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The artist emerges: Visual art learning alters neural structure and function

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The artist emerges: Visual art learning alters neural structure
and function
Alexander Schlegel
a,
, Prescott Alexander
a
, Sergey V. Fogelson
a
,XuetingLi
a,b
,ZhengangLu
a
, Peter J. Kohler
a
,
Enrico Riley
c
, Peter U. Tse
a
,MingMeng
a
a
Dartmouth College, Department of Psychological and Brain Sciences, Hanover, NH 03755, USA
b
Beijing Normal University, National Key Laboratory of Cognitive Neuroscience and Learning, Beijing 100875, China
c
Dartmouth College, Studio Art Department, Hanover, NH 03755, USA
abstractarticle info
Article history:
Accepted 7 November 2014
Available online 15 November 2014
Keywords:
Art
Creative cognition
Perception
Perception-to-action
Plasticity
White matter
Cerebellum
Motor cortex
DTI
fMRI
MVPA
How does the brain mediate visual artistic creativity? Here we studied behavioraland neural changes indrawing
and painting students compared to students who did not study art. We investigated three aspects of cognition
vital to many visual artists: creative cognition, perception, and perception-to-action. We found that the art stu-
dents became more creative via the reorganization of prefrontal white matter but did not nd any signicant
changes in perceptual ability or related neural activity in the art studentsrelative to the control group. Moreover,
the art students improved in their ability to sketch human gures from observation, and multivariate patterns of
cortical and cerebellar activity evoked by this drawing task became increasingly separable between art and non-
art students. Our ndings suggest that the emergence of visual artistic skills is supported by plasticity in neural
pathways that enable creative cognition and mediate perceptuomotor integration.
© 2014 Elsevier Inc. All rights reserved.
Introduction
Art is a complex and uniquely human phenomenon. The creation of
artistic work has historically been a mysterious and poorly understood
process, often even by artists themselves (Stiles and Selz, 2012). How-
ever, according to central tenets of neuroscience, the work of an artist
must be mediated by the brain. How does the brain support the cogni-
tive skills necessary to create art?
Art has appeared in many forms throughout human history. The qual-
ities that distinguish artistic work are thus often difcult to dene. For ex-
ample, while some trompe l'oeil painters such as William Harnett
(Frankenstein, 1953) attain an astounding ability to recreate visual scenes
accurately, representation for other painters such as abstract expression-
ist Barnett Newman (Shiff, 2004) is less important than the concepts or
processes that their works communicate. Nonetheless, most artists, re-
gardless of their motivation or medium, spend years developing patterns
of thought and behavior that lead ultimately to expression in a work of
art. Here, we focused narrowly on a single type of artwork: representa-
tional, two-dimensional visual depictions created from observation. We
necessarily ignored many important factors such as social, cultural, and
affective contexts that are vital to the work of many artists (cf. Stiles
and Selz, 2012). No single study can address every factor that inuences
artistic skill. However, the results presented here may provide a window
into some of the neural processes that endow humans with a seemingly
limitless ability to create new objects, ideas, and processes.
In the current study we investigated how artistic behaviors are
learned, focusing on representational visual art and on three areas of cog-
nition that are relevant to many visual artists: creative cognition, visual
perception, and perception-to-action (Fig. 1A). We asked how skills asso-
ciated with each of these three cognitive domains change and how the
brain reorganizes as students learn to create visual art. We recruited 35
undergraduate college students for monthly testing; 17 of these partici-
pants took a 3-month-long introductory observational drawing or paint-
ing course offered by the Studio Art Department at Dartmouth College,
while 18 control participants did not study art. All participants attended
monthly MRI scanning sessions. Below we introduce the three areas of
cognition that we studied and their potential relevance to visual art.
Creative cognition
Artists are distinguished by the ability to think in new ways, devel-
oping new patterns of and connections between ideas to imagine and
NeuroImage 105 (2015) 440451
Corresponding author at: Department of Psychological and Brain Sciences, H. B. 6207,
Moore Hall, Dartmouth College, Hanover, NH 03755, USA. Fax: +1 603 646 1419.
E-mail address: schlegel@gmail.com (A. Schlegel).
http://dx.doi.org/10.1016/j.neuroimage.2014.11.014
1053-8119 2014 Elsevier Inc. All rights reserved.
Contents lists available at ScienceDirect
NeuroImage
journal homepage: www.elsevier.com/locate/ynimg
create artifacts and processes that have never existed previously. The
sources of this creativity are among the least understood and most my-
thologized aspects of art production (Milbrandt and Milbrandt, 2011;
Taylor, 1976). Creative cognition is notoriously difcult to dene within
ascientic context, partly because creativity can be manifested in myr-
iad domains such as artistic and scienticelds, verbal and visual mo-
dalities, and divergent and convergent thought (Dietrich and Kanso,
2010). Many questions about what makes artists creative remain
open, especially with respect to the brain's role in these creative pro-
cesses. Previous neuroscientic studies have used a range of approaches
to study the neural basis of creativity in artists, but little consensus
about this basis has emerged. For example, Bhattacharya and Petsche
(2005) used EEG to study differences in cortical activity between artists
and non-artists as both produced drawings of their own choice and
found differences in short and long range neural synchronization pat-
terns between the two groups. Kowatari et al. (2009) asked design ex-
perts and novice participants to invent a new type of pen while
undergoing functional MRI (fMRI) scans and found that creative output
was correlated with the degree of dominance of right over left prefron-
tal cortical activity. Limb and Braun (2008) used fMRI to show that jazz
pianists experienced extensive deactivation of prefrontal cortex when
they played improvised compared to over-learned musical pieces.
Solso (2001), on the other hand, found reduced activity in the parietal
cortex in a skilled portrait artist compared to a novice participant as
both produced drawings of faces. While little consensus has emerged
from such studies, the many emerging ndings about both artists and
creative cognition more generally have shown that creativity is a com-
plex rather than monolithic process and that researchers must therefore
avoid the tendency to reduce creativity to simple conceptual constructs
(Arden et al., 2010; Dietrich and Kanso, 2010; Hee Kim, 2006). Thus, in
this study we chose assessments of creativity (described below) that
measured many aspects of creative ability.
A recent study by Jung et al. (2010) investigated the relationship be-
tween white matter organization and creative cognitive ability using
diffusion tensor imaging (DTI). They found an inverse correlation in
the frontal lobes between fractional anisotropy (FA; a measure of the di-
rectionality of water diffusion in white matter) and both divergent
thinkingand openness, such that more creative individuals as measured
by these traits tended to have lower frontal white matter FA. While FAis
often associated with myelination of axons, several other properties
such as axon count, axon packing, and crossing bers can affect the an-
isotropy of water diffusion in the brain as well. While the exact neural
correlates of FA are not determined precisely, DTI nonetheless provides
a non-invasive means of investigating longitudinal changes in the struc-
ture of white matter. Several recent studies have shown that diffusion
tensor imaging (DTI) is an effective tool for tracking learning-related
changes in the white matter organization of the brain in as little as six
weeks or as long as nine months (May, 2011; Schlegel et al., 2012;
Scholz et al., 2009). Even shorter term changes (in as little as ve
days) have been observed in brainstructure using other imaging modal-
ities (Ditye et al., 2013; Driemeyer et al., 2008).
