2.3.3 Material data
A third kind of data is ‘material’ and provides more direct evidence from bodies and brains. This comes from biological psychology and includes biochemical analyses of hormones, cellular analyses, decoding of the human genome and neuropsychological technologies such as brain-imaging techniques. The data that can be collected from the various forms of brain imaging provide direct evidence about structures in the brain and brain functioning, enabling direct links to be made with behaviours and mental processes. For example, you may read about different kinds of failure of remembering, each of which can be shown to be associated with injury to particular locations in the brain. A familiar example of material evidence is the lie-detector technique where the amount of sweat that is excreted under stress changes the electrical conductivity of the skin.
The actual raw data are the measures of the amount of current that passes through the skin, but these data are a direct indication of the amount of sweat produced, which in turn is an indicator of stress and so assumed to be evidence of lying.