Current Visual Pathway Research

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Current visual scanpath research: a review of investigations into the

psychotic, anxiety, and mood disorders

Wei Lin Toha,b,, Susan L. Rossella,b,c, David J. Castlea,d

aDepartments of Behavioural Science and Psychiatry, The University of Melbourne, Melbourne, VIC, Australiab

Cognitive Neuropsychology Laboratory, Monash Alfred Psychiatry Research Centre, School of Psychology and Psychiatry, Faculty of Medicine,

Nursing, and Health Sciences, Monash University, Melbourne, VIC, AustraliacBrain Sciences Institute, Swinburne University of Technology, Melbourne, VIC, Australia

dDepartment of Psychiatry, St Vincent's Mental Health, Melbourne, VIC, Australia

Abstract

The human visual system is comprised of an array of complex organs, which jointly decode information from visible light to construct a

meaningful representation of the surrounding environment. The study of visual scanpaths transpired in a bid to enhance our understanding of

the role of eye movements underpinning adaptive functioning as well as psychopathology and was further aided by the advent of modern eye-

tracking techniques. This review provides a background to the nature of visual scanpaths, followed by an overview and critique of eye

movement studies in specific clinical populations involving the psychotic, anxiety, and mood disorders, and concludes with suggested

directions for future research. We performed a Medline and PsycInfo literature search, based on variations of the terms visual scanpath,

eye-tracking,and eye movements,in relation to articles published from 1986 to the present. Eye-tracking studies in schizophrenia mostly

concurred with the existence of a restricted scanning strategy, characterized by fewer number of fixations of increased durations, with

shorter scanpath lengths, and a marked avoidance of salient features, especially in relation to facial emotion perception. This has been

interpreted as likely reflecting dual impairments in configural processing as well as gestalt perception. Findings from the anxiety and mood

disorders have conversely failed to yield coherent results, with further research warranted to provide corroborating evidence and overcome

identified methodological limitations. Future studies should also look toward applying similar techniques to related disorders as well as

conducting parallel neuroimaging investigations to elucidate potential neurobiological correlates. 2010 Elsevier Inc. All rights reserved.

For the eye altering, alters all.- William Blake, 1757-1827.

The eye bestows the gift of sight, allowing us to make

sense of and navigate through our world. Though

positioned at the gateway to the human visual system, it

forms but one of an array of complex organs, including the

optic nerves and chiasm, lateral geniculate nucleus, and

visual cortex, which jointly decode information fromvisible light to construct a meaningful representation of

the surrounding environment. Accordingly, we are able to

perform intricate tasks, such as ident ifying objects,

perceiving color, and estimating distances, all crucial to

our everyday functioning. Despite these concrete opera-

tions, it is most often the psychological manifestation of

visual information, or visual perception, which is key in

shaping our behaviors and cognition. This review is aimed

at providing a background to the nature of visual scanpaths,

with key consideration to the special case of face

perception, followed by an overview and critique of eye

movement studies in healthy and specific clinical popula-tions involving the psychotic, anxiety, and mood disorders.

We conclude with suggested directions for future research.

1. Physiology of eye movements

The act of seeing is initiated when light enters the cornea

at the front window of the eye and passes through the pupil,

which either contracts or dilates, thereby controlling the

Available online at www.sciencedirect.com

Comprehensive Psychiatry xx (2011) xxx xxxwww.elsevier.com/locate/comppsych

Corresponding author at: Monash Alfred Psychiatry Research Centre,

Prahran VIC 3004, Australia. Tel.: +61 3 9076 8650.

E-mail address:[email protected](W.L. Toh).

0010-440X/$ see front matter 2010 Elsevier Inc. All rights reserved.

doi:10.1016/j.comppsych.2010.12.005
http://dx.doi.org/10.1016/j.comppsych.2010.12.005http://dx.doi.org/10.1016/j.comppsych.2010.12.005http://dx.doi.org/10.1016/j.comppsych.2010.12.005mailto:[email protected]://dx.doi.org/10.1016/j.comppsych.2010.12.005http://dx.doi.org/10.1016/j.comppsych.2010.12.005mailto:[email protected]://dx.doi.org/10.1016/j.comppsych.2010.12.005http://dx.doi.org/10.1016/j.comppsych.2010.12.005http://dx.doi.org/10.1016/j.comppsych.2010.12.005


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amount of light reaching the sensitive foveal membrane

located at the center of the retina[1]. This produces a series

of neural impulses, firing along the optic nerves, to be

ultimately managed in a hierarchical fashion by various parts

of the visual system located in the brain. As the fovea forms

the focus point of the eye, it yields enhanced image

resolution, allowing it to distinguish much more color and

visual detail, whereas the rest of the retina mainly comprises

basic light detectors that act to facilitate efficient peripheral

vision. Therefore, to process a visual scene in its entirety,

voluntary shifts of the eye have to take place to acquire,

fixate, and track the stimulus. By rotating the eye in the

horizontal and vertical planes, different points of interest

may be visually processed. These eye rotations are quantified

in terms of degrees of visual angle, with several successive

rotations required for a complete scan of the visual scene.

Depending on whether the visual stimulus is in motion or

stationary, research has focused on investigating 2 respective

classes of eye movements, namely, smooth pursuit vs

saccades, the latter of which forms the sole interest of thecurrent review.

1.1. The visual scanpath

Early proponents devised the notion of the visual

scanpath in an attempt to provide an integrated account of

how the human visual system was engaged in the formation

of internal memory links that facilitated the processes of

learning and recognition. Accordingly, Hochberg [2]

introduced the idea of a schematic map, representing the

synthesis of sensory information, afforded by successive

foveal glimpses, into an overall percept. This was laterexpanded upon by Noton and Stark [3] in their scanpath

hypothesis, which proposed pattern recognition as a serial

process involving the uptake of sensory details via a fixed

order sequence of eye movements during initial stimulus

detection as well as subsequent reidentification. In this way,

fixed and characteristic scanpaths permitted each individual

feature of the stimulus to be processed visually and laid

down as a corresponding memory trace. The internal

representation of the stimulus was thus thought to be made

up of an alternating progression of sensory and memory

traces accompanied by parallel motor shifts, forming what

was termed afeature ring. Consequently, the reproduction of

successive eye movements in a replica of the originalscanpath promoted verification of ensuing feature memories,

thereby indicating successful pattern recognition.

