Psychophysiological Equipment and Measurements

Introduction

Psychophysiology is the scientific discipline devoted to the study of the interrelationships between the physiological and psychological aspects of behaviour. Such relationships have preoccupied philosophers and scientists throughout history. The different debates about the soul-body, spirit-matter, or mind-brain relationships are all variations on a single theme: the connection between behaviour – our acts, thoughts and feelings – and its sustaining biological body.

The scientific study of the physiological and psychological aspects of behaviour can be approached through different perspectives. The psychophysiological perspective emphasizes the use of physiological measurements to understand the psychological processes underlying behaviour (Turpin, 1989). The focus of psychophysiology is the non-invasive recording of peripheral and central physiological changes while subjects behave under controlled conditions. This approach has mainly used, although not exclusively, humans as research subjects.

The basic assumption of psychophysiology is that the psychological processes of perception, attention, memory, learning, motivation, emotion, and so on are reflected in the efferent physiological changes – the logistic and instrumental precursors of behaviour – as well as in the physiological brain activity. The psychophysiological methods, therefore, are like windows over the living body – muscles, glands and brain-allowing the knowledge of the complex mechanisms controlling human behaviour.

The Electronic and Computer Revolution

Almost all physiological recording methods are based on the bioelectrical nature of the living tissue activity. Therefore, since the discovery of electricity and its basic principles by the end of the 18th century, physiological recording has evolved in parallel with technological evolution. The first psychophysiological instruments were based on the galvanometer: a moving coil suspended in the magnetic field of a permanent magnet that rotates when an electric current flows through the coil. This device, used with any writing system mounted on the moving coil, is the basis of the traditional polygraphs. It allows the detection and measurement of changes in small currents as a function of time.

The moving coil galvanometer was instrumental for the discovery of the main psychophysiological variables: electromyography by Matteucci and Du-Bois Reymond in the middle of the 19th century, electrodermal activity by Vigoroux and Fere in 1888, electrocardiography by Einthoven in 1900, and human electroencephalography by Berger in 1929. The first electronic circuits used valve condensers, diodes and triodes to filter and amplify the bioelectrical signals. These electronic components were too big, not very precise, and used a lot of energy. In the 1940s a new electronic age began with the discovery of semiconductors and the transistors – solid state electronic components – opening the race for miniaturization and speed. In the 1970s the integrated circuits added the possibility of bringing together complex electronic circuits, equivalent to many condensers, diodes and transistors, into a single unit: the chip.

Psychophysiological instruments have benefited from this electronic revolution in three basic aspects. Firstly, by increasing precision and reducing size and weight of the amplifiers. Secondly, by improving the traditional recording systems using the digital computers to represent, store and analyse the psychophysiological signals. This is done through analogue-to-digital converters interfacing the physiological recording output to the computer. And finally, by permitting the discovery of new psychophysiological variables, only available after complex computerized systems [Page 779]have been applied to detect and extract the biological signals. This is the case of the new psychophysiological techniques for recording brain activity: event-related potentials, brain electrical activity mapping, magnetoencephalography, positron emission tomography, and functional magnetic resonance imaging.

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