learning - week 2 Flashcards
what is learning?
the acquisition of (behavioural) information
what is memory?
the retention of information
what are the principles of learning?
memory gets better with more learning
law of diminishing returns
- same amount of learning is eventually less significant
what is the rescorla-wagner rule?
∆V = αβ(λ − ΣV)
what does the rescorla-wagner rule highlight?
the importance of surprise in learning
- the prediction error
which part of the rescorla-wagner shows the potential difference?
(λ − ΣV)
what is evidence for the importance of surprise in learning?
blocking
- if outcome is fully predicted there is no learning
- if know stimulus x is associtated with an outcome
- when x presented with y (xy combination)
- x blocks learning of y
what is the role of surprise in learning?
initial presentation leads to a v. surprising outcome therefore a lot is learned
when memory is well learned stimulus is know
so the outcome is not surprising
what is prediction error?
difference between what is predicted on the basis of prior learning and what actually occurs
(essential to R-W rule)
what does the study of macaque monkeys midbrains demonstrate?
showed that dopamine neurons in the midbrain show exactly the activity that is expected of a prediction error signal
monkeys trained on a pavlovian conditioning task
- a stimulus predicted the delivery of a drop juice reward
- electrophysiological recordings taken from dopaminergic cells in the substantia nigra and ventral tegmental area
- found that dopaminergic cells had a low but consistent rate of baseline firing in absence of any input
when reward not predicted increased dopamine cell firing in response to reward
when reward is expected no increase
when reward is expected but doesnt happen there is a supression of firing
what does the study of macaque monkeys midbrains demonstrate?
- law of diminishing returns
early in learning dopaminergic cells in the substrantia nigra and ventral tegmental area fire intensely when given reward
as learning progresses cells fire less
instead they fire more when stimulus is presented
- indication of a level of expectation of reward
what does the study of macaque monkeys midbrains demonstrate?
- functional relevance to behavioural learning
not evidence that the signal is functioning necessary for learning
- correlation
- need to show that the activity of neurons is required in order for learning to take place
doesn’t show how magnitude of the prediction error determines the extent of learning on that trial
study in humans
fMRI and juice reward
when unexpected there was greater activity in the nucleus accumbens
consistent with the expected activity of a prediction error signal
nucleus accumbens is oone of the major tarhets for the dopminergic cells in the brain
- increased accumbens activity most likely reflects elevated firing of midbrain dopaminergic cells
are predicition error signals just in the midbrain?
no
monkeys + rats
- orbitofrontal cortext
observed currently with midbrain
work together to regulate learning as a result of surprise
exact functional relationship has been analysed using human functioning imaging
Hare et al.
able to distinguish between true prediction error signals and activity that signalled the value of ecpected outcomes
they showed that is was activity in the VENTRAL STRAINTUM alone that followed the pattern expected of a prediction error signal whereas the orbitofrontal cortex appeared to be represented values
what is learning proportional to
the magnitude of the prediction error
