THE PERCEPTION OF TIME. 615 



"Where the first impression falls on one sense, and the 

 second on another, the perception of the intervening time 

 tends to be less certain and delicate, and it makes a differ- 

 ence which impression comes first. Thus, Exner found ^ 

 the smallest perceptible interval to be, in seconds : 



From sight to touch 0.071 



From touch to sight . „ 0.053 



From sight to hearing. 0.16 



From hearing to sight 0.06 



From one ear to another 0.064 



To he conscious of a time interval at aU is one thing ; to 

 tell ivlietlier it he shorter or longer than another interval is a 

 different thing. A number of experimental data are on hand 

 which give us a measure of the delicacy of this latter per- 

 ception. The problem is that of the smallest difference 

 between tico times which we can perceive. 



The difference is at its minimum when the times them- 

 selves are very short. Exner, f reacting as rapidly as possi- 

 ble with his foot, upon a signal seen by the eye (spark), 

 noted all the reactions which seemed to him either slow or 

 fast in the making. He thought thus that deviations of 

 about Yh) °^ ^ second either way from the average were 



at the very utmost can be feit as discrete when they lall on the same spot. 

 The ear, which begins to fuse stimuli together into a musical tone when they 

 follow at the rate of a little over 30 a second, can still feel 133 of them a 

 second as discontinuous when they take the shape of 'beats ' (Ilelmholtz, 

 Tonemptindungen, 3d ed. p. 270). 



* Pfliiger's Archiv, xi. 428. Also in Herrmann's Hdbh. d. Physiol., 2 

 Bd., I. Thl. pp. 260-263. 



f PflJlgcr's Archiv, vri. 639. Tigerstedt (Biliang till Kongl. Svenska 

 V"etenskaps-Akad. Handi.,Bd. 8, Hiifte 2, Stockholm, 1884) revises Exner'a 

 figures, and shows that his conclusions are exaggerated. According to 

 Tigerstedt. two observers almost always rightly appreciated 0.05" or 0.06 ' 

 of leaction-tirae difference. Half the time they did it rightly when the 

 difference sank to 03", though from 0.03" and 0.06" differences were 

 often not noticed at all. Buccola foinid (Le Leirge del Tempo nei Fenom- 

 enl del Pensiero, Miiano. 1^83. p. 371) that, after much practice in making 

 rapid reactions upon a signal, he estimated direcll}', in figures, his own 

 reaction-time, in 10 experiments, with an error of from 0.010" to 0.018"; 

 in 6, with one of 0.005" to 0.009"; in one, with one of 0.002"; and in 3^ 

 with one of 0.003 ', 



