Learning about time Flashcards
what is periodic timing?
learning to respond at a particular time
what is interval timing?
learning to respond after a particular interval of time
Cockroaches and timing, Roberts (1965)
- Increased activity at dusk. When removed visual cues cycle drifted until increased activity started 15 hours before dusk (cycle slightly less than 24 hours).
- Restoring visual cues produced a gradual shift back to correct
time - Entrainment : light acts as a zeitgeber synchronising the
internal clock.
Is the apparent internal 24-hour clock the result of
environmental experience? or innate? 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 and
food delivery signalled a few hours before by a change in lighting - found animals on the 24-hour cycle learned to anticipate food but others didn’t
what physiological system could provide the 24-hour clock?
- The suprachiasmatic nucleus
(SCN) of the hypothalamus - The metabolic rate in the SCN
appears to vary as a function
of the day-night cycle. - Lesions of the SCN abolish the circadian regularity of foraging and
sleeping in the rat - Receives direct and indirect inputs from the visual
system, which could keep circadian rhythms entrained with the real daynight cycle
what cells have a circadian rhythm?
- More recent work suggests every cell in the body has a circadian
rhythm, which are all under the control of the SCN. - This can dictate e.g. circadian variation in
sensitivity of tumours to chemotherapy
what can disruptions in the circadian rhythms cause?
- Disruption in circadian rhythms can be
responsible for physical illness (e.g. shift workers more susceptible to heart disease, diabetes, infections and even
cancer) - Sleep and circadian rhythm disruption is also associated with several types of
mental illness, such as depression, schizophrenia, bipolar illness - In Alzheimer’s disease the
phenomenon of sundowning refers to the worsening of symptoms in afternoon/evening
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). - Found shallow curve after 2 seconds, medium curve after 4 seconds and a flat curve after 8
- this is due to weber’s law
what is Weber’s Law?
- The just noticeable difference when you change a stimulus isvproportional to the initial intensity/magnitude of the changed stimulus.
- Hence in absolute terms small amounts judged more accurately than large amounts
Scalar property of timing equation
∆I / I = k
∆I = just noticeable change (jnd just noticeable difference)
I = original intensity (of the standard)
K = constant
The critical point is that percentage change is more important than
absolute change
standard – comparison / standard
what is scalar timing theory? . Gibbon, Church & Meck, (1984)
- Pacemaker emits pulses at a
roughly constant rate t (there
is random variation). - When a stimulus is presented, a
switch is operated, and the pulses are allowed to accumulate in working memory. This will equal t multiplied by the number of seconds that have passed (N). - 5-second stimulus: successive pulses stored in working memory
- When the reinforcement occurs, pulses stop accumulating; another
switch allows the number
of pulses in working memory (N * t) to be stored in reference memory - this storage is not completely
accurate – there is some memory distortion. This is represented by K, a number that is close to 1:
If K = 1 the memory is accurate;
If K < 1 a smaller number of pulses is stored;
If K > 1 a greater number is stored. - On each trial the animal compares the number of pulses in working memory
(N * t) with a random value drawn from those stored in reference memory Nmx - This is done by the comparator. If the values
are close, then the animal responds. - Another stimulus
occurs, and the
successive number of
pulses is stored in
working memory - The animal uses ONE
of the values in
reference memory to
decide when to
respond - The comparator works out how close the values are using a ratio rule – NOT a difference rule
- The animal uses ONE
of the values in reference memory to decide when to
respond
Problems with scalar timing theory
- there is no physiological evidence for a pacemaker
- Instead of a pacemaker, it has been proposed that timing
could be achieved by a series of oscillators, each of which has two states, on or off. - Another solution that has been proposed is the
Behavioural theory of timing (e.g., Killeen & Fetterman, 1988). - Conditioning and timing supposedly occur at the same time, and yet are controlled by completely different learning
mechanisms
what is 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 behavioural
classes in between reinforcements. A pulse from an internal pacemaker will change the behaviour from one class to another. - The behaviour that is occurring when the next
reinforcer occurs becomes a signal for that reinforcer.
What are real time models? (e.g., Sutton & Barto, 1981)
- They work just like regular conditioning theories.
- However, the
stimulus is assumed to change over the course of its presentation, and this allows the animal to learn about when a reinforcer occurs