and SACHS et a/., 1971). Thus, the differences in half-width that we
have demonstrated using the adaptation technique must be confirmed by other methods,
Orientation
and Spatial Frequency Channels
1111
preferably that used by Sachs et al. The adaptation technique is widely used because it is relatively rapid. However, the neuronal mechanism is not known and the exact significance of adaptation experiments awaits neurophysiological experiments. Lastly, our peripheral data were obtained monocularly, while the equivalent fovea1 data were obtained binocularly (SKARPE and TOLHLJRST,1973). This apparently trivial difference seems to be crucial: in some preliminary experiments, we found that the half-widths of fovea1 elevation curves were greatly affected by closing one eye. In conclusion, we can say that the periphery utilizes channels which are qualitatively similar to those in the fovea. More extensive experimentation is required before it can be certain that there are any quantitative differences between the channels in the two parts of the visual field. Some recent work (TOLHIJIW, 1972; SHAPLEY and TOLHURST, 1973) has shown the existence of broad-band feature detectors in the fovea in addition to the channels; it would be of interest to see if the periphery also possesses such feature detectors as edgedetectors. It is possible that the capabilities of the periphery are determined by the types of detector present as well as by the lower sensitivity and lower optimum spatial frequency. Acknowledgemenrs-We should like to thank Drs. C. BLAKEMORE, G. MANDL and J. G. Roasorc for their helpful discussion and criticism. REFERENCES BLAKEMORE, C. and CAMPBELL,F. W. (1969). On the existence in the human visual system of neurones selectively sensitive to the orientation and size of retinal images. /. Physiol, Lond. 203, 237-260. BLAKEMORE, C. and NACHMIAS, J. (1971). The orientation specificity of two visual aftereffects. /. Ph,vsiol, Lond. 213, 157-174. CAMPBELL,F. W. and GREEN, D. G. (1965). Monocular versus binocular visual acuity. Nature, Loti. 208, 191-192. CA~~PBELL,F. W. and KULIKOWSKI,J. J. (1966). Orientational selectivity of the human visual system. J. Physiol, Land. 187, 437-445. CAMPBELL,F. W. and ROAN, J. G. (1968). Application of Fourier analysis to the visibility of gratings. J. Physiol, Land. 197, 551-566. DAITCH,J. M. and GREEN,D. G. (1969). Contrast sensitivity of the human peripheral retina. Vision Res. 9, 947-952. DANIEL,P. M. and WHITTERIDGE, D. (1961). The representation of the visual field on the cerebral cortex of monkeys. J. Physiol, Land. 159,203-221. ENROTH-CUGELL,CH~U~TINA and ROB~ON, J. G. (1966). The contrast sensitivity of retinal ganglion cells of the cat. J. Physiol; Land. 187, 517-552. GREEN,D. G. (1970). Regional variation in the visual acuity for interference fringes on the retina. J. Physiol, Land. 207, 3X-356. KULIKOWSU, J. J. (1972). Orientational selectivity of human binocular and monocular vision revealed by simultaneous and successive masking. J. Physiol, Land. 226, 67-68P. LICHSTENSTEIN, M. (1963). Spatio-temporal factors in cessation of smooth apparent movement. J. opt. Sot. Am. 53, 304-306. MENDELBAUM, J. and SLOAN, L. L. (1947). Peripheral visual acuity. Am. J. Ophrhul. 30, 581-588. ROBSON,J. G. (1966). Spatial and temporal contrast-sensitivity functions of the visual system. J. o~,t. Sot. Sot. Am. 56, 1141-1142. ROLU, E. T. and COWEY,A. (1970). Topography of the retina and striate cortex and its relationship to visual acuity in Rhesus monkeys and sauirrel monkeys. EXP. Bruin Res. 10. 298-310. SACHS, M. B., NACHMIAS, J. and ROBSON,i. G. (1971). Spatiallfrequency channels in human vision. J. opt. Sot. Am. 61, 1176-1186. SEKULER,R. W. and GANZ, L. (1963). After effect of seen motion with a stabilised retinal image. Science, N. Y. 139,419420. SHAPLEY,R. M. and TOLHLTRST, D. 3. (1973). Edge detectors in human vision. 1. Physiol, tond. 229,165-183. SHARPE,C. R. (1972). The visibility and fading of thin lines visualized by their controlled movement across the retina. J. Physiol, Land. 222, 113-134. SHARPE,C. R. and TOLHIJRST,D. J. (1973). Temporal modulation and the orientation-specificity of human channels. In preparation.
