C82LEA Biology of learning and memory Learning about time Charlotte Bonardi.
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Transcript of C82LEA Biology of learning and memory Learning about time Charlotte Bonardi.
C82LEA Biology of learning and memory
Learning about time
Charlotte Bonardi
We are pretty good at estimating time periods, and makingjudgements about whether intervals are shorter or longer than each other.
We are also sensitive to the day/night time cycle:
jetlag (timing obviously not just to do with the sun)
waking up just before your alarm goes off
We are pretty good at estimating time periods, and makingjudgements about whether intervals are shorter or longer than each other.
We are also sensitive to the day/night time cycle:
jetlag (timing obviously not just to do with the sun)
waking up just before your alarm goes off
How do we do it? Can animals do these things?
How do they do it?
Distinguish periodic (learning to respond at a particular timeof day) and interval timing (learning to respond after a particularinterval of time).
Distinguish periodic (learning to respond at a particular timeof day) and interval timing (learning to respond after a particularinterval of time).
PERIODIC TIMING
e.g. Circadian rhythms. Question: is the cyclical behaviour really controlled by time perse? Or is it controlled by stimuli that are always present at thatparticular time?
Wheel running in the rat (described in Carlson):
4am 8am Midday 4pm 8pm Midnight
ACTIVITY
Light off Light on
4am 8am Midday 4pm 8pm Midnight
ACTIVITY
ACTIVITY
Light off
Light off Light on
Light on
4am 8am Midday 4pm 8pm Midnight
Constant dim light
When no light cues are available they maintain behaviouron an approximately 25-hour cycle
Cockroaches (Roberts, 1965). Increased activity at dusk. Whenremoved visual cues cycle drifted until increased activity started15 hours before dusk (cycle slightly less than 24 hours).
Restoring visual cues produced a gradual shift back to correcttime. Entrainment : light acts as a zeitgeber synchronising theinternal clock.
Cockroaches (Roberts, 1965). Increased activity at dusk. Whenremoved visual cues cycle drifted until increased activity started15 hours before dusk (cycle slightly less than 24 hours).
Restoring visual cues produced a gradual shift back to correcttime. Entrainment : light acts as a zeitgeber synchronising theinternal clock
Question: Is the apparent internal 24-hour clock the result of environmental experience?
Cockroaches (Roberts, 1965). Increased activity at dusk. Whenremoved visual cues cycle drifted until increased activity started15 hours before dusk (cycle slightly less than 24 hours).
Restoring visual cues produced a gradual shift back to correcttime. Entrainment : light acts as a zeitgeber synchronising theinternal clock
Question: Is the apparent internal 24-hour clock the result of environmental experience?
Bolles & Stokes (1965)
Subjects born and reared under either 19, 24 or 29 hour light/dark cycles. Then fed at a regular point in their own particular cycle....
animals on the 24-hour cycle learned to anticipate food....
29 22 15 8 1
Light change
Light change
29 22 15 8 1
but the others didn’t....
29 22 15 8 1
Light change
Is there any evidence for a physiological system that could provide this 24-hour clock?
The suprachiasmatic nucleus (SCN) of the hypothalamusmay be a candidate.
The metabolic rate in the SCN appears to vary as a functionof the day-night cycle.
Lesions of the SCN will abolish the circadian regularity offoraging and sleeping in the rat.
It also receives direct and indirect inputs from the visual system,which could keep circadian rhythms entrained with the realday-night cycle.
INTERVAL TIMING
Consider a normal classical conditioning procedure:
Tone (20 sec) --> food
? ? ?
INTERVAL TIMING
Consider a normal classical conditioning procedure:
Tone (20 sec) --> food
? ? ?
.....so what happens if thestimulus keeps on going(and you omit the food)?
The peak procedure
.....so what happens if thestimulus keeps on going(and you omit the food)?
The peak procedure
Church & Gibbon, 1982
Rats in lit chamber. Occasionally houselight went off for a 0.8, 4.0 or 7.2 sec (the CS). When the lights went on again a lever was presented for five seconds. If the rat pressed the lever after a 4-sec CS it got food, otherwise it did not. Then tested with a range of stimulus durations (0.8 - 7.2 secs).
Response probability
0.8
0.4
0 2 4 6 8
Church & Gibbon, 1982
Rats in lit chamber. Occasionally houselight went off for a 0.8, 4.0 or 7.2 sec (the CS). When the lights went on again a lever was presented for five seconds. If the rat pressed the lever after a 4-sec CS it got food, otherwise it did not. Then tested with a range of stimulus durations (0.8 - 7.2 secs).
