ABSTRACT
Verbal reports are one of the important sources of data in perception, as in other branches of psychology. They serve as a springboard for more systematic investigations of some phenomena, but may be the object of study in their own right. Verbal reports may nevertheless be informative in other ways. For example, an observer might say that he heard a ticking sound that speeded up according to the visibility of the surrounding objects. More precise data about dark adaptation could be obtained with the use of one of the psychophysical methods. They were developed in the nineteenth century for the purpose of estimating how psychological variables were linked with physical ones. The dark adaptation experiment is now almost ready to begin, but subjects still have to be recruited and instructed. Dark adaptation is one facet of the ability of the visual system to respond to any of a huge range of stimulus intensities.
