Classical Conditioning: Mechanisms and Theory

Eyeblink Class Study 60 conditioning trials (blocks of 20) 7 blocks of 4 probe trials C1, P1, C2, P2, C3, P3, P4, P5, P6, P7 Acquisition, extinction

Results: Individual % CR in Block Blocks (of 4 probe trials)

Results: Averaged % CR in Block Blocks (of 4 probe trials)

Unconditional/Conditional US: elicits response without training Cs: elicits response due to training (association) Not quite so clear-cut

Consider Aversive conditioning: tone (CS), mild shock (US) Pavlov: mild shock(CS), food (US) Sign tracking: light (CS), saccharin (US) Taste aversion: flavour of saccharin (CS), illness (US)

Novelty Prior associations Familiar vs. unfamiliar stimuli Not “unlearning” of familiar stimuli, per se Basically, need to learn something different

Latent Inhibition/CS Preexposure Highly familiar stimuli more difficult to associate with US than novel stimuli Preexposure group Phase 1Phase 2Phase 3 Exp. gr.“CS” aloneCS-UStest Cont. gr.nothingCS-UStest Exp.Cont. CR magnitude

Latent Inhibition Habituation function Typically we think of habituating to a US; ambiguity in CS/US designation Attentional processes CS- could also explain, but doesn’t suppress responding to other CS+

US Preexposure Subjects exposed to US before CS-US pairings slower to produce CR Associative interference (Hall 2008) –Association of contextual CS with US during US preexposure –In essence, need to extinguish context CS to associate novel CS with US Could this be habituation of US, too? Test methodology?

Ayres, Moore & Vigorito (1984) Stimulus salience Stimulus novelty Conditioned suppression

Method Stimuli –CS: tone, light –US: shock Stage 1: pair CS with US; suppression ratio Stage 2: pair second CS (novel or familiar) with US; suppression ratio Stage 3: extinction of second CS

Results T-TL-T L-LT-L Stage 1: 1st stim. & shock Suppression Ratio Day Stage 2: 2nd stim. & shock Stage 3: 2nd stim. extinction Tone Light FamiliarNovel Familiars (T-T & L-L) show less suppression than novels (L-T & T-L): preexposure

Salience and Intensity Salience: significance, noticeability, detectability Salience and intensity often used synonymously –Low to moderate levels, probably interchangable –Consider high level stimulus –Physiological damage –Not salient, but definitely intense Better to treat intensity as a component of salience

Salience Increase via: Intensity Relevance –Physiological needs –Similarity of environmental stimuli (e.g., naturalistic CS”)

Belongingness: Stimuli Relevance Equipotentiality principle Pavlov Any stimulus should, relatively, be equally conditionable with any other stimulus –E.g., CS1 easily associated with US1, should also be easily associated with US2 –Easy-to-easy, hard-to-hard But doesn’t always work this way Garcia & Koelling’s work on taste aversion

Stimuli Relevance Biological predispostions; evolved Pigeons –Visual CS associated more easily than auditory CS with food US –But auditory CS easier than visual CS when shock is US Fear conditioning in primates (rhesus monkeys, human children) –CS of snake vs. flower

Wilcoxon et al. (1971) Biological preparedness in conditioning Rats nocturnal, quails diurnal Taste aversion Blue water, sour water Quails: colour --> stronger CS Rats: taste --> stronger CS

Higher Order Few pairings, higher-order Extensive training, CS- Solution: periodic reconditioning of first- order CS 1 US CR CS 2 CS 1 CR First-order Second-order CS 3 CS 2 CR Third-order

Rizley & Rescorla (1972) Extinction of CS 1 does not affect CS 2 CS 1 = tone, US = shock, CS 2 = light Experimental group: 1. CS 1 -US, 2. CS 2 - CS 1, 3. extinguish CS 1, 4. test CS 1 & CS 2 Control group: 1. CS 1 -US, 2. CS 2 -CS 1, 3. nothing, 4. test CS 1 & CS 2

Results Suppression Ratio Acquisition CS 2 (light) CS 2 (light) test CS 1 (tone) test Exp. gr. Cont. gr. CS 2 still shows suppression for both exp. & cont. groups… Even though CS 1 shows no suppression in exp. group.