Therefore, the visual scanpath may be seen as a map that

traces the direction and extent of eye movements during

viewing of a complex visual stimulus and comprises a

sequence of fixations and saccades [4]. Fixations may be

defined as consecutive gaze points within 1 of the visual

field held with a duration of at least 200 milliseconds,

though specific criteria may vary. These represent points of

attention, where the fovea is directed and held stationary

over a specific position on a visual scene, during which

stimulus input is processed in detail. In contrast, saccades

denote rapid voluntary movements between fixations, which

shift the fovea from one particular point of interest to

another. During this time, parallel cognitive processes use

parafoveal and peripheral retinal information to establish the

location of the next fixation[5]. Moreover, external features

of the stimulus, in conjunction with the operation of inner

schematic beliefs, also influence and shape the overall

scanpath pattern[6]. Fixation attention is thus dictated by a

combination of broader top-down cognitive factors, such as

expectations, goals, and memory, to name a few, as well as

specific bottom-up processes, involving visual sensory

input. However, as coarse discrimination occurs rapidly,

whereas the perception of finer details are governed by

later-stage processes of selective attention, the visual

scanpath is largely held as a marker of controlled attention

and reappraisal, rather than an automatic uptake of sensory

information [7]. In other words, visual scanning may be

characterized more as a top-down process regulated by

higher order cognition.

1.2. What is video-oculography?

Historically, insights into visual scanning arose from

direct observation. With the advent of modern eye-tracking

procedures, eye movements can be accurately recorded in a

number of ways. The most popular approach is video-

oculography, involving monocular monitoring of the gaze

direction via infrared light reflecting off the dominant cornea

and pupil [1]. Reflections from these 2 points permit

determination of the spatial position of the eye gaze, which

is recorded by miniature video cameras in terms of an x

-y

coordinate system. The development of novel techniques for

direct detection of the fovea with improved accuracy is also

underway [8]. The main advantages of video-oculography

are its noninvasiveness, robustness, compatibility with a

range of participants, and comprehensive data yield. Recent

technological advances have further enhanced data sampling

rates and gaze resolution, thereby addressing past key

criticisms of this method. Two classes of scanpath

characteristics are typically sampled, namely, spatial and

temporal parameters. At this point, a list of common

scanpath parameters is provided to orientate the reader to a

discussion of significant eye-tracking studies presented in

the following sections. Accordingly, scanpath length refersto the summed distances traveled by the eye during scanning

and is typically measured in degrees of visual angle. It has

also variously been labeled eye scanning length or saccade

amplitude. The number of fixations may intuitively be

defined as the frequency of stationary gaze points acquired

during scanning, whereas fixation durations represent the

time period of these fixations, usually denoted in milli-

seconds. The product of the number of fixations and related

durations thus yields total dwell time. Of late, researchers in

the field have also derived a series of spatial-temporal

indices, for instance, denoting the ratio of fixations to salient

2 W.L. Toh et al. / Comprehensive Psychiatry xx (2011) xxxxxx


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stimulus features, thereby facilitating a more comprehensive

analysis of scanpath data. In this way, eye movement

recordings are believed to provide an objective, online

psychophysiological indicator of sensory processing and

visuospatial cognition.

1.3. The special case of face perception

There is no doubt that faces constitute a psychologically

unique category of stimuli, with a special significance in

our everyday lives, ranging from conveying information

about the emotional states of significant others [9] to acting

as a potential source of knowledge for our attributions[10].

In fact, early studies have long established that we

recognize human faces with greater ease and accuracy,

compared with other forms of pictorial representation, such

as aeroplanes [11] or canine faces [12]. Models of face

processing have likewise posited a discrete pathway for the

treatment of facial stimuli. For instance, Walker-Smith et al

[13]elaborated on the scanpath hypothesis by proposing analternative feature network, involving the initial registration

of an overall face percept, followed by targeted foveal

interest to pertinent regions so as to insert the details of

salient features into a general face framework. Similarly,

Bruce and Young [14] postulated the involvement of

several separable functional components in face processing,

involving structural encoding, recognition of individuality,

and affect analysis, to name a few.

Although a review of contemporary theories of face

processing is not within the scope of the current review, it is

important to note that there are several robust lines of

evidence corroborating the special case of face perception,namely: (i) the ontogeny of face processing, stemming from

research demonstrating innate face preference and categori-

zation abilities in newborn infants [15]; (ii) the clinical

condition of prosopagnosia, characterized by an exclusive

impairment in face recognition[16]; (iii) the face inversion

effect, describing a significant disruption of recognition for

inverted relative to upright faces[17]; and (iv) neuroimaging

studies, pinpointing specialized brain structures, such as the

fusiform face area, as selectively engaged in face perception

[18]. Accordingly, it may be suggested that humans adopt

global or holistic strategies for scanning faces, simulta-

neously perceiving facial features in parallel[19]. Moreover,

configural representation, or the interrelations amonginternal facial features, is crucial in the formation of a

meaningful global structure [20]. In other words, the

perceptibility of faces is profoundly enhanced when salient

features are aligned into a well-defined overall form or

gestalt [21]. In fact, the gestalt theory of visual perception

elucidates how humans perceive individual components of

complex visual stimuli, such as faces, as an organized whole.

At this point, it is sufficient to note that gestalt perception lies

in contrast to sequential processing, where disparate

elements of visual stimuli are processed in a serial, piecemeal

manner (for a full review of gestalt principles, see Bruce et al

[22]). The significance of facial gestalts will be further

discussed in later sections.