Visual perception
The visual system is organized to recover intrinsic properties of per-
ceived objects such as size andreectance. It therefore often counteracts
context-dependent aspects of objects such as distance from the observ-
er and ambient luminance (Todorović, 2002). In other words, the brain
constructs our perception of the world not necessarily in accordance
with the physical stimulation, but rather as it infers things to be intrin-
sically.For instance, a white ower still appears white in a blue-lit room,
even though the ower reects only blue light in such a room. While
such inferences on the part of the visual system permit us to perceive in-
trinsic properties of objects (e.g. size, shape, or pigment), they can also
lead to illusory percepts such as the Craik-O'Brien-Cornsweet and Müll-
er-Lyer illusions (Figs. 1C & D) (Müller-Lyer, 1889; Todorović,1987).
Fig. 1. Experimental design. A. Areas of cognition important to the production of represen-
tational visual art: creative cognition, perception, and perception-to-action pathways. B.
Example prompt and participant response from the TTCT. Participants were instructed
to draw something that no one else would think of, to tell as rich and complete a story
as possible, and to give each response a creative title. C. The CraikO'BrienCornsweet il-
lusion,in which a dark-to-light gradientheading left of centerand a light-to-dark gradient
heading right of center cause a uniform gray rectangle to appear darker on the left side
than on the right side. D. The MüllerLyer illusion, in which a line segment with outward
facing arrow ends appearslonger than an identical-length line segment with inward fac-
ing arrow ends. E. Example stimulus and participant response from the gesture drawing
task. Participants had 30 s to complete a gesture drawing of the observed human gures.
441A. Schlegel et al. / NeuroImage 105 (2015) 440451
One skill acquired by many visual artists is the ability to create pre-
cise, realistic representations of the world. For these representations to
appear realistic, they must reect accurately the physical, rather than
the inferred, properties of the observed environment. A representation-
al artist may therefore need to counteract these inferences. Otherwise,
the brain's corrections would propagate to the artwork and result in in-
correct depictions of the subject matter (e.g. in a painting of a white
ower in a blue-lit room, the ower would look whiter than in real
life). How do representational artists learn to bypass these seemingly
automatic inferential processes? Do their brains reorganize so as to per-
ceive the true physical properties of stimuli directly, or do artists use
other cognitive strategies such as correcting inaccuracies in an artwork
by comparing the actual stimulus with an initial attemptat its represen-
tation? Previous studies have presented conicting ndings in this re-
gard. Graham and Meng (2011) reported that professional painters
were less susceptible than non-artists to the CraikO'BrienCornsweet
effect, suggesting that these artists' direct perceptual experience of lu-
minance had changed as a result of training and practice. However,
Perdreau and Cavanagh (2011) found no differences between the abili-
ties of visual artists and non-artists to overcome luminance and size
constancy operations. Drawing ability, rather than artistic ability more
generally, has been shown to affect size constancy processes
(Ostrofsky et al., 2012), integration of object information (Perdreau
and Cavanagh, 2013), and encoding of object structure (Perdreau and
Cavanagh, 2014). Several other scholars have argued both for and
against differences between the perceptual abilities of artists and non-
artists (Fry, 1920; Gombrich, 1960; Kozbelt and Seeley, 2007; Ruskin,
1857; Thouless, 1932). How representational artists can create faithful
depictions of environments that are ltered through perception is
therefore still an open question.
Perception-to-action
No matter the style or medium in which they work, artists must de-
velop the ability to translate thoughts and perceptual experiences into
skilled actions; in this case, drawing and painting. Here we conceive of
perception-to-action as encompassing those cognitive processes that
involve close interactions between perceptual and motor processes,
broadly dened. Relevant perceptual processes could include visualper-
ception of the subject of an art work or of the artist's own hand, or pro-
prioceptive feedback from hand and arm as a drawing is created.
Relevant motor processes could include both the hand and arm move-
ments that create the art work and the eye movements that direct at-
tention over the subject.
Previous studies have investigated how the drawing habits and abil-
ities of artists differ from those of non-artists. Kozbelt (2001) found that
artists' superior skills in perception, motor actions, and perceptuomotor
integration contribute to their advantage in drawing ability. His data in-
dicated additionally that the perceptual advantages among artists had
developed largely to serve drawing skills. Providing further evidence
for a tight integration between perception and action among artists,
Cohen (2005) found that artists shift their eyes between the drawing
and its subject more frequently and that this gaze frequency correlates
with drawing accuracy. He suggested that frequent eye gaze shifts to
update the contents of perception allow artists to reduce the amount
of (possibly inaccurate) information held in working memory. Glazek
(2012) found additionally that artists engage more efcient visual
encoding and motor output mechanisms when drawing. These results
may also relate to Perdreau and Cavanagh's (2011) argument that art-
ists overcome constancy operations essentially by trial and error: draw-
ing a subject and then making corrections after comparing the drawing
to the subject. If this is the case, one aspect of becoming skilled in draw-
ing may be development of the ability to compare drawing and subject
while creating an artwork.
An inuential model of the visual system proposes that visual infor-
mation processing can be divided primarily along two neural pathways
or processing streams (Goodale and Milner, 1992; Mishkin and
Ungerleider, 1982). The ventral or vision for perception stream is respon-
sible for recovering information about object identity and tracks
features such as size, shape, and color. The dorsal or vision for action
stream is responsible for spatial awareness and the guidance of move-
ments suchas the strokes of a paintbrush. Since artists' perceptual skills
exist to subserve skilled movements, it is possible that a representation-
al visual artist's training can target the functions of the vision for action
stream over those of the vision for perception stream. If so, nding
evidence of differences between the perceptual skills of artists and
non-artists may depend on whether the tests of those skills target purely
perceptual or perception-to-action pathways.
In the current study we investigated behavioral and neural changes
in creative cognition, visual perception,and perception-to-action as fol-
lows. First, in behavioral sessions at the beginning and end of the study,
participants completed the Torrance Tests of Creative Thinking Figural
Form A (TTCT; Fig. 1B) (Torrance, 1969). The TTCT tests for the ability
to think creatively as dened by several factors such as uency, original-
ity, abstractness of thought, the ability to depict complex systems com-
pellingly, and the creative use of imagery and language. The test yields a
single composite creativity index (CI) as well as submeasures that sep-
arately assess many aspects of creative ability. Although the painting
and drawing courses completed by the participants were not designed
explicitly to improve the creative qualities measured by the TTCT, we
hypothesized that training in painting and drawing would transfer to
improvements in some or all of these qualities. Because of the nding
of Jung et al. (2010) we hypothesized additionally that any changes
we observed in the creative thinking abilities of our experimental
group would correlate with corresponding changes in prefrontal white
matter organization.
Second, in order to track the development of perceptual abilities in
our visual art students and test whether improvements in these abilities
entail changes in the activity of the brain's perceptual pathways, we ac-
quired a series of functional scans in each session while participants
judged properties of illusory visual stimuli. For illusory stimuli we
used the CraikO'BrienCornsweet illusion (Fig. 1C) and the Müller
Lyer illusion (Fig. 1D). We chose these two classic visual illusions be-
cause they are cognitively impenetrable. Previous neuroimaging studies
have shown that brain areas implicated in early and mid-level visual
processing underlie the illusory effects (Perna et al., 2005; Plewan
et al., 2012). If perceived strengths and neural correlates of these visual
illusions change as students become artists, it would suggest neural
plasticity at perceptual processing levels. However, no changes in earlier
levels of processing would suggest that artists may have learned to in-
terpret the outputs of early processing differently.
