318 



ROBERT M. BENJAMIN 



stimulus of 46°C for 30 sec, back to body temperature for 15 sec, another 

 test stimulus (43 X) for 30 sec, and so on. The unit had very little spon- 

 taneous discharge, began to respond at about 29°C and began to display its 

 characteristic pattern at about 22°C which consisted of an initial discharge 

 at short intervals with low variability. As the stimulus continued, both 

 the average interval and the variability increased. 



The unimodal temperature units fired quite differently. At the bottom 

 is one example. Notice that it always gave a burst of impulses to a colder 

 stimulus, no matter what the absolute temperature. Look at the change 

 from 43°C to 37.5°C and from 37.5°C to 11°C. In its optimal temperature 

 range (32°-22'') this initial burst was followed by a discharge at relatively 

 constant range of intervals. 



O 

 O 



o 



CM 



X 



LOG MOLAR CONCENTRATION 



Fig. 8. Taste preference curves of the squirrel monkey as determined by the two 

 bottle method. Large dots indicate the lowest concentrations used in the electro- 

 physiological experiments. 



These two patterns of discharge are sufficiently characteristic that one can 

 always identify the modahty of a unit from the record. 



The taste units in the squirrel monkey were routinely tested with mech- 

 anical and temperature stimuh and then subjected to a series of taste solu- 

 tions which consisted of three concentrations each of four old standards : 

 sodium chloride, hydrochloric acid, quinine hydrochloride, and sucrose. 

 The three concentrations were chosen on the basis of behavioral discrimina- 

 tion thresholds as measured by the standard two-bottle preference method 

 (Fig. 8). These are average curves based on the consumption of four 



