Active Ignoring in Early Visual Cortex

Helen E. Payne and Harriet A. Allen

Astratto

■ Selective attention is critical for controlling the input to
mental processes. Attentional mechanisms act not only to select
relevant stimuli but also to exclude irrelevant stimuli. There is
evidence that we can actively ignore irrelevant information. Noi
measured neural activity relating to successfully ignoring dis-
tracters (using preview search) and found increases in both
the precuneus and primary visual cortex during preparation
to ignore distracters. We also found reductions in activity in
fronto-parietal regions while previewing distracters and a re-

duction in activity in early visual cortex during search when a
subset of items was successfully excluded from search, both
associated with precuneus activity. These results are consis-
tent with the proposal that actively excluding distractions has
two components: an initial stage where distracters are encoded,
and a subsequent stage where further processing of these items
is inhibited. Our findings suggest that it is the precuneus that
controls this process and can modulate activity in visual cortex
as early as V1. ■

INTRODUCTION

Efficient mental processing requires that we select from
the world those stimuli that are behaviorally relevant to
our current goals and to ignore those objects that are ir-
relevant. Attentional selection can enhance the neural
processing of attended stimuli, manifested as improve-
ments in reaction time, accuracy, and target detection/
discriminability of cued items (Carrasco, Penpeci-Talgar,
& Eckstein, 2000; Yeshurun & Carrasco, 1999; Posner,
Snyder, & Davidson, 1980). It can also suppress process-
ing of signals evoked by irrelevant stimuli and locations
(Sylvester, Jack, Corbetta, & Shulman, 2008; Ruff & Driver,
2006; Serences, Yantis, Culberson, & Awh, 2004). Fur-
thermore, fMRI studies reveal not only a stimulus evoked
response to an attended target but also increases in ac-
tivation in the portions of visual cortex that represent
the anticipated location of the stimulus, questo è, prepara-
tory activity (per esempio., Macaluso, Eimer, Frith, & Driver, 2003;
Hopfinger, Buonocore, & Mangun, 2000; Ress, Backus, &
Heeger, 2000; Kastner, Pinsk, De Weerd, Desimone, &
Ungerleider, 1999). This preparatory activity is thought to
bias the visual areas to favor the processing of the subse-
quent expected target. In the present study, we are inter-
ested in the complementary effect, that of preparation to
ignore.

Excluding unhelpful or irrelevant stimuli is clearly advan-
tageous. Several behavioral experiments have shown that
if the locations of distracters are known, then their detri-
mental effects on target processing are reduced (Ruff &
Driver, 2006; Serences et al., 2004), and this is linked to
increased neural activity in visual cortex. Control of atten-

University of Birmingham, UK

tion both to targets and away from distracters is likely to
involve a network of fronto-parietal brain regions. Brain re-
gions consistently activated during attentional preparation
following a cue include the intraparietal sulcus, frontal eye
fields, and the superior parietal lobule (SPL) (Sylvester et al.,
2008; Ruff & Driver, 2006; Macaluso et al., 2003; Corbetta,
Kincade, Ollinger, McAvoy, & Shulman, 2000; Hopfinger
et al., 2000; Kastner et al., 1999; Shulman et al., 1999). It
is thought that this network of brain regions is important
for generating biasing signals that modulate activity in visual
cortex (for a review, see Pessoa, Kastner, & Ungerleider,
2003). Given that parts of this network are likely to guide
attention toward targets and away from known distracters,
it is critical to separate these two processes. The preview
search paradigm (Watson & Humphreys, 1997) used here
allows the to-be ignored items to be separated in time
from the attended items. The preview distracters are pre-
sented prior to the addition of the remaining distracters
and a target to the display. Search performance improves
compared to trials where all items are shown at the same
time (a full-set search; Watson & Humphreys, 1997).

Watson and Humphreys (1997) argued that observers
actively apply top–down inhibition to the locations of
previewed distracters, which they termed visual mark-
ing (see also Braithwaite & Humphreys, 2003; Olivers &
Humphreys, 2003; Watson, 2001). Other accounts have
proposed no inhibition of old items and have placed em-
phasis on attention to the new items. Transient luminance
onsets of the new search items may automatically capture
Attenzione (Donk & Theeuwes, 2001) or temporal segmen-
tation between the old and new items may guide attention
( Jiang, Chun, & Marks, 2002). Behavioral evidence from dual-
task studies, on the other hand, (Humphreys, Watson, &
Jolicœur, 2002) and probe-dot detection studies (Humphreys,

© 2011 Istituto di Tecnologia del Massachussetts

Journal of Cognitive Neuroscience 23:8, pag. 2046–2058

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Stalmann, & Olivers, 2004; Olivers & Humphreys, 2002;
Watson & Humphreys, 2000) suggests old items in the
preview search task are actively inhibited. Watson and
Humphreys (2000) conducted a standard preview search
task but on a minority of trials participants were cued to
detect a probe dot. Detection of probes presented at the
locations of previewed distracters was impaired (vs. SU
new distracters), suggesting that information from the
locations of the previewed distracters was inhibited. Simi-
larly, comparing cueing to preview search showed that
participants were better able to exclude previewed items
than noncued items (Allen & Humphreys, 2007UN). Effec-
tively, the visual system reduces the contrast of success-
fully previewed and ignored items (Allen & Humphreys,
2007B).

