4Autokinetic Effect: You can experience this for yourself. For those with normal sight, an unusual effect is noticed when, in a totally dark room, a small candle flame is watched. After a short time, the flame appears to dance around the room. It appears that our vision works best when we have information that al lows a frame of reference. A single light source in an other wise dark room does not afford a reference frame.
Now consider the learner with a severe visual impairment. As sighted people we may be able to see those objects which offer a frame of reference for the object we are presenting as stimulus. But the learner's visual disorder may result in these reference objects going undetected. They may be experiencing something similar to an autokinetic effect. This will result in the object being rather a disturbing experience. For this and the description on using a dark-room with fluorescent lighting, it is therefore worth having more than one object present.
5In a study in British Colombia by Groenveld, Jan and Wong (1988), it is stated that cortical visual impairment (CVI) was the cause of legal blindness in 10% of all children with visual loss. Ellis (1986) found it present in about 20% of severely visually impaired 'mentally retarded' children.