Apparent movement phenomena on crt displays
Hugh M. Bowen, G. Victor Guinness · NASA Technical Reports Server (NASA)
The appearance of movement can occur on CRT's which use a short persistence phoephor ( e .g .> the P -3 1 phosphor decays t o 10% in 40 p s ) and P R F r a t e s between 20 and 50 c p s .Analysis indicates that the apparent movement phenomena a r e due to movements of the eye; under suitable conditions, a stroboscopic interaction may be established between the succession of photic pulses and t h e i r impact at different locations on the r e t i n a .alphanumeric display can appear to rIjump'' o r "dance, extent and type of eye movements ("jumps" a r e analyzed to be associated with saccadic movements, and "dance" with eye t r e m o r ) .apparent movements v a r y f r o m a threshold value, where they can hardly be seen, to an extreme state, where they a r e a predominant property of the display; variations i n the magnitude of the effects depend p r i m a r i l y upon the s p a c e / t i m e c h a r a c t e r i s t i c s of writing and symbol brightness.. Symbols in an depending upon theThe magnitude of the Informal observation of the phenomena suggest that, at their worst, they However, in c a n r e n d e r dilrplays extremely difficult and wearing to observe.l e s s extreme f o r m , the phenomena may be judged to have nuisance rather than detrimental value.An experiment was conducted to estimate whether certain contemporary equipment which uses a P.-31 f a s t phosphor and which evidences the phenomena in muted f o r m is associated with lowered proficiency.Under controlled conditions, o b s e r v e r s undertook data processing t a s k s on a fast-phosphor (P-31) and a slow-phosphor display.however, a trend towards a higher error r a t e with the f a s t phosphor when the t a s k was prolonged (and when the subject o b s e r v e r s reported a feeling of fatigue) was noted.Also, a majority of o b s e r v e r s p r e f e r r e d working with the No definitive conclusions w e r e made; P-12 phosphor.We concluded that t h e r e is a high probability that when the apparent movement phenomena a r e present i n sufficiently potent f o r m , performance will tend to degrade, especially when the o b s e r v e r ' s t a s k is long and arduous. .2. . 4. .