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Abstract:
Healthy aging selectively alters properties of the focus of
visuospatial attention, both slowing disengagement (Greenwood &
Parasuraman, 1994), and decreasing scaling ability (Greenwood et
al., 1997;Greenwood & Parasuraman, 1999). Based on that work,
we proposed that shifting, scaling and saccadic eye movements are
deployed independently as processing tools of visuospatial
attention. To test this model, the role of saccadic eye movements
in modulating search speed was investigated. Young and old
individuals searched for a pink "R" target embedded in an array of
18 pink, blue or green letters (G, N.R) whose location was precued
(SOA 500 msec) with varying precision. Precues encompassed regions
corresponding to 1,4,6,9, or 12 array elements. In addition to
search speed, saccadic eye movements were recorded (ASL 501
infrared corneal reflectance eyetracker). RT to array onset
increased linearly with valid precue size (p<.0001),with a
greater increase in elderly compared to young participants
(p<.05), as reported previously (Greenwood & Parasuraman,
1999). In contrast, the relation of eye movements to valid precue
size was nonlinear, the fewest saccades being made when cues were
middle-sized, regardless of age (p<.02). These results suggest
that in search: (a) as hypothesized, saccades are a separate
processing component of visual attention; (b) a scale of attention
large enough to encompass several array elements reduces the need
for saccades.
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