Читать книгу Abnormal Psychology - William J. Ray - Страница 82

Event-related potentials (ERPs), also known as evoked potentials (EP), show EEG activity in relation to a particular event. Imagine taking a continuous EEG signal during which a picture or tone is presented to an individual a number of times. If we were to take the EEG in the half-second following the stimulus presentation and average these together, we would have the brain response to the stimulus (see Figure 2.13).

The waveform of the ERP is described in terms of positive and negative peaks and the time elapsed from the stimulus presentation. Thus, a P300 waveform is a peak in the ERP in the positive direction occurring 300 milliseconds after the stimulus presentation. Based on early recording equipment characteristics, positive peaks are often shown pointing downward and negative peaks upward. For simplicity, P300 is sometimes referred to as P3, since it represents the third positive peak following a stimulus presentation. Thus, one sees both N1 or P3 as well as N100 or P300 in the literature.

Evoked potentials offer a view of cognitive and emotional processing that takes place in the brain outside of awareness. They are also useful in groups such as infants who cannot respond verbally. In one study, evoked potentials were recorded from 7-month-old infants as they saw faces with emotional expressions. A stronger reaction was seen at around 400 milliseconds when they saw a fearful face as opposed to a happy face (Taylor-Colls & Pasco Fearon, 2015). A common use of evoked potential research in terms of mental disorders has been to show how cognitive and emotional processing differs for those with a disorder and those without. Evoked potentials have also been used to distinguish those with schizophrenia from those without (Laton et al., 2014). In addition, evoked potentials have shown that children with ADHD (attention deficit/hyperactivity disorder) show different types of evoked potential components from those with autism spectrum disorder (Tye et al., 2014).

Figure 2.12 Wavelet Analysis Associated With Seeing the Dalmatian Dog

Source: Reprinted from Catherine Tallon-Baudry & Olivier Bertrand, Oscillatory Gamma Activity in Humans and Its Role in Object Representation, Trends in Cognitive Sciences, Vol. 3, pp. 151–162, Copyright © 1999, with permission from Elsevier.

magnetoencephalography (MEG): brain imaging technique that measures the small magnetic field gradients exiting and entering the surface of the head that are produced when neurons are active