2. Visual scanpath research in nonclinical and

clinical populations

The present review was accomplished based on a Medline

and PsycInfo literature search, using the terms visual

scanpath, visual scanning, visual scan, eye-tracking,

and eye movements, with a follow-up of relevant

literature. Eye-tracking studies among a wide range of

clinical conditions, such as developmental [23] and

neurologic [24] disorders, were uncovered. To ensure

direction and definition, we confined ourselves to the

psychotic, anxiety, and mood disorders, with a particular

focus on articles published from 1986 to the present. This is

because articles before this time were greatly hampered by

existing technology limitations. To set the foundation for a

review of visual scanpath research in clinical populations,we will first discuss how explorations of eye movement

patterns in healthy individuals have contributed to our

knowledge of visual scanning. When perceiving a visual

image, typical eye movement parameters vary as a function

of the nature of the scene as well as actual task demands, for

example, categorization vs memory or recognition. In

general, most fixations will settle upon informative parts

of the scene, with the mean fixation duration and saccade

amplitude respectively tending toward 300 milliseconds and

4to5 [25]. The gist of a scene, however, is extracted almost

instantaneously and can take as little as 40 milliseconds. The

details derived are then used to orientate subsequent fixationsto appropriate points of interest, where further visual

information is acquired.

Owing to its ecologic validity and significance in day-to-

day human interactions, research has examined eye move-

ments in face processing, establishing a typical inverted

triangular pattern of scanning for neutral faces, with most

fixations being focused on salient facial features, notably the

eyes, but also the nose and mouth[13]. More recently, the

focus has turned to detecting differences in recognition

across a range of facial expressions, producing mixed

findings. Accordingly, Green et al [26] described an

extended scanning strategy, comprising increased fixations

of longer durations to salient facial features, along withlonger saccadic distances, but only in response to angry and

fearful emotions. These authors identified a vigilant

scanning strategy reflective of an evolutionary bias in the

appraisal of threat stimuli within a social context. In a

follow-up study, it was observed that schizotypy, or

delusion-proneness, was characterized by reduced number

of fixations to these negatively valenced emotions, likely

suggestive of a hypersensitive avoidance of threat [27].

Another study examining eye movements in schizotypy

uncovered a specific fear recognition deficit that was

believed to be unrelated to anomalies in oculomotor function

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or sustained visual attention[28]. In contrast, Hunt et al[29]

failed to uncover any selective orientation toward angry or

happy faces, whereas Calvo et al[30]reported an advantage

for disgusted, happy, and surprised expressions relative to

angry, fearful, and sad expressions, as shown by earlier

localizations, more efficient detection, and greater response

accuracies. Follow-up research attributed this search advan-

tage to the contribution of affective content and featural

uniqueness[31]. In related research, Bate et al[32]identified

a facilitatory interaction between facial familiarity and

emotion processing; happy expressions promoted the

processing of famous faces, and angry expressions promoted

the processing of novel faces.

Other research examining changes in visual scanning

across the lifespan has noted an age-related decline in

emotion recognition, especially for angry and fearful

expressions [33,34]. Older adults exhibited fewer overall

fixations, which were disproportionately focused on the

lower parts of the face, especially the mouth. These authors

theorized that typical frontal lobe atrophy associated withnormal aging may underlie these scanning styles. In a

separate study investigating sex differences, males were

found to adopt an increased gaze orientation to the nose and

mouth relative to females[35]. Both sexes were nevertheless

equally accurate in identifying facial emotions, though

females exhibited faster reaction times. Taken together,

these studies suggest that eye movements during face

processing in healthy individuals vary as a function of a

range of factors, including age, sex, or specific personality

traits, with negatively valenced emotions perhaps eliciting

more atypical scanning patterns. We will now turn to the

visual scanpath literature in relation to specific classes ofpsychiatric conditions.

2.1. The psychotic disorders

Most visual scanpath research in clinical populations has

focused on the psychotic disorders, especially schizophre-

nia. This disorder has a heterogeneous presentation and may

be classed into various subtypes, but is typically character-

ized by abnormalities in the perception and representation

of reality[36]. Its primary symptoms are bizarre or paranoid

delusions, auditory hallucinations, or grossly disorganized

speech or behavioral patterns, which cause clinically

significant distress and socio-occupational dysfunction. To

date, studies examining eye movements in schizophrenia

have generated fairly consistent findings involving gener-

alized visual scanning deficits. The following sections

provide an overview of this work, organized along a

number of themes, followed by key interpretations and

concluding remarks.

2.1.1. Early visual scanpath studies

A brief outline of early visual scanpath research is

provided, as these studies ignited interest in eye-tracking

investigations in schizophrenia and paved the way for future

inquiries. However, in light of the modern technological

advances in eye tracking, this early literature should be read

with caution. A preliminary study sought to compare the

scanpaths of partially remitted outpatients with schizophre-

nia to healthy controls using light fixation and visual letter

search tasks[37]. Though the schizophrenia group tended to

do worse, these results were not statistically significant, with

the exception of males with chronic unremitting schizophre-

nia who exhibited poor eye-tracking performances. Anom-

alously, patients with catatonic schizophrenia performed

better relative to healthy controls, whereas eye movement

parameters and clinical variables remained largely uncorre-

lated. In follow-up research, the same authors presented a

series of pictures depicting social scenes under free-viewing

conditions. Similarly, there were no observed differences in

fixation or saccade parameters across both populations. Two

discrete styles of visual scanningextensive vs mini-

malwere nevertheless identified and respectively related

to positive and negative schizophrenia symptoms [38].

Another early study also investigated eye movements in

chronic schizophrenia; findings included reduced number offixations of increased durations, amid a limited movement

range in response to a single picture display, as well as

significantly poorer performances during comparisons of a

series of geometric figures [39].

2.1.2. Faces and social scenes

Prominent disturbances in interpersonal communication

and social functioning serve as hallmark features in

schizophrenia. Given the importance of face perception

in social interactions, research exploring various aspects of

face processing in the disorder has uncovered a range of

pervasive deficits, involving judgments of facial attributes,familiarity and identity[40,41], and, most notably, emotion

recognition [42-44]. As a result, numerous studies have

analyzed visual scanpaths in response to facial emotions so

as to gain a better understanding of the nature of these

difficulties. With minor modifications, the basic method-

ology has relied on the presentation of a series of facial

images under free-viewing conditions. The expressions

portrayed were typically the entire range, or a subset, of

the 6 universal human emotions (ie, angry, disgusted,

fearful, happy, sad, and surprised), with a neutral face

serving as the control condition. Initial studies, however,

either relied solely on neutral faces [45-47] or failed to

analyze potential group differences in scanpath parametersacross discrete facial emotions [48-50]. However, on the

whole, virtually all studies have converged on the existence

of a restrictedscanning strategy adopted by schizophrenia

patients, characterized by fewer fixations of increased

durations, with shorter scanpath lengths, and a marked

avoidance of salient facial features, regardless of emotion

valence[45-47,51-53].

