were given a cue which mostly provided accurate information as to the ring in
which the target would be presented. If visual attention is like a spotlight, then
it would be expected that speed and accuracy of performance would be great-
est for targets presented in the inner ring. In fact, performance was best when
the target appeared in the ring that had been cued. This suggests that visual
attention could be allocated in an O-shaped pattern to include only the outer or
themiddlering.
Evidence that is even more difficult to reconcile with the zoom-lens model
was reported by Neisser and Becklen (1975). They superimposed two moving
scenes on top of each other, and found that their subjects could readily attend
to one scene while ignoring the other. The zoom-lens model proposes that the
focus of attention is a given area in visual space, but these findings suggest that
this is sometimes incorrect. It appears that objects within the visual environ-
ment can be the major focus of visual attention.
Section Summary
There is some mileage in the zoom-lens model: attention is typically focused on
only part of the visual environment, and the area covered by focal attention is
variable. However, the evidence suggests that focused visual attention operates
in a more flexible fashion than is envisaged within the zoom-lens model. At-
tention does not have to be focused on an entire area in visual space, but can be
directed to certain objects within that area or to certain significant parts of that
area.
Unattended Visual Stimuli
We saw earlier in the chapter that there is generally rather limited processing
of unattended auditory stimuli. What happens to unattended visual stimuli?
Johnston and Dark (1986, p. 56) reviewed the relevant evidence, and came to
the following conclusion: ‘‘Stimuli outside the spatial focus of attention un-
dergo little or no semantic processing.’’ In contrast, Allport (1989) argued that
the meaning of unattended visual stimuli is generally processed. In order to
understand how these different conclusions were arrived at, it is worth consid-
ering some of the evidence.
Figure 15.5
An indication of the stimulus display used by Juola et al. (1991).
Attention and Performance Limitations 371