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Dynamic Illusory Size-Contrast: A relative-size illusion modulated by stimulus motion and eye movements

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We present a novel size-contrast illusion that depends on the dynamic nature of the stimulus. In the dynamic illusory size-contrast (DISC) effect, the viewer perceives the size of a target bar to be shrinking when it is surrounded by an expanding box and when there are additional dynamic cues such as eye movements, changes in retinal eccentricity of the bar, or changes in the spatial position of the bar. Importantly, the expanding box was necessary but not sufficient to obtain an illusory percept, distinguishing the DISC effect from other size-contrast illusions. We propose that the visual system is weighting the different sources of information that contribute to size perception based on the level of uncertainty in the retinal image size of the object. Whereas the growing box normally has a weak influence on the perceived size of the target bar, this influence is enhanced when other dynamic changes in the environment (e.g., eye movements, changes in retinal eccentricity, and target motion) lead to uncertainty in the retinal size of the target bar. Given the compelling nature of the DISC effect and the inherently dynamic nature of our environment, these factors are likely to play an important role in everyday size judgments.
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Dynamic illusory size contrast: A relative-size illusion
modulated by stimulus motion and eye movements
Ryan E. B. Mruczek
#
$
Department of Psychology, University of Nevada, Reno,
Reno, NV, USA
Christopher D. Blair $
Department of Psychology, University of Nevada, Reno,
Reno, NV, USA
Gideon P. Caplovitz
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$
Department of Psychology, University of Nevada, Reno,
Reno, NV, USA
We present a novel size-contrast illusion that depends
on the dynamic nature of the stimulus. In the dynamic
illusory size-contrast (DISC) effect, the viewer perceives
the size of a target bar to be shrinking when it is
surrounded by an expanding box and when there are
additional dynamic cues such as eye movements,
changes in retinal eccentricity of the bar, or changes in
the spatial position of the bar. Importantly, the
expanding box was necessary but not sufficient to obtain
an illusory percept, distinguishing the DISC effect from
other size-contrast illusions. We propose that the visual
system is weighting the different sources of information
that contribute to size perception based on the level of
uncertainty in the retinal image size of the object.
Whereas the growing box normally has a weak influence
on the perceived size of the target bar, this influence is
enhanced when other dynamic changes in the
environment (e.g., eye movements, changes in retinal
eccentricity, and target motion) lead to uncertainty in
the retinal size of the target bar. Given the compelling
nature of the DISC effect and the inherently dynamic
nature of our environment, these factors are likely to
play an important role in everyday size judgments.
Introduction
Having accurate perceptual representations of object
size is crucial for interacting with the world around us.
However, an object’s size is not inherently represented
in the size of its projected retinal image. Rather, the
perceived size of an object is constructed by integrating
multiple sources of information including, but not
limited to, retinal image size, physical and perceived
distance (Berryhill, Fendrich, & Olson, 2009; Boring,
1940; Emmert, 1881; Ponzo, 1911), an object’s geo-
metrical and textural properties (Giora & Gori, 2010;
Kundt, 1863; Lotze, 1852; Oppel, 1855; Helmholtz,
1867; Westheimer, 2008), knowledge of an object’s
typical size (Konkle & Oliva, 2012), and the relative size
of different objects in a scene (Coren & Girgus, 1978;
Roberts, Harris, & Yates, 2005; Robinson, 1972). The
roles these different sources of information play in the
construction of perceived size can be revealed through a
number of illusions in which the size of an object is
misperceived. For example, classical size-contrast and
size-assimilation illusions such as the Ebbinghaus
illusion (Burton, 2001; Thi´
ery, 1896) or the Delboeuf
illusion (Delboeuf, 1892) demonstrate that the size of a
surrounding context can influence the perceived size of
a central object (Figure 1). More recently described
illusions, such as the ‘‘binding ring illusion’’ (Mc-
Carthy, Kupitz, & Caplovitz, 2013), the ‘‘StarTrek
illusion’’ (Qian & Petrov, 2012), the ‘‘shrinking building
illusion’’ (Fukuda & Seno, 2011), and the ‘‘breathing
light illusion’’ (Anstis, Gori, & Wehrhahn, 2007; Gori,
Giora, & Agostini, 2010; Gori & Stubbs, 2006), further
demonstrate that the perceived size of an object is
influenced by the context in which it is viewed.
Together, these illusions have provided insights into
our understanding of how we perceive the size of an
object. Additionally, understanding such illusions may
have practical implications, such as the potential effects
of plate size on food consumption (van Ittersum &
Wansink, 2012) and the effects of striped clothing on
bodily appearance (Ashida, Kuraguchi, & Miyoshi,
2013; Thompson & Mikellidou, 2011). In this paper, we
introduce a novel size illusion that highlights the role of
Citation: Mruczek, R. E. B., Blair, C. D., & Caplovitz, G. P. (2014). Dynamic illusory size contrast: A relative-size illusion modulated
by stimulus motion and eye movements. Journal of Vision,14(3):2, 1–15, http://www.journalofvision.org/contents/14/3/2,
doi:10.1167/14.3.2.
Journal of Vision (2014) 14(3):2, 1–15 1http://www.journalofvision.org/content/14/3/2
doi: 10.11 6 7 / 1 4 . 3.2 ISSN 1534-7362 Ó2014 ARVOReceived October 30, 2013; published March 3, 2014
visual motion in modulating the contribution of
different sources of information in determining the
perceived size of an object.
One of us (R. E. B. M.) first noticed the illusion
while watching videos with his children using Apple’s
QuickTime (v10.1, Apple Inc., Cupertino, CA). In
QuickTime, the playback controls are contained within
a black bar that is positioned at the center-bottom of
the video window by default. When transitioning from
‘‘windowed’’ mode to ‘‘full-screen’’ mode, the video
dynamically expands to fill the monitor. At the same
time, the position of the control bar changes, but the
physical size of the control bar does not. However, the
perceived size of the control bar changes dramatically,
appearing to shrink when going to full-screen mode
and to grow when going back to windowed mode. As
the magnitude of the illusion primarily depends upon
the dynamic change in the relative size of the target bar
and the surrounding background, we have termed the
effect ‘‘dynamic illusory size contrast’’ (DISC). In
comparison to other illusions of size contrast (e.g., the
Ebbinghaus and Delboeuf illusions, Figure 1), the
DISC effect is strikingly compelling. It may be that this
arises because, unlike other classic size-contrast illu-
sions that are static in nature, the size of the target bar
in the DISC stimulus is perceived to continuously
change in a smooth fashion.
In order to explore this illusion in a more controlled
fashion, we created a simplified version with a
surrounding context (a solid white box), a central target
object (a black rectangle), and a fixation point. Readers
can experience the DISC stimulus for themselves by
viewing Movie 1. Note that although the size of the
black bar appears to shrink as the surrounding box
grows and to grow as the surrounding box shrinks, it is
not changing. We think readers will find that the
perceived change in size in the DISC effect is greater
than one may experience by simply comparing two still
images depicting the smallest and largest box sizes of
the video sequence (Figure 2).
What is it about this dynamic display that leads to
such a robust change in the perceived size of the inner
bar? We identified four potential factors that could
contribute to the DISC effect: (a) the relative size
change between surrounding box and target bar; (b) the
change in real-world position of the target bar; (c) the
change in retinal eccentricity of the target bar; and (d)
the execution of a smooth pursuit and/or saccadic eye
movements. In the following set of experiments, we
systematically explore the contributions that each of
these factors make to the magnitude of the DISC effect.
Our results demonstrate that the contribution of
relative size carries more weight in a dynamic
environment in which both the target bar and
contextual surround are physically moving or are
perceived to be moving. In our interpretation of these
results we raise the hypothesis that the dynamic nature
of the stimulus leads to greater uncertainty about the
retinal size of the target object. As a result, other
sources of information (i.e., relative size) contribute
more to its perceived size, thereby increasing the
magnitude of the illusory percept.
Figure 1. Classic size-contrast illusions. In the Ebbinghaus (A)
and Delboeuf (B) illusions, the inner filled circle is perceived to
be larger on the right and smaller on the left. In fact, all filled
circles are the same physical size.
Movie 1: Full Oblique condition. Note that the black target bar
appears to shrink and expand as the surrounding box expands
and shrinks. Click on the image to view the movie. Movies are
best viewed in looped mode.
Journal of Vision (2014) 14(3):2, 1–15 Mruczek, Blair, & Caplovitz 2
Methods
Participants
Observers in each experiment consisted of student
volunteers participating in exchange for course credit
from the University of Nevada, Reno. Fifteen partic-
ipants completed Experiment 1; 11 participants com-
pleted Experiment 2; and 11 participants, seven of
whom also completed Experiment 2, completed Ex-
periment 3. Prior to participating, each observer
provided informed consent according to the guidelines
of the Department of Psychology and the Institutional
Review Board of the University of Nevada, Reno. The
research protocol of all experiments adhered to the
tenets of the Declaration of Helsinki. All participants
reported normal or corrected-to-normal vision and
were naive to the specific aims and designs of the
experiments.