Finally, to assess learning-related changes in perception-to-action
pathways, we acquired a functional scan during each session in which
participants made quick, 30 second gesture drawings based on observa-
tion of human gures (Fig. 1E). Gesture drawing is a technique often
used among representational artists to develop more direct translation
of visual observation to hand and arm movements. In creating gesture
drawings, one is often discouraged from devoting attention to the art
work itself, focusing more on translating directly from the perceived
form and gesture to motor actions that faithfully capture those aspects
of the subject on the canvas. This was especially true in the current
study, since participants lay with their heads still in the scanner and
had little opportunity to see the drawings as they were produced. If vi-
sual art training targets perception-to-action, we hypothesized that
changes in neural activity would be observed in the corresponding
perceptuomotor pathways among our art students.
Until recently, plastic reorganization of the brain was thought to
occur mainly during childhood and adolescence, leaving adults with
limited means to learn new skills. Research in the last two decades
has convincingly overturned this belief, revealing a brain that remains
able to reorganize with learning well beyond early developmental pe-
riods (Draganski et al., 2004; Lövdén et al., 2010; May, 2011; Schlegel
442 A. Schlegel et al. / NeuroImage 105 (2015) 440451
et al., 2012; Scholz et al., 2009; Taubert et al., 2010). Structural changes
in the adult brain have been observed with interventions lasting aslittle
as six weeks (Draganski et al., 2004). Our previous work has shown that
novel insights can be gained into the neural processes underlying spe-
cic behaviors by studying howthe adult brain changes as thosebehav-
iors are learned (Schlegel et al., 2012). Thus, studying how the brain
changes as students become artists may reveal insights into how the
brain mediates artistic work.
Materials and methods
Participants
Prior to participating, 45 participants (26 females, aged 1922 years)
with normal or corrected-to-normal visual acuity gave informed writ-
ten consentaccording to the guidelines of Dartmouth College's Commit-
tee for the Protection of Human Subjects. Data from 10 participants who
withdrew before completion of the study were discarded before further
analysis. Our nal study cohort consisted ofan experimental group of 17
undergraduate students (13 females, aged 1822 years) who completed
a three-month-long course in either introductory drawing or introduc-
tory painting, and a control group of 18 undergraduate students (9 fe-
males, aged 1922 years) who did not study art. Participants were
recruited for the study during the rst week of courses, and we there-
fore did not control the group assignment. Control participants were re-
cruited from a group of students taking an introductory organic
chemistry course. Our strategy was to choose a control group that en-
gaged in an equally intensive course of study, but within a system that
required closed rather than open-ended solutions. While no signicant
differences in gender, age, handedness, or grade point average existed
between the two groups (Table S1), we were not able to precisely
match these characteristics because of the nature of the group
assignment.
Drawing & painting courses
Experimental participants completed either an introductory course
in observational drawing, or a similar course in painting for which the
drawing course was a prerequisite. Both courses were 11 week,
undergraduate-level classes offered for credit through the Studio Art
Department at Dartmouth College. Classes met for 4 h each week,
with approximately 1520 additional hours spent on work per week
outside of class. The purpose of the introductory drawing course was
to develop technical and expressive drawing abilities in terms of line,
scale, space, light, and composition. Work was primarily observational,
although non-observational drawing was also explored. The painting
course further developed the topics from the drawing course, and also
addressed paint application and color theory, mixing, and composition.
Both courses focused additionally on the development of artistic expres-
sion and on the critical analysis of art works. Detailed course descrip-
tions are provided for both courses as supplemental text.
Procedure
Participation consisted of two half-hour-long behavioral sessions,
one at the beginning and one at the end of the study, during which par-
ticipants completed the Torrance Tests of Creative Thinking (TTCT) Fig-
ural Form A, and four one-hour-long magnetic resonance imaging
(MRI) sessions, one per month, during which we collected several func-
tional and structural scans. Functional data were collected as partici-
pants performed two types of behavioral tasks. In the rst task,
participants made judgments about the physical characteristics of visual
illusion stimuli. In the second task, participants produced gesture draw-
ings basedon observation of photographs of human models. These tasks
are described in further detail below. DTI data were collected as partic-
ipants rested but lay still in the scanner.
TTCT task
The TTCT Figural Form A is a timed 30 min, standardized pencil and
paper test of creative thinking. The test consists of three 10 minute ac-
tivities in which participants are instructed to complete partially
drawn gures by thinking of things no one else would think of and by
telling as creative and elaborate a story as possible (e.g. Fig. 1B). Partic-
ipants took the TTCT twice, once at the beginning and once atthe end of
the study.
Illusion task
Stimuli were modeled after the CraikO'BrienCornsweet illusion
(Fig. 1C) and the MüllerLyer illusion (Fig. 1D), with actual differences
introduced in luminance and length, respectively. In a given trial, an il-
lusory stimulus was presented for 1 s and the participant had 2 s from
stimulus onset to indicate which side was either brighter (for the
CraikO'BrienCornsweet or luminancetask)orlonger(fortheMüll-
erLyer or lengthtask) before the next stimulus appeared. The Craik
O'BrienCornsweet illusion stimulus measured 22.72° of visual angle
wide and 17.14° tall, while each center gradient was wide. The Müll-
erLyer line segments were oriented vertically and centered on the
screen, with a horizontal separation between them. Line segments
ranged in length from to 8°. The gradient directions and lighter side
for the luminance task and the arrow end direction and longer side for
the length task were counterbalanced across trials, and participants
were not given feedback on their responses. During each session, partic-
ipants completed one fMRI run of each illusion task. A run consisted of
ve blocks of 20 trials each, yielding 100 trials per task, participant,
and session. Blocks were interleaved with 12 second rest periods.
Gesture drawing task
Stimuli consisted of grayscale photos of human gures in various
poses (e.g. Fig. 1E). Before the rst scan, participants were shown exam-
ples of gesture drawings and instructed that gesture drawing is an activ-
ity in which uid, continuous strokes are used to build up the form and
movement of the observed gure quickly rather than to capture ne de-
tails. In each trial, a gure was shown to the participant who then had
30 s to complete a gesture drawing of that gure. Participants used a
#2 pencil while lying supine in the scanner and resting a wedge-
shaped drawing pad and paper on their abdomens. Because of their po-
sition and the instruction to keep their head still during scans, partici-
pants had little opportunity to view the gesture drawings as they
were produced. This constraint was not a major concern because, as
discussed above, gesture drawing technique stresses that attention be
maintained on the subject rather than the art work. An experimenter
stood at the side during the scan to provide a new piece of paper in be-
tween drawings. During each session, participants completed one fMRI
gesture drawing run, consisting of 10 drawings interleaved with 14 sec-
ond rest periods.