C. R. SRARPE AND D. 3.
2112
TOLHURST
Srohx. J. (1965). A quantitative analysis of the distribution of ganglion cells in the cat’s retina. J. camp. Neuroi. 124,337-352. TO-T, D. f. (1972). On the possible existence of edge detectors neurones in the human visual system. Visian Res. 12, 797-804. TROXLER,D. (1804). Ueber das Verschwinden gegebner Gegenstande innerhalb unseres Gesichtskreises. Opkrkai. Bibiiotkek. (edited by K. HIMLY and J. A. SCHMIDT),2/Z,l-53. WIESEL,T. N. (1960). Receptive fields of ganglion cells in the cat’s retina. J. PkysioL Lord 153, 553-594. WOHLGE.~, A. (1911). On the aftereffect of seen movement. Br. J. Psyckol. Monogr. Suppi., 1, l-l 17.
Abstract-The technique of spatial adaptation has been used to demonstrate the existence of channels responsive to only limited ranges of spatial frequency and orientation in the periphery of the visual field. These channels are qualitatively similar to those found in the fovea. The effects of temporal modulation on the properties of these channels were studied. Unlike the fovea, peripheral channels responsive to moving stimuli may be more selective as to the orientation of stimulus that will excite them than are peripheral channels responding to stationary stimuli.
R&sum&--On emploie la technique d’adaptation spatiale pour demontrer I’existence de canaux qui ne ripondent qu’8 des domaines limit& de frequence spatiale et d’orientation ti la periphtrie du champ visuel. Ces canaux sont qualitativement semblables a ceux que I’on trouve dans la fovea. On Otudie les effets de la modulation temporelle sur les proprietes de ces canaux. Contrairement a la fovea, les canaux pCriphCriques qui rkpondent aux stimuli mobiles peuvent etre plus s&&ifs quant 8 l’orientat~on du stimulus qui les excite que tes canaux pCrip&iques repondant B des stimuli stationnaires.
Zusammenfassung-Die Technik der raumlichen Adaptation wurde benutzt, urn die Existenz von Kanllen, die nur in einem begrenzten Ortsfrequenz- und Orientierungsbereich reagieren, in der Peripherie des visuellen Feldes zu demonstrieren. Diese Kanale ihneln deoen in der Fovea qualitativ. Die Auswirkung einer zeitlichen Modulation auf die Eigenschaften dieser KanSle wurde untersucht. Im Unterschied zur Fovea kiinnten periphere Kanale, die auf sich bewegende Reize reagieren, starker selektiv beziiglich der Orientierung der zu erregenden Reize sein, als periphere Kaniile, die auf stationlre Reize antworten.
PearoMe-Meronmca lSpO'ZTpaHCTBeHHOiiananlamni 6brjraUCIIOOnb30BaHa ,!T;fR TOTO, 'fro661 no~a3aTbcyIUeCTao~a~~exaifano~or~e~a~~~onb~oHaorpa~~~eHRb~;IUa~a30~npoc~atrcrt3eEnizzs Yac-roT A oprreHtawi= Ha nepsi$epus5 rionsf3pefnis. Ka=recn3eeHHo ~TH iwia;Ibl ~OXOlicaKaTe,KOTO~bXe6b~HalineHb~~-?li~O~e~bHO2i~~a~.6bL~BfC~eT(OB~HbIBjfHR~k~1~pe~e~~0~~o~lyn~u~~Hac~o~~aa3~~x~a~a~o~.Bo~11~~ueo~~aea,nep~~ep~ecX~e XaHanbI, OTBe'IafoIIDie Ha ,%BEKyuniecn CTHMynbr, MoryT 6brTb 6onee w36uparenbHbafH no oTHorneww3 K opaeH_rauwa~yna,KoTopbt21: BX 6yneT Bo3Byxcnan,qehf nepw@epnrech7le xananbr, pearripyronnie
na cramfoaapnbre
crfib5ynbr.
13. pp.
2IOWll2.
ORIENTATION
Pergamon Press 1973. Printed in Great Britain.
