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