Discrimination of Shades of Gray for Different intervals
of Time.
By
Frank Angell.
Leland Stanford Univ., Calif.
In an early number of the Phil. Stud. (Yol. Y) Alfred Lehmth
gives some curiously neglected results of experiments on what has
been commonly called Sensory Memory. Lehmann is working with
the simplest form of recognition in order to decide between the rival
claims of the Similarity and Contiguity theories of Association, and
to this end he devises experiments to show that recognition often
takes place only by means of contiguous association. He shows, for
example that so long as the number of shades in a series of grays
does not exceed the number of commonly used therms for the shades,
viz: black, white, dark gray, light gray and gray, the recognition of
any given shade takes place with great accuracy. When the number
of shades is raised from five to six, the accuracy of recognition falls
off over 25^, and when the series is increased to nine, the recog¬
nition amounts to hardly more than guessing. When, however, an
observer had learned to associate a name with each of the nine shades
of gray, the number of correct »recognitions« rose from 46^ to 75#.
Further, argues Lehmann, if the perception of a likeness or
difference between two shades of gray exposed in succession, amounts
to classifying each shade in a scale — to naming it — then recog¬
nition of this kind should be practically independent of the time
interval between the exposure of the two shades. If the reagent
thinks »light« to himself, and classifies the second as »dark« or
»medium«, the interval of time between the two exposures will make
no difference to the accuracy of the judgments. There is no question
Wundt, Philos. Studien. XIX. 1