Based on a variant of the standard paradigm, Williams

et al [47] displayed nondegraded and degraded neutral

faces, followed by a recognition task with dual levels of

complexity. Relative to healthy controls, schizophrenia



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patients exhibited scanpath disturbances that were most

marked for nondegraded faces, with reduced recognition

accuracies for the more difficult task condition. In follow-

up research, Loughland et al [52,53] administered an

added affect recognition task, using faces depicting happy,

neutral, and sad emotions. In the context of overall

restricted scanpaths, the eye movements of schizophrenia

patients were notably impoverished for happy faces, yet

with superior recognition accuracy, but conversely some-

what normalized in terms of increased attentional focus to

salient facial features for sad faces. These observations

were respectively interpreted in view of past research

documenting an emphasis on holistic processing for happy

faces[54]as well as an undue bias toward negative stimuli

in psychosis [55]. Using an inclusive range of facial

emotions, Bestelmeyer et al [51]suggested that the pattern

of spatial scanning characteristics observed may serve as a

unique biomarker, effectively distinguishing schizophrenia

from other disorders. In a similar vein, Nishiura et al [56]

examined the spatial distribution of gaze points and totalscanpath lengths during the presentation of smiling vs

crying baby faces and reported that schizophrenia patients

showed significant eye movement disturbances, which

were especially prominent in the left visual field for

smiling baby faces.

In contrast, other studies have focused on temporal

scanning parameters in an attempt to elucidate early vs later-

stage face processing. In this regard, schizophrenia patients

were found to exhibit reduced number of fixations of shorter

durations in relation to neutral faces, which were most

marked during the first 3 seconds directly following stimulus

presentation[45]. According to Rosse et al[48],preattentive

fixations may be defined as those less than or equal to 50.1

milliseconds and are believed to implicate configural

processing in an automatic manner due to their brevity of

operation. This is in contrast to serial search processes,

which necessitate longer scrutiny times to aid the sequential

perception of individual features. Using affect recognition

and gaze discrimination tasks, Rosse et al [48] thus

uncovered that schizophrenia patients displayed significantly

decreased preattentive fixations, which inversely correlated

with their clinical symptoms. In follow-up research involv-

ing the presentation of upright and inverted faces, it was

shown that the former drew significantly more preattentive

saccades from healthy controls, whereas the eye movementsof schizophrenia patients did not differ between orientations

[49]. In light of these findings, it was suggested that deficient

scanning strategies in schizophrenia are likely to reflect an

overreliance on sequential processing as a result of impaired

gestalt perception[48,49]. Individuals with the disorder are

not only believed to have difficulties forming an initial

facepercept but also fail in the global integration of stimuli

into a meaningful gestalt. In other words, they perceive faces

in a fragmented, serial manner, such that extraneous areas are

treated as equally critical as salient feature regions. Further

impairments in configural processing are also likely (eg,

Joshua and Rosell [57]), given an absence of the face

inversion effect.

To further enhance ecologic validity, a related area of

research has used social scenes. Using a sketch of a mother

with her child, Nieman et al [58]found that schizophrenia

patients tended to fixate more on both faces relative to

healthy controls, resulting in poorer performance in an

associated working memory task based on external features

of the drawing. More recently, Green et al [59] asked

participants to perform a mental state inference task during

the presentation of image pairs depicting target characters in

emotion-congruent social contexts vs those with limited

situational cues. Relative to healthy controls, schizophrenia

patients displayed longer fixation durations in context-

embedded situations, reduced saccadic activity in context-

free situations, as well as a larger proportion of total dwell

time viewing faces in both conditions. This failure to

perform rapid scanning and uptake of social contextual

information was further correlated with significant impair-

ments during mental state assessments. The findinginvolving augmented facial focus in social scenes is not

incongruent with the avoidance of salient facial features

documented in research using faces only. In particular, it

remains unclear whether this increased facial fixation

during social scene scans was directed at salient or

nonsalient facial regions. Therefore, though opposing

viewing strategies for faces and social scenes may osten-

sibly exist in schizophrenia, a more inclusive interpretation

points toward a restricted scanning strategy, encompassing a

local viewing bias. This interpretation was further supported

by de Wilde et al [60], who reported that schizophrenia

patients exhibited shorter scanpath lengths and increasedstaring behaviors, especially directed toward localized

details, based on social scenes depicted in Thematic

Apperception Test cards. In this sense, a greater focus on

the nonsalient features of faces and other visual stimuli in

social scenes at the expense of pertinent contiguous

information likely contributes toward misinterpretations of

real-life social interactions.

2.1.3. Geometric figures, objects, and line drawings

There has been a great deal of visual scanpath research in

schizophrenia that has used geometric figures. In particular, a

group of Japanese researchers has published a large series of

studies stemming from the late 1980s to the present based ona standardized experimental paradigm (see Akiyama et al

[61]for a review). In sum, this involved a brief presentation

of a unique S-shaped target figure, which participants were

asked to subsequently reproduce from memory. Two slightly

dissimilar figures were next displayed for comparison with

the original target, followed by a repetition of the drawing

memory task. A responsive search score (RSS) was

calculated as a function of the number of sections of the

figures fixated upon. This task was also administered to a

range of clinical populations with temporal lobe epilepsy

[62], frontal lobe lesions [63], and anxiety and/or mood



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disorders[64], to name a few. When schizophrenia patients

in acute, chronic, and remitted states were assessed[65-67],

it was concluded that the entire schizophrenia group

consistently exhibited the lowest RSS, with chronic patients

further displaying a significantly decreased mean eye

scanning length. It was thus suggested that these eye

movement parameters could potentially serve as a nosolog-

ically specific indicator for the disorder. Discriminant

analysis revealed that individuals with schizophrenia could

be differentiated from those without, with a sensitivity and

specificity of 76.7% and 81.4%, respectively [68]. This

methodology has since been replicated across global World

Health Organization collaborative research sites[69], most

recently with the aid of a digital computerized system to

handle extensive data loads[70].