Data from five additional participants were excluded
due to the participants’ mix-up in the response buttons,
extreme response bias, or high variability of responses
for the same trial parameters leading to poor psycho-
metric curve fitting.
Apparatus and display
Stimuli were presented on a ViewSonic Graphic
Series G220fb monitor (20-in., 1024 ·768 pixel
resolution, ViewSonic Corporation, Walnut, CA) with
an 85-Hz refresh rate. The stimulus computer was a
2.5-GHz Mac Mini (Apple Inc., Cupertino, CA) with
an Intel HD Graphics 4000 768 MB graphics processor
(16 GB of DDR3 SDRAM). Stimuli were created and
presented with the Psychophysics Toolbox (Brainard,
1997; Pelli, 1997) for MATLAB (version 2012b,
Mathworks Inc., Natick, MA). The stimuli consisted of
a black (0.44 cd/m
2
) target bar, a black (0.44 cd/m
2
)
and red (18.94 cd/m
2
) fixation spot, and a white (100.20
cd/m
2
) surrounding box presented on a black (0.44 cd/
m
2
) background. Participants viewed the stimuli
binocularly from a distance of 73 cm with their chin
positioned in a chin-rest. Eye movements were not
monitored.
Trial overview
Here, we outline the general trial structure for all
experiments. The specific details of each trial type are
outlined below. The general trial structure for one
condition is outlined in Figure 3A. A summary of the
dynamic components that are included in each condi-
tion is shown in Table 1. We also provide video
versions of all our stimuli so that the readers may
experience the reported effects for themselves, although
it should be noted that the stimuli used in the
experiments consisted only of the first half of each
‘‘loop-able’’ movie demo.
Every trial was initiated with the presentation of a
fixation spot that consisted of an inner black circle (0.18
radius) enclosed by an outer red circle (0.28radius).
After this 500-ms fixation period, participants were
shown a static stimulus consisting of a fixation spot and
a vertically oriented target bar (;3.28height ·0.58
width) positioned within the borders of a surrounding
Figure 2. Static frames depicting the smallest (left) and largest (right) box sizes of the video sequence in Movie 1. We invite readers to
compare the size of the black bar in both frames, which are physically identical, and to then compare the subjective magnitude of this
illusory effect with that perceived from the DISC stimulus in Movie 1.
Journal of Vision (2014) 14(3):2, 1–15 Mruczek, Blair, & Caplovitz 3
white box (;48for all but one condition; ;108for the
Rigid Box condition of Experiment 2). The fixation
spot was centered within the surrounding box and the
target bar was vertically centered 1.58to the right of
fixation and 0.58from the right edge of the box. On
trials in which the fixation spot translated and the
subject was required to smoothly pursue the fixation
spot, an arrow indicated the impending direction of
motion. On trials with no translation of the fixation
spot, a circle cue appeared around the fixation. The
stimulus remained static for the 500-ms cue period and
then smoothly changed over a 400-ms animation
period. The particular dynamic changes to the stimuli
were specific to each experimental condition (see
Figure 3. An outline of the Full Oblique condition. (A) The timeline of events for a single trial from the Full Oblique condition. A video
of this condition is shown in Movie 1, although readers should note that the actual trials consisted only of the first half of each ‘‘loop-
able’’ movie demo. (B) The initial (left) and final (right) stimulus configuration of the animation period. All conditions started from the
same initial configuration, except the Rigid Box condition of Experiment 2.
Condition label Experiment Expanding box Bar motion Increasing eccentricity Eye movements Movie demo
Full Oblique 1, 2, 3 þþ þ þMovie 1
Full Horizontal 1 þþ þ þMovie 2
Stationary Bar 1 þþþMovie 3
Full Opposing Horizontal 1 þþ þ þMovie 4
Fixed Eyes 1 þþ þ Movie 5
Pure Size-Contrast 1 þ Movie 6
Constant Eccentricity 2 þþ þMovie 7
Rigid Box 2 þþ þMovie 8
Static Frames 3 þþ þ þMovie 9
Table 1. All experimental condition labels and their associated movie demo. Note:Aþor – indicates the presence or absence of a
given dynamic component, respectively.
Journal of Vision (2014) 14(3):2, 1–15 Mruczek, Blair, & Caplovitz 4
below), but included one or more of the following: a
uniform increase in the size of the surrounding white
box from ;48to ;108, a translation of the
surrounding box, a translation of the fixation spot, a
translation of the target bar, and an increase or
decrease in the vertical extent of the target bar. On
trials in which the surrounding box expanded, it
increased in size from ;48to ;108over the 400-ms
animation period (i.e., each edge of the box expanded
outward at a rate of ;7.68/s). On all trials, the bar
remained vertically centered at a fixed distance of 0.58
from the right edge of the box throughout the trial.
After the 400-ms animation period, the stimulus, except
for the fixation spot, was removed and participants
reported whether the target bar had increased or
decreased in length by pressing one of two buttons on a
keyboard. Participants were instructed to maintain
fixation on the fixation spot at all times and covertly
attend to the size of the target bar. No feedback was
provided to the participants.
The experiments used a nulling technique in which
the physical change in target bar length during the
animation phase was adjusted from trial-to-trial to
minimize the participant’s perceived change in size. The
decision to use a nulling technique was based on our
past experience of successfully applying it to quantify
other dynamic illusions (e.g., Caplovitz, Paymer, &
Tse, 2008; Caplovitz & Tse, 2007). On each trial, the
physical change in target bar length was selected from
one of 18 growth rates spanning a range of ;677%,
with equal spacing between rates, using an adaptive
staircase procedure. Negative growth rates indicate that
the bar was contracting and positive growth rates
indicate that the bar was expanding. Thus, in the most
extreme conditions of the staircase, the length of the
target bar would be either 77%longer or 77%shorter at
the end of the animation than at the beginning. Each
condition in each experiment used six pseudorandomly
interleaved staircases, with half starting from the
minimum growth rate and half starting from the
maximum growth rate (four staircases were used for
two participants in Experiment 1). Each staircase lasted
for a total 25 trials. For each staircase, the growth rate
on subsequent trials was adjusted depending on the
participant’s response. If the participant indicated that
the bar appeared to have shrunk, then the next trial in
the same staircase would use the next highest growth
rate (always moving one step at a time), and vice versa.
To minimize the influence of environmental cues
(e.g., the edge of the monitor), the starting position of
the entire stimulus was randomly varied by up to 618
horizontally and vertically from the center of the
screen. To avoid participants developing a template of
the initial size of the box and bar, each varied
independently by up to 2%from trial to trial.
Experiment 1
In Experiment 1 we sought to reproduce our original
observation with a controlled stimulus. In addition, we
tested whether changes in real-world position of the bar
and the execution of a smooth pursuit and/or saccadic eye
movements modulate the magnitude of the DISC effect.
Experiment 1 contained six distinct conditions
(Table 1). The six conditions differed in their dynamic
component, although the retinal stimulation was
largely matched across conditions (excluding the Pure
Size-Contrast condition, see below) for a given growth
rate of the bar.
Figure 3 and Movie 1 depict the simplified version of
our original observation. As this stimulus contains all
dynamic components with movement vectors at an
oblique angle, we refer to it as the Full Oblique
condition. As can be seen in Movie 1, the fixation spot
maintained its position at the center of the surrounding
box, which translated down and to the right as it
expanded in size. Specifically, in this condition, the
center of the box and the fixation spot translated at an
oblique angle 458down and to the right over a distance
of ;3.18(4.48for two participants), corresponding to a
speed of ;7.68/s (11.18/s for two participants). The
target bar translated at a 22.58angle (26.68for two
participants) down and to the right over a distance of
;5.78(7.08for two participants), corresponding to a
speed of ;148/s (17.58/s for two participants).
The Full Horizontal condition (Movie 2) was similar
to the Full Oblique condition in that it contained all the
dynamic components described above, but all transla-
Movie 2: Full Horizontal condition. All translations were
constrained to the horizontal meridian. Click on the image to
view the movie. Movies are best viewed in looped mode.
Journal of Vision (2014) 14(3):2, 1–15 Mruczek, Blair, & Caplovitz 5
tions were constrained to the horizontal meridian. In this
condition, the surrounding box translated horizontally
as it expanded in size. The fixation spot and the target
bar translated to the right, such that the fixation spot
maintained its centered position and the target bar
maintained its position along the right edge of the
surrounding box. As in the Full Oblique condition, the
center of the box and the fixation spot translated a
distance of ;3.18, corresponding to a speed of ;7.68/s.
