Chapter 2: Habituation & Other Forms of Stimulus Learning

PSY 445: Learning & Memory

The act of attending to novel or unexpected stimuli “Investigative reflex”

Composite of several possible physiological and behavioral reactions Startle response

▪ Several different body movements may be involved here

Sense receptors are activated ▪ This orienting of receptors has evolutionary

basis▪ Defensive behaviors are primed

Increase in arousal ▪ Physiological▪ Psychological

Affected by:Stimulus intensityExpectancyRelevancePotential for danger

Q: Is OR learning?A: No--there is no permanent change in

behavior or knowledge. The OR is an innate response.

A decrease in the magnitude of the OR as a result of repeated stimulationOrganisms decrease responding to a stimulus after repeated exposuresA simple form of learning in which the organism learns something about a single stimulusCommon examples:

Noises in your houseTrafficAir conditioning/furnace

Most pervasive form of learningHas received little attention compared to more complex forms of learningOversight may have resulted from belief that habituation is not “real” learningMany theorists believe that learning only occurs in situations where connections are formed between two or more events: “associative learning”

Habituation is considered by most to be a learned decrease in responding to repeated stimulationHowever, there are some alternative explanationsWe will discuss these later

Whole-Body Startle ReactionReaction to loud sounds is studied using laboratory animalsIn rats, we can measure startle in a stabilimeter chamberRat jumps, chamber bounces and sensors detect the amount of movement

Skin Conductance ResponseElectrodes placed on bodies of humans

Siddle, Kuiack, & Kroese (1983)

Eye Fixations to Novel StimuliMeasurement of change in duration or number of eye fixationsNovelty Recognition TaskNew objects added to test environment; active exploration indicates orienting

Thompson & Spencer (1966)Parametric: taking one dimension of an independent variable and systematically varying it to map out the changes that occurThese researchers derived several parametric features of habituationSee next few slides

Number of repetitions of a stimulusExact number required for OR decrement varies considerablyAnywhere from one, to hundreds of presentations

If stimulus is not presented for a period of time, the OR tends to spontaneously recoverIf the delay interval is sufficiently long, the OR may recover completely

Habituation occurs more quickly on each successive occasion

Savings EffectAmount of recovery of the OR is less after each delay interval

The shorter the interval between stimulus presentations, the more quickly responding decreases

Gatchel (1975)One group tone presented every 20 seconds; another group every 100 secondsBy last 15 presentations, 20 second group had less responses to the tone

Massed Practice: more habituation in the short run

Spaced Practice: habituation lasts longer - less spontaneous recovery

Habituation to a stimulus can be temporarily blocked by a novel stimulusThe novel stimulus increases the OR to the original stimulus when the original is re-presented

Siddle (1985)Participants receive 15 presentations of 4-second tone

OR decreases to almost nothing as the result of habituation

New stimulus (patch of red light) is presented New OR specific to light occurs

Tone is then presented again (16th time overall) OR increases as compared to 15th

presentation; dishabituation has taken placePresenting the tone again will lead to the reappearance of habituation; OR returns to previous low level

Habituation may spread to similar stimuliThe more similar the stimuli, the greater the degree of generalization

Nonlearning Explanations Dual Process Theory Aplysia: A Model System Cognitive Theories

Habituation is due to sensory adaptation Sense receptors simply become less sensitive

with repeated stimulus presentationNot a decrease in motor responsivity:

but it is simply fatigue Response system has become depleted; we

become too tired to respond Recovery after rest does not prove that

response decrement was learned

Very questionable explanationsSeems that if you change the stimulus, an increase in responding will occur

See study by Siddle, Kuiack, & Kroese (1983) (mentioned earlier) as evidence of this

Stimulus specificity

Habituation is stimulus-specific-if you change the stimulus, see recovery of the response

Sensitization is not highly stimulus-specific -if an animal is aroused, it is usually aroused to a variety of cues

Effects of strong extraneous stimuli

If you change the nature of the eliciting stimulus you see recovery of the habituated response Can also see recovery of the response if the animal is given a rest period = spontaneous recovery

The response can also be restored by presenting a strong stimulus (dishabituation)

Repeated stimulation of Spinal-Reflex (S-R) pathway leads to a decline in ability of stimulus to evoke response: habituation

However, it also leads to activation of the state system, increasing the general tendency to respond: sensitization Two competing tendencies are occurring

SensitizationAn increase in the magnitude of the OR as a result of repeated stimulationTypically occurs only with very intense stimuli accompanied by physiological arousalMultiple experiences to a stimulus may enhance responding

Q: Is sensitization learning?A: No.