Other researchers have also used a variety of diagrams,

including the Wechsler Adult Intelligence Scale picture

completion task[71], Rey-Osterrieth Complex Figure[46],

smiley faces and scene drawings[72], Rorschach inkblots

[58,73], Benton Visual Retention Test [74], natural land-scapes and fractal patterns [51,75], as well as static linear

segments [76]. It was generally found that schizophrenia

patients exhibited the predicted restricted viewing strategy

relative to healthy controls. There were, however, a few

exceptions, with Manor et al [46] and Cocchi et al [76]

reporting comparable fixation dynamics across schizophre-

nia and healthy control groups. On the whole, the evidence

seems to denote the existence of visuospatial working

memory deficits in schizophrenia, superimposed upon a

faulty oculomotor processing system.

2.1.4. Trait vs state markers

A recurring argument relates to whether deficits in visual

scanning in schizophrenia would more accurately serve as a

trait or state marker. The evidence concerning this dispute

tends to be mixed and primarily derives from 2 sources,

namely, longitudinal and family studies. Accordingly, a line

of research has tracked the stability of scanpath deficits over

the longitudinal course of the disorder by monitoring

schizophrenia patients across acute, chronic, and remitted

states. Several researchers observed that scanpath anomalies

tended to be transient, with relative normalization of eye

movement patterns following improvements in clinical

symptoms [38,77,78]. Other studies have conversely

reported these deficits as not only persisting over time butalso being largely unrelated to changes in psychopathology

and medication status[50,67]. More recently, Kallimani et al

[79] studied the effect of change in clinical status on eye

movement dysfunction using a wide range of oculomotor

tasks and deduced that saccadic parameters were stable at

both individual and group levels, whereas fixation dynamics

tended to be more state dependent. In a separate attempt to

resolve this conflict, other studies have explored the

existence of comparable scanning difficulties in first-degree

relatives of schizophrenia probands. In support of the trait

hypothesis, Loughland et al [80] suggested that relatives

exhibited an attenuated form of the typical restricted

scanning strategy, compounded by a distinct pattern of

increased staring toward happy expressions as well as an

extreme avoidance of salient facial features, especially for

sad expressions (the latter of which was even more marked

than in schizophrenia patients). Several authors have equally

proposed that eye movement dysfunction may serve as an

endophenotype for schizophrenia, corroborating its use as a

specific biological trait marker[81,82]. In contrast, de Wilde

et al [60] reported that unaffected siblings of probands did

not differ from healthy controls on scanpath variables to

Thematic Apperception Test cards, thereby creating concern

about using eye movement parameters as a potential

vulnerability marker. On the whole, support for the trait

hypothesis appears marginally stronger, but further research

elucidating the unique contributions of specific spatial and

temporal scanpath parameters is crucial to clarify the trait vs

state debate.

2.1.5. Symptoms and syndromesTraditional theories of schizophrenia have proposed

diverse classification schemes, ranging from Schneiderian

first-rank symptoms [83] to positive symptoms (eg,

delusions, hallucinations, or thought disorder) vs negative

symptoms (eg, blunted affect, alogia, or anhedonia) [84]

as well as Liddle's [85] 3-factor model, comprising the

dimensions of psychomotor poverty, disorganization, and

reality distortion. Some researchers have thus assumed

investigations from the perspective of uncovering correla-

tions between scanpath aberrations and specific symptom

or syndrome factors. An initial study proposed a rather

simplistic theory relating extensive and restricted scanningstyles to positive and negative symptoms respectively

[38]. Though later research has reported minimal relations

between eye movement parameters and symptom com-

plexes[47,53], associations between staring behaviors and

negative symptoms have been found [56,64,66,73]. For

example, Streit et al [50] detected narrow and constrained

staring behaviors in line with signs of affective flattening.

In addition, Obayashi et al [67] described a correlation

between mean eye scanning length and negative symp-

toms, which was further suggested as a possible

sensitivity index for chronicity. In terms of Liddle's [85]

model, Loughland et al [53] found that psychomotor

poverty was associated with decreased fixations of shorterdurations for happy faces, whereas disorganization was

similarly associated with reduced foveal attention, but

extended raw scanpath lengths for happy faces. However,

the sparse and random nature of these observations has

precluded meaningful interpretations; systematic investiga-

tions into the area are necessary to elucidate further

significant relationships.

2.1.6. The special role of delusions

Delusionshave typically been seen as a central feature of

schizophrenia and may be defined as erroneous beliefs,



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involving a misinterpretation of reality, routinely sustained

with high levels of conviction, despite clear evidence to the

contrary [36]. Several researchers have thus proposed

exploring information processing biases possibly underlying

delusions using visual scanpaths [86-88]. An initial com-

parison of eye movements among deluded and nondeluded

schizophrenia patients and healthy controls used single and

paired facial stimuli [77,78]. Relative to other groups, the

deluded patients used a staring strategy, with decreased

fixations of longer durations directed disproportionately at

nonsalient feature areas, despite similar recognition accura-

cies. Subsequent symptom improvement, however, initiated

relative normalization of viewing strategies during follow-up

assessment. Expanding upon their research protocol, the

same authors presented neutral, ambiguous, or overtly

threatening social scenes to schizophrenia patients bearing

either persecutory or nonpersecutory delusions[89]. Relative

to other groups, the schizophrenia patients with persecutory

delusions exhibited an atypical scanning pattern only for

ambiguous scenes, with significantly increased viewingtimes for nonthreatening foreground areas. Inappropriate

threat appraisal within a social context was hence theorized

as linked to the presence of persecutory delusions. In a later

study, Green et al[90]administered a standard facial affect

paradigm to deluded and nondeluded schizophrenia patients,

with the former demonstrating respectively increased and

decreased fixations to happy and fearful emotions. This

occurred in the context of an overall restricted scanning

strategy to negatively valenced emotions across both

schizophrenia groups, suggestive of a vigilance-avoidance

style of attention operating across early and later stages of

information processing.