To maintain its position relative to the surrounding box,
the target bar translated to the right over a distance of
;6.28, corresponding to a speed of ;15.28/s.
In the Stationary Bar condition (Movie 3), the physical
position of the target bar on the screen did not change over
the course of the animation. In this condition, the
surrounding box translated to the left as it expanded in
size. The fixation spot also translated to the left to
maintain its central position relative to the surrounding
box. The center of the box and the fixation spot translated
over a distance of ;3.18, corresponding to a speed of
;7.68/s. These values were chosen so that the stationary
target bar maintained its position along the right edge of
the surrounding box throughout the trial.
Unlike the Full Horizontal condition, the fixation
spot translated away from the bar in the Stationary Bar
condition. To verify that this change did not account
for potential differences in the magnitude of the illusion
between these conditions, we included a Full Opposing
Horizontal condition as a control (Movie 4). This
control condition contained all four dynamic compo-
nents, as in the Full Horizontal Condition, but the
fixation spot translated away from the bar, as in the
Stationary Bar condition. In this control condition, the
fixation spot maintained its central position relative to
the surrounding box as both translated to the left, while
the surrounding box expanded in size. Each translated
over a distance of ;1.58, corresponding to a speed of
;3.88/s. In order to maintain its position along the
right edge of the surrounding box, the target bar
translated to the right covering a distance of ;1.58,
corresponding to a speed of ;3.88/s.
The Fixed Eyes condition (Movie 5) did not contain
any smooth pursuit eye movement and the fixation spot
remained stationary throughout the trial. In this
condition, the surrounding box did not translate,
although it still expanded in size. To maintain its
relative position to the right edge of the expanding box,
the black bar translated to the right over a distance of
;3.18, corresponding to a speed of ;7.68/s.
The only dynamic change in the Pure Size-Contrast
condition (Movie 6) was the relative size change
between the surrounding box and the target bar. In this
condition, the center of the expanding surrounding box
translated to the left over a distance of ;3.18,
corresponding to a speed of at 7.68/s. The fixation spot
and the target bar remained stationary.
Thirteen participants completed 150 trials for each
condition, except the Pure Size-Contrast condition, for
a total of 750 trials in a single session (5 conditions ·6
interleaved staircases/condition ·25 trials/staircase).
Six of these same participants completed an additional
150 trials (6 interleaved staircases ·25 trials/staircase)
of the Pure Size-Contrast condition in a separate
session. Two participants completed 100 trials for each
condition, except the Pure Size-Contrast, for a total of
Movie 3: Stationary Bar condition. The physical position of the
target bar does not change. Click on the image to view the
movie. Movies are best viewed in looped mode.
Movie 4: Full Opposing Horizontal condition. The fixation spot
translates away from the target bar. Click on the image to view
the movie. Movies are best viewed in looped mode.
Journal of Vision (2014) 14(3):2, 1–15 Mruczek, Blair, & Caplovitz 6
500 trials in a single session (5 conditions ·4
interleaved staircases/condition ·25 trials/staircase).
Experiment 2
Experiment 2 was designed to further investigate the
factors that influence the DISC effect. Specifically, this
experiment tested whether the DISC effect is modu-
lated by changes in target eccentricity as the bar moves
across the screen and the degree to which it depends on
the dynamic change in the size of the surrounding box.
Experiment 2 contained three conditions (Table 1).
The first condition was a replication of the Full Oblique
condition (Figure 3 and Movie 1), which led to the
largest illusory effect in Experiment 1. The remaining
conditions (described below) tested the contribution of
target eccentricity and the size change of the sur-
rounding box, respectively, by removing each of these
dynamic components from the full stimulus. The eye
movement necessary to maintain gaze on the fixation
spot was matched across the three conditions.
The Constant Eccentricity condition (Movie 7)
shared all dynamic components with the Full Oblique
condition except that the eccentricity of the target bar
did not increase over the course of the trial. In this
condition, the surrounding box translated at an oblique
angle of 67.58down and to the left over a distance of
2.38, corresponding to a speed of 5.88/s. The fixation
spot and target bar translated together at an oblique
angle of 458down and to the right over a distance of
3.18, corresponding to a speed of 7.68/s, thereby
maintaining their positions relative to the right edge of
the surrounding box.
The Rigid Box condition (Movie 8) was identical to
the Full Oblique condition, except that the surrounding
box started off large, and remained unchanging in a
position that matched the final configuration of the
Full Oblique condition. In other words, the large box
remained rigid while the fixation spot and the black
target bar translated together down and to the right.
Movie 6: Pure Size-Contrast condition. The only dynamic change
is the relative size change between the surrounding box and the
target bar. Click on the image to view the movie. Movies are
best viewed in looped mode.
Movie 7: Constant Eccentricity condition. The distance between
the target bar and fixation point does not change. Click on the
image to view the movie. Movies are best viewed in looped
mode.
Movie 5: Fixed Eyes condition. The fixation spot remains
stationary. Click on the image to view the movie. Movies are
best viewed in looped mode.
Journal of Vision (2014) 14(3):2, 1–15 Mruczek, Blair, & Caplovitz 7
Specifically, the box (10.18sides) was stationary
throughout the trial in a position such that the final
location of the target bar was vertically centered along
the right edge of the box. Respectively, the fixation spot
and the target bar translated at oblique angles of 458
and 22.58down and to the right over distances of 3.18
and 5.78, corresponding to speeds of 7.68/s and 148/s.
All participants completed 150 trials for each
condition for a total of 450 trials in a single session (3
conditions ·6 interleaved staircases/condition ·25
trials/staircase).
Experiment 3
In Experiment 3 we sought to verify that the dynamic
nature of the stimulus is a key factor driving the DISC
effect. Specifically, we compared the size-contrast effect
for the dynamic version of the stimulus with that found
under comparable, but static conditions.
Experiment 3 contained two conditions (Table 1).
For comparison, we replicated the Full Oblique
condition (Figure 3 and Movie 1) and, in addition,
included a nondynamic Static Frames condition. The
initial and final configurations of the Static Frames
condition (Movie 9) were identical to the Full Oblique
condition, but during the 400-ms animation period the
box and the bar were not shown. In other words, the
dynamic phase consisted only of a moving fixation
point. At the end of the animation period the full
stimulus reappeared with the size and position of the
box and bar matched to the final position of the Full
Oblique condition. Participants viewed this still frame
for 200 ms before the box and bar were extinguished.
Participants then indicated whether the bar appeared to
have grown or shrunk in the final configuration
compared to the initial configuration.
Participants completed 150 trials for each condition
for a total of 300 trials in a single session (2 conditions
·6 interleaved staircases/condition ·25 trials/
staircase).
Analyses
Data from all trials of a given condition, indepen-
dent of the staircase procedure, were combined to
calculate psychometric curves (Leek, 2001; Leek,
Hanna, & Marshall, 1992) describing the relationship
between the growth rate of the bar and the participant’s
perception of bar size. We plotted the proportion of
trials in which the participant reported that the bar was
growing as a function of the actual growth of the bar in
units of percentage of the initial bar size (see Figure 4
for an example). Given our two-alternative forced
choice paradigm, we used the following sigmoidal
shaped binomial-logit function to model the data
(Wichmann & Hill, 2001) for each condition and
participant independently using the MATLAB glmfit
command:
fðxÞ¼eb1þxb2=ð1þeb1þxb2 Þ
The point of subjective equality (PSE) was deter-
mined by interpolating the chance level response
Movie 8: Rigid Box condition. There is no relative size change
between the surrounding box and the target bar. Click on the
image to view the movie. Movies are best viewed in looped
mode.
Movie 9: Static Frames condition. The dynamic phase consists
only of a moving fixation point, without the surrounding box
and the target bar. Click on the image to view the movie.
Movies are best viewed in looped mode.
Journal of Vision (2014) 14(3):2, 1–15 Mruczek, Blair, & Caplovitz 8
probability (0.5) from the function fit to the data (PSE
¼–b
1
/b
2
). The PSE represents the growth rate at
which the participant had an equal probability of
perceiving the bar as shrinking or growing for a given
condition. If there were no illusory DISC effect (i.e.,
veridical perception), we would anticipate a PSE of
zero. Alternatively, if the DISC effect was perceived, we
would anticipate a PSE greater than zero as physical
growth of the target bar would be necessary to cancel
or null the illusory reduction in perceived size. We note
that we obtained similar results when we defined PSEs
based on the average of the last five reversals of each
independent staircase.
To avoid the assumptions of parametric statistical
tests, we analyzed the data using a series of standard
nonparametric tests and randomization procedures.