MRI acquisition
MRI data were collected using a 3.0-Tesla Philips Achieva Intera
scanner with a 32-channel sense head coil located at the Dartmouth
Brain Imaging Center. T2*-weighted gradient echo planar imaging
scans were used to acquire functional images covering the
whole brain (2000 ms TR, 20 ms TE; 90° ip angle, 240 × 240 mm FOV;
3×3×3.5mm
3
voxel size; 0 mm slice gap; 35 slices). One T1-weighted
structural image was collected each session using a magnetization-
prepared rapid acquisition gradient echo sequence (8.176 ms TR;
3.72 ms TE; ip angle; 240 × 220 mm
2
FOV; 188 sagittal slices;
0.9375 × 0.9375 × 1 mm
3
voxel size; 3.12 min acquisition time). One
diffusion-weighted scan was collected each session to acquire diffusion
tensor imaging (DTI) data (32 directions; 1000 s/mm
2
b-value; 8.379
443A. Schlegel et al. / NeuroImage 105 (2015) 440451
s TR; 73.49 ms TE; 90° ip angle; 224 × 224 mm
2
FOV; 70 axial slices;
2×2×2mm
3
voxel size; one additional b = 0 s/mm
2
image; 2 signal
averages per volume; 10.47 min acquisition time).
MRI data preprocessing
fMRI and DTI data were preprocessed using FSL (Smith et al., 2004).
Functional data were motion and slice scan time corrected, temporally
high pass ltered with a 1/100 Hz cutoff, and spatially smoothed with
a 6 mm full-width-at-half-maximum Gaussian kernel. For each DTI
data set, fractional anisotropy (FA), radial diffusivity (RD), axial diffusiv-
ity (AD), and mean diffusivity (MD) were reconstructed, z-transformed
to reduce the effect of potentialunexpected changesin equipment func-
tion over time, and normalized to a standard 2 × 2 × 2 mm
3
template in
Montreal Neurological Institute (MNI) space via FSL's FNIRT non-linear
registration tool. High-resolution anatomical images were processed
using the FreeSurfer image analysis suite (Dale et al., 1999).
DTI data analyses
Our DTI data analyses followed the procedure from Schlegel et al.
(2012).
Whole-brain GLM
A cross-subject longitudinal GLM analysis using FSL's randomise tool
was performed on the whole-brain FA data (5000 permutations,
within-subject only). Data from all four sessions were included in the
analysis. Only data from white matter were analyzed,as determined in-
dividually for each participant by FreeSurfer's automatic segmentation
algorithm. Additionally, each voxel location in MNI space was only in-
cluded in the analysis if at least 75% of participants had white matter
at that location. Even for locations that passed the 75% threshold, data
from non-white matter at those locations were excluded from the anal-
ysis. This process allowed for as much of the white matter data as pos-
sible to be included without risking errors due to potential
misregistration between white and non-white matter regions.Included
in the GLM design matrix were predictors to account for existing differ-
ences between participants and predictors for time, separated by group.
t-contrasts were dened to assess group by time interaction effects, and
the resulting statistical maps were threshold-free cluster enhanced and
false discovery rate (FDR) corrected for multiple comparisons (Smith
and Nichols, 2009). The same analysis was also performed for RD, AD,
and MD measures.
Time course
For each participant, the same GLM as in the whole-brain longitudi-
nal DTI analysis was performed with that participant's data left out. The
participant's FA data at voxels with p0.05 (uncorrected) in the group
by time interaction contrast of this analysis were then averaged to com-
pute one mean FA value for that participant at each time point. Uncor-
rected pvalues were used in this voxel selection procedure to
maximize the amount of meaningful data included in the time courses,
while excluding the data to be averaged from the voxel selection step
prevented type I errors in the GLM analysis from propagating to the
time courses (i.e. decreasing the slope of the participant group and in-
creasing the slope of the control group articially). Results for each par-
ticipant were converted to percent change from the t = 0 value of a
best-t line for that participant's data, and these time courses were
then averaged by group and shown in Fig. 3B.
Structural MRI data analysis
The same whole-brain longitudinal GLM analysis as described for
the DTI data analyses was performed on gray matter thickness data as
reconstructed by FreeSurfer.
TTCT data analyses
Behavioral
The TTCTs were scored independently and blindly according to
standard rating procedures (see Torrance, 1969) by two indepen-
dent raters who also evaluated the gesture drawings (described
below). Inter-rater reliability was excellent (α=0.94forthecom-
posite creative index [CI]). The group by time interaction term of a
two-way, repeated measures ANOVA evaluated whether the change
in CI over the study differed between the two groups. A factor analysis
was performed on all TTCT subscores including a modication of the
checklist of creative strengths in which the total number of instances of
each checklist item was recorded for each test section. Factors were ex-
tracted based on principal components with eigenvalues greater than 1
and varimax rotated (resulting in the ve factors shown in Fig. 2B). Ad-
ditional one-tailed, unpaired t-tests evaluated whether each of these
factors increased more in the experimental group than the control
group over the study period. p-Values were FDR corrected for the ve
comparisons.
Correlation with DTI data
For each identied TTCT factor, a between-subject correlation analy-
sis was performed comparing the change in factor score between the
two test administrations and the slope of the FA changes calculated
above. For Factor 2, which showed a signicant result in this analysis,
the same correlation analyses were performed between FA slope and
the change in the four TTCT subscores that loaded highly (coef-
cient 0.4) onto this factor. The resulting p-values were FDR corrected
for multiple comparisons across the four submeasures.
Illusion data analyses
Behavioral
We reconstructed a psychometric c urve for each fMRI illusion run by
tting a Weibull function to participant responses for that run. Re-
sponses were coded for the CraikO'BrienCornsweet luminance task
based on whether the participant chose the side with the lighter or
darker gradient and for the MüllerLyer length task based on whether
the participant chose the arrow with the outward or inward facing
ends. The tparameter from the Weibull t gives an estimate of the
point of subjective equality (or the actual luminance or length differ-
ence that led the participant to make each choice with equal probabili-
ty) and hence the strength of the illusory effect. The bparameter from
the t determines the steepness of the psychometric curve and thus in-
dicates the consistency of the participant's decision criterion. The group
by time interaction terms from longitudinal linear mixed model (LMM)
analyses were used to determine whether the trajectory of these two
parameters differed between the two groups over the study period.
fMRI univariate
A whole-brain longitudinal GLM analysis was carried out for each il-
lusion task to determine whether brain activity changed differentially
between the two groups during the study. Only data from cortical
gray matter and subcortical structures were analyzed, as determined
by FreeSurfer's automatic segmentation algorithm (Dale et al., 1999).
Arst-level GLM in FSL's FEAT tool for each participant and session
used a boxcar predictor to model differences in blood-oxygenation
level dependent (BOLD) measurements between task and rest, con-
volved with a double-gamma hemodynamic response function (Smith
et al., 2004). The model parameter estimates from this analysis were
passed to a higher-level longitudinal GLManalysis using FSL's randomise
tool (5000permutations, within-subject only), like that used for the DTI
analysis described above. t-Contrasts were dened to assess group by
time interaction effects, and the resulting statistical maps were
threshold-free cluster enhanced and FDR corrected for multiple
comparisons.
444 A. Schlegel et al. / NeuroImage 105 (2015) 440451
fMRI multivariate
Multivariate pattern classications were carried out using PyMVPA
(Hanke et al., 2009;seeNorman et al., 2006 for a detailed introduction
to multivariate classication analysis). For each session we performed
a whole-brain, cross-subject multivariate classication analysis, in
which we trained a machine classier to distinguish between experi-
mental and control participants based on patterns of brain activity
measured during the gesture drawing task. We used a whole-brain clas-
sication procedure rather than a searchlight analysis for two reasons.
