luminance-duration threshold relationship under monocular and binocular viewing conditions

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA VOLUME 63. NUMBER 8 AUGUST 1973 Letters to the Editor Luminance-duration threshold relationship under monocular and binocular viewing conditions* Rockefeller S. L. Young and Robert E. Cole Laboratory of Sensory Sciences, University of Hawaii, Honolulu, Hawaii 96822 (Received 15 March 1973) Index Heading: Vision. In the majority of studies concerned with the relation- ship between threshold luminance and flash duration, measurements are taken with only one eye, either in the subject's left or right eye. 1 Two important exceptions, however, are the frequently cited studies of Karn, 2 in which binocular viewing was used, and Graham and Margaria, 3 in which left- and right-eye views were alternated between trials. Although the results of these studies are in general agreement, it is important to know what specific differences, if any, occur under different viewing conditions so that the results of these early studies can be compared with those of later works. In this paper, we report on the effects of left- monocular, right-monocular, and binocular views on dark-adapted foveal thresholds determined with a test field of 1' visual angle at 12 flash durations. The threshold procedure used was an abbreviated variation of the "up-and-down" method described by Stewart. 1 The threshold luminance was determined by averaging the minimum luminance required to just see the test flash on an ascending series and the maximum lumin- ance required to just not see on a descending series of threshold determinations. In total, threshold measures as described were determined as a function of 12 dura- tions under the three viewing conditions and were replicated three times for each subject. The complete data for four subjects were tested in a three-way analysis of variance design. The results are shown in Fig. 1, where threshold luminance, averaged over subjects, is plotted on logI×T vs logT coordinates to show the classic luminance-duration relationship. The effect of duration on threshold luminance is illustrated by a monotonic increase of threshold energy (I×T) as a function of duration. The solid lines were fitted in accordance with the method suggested by Rouse 4 and represent the theoretical relationships monocular conditions are described equally well by Eqs. (1) and (2). This finding supports Karn's binocular data 2 and Rouse's monocular results. 4 The effect of viewing condition can be seen in Fig. 1 as the decrease of threshold for binocular as compared to monocular viewing. Although there is some indication that the binocular-monocular difference may be reduced by longer flash durations, this was not supported by our statistical analysis. In summary, our results indicate that there is little change of the luminance-duration relationship when measured under binocular- or monocular-viewing con- ditions. The main difference was a slight decrease of the binocular threshold, as compared to monocular thresh- olds. Although the lower binocular threshold is con- sistent with the general result of studies in which binocular and monocular sensitivity differences were compared, 5 it may be important to emphasize that the magnitude of this phenomenon, i.e., of the order of about 0.10 log decrement, is rather small relative to the range of brightness over which the visual system is capable of responding. Within the practical limits of a 0.10 log-unit margin, we can regard binocular and and It appears that the data for both the binocular and FIG. 1. Threshold energy as a function of flash duration for left- and right-monocular and binocular viewing (indicated by , 3, and • , respectively). The theoretical curves were fitted only to the right-eye and binocular data. The curve for the left eye was similar to that for the right eye; it was omitted for clarity. 1014

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Page 1: Luminance-duration threshold relationship under monocular and binocular viewing conditions

JOURNAL OF THE OPTICAL SOCIETY OF AMERICA VOLUME 63. NUMBER 8 AUGUST 1973

Letters to the Editor

Luminance-duration threshold relationship under monocular and binocular viewing conditions*

Rockefeller S. L. Young and Robert E. Cole Laboratory of Sensory Sciences, University of Hawaii, Honolulu, Hawaii 96822

(Received 15 March 1973)

Index Heading: Vision.

In the majority of studies concerned with the relation­ship between threshold luminance and flash duration, measurements are taken with only one eye, either in the subject's left or right eye.1 Two important exceptions, however, are the frequently cited studies of Karn,2 in which binocular viewing was used, and Graham and Margaria,3 in which left- and right-eye views were alternated between trials. Although the results of these studies are in general agreement, it is important to know what specific differences, if any, occur under different viewing conditions so that the results of these early studies can be compared with those of later works.

In this paper, we report on the effects of left-monocular, right-monocular, and binocular views on dark-adapted foveal thresholds determined with a test field of 1' visual angle at 12 flash durations. The threshold procedure used was an abbreviated variation of the "up-and-down" method described by Stewart.1

The threshold luminance was determined by averaging the minimum luminance required to just see the test flash on an ascending series and the maximum lumin­ance required to just not see on a descending series of threshold determinations. In total, threshold measures as described were determined as a function of 12 dura­tions under the three viewing conditions and were replicated three times for each subject. The complete data for four subjects were tested in a three-way analysis of variance design.

The results are shown in Fig. 1, where threshold luminance, averaged over subjects, is plotted on logI×T vs logT coordinates to show the classic luminance-duration relationship. The effect of duration on threshold luminance is illustrated by a monotonic increase of threshold energy (I×T) as a function of duration. The solid lines were fitted in accordance with the method suggested by Rouse4 and represent the theoretical relationships

monocular conditions are described equally well by Eqs. (1) and (2). This finding supports Karn's binocular data2 and Rouse's monocular results.4

The effect of viewing condition can be seen in Fig. 1 as the decrease of threshold for binocular as compared to monocular viewing. Although there is some indication that the binocular-monocular difference may be reduced by longer flash durations, this was not supported by our statistical analysis.

In summary, our results indicate that there is little change of the luminance-duration relationship when measured under binocular- or monocular-viewing con­ditions. The main difference was a slight decrease of the binocular threshold, as compared to monocular thresh­olds. Although the lower binocular threshold is con­sistent with the general result of studies in which binocular and monocular sensitivity differences were compared,5 it may be important to emphasize that the magnitude of this phenomenon, i.e., of the order of about 0.10 log decrement, is rather small relative to the range of brightness over which the visual system is capable of responding. Within the practical limits of a 0.10 log-unit margin, we can regard binocular and

and

It appears that the data for both the binocular and

FIG. 1. Threshold energy as a function of flash duration for left- and right-monocular and binocular viewing (indicated by , 3, and • , respectively). The theoretical curves were fitted only to the right-eye and binocular data. The curve for the left eye was similar to that for the right eye; it was omitted for clarity.

1014

Page 2: Luminance-duration threshold relationship under monocular and binocular viewing conditions

August 1973 L E T T E R S T O T H E E D I T O R 1015

monocular viewing as comparable in the study of the luminance-duration relationship.

*Research supported in part by PHS Research Grant No. NS-06890 from the National Institute of Neurological Diseeises and Stroke.

'For example, see recent studies by D. Regan and C. W. Tyler, J. Opt. Soc. Am. 61, 1414 (1971); L. Ronchi and O. Novakova, J. Opt. Soc. Am. 61, 115 (1971); B. R. Stewart, J. Opt. Soc. Am. 62, 449 (1972).

2 H. W. Kam, J. Gen. Psychol. 14, 360 (1936). 3 C. H. Graham and R. Margaria, Am. J. Physiol. 113, 299

(1935). 4 R. O. Rouse, J. Opt. Soc. Am. 42, 626 (1952). 5 See D. H. Westendorf, R. R. Blake, and R. Fox, Percept.

Psychophys. 12, 445 (1972); O. Braddick, Vision Res. 12, 1435 (1972); J. C. Stevens, Percept. Psychophys. 2, 451 (1967); L. M. Hurvich and D. P. Jameson, The Perception of Brightness and Darkness (Allyn and Bacon, Boston, 1966), p.34.