However, we note that when the data were analyzed
using parametric alternatives, the significance and the
interpretation of the results were not qualitatively
different. To determine whether the DISC effect was
observed for each condition, PSEs were compared
against zero using a nonparametric Wilcoxon signed-
rank test. To determine whether experimental manip-
ulations in the stimulus influenced the magnitude of the
DISC effect, pair-wise comparisons across conditions
within an experiment were performed using a two-
tailed nonparametric permutation test for paired data.
The mean difference in PSEs across two conditions was
compared to a distribution of differences obtained for
every possible permutation of each participant’s values
(number of permutations ¼2
N
, where Nis the number
of participants for that experiment; n
perm
¼32,768 for
Experiment 1; n
perm
¼2,048 for Experiments 2 and 3).
This is equivalent to randomly flipping the sign of the
PSE difference across the two conditions for each
participant. For this test, the p-value was defined as the
proportion of random permutations of the data that
yielded a difference in the PSEs for two conditions that
was equal to or greater than the actual observed
difference. The paired comparisons followed an initial
nonparametric Friedman’s test for repeated-measures
data to verify a main effect of condition. As we only
made a small number of a priori comparisons in each
experiment informed by our experimental design and
hypotheses, we report uncorrected p-values and assess
statistical significance using an aof 0.05.
Results
PSE
For one representative participant from Experiment
1, Figure 4 shows the proportion of trials in which the
participant reported that the target bar was growing as
a function of the actual growth of the bar for the Full
Oblique condition and the corresponding psychometric
function that was fit to the data from which the PSE
was interpolated. For the example shown in Figure 4,
the PSE was 12.2%.
Experiment 1: An interaction between size
contrast and other dynamic factors underlies
the DISC effect
In Experiment 1 we sought to reproduce our original
observation with a controlled stimulus and to explore
the contribution of dynamic changes in size contrast,
eye movements, and stimulus motion in modulating the
magnitude of the DISC effect. This experiment
included six conditions (Table 1): Full Oblique, Full
Horizontal, Stationary Bar, Full Opposing Horizontal,
Fixed Eyes, and Pure Size-Contrast. We first consider
the five conditions completed by all subjects and then
consider the Pure Size-Contrast condition at the end of
this section. Overall, the results show that the DISC
effect cannot be completely explained by changes in
Figure 4. Example of a psychometric curve for the Full Oblique
condition from one representative subject. The proportion of
trials in which the participant reported that the target bar was
growing is plotted against the actual growth rate of the bar.
Positive growth rates indicate that the bar was physically
growing, and negative growth rates indicate that the bar was
physically shrinking. The total number of trials performed at
each growth rate across six adaptive staircases is shown across
the top. The raw data (circles) were modeled with a sigmoidal
shaped binomial-logit function (solid gray line). The black arrow
indicates the PSE, defined as the growth rate at which the fitted
curve crossed 0.5 (horizontal dashed gray line). The PSE (12.2%)
represents the growth rate at which the participant had an
equal probability of perceiving the bar as shrinking or growing
for a given condition. If no illusory percept was observed, we
would expect a PSE of zero (vertical dashed gray line). Error bars
represent SEM.
Journal of Vision (2014) 14(3):2, 1–15 Mruczek, Blair, & Caplovitz 9
relative size between the box and the bar. Rather, size
contrast interacts with other dynamic components,
such as eye movements and changes in the spatial
position of the bar, to drive the DISC effect.
Figure 5A shows the mean PSE across participants
for the first five conditions of Experiment 1. PSEs were
significantly greater than zero for all of these conditions
(p,0.013, one-sample Wilcoxon signed rank test)
indicating that the bar had to be physically growing for
participants to perceive it as not changing in length
over the course of the animation. Friedman’s test
revealed a significant difference among the distribu-
tions of PSEs across the five conditions (v
2(4)
¼17.5, p¼
0.0015). We explored this main effect of condition more
closely using a set of a priori comparisons based on the
experimental design and hypotheses for Experiment 1.
The Full Oblique (Movie 1) and Full Horizontal
(Movie 2) versions of the stimulus contained all four
dynamic factors: a relative size change, a change in the
spatial position of the bar, a change in retinal
eccentricity, and eye movements. These conditions were
matched for retinal stimulation, but contained different
motion vectors of the stimulus elements. The magni-
tude of the illusory percept, as quantified by the PSE,
was significantly greater for the oblique motion vector
of the Full Oblique condition (M¼15.2%) than the
horizontal motion vector of the Full Horizontal
condition (M¼10.8%;p¼0.002, permutation test), and
was in fact the most effective stimulus configuration
that we tested. However, given that the remaining
conditions of Experiment 1 all contained horizontal
translations of the stimulus elements, we used the Full
Horizontal condition for comparison.
In the Stationary Bar condition (Movie 3), the
spatial position of the target bar remained fixed
throughout the trial. The PSEs for this condition (M¼
6.5%) were lower than those for the Full Horizontal
condition (M¼10.8%), although this difference was
only marginally significant ( p¼0.055, permutation
test). Thus, when the bar was not translating in space,
the magnitude of the illusion was diminished. This was
not a result of the fact that the eye movement was
directed away from the target bar in the Stationary Bar
condition and towards the target bar in the Full
Horizontal condition. The Full Opposing Horizontal
condition (Movie 4), which also contained an eye
movement directed away from the bar, yielded a PSE
(M¼9.8%) that was significantly larger than for the
Stationary Bar condition (M¼6.5%;p¼0.043,
permutation test), but not significantly different than
those for the Full Horizontal condition (M¼10.8%;p¼
0.53, permutation test). Overall, these results suggest
that a stationary bar diminished the influence of the
expanding box on the perception of the size of the bar.
Figure 5. Mean PSEs for Experiments 1 (A), 2 (B), and 3 (C). The darker bars represent the Full Oblique condition, which was the
identical in all three experiments. Symbols below the bars indicate the significance of one-sample comparisons against zero (Wilcoxon
signed rank test) to test for significant illusory percepts. Symbols above the solid lines indicate the significance of pairwise
comparisons (permutation test), the subset of which was selected based on a priori hypotheses and experimental design. *p,0.05,
#p¼0.055, and n.s.¼nonsignificant difference. Error bars represent 95% confidence intervals.
Journal of Vision (2014) 14(3):2, 1–15 Mruczek, Blair, & Caplovitz 10
One possibility is that retinal image size of a stationary
object can be more easily tracked across other dynamic
changes, such as pursuit eye movements. With less
uncertainty in the size information provided by the
retinal image, less weight is given to the relative size
information provided by the expanding box. However,
as noted above, perception was not veridical in this case
and there was still a significant illusion.
In the Fixed Eyes condition (Movie 5), participants
fixated a stationary spot throughout the duration of the
animation. PSEs for this condition (M¼10.2%) did not
differ significantly from the Full Horizontal condition (M
¼10.8%;p¼0.64, permutation test). This suggests that eye
movements are not a necessary component for the DISC
effect. However, as can be experienced in Movie 6, we
noted that there was little-to-no illusory effect when the
expanding box was the only dynamic component in the
stimulus. In other words, the DISC effect is more than a
straightforward illusion of size contrast.
To confirm this observation, we ran six of the
participants from Experiment 1 in this Pure Size-
Contrast condition (Movie 6) in a separate session.
PSEs for the Pure Size-Contrast condition did not
differ significantly from zero (M¼4.5%,p¼0. 25, one-
sample Wilcoxon signed rank test; note also that one
participant had a very large PSE of 21.6%, which
skewed the overall mean), indicating that perception
was generally veridical in this condition. Moreover,
PSEs for this condition were significantly lower than
PSEs derived from the same six subjects in the
Stationary Bar condition (Movie 3; M¼11.1%;p¼
0.031). Thus, the relative size change between the box
and the bar was not sufficient to drive the DISC effect
and, importantly, cannot account for illusory percept in
the Stationary Bar condition. Rather, it is the
interaction between the relative size change and other
dynamic factors such as eye movements and motion of
the target bar that underlies the DISC effect.
Experiment 2: Changes in surround size are
necessary for the DISC effect
Experiment 1 showed that size contrast is not
sufficient to explain the DISC effect. However, the
results do not address whether size contrast is a
necessary component. In Experiment 2 we investigate
this question, as well as the potential role of dynamic
changes in target eccentricity in the DISC effect. This
experiment included three conditions (Table 1): Full
Oblique, Constant Eccentricity, and Rigid Box. Over-
all, the results show that changes in relative size, but
not eccentricity, are necessary for the DISC effect.
