Learning about time

Question 1

what is periodic timing?

Answer 1

learning to respond at a particular time

Question 2

what is interval timing?

Answer 2

learning to respond after a particular interval of time

Question 3

Cockroaches and timing, Roberts (1965)

Answer 3

• 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.

Question 4

Is the apparent internal 24-hour clock the result of
environmental experience? or innate? Bolles & Stokes (1965)

Answer 4

• 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

Question 5

what physiological system could provide the 24-hour clock?

Answer 5

• 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

Question 6

what cells have a circadian rhythm?

Answer 6

• 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

Question 7

what can disruptions in the circadian rhythms cause?

Answer 7

• 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

Question 8

Church & Gibbon, (1982)

Answer 8

• 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

Question 9

what is Weber’s Law?

Answer 9

• 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

Question 10

Scalar property of timing equation

Answer 10

∆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

Question 11

what is scalar timing theory? . Gibbon, Church & Meck, (1984)

Answer 11

• 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

Question 12

Problems with scalar timing theory

Answer 12

• 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

Question 13

what is Behavioural theory of timing? (e.g., Killeen & Fetterman, 1988)

Answer 13

• 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.

Question 14

What are real time models? (e.g., Sutton & Barto, 1981)

Answer 14

• 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