In this task focused attention is being measured according to a “signal detection” paradigm. Signal and Noise stimuli are randomly presented for a very short duration, in order to engage a decision process based on sparse information about the stimulus.
In a learning phase the patient is stepwise adapted to the stimulus. Starting with a stimulus duration of 1000 msec, the patient’s responses must be 75% correct. Then the patient enters the next phase, a stimulus duration being decreased in steps of 200 msec less, until a duration of 400 msec is reached.
After this training phase the stimulus duration in the test will be 100 msec. Cyclus time of a whole stimulus is 4000 msec. A selection can be made from two condit- ions, 450 or 680 stimuli (i.e. 30 or 45 minutes total testing time).
The signal detection paradigm yields two parameters:
- d’ (perceptual sensitivity) – Values of 2 and higher points to a good discrimination ability.
- á (response bias) – is the patient more inclined to say “yes’ or “no”. Values below 1 will reflect impulsive responding, higher values than 1 indicate a conservative way of responding.
Perceptual sensitivity for both groups
Davies, D.R. and Parasuraman, R. (1982) The psychology of vigilance. Academic Press. London.