Figure 5B shows the mean PSE across participants for
all conditions of Experiment 2. First, it is worth noting
that the effect for the Full Oblique condition of
Experiments 1 and 2 are of similar magnitudes
demonstrating the robust and replicable nature of the
DISC effect. In Experiment 2, PSEs were significantly
greater than zero for the Full Oblique condition (Movie
1, p¼0.003, one-sample Wilcoxon signed rank test) and
the Constant Eccentricity (Movie 7, p¼0.01, one-sample
Wilcoxon signed rank test) indicating that in both cases
the bar had to be physically growing for participants to
perceive it as not changing in length over the course of
the animation. In contrast, PSEs for the Rigid Box
condition (Movie 8) did not differ significantly from zero
(p¼0.83, one-sample Wilcoxon signed rank test),
indicating that perception was generally veridical in this
condition. Friedman’s test revealed a significant differ-
ence among the distributions of PSEs across the three
conditions (v
2(2)
¼16.9, p¼0.0002). We explored this
main effect of condition more closely using a set of a
priori comparisons based on the experimental design
and hypotheses for Experiment 2.
PSEs for the Constant Eccentricity condition (M¼
16.4%) did not differ significantly from the Full
Oblique condition (M¼15.6%;p¼0.91, permutation
test). Thus, keeping the target bar at a fixed eccentricity
relative to fixation spot did not have a significant effect
on the magnitude of the illusion. Although this suggests
that eccentricity is not a necessary component, changes
in target eccentricity may be one dynamic factor that
interacts with the expanding surround to drive the
DISC effect (see Pure Size Contrast above).
PSEs for the Rigid Box condition (M¼2.4%) were
significantly lower than those for the Full Oblique
condition (M¼15.6%;p¼0.03, permutation test).
When the size of the box is held constant, observers do
not experience illusory percepts of size at all, even in the
presence of other stimulus motion and eye movements.
Thus, the dynamic change in the size of the surround-
ing box is indeed a primary and necessary component
to produce the DISC effect. In conjunction with the
observations from the Pure Size-Contrast condition
above, these data demonstrate that size contrast is a
necessary factor, but by itself cannot sufficiently
explain the magnitude of the illusory percept.
Experiment 3: The DISC effect depends on the
dynamic nature of the stimulus
In Experiment 3, we sought to verify that the
dynamic nature of the stimulus is a key factor driving
the DISC effect. This experiment included two condi-
tions (Table 1): Full Oblique and Static Frames. The
results show that the DISC effect is only observed
under dynamic stimulus conditions.
Figure 5C shows the mean PSE across participants
for both conditions of Experiment 3. PSEs were
significantly greater than zero for Full Oblique condition
Journal of Vision (2014) 14(3):2, 1–15 Mruczek, Blair, & Caplovitz 11
(Movie 1, p¼0.001, one-sample Wilcoxon signed rank
test), replicating the results from Experiments 1 and 2. In
contrast, PSEs for the Static Frames condition (Movie 9)
did not differ significantly from zero ( p¼0.90, one-
sample Wilcoxon signed rank test), indicating that
perception was generally veridical in this condition. A
paired comparison between these two conditions re-
vealed that PSEs for the Full Oblique condition (M¼
19.0%) were significantly higher than for the Static
Frames condition (M¼1.8%;p¼0.001, permutation
test). This demonstrates that the dynamic nature of the
DISC stimulus is a principal factor contributing to the
illusory percept, distinguishing it from static size-
contrast illusions (see also Movie 1 and Figure 2).
Discussion
Here we introduce a novel size-contrast illusion
termed the DISC effect, which reveals that under
certain circumstances a dynamic and continuous
change in the size of a surrounding object dramatically
influences the perceived size of an inner target object
(Movie 1). Our results show that this illusion is robust
and reproducible, occurring across a variety of dynamic
manipulations of the stimulus.
We identified four dynamic changes that may
contribute to the magnitude of the DISC effect: (a) the
relative size change between surrounding box and inner
bar; (b) the change in the real-world position of the bar;
(c) the change in retinal eccentricity of the bar; and (d)
the execution of a smooth pursuit/saccadic eye
movements. By systematically removing each of these
factors from the full version of the stimulus, we show
that the DISC effect is primarily driven by the change
in relative size between the surrounding box and the
inner bar, but that the illusion requires the presence of
additional dynamic factors.
The relative size change between the surrounding
box and the inner bar appears to be a necessary factor
for the DISC effect, as indicated by the fact that there
was no illusory percept of bar size when the
surrounding box was static and unchanging (Experi-
ment 2, Rigid Box condition, Movie 8). However,
although the relative size change was necessary for the
DISC effect, it was not sufficient; in isolation, an
expanding box did not alter the perception of the bar’s
length (Experiment 1, Pure Size-Contrast condition,
Movie 6). Thus, the DISC effect is a size-contrast
illusion that is driven by the interaction between a
relative size change and other dynamic factors, such as
eye movements and stimulus motion.
The magnitude of the illusion was not diminished in
the Fixed Eyes condition, which did not include eye
movements (Movie 5). This is perhaps surprising, given
the spatial distortions that can occur during smooth
pursuit and saccadic eye movements (Hamker, Zirnsak,
Ziesche, & Lappe, 2011; Schutz, Braun, & Gegenfurt-
ner, 2011). However, it is not clear that the types of
spatial distortions previously reported during eye
movements would affect the perceived vertical extent of
a moving bar. It remains an open question as to
whether the vertical component of the eye movement is
a contributing factor to our observation of the largest
magnitude illusion in the Full Oblique stimulus.
As with eye movements, the magnitude of the illusion
was not diminished when changes in target eccentricity
were removed in the Constant Eccentricity condition
(Movie 7). Although there is some evidence that the size
of an object is perceived to be smaller for peripheral
stimuli (Bedell & Johnson, 1984; James, 1890; Helm-
holtz, 1867), this effect is modest and our data indicate
that it is not a principal factor for the DISC effect.
Interestingly, when the target bar was not translating
in real-world coordinates (Stationary Bar condition,
Movie 3), and the other three dynamic features were
present, the magnitude of the illusion was diminished.
Thus, whereas some form of additional stimulus
motion in conjunction with the relative size change is
necessary for the illusion, a change in the real-world
position of the bar seems to be particularly effective.
In the case of size perception, environmental cues
(e.g., changes in retinal image size, relative size, and
perceived depth) may drive the internal representation
of an object’s size to be updated, if such cues are strong
enough. Our data show that certain cues, such as
relative size, may be weak and ineffective under some
conditions, but robustly effective under others. What
aspect of the DISC stimulus is triggering the illusion
and leading to the pattern of results that we observed?
We propose that the visual system is weighting the
different sources of information that contribute to size
perception based on the level of uncertainty in the
retinal image size of the object. Whereas the growing
box normally has a weak influence on the perceived size
of the target bar, this influence is enhanced when other
dynamic changes in the environment lead to uncer-
tainty in the retinal size of the bar. Smooth pursuit and
saccades lead to retinal jitter and the need to cancel out
motion induced by eye movements. Changes in target
eccentricity require the integration of the retinal image
across different portions of the retina to track the same
object. Both of these contribute to noise in the retinal
image size of an object, and therefore, the need to
inform size judgments based on other available
information. Interestingly, the retinal image of a
stationary bar in real-world coordinates, even in the
presence of eye movements and increasing target
eccentricity, appears to be tracked more easily, leading
to less uncertainty and a weaker illusory effect.
Journal of Vision (2014) 14(3):2, 1–15 Mruczek, Blair, & Caplovitz 12
An alternative explanation for the observed pattern of
results may be that in conditions in which we observed
an illusory effect the target bar was perceptually grouped
with the contextual surround. However, an objective
rule that governs this grouping is not obvious. First, the
conditions of Experiment 1 (excluding the Pure Size-
Contrast condition) were matched for retinal stimula-
tion. Thus, the configural relationship between the target
bar and the surrounding box was consistent across
conditions; in each case the target bar was encapsulated
by the expanding box and always at the same relative
distance from its edge. Second, as can be experienced by
viewing the movie demos (e.g., Full Horizontal condi-
tion, Movie 2), the magnitude of the illusion is greatly
diminished by fixating the target bar rather than the red
fixation point. It is unclear why this would lead to the
target bar being ‘‘ungrouped’’ from the expanding box.
In contrast, this observation is nicely explained by the
retinal uncertainty hypothesis outlined above because
visual acuity is greatly enhanced near the fovea. Thus,
we conclude that the DISC effect represents a novel
illusion that is driven by the interaction between size
contrast and other dynamic factors that increase retinal
uncertainty.
Throughout this manuscript, we have considered the
DISC effect to be fundamentally a size-contrast illusion.