2.1.7. Implications and conclusions

Thus far, research examining visual scanpaths in

schizophrenia has revealed fairly consistent findings,

indicative of generalized scanning deficits of a restricted

nature, characterized by fewer fixations of increased

durations, with shorter scanpath lengths, and a marked

avoidance of salient features across a range of visual stimuli.

This has been interpreted as likely reflecting dual impair-

ments in configural processing as well as gestalt perception

[48,49,57]. However, methodological limitations of existing

studies remain to be addressed. As mentioned, early studies

were confined by the technical restrictions of the time,meaning their measurement methods and data accuracy are

debatable (eg, [37-39]. Though this has largely been

remedied by current advances in eye-tracking technology,

some later studies have been fraught with other forms of

inconsistencies. First, the quality of visual stimuli used has

varied. Two superior examples include images of facial

emotion from Ekman and Friesen[91]as well as Mazurski

and Bond[92], though the sharper definition offered by the

former perhaps surpasses the realistic colors of the latter.

Second, inadequate participant matching was common, for

instance, with Rosse et al [48] using cocaine use disorder

patients as control participants. These disparities have made

it difficult to perform comparisons across studies, or derive

firm overall conclusions.

Another source of discrepancy relates to the medication

status of patients. Most studies have suggested that

antipsychotic medications have minimal impact on eye

movements[38,50,93], but de Wilde et al [60]has asserted

that typical antipsychotic chlorpromazine may ameliorate

scanning deficits. Only a single study to date has explicitly

investigated the effects of atypical (risperidone) vs typical

(haloperidol) antipsychotic medication on facial affect

recognition in schizophrenia [94]. Notably, risperidone-

treated patients displayed a relatively normalized pattern of

foveal attention to the salient facial features of happy and

neutral expressions, along with a concomitant recognition

accuracy comparable to healthy controls. However, caution

must be applied in interpreting these findings, because

comparisons between these 2 drugs are fraught with potential

complications. In particular, haloperidol is known for its

extrapyramidal adverse effects, which could include directvision disturbances (eg, pupil dilation, blurred or double

vision), movement problems (eg, ataxia, tardive dyskinesia)

as well as general concentration and memory difficulties

[95], all of which would clearly exert a considerable

detrimental impact on scanning performance. Future research

should therefore focus on examining the latent effects of

atypical antipsychotics on eye-tracking function, with special

notice to the length and dosage of administration as well as

possible side effect profiles.

On a more positive note, the involvement of schizophre-

nia patients across differing illness stages, ranging from

those experiencing a recent onset[58,75]to acute, chronic,and remitted populations [66], as well as other forms of

psychoses, including those induced by methamphetamine

[96,97] or cannabis [75] is encouraging. This is advanta-

geous because gathering eye-tracking statistics over the

course of various psychotic disorders will allow tracking of

fluctuations in eye movement dysfunction. Such progress

has been augmented by neuroimaging studies [98,99],

facilitating the identification of significant neurobiological

correlates. The extensive array of tasks, in conjunction with

neuropsychological assessments, have further corroborated a

cognitive profile for schizophrenia, represented by signifi-

cant frontal lobe dysfunction, alongside visuospatial work-

ing memory deficits [63,71,73]. Moreover, eye movementresearch in schizophrenia does carry direct therapeutic

implications, in terms of the remediation of faulty facial

emotion perception, with attendant benefits for the day-to-

day social living of affected individuals. To this end, several

training packages, to be delivered with the aid of eye-

tracking technology, have been offered [100-102]. In

particular, the Micro-Expression Training Tool developed

by Russell et al[101]fostered a more adaptive face-viewing

strategy in terms of increased fixations and dwell times

within salient feature regions as well as associated improve-

ments in emotion recognition. In the future, the utility of



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these techniques may be enhanced via integration with other

key therapeutic elements within a comprehensive cognitive

remediation program.

2.2. The anxiety disorders

A small number of studies have sought to examine

potential eye movement dysfunction in anxious individuals.When persons with varying levels of trait anxiety were

exposed to angry and happy faces, all participants initially

oriented their gaze more toward angry faces, but only

persons with high trait anxiety exhibited ensuing avoidance

behaviors[103]. Using positive, neutral, and threat images,

another study conversely showed that participants with high

trait anxiety did display early preferential attention for

affective stimuli, but also experienced difficulties in

subsequent disengagement, as evidenced by increased

fixation times[104]. In a separate investigation, Calvo and

Avero[105]found that high trait anxiety had a facilitatory

effect on the reading of posttarget words conveying a

congruent threat event, but a converse inhibitory effect whenan incongruent threat event was being described. This was

interpreted as indicative of a controlled selective bias toward

threat prediction in individuals with elevated levels of trait

anxiety. There has also been preliminary research exploring

visual scanpaths in certain anxiety disorders, including

phobias, obsessive-compulsive disorder (OCD), posttrau-

matic stress disorder (PTSD), and generalized anxiety

disorder (GAD), each of which is reviewed, in turn, in the

following subsections.

2.2.1. Social phobia and specific phobias

Social phobia (SP) is characterized by a marked andpersistent fear of social situations and its attendant prospect

of negative evaluation by others, often provoking a

significant anxiety response [36]. Most visual scanpath

research in the anxiety disorders has focused on SP,

ostensibly because of a classic avoidance of eye contact

exhibited in social situations. Using the standard facial affect

paradigm, involving angry, happy, neutral, and sad expres-

sions, a hyperscanning strategy was uncovered, repre-

sented by reduced fixations in frequency and duration, as

well as increased raw scanpath lengths [106,107]. Further-

more, it was demonstrated that individuals with SP displayed

an active avoidance of salient facial features, especially the

eyes, coupled with extensive scanning of nonsalient facialregions, which was most marked for negatively valenced

emotions. This was construed as a hypervigilance to social

threat, resulting in a diminished ability to acquire ample

information for the accurate interpretation of social interac-

tions. In an assessment of socially anxious individuals,

Meyer [28], on the other hand, found that their affect

recognition performance did not differ from that of healthy

controls. More recently, Wieser et al [108] investigated

visual scanpaths in SP using a novel and ecologically valid

approach, which entailed the presentation of animated movie

clips, depicting neutral faces bearing either a direct or

averted gaze, to individuals with differing levels of social

anxiety. Regardless of gaze orientation, high socially

anxious participants were found to fixate more on the eye

regions, and moreover, responded to direct gazes with

increased physiological arousal in terms of more pronounced

cardiac acceleration. These disparate findings, involving

significant gaze avoidance [106,107] vs preferential atten-

tion [108] to social threat, may perhaps be reconciled by

considering differences in illness severity; individuals with

SP may be inclined to use avoidance as a coping mechanism,

whereas socially anxious persons may be predisposed to seek

out and misjudge instances of interpersonal threat.

