Читать книгу Social Psychology - Daniel W. Barrett - Страница 90

An EEG measures electrical activity generated by the brain, whereas an MEG targets the magnetic signals associated with electrical output. You have most likely read about EEG in your introduction to psychology course in the context of measuring brain wave patterns as a way to identify and track the stages of sleep. EEGs are also used to record abnormal electrical activity associated with epilepsy. Regardless of its purpose, an EEG is conducted by placing electrodes at numerous places on the scalp in order to detect brain wave patterns. Social psychologists are specifically interested in how the brain responds to particular social stimuli and therefore focus on changes in the electrical activity, called event-related potentials (ERPs), during and immediately after stimulus presentation. These stimuli can be visual, auditory, olfactory, or tactile (Cacioppo, Lorig, Nusbaum, & Berntson, 2004).

A patient undergoes an electroencephalography (EEG). EEG examines the electric activity of the brain using electrodes placed at key places on the skull.

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Given that ERPs are fairly weak and can easily be drowned out by baseline electrical activity, researchers enhance signal detection by gathering data over many trials and averaging the data from multiple electrodes. MEGs typically utilize form-fitting caps with multiple electrodes that, like EEGs, examine how the brain responds to various stimuli. Both technologies are useful for examining these responses over time. For instance, researchers interested in person perception have measured differences in ERPs with an EEG immediately after a person’s exposure to body movements (Puce & Perrett, 2005) or to faces from blacks and whites (Ito, 2011). The magnitude of the ERP should increase when a person is exposed to stimuli she perceives as very different from one another (such as when viewing a black and then a white face). Similarly, ERPs associated with the categorization of faces have been studied using MEG (Bartholow & Dickter, 2007; Liu, Harris, & Kanwisher, 2002). Figure 2.7 shows how the amplitude of the ERP response at particular brain sites is greater after exposure to human faces than to other objects (Liu et al., 2002). This difference in activation provides further evidence that the brain processes social and nonsocial information in different ways.

Figure 2.7 Strength of ERP Response to People Versus Other Objects

Source: Liu, J., Harris, A., & Kanwisher, N. (2002). Stages of processing in face perception: An MEG study. Nature Neuroscience, 5(9), 911.

Event-Related Potentials (ERPs): Changes in electrical activity in the brain that reflect how it responds to particular stimuli