However, an alternative explanation may be one of
dynamic size constancy. One might argue that the
expanding box in the DISC stimulus is consistent with
the stimulus getting closer, and since the retinal image of
the bar is not growing as expected, the bar is perceived
to be shrinking. This is the explanation put forth for two
perceptually related illusions, the shrinking building
illusion (Fukuda & Seno, 2011), in which a distant
building viewed through a window appears to shrink as
you move closer to the window, and the StarTrek
Illusion (Qian & Petrov, 2012), in which dots in an
expanding optic flow field appear to shrink (as well as
increase in brightness). Both illusions are driven
primarily by changes in perceived depth due to self-
motion (shrinking building illusion, Fukuda & Seno,
2011) or optic flow cues (StarTrek illusion, Qian &
Petrov, 2012). Schrater, Knill, and Simoncelli (2001)
showed that changes in stimulus size (i.e., ‘‘scale-change’
information) could substitute for optic flow information
and influence perceived depth. In addition, in the
Constant Eccentricity condition (Movie 7), there is an
illusory reduction in the distance between the fixation
spot and the bar as the box expands, which is consistent
with a size constancy effect. However, we feel that size
constancy does not offer a compelling explanation of the
DISC effect. First, it is the authors’ impression, and the
reader may concur by viewing the movie demos (see
Movie 1, best viewed in ‘‘looped’’ mode), that the DISC
stimulus does not induce a strong perceived change in
depth, unless the observer exerts great top-down
influence. The observer may also notice that if they are
able to self-induce modulations in perceived depth the
magnitude of the size illusion is not greatly affected. We
note, however, that the size contrast and size constancy
hypotheses make similar predictions in many cases.
Given that we did not explicitly control or quantify
perceived distance in our experiment, fully dissociating
these competing hypotheses is left to future studies.
Although the dynamic nature of the illusion is
dependent on the presence of motion in the stimulus
(see Experiment 3), we noticed that a smooth change in
the stimulus is not critical, as long as there was a
perception of motion of the stimulus components. As
seen in Movie 10, the illusion is subjectively strong
when the two frames depicting the endpoints of the Full
Oblique condition (Figure 2) are presented sequentially
and without a delay between frames. Under these
conditions, there is an induction of apparent transfor-
mational motion (Hikosaka, Miyauchi, & Shimojo,
1991; Tse, Cavanagh, & Nakayama, 1998). In apparent
transformational motion, although there is no actual
motion between the two frames, the perception is of a
continuously, though quickly, changing form from one
frame to the next. In our case, the size of the box is
perceived to rapidly expand and contract. Thus, we
would expect that any stimulus that activates the neural
circuits for motion perception (Tse, 2006) would be
sufficient for the DISC effect.
Finally, it is worth noting the DISC effect may
asymptote over the course of the dynamic animation
period that we selected. In the case where the target bar
Movie 10: Apparent transformational motion stimulus. The DISC
illusion can be observed when two static frames are presented
sequentially and without a delay between frames. Click on the
image to view the movie. Movies are best viewed in looped
mode.
Journal of Vision (2014) 14(3):2, 1–15 Mruczek, Blair, & Caplovitz 13
was actually growing, some of our participants reported
that there was initially a strong percept of a shrinking
bar followed by a percept of a growing bar. If subjects
based their responses on the perceived physical change
in the size of the target observed at the very end of these
trials, despite having observed an illusory shrinkage of
the target at the beginning of the trial, this would lead to
an underestimation of the magnitude of the DISC effect.
This may explain why the DISC effect is subjectively
more compelling than static size-contrast illusions, yet
the empirically derived magnitude of the DISC effect in
our strongest (Full Oblique) configuration (M¼16.4%
across Experiments 1, 2, and 3) is comparable to
reported magnitudes for classic size-contrast illusions,
such as the Ebbinghaus illusion (up to ;18%,Robertset
al., 2005). The reader may experience the qualitative
difference between these illusions for himself or herself
by comparing the percept produced by the classic size-
contrast illusions presented in Figure 1 and that of the
DISC stimulus in Movie 1. Consistent with this
subjective sensation, the non-dynamic Static Frames
version of our stimulus (Experiment 3, Movie 9) led to
no illusory percept (see also Figure 2).
Conclusion
In conclusion, the DISC effect demonstrates that the
contribution of relative size to judgments of stimulus
size is modulated by other dynamic factors, including
changes in the spatial position and retinal eccentricity
of a target object and the execution of eye movements.
Given the compelling nature of this effect and the
inherently dynamic nature of our visual environment,
these factors are likely to play an important role in
everyday size judgments.
Keywords: size perception, form-motion interaction,
size illusion, motion illusion
Acknowledgments
This work was supported by an Institutional
Development Award (IDeA) from the National Insti-
tute of General Medical Sciences of the National
Institutes of Health (1P20GM103650-01) and a grant
from the National Eye Institute of the National
Institutes of Health (1R15EY022775).
Commercial relationships: none.
Corresponding author: Ryan E. B. Mruczek.
Email: rmruczek@unr.edu.
Address: Department of Psychology, University of
Nevada, Reno, Reno, NV, USA.
References
Anstis, S., Gori, S., & Wehrhahn, C. (2007). Afterim-
ages and the breathing light illusion. Perception,
36(5), 791–794.
Ashida, H., Kuraguchi, K., & Miyoshi, K. (2013).
Helmholtz illusion makes you look fit only when
you are already fit, but not for everyone. i-
Perception,4(5), 347–351, doi:10.1068/i0595rep.
Bedell, H. E., & Johnson, C. A. (1984). The perceived
size of targets in the peripheral and central visual
fields. Ophthalmic & Physiological Optics,4(2),
123–131.
Berryhill, M. E., Fendrich, R., & Olson, I. R. (2009).
Impaired distance perception and size constancy
following bilateral occipitoparietal damage. Ex-
perimental Brain Research,194(3), 381–393, doi:10.
1007/s00221-009-1707-7.
Boring, E. (1940). Size constancy and Emmert’s law.
American Journal of Psychology,53(2), 293–295.
Brainard, D. H. (1997). The Psychophysics Toolbox.
Spatial Vision,10(4), 433–436.
Burton, G. (2001). The tenacity of historical misinfor-
mation: Titchener did not invent the Titchener
illusion. History of Psychology,4(3), 228.
Caplovitz, G. P., Paymer, N. A., & Tse, P. U. (2008).
The drifting edge illusion: A stationary edge
abutting an oriented drifting grating appears to
move because of the ‘‘other aperture problem.’
Vision Research,48(22), 2403–2414, doi:10.1016/j.
visres.2008.07.014.
Caplovitz, G. P., & Tse, P. U. (2007). Rotating dotted
ellipses: Motion perception driven by grouped
figural rather than local dot motion signals. Vision
Research,47(15), 1979–1991, doi:10.1016/j.visres.
2006.12.022.
Coren, S., & Girgus, J. S. (1978). Seeing is deceiving:
The psychology of visual illusions. Hillsdale, NJ:
Lawrence Erlbaum.
Delboeuf, M. J. (1892). Sur une nouvelle illusion
d’optique [On a new optical illusion]. Bulletin de
l’Acad ´
emie Royale de Belgique,24(3), 545–558.
Emmert, E. (1881). Gr¨
ossenverh¨
altnisse der Nachbilder
[Translation: Size relationships of afterimages].
Klinische Monatsbl ¨
atter f ¨
ur Augenheilkunde und f ¨
ur
augen ¨
arztliche Fortbildung,19, 443–450.
Fukuda, H., & Seno, T. (2011). Shrinking neighbors: A
quantitative examination of the ‘‘shrinking building
illusion.’’ Seeing & Perceiving,24(6), 541–544, doi:
10.1163/187847611X603756.
Giora, E., & Gori, S. (2010). The perceptual expansion
of a filled area depends on textural characteristics.
Vision Research,50(23), 2466–2475, doi:10.1016/j.
visres.2010.08.033.
Journal of Vision (2014) 14(3):2, 1–15 Mruczek, Blair, & Caplovitz 14
Gori, S., Giora, E., & Agostini, T. (2010). Measuring
the breathing light illusion by means of induced
simultaneous contrast. Perception,39(1), 5–12.
Gori, S., & Stubbs, D. A. (2006). A new set of
illusions—The dynamic luminance-gradient illusion
and the breathing light illusion. Perception,35(11),
1573–1577.
Hamker, F. H., Zirnsak, M., Ziesche, A., & Lappe, M.
(2011). Computational models of spatial updating
in peri-saccadic perception. Philosophical Transac-
tions of the Royal Society of London B: Biological
Sciences,366(1564), 554–571, doi:10.1098/rstb.
2010.0229.
Helmholtz, H. von. (1867). Handbuch der physiologi-
schen optik [Translation: Treatise on Physiological
Optics] (1st ed.). (J. P. L. Southhall, Trans.).
Leipzig: Voss.
Hikosaka, O., Miyauchi, S., & Shimojo, S. (1991).
Focal visual attention produces motion sensation in
lines. Investigative Ophthalmology & Visual Science,
22(Suppl), 144.
James, W. (1890). Principles of psychology (Vol. II).
London: Macmillan.
Konkle, T., & Oliva, A. (2012). A familiar-size Stroop
effect: Real-world size is an automatic property of
object representation. Journal of Experimental
Psychology: Human Perception & Performance,
38(3), 561–569, doi:10.1037/a0028294.