First, searchlight analyses are only sensitive to localized patterns of in-
formation, since each classication is performed only on a localized
cluster of voxels. A whole-brain classication allows patterns to be dis-
tributed across the brain, as might be expected for complex cognitive
processes. Second, searchlight analyses entail a large number of multi-
ple comparisons that can be avoided by performing a single whole-
brain classication. As classication data we used the parameter esti-
mates (i.e. beta values)fromtherst-level univariate analysis de-
scribed above. These parameter estimates represent the change in
brain activity in each voxel while drawing, compared to rest. During
classication, the machine classier is rst trained by providing it with
a set of patterns along with the associated labels (in this case experi-
mentalor control). After training, the classier is tested by giving it
a new pattern that was held out of the training step and determining
whether it can assign the correctlabel to that pattern. This training/test-
ing step is repeated in a cross-validation procedure in which each pat-
tern is successively held out of the training data and included in the
testing data. If the classier can label the test patterns correctly above
chance over all of the cross-validation folds, then information exists
within the patterns that distinguishes the two groups. In a whole-
brain classication, an initial voxel selection procedure is conducted to
determine a subset of voxels in the whole cortex to include in the
classication. Specically, in each fold of the cross-validation we rst
performed a one-way ANOVA between the two groups' parameter
estimates (leaving out data from the held out participant). The 1% of
voxels with the highest F-scores in this ANOVA were then selected for
training and testing. This selection procedure allowed us to reduce the
dimensionality of the multivariate patterns in a principled way while
not biasing the classication results, since the testing data were left
out of the selection mechanism. One limitation of the whole brain
classication selection procedure is that it may discard voxels that still
contain information that distinguishes the two groups, but not enough
to pass the selection threshold (i.e. not showing large enough between
group differences). The selection threshold we chose, however, allowed
us to strike a balance between nding information if it was present and
avoiding overtting of the data. We used a linear support vector ma-
chine (SVM) as our classication algorithm, and leave-one-subject-out
cross validation (i.e. one participant's data were held out from the train-
ing set in each cross-validation fold). Because the training data were un-
balanced between groups, we included an additional step in which the
classier was trained and tested 10 times for each cross-validation
fold, using a random subset of balanced data for training. The classier
performance for each fold was then calculated as the average perfor-
mance across those 10 subfolds. Classication accuracies from these
analyses were compared to chance using one-tailed Monte Carlo tests
with 1000 permutations.
Gesture drawing data analyses
Behavioral
All gesture drawings were digitized and scored independently and
blindly by two trained raters. One rater was a visual artist who was
not familiar with the participants' artwork and the other was a research
assistant who was trained by the rst rater. The score for each drawing
was an integer between 1 (lowest quality) and 10 (highest quality),
based on an assessment of line quality, resemblance to the gure, and
expressiveness of the depicted gestures. The inter-rater reliability was
excellent (α= 0.82). The group by time interaction effect from an
LMM analysis was used to determine whether the change in these rat-
ings differed between the two groups over the study period.
fMRI
To evaluate whether differences in head movement could have led
to our observed effects, we conducted two-tailed, unpaired t-tests
Fig. 2. Results of creative thinking analysis. Asterisks indicate signicance. Errorbars indi-
cate standard errors of the mean. A. Art students increased in creative thinking ability
compared to the controls, as measured by the TTCT composite creative index. B. A factor
analysis of the 18 TTCT submeasures revealed ve factors that accounted cumulatively
for 59.7% of variance in the participant responses. Factor loadings for each submeasure
are shown, multiplied by 10 for presentation. Loadings with magnitude greater than 0.4
are highlighted andcolor coded by increasing magnitude (red to yellow). C. Scores for Fac-
tors 1 through 3increased in art students relative to controls, indicating that art students
improved in their ability to think divergently, model systems and processes, and portray
imagery. p-Values are FDR corrected for the ve comparisons.
445A. Schlegel et al. / NeuroImage 105 (2015) 440451
between the two groups for each session using the per-run mean rela-
tive displacement as reported by FSL's MCFLIRT tool. Univariate and
multivariate analyses were carried out on the gesture drawing fMRI
data as in the illusion analyses described above. To conrm that the
above-chance multivariate classication accuracies observed were not
due to gross BOLD level differences between the two groups, an addi-
tional higher-level univariate whole-brain GLM analysis wasperformed
for each session using randomise (5000 permutations, threshold-free
cluster enhanced and FDR corrected for multiple comparisons), with t-
contrasts dened to evaluate between-group BOLD differences. As an
additional control to conrm that the effects we observed were due to
ne-scale patterns of activity, the same multivariate analysis was per-
formed using the mean pattern values as samples rather than the pat-
terns themselves.
Results
Creative cognition
In behavioral sessions at the beginning and end of the three month
study period, participants completed the TTCT Figural Form A, a test of
conceptual creativity. All tests were scored independently and blindly
by two trained raters. The inter-rater reliability was excellent (α=
0.94). For each participant, we calculated the change between the two
sessions in the composite creative index (CI) given by the TTCT
(Fig. 2A). A two-way, repeated measures ANOVA comparing the abso-
lute TTCT CI scores showed a signicant interaction between group
and time, indicating that the art students' creative thinking ability im-
proved signicantly compared to control participants during the study
(F(1,32) = 4.47, p= 0.0423). Note that differences between the two
groups' CI measures existed at the rst session (t(32) = 3.85, pb
0.001; see Table S2). Because creativity is a complex trait (Dietrich
and Kanso, 2010; Hee Kim, 2006),reducing creativecognition to a single
quantity such as CI would limit our understanding of the changes that
occurred. CI is actually derived from 18 different submeasures of crea-
tivity (see Fig. 2B), so we performed a factor analysis on these
submeasures in order to extract multiple dimensions along which to ex-
amine the changes that occurred among our participants. This analysis
yielded ve factors that together explained 59.7% of the variance in
the TTCT data (Fig. 2B). The submeasures uency,originality,breaking
boundaries,elaboration, and resisting premature closure loaded highly
onto Factor 1. These submeasures all target divergent thinking, dened
as the ability to produce many (uency,elaboration)original(originality,
breaking boundaries,resisting premature closure) solutions to a problem
(Guilford, 1967). Storytelling articulateness,synthesis of gures,depicting
movement or action, and emotional expressiveness loaded highly onto
Factor 2. These submeasures all required the modeling of a system or
process (story narratives, the continuation of a theme over multiple
panels, movements and actions, and emotional states). Richness of imag-
ery,colorfulness of imagery,andelaboration loaded highly onto Factor 3
and shared a common theme of requiring the depiction of rich, complex,
effective imagery. Expressiveness of titles,abstractnessof titles,andhumor
loaded highly onto Factor 4, withthe common theme ofinvolving verbal
creativity. And originality and synthesis of lines loaded highly onto Factor
5, with no discernible interpretation.
We calculated the change in each of these ve factor scores for each
participant and performed one-tailed, unpaired t-tests between the ex-
perimental and control groups to determine which factors were respon-
sible for the improvements in creative thinking among the art students.
The results of this analysis showed that art students improved over con-
trols in the creative qualities captured by Factors 1, 2, and 3 (divergent
thinking, modeling of systems and processes, and imagery; Fig. 2C;
Table S3). Factors 4 and 5 showed no signicant changes between the
two participant groups.