AND SPATIAL FREQUENCY IN PERIPHERAL VISION
CHANNELS
C. R. SEURPE’and D. J. TOLI-KJRST* Physiological
Laboratory,
Cambridge CB2 3EG, England
(Received 14 July 1972; in revisedform
13 January, 1973)
INTRODUCTION
abundant psychophysical evidence for the existence of systems of channels in the visual system of man seIectively sensitive to limited ranges of spatial frequency and orientation of periodic patterns (SACHS, NACHMIAS and ROBSON,1971; BLAKEWORE and CAMPBELL, 1969 ; CAMPBELLand KULIKOWSKI,1966; BLAKEMORE and NACHMIAS,1971). These studies have all been concerned with central vision. One naturally asks whether peripheral vision utilizes similar channels. Preliminary evidence (SHARPE,1972), showing width and orientation specific fading of the moving entopic shadows of the retinal blood vessels, suggests that this may be so; these blood vessels lie only on the peripheral retina. It is known that subjects are more sensitive to temporally modulated patterns than to stationary patterns in the periphery (see TROXLER,1804). A similar effect is seen in central vision but only at low spatial frequencies (ROBSON,1966). Perhaps, as would be expected from the inability of the periphery to detect fine detail, the high spatial frequency channels are simply absent in the periphery. In other words, is the periphery organized in the same way as the fovea, but with a relative absence of high spatial frequency channels? An attempt is made to answer this question by using spatial adaptation to define channels. BLAKEMORE and CAMPBELL (1969) showed that prolonged viewing of a sinusoidal grating of high contrast elevated the contrast threshold to gratings over only a limited range of spatial frequency, the elevation being maximal at the adapting frequency. Subsequently, BLAKEMORE and NACHMIAS(1971) showed that adaptation is also orientation-specific, and they develcped the method of equivalent contrast to determine the orientation specificity of the effects of adaptation. These techniques have been used in this study to show the existence of spatial frequency and orientation channels in peripheral vision, and to examine the effects of various types of temporal modulation on the properties of these channels. The experiments to be reported here were carried out under photopic conditions. THERE IS
METHODS Gratings, whose luminance was sinusoidally modulated along one axis. were generated on the face of a cathode ray tube (P31 phosphor) by the method described by CAMPBELL and ROEWN (1968). The screen subtended 3.8” of visual angle. Its space-averaged mean luminance was estimated as 140 cd/m2 using an SE1 spot-photometer. The retinal illumination was thus about 2500 td. The screen was brighter than the background (the white wall of a well-lit room). The contrast of the stimuli was defined as (L,.. -&,,)/ I Recipient of a studentship from the MRC of Canada. Present address: Unit, Dept. of Physiology, McGill University, Montreal, Canada. * Recipient of a Scholarship from the MRC of Great Britain. 2103
Aviation Medical Research
C. R. SHARE
‘104
ASD D.J.
TOLHURST
f&n,, f Li,)
where L,,, is the luminance of the peak of the sinusoidal grating and Lmin the iuminance Contrast thus varies between 0 and 1. The voltage required to give a contrast of 03 was determined exactly and, thereafter, the contrast of the stimulus was calculated from the amplitude of the electrical signal fed to the Z-asis of the CRT. The gratings could be caused to drift laterally, could be switched on and off repetitively or could be held stationary. The orientation of the grating could be changed by rotating the deflection coils of the CRT, The subject set his threshold by changing the amplitude of the signal fed to the Z-axis of the CRT (and hence the contrast) using a logarithmic attenuator having steps of 0.025 log units. The results are expressed as contrast semiticity, the reciprocal of the threshold contrast. The mean luminance of the screen was unaffected by changes in the contrast, spatial frequency or temporal frequency. In experiments involving central vision, the subject either viewed a small spot in the centrz of the screen when the stimuli were moving or allowed his eyes to roam randomly when the stimulus was stationary; in rhis way after images of the adapting grating were not generated. Both eyes were used for fovea1 experiments. The peripheral experiments, however, were carried out with monocular vision. The subject fixated a small spot IO” to the left of the centre of the screen, using his left eye alone; his right eye was closed. Thus, the temporal resion of one retina was used. Two subjects, both experienced observers, were used. DJT was an emmetrope; CRS was a well-corrected myope. of the trough.
RESULTS
Infruence of temporal modulation on contrast sensitivity
The peripheral contrast sensitivity to sinusoidal gratings as a function of spatial frequency is shown in Fig. 1. The open squares show the sensitivity to stationary gratings, the filled circles for patterns flashed on and off at 5 Hz, and the open circles for gratings drifting laterally at 5 Hz. This temporal frequency was chosen because it was the one to which the subjects were most sensitive, at ail spatial frequencies. For comparison, similar data are presented in Fig. 2 for fovea1 viewing. Strictly speaking, the two sets of data are not directly comparable as the peripheral data were obtained
Spatial
frequency,
c/deg
FIG. 1. Contrast sensitivity for vertical sinusoidal gratings in the periphery of the visual field. The gratings were viewed with the left eye 10” into the temporal hem~etina. The aatings were either stationary (a), switched on and off at 5 Hz (Of or drifted away from the fovea at 5 Hz (0). Subject CRS.
