https://www.elsevier.

com/journals/vision-research/0042-6989/guide-for-authors#39001




Visual Search: A Review



By
Carissa Alexa Romero



Date
04/21/2014











________________________
Carissa A. Romero
800 N State College Blvd
Fullerton, CA 92831
(786)234-9815
Carissa.romero@csu.fullerton.edu







Abstract
Of the five senses, sight is the most highly developed and perhaps the most important in humans.
More than 50% of the human brains cerebral cortex is dedicated to processing visual input
alone. In fact, vision supports many critical functions such as navigation. Interest in visual
science has dramatically increased throughout the years, prompting studies focusing on visual
search as a necessary and important tool. These studies deliver insight into the many topics that
can be studied using a visual search, such as decision-making and attention. They also explain
the strategies and mechanisms that the brain uses to facilitate a visual search, including
knowledge of a distractor and a target. The overall purpose of this review is to examine the
professional and everyday usefulness of visual searches and the mechanisms and strategies
behind them, such as saliency and attention. It is also suggested that future studies focus on how
a personality trait can impact visual search performance.
Keywords: senses, cerebral cortex, visual input, visual science, visual search









TITLE: Vision Search: A Review
PRINCIPAL INVESTIGATOR: Carissa Romero
INTRODUCTION AND BACKGROUND
The five senses have developed over time, enabling humans to interact favorably with
their surrounding environment (Lu & Dosher, 2013). Our interactions with the physical world
around us form our greatest memories and have a pronounced influence on ones self-concept
(Nassi & Callaway, 2009). Among the five senses, sight is considered to have the greatest impact
on our lives and is the most highly developed in humans (Lu & Dosher, 2013). However, visual
diseases, such as face blindness, challenge individuals and create medical and economic changes.
More than 2 million Americans over the age of 40 experience poor vision and approximately 1
million are legally blind (Leonard, 2001). The total economic impact of visual diseases exceeds
$50 billion dollars annually, illustrating the need to understand and study the unknown
mechanisms of the visual system (Leonard, 2001).
Visual searches are an integral part of the visual system and the way we perceive the
world (Nakayama & Martini, 2011). A visual search task is described as searching for a target
among distractors (Eckstein, 2011). Looking for someone in a crowd or a particular application
on your cell phone can be thought of as a visual search. A visual search can also be applied to
more vital tasks such as a radiologist searching for abnormalities in X-ray imagery or a scientist
searching for weather anomalies in GPS imagery (Eckstein, 2011). It is difficult to trace the
exact origins of the study of visual search, however Edward Bagnall Poulton (1890) is known as
one of the earliest researchers to formulate visual search theories. He was concerned with how
certain animals could successfully avoid being seen by implementing camouflage (Poulton,
1890).
Poultons (1890) early inquiries were followed by Hubel and Wiesel (1959; 1968), whose
work with the visual system of cats and monkeys earned them a Nobel Prize in 1981(Nakayama
& Martini, 2011). Hubel and Wiesel (1959; 1968) suggested that certain neurons respond to
certain colors, bars, and edges. Shortly after this discovery, other researchers (Campbell, Cooper,
& Enroth-Cugell, 1969) contested Hubel and Wiesels (1959; 1968) theory about cortical
neurons, indicating that neurons also code orientation and spatial frequency through Gabor
filters. It is now understood that features such as shape, texture, hue, movement, orientation, and
depth characterize our perception of the world (Livingstone & Hubel, 1988).
Although we may view these features as a unified whole, information is actually
processed through independent circuits whose roles are rather distinct (Livingstone & Hubel,
1988). Modality-specific channels that correspond to our senses guide sensory information
arriving from the environment to the brain (Nassi & Callaway, 2009). Collectively, a visual
search is made up of intricate processes that include eye movement, covert visual attention and
processing, temporal incorporation of information, and strategies to combat limitations
(Eckstein, 2011).
VISUAL SEARCH LIMITATIONS
Visual searches may be seemingly simple, however there are several factors that can pose
visual processing limitations. Exploring these limitations can enable us to uncover mechanisms
that optimize visual search. At any given moment, the amount of information accessible to the
visual system is greater than what we are capable of fully processing (Chisholm, Theeuwes &
Kingstone, 2010). At times we may miss targets or incorrectly choose a non-target due to non-
uniform processing across the visual field (Eckstein, 2011). Visual stimuli that fall in the foveal
area are processed with higher spatial resolution and distinguishability between an object and its
background than the stimuli that fall on the periphery (Eckstein, 2011). The further away a visual
stimulus is from the fovea or fixation point, the less accurate the processing, particularly if the
stimulus is presented with a short temporal duration (Eckstein, 2011).
