1. A testing apparatus for testing a user's attention to distinguish delirium from dementia and normal cognition, comprising a stimulus provider and a controller for controlling the stimulus provider to provide at least one target stimulus, wherein the controller is configured to perform at least one operating procedure and the at least one operating procedure comprises controlling the stimulus provider to provide a sequence of target stimuli to the user, wherein the controller is configured to control the stimulus provider to provide a delay between each target stimulus of the operating procedure and the delay between each target stimulus is between 2050 ms and 4050 ms; each stimulus is provided for a duration in the range between 600 ms to 1400 ms; the sequence consists of between 1 and 14 of the target stimuli; a combination of the delay, the duration and number of target stimuli in the sequence is selected to distinguish delirium from dementia and normal cognition; and the operating procedure comprises a counting test and the apparatus comprises an input device configured to receive a user count of the number of the target stimuli in the sequence in a form of a single response, the input device comprising at least one of: a data input device for an operator to enter the response, or a user input device for the user to enter the response.