There are lots of different ways in which we might encounter numerical information as we move through the world; for example, written digits, spoken or written number words, dice, Roman numerals, or just collections of objects. A key question for psychologists is how this kind of information is processed and whether different forms of numerical information are processed in the same way. A fundamental distinction in this debate is the difference between what we might call “symbolic” representations of quantity (for example, digits) and “non-symbolic” representations of quantity (for example, a pile of stones). Are these different forms of quantity information processed in the same way? Or are they fundamentally different?
One very robust finding about the way that people process number is that we appear to associate number with space. For example, if we present digits on a screen and ask people to indicate with their left and right hands whether the digits are odd or even, people tend to be faster to respond to smaller numbers with their left hand and faster to respond to larger numbers with their right hand. This is called the SNARC effect (short for “spatial numerical association of response codes”), and it suggests that there is a fundamental link between number and space. This is sometimes called the “mental number line” and can be thought of as something akin to a “ruler” in people’s heads, with small numbers on the left and larger numbers on the right.
While the SNARC effect has been demonstrated many times for symbolic representations of quantity such as written numbers, there is less evidence for whether it occurs for “non-symbolic” quantities (i.e., groups of objects). Indeed, research in the School of Psychology’s Language and Number lab, led by Dr Sandie Cleland had previously failed to find a SNARC effect for these types of quantities, and we concluded that quantities are not processed in the same way as symbolic representations of number such as digits.
In the current series of studies, we investigated whether people showed SNARC effects when they responded to arrangements of circles presented on a computer screen. People in our experiments were presented with circles on a screen and asked to indicate whether the circles were blue or green. We investigate (1) whether people showed a SNARC effect for this task, and (2) whether it mattered how the circles were arranged.
Unexpectedly, we found a SNARC effect! People were generally faster to respond to smaller numbers of circles with their left hands and faster to respond to larger numbers of circles with their right hand. However, the size of the circles seemed to matter; if the size of the individual circles got smaller as the number of circles increased, the effect disappeared. This may be because people were receiving conflicting cues about the quantity of objects on the screen; this makes sense when we think about quantity usually works – if I have two apples in a bag and I add another ten apples, the apples do not get smaller because there are more of them.
Our findings of a SNARC effect for groups of circles conflicts with our previous findings and has led us to rethink our understanding of the relationship between number and space; generally, the current findings support an account where people associate number with space regardless of the form of the numerical information.
Watch a video for an Experimental Psychology Society (EPS) poster session from Sandie here.
Hear about a previous study from Sandie where they did not find an effect here.
This research was conducted by Sandie Cleland and Rebecca Bull.
Dr Sandie Cleland, School of Psychology
