Learning that occurs as the result of the presentation of a single stimulus.

1.  Habituation

Decrease in the strength of a response following repeated presentations of a single stimulus.  Stimulus initially results in a STARTLE RESPONSE (orientation, increased awareness & attention, fight or flight) which dissipates after a few trials.

Alternative Explanations

      a.  muscle fatigue

muscles unable to respond?  change stimulus or intensity of stimulus

      b.  sensory adaptation

fatigue of sensory system?  reintroduce stimulus when not expected

2.  Sensitization

Increase in the strength of a response following repeated presentations of a stimulus -- "opposite" of habituation.

3.  Groves & Thompson (1970)

dominant theory of how HABITUATION & SENSITIZATION works is called the DUAL PROCESS THEORY proposed by GROVES & THOMPSON (1970)

• DUAL PROCESS THEORY hypothesizes that there are 2 processes that underlie the increase in responsiveness seen in SENSITIZATION and the decrease in responsiveness seen in HABITUATION.

• There's the SENSITIZATION PROCESS and the HABITUATION PROCESS and these processes are not mutually exclusive -- that is, they can BOTH be activated at the same time.

a. HABITUATION NEURAL PROCESSES occur in what Groves & Thompson call the S-R SYSTEM which is analogous to the REFLEX ARC.  EVERY presentation of a stimulus activates this system.

b. SENSITIZATION NEURAL PROCESSES occur in the STATE SYSTEM which determine's the Animal's general level of responsiveness or "AROUSAL".  Only arousing events activate this system.

The S-R SYSTEM works together with the STATE SYSTEM and the net result is behavior. .  The outcome -- whether we habituate or sensitize -- will depend upon which is stronger in any given set of circumstances.

3.  Davis (1974)

Rats in an apparatus with movable floors called stabilimeter chambers, repeated pairings of loud tone (110dB) = habituation, loud tone over 60db background noise = habituation, loud tone over 80db background noise = sensitization.

Results support GROVES & THOMPSON (1970)

THE LOUDER BACKGROUND NOISE CHANGED THE AROUSAL LEVEL OF RATS = INCREASED NOISE, INCREASED AROUSAL, INCREASED RESPONDING

They would say that when the rats were tested with a relatively quiet background noise, there wasn't much to produce changes in the STATE SYSTEM so the S-R SYSTEM won out and the rats habituated.

When the rats were tested in a loud background noise, the background noise probably increased arousal (the STATE SYSTEM) and the rats increased responding, that is they sensitized.