How are thinking skills tested?

Many studies of ageing include tests that measure thinking skills. This is especially common in research to uncover factors that help thinking skills age well.

What can be measured?

Our brains make knowledge and manipulate information. They use many different processes to do this. Psychologists are still working out what the processes are, but they agree on which types of thinking skill can be reliably measured for research purposes. These include:

• how well we remember
• how fast we think
• how well we can visualize two- and three-dimensional spatial problems
• how good our language skills are
• how well we can organize our thinking, especially if we have more than one thing to think about at the same time
• how good our number skills are
• how vast our store of knowledge is

Scientists use tests that measure these thinking skills, and/or others, in studies of how well thinking skills are ageing.

Some people have generally better thinking power than others and tests confirm that people who do well at one type of thinking skill tend to do well on all the others. Therefore, people can be measured for how much general intelligence they have.

It’s not the whole story, though. Apart from general intelligence, people differ on specific thinking skills. So it’s important to use a number of tests to understand how an individual’s brain functions, both in general and in specific ways.

‘Fluid’ and ‘crystallized’ thinking skills

Like any machine that makes things, there are two ways in which you can test the brain's thinking skills. You can ask a machine to make something here and now and assess how efficient it is, or you can ask to see the warehouse store of the things it’s made in the past and assess their quality and quantity.

Psychologists often separate thinking skills into two broad types: ‘fluid’ thinking skills, which make knowledge here and now, and ‘crystallized’ thinking skills, which reflect knowledge we have made and warehoused through our lives.

Fluid

‘Fluid’ thinking skills are tested by asking the brain to work with new material, often under time pressure. These tests don’t require previous knowledge. When you’re asked to perform a test of fluid thinking, it feels like an effort. The tests involve reasoning your way through new problems, such as puzzles where you have to work out the logical sequence in an abstract pattern and then choose a shape that completes it.

The average person has their peak fluid ability in their 20s. After that, people typically decline in their ability to do these tasks.

Crystallized

'Crystallized’ thinking skills are measured mostly by tests of knowledge.The idea is we will have picked up information and facts about the world, amassing a mental storehouse that we can use in everyday life. Brighter people tend to pick up and deploy more. Vocabulary tests are widely used to assess crystallized intelligence. When you’re asked to perform a test of crystallized thinking, it typically doesn’t feel like an effort because you tend to know the answer or you don’t.

Crystallized skills peak later in life than fluid skills, often in the 40s, and don’t decline very much after then in healthy people. Older people often have better crystallized skills than their younger counterparts. It’s not hard to imagine that crystallized skills are part of what people mean when they talk about the ‘wisdom of age’.

Everyday life

Fluid and crystallized thinking skills matter in real life. The laboratory tests used to measure them may seem abstract, but the skills are what we use for everyday tasks like counting change in shops, reading and understanding medicine labels, and doing household tasks.

We all want to know how to stay as sharp as possible throughout our lives. The scientists’ goal is to discover how we can build up, preserve and protect all our thinking skills as we age.

Suggested reading

• Salthouse, T. (2004) What and when of cognitive ageing. Current Directions in Psychological Science 13(4), 140-144.

With thanks for this page to scientists in the University of Edinburgh’s Centre for Cognitive Ageing and Cognitive Epidemiology.

The photos in this section are of participants in The Disconnected Mind research project carrying out cognitive tests. Thank you to the Wellcome Library, London, for the photos.