The Autokinetic Effect

A striking illusion of motion 
occurs when a single star seen 
against an otherwise 
homogeneous sky appears to 
drift across the field of vision. 
This illusion can be recreated 
in the laboratory by asking 
observers seated in an 
otherwise dark room to view a 
single spot of light. Soon the 
spot appears to drift slowly in a 
particular direction. This 
autokinetic effect, as it is 
called, is highly susceptible to 
suggestion, the studies of social 
psychologists show. When 
"planted" subjects report 
motion of the spot in a certain 
direction, or of a particular 
magnitude, a naive subject will 
often report perceiving the spot 
to move in just that way

    What causes the autokinetic 
effect? Investigators do not 
know for sure, but certain facts 
about motion perception 
already discussed here shed 
some light on it. We have seen 
the importance for motion 
perception of an object’s 
change in location relative to 
other objects or to a frame of 
reference. Conversely, the 
absence of an object’s change 
in location relative to a 
background must be important 
information in perceiving an 
object as stationary. In other 
words, a stationary spot seen 
within a stationary rectangle 
will not appear to move, no 
matter how long we look at it. 
But without the rectangle, the 
spot’s location in a 
homogeneous background (such 
as a dark room) is not 
sufficiently anchored to a 
frame of reference.