0 2 4 6 8
0.8
0.4
Food after2 seconds
0 2 4 6 8
0.8
0.4
Food after2 seconds
0.8
0.4
0 2 4 6 8
Food after4 seconds
0 2 4 6 8
0.8
0.4
Food after2 seconds
0.8
0.4
0 2 4 6 8
Food after4 seconds
0 2 4 6 8
0.8
0.4Food after8 seconds
Weber’s Law
The generalisation that the just noticeable difference isproportional to the magnitude of the stimulus.
Hence small amounts judged more accurately than large amounts
Weber’s Law
The generalisation that the just noticeable difference isproportional to the magnitude of the stimulus.
Hence small amounts judged more accurately than large amounts
One versus two
Weber’s Law
one versus two – absolute difference of one
- difference as % of whole 0.5
One versus two
Nineteen versus twenty
Weber’s Law
19 versus 20 – absolute difference of one
- difference as % of whole 0.05
Weber’s Law
for comparable difficulty to the one versus two comparison youneed to compare 20 versus 10...
ten versus twenty
Weber’s Law
This may be called the scalar property of timing (it appliesto other judgements too).
I / I = k
I = Just discriminable change in intensityI = original intensity k = constant
One versus twoDifference = 2-1 = 1Ratio = (2-1)/2 = 0.5
One versus twoDifference = 2-1 = 1Ratio = (2-1)/2 = 0.5
Nineteen versus twentyDifference = 20-19 = 1Ratio = (20-19)/20 = 0.05
pacemakert pulses per second
response?
Scalar timing theory
e.g. Gibbon, Church & Meck, (1984)
Working memory N * t
Reference memory K * N * t
comparator
response?
Pacemaker emits pulses at aconstant rate t (although theremay be some random variation).
Working memory N * t
Reference memory K * N * t
comparator
pacemakert pulses per second
response?
Pacemaker emits pulses at aconstant rate t (although theremay be some random variation).
When a stimulus is presented, aswitch is operated, and the pulsesare allowed to accumulate in working memory. This will equalt multiplied by the number of seconds that have passed (N).
Working memory N * t
Reference memory K * N * t
comparator
pacemakert pulses per second
Process 1:
Storing duration of a stimulus inShort term memory
Working memory N * t
Reference memory K * N * t
response?
5-second stimulus:successive pulses stored in working memory
t = 1 per second(ish)
1
comparator
pacemakert pulses per second
comparator
response?
t = 1 per second(ish)
5-second stimulus:successive pulses stored in working memory
2
Working memory N * t
Reference memory K * N * t
pacemakert pulses per second
response?
t = 1 per second(ish)
5-second stimulus:successive pulses stored in working memory
3
Working memory N * t
Reference memory K * N * t
comparator
pacemakert pulses per second
response?
t = 1 per second(ish)
5-second stimulus:successive pulses stored in working memory
4
Working memory N * t
Reference memory K * N * t
comparator
pacemakert pulses per second
response?
t = 1 per second(ish)
5-second stimulus:successive pulses stored in working memory
5
Working memory N * t
Reference memory K * N * t
comparator
pacemakert pulses per second
Process 2:
Storing duration of a stimulus inReference memory
Working memory N * t
response?
When the reinforcement occurs,pulses stop accumulating; the numberof pulses in working memory (N * t)is now stored in reference memory
5
Reference memory K * N * t
comparator
5.1
pacemakert pulses per second
response?
When the reinforcement occurs,pulses stop accumulating; the numberof pulses in working memory (N * t)is now stored in reference memory;
this storage is not always completelyaccurate -- there is some memory distortion. This is represented by K, a number that is close to 1.If K=1 then the memory is accurate;if K<1 then a smaller number of pulses isstored; if K>1 then a greater numberis stored.
Working memory N * t
Reference memory K * N * t
comparator
5.1
pacemakert pulses per second
response?
After several trials there will be severalnumbers stored in reference memoryNm1, Nm2, Nm3, etc -- each equal to theK * N * t for that particular trial.
Working memory N * t
Reference memory K * N * t
comparator
5.1
pacemakert pulses per second
response?
After several trials there will be severalnumbers stored in reference memoryNm1, Nm2, Nm3, etc -- each equal to theK * N * t for that particular trial.
Working memory N * t
Reference memory K * N * t
comparator
5.1 4.7
pacemakert pulses per second
response?
After several trials there will be severalnumbers stored in reference memoryNm1, Nm2, Nm3, etc -- each equal to theK * N * t for that particular trial.
Working memory N * t
Reference memory K * N * t
comparator
5.1 4.7 4.9
pacemakert pulses per second
response?
After several trials there will be severalnumbers stored in reference memoryNm1, Nm2, Nm3, etc -- each equal to theK * N * t for that particular trial.
Remember the error on each trial will not be the same
Working memory N * t
Reference memory K * N * t
comparator
5.1 4.7 4.9 5.0
pacemakert pulses per second
Process 3:
Using stored value in reference memory to decide whether or not to respond on the
next trial
response?
