How many objects can you instinctively count?

25 January 2009

Question

Say you had three eggs on the table, by simply looking at them you can tell that there are three eggs (without counting one, two, three etc...). My question is, how many eggs or any other objects does there have to be until you have to start counting them?

Answer

We put this to Dr Roy Allen, School of Psychology, University of Aberdeen:

He's talking about subitising and subitising is our apparent ability to instantly apprehend the quantity of a small group of objects without needing to consciously count each one individually. Unfortunately this is a research topic which has quite a heated debate about it. A lot of people argue that subitising as such doesn't exist at all and that really is some form of fast counting which is conscious. It's very difficult to research into subitising simply because you have to eliminate conscious counting. The only way to do that is to present stimuli very quickly, very short periods of time. Something like 50ms and then ask people to give their impression of the quantity of objects that they actually see. This particular person's question is quite difficult to answer because as long as the objects are present for a long length of time there's always the possibility that they might also be counting as well as subitising. The answer to the question is probably 3 or 4 in the true sense of subitising. We probably do this by some form of pattern recognition. There's some correlation between quantity and particular shape. For example, a triangle - three objects is always a triangle or almost invariably a triangle; two objects always form the ends of a straight line.

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