A limited number of studies have also used eye-tracking

to investigate spider phobia. Rinck and Becker [109]

presented categories of animal pictures (including spiders)

and reported that spider phobic participants more often

directed their initial fixation toward spider pictures,

followed by a rapid shift of attention away from the fear-

relevant stimuli, resulting in shorter overall fixation

durations. Other typical paradigms were saccadic (prosac-cades vs antisaccades) and visual search tasks. In terms of

the former, Trippe et al [110] presented participants with

pairs of fear-provoking spider pictures alongside neutral

pictures, with instructions to fixate on a target category.

Participants exhibited significantly more errors and in-

creased latencies during prosaccades to spider pictures, but

were quicker to perform antisaccades from spider pictures,

signifying a propensity for threat avoidance. In another

study, it was conversely established that spider phobic

participants not only fixated more quickly on fear-relevant

targets but also displayed longer latencies when asked to

turn their attention away from those images [111]. I n aseparate line of enquiry, Rinck and Becker [112] admin-

istered a range of visual search tasks and observed that

spider phobic participants displayed faster detection and

increased attentional disruption to spider pictures. Likewise,

another visual search task conducted amid an array of task-

irrelevant distractors revealed greatest fixation durations for

spider distractors [113]. On the whole, it remains unclear

whether the mechanisms of initial attentional capture

followed by active avoidance or delayed disengagement

of attention from threat stimuli chiefly underpins spider

phobia. Additional research is thus warranted to clarify the

temporal pattern of eye movement dysfunction in both SP

and specific phobias.

2.2.2. Other anxiety disorders

Scant eye-tracking research has been conducted in other

anxiety disorders, with the exception of a few studies

devoted to OCD, PTSD, and GAD. Before proceeding, it is

important to delineate key differences amongst these

disorders, though each is primarily characterized by

excessive and overwhelming feelings of anxiety. Accord-

ingly, OCD is defined by the manifestation of recurrent

thoughts, images, or impulses experienced as inappropriate

or intrusive, thereby prompting repetitive behaviors or



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mental rituals aimed at neutralizing the distress, but

performed in an excessive or irrational manner [36]. In

contrast, PTSD typically develops as a cluster of disturbing

symptoms following an extreme traumatic stressor, whereas

GAD is experienced as undue anxiety and worry over a

range of concerns, attended by somatic symptoms. In an

exploratory eye movement analysis, reduced RSS, number

of fixations, and total scanpath lengths were found in OCD

and significantly correlated with specific clinical symptoms

[114]. Differences in eye-tracking performance between

medicated and nonmedicated OCD groups have also been

observed [115]. However, Kojima et al [64] found no

significant differences between OCD patients and healthy

controls in this regard. In a separate study, PTSD participants

showed increased initial fixations to threat stimuli and

greater overall skin conductance orienting responses in

relation to a display of disorder-specific threat and nonthreat

words[116]. In an investigation of the direction and latency

of initial gazes to pairs of emotional faces, GAD participants

were found to fixate more quickly and frequently on threatfaces[117]. When presented with complex pictures depict-

ing potential, latent, direct threat, or nonthreat themes,

Freeman et al [118] reported that individuals with GAD

failed to exhibit any atypical scanning strategies. At present,

it appears that a consistent and coherent account of eye

movement dysfunction in these anxiety disorders is missing.

Moreover, a lack of corroborating studies and certain

methodological limitations (outlined in the next section)

render these results tentative at best.

2.2.3. Implications and conclusions

On the whole, the most convincing evidence pertaining to

eye-tracking anomalies in the anxiety disorders comes fromSP, with a dearth of relevant studies in other areas precluding

further meaningful conclusions. In addition, existing re-

search tends to suffer from a range of methodological

limitations. Foremost, small participant numbers diminished

the power of the studies, making it less likely for significant

effects to be statistically detected. Some studies, moreover,

used skewed participant groups, for instance, involving

subclinical populations[111]or solely females[108]. Other

inconsistencies include uncontrolled medication status in

almost all studies as well as comorbidity with additional

anxiety disorders and/or secondary depressive conditions

[118]. However, it remains a worthwhile endeavor topersevere with further eye-tracking research into the anxiety

disorders, because preliminary findings from SP show

promise for clinical applications, akin to the cognitive

remediation treatments offered in schizophrenia.

2.3. The mood disorders

A small amount of research has explored visual scanpaths

in the mood disorders, chiefly major depressive disorder

(MDD). Key features of the disorder include depressed mood

and/or loss of interest or pleasure in nearly all activities,

accompanied by a constellation of cognitive and somatic

symptoms[36]. Only half of the studies were actually aimed

at examining eye movements in MDD per se, whereas the

remaining research used mood disordered participants as a

psychiatric control group in eye-tracking studies of schizo-

phrenia. Of the former, Eizenman et al[119]presented MDD

participants with a competing array of visual images

depicting differing themes of dysphoria, neutral, social,

and threat, and reported that MDD participants exhibited

increased fixation durations and dwell times for dysphoric

images. This was interpreted as not merely suggesting a

general eye movement bias toward negatively valenced

information as demonstrated by Caseras et al [120], but

rather a selective allocation of attention to specific content

portraying loss and sadness. In follow-up research, Kellough

et al[121]used a similar paradigm but extended the exposure

time to 30 seconds (instead of the 10.5 seconds in the

original study) to examine the time course of such biased

attention. Though the MDD participants likewise focused

more attention on the dysmorphic images, this was found to

be due to a significantly greater number of fixations. Theserepeated fixations were hypothesized as underpinning