Preview search, Perciò, offers a way to investigate
neural mechanisms underlying ignoring known distracters.
Recent neuroimaging studies (Dent, Allen, & Humphreys,
in press; Allen, Humphreys, & Matthews, 2008; Olivers,
Smith, Matthews, & Humphreys, 2005; Pollmann et al.,
2003) compared neural activity in response to preview
trials to that in response to nonpreview search baseline
trials. Trials consisted of two displays. The preview con-
dition first display was a true preview; items remained on
the screen when the new items appeared. In the baseline
conditions, the items in the first display disappeared and
were replaced by distracters in different locations. Così,
the first displays of preview trials and baseline trials were
visually identical but the attentional set of the participants
was different between the conditions; the first display in
baseline trials required only passive viewing, whereas the
preview trials would reveal the processes involved with
ignoring stimuli. These studies have consistently demon-
strated enhanced neural activation in posterior parietal cor-
tex (in particular, the SPL and the precuneus) for preview
trials relative to baseline. The SPL/precuneus is proposed
to set up a spatial representation of the old previewed
distracters so that these items are biased in favor of the
subsequently presented new search items. This is sup-
ported by computational modeling (Mavritsaki, Allen, &
Humphreys, 2009). Mavritsaki et al. (2009) used the spik-
ing Search over Time and Space (sSoTS) model to analyze
the preview search fMRI data from Allen et al. (2008) by
including inhibition (suppressing old distracters) and exci-
tazione (anticipation for target) as regressors and found
that the activation in the precuneus reported by Allen
et al. could be predicted by the inhibition.

Here we investigate what effect these parietal activa-
tions have on visually responsive cortex by presenting
stimuli to different retinal locations (cioè., the four visual
field quadrants). It is an open question as to what effect
previewing distracters has on sensory brain areas. Tradi-
tional models of visual attention would predict that un-
attended stimuli (cioè., uncued) would lead to a decrease
in neural activation in brain areas specialized for vision
(Gazzaley, Cooney, McEvoy, Knight, & DʼEsposito, 2005;
Smith, Singh, & Greenlee, 2000). In contrasto, when pre-

viewing face distracters, Allen et al. (2008) found an in-
crease in activation in face processing areas, even during
the initial preview display. This enhanced neural activation
in response to the preview trials may reflect an active
ignoring process that is distinct from passive viewing (O
simply attending elsewhere) of the same stimuli.

If a similar pattern of activation is found in early visual
cortex as in category-specific regions, then this might be
viewed as a signature for active ignoring. Given that at-
tending to a stimulus at a particular spatial location will en-
hance striate cortex blood oxygenation level dependent
(BOLD) activation (per esempio., Gandhi, Heeger, & Boynton, 1999;
Martínez et al., 1999; Somers, Dale, Seiffert, & Tootell,
1999), it is important to relate any activation change in
early visual areas with successful ignoring rather than sim-
ply the intent to ignore. Secondo, we investigate the func-
tional relationship between activity in precuneus regions
and changes in activity in visual cortex. Previously, it has
been assumed that if parietal and visual areas both change
in activation in preview trials, then one must drive the
other. Here, we take this one step further and look for
brain regions where activation appears to be part of a
functional network and link this to successfully ignoring
previewed items.

By using the preview search paradigm, we are able to
separate changes in activation related to successful ignor-
ing from changes related to the target. We follow the logic
of Dent et al. (in press), Allen et al. (2008), and Pollmann
et al. (2003), and include catch trials to measure the pure
neural activity associated with previewing informative (cioè.,
in the preview condition) and uninformative (cioè., in the
baseline condition) first displays without any contamina-
tion from the neural activity arising from the search dis-
plays. This is comparable to experiments (Macaluso et al.,
2003; Hopfinger et al., 2000; Kastner et al., 1999) that sep-
arate the neural activity associated with the cue (cioè., IL
preparatory activity) with that associated with the target.

METHODS

Participants
Eighteen paid participants (14 women, 18–35 years old,
M = 24.3 years) gave written informed consent in accor-
dance with the ethical procedures of the Birmingham Uni-
versity Imaging Centre, Birmingham, UK. All had normal
or corrected-to-normal vision.

Stimuli and Apparatus

Experiments were created in Matlab (The Mathworks, Natick,
MA) using the Psychophysics Toolbox (Brainard, 1997;
Pelli, 1997). The distracter stimuli were white uppercase
Lʼs, presented at four different orientations on a black
background (0°, 90°, 180°, and 270°; Guarda la figura 1). The tar-
get stimulus was a white uppercase T, presented either

Payne and Allen

2047

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Figura 1. Experimental
procedure and stimuli.
Participants were instructed
to fixate on the central square
throughout the entire scan.
(UN) A preview search trial
(10 items). The distracters in
the first display remained on
the screen when the remainder
of the distracters and the
target (a T tilted ±90° from
vertical) appeared in the search
display. (B) A full search trial
(6 items). The first display was
uninformative; the distracters
offset at the start of the search
display and were replaced with
new distracters and a target
in the same quadrant. IL
target always appeared in the
search display for the preview
search and full search trials.
(C) A preview-only/dummy
trial. No search display was
presented for these trials.
During the end fixation for the
preview search and full search
trials, the fixation square
provided feedback; it changed
to a rectangle if the response
was incorrect (UN).

