Learning in Lizards 
175 
ment consisted of 3 minutes of heat from 
the substrate and a meal worm. Experiments 
done at body temperatures of 43±2°C re- 
vealed an interesting age difference in learn- 
ing. Young lizards reached criterion on the 
average of 35 trials, while older lizards 
reached criterion on the average of 57 trials. 
This result may have nothing to do with age, 
but may simply reflect a more rapid warming 
of the smaller animals. Thus the reward 
“magnitude” may be greater for the younger 
than the older lizards. Reversal learning in 
Anolis carolinensis has been investigated by 
Peterson (MS; Peterson, Norton, and Rich- 
ardson, 1975). 
Vance and Baird (MS and personal com- 
munication) studied learning behavior in the 
nocturnal banded gecko, Coleonyx variegatus, 
using 1 minute in a dark box as positive 
reinforcement, and light as negative rein- 
forcement. Experiments were done at 15° 
and 30 °C. The most rapid learning of bright- 
ness and pattern discrimination occurred at 
30°C. The mean (and range) of trials to 
criterion for a brightness discrimination was 
201 (40 to 300) at 15°; and 77 (16 to 110) 
at 30°; for pattern discrimination, no test 
at 15°; and 100 (40 to 160) at 30°. The 
lizards did not show any spatial reversal 
learning when tested at 30 °C. 
THERMAL REINFORCEMENT FOR 
MAZE LEARNING 
Experiments in my laboratory were under- 
taken to learn whether or not heat would 
serve as a reinforcement for maze learning 
in lizards. In a simple T-maze an infrared 
heat lamp was used to supply reinforcement. 
If the lizard went to the wrong box, it was 
allowed to explore the maze until it found 
the reward box or until 30 minutes had 
elapsed. Lizards quickly learned to go to the 
warm end of the maze. Lizards could see 
the light of the infrared bulb but could not 
detect the differences in temperature at the 
choice point. Lamps were kept on at the 
same end (left or right) for 12 trials, 
switched for 7 trials, and then switched 
again for a total of 24 trials (12-|-7 -}-6=24). 
Two chuckwalas, Sauromalus obestis, learned 
to go to the reward end on the first and 
second trials. One Cnemidophorus tigris 
learned the initial direction in two trials and 
switched immediately (1 trial) after the 
lights were reversed. After switching, all 
lizards had correct responses until the next 
switch. A single Ctenosaura hemolopha 
seemed so disturbed by the apparatus and 
the observer that it often refused to move 
from the starting position. It is not clear to 
me, however, whether the testing procedure 
reveals learning or simply rapid detection 
of thermal information. As a control for this 
possibility, Myres placed three Dipsosaurus 
in a T-maze and taught them to turn either 
right or left by the technique of corrected 
trials with 2 minutes of radiant heat as 
reinforcement. The heat lamp was not turned 
on until after the lizard reached the correct 
goal box. The average time to complete 5 
sets of 5 trials each was reduced from 3.51 
to 0.51 minutes, and the average number of 
incorrect responses for the 5 sets decreased 
from 4 to 2. This result suggests that the 
lizards learned the task, a finding in agree- 
ment with maze learning studies of others 
(Julian and Richardson, 1968; Krekorian, 
Vance and Richardson, 1968). 
OPERANT CONDITIONING IN LIZARDS 
In 1961, Anderson and I initiated a study 
on the use of heat as a reinforcer in learn- 
ing. Western fence lizards, Sceloporus oc- 
cidentalis, were used. They were placed in 
a box in which the weight of a lizard on one 
side activated a microswitch and turned on 
a 250 w infrared lamp. When the lizard left 
that side of the box, the lamp would turn off. 
Lizards placed in the box on the nonreward 
side would explore until by chance they 
entered the side containing the microswitch. 
When the lamp turned on they would bask 
up to an average body temperature of 38 °C 
and then go to the cool side of the box. As 
soon as their body temperature dropped to 
an average of 24.5°, they would go to the 
