Olds & Milner (1954) - Classic Study Flashcards
What were the aims of Olds & Milner’s study?
Investigate whether electrical self-stimulation of the brain acts as a reward, a punishment or a neutral stimulus
Discover if stimulation has a reinforcing effect on behaviour
Find structures in the brain involved in this reinforcing situation
What research method did Old & Milner use?
An animal laboratory experiment
What were the IV & DV of Olds & Milner’s study?
IV - location in the brain of an electrode delivering electrical self-stimulation
DV - number of lever presses when stimulation was switched on (acquisition) and when switched off (extinction)
How were the sample of Olds & Milner’s study? What happened to them prior to testing commencing?
Electrodes implanted in the brains of 15 male rates under anaesthesia and fastened to the skull using screws
Electrodes inserted into different parts of the brain for each rat
How long was the recovery phase of Olds & Milner’s study?
Rats were given three days to recover from the implantation before testing began
What happened after the recovery phase of Olds & Milner’s study?
Electrodes connected to an electrical lead suspended from the ceiling of a Skinner box
Box designed so that electrodes had minimal interference with the health or free movement of the rats
Electrical stimulation occurred only when the rat pressed the lever
Each rat had one-hour pre-testing session on the fourth day after implantation so researcher could work out minimum voltage needed to produce and effect on rats behaviour
Which two ways were rats tested in Olds & Milner’s study?
On subsequent days, each rat was tested in two ways:
Acquisition testing - 3 hours per day, rats self stimulated (pressed the lever)
Extinction testing - 30 minutes per day pressing the lever didn’t produce brain stimulation
How was data collected in Olds & Milner’s study? How were the rats scored?
Each rat provided 2 scores:
- acquisition score - proportion (%) of time pressing the lever when stimulation was present
- extinction score - proportion (%) of time pressing the lever when stimulation was absent, this is the baseline measure
What did the scores in Olds & Milner’s study mean?
An acquisition score above the extinction score was evidence that the stimulation was rewarding
An acquisition score below the extinction score indicated stimulation was acting as a punishment
What happened after testing in Olds & Milner’s study?
Rats were killed, their brains frozen, cut into sections, stained and examined
Done to see where the electrode tip was implanted and thus which brain structures were stimulated
What were the results of Olds & Milner’s study?
Rewarding stimulation was found in 7 out of 15 rats tested
Which areas of the brain were focused on in Olds & Milner’s study?
Septal area - 4 rates stimulated here spent 75-92% pressing the lever in acquisition time but only 8-21% in extinction time
Mammillothalamic tract - only 1 rat stimulated here, spent 71% lever pressing during acquisition and only 9% during extinction
Cingulate cortex - 2 rats stimulated here spent 36-37% lever pressing during acquisition and 9-10% during extinction
What were the conclusions of Olds & Milner’s study?
Septal areas of the brain, and to a lesser extent the mammillothalamic tract and cingulated cortex, are part of a system of structures associated with rewarding effects when stimulated
Stimulation of other areas tested had either a neutral or punishing effect
What were the strengths of Olds & Milner’s study?
Controlled environment
Reliability
Psychology in society
What were the weaknesses of Olds & Milner’s study?
Replicability
Sample size
Unnatural
Why is controlled environment a strength of Olds & Milner’s study?
Study conducted in controlled environment in which all rats were implanted with electrodes and tested in the same way
Environment with external variables minimised thereby increasing the experimental validity of the research findings
Why is reliability a strength of Olds & Milner’s study?
Some reliability in that more than one rat was stimulated in the septal area and these rats showed similar percentages when it came to lever pressing activity
Why is psychology in society a strength of Olds & Milner’s study?
Provided a unique opportunity to explore the effects of drugs on animals, despite this not being the original aim of the study
Provided some insight into why humans return to behaviour they consider to be rewarding, although rats have a different brain structure from humans
Why is replicability a weakness of Olds & Milner’s study?
There was some variation in the voltage of the stimulation given to some rats
This introduces a possible inconsistency that may affect the results
Reduces replicability of the study as future experiments may have rats that require different voltage amounts before they respond
Why is sample size a weakness of Olds & Milner’s study?
Number of rats with electrodes in each area of the brain differed, with some areas only being observed by one rat
Same findings may not be found if an even number of rats were investigated for each area of the brain
Could be argued the sample size was insufficient to provide meaningful results or to be able to draw conclusions from the experiment
Why is the experiment being unnatural a weakness of Olds & Milner’s study?
The setting of the experiment and conditions they were exposed to are not natural for a rat
e.g. wires attached to their skulls and being given eclectic shocks
May have influenced their behaviour so that what was observed was a reaction to experimental conditions rather than their behaviour being due to reinforcement