Holland & Rescorla (1975) CS 1 = light, CS 2 = tone, US = food CS 1 -US then CS 2 -CS 1 Then satiate (devalue) US Test: –CS 1 ’s CR weakened –CS 2 ’s CR unaffected Manipulating CS 1 -US relationship doesn’t seem to affect CS 2 ’s representation

Sensory Preconditioning Pair two stimuli (e.g., light and tone) Pair one with US… becomes a CS Now second stimulus also makes CR

Blocking Pair CS 1 and US repeatedly Make compound CS1-CS2 and keep pairing with US CS 1 gives strong CR CS 2 gives weak CR

Value of Classical Conditioning Preparedness Evolution, survival mechanisms Foresight, anticipation

Zamble et al. (1985) Male rats Give male repeated access to receptive females; pair with explicit CS With CS, initiates copulation sooner, ejaculates quicker Competitive advantage over other males

Hollis (1984) Blue gourami Males hold territory Attack intruders Condition light with intruder –Resident attacks intruder sooner –Resident won conflict more often

Learning and Homeostasis Preparation Homeostatic systems Feedback lag in control system Classical conditioning associations can influence homeostatic systems Prepare for events that will perterb the system Minimize lag

Effects Generally, very adaptive However, sometimes difficulties Conditioned compensatory responses Drug tolerance S. Siegel’s work on drug tolerance –Contextual CS prepare opposing CR to maintain homeostasis –Difficulties if contextual CS absent

Stimulus Substitution Theory Pavlov’s theory Through repeated pairings of the CS and the US the CS becomes a substitute for the US so that all responses initially elicited only by the US are now also produced by the CS

Jenkins & Moore (1973) Pigeons Food or water as US CR food = pecked response key as if eating; rapid pecks with open beak CR water = pecked response key as if drinking; slower pecking with beak closed, often with swallowing waterfood

Problems with Stimulus Substitution Theory CS not a complete substitute for US –E.g., eyeblink differences –Magnitudes CSs produce different responses –Omissions and additions –E.g., conditioned suppression in rats US = shock, UR = flinch, CS = tone, CR = freeze Conditioned compensatory responses

Nervous System What is Learned in Classical Conditioning? US centre, Response centre, CS centre CS CentreUS Centre Response Centre US CS Response S-S S-R

S-S or S-R Connections? Stimulus-Stimulus (S-S) Theory –Two associations Learned CS centre to US centre Innate US centre to response centre Stimulus-Response (S-R) Theory –One association CS centre to response centre CS Centre US CentreResponse Centre CS Centre US CentreResponse Centre

Rescorla’s (1973) Experiment Habituation to weaken US-response link Conditioned suppression procedure –Loud noise Experimental protocol GroupPhase 1Phase 2Test Habituation Control Noise (habituation) No stimuli Light: low CR Light: high CR Light Noise Results Control: high CR Habituation: low CR Supports S-S theory

CS/US Influence on CR Timberlake & Grant (1975) –Second rat as CS in sign tracking –CR --> social, not consumatory behaviour Akins (2000) –Male quails’ behaviour sequence –General or focal search for female –CS = visual stimulus, US = female quail –CS-US interval short (1 min.) or long (20 min.)

Akins (2000) % Time near CS Focal Search CS-US Interval (min.) 120 Crossings (Pacing) General Search CS-US Interval (min.) 120 Paired CS &US Unpaired CS & US

Re: S-S Theory Requires flexibility in CR-UR relationship CSs not associated with all aspects of US CS and US can interact CR depends on sensory properties of CS and presentation context

Rescorla-Wagner Model Learning is a discrepancy between –Expectation –Occurrence Level of surprise --> degree of conditioning –More surprising, more learning –Early vs. later trials

Mathematical Model  V n = k( - V n ) V = CS-US associative strength  V = change in associative strength per trial k = salience of stimuli  = asymptotic maximum of V (due to US)  - V = “suprisingness”

R-W and Blocking CS 1 paired with US repeatedly Vcs 1 approaches l By the time CS 2 added, very little associative strength left to be acquired CS 1 very predictive of US; little “surprise” left, so not much need for CS 2