Orientation
and Spatial Frequency Channels
2105
monocularly and the fovea1 data bin~larIy. CAMPBELLand GREW (1965) have shown that, in the fovea, the binocular sensitivity is about t/2 times the monocular sensitivity. However, the sensitivity to gratings in the periphery is considerably less than would be expected by simply closing one eye; the sensitivity to both stationary and drifting gratings is reduced by about the same factor. The sensitivity curves are shifted towards lower spatial frequencies in the periphery. The frequency at which the sensitivity is greatest is about 4 c/deg in the fovea but only about 2 c/deg in the periphery. Further, the high frequency fall-off in sensitivity is considerably steeper in the periphery, the curve extrapolating to about 9 c/deg compared to the fovea1 value of about 40 c/deg. This shift to low spatial frequencies presumably reflects the difficulty with which fine detail is seen by the periphery.
Spatial frequency,
c/deg
Fro. 2. Contrast sensitivity for vertical sinusoidal gratings viewed with the fovea; both eyes were used. The gratings were either stationary (El), switched on and off at 5 Hz (0) or drifted laterally at the same rate (0). Subject CRS. When the grating is temporally modulated, the low spatial frequency fall-off in sensitivity becomes less severe in both regions of the visual field. The sensitivity for on-off stimuli begins to differ from that for stationary stimuli only at low spatial frequencies. At these frequencies, it was noted that the on-off stimuli appeared to move to and fro in steps, the size of half a period of the grating. At higher spatial frequencies, no such movement was apparent at the detection threshold: the stimuli appeared to be stationary. Similarly, in the periphery, drifting gratings appeared to be stationary at threshold when their spatial frequency was greater than about 4 c/deg (cf. LICHTWSTEIN,1963). Spatial freqtdency selective channels
B~KE~o~ and CAMPBELL(1969) found that prolonged viewing of a high contrast sinusoidal grating elevated the contrast threshold over a spectrum of spatial frequency V.R.13/Il-H
2106
c.
R. SHARPE
AND
D. J. TOLHURST
with a bandwidth of about an octave at half-amplitude, centered on the adapting spatial frequency. This phenomenon is termed “spatial adaptation”. We have used this effect to show the existence of channeis selectively sensitive to limited ranges of spatial frequency in peripheral vision, for stationary and drifting gratings. The procedure was as follows. The subject determined his contrast thresholds over a range of spatial frequencies, five readings being taken at each point; the standard error of these readings was about 15 per cent. He then viewed a high contrast grating of one particular spatial frequency for 3 min before redetermining his threshold for each of the test stimuli. Between each threshold reading, the subject re-adapted for about 20 sec. The change in threshold caused by the adaptation was expressed as relative threshold elevation which is defined as Rel. elev. =
sensitivity before adapting - 1. sensitivity after adapting
Figure 3 (filed circles) shows the adaptation curve after adapting to and testing stationary gratings in the periphery. The threshold was affected only over a narrow range of spatial frequency with the maximum effect at the adapting frequency. The shape of the curve drawn through the points is very similar to that used by BLAKEMORE and CAMPBELL (1969) to describe their results on the fovea. When the subject adapted to and tested moving gratings in the periphery, the threshofd elevation was spread over a slightly narrower range of spatial frequency {Fig. 3, open circles). The adapting grating drifted backwards and forwards, changing its direction every le.5 set; in this way, the waterfall aftereffect was eliminated (WOHLGEMUTH,1911).
Test spatial frequency,
c/deg
FIG. 3. Spatial frequency speciticity of the relative elevation of threshoId for sinusoidal gratings after adapting to a high contrast grating of 2 c/deg (arrow). Ah gratings were vertical and were viewed with the peripheral visual field. The filled circles show the effects of adapting to and testing stationary gratings; the adapting grating had a contrast of 055. The open circles show the effects of adapting to and testing gratings which drifted at 5 Hz; the adapting grating had a contrast of O-1. Subject CRS.
