Three types of alpha waves. The arrows indicate the beginning and the end of high activity in a column. The horizontal lines represent the duration of activity at the high level. The small blue bars indicate that the initial part of the downward slope often has a decisive start. The yellow and purple bars indicate that the upward slope is less steep than the downward slope. The vertical lines illustrate how the wavelength was measured. The EEGs are from participants 59, 51, and 149 in a previous study (Johannisson 2016).