sufficient reliability (by sufficient variety in the topics of the paragraphs and otherwise). Second, the scoring requires judgment, and provision must be made to free the results from the personal equations of the scorers. We are now experimenting with a form where the individual selects the right answer instead of writing it, which will do away with this second disadvantage. It remains to be seen, however, whether this selective form will show the same high correlations with a criterion of intelligence that the customary form has shown.

REFERENCES

GATES, A. I., '21. An Experimental and Statistical Study of Reading and Reading Tests (Continued). Journal of Ed. Psy., Vol. 12, pp. 378–391.

Dunlap, K., and SNYDER, A., '20. Practice Effects in Intelligence Tests. JOURNAL OF EXP. PSYCHOLOGY, Vol. 3, pp. 396–403.

RICHARDSON, F., and Robinson, E. S., '21. Effects of Practice upon the Scores and Predictive Value of the Alpha Intelligence Examination. JOURNAl of Exp. PSYCHOLOGY, Vol. 4, pp. 300–317.

YOAKUM, C. S., And Yerkes, R. M., '20. Army Mental Tests.

THE CONDITIONED PUPILLARY REACTION

BY HULSEY CASON

Columbia University

SECTION I

Introduction

Much of the work which has been done on the conditioned 'reflex' is open to the criticism that the experiments involved 'voluntary factors' which complicated and in some instances vitiated the conclusions reached. We are not absolutely certain that all of the conditioned reactions which have been secured were 'reflexes' in a strict sense. The rôle which is played by 'conscious' factors, in the opinion of the present writer, looms up as a formidable factor. Much of the work of Pawlow and his associates, Watson's emotion experiment with the baby, and the latter's work on animals is strong argument in favor of the conditioned reflex being a real thing. The writer is of the opinion that the experiment now about to be described furnishes conclusive proof that a reaction may be conditioned without any direct aid from the 'voluntary factors.'

In beginning work on the conditioned reflex, it was our purpose to arrange an experiment which would eliminate these voluntary factors as far as possible. I was somewhat surprised to find that very few reflexes were suited to such an undertaking. Furthermore, it might be observed here that in almost any sort of conditioned reflex experiment, it is desirable (a) that the reflex used be one which can be called out repeatedly, (b) the reflex should be one which does not change markedly in appearance or fatigue easily with repetition, and (c) the reflex response should be adapted to objective registration. Just a little thought on the matter will, I think, convince the reader that there are few reflexes

which meet all of these requirements. The pupillary reflex, selected for this particular experiment, has the following very obvious advantages: (a) it can be readily evoked by a change in the intensity of light falling on the retina, (b) it does not fatigue markedly if proper precautions are taken, (c) changes in the size of the pupil can be easily observed with suitable apparatus, which I may say was available for the present experiment, (d) the fundamental stimulus (change in light intensity) calling out the pupillary reflex can be easily controlled, and (e), what is probably most important of all, this particular reflex cannot be controlled voluntarily in a strict sense. The fact that the pupillary reflex is not subject to voluntary control in a strict sense makes the conditioned pupillary reaction which was secured in this experiment both interesting and suggestive on theoretical grounds.

This experiment was carried out in the Columbia University laboratory, during the year 1921-1922. The writer wishes to make a very grateful acknowledgment to Professors R. S. Woodworth and A. T. Poffenberger, and to Mr. Arthur L. H. Ruben for many valuable suggestions and criticisms.

The 'fundamental' stimulus used was a change in the intensity of light falling on the retina. The 'conditioned' stimulus was generally the sound of an electric bell. The change in light intensity (followed of course by a change in the size of the pupil) and the bell stimulus were repeated together a large number of times. The purpose of the experiment was to see whether the change-in-size-of-the-pupil could not eventually be conditioned to the bell, that is to say, whether giving the bell stimulus alone could not eventually cause a pupillary reaction.

I was fortunate in having the use of an instrument which was constructed especially for measuring the size of the pupil and for controlling the light stimulus. This apparatus was devised by Karl Weiler in Munich, and is referred to as the 'Weiler apparatus.' I have included a brief description of its most essential features in section 3 of this report.

At the beginning of each experiment, I measured the natural effect of the bell stimulus on the size of the pupil.

The bell caused a slight dilatation in the case of every subject tested. Next followed a long period during which I would cause the pupil to make a marked change in size, by altering the light stimulus, and I would give the bell stimulus while this change was taking place. At the end of an experiment with a subject, I again measured the size of the pupil, with and without the bell, and found that the 'training' had left its mark. The change in light intensity, immediately followed by the bell stimulus, will hereafter be referred to as 'training stimuli.'

Two different procedures were used in giving these training stimuli. In one procedure, the light was turned off, and the bell stimulus was present during a dilatation of the pupil, as the training stimuli. It will be seen later that after this training a dilatation of the pupil was conditioned to the bell, i.e., ringing the bell would now cause the pupil to dilate more than it had done at the beginning of the experiment. In the other procedure, the light was turned on, and the bell stimulus was present during a contraction of the pupil, as the training stimuli. After this training had been continued for some time a contraction of the pupil was definitely conditioned to the sound of the bell, i.e., ringing the bell would now cause the pupil to actually contract. The same light which was used during the training period was always present when measurements of the size of the pupil were being made, both before and after training, and with and without the bell. The first procedure will be referred to as the 'training towards dilatation'; the second as the 'training towards contraction.'

The next section is a brief statement of certain general characteristics of the pupillary reflex which concern us particularly. The rest of the report is in the form of the usual laboratory experiment. Section 3 contains a short description principally of what the apparatus can do. Section 4 contains an outline of the procedure. In section 5 the results of all the experiments with the pupillary reflex are discussed somewhat in detail; and in section 6 the main conclusions which seem justified from the whole experiment are stated.

SECTION 2

The Pupillary Reflex

Of the two layers of unstriated muscle fibers of the iris, one layer is circularly arranged so that by its contraction it acts as a sphincter and causes the pupil to contract, the other layer is arranged radially so that by its contraction it causes the pupil to dilate. When light is thrown on the eye, there is an average latency in pupillary contraction of 0.2 sec. (19, 164). The pupil then makes a rather quick contraction, gradually slowing up until 0.87 sec. have passed. This is followed by some slight fluctuations; but 1.2 sec. after the original stimulus was received the pupil practically reaches a level (19, 168–169). These are only average figures, even normal people showing marked variations from them.

If a light of a certain intensity is falling on one eye, and a light of the same intensity is thrown on the other eye, both pupils will make a further contraction. Using very bright light, Weiler was able to produce a 'secondary reaction' of about 0.45 mm. (19, 167). Increasing the light for one eye caused an average contraction of 1.3 mm.; while increasing the light for both eyes caused an average contraction of 1.7 mm.

The pupil appears to make very fine reactions to a great many stimuli. The result in man is that the iris is probably always making fine, oscillatory movements (19, 111; 12, 185-248).

Some of the circumstances under which contraction of the pupil occurs are as follows:

1. Increase in the intensity of light. In man, the light falling on one eye causes simultaneous contraction of both pupils (19, 169; 11, 267). If a light which has caused a very large contraction of the pupil is continued, the pupil gradually relaxes with the adaptation of the retina to light.

2. Convergence of the visual axes (16, 73-100). A change in convergence, without a change in accommodation, is sufficient to provoke the pupillary reflex; the contraction being due solely to convergence, to the exclusion of the