Thompson & Glanzman (1976)Two types of spinal neurons involved in reacting to repetitive eliciting stimuli

Type H Type S

Overall behavioral response depends on the balance between these two factorsSeveral variables involved but stimulus intensity appears to be the most influential

Davis (1974)ProcedureTwo groups of rats tested for startle response

Similar startle-eliciting tones (110 decibels)Background noise level

Different levels – either 60 or 80 decibelsResultsQuieter background showed habituation; louder background showed sensitization

See next slide

Davis (1974)

InterpretationLoud background noise level activated the Type S neurons to a degree that counteracted the habituation that was occurring in the Type H neurons

Results

A second physiological approach looks at underlying synaptic events related to learning

Aplysia, ocean-dwelling slug

Aplysia Simple snail with few neuronsHowever, nerve cells are relatively large; functions are knownUses a siphon to take in sea water from which food is filtered; can be withdrawn back into the body in times of dangerStimulation of siphon (touch or squirt from water jet) elicits this withdrawal

Kandel (2006)Both dishabituation and spontaneous recovery of siphon withdrawal to tactile stimulation was witnessedAfter six touches, responding nearly ceased (habituation)A light is then flashedResponding occurs to next touch (dishabituation)Later light is flashedNot much response60:00 rest interval – responding occurs to next touchShortly, later rehabituationLight stimulus again presented with same results as before

Sokolov (1963)We have a comparator mechanism in our brain which compares current sensory input to the model stored in memory to determine whether the stimulus is familiar

Theories of Wagner (1976; Whitlow & Wagner, 1976) and Olson (1976) elaborate on memory systemDual Memory TheoryPosit that a stimulus could be represented in short-term memory (STM), long-term memory (LTM), or bothDurable habituation seen across sessions or long interstimulus intervals reflects the formation of a long-term representation of the stimulusAlso, stimulus may be recognized if it has just occurred (STM)

Dual Memory Theory

Habituation: Massed presentations > Spaced presentations

Massed (STM & LTM) Spaced (LTM)

Because habituation is a relatively enduring change in central nervous system that occurs in many species and response systems, it demands much greater attention by experimental psychologists than it has received so farThe ability to disregard often-repeated, largely unimportant stimuli is likely linked to survival Habituation may pave the way for animals to attend to more important events: novel stimuli or those heralding significant events like food, mates, and predators

Exposure to a stimulus can affect later learning of that stimulusEasier to use a familiar stimulus for new learning than attempting new learning with an unfamiliar stimulusOnce we have learned to perceive a particular stimulus, we are better able to learn other things about that stimulusBut sometimes its not so easy to recognize and identify a stimulus See next slide

Nickerson & Adams (1979)

Presenting contrasting stimuli Different presentations help with

distinctionTransfer from easy to difficult

stimuli Easy trials seem to help with the more

difficult onesAttention and feedback

Intention to focus on differences and feedback concerning correctness helps

Preference for familiar stimuliPriming facilitationPotentiated startle

Mere exposure effect Increased liking of familiar stimulus

Herman Miller Aeron Chair

Wiggs (1993)ProcedureTested the “liking” of Japanese ideogram stimuliParticipants: College-aged and elderly from USComplex symbols originally presented for two seconds Later these and new symbols were presentedResults Stimuli seen three times previously were more liked than stimuli seen once or never before

Examples of ideogram stimuli used in this experiment

Wiggs (1993)

InterpretationWe seem to be attracted to things we are familiar with

Results

Kunst-Wilson & Zajonc (1980)ProcedureFlashed pictures at subliminal speedsLater shown some pictures that were previously presented and some that were notResultsIdentification was at chanceLiking was consistent for previously shown picturesInterpretationConscious recall not necessary for perceptual learning to occur

Priming occurs when one when presentation of a stimulus facilitates the processing of a closely following repetition of the same or a related stimulus

Startle can be magnified when the startle stimulus occurs in the presence of other, background sources of arousalFor example, neural arousal elicited by the startle noise can combine with arousal due to nervousnessIn lab, high anxiety people produce larger startle responses to loud noises

Exposure used to help with phobiasSystematic desensitizationEmotional flooding (implosion)Virtual reality exposure therapies

Some slides of this presentation prepared with the help of the following websites:www.psychology.iastate.edu/~./.../aobrien/.../8-30-05.pptdogsbody.psych.mun.ca/2250/lecture%201.pptdogsbody.psych.mun.ca/2250/lecture%202.pptwww.psychology.nottingham.ac.uk/staff/cmb/.../mlp2.ppt