Hi Harriet,
Visual scanning involves searching a space (involving head and/or eye movement). Tasks involving navigation or searching a room (i.e., describe everything you see on the affected side) would involve the person moving their head and eyes. Visual scanning tasks to aid in tasks like reading or eating may only involve eye movement.
Smooth pursuits involve tracking a moving object with the eyes. Pursuits are a MOTOR skill. Pursuit eye movements could be tracking a physical object (i.e., a rolling ball or examiner’s fingertip) or an image on a screen (i.e., moving dots on a computer monitor).
Optokinetic stimulation is a SENSORY technique involving taking in complex visual information. Optokinetic stimulation can be used to treat visual vertigo in vestibular rehab with optokinetic stimulation on a screen or without technology (disco ball, Christmas lights, etc.). For the treatment of left neglect, a person would likely watch targets moving leftward across a screen to induce optokinetic nystagmus.
In practice, smooth pursuits and optokinetic stimulation may be closely linked (if someone tracks leftward moving objects during optokinetic stimulation), but they are distinct interventions.
Hope this helps!
Chrissy