In all these points, he corresponds to the common group of strong visualizers who learn to depend so exclusively on visual images that all other less dominant faculties of sensory reproduction fall into disuse. Throughout this paper we shall frequently allude to the part played in H.'s answers by these vivid mental images.
He was able to reproduce the image of a thing seen with such accuracy that it could be searched for details, at first unnoticed. But this was not the case with any other sensory impression. As soon as the stimulus was removed, he retained so much only as had been noticed at the time; for he was unable to reproduce any sensory images, except those of vision. This peculiarity common to most of those who visualize strongly leads to the following difficulty in testing sensation. Suppose that H. was returning correct answers to stimuli of different kinds applied to the affected area; the one was said to cause a sensation of touch, another appeared hot, and a third seemed to be cold. If, after withdrawing the cold object, R. inquired unexpectedly concerning the nature of the referred sensation, H. was frequently puzzled. Had the question referred to the qualities of a thing seen, H. would have recalled the visual image, examined it carefully and answered accordingly. But as he could not recall any tactile or thermal image of the cold object, he was unable to answer a question relating to some sensory quality to which his attention had not been directed at the time. A prick or other painful stimulus, however intense, evoked a sensation that could not be reproduced.
In the same way when tested with the compasses, H. might answer "two" rightly or wrongly; but if, after the points were withdrawn, he was asked unexpectedly whether they seemed close together or far apart, he was unable to give an opinion. This occurred when the test was applied over both normal and abnormal parts, provided the compasses were suitably adapted.
Again, some unexpected feature in the sensation might arouse H.'s attention, but inability to reproduce the sensory image greatly hindered its introspective study. It was often necessary to repeat the stimulus several times before H. could appreciate each separate aspect of the sensation.
Now, sense-organs, and particularly those of the skin, do not react in an exactly similar way to every repetition of the stimulus. As this is particularly the case with those of the protopathic system, H.'s inability to recapture the features of a somatic sensation in the form of a reproduced image considerably hindered his introspective analysis. For this