On each trial the animal compares thenumber of pulses in working memory(N * t) with a random value drawn fromthose stored in reference memory Nmx.
Working memory N * t
Reference memory K * N * t
comparator
pacemakert pulses per second 5.1 4.7 4.9 5.0
response?
On each trial the animal compares thenumber of pulses in working memory(N * t) with a random value drawn fromthose stored in reference memory Nmx.
This is done by the comparator. If the valuesare close, then the animal responds.
Working memory N * t
Reference memory K * N * t
comparator
pacemakert pulses per second 5.1 4.7 4.9 5.0
response?
1.0
Another stimulus occurs, and the successive number of pulses is stored in working memory
Working memory N * t
comparator
pacemakert pulses per second
Reference memory K * N * t
5.1 4.7 4.9 5.0
response?
2.0
Another stimulus occurs, and the successive number of pulses is stored in working memory
Working memory N * t
comparator
pacemakert pulses per second
Reference memory K * N * t
5.1 4.7 4.9 5.0
response?
2.0
The animal uses ONE of the values in reference memory to decide when to respond
Suppose 2 seconds have passed; N * t =2
Working memory N * t
comparator
pacemakert pulses per second
Reference memory K * N * t
5.1 4.7 4.9 5.0
response?
The comparator works out how closethe values are using a ratio rule -- NOTa difference rule
i.e. NOT N * t - NMx
but N * t - NMx / NMx
This is one of the reasons that accuracyis better with short intervals.
comparator
pacemakert pulses per second 2.0
Working memory N * t
Reference memory K * N * t
5.1 4.7 4.9 5.0
NO RESPONSE
comparator
pacemakert pulses per second 2.0
Working memory N * t
Reference memory K * N * t
5.1 4.7 4.9 5.0
2 - 5.1 / 5.1 = .61
Large therefore don’t respond
Suppose 2 seconds have passed; N * t =2
response?
3.0
Working memory N * t
comparator
pacemakert pulses per second
Reference memory K * N * t
5.1 4.7 4.9 5.0
response?
4.0
Working memory N * t
comparator
pacemakert pulses per second
Reference memory K * N * t
5.1 4.7 4.9 5.0
response?
5.0
The animal uses ONE of the values in reference memory to decide when to respond
Suppose 5 seconds have passed; N * t =5
Working memory N * t
comparator
pacemakert pulses per second
Reference memory K * N * t
5.1 4.7 4.9 5.0
5.0
Suppose 5 seconds have passed; N * t =2
Working memory N * t
comparator
pacemakert pulses per second
Reference memory K * N * t
5.1 4.7 4.9 5.0
5 - 4.7 / 4.7 = .06
Small therefore respond
RESPONSE
Potential problems with scalar timing theory
1) There is as yet no physiological evidence for a pacemaker
Alternatives have been proposed:
(i) Instead of a pacemaker, it has been proposed that timingcould be achieved by a series of oscillators, each of which hastwo states, on or off. If each oscillator switches after a differentperiod of time, then the entire pattern of activation could be used to determine the exact time (e.g., Gallistel, 1990; Church& Broadbent, 1991):
Potential problems with scalar timing theory
1) There is as yet no physiological evidence for a pacemaker
Alternatives have been proposed:
(i) Instead of a pacemaker, it has been proposed that timingcould be achieved by a series of oscillators, each of which hastwo states, on or off. If each oscillator switches after a differentperiod of time, then the entire pattern of activation could be used to determine the exact time (e.g., Gallistel, 1990; Church& Broadbent, 1991):
R G
Potential problems with scalar timing theory
1) There is as yet no physiological evidence for a pacemaker
Alternatives have been proposed:
(i) Instead of a pacemaker, it has been proposed that timingcould be achieved by a series of oscillators, each of which hastwo states, on or off. If each oscillator switches after a differentperiod of time, then the entire pattern of activation could be used to determine the exact time (e.g., Gallistel, 1990; Church& Broadbent, 1991):
RR RG GR GG
Potential problems with scalar timing theory
1) There is as yet no physiological evidence for a pacemaker
Alternatives have been proposed:
(i) Instead of a pacemaker, it has been proposed that timingcould be achieved by a series of oscillators, each of which hastwo states, on or off. If each oscillator switches after a differentperiod of time, then the entire pattern of activation could be used to determine the exact time (e.g., Gallistel, 1990; Church& Broadbent, 1990):
RRR RRG RGR RGG GRR GRG GGR GGG
Potential problems with scalar timing theory
(ii) Another solution that has been proposed is the Behavioural theory of timing (e.g., Killeen & Fetterman, 1988).
