Figure 1.

Schematic representation of the visual stimulus during background visual stimulation (A) and during target visual stimulation (B). During background visual stimulation, circles fill with colour in a clockwise direction at a rate of one every six seconds. As the next circle in the sequence is filled with colour, the previous circle empties. During target visual stimulation, there is a failure of a circle to fill with colour and the next circle following the empty circle fills with colour. When subjects detect the target visual stimulus, they indicate by pressing a button on a game pad. (C) Simplified schematic of protocol for selective and divided attention experiments. Note: The order of visual and oesophageal background and target stimuli are counterbalanced across all subjects for both selective and divided attention tasks. An interstimulus of six seconds occurs between each visual and oesophageal stimulus.