Fig. 4

The NFB task. At the beginning of each trial, a fixation mark is shown at the center of the screen. Participants are asked to maintain fixation at the center of the screen (fixation cross/arrow) for the full duration of each trial. A feedback thermometer was displayed just above the fixation mark, with height (indicated in red) representing the speed of attention switch in the previous trial. On the left and right side of the screen were displayed two apertures equidistant from the fixation mark. Each aperture contained a random dot kinematogram (RDK) consisting of an equal percentage of red and green dots. In each aperture, the dots moved in diagonal planar motion with the green dots moving orthogonally to the red dots. During the “Init. Attend Period”, an arrow was superimposed on the fixation cross, which indicates the hemifield that the participant was required to attend. The arrow sign was obtained by adding two skewed lines on one horizontal end of the fixation cross, thus keeping the center of the fixation mark unchanged. The subjects continue to fixate the intersection point of the two perpendicular lines of the cross when the arrow was present and not move the eyes to the attended hemifield. At the same time, a disc superimposed on the RDK was displayed in the opposite aperture and was set to change location and color (red or green) at random time intervals throughout each trial. After a variable period of time, the RDK (red or green) in the attended aperture may change direction; if the attended dots change direction, the participant must switch attention to the aperture in the opposite hemifield and as quickly and as accurately as possible indicate by a button press the color of the disk (red or green). The two apertures are removed from the screen concurrently with the participant response (or if no response is entered after a delay of 300–500 ms) and the height of the thermometer is updated to reflect the switch time of the previously completed trial. In the case of catch trials (when the direction of motion in the attended RDK does not change) the height of the thermometer does not change