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An Investigation of Linear Separability in Visual Search for Color Suggests a Role of Recognizability

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Journal of Experimental Psychology: Human Perception and Performance
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Garry Kong
Garry Kong
Garry Kong
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David Alais at The University of Sydney
David Alais
Erik Van der Burg at Vrije Universiteit Amsterdam
Erik Van der Burg
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Abstract

Visual search for color is thought to be performed either using color-opponent processes, or through the comparison of unique color categories. In the present study, we investigate these theories by using displays with a red or green hue, but varying levels of saturation. The linearly inseparable nature of this display makes search for the midsaturated target inefficient. A genetic algorithm was employed, which evolved the distractors in a search display to reveal the processes that people use to search color. Results show that participants were able to search within only midsaturated red items, but not within only midsaturated green items, providing evidence for color categories, as in English there is a basic color label for midsaturated red (i.e., pink), but not for midsaturated green. A follow-up experiment revealed that it was possible to search within midsaturated green items if the exact target color was primed before each trial. We therefore suggest that both priming and a unique color category increase the recognizability of the target color, which has been speculated to increase visual search performance.
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An Investigation of Linear Separability in Visual Search for Color
Suggests a Role of Recognizability
Garry Kong and David Alais
The University of Sydney
Erik Van der Burg
The University of Sydney and Vrije Universiteit Amsterdam
Visual search for color is thought to be performed either using color-opponent processes, or through the
comparison of unique color categories. In the present study, we investigate these theories by using
displays with a red or green hue, but varying levels of saturation. The linearly inseparable nature of this
display makes search for the midsaturated target inefficient. A genetic algorithm was employed, which
evolved the distractors in a search display to reveal the processes that people use to search color. Results
show that participants were able to search within only midsaturated red items, but not within only
midsaturated green items, providing evidence for color categories, as in English there is a basic color
label for midsaturated red (i.e., pink), but not for midsaturated green. A follow-up experiment revealed
that it was possible to search within midsaturated green items if the exact target color was primed before
each trial. We therefore suggest that both priming and a unique color category increase the recogniz-
ability of the target color, which has been speculated to increase visual search performance.
Keywords: visual search, attention, genetic algorithm, priming, linguistic relativity
Visual search is a commonly used task in psychophysical ex-
periments. It was originally used to identify basic features through
which the visual system analyzed a stimulus. This idea stemmed
from feature integration theory (Treisman & Gelade, 1980) which
postulated that “pop-out” search indicated the presence of a basic
feature in the visual system. While this idea has been refuted, in
part through the existence of “pop-out” with stimuli not defined by
a basic feature (e.g., Enns & Rensink, 1990;Wang, Cavanagh, &
Green, 1994), it has initiated the debate on whether visual search
is driven by early or late visual processes. For example, visual
search for color has been argued to be based on the low-level
color-opponent channels (Lindsey et al., 2010), but others have
argued that it is based on a limited number of basic color terms
(D’Zmura, 1991;Yokoi & Uchikawa, 2005).
The idea that visual search for color is driven by color-opponent
processes is derived from low-level color perception in the lateral
geniculate nucleus (LGN). Here, cells that respond to color are
tuned to one of three axes: red-green, blue-yellow, and luminance
(Derrington, Krauskopf, & Lennie, 1984). Support for the idea that
these cells affect visual search come from Lindsey et al. (2010),
who investigated visual search with targets of desaturated colors
among white and saturated distractors. They found that search for
some colors, mainly the reddish colors, was faster than for others,
and that this search advantage was modeled well by the theoretical
outputs of the three types of opponent cells in LGN. On the other
hand, evidence against this theory comes from D’Zmura (1991; see
also Bauer, Jolicoeur, & Cowan, 1998), who found that the diffi-
culty of visual search for color depended on whether or not the
target was collinearly flanked by its distractors when represented
in CIE color space, that is, the principle of linear separability. This
was the case with all color pairings including those that could not
be explained by the color-opponent channels. For example, the
search for an orange target among yellow-green and purple dis-
tractors was efficient, despite the red-green axis being unable to
differentiate orange and purple, and the blue-yellow axis being
unable to differentiate between orange and yellow-green. More
recently, (Wool et al., 2015) performed a visual search task with a
target that was a subjectively defined “unique hue,” colors that lie
purely on one end of color opponent axes, among distractors that
were “complementary,” the color that occupies the opposite end of
an objectively defined color circle. They found no search advan-
tage for the unique hue, concluding that as a color that maximizes
the response of one axis had no search advantage over a color that
spreads its response over two axes, visual search for color must not
be using opponent processes.
The proposal that visual search for color is based on a limited
number of basic color terms stems from research motivated by the
idea of linguistic relativity, a theory that suggests that the way we
process and encode colors is influenced by the terms we use to
label color (Brown & Lenneberg, 1954). Specifically for visual
search, it suggests that visual search performance depends on the
color category one encodes the target and distractors with. This
idea has found some support in a visual search study by Yokoi and
Uchikawa (2005) who used a heterogeneous display of colors and
found that reaction time (RT) was correlated with the number of
distractors that shared a linguistic label with the target. Another
study that somewhat supports this idea is by Pilling and Davies
This article was published Online First June 20, 2016.