Orientation and Spatial Frequency Channels
2107
The slight narrowing of the etevation curve was also found when the gratings were flashed on and off repetitively rather than being made to drift. Onfy a small number of experiments were carried out and the proposed effects of temporal modulation must be confirmed. Orientcition-specific
channels
BLAKEMORE and NACHMIAS(1971) have developed a method for determining the orientation-specificity of threshold elevation from adaptation experiments; simple non-linearities in the adaptation process can be overcome. Prolonged viewing of a grating raises the threshold for that grating to an extent dependent on the contrast of the adapting pattern; the lower the adapting contrast, the less the threshold is elevated. The threshold can also be elevated by adapting to gratings of different orientations. At any one adapting contrast, the more different are the adapting and testing orientations, the less the amount of threshold elevation. Thus, it is possible “to express the decfine [of the effect] with increasing discrepancy between adapting and testing orientations as an equivalent reduction in contrast of an adapting grating of the same orientation as the test pattern” (BLAKEMORE and NACHMIAS,1971). We have used this method to examine the effects of temporal modulation on the orientation specificity of peripheral channels and to compare these channels to those in the fovea (SHARPEand TOLHURST,1973). The specificity was determined from two experiments. in the first, the subject adapted to gratings of one orientation (the same as that of the test grating) and several different contrasts; and, in the second, he adapted to gratings of one contrast but several different orientations. The test grating was the same throughout. The contrast chosen for the latter experiment was generally the highest contrast which did not produce saturation of the threshold elevation effect. Figure 4 shows the threshoId elevation (in log units) of a 0” (i.e. vertical, moving to the left) sinusoidal grating after adapting to gratings of different orientations and directions of drift. All gratings had a spatial frequency of 2 c/deg and drifted steadily at 5 Hz (2_5”/sec); the adapting gratings had a contrast of 0.1. The convention for labelling the orientation and direction of drift was as follows: 0” refers to a vertical grating drifting to the left, while 180” refers to a vertical grating drifting to the right. A horizontal grating drifting downwards is considered to be 90”. The stimulus was presented 10’ into the temporal retina of the left eye, and so a grating drifting to the left would move away from the fovea. Figure 4 shows that the threshold for a drifting grating can be elevated by adapting to gratings that drift either in the same or opposite directions, but not in directions differing by more than about 60” from these two directions. It wilf be noticed that the grating moving in the same direction is the most effective adapting stimulus. Thus, adaptation in the periphery is both orientationand direction-specific, as it is in the fovea (SEKULERand GANZ, 1963). Figure 5 illustrates the equivalent contrast transformation: the data for the peak centred on 0” are replotted, together with a graph of threshold elevation as a function of the adapting contrast of a 0” grating. This and other elevation vs contrast functions were well fitted by a straight line on log-log co-ordinates over much of the contrast range; at higher contrasts the curve flattened off. From this figure, the adapting effect of a non-vertical grating can be expressed in terms of the adapting contrast of a vertical grating required to produce the same elevation of threshold. For example, adapting to a 20” off-vertical grating with a contrast of 0.1 produced the same elevation of threshold as adapting to a 0” grating with a contrast of about O-04; the equivalent contrast of the 20” grating is thus 044. Figure 6 (solid curve) plots the equivalent contrast against the orientation of the adapting grating,
2108
C.
R.
SHARPE
AFiT)
D. J. Tomms-r
2-O ce’deg
5Hz
I
f
300
11 0
I 60
I
I 120
T
drift
I!
I! 240
I80
Orientation of adapting grating,
de9
FIG. 4. Elevation of the contrast threshoId of a vertical drifting grating after adapting to gratings drifting at other orientations and directions. All gratings had a spatial frequency of 2 c/deg and drifted at 5 Hz; the adapting gratings had a contrast of O-1. The test grating had an orientation defined as 0” (vertical, drifting to the left). 180” refers to a vertical grating drifting to the right, while 90” refers to a horizontal grating drifting downwards. The threshold elevation is orientation specific; adapting gratings were effective only when their orientation was within 60’ of the vertical. Further, the effect was directionally speczfic: compare the effects of adapting to a grating at 0” and 180”. Each point is the mean of five threshold settings and the standard error is indicated. The dashed horizontal lines show the range of threshold elevation which,
statistically, was not significant. Subject DJT.
for those adapting gratings determining the orjentation
centred around 0”. The width of the channel was specified by which was equivalent to a vertical grating of half the contrast.
This quantity (termed the half-width at half amplitude) is indicated by the f3Ied arrow and is about 6-Y. Figure 6 (broken curve) also shows the results of the equivalent contrast transformation for the reverse direction, centred around adapting gratings of 180”. The adapting effect
2-O 5Ht 0.50
0.25 0~
0
20
Orient&ion.
40
60
deg
Adaptingcontrost
FIG. 5.The equivaient contrast transfo~ation. On the left, the decline of threshold elevation with increasing discrepancy between test and adapting orientations is plotted. The data are taken from Fig. 4; the test grating had an orientation of 0’ and the adapting gratings had a contrast of @l. On the right is plotted the decline of adapting effect of a vertical grating as its contrast is decreased. A change in the adapting orientation with constant contrast is equivalent to a decrease in the contrast at one orientation.