When the animal gets a reward, this stimulates behaviour.The animal moves across an invariant series of behaviouralclasses in between reinforcements. A pulse from an internalpacemaker will change the behaviour from one class toanother. The behaviour that is occurring when the nextreinforcer occurs becomes a signal for that reinforcer.
Potential problems with scalar timing theory
(ii) Another solution that has been proposed is the Behavioural theory of timing (e.g., Killeen & Fetterman, 1988).
When the animal gets a reward, this stimulates behaviour.The animal moves across an invariant series of behaviouralclasses in between reinforcements. A pulse from an internalpacemaker will change the behaviour from one class toanother. The behaviour that is occurring when the nextreinforcer occurs becomes a signal for that reinforcer.
Wipe whiskersWash faceEat the food Explore corner
Potential problems with scalar timing theory
2) Conditioning and timing supposedly occur at the same time,and yet are controlled by completely different learning mechanisms.
Some theories of timing try and explain conditioning; e.g.,Gibbon & Balsam (1977).
Potential problems with scalar timing theory
2) Conditioning and timing supposedly occur at the same time,and yet are controlled by completely different learning mechanisms.
Some theories of timing try and explain conditioning; e.g.,Gibbon & Balsam (1977).
Calculate rate of reinforcement during stimulus, and rate ofreinforcement during background. If first is higher than second,get conditioning.
Potential problems with scalar timing theory
2) Conditioning and timing supposedly occur at the same time,and yet are controlled by completely different learning mechanisms.
Some theories of timing try and explain conditioning; e.g.,Gibbon & Balsam (1977).
Calculate rate of reinforcement during stimulus, and rate ofreinforcement during background. If first is higher than second,get conditioning.
6 reinforcers in 60 minutes of background = 1/10 = 0.14 reinforcers in 15 minutes of stimulus = 4/15 = 0.27 0.27 > 0.1
This theory cannot explain basic phenomena, like blocking.
Some conditioning models try to explain timing -- e.g.Real time models (e.g., Sutton & Barto, 1981).
They work with the Rescorla- Wagner model, just likeregular conditioning theories. However, the stimulus isassumed to change over the course of its presentation, andthis allows the animal to learn about when a reinforcer occurs.
This theory cannot explain basic phenomena, like blocking.
Some conditioning models try to explain timing -- e.g.Real time models (e.g., Sutton & Barto, 1981).
They work with the Rescorla- Wagner model, just likeregular conditioning theories. However, the stimulus isassumed to change over the course of its presentation, andthis allows the animal to learn about when a reinforcer occurs.
Stimulus trace:
Food
General references
Bouton, M.E. (2007). Learning and Behavior. Sinauer Associates.
Carlson, N.R. (2001) Physiology of Behaviour. Allyn & Bacon. Chapter 9.
Domjan, M. (1988). The principles of learning and behavior. Brooks/ColePublishing Company. Chapter 12.
Pearce, J.M. (1997). Animal Learning and Cognition. Lawrence Erlbaum Associates. Chapter 7.
Shettleworth, S.J. (1998). Cognition, Evolution and Behaviour. Oxford University Press. Chapter 8.
Wynne, C.D.L. (2000). Animal Cognition. Macmillan. Chapter 5 pp.96-101
Specific references
Bolles, R.C., & Stokes, L.W. (1965). Rat’s anticipation of diurnal and a-diurnal feeding. Journal of Comparative and Physiological Psychology, 60, 290-294.Church, R.M., & Broadbent, H.A. (1991). A connectionist model of timing. In M.L.Commons, S Grossberg, & J.E.R. Staddon (Eds.) Neural network models of conditioning and timing (pp.225-240). Hillsdale, N.J.: Lawrence Erlbaum AssociatesChurch, R.M., & Gibbon, J. (1982). Temporal generalization. Journal ofExperimental Psychology: Animal Behaviour Processes, 8, 165-186.Gallistel, C.R. (1990). The organisation of learning. Cambridge, MA: MIT Press.Gibbon, J., Church, R.M., & Meck, W.H. (1984). Scalar timing in memory.In J. Gibbon & L. Allen (Eds.) Time and time perception, Annals of the New York Academy of Sciences (Vol. 423, pp.52-77). New York: New YorkAcademy of Sciences.Gibbon, J., & Balsam, P. (1981). Spreading association in time. In C.M. Locurto,H.S. Terrace & J. Gibbon (Eds.) Autoshaping and conditioning theory (pp.219-253).New York: Academic Press.Killeen, P.R., & Fetterman, J.G. (1988). A behavioral theory of timing. PsychologicalReview, 95, 274-295.Roberts, S.K. (1965). Photoreception and entrainment of cockroach activityrhythms. Science, 148, 958-960.Sutton, R.S., & Barto, A.G. (1981). Toward a modern theory of adaptive networks:Expectation and prediction. Psychological Review, 88, 135-170.