Psy 551:  Learning Theory
Handout on Hull and Reinforcement by Drive Reduction

According to Hull, an organism is a biological mechanism whose
aim is to survive.  Survival is conceived of primarily in terms
of substances that must be taken in or eliminated for the
individual to survive, and of those interactions necessary to
species survival.  Examples include hunger, thirst, air,
temperature regulation, defecation, urination, rest, sleep,
activity, sexual intercourse, nest building, care of the young,
and relief from pain.  Deprivation of needed substances or
activities creates a drive state, which gives rise to internal
drive stimuli.  Primary motivation or the energizing of behavior
occurs by virtue of the presence of the internal stimuli arising
from the drive.  Those responses that are successful in reducing
drive stimuli and achieving homeostasis became permanent parts of
the organism's behavioral repertoire, thereby increasing the
probability of survival.  Reinforcement then is a matter of drive
stimulus reduction.

Many of the challenges to the Hullian system focussed on the
theoretical concept of reinforcement as drive reduction.
Reinforcement by drive reduction is understandable in cases of
food, water, or relief from pain.  However, other research
findings are also relevant.

1.  Organisms don't start eating until well after a deficit
exists in their tissues.  Moreover, they stop eating before the
deficit is rectified in their tissues.

2.  When presented with a stimulus correlated with the
availability of food, hungry organisms don't necessarily start
salivating before they start responding.  Moreover, they don't
necessarily stop salivating before they stop responding.

3.  Sheffield gave saccharine to rats for running a maze.  The
saccharine functioned marvelously as a reinforcer.  Saccharine is
a noncaloric, nonnutritive sweetener that could not reduce any
metabolic or tissue need.  How could it then serve as a
reinforcer?  Hullians typically suggested that it tasted sweet,
and when the rat was deprived of food, it was in an important
sense deprived of things that tasted good.  Saccharine could
serve as a reinforcer because it reduced the rat's need to eat
things that tasted good.

4.  Butler showed that monkeys will manipulate mechanical puzzles
for 10 hours straight, with little sign of slowing down.  They
will also manipulate latches to unlock viewing doors through
which they can see what is in an adjacent room.  Other research
showed that rats will press a lever when the only consequence is
to briefly illuminate a light ("sensory" reinforcement).  These
results suggest manipulation, curiosity, exploration, or even
simple sensory changes can be important contributors to behavior. 
What drive is involved?  One can postulate a manipulation drive,
a curiosity drive, or an exploratory drive, but what metabolic
need is involved?  Is species survival involved, as in
reproduction?

5.  A male rat will run increasingly rapidly down a runway for
the opportunity of mounting a female, even though he will be
pulled off before ejaculation.  This activity seems to involve an
increase in stimulation, yet it functions as a reinforcer.

6.  ICS (also called ESB) will function as a reinforcer, yet what
need is being reduced?  In what sense is the organism deprived,
or being subjected to aversive stimulation?

7.  Oxygen is necessary for life, yet we have no independent
drive for oxygen.  If we hold our breaths for a short period of
time and begin to feel an increasing need to breathe, the need
comes from the build up of carbon dioxide, not the lack of
oxygen.  A pilot can pass out at high altitudes unless the pilot
wears an oxygen mask, or a person repairing a running car in an
enclosed garage may suffocate if there is no ventilation.

8.  What about social motives, self-actualization, etc.?


For the most part, the Hullians responded to these challenges by
postulating new drives, or by postulating new underlying
mechanisms, either physiological or conceptual.