The conditioned pupillary reaction.

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Abstract
Much of the work on conditioned reflexes has been criticized that voluntary factors may have affect the mechanisms under investigation. To avoid this complication the present experiment was done upon the pupillary reflex, which in a strict sense is not subject to voluntary control. The experiment sought to determine whether the change in size of the pupil caused by a change in the intensity of light thrown on the retina could be conditioned to the sound of a bell.A special apparatus was employed, for nine Ss, which measured changes in the size of the pupil and controlled the intensity of the visual stimulus. Two procedures were followed during the training period. In one procedure the light was turned off and the sound of the bell was present while the δilatation' of the pupil was in progress; in the other procedure the light was turned on and the bell sounded during a ςontraction' of the pupil. The training series were completed in one continuous sitting of 3 hours and 20 minutes.For both procedures, it was evidenced that the pupillary reflex had become conditioned to the auditory stimulus, although the evidence was more positive for contraction than for dilatation. The average amount of conditioned contraction was 0.527 mm., while the conditioned dilatation averaged 0.114 mm. F urther experiments indicated that a conditioned reflex of the pupil probably could not be established βefore' the change in the size of the pupil, and certainly not αfter' the change; but that it could be readily established δuring' the change in size. Trials with the sound of a bell and the buzzing sound of a telephone receiver furnished positive evidence that the reflex was conditioned to a specific stimulus and not to any stimulus affecting the nervous system at the time. From Psych Bulletin 19:11:00753. (PsycINFO Database Record (c) 2006 APA, all rights reserved)

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