Visual clutter, such as crowding, can also limit a visual search. Crowding the periphery
with other objects can cause fewer fixations towards the target (Eckstein, 2011). On the other
hand, environment variability can cause confusion between a distractor and a target (Eckstein,
2011). Due to visual clutter, it is imperative that viewers select the information that is most
relevant (Chisholm et al., 2010). Even though there are limitations to a visual search, our brain
can employ optimizing strategies guiding our advanced understanding of the visual environment.
VISUAL SEARCH STRATEGIES
Eckstein (2011) explains that saliency is one brain strategy that optimizes a visual search.
Salience refers to an item that stands out amongst other items in the same vicinity. Eckstein
(2011) suggested that angling ones eyes so that the foveae are directed at a salient image would
be beneficial (Eckstein, 2011). Fixations in a short display seem to be directed by salient images
more than non-salient images (Eckstein, 2011). The use of saliency as a strategy to combat
processing limitations resulted due to the brains incapability of processing information that is
displayed in a short period of time (Eckstein, 2011).
Prior knowledge can also facilitate a visual search (Chisholm et al., 2010). Search time
can be reduced if a preview picture of the target is shown. In a search, eye movement is directed
toward a target, but can also be directed towards non-target objects (distractors) that have similar
physical attributes to the target (Chisholm et al., 2010). Eye movements from one fixation to
another (saccades) are controlled by the detectability of a target in the periphery (Chisholm et al.,
2010).
Additionally, Chisholm et al. (2010) explains that probability of location and predictive
cues can enhance a visual search. Target detection performance is often improved when a target
either co-occurs with other elements (cues) or when the probability of a location containing the
target is high (Chisholm et al., 2010). Search time and accuracy are also improved with repeated
presentations relevant to the contextual cueing paradigm, which pertains to guidance in attention
(Chisholm et al., 2010). This guidance results from past experiences with a given visual scene
(Eckstein, 2011).
Eye movements are also typically guided to expected locations, especially in natural
scenes (Eckstein, 2011). For example, if you were looking for a boat you would first look
towards an area containing water rather than the sky or land. An organism intending to optimize
their visual search performance should be expected to use similar templates that mediate eye
movements and perceptual decision (Eckstein, 2011). While eye movements and perception are
linked, there are two distinct pathways in the brain that process any given visual information, the
ventral stream (perceptual decisions) and the dorsal stream (action) (Nassi & Callaway, 2009).
VISUAL SEARCH MODELS
Based on the recognized visual search knowledge, several models have been formulated
(Eckstein, 2011; Nakayama & Martini, 2011). Numerous models focus on covert attention,
which is the processing of a visual scene without having to change the point of fixation
(Eckstein, 2011; Nakayama & Martini, 2011). The process of studying covert attention involves
implanting a target amongst varying distractors and measuring the reaction time or accuracy of
finding the target (Eckstein, 2011). One covert attention model is the serial covert attention
model, which involves the random processing of one item at a time, suggesting that the greater
the amount of items the greater the overall reaction time (Eckstein, 2011).
Treisman and Gelade (1980) established a covert attention model known as the Feature
Integration Theory (FIT), consisting of two stages (preattentive and attentive). A preattentive
stage segments the visual field and holds information briefly, while an attentive stage processes
information in more detail (Treisman & Gelade, 1980). If a green circle were amongst a field of
red circles it would pop out because it is the only point of activity (Treisman & Gelade, 1980).
Pop out occurs in a visual search when reaction time remains constant, regardless of how many
distractors are present (Nakayama & Martini, 2011).
VISUAL SEARCH INTO THE FUTURE
While many studies have examined the factors influencing visual search performance,
how a personality trait may affect a visual search task has not been investigated. Future studies
can seek the potential relationship between a personality trait, such as competitiveness, and
improvement in reaction time in a visual search task. Future studies could utilize a questionnaire
to measure competitiveness and employ a common visual search stimulus to measure effects.
Any insight into the mechanisms that effect our perception of a visual environment are useful to
the visual science field since there are still several unknowns. If a relationship is found between
competitiveness and visual search, the results may be applied to certain careers such as airport
security or military snipers. When it is your job to actively search for a target amongst several
distractors it is relevant to know whether or not your personality is affecting your performance.
Although our understanding of the visual system has come a long way there is still additional
research to be done in the future.
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