In order to assess whether these improvements in creative ability re-
lated to changes in white matter structure, we rst performed a whole-
brain (white matter only), permutation-based longitudinal GLM analy-
sis on the Fisher's Z transformed fractional anisotropy (FA) values de-
rived from the DTI scans collected for each participant and session. FA
quanties the degree to which the diffusion of water is biased in partic-
ular directions andis associated withvariations in axoncount and diam-
eter, density of axonal packing, myelination, and the coherence of axon
ber bundles (Beaulieu, 2011). This analysis revealed bilateral, prefron-
tal white matter clusters in which FA decreased in art students relative
to controls over the course of the study (Fig. 3A; all ps FDR corrected for
multiple comparisons). No other signicant effects of training were
found (no voxels were signicant after FDR correction) when the
same analysis was applied to radial diffusivity (amount of diffusion per-
pendicular to the principal axis), axial diffusivity (amount of diffusion
parallel to the principal axis), mean diffusivity (mean amount of diffu-
sion), or cortical gray matter thickness instead of FA.
To conrm that the clusters identied in the longitudinal FAanalysis
were associated with absolute decreases in FA in the art students rather
than increases in FA in the control group, we calculated the mean per-
cent change in FA within these clusters for each participant and session
in both groups. However, calculating FA time courses directly from the
voxels that reached signicance in the longitudinal analysis would de-
crease the slope of the experimental group's time course and increase
the slope of the control group's time course articially due to noise-
induced false positives in the whole-brain analysis. In order to prevent
these false-positives from affecting the result, for each participant we
calculated the mean FA percent change at each time point only in voxels
that were signicant in the same longitudinal GLM analysis conducted
with that participant's data left out (cf. Schlegel et al., 2012). An LMM
analysis of these FA change time courses revealed that art students ex-
perienced a progressivedecrease in FA in bilateralprefrontal white mat-
ter (group by time interaction term t=2.41, p= 0.016; Fig. 3B).
To evaluate whether a relationship existed between the visual art
students' decreases in prefrontal FA and increases in creative ability,
we performed correlation analyses between the FA percent change cal-
culations and the changes in each factor score between the two admin-
istrations of the TTCT,with results shownin Fig. 4A. After FDR correction
for multiple comparisons across the ve factors, onlychanges in Factor 2
showed a signicant inverse correlation with FA percent change. There-
fore, decreases in FA in prefrontal white matter were associated with in-
creases in the ability to model systems and processes creatively.
Additional correlation analyses with the four TTCT submeasures that
loaded highly onto Factor 2 revealed thatchanges in three of these sto-
rytelling articulateness, portraying movement or action, and emotional
expressiveness showed an inverse relationship with changes in pre-
frontal white matter FA (Fig. 4B; all ps FDR corrected for multiple com-
parisons across the four submeasures). Changes in the fourth
submeasure synthesis of gures showed no signicant correlation
with changes in prefrontal FA.
Visual perception
During each scanning session, participants completed two block-
design runs in which they made judgments about two types of illusory
visual stimuli. In the rst luminancerun, stimuli were based on the
CraikO'BrienCornsweet illusion (Fig. 1C). In this illusion, a dark-to-
light gradient and a light-to-dark gradient heading in opposite direc-
tions from the center of a uniform gray rectangle cause the rectangle
to appear darker on one side than the other. We introduced actual dif-
ferences in the luminance between the two sides of the rectangle and
asked participants to judge which side was lighter. In the second
lengthrun, stimuli were based on the MüllerLyer illusion (Fig. 1D),
in which a line segment with outward facing arrow ends appears longer
than an identical line segmentwith inward facingarrow ends. We intro-
duced actual differences in the length of the two line segments and
asked participants to judge which line segment was longer. We then es-
timated psychometric response curves for each task, session, and
446 A. Schlegel et al. / NeuroImage 105 (2015) 440451
participant in order to assess a) the point of subjective equality and thus
strength of the illusory effect and b) the steepness of the psychometric
curve and thus the consistency of the participants' decision criteria.
Using these data, we performed an LMM analysis to evaluate whether
either measure changed differentially between the two groups during
the study and found no effect in either measure or task (Fig. S1 &
Table S4; all psN0.05, uncorrected). Although we found no enhance-
ment in perceptual ability in the experimental group, we were still curi-
ous whether training would lead to differences in brain activity while
making perceptual judgments. To address this question, we rst per-
formed whole-brain univariate longitudinal analyses on the BOLD mea-
surements from each of the illusion tasks. For each task we used a
permutation-based GLM with t-contrasts dened to assess group by
time interactions in BOLDactivity, and found no signicant effects for ei-
ther task (all psN0.05, FDR corrected for multiple comparisons). While
there were nounivariate BOLD differences between the groups, it is still
possible that differences in more ne-grained patterns of activity arose
between the groups as a result of the art students' training. To assess
this possibility, we performed a whole-brain multivariate classication
analysis for each session and illusion task in which we trained a linear
SVM to classify between the experimental and control groups based
on patternsof BOLD activity (Norman et al., 2006). If pattern level differ-
ences did arise as the art students learned, we would expect classica-
tion accuracy to increase progressively across the sessions. In order to
reduce the dimensionality of the classication patterns, we used an ini-
tial voxel selection procedure to choose the 1% of voxels that showed
the highest F-scores in a one-way ANOVA between the two groups' pa-
rameter estimates in a GLM contrast of task vs. rest, excluding the cross-
validation holdout sample. None of these classication analyses
achieved accuracies signicantly above chance (one-tailed Monte
Carlo test,Fig. S2 & Table S5; all psN0.05, uncorrected). The lack of effect
in any of these analyses supports our behavioral ndingthat no changes
occurred between the two groups in these tasks and suggests that the
art training did not lead to changes in perceptual skill or strategy in
the perceptual judgment tests that we used.
Perception-to-action
In each scanning session, participants also completed one block-
design run in which theycreated 30 second gesture drawings while ob-
serving grayscale images of human gures in various poses (Fig. 1E).
Each drawing was scored independently and blindly by two trained
raters based on an assessment of line quality, resemblance to the ob-
served gure, and recognizability and expressiveness of the depicted
gestures. The inter-rater reliability was excellent (α= 0.82). The
drawing ratings were averaged for each participant and session. A
two-tailed, unpaired t-test found no signicant difference between the
two groups' drawing skills in the rst session (t(33) = 1.56, p=
0.128). However, an LMM analysis performed on these mean ratings
conrmed that the art students improved over time in gesture drawing
ability relative to the controls (group by time interaction t= 3.06, p=
0.003; Fig. 5A).
Thus, the art students improvedin both creative cognitive ability and
in technical skills related to gesture drawing. To evaluate whether these
two areas of improvement were related, we performed a correlation
analysis between the change in TTCT CI between our two test adminis-
trations and the slope of our experimental participants' gesture drawing
ability over the four neuroimaging sessions. We found no signicant re-
lationship between change in creativity and change in gesture drawing
ability (r(14) = 0.0606, p= 0.412). This null nding underscores the
separation between creative and t echnical abilities and the m ultifaceted
nature of the training program undertaken by the art students.