Overexpectation Effect Predicted by Rescorla-Wagner model before being empirically demonstrated GroupPhase 1Phase 2TestResults Overexpectation Control L... 1 food T... 1 food L... 1 food T... 1 food L+T... 1 food no stimuli LTLT LTLT moderate CR strong CR

Conditioned Inhibition Excitatory CS paired with inhibitory CS Opponent process system Example: tone = CS+, light = CS- Start values: V tone = 100.0, V light = 0.0, k = 0.2, = 0.0 We define V sum = V tone + V light And  V n = k(V max - V sum )

V sum V tone V light Associative Strength Trials Trial  VnVtoneVlightVsum = = 22 CS+CS-  V 1 =0.2(0-100)=-20  V 2 =0.2(0-60)=-12  V 3 =0.2(0-36)=-7.2

CS Preexposure Effect Preexposure group: give CS alone Control group: pair CS with US Test: how long to get CR in both groups “Habituation” in preexposure group –Learn to pay less attention to CS –CS irrelevant, nonpredictive –Must “unlearn” during test phase

CS Preexposure Effect Not explained by Rescorla-Wagner model First preexposure trial –No prior conditioning V n = 0, = 0 But, something is learned Salience variable, not constant –Salience of CS decreases during preexposure –Pay less attention to CS

Other Issues Extinction –Not return to zero CS- –Extinguished not by being presented by itself but by extinguishing CS+ Stimuli must be either CS+ or CS-, not both depending on context

Attentional Models Numerous stimuli in environment Can’t attend to them all Selectively process (remove signal from noise) E.g., cocktail party effect –Attend to one conversation at a time –Your name

Mackintosh’s Theory Treats salience as a variable, not a constant Consider two stimuli, L and T If L is a better predictor of the US, then the salience L will increase and salience T will decrease Attend to the more informative stimulus

Mackintosh: Blocking Trained on CS L ; salience L high because CS L is predictive of US In compound CS phase this means salience T will drop towards zero CS T will receive little attention, hence the weak CR

Pearce & Hall’s Theory CSs become ineffective whenever the US is already well predicted If situation changes so that US is surprising then more learning about the CS Attention to CS depends on surprisingness of US on previous trial Assume surprisingness of US will alter attention paid to CSs on subsequent trials –Contrast to R-W (surprisingness of US on trial determines what is learned on that same trial)

Attentional Theories and Blocking On first compound CS trial, CS2 should be quite surprising (previously only CS1 paired with US) Should result in heightened attention to (and learning about) CS2 on subsequent trials But, CS1 blocks learning about CS2 on first compound CS trial

Temporal Coding Hypothesis Contiguity ISI: short delay vs. long delay and trace ITI: generally, stronger CR with it is spaced further apart CS duration: can also influence learning Learn not only that CS is paired with US but also when the US will occur

Holland (2000) US = food CS = noise CR = time at food cup Two CS durations (trial duration = T) of 10 or 20 seconds Six it is (15 to 960 seconds) Results explainable by I/T ratio I/T Ratio Time at Food Cup (CR) T = 10 sec. T = 20 sec.

Rate Estimation Theory Extension of relative-waiting-time hypothesis –CS only informative about US if you spend less time waiting for US when CS is present Nonassociative theory CRs reflect subjects estimates of rate of US presentations during CS and absence of CS Doesn’t fit will with neurophysiological data on associative learning Heavy computational burden –May work in controlled (restricted) laboratory environment, but in real world environment?

Comparator Hypothesis Traditional interpretation is that blocking from failure to learn about CS 2 Comparator assumes that subject learns about CS 2, but ability to respond is blocked Revaluation effects Extinguishing CS 1 can result in CS 2 now producing a CR

Comparator Hypothesis Theory of performance, not learning Condioned responding depends on: –Associations between CS and US –Associations between US and other stimuli (comparator cues; may include experimental context)

Comparator Hypothesis Only allows formation of excitatory associations with US Excitation or inhibition determined by relative strengths of excitatory conditioning to target CS as opposed to other comparator stimuli If excitatory value of CS greater than that of comparator stimuli, then CS+; if lower, then CS- In essence, another opponent process model