The phenomenon of change blindness (CB) has recently been investigated from a number of perspectives. Basically it entails the limited ability to perceive gross changes in one’s visual environment. In a recent experiment, Simons and Levin (1998) showed that persons do not notice when a stranger asking them for directions is switched with another person when the switch
is concealed briefly by two persons walking between them carrying a door. CB specifically pertains to a limited ability to perceive disparity in scenes, changes between elements (‘second-order information’) and personal visual
impressions (Rensink 2000:2). The rider is that the changes must occur during a flicker, saccade, blink, similar interruption or an eye movement
(Simons & Levin 1997; Rensink 2000). One popular way to investigate change blindness is by means of the so-called flicker technique (see Simons
2000). This entails showing persons a series of slides of real-world scenes. A particular aspect of the scene is then changed. The original and the changed slide are shown consecutively with a brief blank slide inserted between them. The interposition of the grey slide creates a flickering display. It was hypothesised that this brief interruption in the visual sequence makes it difficult to perceive the changes in the scenes as it disturbs our ability to pinpoint specific changes in the scenes by interposing a series of transient movement changes in the flicker cycle. A number of interesting conclusions
were made on grounds of this difficulty to perceive the change in elements of a scene. Firstly, that the brain does not build up or internalise a reasonably full and rich visual representation of the environment. Secondly, CB
indicates that this representation is unstable and very sketchy and that one possibly relies on the external environment as a form of a memory extension.