Learning about Time

Question 1

Periodic timing

Answer 1

learning to respond at a particular time of day e.g. Circadian rhythms

Question 2

interval timing

Answer 2

learning to respond after a particular interval of time

Question 3

Wheel running in the rat (described in Carlson)

Answer 3

How activity varies with time of day - rodents more active at night - nocturnal animals.

Question 4

What happens in constant dim light when no light cues are available?

Answer 4

• Cockroaches (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.

Question 5

Is the apparent internal 24-hour clock the result of environmental experience? or innate?

Answer 5

• 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

Animals on 24 hr cycle learned to anticipate food but others didnt (cannot learn, have something built into them)

Question 6

The suprachiasmatic nucleus (SCN)

Answer 6

• 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 day-night cycle.

Question 7

Disruption in circadian rhythms can be responsible for…

Answer 7

physical illness (e.g. in 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

The peak procedure

Answer 8

condition rat for 20 seconds - food, add occasional trials - no food delivered, find - start responding = low, increases where food is delivered, goes down - evidence they know when food is coming. Animals good at learning when food will come - encoding timing

Question 9

Church & Gibbon, 1982

Answer 9

• 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).

Animals = accurate - got closer to critical second - peak of responding that 4 seconds = good. Nice generalization gradient

Question 10

Weber’s Law

Answer 10

• The just noticeable difference when you change a stimulus is proportional to the initial intensity/magnitude of the changed stimulus.

Hence in absolute terms small amounts judged more accurately than large amounts you can tell one from two sugars more easily than eight from nine

Question 11

The weber fraction

Answer 11

the smallest amount of weight change detectable by human touch is 2%

Question 12

Weber’s law for time

Answer 12

• DI / I = k
  
  • DI = Just discriminable 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

Question 13

Our ability to predict time conforms…

Answer 13

to Weber’s law

Question 14

Gibbon, Church & Meck = Scalar Timing Theory process

Answer 14

Process 1: Storing duration of a stimulus in Short term memory

Process 2: Storing duration of a stimulus in Reference memory

Process 3: Using stored value in reference memory to decide whether or not to respond on the next trial

Question 15

Process 3: Using stored value in reference memory to decide whether or not to respond on the next trial

Answer 15

On each trial animal compares no. of pulses in WM (N * t) with a random value drawn from reference memory. This is done by comparator.

If values are close animal responds

Comparator works out how close they are using ratio rule NOT difference i.e N*t - NMx / NMx

Small value i.e .06 = respond
Large value i.e .61 = do not respond

Question 16

Process 1: Storing duration of a stimulus in Short term memory

Answer 16

t = ? per second
N = no. of seconds

Question 17

Process 2: Storing duration of a stimulus in Reference memory

Answer 17

When reinforcement occurs, pulses stop accumulating, another switch allows no. of pulses to be stored in reference memory

this storage is not completely accurate. some MEMORY DISTORTION represented by K , a number 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

After several trials there will be several numbers in reference memory

Question 18

Problems with scalar timing theory

Answer 18

1. There is as yet no physiological evidence for a pacemaker.
2. Conditioning and timing supposedly occur at the same time, and yet are controlled by completely different learning mechanisms.

Question 19

Solution for pacemaker problem

Answer 19

Alternatives have been proposed:
i. 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.

• If each oscillator switches after a different period of time, then the entire pattern of activation could be used to determine the exact time (e.g., Gallistel, 1990; Church & Broadbent, 1991): let’s say on = red, off = green

Question 20

Behavioural theory of timing

Answer 20

○ 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.