Experimental design of key-press procedure. Drawing at top and plots below schematize the experimental design, its output data, and 1 type of data summary. The drawing illustrates the 4 potential responses to increase, decrease, variably increase or decrease, or accept the default viewing time of 8 seconds. The default condition controls for those who intended to press the key to increase or decrease viewing time, but who did not act on this intention. This model integrates the stimulus presentation and the time course of potential responses by participants. The traces of individual responses to each picture are shown with raster plots from an anonymous participant in the lower left. Each time interval during which this subject viewed a particular stimulus is indicated by a pink color bar, above which is a blue trace of actual key-press data set to the default baseline for viewing. The bar graph shows summary data (location and standard errors) for the different facial expressions. All responses in the graph are coded as time alterations from the default. * Indicates fixation point.