Orientation
2109
and Spatial Frequency Channels
0.1
z-
-
z e
0.03
0 E 4 0 .g w”
I
I
I
I
20
30
40
50
I
0.01
IO
Orientation.
deg
FIG. 6. Contrast of vertical grating to which gratings of one contrast but various orientations are equivalent. The solid curve shows the transformed data of Figs. 4 and 5, while the dashed curve shows the transform of the data centred on the reverse direction (180’). The arro*s indicate the orientations which were equivalent to a vertical grating with half the contrast. The half-widths at half-amplitude of the two curves are about 6.5”.
of an off-180” grating was expressed as the contrast of 180’ grating that gave identical elevation of the threshold for the 0” test grating. The dashed arrow indicates the half-width of this channel; it is 6-S’. Table 1 summarizes the results of this and similar experiments. In general, when the gratings were moving, the half-widths were in the range of 6-8’. The results of adapting to and testing stationary gratings in the periphery are also illustrated in Table I. The half-widths were considerably broader, being about 12-20”. Thus, in the periphery, temporal modulation causes a large difference in the half-widths of the elevation curves. TABLE 1. PERIPHERAL VIEWING--MONOCULAR
Stationary
Drifting at 5 Hz
Spatial frequency (c/deg)
Subject
4.9 1.8 4.4 2-o 1.8
C.R.S. C.R.S. D.J.T. D.J.T. C.R.S.
4.4 2.0
D.J.T. D.J.T.
2.0
D.J.T.
1 In these cases testing was done at 45”.
Half width at half amplitude (deg) 15.0 20.0 15.5 12.0 11.5 5.5 8.5 6.5 6.5 7.0 5.0
for for for for for for for
adapting adapting adapting adapting adapting adapting adapting
same direction opposite direction same direction same direction opposite direction same direction’ opposite direction’
2110
C.
R.
SHARPE
AND
D.J.
TOLHLXST
DISCUSSION
At any one background luminance, peripheral vision is far less acute than is fovea1 vision (MENDELBAUM and SLOAN,1947). This is reelected in our Fig, I: the highest spatial frequency of sinusoidal grating detectable 10” into the periphery is only about 9 c/deg. This should be compared with the equivalent fovea1 parameter of 40-50 c’deg. This finding has an immediate neurophysiological correlate. WIESEL (1960) and EXROTH-CUGELLand ROBSOK(1966) found that retinal ganglion cells in the cat tended to have much larger receptive fields when in the periphery of the visual field. We have also confirmed the observation of DNTCH and GREEN(1969) that the sensitivity to gratings is less in the periphery than it is in the fovea. Our data shows that the sensitivity at the optimum spatial frequency falls by a factor of about four when viewed 10” into the periphery. GREEN(1970) showed that this fall in sensitivity was not due to optical factors, and it is more likely that the sensitivity is lower because there are fewer neurones subserving the peripheral retina. STONE (1965) found that the number of ganglion cells per square millimetre on the cat’s retina decreased with increasing distance from the c:ntre of the visual field. D.-ZMELand WHITTERIDGE (1961) and ROLLSand COWEY (1970) found a corresponding decrease in the cortical “magnification factor” (millimetres along the surface of the visual cortex per degree of visual angle). A third reported difference between the periphery and the fovea is that, in the periphery, one is much more sensitive to moving than to stationary patterns (e.g. TROXLER,18M). Our data provide little obvious support for this proposition. There is a fall in sensitivity to both moving and stationary gratings in the periphery, the scaling factor being much the same for the two types of stimulus. However, the sensitivity curves in the periphery are biased towards low spatial frequencies where movement does cause an increase in sensitivity in the fovea as well as the periphery. It is only at high and medium spatial frequencies, which are poorly served in the periphery, that movement does not cause an increase in sensitivity (e.g. ROBSON,1966). There appear to be fewer neurones in the periphery and these tend to have larger receptive fields than those in the fovea. The results of this paper suggest that the remaining neurones are utilized in much the same way as those in the fovea. By the method of spatial adaptation, we have shown that the peripheral retina possesses channels which each respond to limited ranges of stimulus orientation and spatial frequency; there are also directionally specific units. In the spatial frequency domain, our results differ little from similar experiments in the fovea. But, the orientation specificities of the elevation curves are different (cf. fovea1 results of SHARPEand TOLHURST,1973). In the periphery, we found that adaptation was much more specific when the stimuli were temporally modulated; just the reverse is true in the fovea. This might support the notion that the periphery is concerned with the analysis of temporal changes, while