Information Processing in the Time Domain 



333 



per second component. This linear relationship holds throughout 

 the band pass range. The second derivative multiplies the forty 

 cycle component by a factor of 4, the eighty cycle component by 

 a factor of 16, etc., in this example. Figure 2 illustrates this deriva- 

 tive processing as it is applied to the electroencephalogram. The 

 faster frequency components present in a complex primary wave 

 become full-fledged baseline crosses because of the relative accentu- 

 ation of the faster frequencies. Period analysis proceeds by generat- 

 ing square waves at the baseline cross of the primary, the first 

 derivative and the second derivative. As can be seen in Figure 2, 

 the square wave train designated as major period reflects the domi- 



Fig. 2. Pulse JVidth Conversion: EEC. The process of period analysis applied to 

 the left parieto-occipital electroencephalogram. The 60 cycle per second artifact 

 superimposed on the original primary trace is markedly reduced by the rejection 

 notch of the selective frequency amplifier, as seen in the filtered primary. The 

 "fragmented" appearance of the second derivative minor period results from the 

 high inertia pen system which cannot foUow^ a true square wave at these fre- 

 quencies. Paper speed 60 millimeters per second. 



