tesis doctoral - e-Spacio - Uned

Organización perceptiva y procesamiento visual preatencional
DESIGN, PROCEDURE AND RESULTS
In this experimental phase, a visual search task was included as indirect measure of
preattentive processing of grouped pattern. Two different experiments were conducted.
Experiment 5 included a compound visual search of the same four grouped patterns
used in previous experiments. Compared to Experimental Phase I, the main variation affected
the attentional task phase. At the beggining of this phase, one of the four patterns was
displayed at fixation in order to inform participants what the target was. Then, participants had
to find the target pattern and indicated the identity of the letter inside ("H" or "S") by pressing a
numerical keyboard button (number 1 or 2) as quickly as possible. Similarly to previous
experiments, two different experimental groups participated in the experiment, a "preattentive"
and an "attentional" group. Preexposure was manipulated introducing four different SOAs: 86
ms, 257 ms, 1000 ms and control or non-preexposure condition.
Differently to Experimental Phase I, no effects of preexposure were observed in
"preattentive" group. The "attentional" group showed a better performance with a SOA of 1000
ms, compared to the rest of preexposure conditions. A reduced error average and RT in this
condition suggested that attention devoted to the grouped patterns during a large period of time
(1000 ms) can improve subsequent visual search of one of these patterns. This result is
consistent with previous studies that used the preview search task (see Watson, Humphreys y
Olivers, 2003, for a review) showing that it is necessary an interval of at least 400 ms to obtain
a preview benefit on the subsequent search task.
Experiment 6 make use of a simple visual search composed by new grouped patterns.
The goal was to manipulate the set size of search as an experimental factor. This new factor
called set size included three different conditions: two, four or eight stimuli, displayed around
fixation. In a similar way that Experiment 3, we included a factor that compared preexposure of
position markers versus preexposure of grouped patterns. There were three differents intervals
of preexposure: 86 ms, 257 ms and 1000 ms. Participants had to indicate whether a grouped
pattern displayed at fixation at the end of the digit task, was present or absent.
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