In another line of this 
research, the speed of 
identifying a word or picture 
flashed on a screen is 
measured. Researchers have 
found that the speed of 
response is increased if a word 
or picture with the same or 
similar meaning is presented 
before the critical one, an 
effect known as priming. Such 
priming seems to occur even if 
the subject is unaware of the 
preceding item. Thus we might 
justifiably maintain that 
unconscious semantic 
processing of a stimulus occurs 
and can affect recognition.

    Priming can also have the 
opposite effect, playing a 
negative role in the processing 
of a word or picture that follows 
the priming stimulus. Steven 
Tipper, then at Oxford, 
performed an experiment along 
the lines of the one illustrated 
at left using overlapping red 
and green figures. On each 
trial, one familiar object 
outlined in red overlapped 
another, outlined in green. For 
each pair of figures the subject 
was to attend to the object in 
red, let us say the kite, and to 
name it as fast as possible. 
Presumably the green object, 
the trumpet, is not attended to 
and thus not consciously 
perceived. On the next trial the 
previously unattended object is 
now red instead of green and 
paired with some other object 
colored green. Therefore the 
subject is to say "trumpet" or 
"bugle" as soon as possible 
because it is now the red object. 
Tipper found that the time 
required to respond to the red 
trumpet is significantly 
increased, following a trial in 
which it was to be ignored, an 
effect now referred to as 
"negative priming."