174 
Brattstrom 
then ran rats in the same maze using food 
as a reward and showed that they learned 
at approximately the same rate. 
COLOR DISCRIMINATION 
Color plays an important role in the pro- 
tective coloration and displays of lizards and 
in the protective or aposematic color of their 
prey. (Rensch and Adrian-Hinsberg, 1962; 
Swiezawska, 1949; Wagner, 1933). Sexton 
(1964) showed that Anolis carolinensis, 
given a large variety of insects to choose 
from, learned to eat those that were the 
least distasteful. Later, however, Sexton, 
Hoger, and Ortleb (1966) found that, if the 
lizards were hungry, they would eat more of 
the distasteful insects. These lizards may 
have been responding to the insect’s shape 
and pattern as well as color. Romspert, in my 
laboratory, exposed the whiptail lizard, 
Cnemidophorus tigris, to meal worms in- 
jected with green and red food coloring hav- 
ing no taste. The red worms were also in- 
jected with Angostura Bitters. After 1 to 2 
trials, lizards learned to reject the red 
worms. This rejection continued for 7 to 11 
trials (of 1 to 24 hours length). Subsequent 
contact (1 to 2 exposures) with bitter worms 
sustained the rejection behavior. The lizards 
may or m.ay not have discriminated hues, 
rather than colors, and the aromatic effect 
of the bitters may have been a factor. 
Benes (1969) studied color discrimination 
in whiptail lizards. She found that some 
lizards reached criterion in 6 to 10 trials, 
while others required 30 to 149 trials to 
reach criterion. Retention of discrimination 
ability (errorless periods) ranged from 3 
to 14 weeks (13 to 74 trials). 
USE OF ECOLOGICALLY RELEVANT 
REINFORCERS 
While food is often useful as a reward in 
learning studies on birds and mammals, the 
size and energy requirements of lizards are 
such that satiation may develop before learn- 
ing a given task. In connection with research 
on thermoregulation, I began a series of stud- 
ies on learning, using heat as reinforcement. 
These studies, based on those of Weiss (1957) 
and Weiss and Laties (1961), utilized shuttl- 
ing, bar pressing, maze learning, and other 
tasks (see below). Vance and Richardson and 
their co-workers also used ecologically rele- 
vant rewards, including heat from the sub- 
strate, radiant heat, a simulated burrow for 
escape for diurnal lizards, and a dark box 
for nocturnal lizards (Garzanit and Rich- 
ardson, 1974; Julian and Richardson, 1968; 
Richardson and Julian, 1974; Vance, Rich- 
ardson, and Goodrich, 1965). White (per- 
sonal communication) had had success using 
dried lettuce wafers as a reinforcement for 
the large Iguana iguana. 
Vance, Richardson, and Goodrich (1965) 
studied brightness discrimination in the col- 
lared lizard, Crotaphyttcs collaris, using meal 
worms and 3 minutes of substrate heat as 
rewards, and shock to punish incorrect re- 
sponses. With five trials per day for 5 weeks, 
lizards reached criterion in 335 trials, 
whereas rats in the same maze required 105 
trials. Better performance was shown by the 
desert iguana, Dipsosaurus dorsalis (Gar- 
zanit and Richardson, 1974; Peterson, MS). 
Krekorian, Vance, and Richardson (1968) 
found temperature dependent maze learn- 
ing (two mazes of 2 and 4 choice points) in 
the desert iguana, Dipsosaurus dorsalis, with 
heat from the substrate as reinforcement. 
Lizards kept at substrate temperatures of 
22 °C between trials showed no learning at 
125 trials, while those kept at 32°C did better 
than those at 27 °C, (Mean trials to criterion 
for Maze I were 125 at 22°, 105 at 27°, 
65 at 32°; for Maze II, 160 at 27°, 105 at 
32°). 
Davidson and Richardson (1970) showed 
that classical conditioning of autonomic and 
skeletal responses in Crotaphytus collaris 
took far fewer trials (150 vs. 600) when the 
body temperature was raised from 27-29° 
to 35 °C. Reversal learning in Dipsosaurus 
was studied by Vance and Richardson 
(1966), using brightness and position cues 
for discrimination and reversals. Reinforce- 