the fovea is capable of acute spatial vision. But, this conclusion requires confirmation with other experimental techniques. Other methods have been used to demonstrate the existence of channels in fovea1 vision (e.g. CAMPBELL and KULIKOWSKI,1966; SACHS et al., 1971). Under identical viewing conditions, two different methods do not give the same quantitative results; KULIKOWSKI (1972) found that the half-width of orientation “channels” was twice as great using the technique of simultaneous masking as when adaptation was used. Similarly, estimates of the specificity of spatial frequency channels in the fovea differ markedly (cf. the results of BLAKEMORE and CAMPBELL, 1969 and SACHS et a/., 1971). Thus, the differences in half-width that we
have demonstrated using the adaptation technique must be confirmed by other methods,
Orientation
and Spatial Frequency Channels
1111
preferably that used by Sachs et al. The adaptation technique is widely used because it is relatively rapid. However, the neuronal mechanism is not known and the exact significance of adaptation experiments awaits neurophysiological experiments. Lastly, our peripheral data were obtained monocularly, while the equivalent fovea1 data were obtained binocularly (SKARPE and TOLHLJRST,1973). This apparently trivial difference seems to be crucial: in some preliminary experiments, we found that the half-widths of fovea1 elevation curves were greatly affected by closing one eye. In conclusion, we can say that the periphery utilizes channels which are qualitatively similar to those in the fovea. More extensive experimentation is required before it can be certain that there are any quantitative differences between the channels in the two parts of the visual field. Some recent work (TOLHIJIW, 1972; SHAPLEY and TOLHURST, 1973) has shown the existence of broad-band feature detectors in the fovea in addition to the channels; it would be of interest to see if the periphery also possesses such feature detectors as edgedetectors. It is possible that the capabilities of the periphery are determined by the types of detector present as well as by the lower sensitivity and lower optimum spatial frequency. Acknowledgemenrs-We should like to thank Drs. C. BLAKEMORE, G. MANDL and J. G. Roasorc for their helpful discussion and criticism. REFERENCES BLAKEMORE, C. and CAMPBELL,F. W. (1969). On the existence in the human visual system of neurones selectively sensitive to the orientation and size of retinal images. /. Physiol, Lond. 203, 237-260. BLAKEMORE, C. and NACHMIAS, J. (1971). The orientation specificity of two visual aftereffects. /. Ph,vsiol, Lond. 213, 157-174. CAMPBELL,F. W. and GREEN, D. G. (1965). Monocular versus binocular visual acuity. Nature, Loti. 208, 191-192. CA~~PBELL,F. W. and KULIKOWSKI,J. J. (1966). Orientational selectivity of the human visual system. J. Physiol, Land. 187, 437-445. CAMPBELL,F. W. and ROAN, J. G. (1968). Application of Fourier analysis to the visibility of gratings. J. Physiol, Land. 197, 551-566. DAITCH,J. M. and GREEN,D. G. (1969). Contrast sensitivity of the human peripheral retina. Vision Res. 9, 947-952. DANIEL,P. M. and WHITTERIDGE, D. (1961). The representation of the visual field on the cerebral cortex of monkeys. J. Physiol, Land. 159,203-221. ENROTH-CUGELL,CH~U~TINA and ROB~ON, J. G. (1966). The contrast sensitivity of retinal ganglion cells of the cat. J. Physiol; Land. 187, 517-552. GREEN,D. G. (1970). Regional variation in the visual acuity for interference fringes on the retina. J. Physiol, Land. 207, 3X-356. KULIKOWSU, J. J. (1972). Orientational selectivity of human binocular and monocular vision revealed by simultaneous and successive masking. J. Physiol, Land. 226, 67-68P. LICHSTENSTEIN, M. (1963). Spatio-temporal factors in cessation of smooth apparent movement. J. opt. Sot. Am. 53, 304-306. MENDELBAUM, J. and SLOAN, L. L. (1947). Peripheral visual acuity. Am. J. Ophrhul. 30, 581-588. ROBSON,J. G. (1966). Spatial and temporal contrast-sensitivity functions of the visual system. J. o~,t. Sot. Sot. Am. 56, 1141-1142. ROLU, E. T. and COWEY,A. (1970). Topography of the retina and striate cortex and its relationship to visual acuity in Rhesus monkeys and sauirrel monkeys. EXP. Bruin Res. 10. 298-310. SACHS, M. B., NACHMIAS, J. and ROBSON,i. G. (1971). Spatiallfrequency channels in human vision. J. opt. Sot. Am. 61, 1176-1186. SEKULER,R. W. and GANZ, L. (1963). After effect of seen motion with a stabilised retinal image. Science, N. Y. 139,419420. SHAPLEY,R. M. and TOLHLTRST, D. 3. (1973). Edge detectors in human vision. 1. Physiol, tond. 229,165-183. SHARPE,C. R. (1972). The visibility and fading of thin lines visualized by their controlled movement across the retina. J. Physiol, Land. 222, 113-134. SHARPE,C. R. and TOLHIJRST,D. J. (1973). Temporal modulation and the orientation-specificity of human channels. In preparation.