Garry Kong and David Alais, School of Psychology, The University of
Sydney; Erik Van der Burg, School of Psychology, The University of
Sydney and Department of Cognitive Psychology, Vrije Universiteit Am-
sterdam.
Correspondence concerning this article should be addressed to Garry
Kong, School of Psychology, The University of Sydney, Camperdown,
2006, Australia. E-mail: garry.kong@sydney.edu.au
This document is copyrighted by the American Psychological Association or one of its allied publishers.
This article is intended solely for the personal use of the individual user and is not to be disseminated broadly.
Journal of Experimental Psychology:
Human Perception and Performance
© 2016 American Psychological Association
2016, Vol. 42, No. 11, 1724–1738
0096-1523/16/$12.00 http://dx.doi.org/10.1037/xhp0000249
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... For instance, it is difficult to recognize a visual object in peripheral vision when surrounded by nearby clutter (i.e., visual crowding; see Whitney & Levi, 2011 for a review), and it is difficult to find a visual target in a cluttered environment (i.e., visual search; Wolfe, 1994). However, performance is only affected by clutter when the target and clutter have similar features, such as orientation, color, shape, luminance, motion, flicker (see, e.g., Bouma, 1970;Cass et al., 2011;Cass & Van der Burg, 2023;Duncan & Humphreys, 1989;Kong et al., 2016Kong et al., , 2017Kooi et al., 1994;Van der Burg et al., 2017. In contrast, if a single target feature differs from the clutter feature (e.g., being the only red item among green items), then it becomes easy to find such a salient item (Itti et al., 1998;Wolfe & Horowitz, 2004). ...
... Nevertheless, in our study the presence of clutter had no significant effect on the objective performance measures. The lack of a clutter effect was surprising since it is known from the literature that it is difficult to find or identify a visual target when it is surrounded by nearby similar distractor objects (Bouma, 1970;Cass et al., 2011;Cass & Van der Burg, 2023;Duncan & Humphreys, 1989;Kong et al., 2016Kong et al., , 2017Kooi et al., 1994;Rosenholtz et al., 2007;Van der Burg et al., 2017;Whitney & Levi, 2011). In our case, the clutter was similar to the target in terms of size, color, luminance, orientation and even shape and, the clutter made it even more difficult to track the moving target due to occlusion (see Figure 4). ...
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... Interestingly, the camouflage technique had a major impact on the detection rate as dynamically adapting the camouflage to its environment was more efficient than the adaptative static camouflage technique and the standard Dutch woodland camouflage suit. That the dynamic adaptive camouflage pattern resulted in the best performance is not surprising, as it is known from the visual search literature that a target is more difficult to find when it is very similar to its surrounding than when it is dissimilar to its surrounding [12,18,32]. ...
... Interestingly, Van der Burg and colleagues found compelling evidence that a motion transient did pop-out, but only when this transient resulted in a (temporarily) unique motion direction compared to the motion direction of the other moving objects (e.g., when all the other objects move in the opposite direction). What is most likely important for visual search and for camouflage efficiency, is that an object (like a static or dynamic soldier) stands out from its surrounding when at least a single feature is unique compared to its environment (and/or surrounding distractor elements) [17,32,33]. ...
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... p < .001, indicating that the detection rate decreases when search becomes more difficult 9,11,25 . ...
... First, the conspicuity experiment was relatively brief compared to the visual search experiment. One reason is that for a typical visual search study one needs approximately 20 trials per condition to estimate the search efficiency for each condition, as the search path can vary largely from one trial to another (especially when search is very inefficient, and a scan through the scene occurs serially, see e.g., 25,26 ). Moreover, the strong correlation that we observed between the two sessions in the conspicuity experiment suggests that the responses were very accurate, and indicates that a single session may already be sufficient to measure target conspicuity. ...
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... Some of this is due to the inability to use Becker's relational guidance when targets are not linearly separable from distractors, and some of the difficulty is due to added bottom-up (DD similarity) noise produced by the highly salient contrast between the two types of yellow and red distractors. Note, however, that attention can still be guided to the orange targets, showing that topdown guidance is not based entirely on a single relationship (for more, see Kong, Alais, & Van der Berg, 2016;Lindsey et al., 2010). Moreover, Buetti et al. (2020) have cast doubt on the whole idea of linear separability, arguing that performance in the inseparable case can be explained as a function of performance on each of the component simple feature searches. ...
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... Some of this is due to the inability to use Becker's relational guidance when targets are not linearly separable from distractors, and some of the difficulty is due to added bottom-up (DD similarity) noise produced by the highly salient contrast between the two types of yellow and red distractors. Note, however, that attention can still be guided to the orange targets, showing that topdown guidance is not based entirely on a single relationship (for more, see Kong, Alais, & Van der Berg, 2016;Lindsey et al., 2010). Moreover, Buetti et al. (2020) have cast doubt on the whole idea of linear separability, arguing that performance in the inseparable case can be explained as a function of performance on each of the component simple feature searches. ...
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View
... Interestingly, the camouflage technique had a major impact on the detection rate as dynamically adapting the camouflage to its environment was by far more efficient than the adaptative static camouflage technique and the standard Dutch woodland camouflage suit. That the dynamic adaptive camouflage pattern resulted in the best performance is not surprising, as it is known from the visual search literature that a target is more difficult to find when it is very similar to its surrounding than when it is dissimilar to its surrounding [34][35][36] . ...
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