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Basic steps in building a cognitive psychology experiment

Making an experiment - part 1
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It is typically the case that cognitive psychologists test many people in their experiments and consequently they are not so concerned with how any particular person performs. The basic point is that we can advance our understanding by observing how people on average behave when we put them to the test. It is not the repetition of identical behaviour that is key but repeated patterns of behaviour. Moreover, we tend to hedge our bets and qualify our conclusions with statements about statistical expectations. For instance, in order to determine whether division is more mentally demanding than addition, we might time how long it takes people to answer some simple questions and see how quickly and accurately they are in doing different kinds of arithmetic.
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We might conclude – On the basis of the present findings – it is highly likely that most people will do better in a test of mental addition than mental division. Bearing all of this mind we still need to be clear about how to develop experimental tests of our hypotheses. A simple rule is to keep everything the same except for the one thing you want to change. So we could ask the question, “Are people better at solving crossword puzzles in the morning or the afternoon? One way to test this would be to take the same person and get them to solve one crossword puzzle in the morning and one in the afternoon.
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In both cases they are given 15 mins to complete the task. Now tot up the number of clues that are solved correctly and compare their morning and afternoon scores. Now this is far from the perfect experiment but this does give an example of what we mean by keeping everything the same except for the one thing that you want to change. The only thing we want to change is the time of day of the testing. Repeat this exact experiment with a lot of people and then only thing that is systematically changing is the time of test. Everyone is tested under the same conditions in the morning and in the afternoon.
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What we also need to bear in mind is that it is really only worthwhile running an experiment if the basic question remains unresolved. A key preliminary step in generating any experiment is to go and find out what is already known and what remains unknown. It is this kind of fact finding that allows you to generate a sensible hypothesis in the first place. Upon reflection the experiment we outlined is not great. Lets assume that our experiment shows that people do get more clues correct in the morning than the afternoon. So we conclude that people are better at solving crossword puzzles in the morning than in the afternoon. Well maybe?
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What else might be going on here – what have we perhaps overlooked in jumping to this conclusion?
In this video Rob lays out some basic considerations that should be borne in mind when we intend to develop an experimental test of a question about how the mind works.

So there are things that we change and things that we measure and we must try and make sure that the thing that we are changing is responsible for the changes in what we are measuring. As experimental psychologists, we must be on the constant look out for other things that might be changing as we test our participants: Such things are sometimes called uncontrolled variables – things that change that we have no control over.

Most of the time we may be able to ignore these on the assumption that these are changing randomly over time. However, we must be particularly aware of any possible uncontrolled variables that are confounded with the thing we are changing – these are things that vary consistently with the thing we are varying and these are known as confounding variables. The problem now is that if you have two things that are varying consistently with one another then you do not know which is responsible for the changes in the thing you are measuring.

You need to consider what a possible confounding variable is in the experiment Rob has discussed.

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Introduction to Cognitive Psychology: An Experimental Science

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