C. R. SRARPE AND D. 3.
2112
TOLHURST
Srohx. J. (1965). A quantitative analysis of the distribution of ganglion cells in the cat’s retina. J. camp. Neuroi. 124,337-352. TO-T, D. f. (1972). On the possible existence of edge detectors neurones in the human visual system. Visian Res. 12, 797-804. TROXLER,D. (1804). Ueber das Verschwinden gegebner Gegenstande innerhalb unseres Gesichtskreises. Opkrkai. Bibiiotkek. (edited by K. HIMLY and J. A. SCHMIDT),2/Z,l-53. WIESEL,T. N. (1960). Receptive fields of ganglion cells in the cat’s retina. J. PkysioL Lord 153, 553-594. WOHLGE.~, A. (1911). On the aftereffect of seen movement. Br. J. Psyckol. Monogr. Suppi., 1, l-l 17.
Abstract-The technique of spatial adaptation has been used to demonstrate the existence of channels responsive to only limited ranges of spatial frequency and orientation in the periphery of the visual field. These channels are qualitatively similar to those found in the fovea. The effects of temporal modulation on the properties of these channels were studied. Unlike the fovea, peripheral channels responsive to moving stimuli may be more selective as to the orientation of stimulus that will excite them than are peripheral channels responding to stationary stimuli.
R&sum&--On emploie la technique d’adaptation spatiale pour demontrer I’existence de canaux qui ne ripondent qu’8 des domaines limit& de frequence spatiale et d’orientation ti la periphtrie du champ visuel. Ces canaux sont qualitativement semblables a ceux que I’on trouve dans la fovea. On Otudie les effets de la modulation temporelle sur les proprietes de ces canaux. Contrairement a la fovea, les canaux pCriphCriques qui rkpondent aux stimuli mobiles peuvent etre plus s&&ifs quant 8 l’orientat~on du stimulus qui les excite que tes canaux pCrip&iques repondant B des stimuli stationnaires.
Zusammenfassung-Die Technik der raumlichen Adaptation wurde benutzt, urn die Existenz von Kanllen, die nur in einem begrenzten Ortsfrequenz- und Orientierungsbereich reagieren, in der Peripherie des visuellen Feldes zu demonstrieren. Diese Kanale ihneln deoen in der Fovea qualitativ. Die Auswirkung einer zeitlichen Modulation auf die Eigenschaften dieser KanSle wurde untersucht. Im Unterschied zur Fovea kiinnten periphere Kanale, die auf sich bewegende Reize reagieren, starker selektiv beziiglich der Orientierung der zu erregenden Reize sein, als periphere Kaniile, die auf stationlre Reize antworten.
PearoMe-Meronmca lSpO'ZTpaHCTBeHHOiiananlamni 6brjraUCIIOOnb30BaHa ,!T;fR TOTO, 'fro661 no~a3aTbcyIUeCTao~a~~exaifano~or~e~a~~~onb~oHaorpa~~~eHRb~;IUa~a30~npoc~atrcrt3eEnizzs Yac-roT A oprreHtawi= Ha nepsi$epus5 rionsf3pefnis. Ka=recn3eeHHo ~TH iwia;Ibl ~OXOlicaKaTe,KOTO~bXe6b~HalineHb~~-?li~O~e~bHO2i~~a~.6bL~BfC~eT(OB~HbIBjfHR~k~1~pe~e~~0~~o~lyn~u~~Hac~o~~aa3~~x~a~a~o~.Bo~11~~ueo~~aea,nep~~ep~ecX~e XaHanbI, OTBe'IafoIIDie Ha ,%BEKyuniecn CTHMynbr, MoryT 6brTb 6onee w36uparenbHbafH no oTHorneww3 K opaeH_rauwa~yna,KoTopbt21: BX 6yneT Bo3Byxcnan,qehf nepw@epnrech7le xananbr, pearripyronnie
na cramfoaapnbre
crfib5ynbr.