Next, we asked whether the experimental group's enhancement in
drawing ability tracked changes in gesture drawing related brain activ-
ity over the course of the study. To control for the possibility that differ-
ences in drawing-induced head movements between the two groups
could have led to differences in BOLD measurements, we performed
per-session two-tailed, unpaired t-tests on our fMRI motion correction
mean relative displacement measurements. During no session was
there a signicant difference in head movement between the two
groups (all psN0.05, uncorrected; Table S6). We performed whole-
brain univariate longitudinal and whole-brain multivariate cross-
subject classication analyses as described above for the illusion tasks.
As in the illusion tasks, no signicant univariate differences in brain ac-
tivity developed over time between the two groups (all psN0.05, FDR
corrected for multiplecomparisons). This suggests thatno mean activity
differences between participant groups developed over the course of
the study, as might be expected if, for instance, art students drew
more vigorously as they underwent training. However, we did nd
that the SVM classier in our whole-brain multivariate analysis distin-
guished more accurately between art students and controls based on
drawing-related brain activity as the study progressed (Fig. 5B;
Table S7). Initially, the classier failed to distinguish signicantly be-
tween the groups (p= 0.249 in a one-tailed Monte Carlo test compared
to chance),but by the end of the study the classier achieved 82.9% clas-
sication accuracy (p= 0.002 in the same test). To determine which
areas of the brain showed patterns of activity that supported the classi-
cation between art students andcontrols, we visualized the voxels that
were selected by our voxel selection procedure in at least 50% of classi-
cation folds (Fig. 5C). Although clusters of voxels were selected
Fig. 3. Results of longitudinal analysis of white matter structure. Error bars indicate standard errorsof the mean. A. Voxels that showed a progressive decrease in Fisher's Z transformed
fractional anisotropy(FA) in art students relative to controls, shown within a glass brainin MNI space (p0.05, FDR corrected for multiple comparisons). All voxels are inwhite matter,
and the majority of voxels arewithin the frontal lobe.B. Time course of FA in signicant voxelsfrom the analysisin panel A. The art students' prefrontal FA decreased progressively overthe
study period.
447A. Schlegel et al. / NeuroImage 105 (2015) 440451
throughout the brain, with some clusters being chosen presumably due
to noise, thelargest cluster selected in each month occurred consistent-
ly in the right hemisphere of the cerebellum. Buckner et al. (2011) dem-
onstrated previously that regions of the cerebellum overlapping with
those found in the present analysis project to the hand and arm regions
of left primary motor cortex and are involved in proprioceptive feed-
back. Miall et al. (2001) found evidence that similarly overlapping re-
gions are responsible for coordinating eye and hand movements.
Subsequent work has conrmed their ndings and found that these cer-
ebellar regions change with visuomotor task learning (Floyer-Lea and
Matthews, 2004; Maquet and Schwartz, 2003). Interestingly, the selec-
tion procedure chose clusters of voxels consistently in the left motor
cortex as well (see Fig. 5C). These chosen voxel clusters suggest that
the classication analysis picked up on patterns of complex hand- and
arm-related motor activity. To conrm that these signicant classica-
tions did not occur due to gross BOLD level differences in activity
between the groups, for each session we performed a whole-brain uni-
variate GLM analysis to assess differences in brain activity between art
students and controls. No voxels in any of these analyses reached signif-
icance (all psN0.05, FDR corrected for multiple comparisons). As a fur-
ther control to test whether mean activity levels or ne grained spatial
patterns of information were responsible for the signicant classica-
tion result, we tested our classier again, this time using the mean
value of each pattern rather than the pattern itself. None of these classi-
cations achieved accuracies signicantly greater than chance (all psN
0.05, uncorrected). Thus, ne-scale patterns of gesture drawing related
neural activity in the cerebellum and cortex increasingly differentiated
art students from controls during the course of the study, while overall
neural activity levels remained the same. These results suggest that our
participants' training in visual art entailed a reorganization of ne scale
functions in these areas.
Discussion
Here we show that the brains of young adults reorganize as they learn
to create visual art. Our controlled, longitudinal design involving training
over three months allowed us to rule out possible confounding effects of
normal aging and maturation as well as differences in motivation and ini-
tial expertise levels between the experimental and control groups. We did
not nd any improvements in the art students' purely perceptual skills or
related brain activity relative to a control group of students who did not
study art. We did, however, nd that the art students improved in the
ability to quickly translate observations of human gures into gesture
drawings and that ne-grained patterns of drawing-related neural activ-
ity in the cerebellum and cerebral cortex increasingly differentiated the
art students from the control group over the course of the study. This nd-
ing complements a recent correlational study by Chamberlain et al.
(2014) showing that gray matter density in left anterior cerebellum and
right medial frontal gyrus is higher in individuals who have trained in ob-
servational drawing. From their nding, it was concluded that observa-
tional drawing ability depends on differences in structural organization
related to ne motor control in these areas. However, we did not nd
that gray matter thickness changed as a function of training in these or
any other cortical areas. There are many possible interpretations of this
discrepancy, among them that Chamberlain and colleagues' cross-
sectional design could have found pre-existing differences in gray matter
organization that determined innate potentialities for differences in
drawing ability. Interestingly, the art students in our study also improved
in measures of creative thinking, specically in their ability to think diver-
gently, model systems and processes, and use imagery. Increases in their
ability to model systems and processes creatively correlated with de-
creases in the fractional anisotropy (FA) of prefrontal white matter. Con-
sistent with a previous study that found creative ability to be negatively
correlated with prefrontal white matter FA (Jung et al., 2010), our results
suggest that changes in prefrontal white matter FA may underlie the pro-
cesses by which art training leads to increased creative ability. The lack of
correlation between our observed improvements in TTCT scores and ges-
ture drawing ability supports the view that artistic training is a multifac-
eted process involving the development of both creative cognitive and
technical skills.
Our results are also consistent with models that attribute improve-
ments in representational artists' skills to their ability to translate percep-
tion into creative action rather than to perceive the world differently (cf.
Gombrich, 1960). Like Perdreau and Cavanagh (2011), we found no spe-
cial ability among artists to extract veridical properties of the physical en-
vironment through purely perceptual processes. It should be noted,
however, that both our study and that of Perdreau and Cavanagh tested
a specic subset of perceptual abilities; it is possible that other tests
could have revealed changes in perceptual ability that our studies were
unable to observe. We did, nonetheless, nd that art students and non-
artist controls became progressively more distinguishable via drawing-
related patterns of neural activity in regions of the cerebellum and
Fig. 4. Results of correlation analysis between changes in white matter organization and
changes in creative thinking. A. Correlations between changes in factor scores (Fig. 2)
and changesin prefrontal whitematter FA (Fig. 3). Changesin Factor 2 inverselycorrelated
with changesin prefrontalFA. All ps are FDR corrected for theve comparisons. B. Changes
in three of thefour TTCT submeasures that loadedhighly onto Factor2 also showed an in-
verse correlation with changes in prefrontal FA. All ps are FDR correcte d for the four
comparisons.
