  When studying how people search for objects in scenes, the inhomogeneity of
the visual field is often ignored. Due to physiological limitations peripheral
vision is blurred and mainly uses coarse-grained information (i.e., low spatial
frequencies) for selecting saccade targets, whereas high-acuity central vision
uses fine-grained information (i.e., high spatial frequencies) for analysis of
details. Here we investigated how spatial frequencies and color affect object
search in real-world scenes. Using gaze-contingent filters we attenuated high
or low frequencies in central or peripheral vision while viewers searched color
or grayscale scenes. Results showed that peripheral filters and central
high-pass filters hardly affected search accuracy, whereas accuracy dropped
drastically with central low-pass filters. Peripheral filtering increased the
time to localize the target by decreasing saccade amplitudes and increasing
number and duration of fixations. The use of coarse-grained information in the
periphery was limited to color scenes. Central filtering increased the time to
verify target identity instead, especially with low-pass filters. We conclude
that peripheral vision is critical for object localization and central vision
is critical for object identification. Visual guidance during peripheral object
localization is dominated by low-frequency color information, whereas
high-frequency information, relatively independent of color, is most important
for object identification in central vision.
