We turn to the nature of the process in volved in comparison and discrimination. When we set out to determine a just noticeable difference it is necessary to ensure a proper at titude on the part of the observer; he must not only be disposed toward the specific problem in hand, but, to avoid the difficulties of language, he must also have the form of the judgment literally put in his mouth. If, for example, we are to find the just noticeable difference of tonal pitch, then the observer will be given some such instruction as the following: "You will hear two tones in succession; you are to judge the second in terms of the first, and you are to report whether it is (higher,' or (equal.) p The acceptance of this instruction by the observer determines the nature of his response; he knows what the categories of judgment mean, and the tonal impression au tomatically touches off the report. There is no comparison or discrimination in the popular sense of these terms; the procedure is as if the judgment were already made in the acceptance of the instruction and the sound itself releases now this, and now that, form of report. For merly, it was thought that in the event of suc cessive impressions the judgment was mediated by an image of the first tone. When, how
ever, the comparison is direct, as in the case described, no image or any other process than the bare impression itself is necessary. In deed, in some cases a long-practised observer will judge by absolute impression, i.e., the re port is released upon the appearance of the first tone. Even here, the second tone (which in such a case is the standard of comparison) is not necessarily imaged. Such a discrimina tion is, of course, far removed from those of everyday life. In the laboratory we reduce the mechanism to its lowest terms; in ordinary dis crimination we are not disposed to observe a single attribute, and the discriminative con sciousness must, on that account, be much more complex than the artificial conditions of the laboratory have shown it to be.
Bibliography.— Ebbinghaus, H.,
zfige der Psychologie) (Leipzig 1905) ; Fech ner, G. T.,