448 A. Schlegel et al. / NeuroImage 105 (2015) 440451
motor cortex that have been shown previously to mediate ne motor
control, proprioceptive feedback, and coordination between eye and
hand movements, and are likely involved in non-motor cognit ive process-
es as well (Buckner, 2013; Floyer-Lea and Matthews, 2004; Maquet and
Schwartz, 2003; Miall et al., 2001). Thus, our ndings provide evidence
that visual art training changes neural processing in regions that mediate
integration between perception and action. These results are consistent
with the possibility that differences in at least some representational
artist's perceptual abilities may only become apparent when coupled
with action, such as the skilled strokes of a paintbrush or the building
up of a work of art over time through continuous comparison between
what is observed and what is produced. In line with this view, Kozbelt
(2001) showed that artists were better at several perceptual tasks but
also that these advantages had developed largely to support drawing
skills. Future research could help resolve these issues by examining
explicitly the source of representational artists' increased accuracy in
creating art works from observation.
The prefrontal cortex is associated with many complex behaviors that
involve long-term goal making and planning (Miller et al., 2002; Tanji and
Hoshi, 2001), generating novel and exible rules (Rougier et al., 2005),
and imagining future events (Addis et al., 2007), among other abilities.
Common to many of these skills is the ability to represent complex pro-
cesses that do not currently and may neverexistintheimmediateexter-
nal environment (Frick et al., 2014). The prefrontal cortex therefore likely
plays an important role in creative behavior and especially the creative
work of an artist, which requires the exible development of novel and
complex thoughts, processes, and objects. Indeed, Jung et al. (2010)
used DTI to nd that more creative individuals exhibited lower FA in pre-
frontal white matter tracts. However, the causal inferences that can be
made from their cross-sectional design are limited. While their results
are consistent with our ndings, our longitudinal design provides addi-
tional evidence that creative cognition can improve with training on a
time scale of three months and that prefrontal white matter reorganizes
as participants become more able to think creatively.
It is worth noting that DTI measures water diffusion and so provides
only an indirect measure of white matter organization. The precise micro-
structural correlates of FA are generally difcult to elucidate, although FA
is associated with several properties of individual axons and axon bundles
(Beaulieu, 2011). As creative thought often requires forming many con-
nections between disparate concepts, one possibility for the effects we
observed is that improvements in creative thinking are associated with
an increase in the complexity of axonal packing (i.e. a more complex
pattern of connectivity) in the frontal lobes. It is also possible that axonal
demyelination played a role. Evidence has been found of experience-
dependent myelination of axons in mice (Demerens et al., 1996), but a de-
crease in FA such as observed in the present study would be associated
with decreases in axonal myelination and would require that previously
unobserved learning-induced demyelination processes exist in the adult
human brain. To speculate, this demyelination could occur as art students
develop more efcient processing pathways (Solso, 2001)orasmorecre-
ative individuals learn to avoid use of frontal inhibitory circuits. There is
evidence that creative activity involves the inhibition of prefrontal activity
Fig. 5. Resultsof the gesture drawinganalysis. Error bars indicate standarderrors of the mean. A. A longitudinal LMM analysis revealed that art studentsimproved progressively in gesture
drawing ability relative to controls overthe four sessions of the study.B. A whole-brain multivariate between-group linear SVM classicationanalysis based on patterns of gesture draw-
ing-related brain activity improved progressively in its ability to distinguish art students from controls. Plot shows classication accuracy over time. Initially, the classier could not dis-
tinguish art students from controls. By the end of the study, the classier could distinguish between the groups with 82.9% accuracy (#: p0.1, **: p0.01). C. Voxels selected in each
session by the analysis in panel B to be includedin the classication patterns, in MNI space. Voxels are included in these plots if they were selectedin at least 50% of the cross-validation
folds. The largest clusterin each session is colored green.In each session, this cluster is in the area of the right anterior lobe ofthe cerebellum that projects to the hand and arm regions of
the left motor cortex.
449A. Schlegel et al. / NeuroImage 105 (2015) 440451
(Limb and Braun, 2008). Alternatively, development of the glial support
network resulting from increased use of the white matter tracts we iden-
tied (e.g. to actively direct creative thought) could have led to a more
complex extra-axonal environment and thus decreased FA. For instance,
oligodendrocytes extend processes that wrap myelin sheaths around
axons in an activity-dependent manner (Barres and Raff, 1993;
Demerens et al., 1996). While increases in myelination may increase FA,
extension of the orthogonally-oriented processes of oligodendrocytes
might randomize water diffusion and thereby lower FA. Evidence exists
that glial cells are modied by neuronal activity (Barres and Raff, 1993;
Ishibashi et al., 2006), but we are not aware of direct evidence that
these changes can affect FA. Future work that elucidates the cellular
basis of learning-induced changes in white matter organization could
shed further light on interpreting the results presented here.
How does the human brain mediate complex, creative processes
such as the construction of representational works of visual art? An-
swers to this and related questions will not only illuminate the artistic
process itself but could also lead to a more general understanding of
the exible behaviors that set humans apart as a species. An artist's
work is not an innate skill and so must be developed through study
and practice. The present study reveals that, at least in some cases, artis-
tic development is a complex process involving changes in behavior
along with the reorganization of both the structure and function of the
brain. While we documented changes in specic aspects of creative cog-
nition and in the integration of perception andaction, future research in
different artistic disciplines and among different populations will un-
doubtedly reveal further complexity in the creative learning process.
Acknowledgments
We thank Brenda Garand for her advice and support. This study was
funded by a National Science Foundation Graduate Research Fellowship
(No. 2012095475) to AS, Templeton Foundation Grant 23437 to PUT,
and Dartmouth Internal Funding to MM.
AS, ER, PUT, and MM designed the study. ER taught the art courses
(with other professors). AS, PA, SVF, XL, and ZL collected data. AS and
SVF developed analytical tools. AS, PA, SVF, and PJK analyzed the data.
All authors were involved in writing the paper.
Appendix A. Supplementary data
Supplementary data to this article can be found online at http://dx.
doi.org/10.1016/j.neuroimage.2014.11.014.
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Research to date has produced widely divergent findings in terms of the degree of lightness constancy shown by individuals, and there are hosts of competing models of lightness processing in the brain. We argue here that visual artists–especially painters of representational works–are a useful cohort for investigations of lightness perception because the task of creating representational paintings would appear to require artists to judge natural scene luminance (what artists call “value”) accurately in the face of visual system efforts to normalize perceived intensity. Here we investigate the ability to judge illusory luminance differences in a Craik-O'Brien-Cornsweet stimulus in artists with varying expertise. In a 2AFC staircase design, professional realist painters (N = 2) show lower overall PSE (point of subjective equality) with respect to real luminance differences, compared to student artists (N = 3) and non-artists (N = 9) considered together. For artists vs. non-artists, this result holds at 2 of 3 levels of illusory contrast (i.e., the contrast of the luminance ramp in the center of the illusory stimulus). In addition, there is an inverse correlation between the subjects' reported number of hours spent painting or drawing per week and PSE for the same two illusory contrasts (R² ≥ .18). Artistic training regimes–and perhaps innate endowments–that lead to the putative ability to judge luminance accurately may be seen as analogous to those that allow superior pitch judgment (e.g., absolute or relative pitch) in musicians, and therefore we provisionally term superior luminance judgment as absolute (or relative) value. Artists with this ability are of interest to vision science, much as musicians with superior pitch perception have long been studied by audition researchers to elucidate neural processing of acoustic tone. Tests aimed at determining the factors involved in artists' ability to judge luminance and tests quantifying luminance judgment in naturalistic conditions are also described.