Kundt, A. (1863). Untersuchungen ¨
uber Augenmass
und optische T¨
auschungen [Translation: Studies on
visual judgment and optical illusions]. Poggendorffs
Annalen der Physik u Chemie,120(30), 118–158.
Leek, M. R. (2001). Adaptive procedures in psycho-
physical research. Perception & Psychophysics,
63(8), 1279–1292.
Leek, M. R., Hanna, T. E., & Marshall, L. (1992).
Estimation of psychometric functions from adap-
tive tracking procedures. Perception & Psycho-
physics,51(3), 247–256.
Lotze, R. H. (1852). Medicinische psychologie oder
Physiologie der Seele [Translation: Medical psy-
chology or physiology of the soul]. Leipzig: Weide-
mann.
McCarthy, J. D., Kupitz, C., & Caplovitz, G. P. (2013).
The binding ring illusion: Assimilation affects the
perceived size of a circular array. F1000 Research,
2(58), 1–15, doi:10.12688/f1000research.2-58.v2.
Oppel, J. J. (1855). ¨
Uber geometrisch-optische
t¨
auschungen [Translation: On geometrical-optical
illusions]. Jahresbericht des physikalischen Vereins
zu Frankfurt am Main, pp. 39–47.
Pelli, D. G. (1997). The VideoToolbox software for
visual psychophysics: Transforming numbers into
movies. Spatial Vision,10(4), 437–442.
Ponzo, M. (1911). Intorno ad alcune illusioni nel
campo delle sensazioni tattili sull’illusione di
Aristotele e fenomeni analoghi [Translation: On
some illusions in the field of tactile sensations on
the illusion of Aristotle and similar phenomena].
Archive f ¨
ur die Gesamte Psychologie,16, 307–345.
Qian, J., & Petrov, Y. (2012). StarTrek illusion—
General object constancy phenomenon? Journal of
Vision,12(2):15, 1–10, http://www.journalofvision.
org/content/12/2/15, doi:10.1167/12.2.15.
[PubMed][Article]
Roberts, B., Harris, M. G., & Yates, T. A. (2005). The
roles of inducer size and distance in the Ebbinghaus
illusion (Titchener circles). Perception,34(7), 847–
856.
Robinson, J. O. (1972). The psychology of visual
illusions. London: Hutchinson Education.
Schrater, P. R., Knill, D. C., & Simoncelli, E. P. (2001).
Perceiving visual expansion without optic flow.
Nature,410(6830), 816–819, doi:10.1038/35071075.
Schutz, A. C., Braun, D. I., & Gegenfurtner, K. R.
(2011). Eye movements and perception: A selective
review. Journal of Vision,11(5):9, 1–30, http://
www.journalofvision.org/content/11/5/9, doi:10.
1167/11.5.9. [PubMed][Article]
Thi´
ery, A. (1896). ¨
Uber geometrisch-optische
T¨
auschungen [On geometric-optical illusions]. Phi-
losophische Studien,12, 67–126.
Thompson, P., & Mikellidou, K. (2011). Applying the
Helmholtz illusion to fashion: Horizontal stripes
won’t make you look fatter. i-Perception,2(1), 69–
76, doi:10.1068/i0405.
Tse, P. U. (2006). Neural correlates of transformational
apparent motion. Neuroimage,31(2), 766–773.
Tse, P. U., Cavanagh, P., & Nakayama, K. (1998). The
role of parsing in high-level motion processing. In
T. Wantanabe (Ed.), High-level motion processing:
Computational, neurobiological, and psychometric
perspectives (pp. 249–266). Cambridge, MA: MIT
Press.
van Ittersum, K., & Wansink, B. (2012). Plate size and
color suggestibility: The Delboeuf illusion’s bias on
serving and eating behavior. Journal of Consumer
Research,39(2), 215–228.
Westheimer, G. (2008). Illusions in the spatial sense of
the eye: Geometrical-optical illusions and the
neural representation of space. Vision Research,
48(20), 2128–2142, doi:10.1016/j.visres.2008.05.016.
Wichmann, F. A., & Hill, N. J. (2001). The psycho-
metric function: I. Fitting, sampling, and goodness
of fit. Perception & Psychophysics,63(8), 1293–
1313.
Journal of Vision (2014) 14(3):2, 1–15 Mruczek, Blair, & Caplovitz 15
... We recently introduced a novel illusion called the Dynamic Illusory Size-Contrast (DISC) effect, which highlights the role of dynamic visual information in modulating the contribution of different sources of information in determining the perceived size of an object (Mruczek et al., 2014). In the DISC effect, the viewer perceives the size of a target bar to be shrinking when (1) it is surrounded by an expanding box and (2) there are additional dynamic cues such as eyes movements or bar motion (Figure 2). ...
... The stimulus configuration depicted here matches the one used for the Static condition of Experiment 1, in which participants adjusted the physical size of the center circle on the left to perceptual match the size of the central circle on the right. (Mruczek et al., 2014). The information uncertainty hypothesis suggests that the DISC effect should not be limited to the specific stimulus we originally examined. ...
... In stark contrast, adding target motion by having the entire stimulus translate across the screen led to an illusory effect size (∼37%, Dynamic-Moving condition) that was almost twice that of the classic static Ebbinghaus. It is this huge discrepancy between the Stationary and Moving dynamic conditions, also replicated in Experiment 2 (∼5 vs. ∼35%), that exemplifies what we have previously termed the Dynamic Illusory Size Contrast (DISC) effect (Mruczek et al., 2014). By itself, a dynamic change in the inducers is insufficient for strongly biasing perception. ...
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The Ebbinghaus illusion is a classic example of the influence of a contextual surround on the perceived size of an object. Here, we introduce a novel variant of this illusion called the Dynamic Ebbinghaus illusion in which the size and eccentricity of the surrounding inducers modulates dynamically over time. Under these conditions, the size of the central circle is perceived to change in opposition with the size of the inducers. Interestingly, this illusory effect is relatively weak when participants are fixating a stationary central target, less than half the magnitude of the classic static illusion. However, when the entire stimulus translates in space requiring a smooth pursuit eye movement to track the target, the illusory effect is greatly enhanced, almost twice the magnitude of the classic static illusion. A variety of manipulations including target motion, peripheral viewing, and smooth pursuit eye movements all lead to dramatic illusory effects, with the largest effect nearly four times the strength of the classic static illusion. We interpret these results in light of the fact that motion-related manipulations lead to uncertainty in the image size representation of the target, specifically due to added noise at the level of the retinal input. We propose that the neural circuits integrating visual cues for size perception, such as retinal image size, perceived distance, and various contextual factors, weight each cue according to the level of noise or uncertainty in their neural representation. Thus, more weight is given to the influence of contextual information in deriving perceived size in the presence of stimulus and eye motion. Biologically plausible models of size perception should be able to account for the reweighting of different visual cues under varying levels of certainty.
... We recently described a novel illusory effect that we term dynamic illusory size contrast, or the DISC effect, which highlights the role of dynamic visual information in modulating the contribution of different cues to perceived size (Mruczek, Blair, & Caplovitz, 2014;Mruczek, Blair, Strother, & Caplovitz, 2017a). In the DISC effect, the viewer perceives a target object to be dramatically shrinking when (1) it is surrounded by an expanding context and (2) there are additional dynamic cues such as eyes movements or target motion. ...
... Considering these empirical observations, we have proposed the precision hypothesis (previously referred to as the uncertainty hypothesis; Mruczek et al., 2014;Mruczek et al., 2015Mruczek et al., , 2017a. This hypothesis states that the precision of the representation of an object's angular size will influence how it will interact with representations of the surrounding context. ...
... We have previously proposed (Mruczek et al., 2014;Mruczek et al., 2015) that the dynamic motion of the target results in a less precise representation of that target. To support this contention in the context of the current experiment, we extracted a quantitative behavioral metric of precision-namely, the maximum slope of the psychometric curves (i.e., the slope at the inflection point). ...
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Full-text available
We recently showed that motion dynamics greatly enhance the magnitude of certain size contrast illusions, such as the Ebbinghaus and Delboeuf illusions. Here, we extend our study of the effect of motion dynamics on size illusions through a novel dynamic corridor illusion, in which a single target translates along a corridor background. Across three psychophysical experiments, we quantify the effects of stimulus dynamics on the Ebbinghaus and corridor illusions across different viewing conditions. The results revealed that stimulus dynamics had opposite effects on these different classes of size illusions. Whereas dynamic motion enhanced the magnitude of the Ebbinghaus illusion, it attenuated the magnitude the corridor illusion. Our results highlight precision-driven weighting of visual cues by neural circuits computing perceived object size. This hypothesis is consistent with observations beyond size perception and may represent a more general principle of cue integration in the visual system.
