Relationship
Between Accuracy of Search and Extended Exposure-Time
R.T. Solman |
In
an attempt to bridge the gap between search under time-limited (brief
exposures) and list conditions, two experiments were designed to
extend a previously obtained (Solman, 1975b) relationship between
accuracy of search and exposure-time. In Experiment 1 subjects searched
circular arrays of letters for a pre-specified target. Responses
were sampled over an exposure-time range of 100 to 500 msec, and,
in accord with Neisser's (1967) description of selection during visual
search, it was anticipated that the available time would be sufficient
for subjects to carry out a further selection on those occasions
when the initial target candidate proved to be incorrect. The results
however gave no obvious indication that subjects had attempted to
compensate for incorrect selections, and it was suggested that as
the physical stimulus was present for a maximum period of 1 SO msec
(longer exposure-times were composed of an 180 msec presentation
plus a period of blank field}, a second take might (a) have been
ineffective due to the effects of image decay, or (b) have been impossible
if associated with an eye movement. In Experiment 2 the time course
data obtained in Experiment 1 was supplemented for short times (i.e.,
exposure-time varied from 15 to 400 msec), and the decay theory proposed
as an explanation of the results obtained in that study was tested.
The results ruled out image decay as an explanation of the previous
findings. They also showed that the opportunity for eye movements
need not prompt subjects to have a second go at selecting the target,
although it was possible that the design of the study precluded effective
use of this option. In discussion it was suggested that there may
be fundamental differences between search under time-limited and
list conditions.
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