elaborative processing of dysphoric stimuli, akin to a

ruminative cognitive style partially liable for the mainte-

nance of MDD. During repeated pretreatment and posttreat-

ment assessments, existing eye movement dysfunctions was

found to remain largely unchanged, despite improvements in

clinical symptoms, thereby alluding to the trait-like nature of

these anomalies [122]. As mentioned, other studies in the

area pertained to a comparison between MDD and

schizophrenia samples and will thus only be summarized

briefly. Although no distinct scanning style has been isolated

for the disorder, the eye-tracking performance in MDD hasbeen suggested as intermediate between that of schizophre-

nia and healthy controls, especially in terms of fixation

frequency [64,123], though David et al [124] found no

differences between schizophrenia and MDD patients. On

the other hand, Loughland et al [52]administered face and

affect recognition tasks to mood disordered participants and

concluded that their functioning was superior to schizophre-

nia patients and equal with healthy controls, except for a

marked avoidance of salient facial features across all

emotions, particularly for degraded faces.

Once again, these studies have suffered from a range of

methodological limitations, including a lack of corroborating

research, limited sample sizes, skewed participant groups(eg, involving only young adults[121]or mixed unipolar and

bipolar affective patients [52]), uncontrolled medication

status, and undiagnosed comorbidities, thereby rendering

any present conclusions speculative, in anticipation of

further investigations.

3. Directions for future research

In terms of suggested directions for future research, 2

main avenues appear to deserve further exploration. First,



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eye-tracking techniques may be productively applied to a

range of other psychological disorders, notably those keenly

involving elements of social perception. This has already

been initiated for conditions, such as the autism spectrum

disorders [125], and remains to be applied to other

disorders, such as body dysmorphic disorder (BDD). In

particular, relevant findings in BDD will help to inform

existing debates in terms of its nosologic classification,

which has long been disputed. At present, BDD is

categorized as a somatoform disorder [36], but various

arguments have been made toward its reclassification

amongst the newly conceptualized obsessive-compulsive

spectrum disorders, anxiety disorders, or even psychotic

disorders (see Toh et al [126]for a comprehensive review).

Distinct similarities and differences in eye-tracking perfor-

mance in BDD relative to OCD, schizophrenia, and other

psychiatric disorders would therefore shed further light on

these prevailing nosologic debates. Such a bottom-up

approach will also permit a more detailed delineation of

potential domains of executive dysfunction, for instance,involving attentional biases or deficits in visual organization

and processing. Second, concurrent neuroimaging studies

will facilitate investigations into potential neurologic

deficits, upon the detection of eye movement dysfunction.

More specifically, parallel brain imaging techniques will

help to isolate functional and structural cerebral anomalies,

which likely contribute toward eye-tracking deficits. This

has been previously attempted in schizophrenia [98,99]and

forms the next logical step for related studies of similar

conditions. In this way, linking behavioral disturbances with

underlying neurobiological correlates should in turn not

only advance existing etiologic formulations but also assistin the identification of specific endophenotypes underpin-

ning related psychological disorders.

To facilitate such future research and overcome the

existing methodological inconsistencies, which have

plagued visual scanpath research to date, it would be prudent

to recommend a standardized set of experimental tasks,

naturally with the option of modifications beyond this fixed

paradigm. In line with the findings of the current review,

relevant stimuli used should include emotional faces as well

as geometric figures. For the standardized facial affect

paradigm, the general consensus has been that 5- to

10-second presentations of a series of facial images depicting

the entire range of the 6 universal human emotions (ie, angry,disgusted, fearful, happy, sad, and surprised), along with a

neutral face serving as the control condition under free-

viewing conditions would suffice. The best available stimuli

for this task is probably the set of facial images by Ekman et

al[91], though these ideally require updating, with inclusion

of full color. In terms of the geometric figure, the wide

assortment used thus far in research precludes an unequi-

vocal decision, but perhaps the Rey-Osterrieth Complex

Figure, with its well-documented validity and reliability

[127], would be a sound choice. Additional novel research

thereafter involving the use of complex social scenes as well

as digitalized moving images would serve as a constructive

adaptation. On the whole, such a systematic approach will

certainly add to the growing body of knowledge concerning

how attentional allocation and visual anomalies contribute

toward the etiology and maintenance of a range of

psychiatric presentations.

4. Conclusion

Advances in modern eye-tracking techniques have

rendered this line of research especially fruitful. Studies

analyzing visual scanpaths in schizophrenia have been fairly

well documented, converging on generalized scanning

deficits of a restricted nature, characterized by fewer

fixations of increased durations, with shorter scanpath

lengths, and a marked avoidance of salient features across

a range of visual stimuli, but notably in relation to facial

emotion perception[45-47,51-53]. There is thus an emerging

consensus involving dual impairments in configural proces-sing as well as gestalt perception. In other words, individuals

with the disorder are not only unable to form significant

connections between discrete portions of a face but also fail

to integrate it into a meaningful global structure. Added

research is nevertheless essential to clarify the trait vs state

debate and to elucidate the contributions of specific

symptoms and syndromes and, in particular, delusions. In

relation to the anxiety disorders, explorations into SP have

proposed a hyperscanning strategy, represented by reduced

number of fixations of shorter durations and increased

scanpath lengths, coupled with a respective avoidance and

scrutiny of salient and nonsalient facial features, most

evident for negatively valenced emotions [106,107]. Theother anxiety disorders offered a less coherent picture,

necessitating further investigations. From the perspective of

the mood disorders, the most striking finding related to

disproportionate foveal attention to dysphoric images,

analogous to the classic ruminative thinking style frequently

underlying MDD [119,121]. However, existing methodo-

logical limitations, involving a lack of corroborating studies,

limited sample sizes, skewed patient demographics, uncon-

trolled participant comorbidities, and medication status, need

to be overcome. Future endeavors could yield valuable

clinical utility, in light of treatment applications already

evident for schizophrenia.

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