... Results showed that the lengths of the objects were consistently underestimated during the exposure to auditory motion cues increasing in intensity and bandwidth, and therefore compatible with forward self-motion. This phenomenon resembles the dynamic Ebbinghaus illusion, which was recently reported by Mruczek and colleagues 24,25 . They modified the classic Ebbinghaus illusion so that the target object was surrounded by an array of similar objects that expanded and contracted in size and bandwidth. ...
... In the dynamic Ebbinghaus illusion, the concept of motion is introduced as another factor that can influence the construction of the perceived size of the target object. Mruczek and colleagues 24,25 showed that the target object was perceived to be smaller as the surrounding objects increased in size, much like what was observed in our experiments. The dynamic Ebbinghaus illusion 24,25 reveals the prominent role of motion information in determining visual representations of object size. ...
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Full-text available
Changes in the retinal size of stationary objects provide a cue to the observer’s motion in the environment: Increases indicate the observer’s forward motion, and decreases backward motion. In this study, a series of images each comprising a pair of pine-tree figures were translated into auditory modality using sensory substitution software. Resulting auditory stimuli were presented in an ascending sequence (i.e. increasing in intensity and bandwidth compatible with forward motion), descending sequence (i.e. decreasing in intensity and bandwidth compatible with backward motion), or in a scrambled order. During the presentation of stimuli, blindfolded participants estimated the lengths of wooden sticks by haptics. Results showed that those exposed to the stimuli compatible with forward motion underestimated the lengths of the sticks. This consistent underestimation may share some aspects with visual size-contrast effects such as the Ebbinghaus illusion. In contrast, participants in the other two conditions did not show such magnitude of error in size estimation; which is consistent with the “adaptive perceptual bias” towards acoustic increases in intensity and bandwidth. In sum, we report a novel cross-modal size-contrast illusion, which reveals that auditory motion cues compatible with listeners’ forward motion modulate haptic representations of object size.
... Similarly, the orientation of local Gaussian blobs translating across the visual field can influence the perceived shape of an object they are grouped into (McCarthy, Cordeiro, & Caplovitz, 2012). Moreover, adding translational motion to classic illusions, such as the Ebbinghaus Illusion, results in a more robust illusory size distortion (Mruczek, Blair, & Caplovitz, 2014). Experiments 2 to 5 in the current study shows that for a static display, a feature of the component elements, triangle orientation, can influence the perceived size of the global percept. ...
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To accomplish the deceptively simple task of perceiving the size of objects in the visual scene, the visual system combines information about the retinal size of the object with several other cues, including perceived distance, relative size, and prior knowledge. When local component elements are perceptually grouped to form objects, the task is further complicated because a grouped object does not have a continuous contour from which retinal size can be estimated. Here, we investigate how the visual system solves this problem and makes it possible for observers to judge the size of perceptually grouped objects. We systematically vary the shape and orientation of the component elements in a two-alternative forced-choice task and find that the perceived size of the array of component objects can be almost perfectly predicted from the distance between the centroids of the component elements and the center of the array. This is true whether the global contour forms a circle or a square. When elements were positioned such that the centroids along the global contour were at different distances from the center, perceived size was based on the average distance. These results indicate that perceived size does not depend on the size of individual elements, and that smooth contours formed by the outer edges of the component elements are not used to estimate size. The current study adds to a growing literature highlighting the importance of centroids in visual perception and may have implications for how size is estimated for ensembles of different objects.
... Geometric biases of size perception, one of the most frequently discussed consequences of visual frames (Gillam, 1980;Mruczek, Blair, & Caplovitz, 2014), are the focus of this study. Here, a contextual frame induces a distorted size perception of a target stimulus in the same scene (Brigell, Uhlarik, & Goldhorn, 1977;Gillam, 1980). ...
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Perceived product size is a key concern in online retail, particularly in fashion and grocery. The screen on which consumers view a product (e.g., desktop or mobile) might constitute a frame that biases size perception, on the basis of assimilation and contrast effects (pool and store theory). The rise of mobile commerce exacerbates this issue, as framing effects might be stronger versus desktop settings as screens are smaller. Further, as mobile phone's screen orientation varies situationally (vertical vs. horizontal), the perceived product size might vary, depending on the interaction of screen and product orientation. By introducing the framing ratio as a means to predict extent, dimensionality and symmetry of size biases, we generalize specific findings from extant research. Empirically, four experimental studies demonstrate that contextual frames (i.e., vertical vs. horizontal screens) and product orientation (e.g., jeans vs. shoes) interact to bias the size perception, in that sizes are overestimated on the dimension that approaches the frame (high framing ratio), compared with conditions where the frame is distant (low framing ratio). If product size is misperceived, willingness to pay might be affected (e.g., for groceries). Thus, size perceptions have a direct impact on managerially relevant variables.
... Given the assumption of stability, which is prioritized by the visual system (Glennerster et al., 2006), any signal of change might be ignored when one is faced with information indicating a stable environment. This possibility could be tested by examining whether action-specific effects are noticeable in conditions that do not specify stability, such as was done with the Dynamic Ebbinghaus illusion (Blair et al., 2014). Virtual environments might be useful in this case, as they can be rendered with varying degrees of stability. ...
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Golf holes look larger to golfers who are playing better than others, and hills look steeper to people who are fatigued from a long run-or so claims the action-specific account of perception. According to this account, spatial perception of slant, distance, and size is influenced by the perceiver's ability to perform actions such as walking, throwing, or grasping. This claim is based on empirical findings that observers report hills as steeper, distances as farther, and objects as smaller when they are less capable of acting on the objects. Recently, Firestone (2013) challenged the claim that these reports reflect genuine differences in perception. One argument he levied against a perceptual interpretation is that people are not aware of these perceptual differences related to action, and they should be. Here, I argue that awareness is not a necessary condition for an effect to be perceptual, as evidenced by a lack of awareness in the case of a classic visual illusion. However, to make a strong claim for genuine effects in perception, the action-specific account must specify a perceptual mechanism, and it has yet to do so.
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Urbanisation is growing rapidly. We review evidence that this growth is altering the default information processing style of human beings by impacting both overt and covert processes of attentional selection (i.e. attentional selection with and without eye movements respectively), in ways consistent with reduced attentional engagement and increased exploration. While the factors and systems mediating these effects are likely to be many and various, we focus on one system which may be responsible for mediating effects on both covert and overt attentional selection. Specifically, the neuromodulatory locus coeruleus-norepinephrine (LC-NE) system is key to regulating cognitive function in a behaviourally relevant and arousal-dependent manner and therefore well suited to supporting adaptation to the profound socio-ecological changes inherent in urbanisation.
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The psychometric function relates an observer’s performance to an independent variable, usually some physical quantity of a stimulus in a psychophysical task. This paper, together with its companion paper (Wichmann & Hill, 2001), describes an integrated approach to (1) fitting psychometric functions, (2) assessing the goodness of fit, and (3) providing confidence intervals for the function’s parameters and other estimates derived from them, for the purposes of hypothesis testing. The present paper deals with the first two topics, describing a constrained maximum-likelihood method of parameter estimation and developing several goodness-of-fit tests. Using Monte Carlo simulations, we deal with two specific difficulties that arise when fitting functions to psychophysical data. First, we note that human observers are prone to stimulus-independent errors (orlapses). We show that failure to account for this can lead to serious biases in estimates of the psychometric function’s parameters and illustrate how the problem may be overcome. Second, we note that psychophysical data sets are usually rather small by the standards required by most of the commonly applied statistical tests. We demonstrate the potential errors of applying traditionalX 2 methods to psychophysical data and advocate use of Monte Carlo resampling techniques that do not rely on asymptotic theory. We have made available the software to implement our methods.
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Our perception of an object's size arises from the integration of multiple sources of visual information including retinal size, perceived distance and its size relative to other objects in the visual field. This constructive process is revealed through a number of classic size illusions such as the Delboeuf Illusion, the Ebbinghaus Illusion and others illustrating size constancy. Here we present a novel variant of the Delbouef and Ebbinghaus size illusions that we have named the Binding Ring Illusion. The illusion is such that the perceived size of a circular array of elements is underestimated when superimposed by a circular contour - a binding ring - and overestimated when the binding ring slightly exceeds the overall size of the array. Here we characterize the stimulus conditions that lead to the illusion, and the perceptual principles that underlie it. Our findings indicate that the perceived size of an array is susceptible to the assimilation of an explicitly defined superimposed contour. Our results also indicate that the assimilation process takes place at a relatively high level in the visual processing stream, after different spatial frequencies have been integrated and global shape has been constructed. We hypothesize that the Binding Ring Illusion arises due to the fact that the size of an array of elements is not explicitly defined and therefore can be influenced (through a process of assimilation) by the presence of a superimposed object that does have an explicit size.