Learning About Time

Front 1

We are good at estimating time periods, making judgements about whether time intervals are shorter/longer than each other. We are sensitive to the time of day - we live on a 24 hour cycle.

Back 1

Periodic Timing: learning to respond at a particular time of day. E.g. circadian rhythms - is cyclical behaviour controlled by time? Or is it controlled by stimuli present?

Front 2

Carlson: when no light cues are available, rats maintain behaviour on an approsimate 25-hour cycle (run more). They ran more when the lights were off - rats have something internal telling them what time it is.

Back 2

Roberts (1965) - cockroaches displayed increased activity at dusk: when visual cues were removed, the 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 synchronisng the internal clock

Front 3

Bolles and Stokes (1965) - pps born and reared under 19, 24 or 29 hour light/dark cycles. They are fed at a regular point in their own particular cycle. Only animals on 24 hour cycle learned to anticipate the food. Environment cannot help predict when food is coming.

Back 3

Suprachiasmatic Nucleus (SCN) of hippocampus: physiological system which could provide a 24 hour clock. Metabolic rate of SCN appears to vary as a function of day - night cycle.

Front 4

Different organs are active at different times - chemotherapy conducted when activity of the target organ is at its maximum. Alzheimer's shows links to Circadian Rhythm - symptoms show at times of day

Back 4

Lesions of the SCN - abolish circadian regularity of foraging/sleeping in rats. It also receives direct and indirect inputs from the visual system, which could keep circadian rhythms entrained with the real day-night cycle

Front 5

Interval training - normal classical conditioning: Tone (20 secs) - food.. Animal will learn that tone means food and that length of tone is important.

What happens if stimulus keeps on going and food is omitted? PEAK PROCEDURE - increase in response 1 minute until 20 seconds when it peaks and activity decreases again

Back 5

Church & Gibbon (1982) - rat lit in chamber. Occasionally, light went off for 0.8, 4 or 7.2 seconds (CS). When the light came on again, a lever was presented for 5 seconds. If the rat pressed the lever after a 4second CS it got food, otherwise it did not.

Rat then tested with a range of stimulus durations (0.8-7.2 seconds) and at 4 seconds rat pressed lever a lot: knew what 4seconds was.

Same result when lever at diff times

Front 6

Weber's Law - JND is proportional to the magnitude of the stimulus. Hence, small amounts are judged accurately than large amounts.

Can look at a difference as 'absolute' - e.g. 1 or % difference e.g. 0.5

What proportion of small one does large one take? % diff is more important that absolute difference

Back 6

May be called the scalar property of timing - depends on magnitude of what you are judging

JND in intensity/original intensity = konstant

19 vs. 20 = abs diff = 1 and ratio = 20-19/ 20 = 0.5

Front 7

Scalar Timing Theory = pacemaker pulses away at a steady rate at 't' pulses per second. Stimulus comes and automatically time it: N*t.

Reward is presented - acknowledge that memory is important - goes into reference memory = k*N*t: need to keep track and remember long term

Back 7

1) Pacemaker - emits pulses at a constant rate (some random variation)

Front 8

2) Storing duration of stimulus in STM - stimulus is presented, switch is operated, no. of pulses that accumulate in working memory = t * N (no. of seconds)

Back 8

3) Storing duration of stimulus in reference memory: when reinforcement occurs, pulses stop accumulating. The number of pulses in WM is now stored in reference memory. Transfer is not completely exact - K is around 1 due to some memory distortion.

If K = 1, memory is accurate

Front 9

4) Using stored volume in reference memory to decide whether to respond: 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.

This is done by a comparator. Takes the absolute difference as a proportion of what is being times: not absolute difference

Back 9

Problems with Scalar timing theory - 1) no pacemaker has been found in brain. Instead of pacemaker - may be a series of osscilators each of which has two states - on/off

If each oscilator switches after a different period of time, then the entire pattern of acqusition could be used to determine the exact time

Front 10

Some on for 12 off for 12, some for 6 off for 6 etc. Each intervals identify by pattern of 'on' and 'off' ness - could uniquely identify tiniest period of time by combinations of on and off

Back 10

Behavioural theory of timing: animal gets a reward - stimulating behaviour. Animal moves across on 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 next reinforcer occurs becomes a signal for that reinforcer (based on routine)

Front 11

Conditioning and timing occur at same time?

calculate the rate of reinforcement during stimulus, and rate of reinforcement during background. If first higher than second, get conditioning.

6 reinforcers in 60 mins of background = 1/10 - 0.1

4 in 15 mins = 4/15 = .27

.27>.1

Back 11

PROBLEM - cannot explain blocking - some condiitoning models explain timing, e.g. deal time models. Stimulus assumed to change over prsentation: allowing animal to learn about when a reinforcer occurs.