90° right or 90° left of vertical (randomly on each trial). IL
two line components making up each letter were identical
in length. The fixation consisted of a centrally located red
square (0.27° × 0.27°, at a distance of 65 cm).

Possible stimulus locations were arranged on a circular
140-cell virtual matrix that consisted of eight concentric cir-
cular grids with radii of 1°, 2.1°, 3.2°, 4.9°, 7°, 9.1°, 11.2°,
and 14°. Stimuli were scaled according to the human cor-
tical magnification factor (Dougherty et al., 2003; Horton
& Hoyt, 1991), resulting in 4, 8, 16, 12, 20, 24, 32, E 24
cells per circular grid. The stimuli presented on the three
innermost circular grids subtended 0.63° × 0.63°, il prossimo
four grids presented stimuli subtending 1.37° × 1.37°, E
the outermost ring presented stimuli subtending 2.41° ×
2.41°. The display was divided along the vertical and hor-
izontal meridians to create four quadrants resulting in 35
possible stimulus locations per quadrant. Stimuli were ran-
domly assigned to cells in one quadrant for each trial, E
were positioned in the center of each cell. There were two
set sizes of 6 E 10 stimulus items.

Behavioral Methods

Participants completed four experimental scans (each 14 min
26 sec). Each scan consisted of two blocks of trials: a pre-
view block and a full (baseline) block. There were two
types of trial in the preview block: preview search (n = 20)
and preview only (n = 12). A preview search trial was
composed of two consecutive 2-sec displays. The first was

the preview display which presented half of the distracter
items (either 3 O 5) followed by the second, search, dis-
play, where the remainder of the distracter items (either
2 O 4) plus the target (always present) joined the pre-
viewed items on the screen. Participants indicated, us-
ing a response box held in the right hand, whether the T
was tilted leftward or rightward. If a response was not
made within 2 sec, it was counted as being incorrect. UN
preview-only trial consisted only of the initial preview dis-
play followed by 2 sec of fixation. Participants did not know
when these trials would occur and were instructed not
to respond on these trials. All trials began and finished with
a 1-sec fixation, and feedback was given during the end fixa-
tion for a preview search trial via a change in shape of the
fixation marker (see Figure 1A and C). Trial order and ITI
length (between 4 E 12 sec) were randomly selected
separately for each participant using Optseq2 (http://surfer.
nmr.mgh.harvard.edu/optseq). For each combination of
set size and quadrant there were 10 preview search trials
E 6 preview-only trials across all four scans.

There were also two trial types in the full block: full
search and dummy trials (see Figure 1B and C). These
trials were identical to those in the preview block in terms
of the trial numbers, trial sequence, set sizes, and presen-
tation quadrants. Tuttavia, for the full search trials, IL 3
O 5 distracters presented in the first display disappeared
with the onset of the search display and were replaced by
5 O 9 new distracters (plus the target) in the same quad-
rant. The final number of items in the search display of the

2048

Journal of Cognitive Neuroscience

Volume 23, Numero 8

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full search condition matched the final number in the pre-
view search condition. The dummy trials were visually the
same as preview-only trials.

The order of the two blocks within a scan was counter-
balanced across participants and scans. Each scan began
and ended with 30 sec of fixation. Prior to each block,
there was a 3-sec instruction indicating the following
block type. The two blocks were separated by a 31-sec fix-
ation screen. Participants were instructed to fixate the cen-
tral square for the entirety of the scan, and to use their
peripheral vision to perform the task. Participants were en-
couraged to actively ignore the previewed distracters in
the preview block and were informed that it would not
be useful to ignore the distracters in the first displays of
the trials in the full block. All participants undertook a
practice session outside the scanner prior to the experi-
ment (average correct performance = 84%).

fMRI Methods

Data were acquired using a 3-T Philips Achieva MRI scanner.
Participants lay in the scanner and viewed the projector
screen through a tilted mirror on the eight-channel SENSE
head coil. If necessary, participants wore MRI-compatible
glasses to correct vision. The BOLD signal was measured
using a T2*-weighted echo-planar imaging sequence (con
32 ascending slices, a repetition time of 2000 msec, a time
to echo of 35 msec, a flip angle of 85°, and a resolution of
2.5 mm3). A T1-weighted high-resolution anatomical scan
(1 mm3) was acquired during the same session.

The fMRI Expert Analysis Tool (FEAT) Version 4.0.4 (part
of FMRIBʼs software library, available at www.fmrib.ox.ac.
uk/fsl) was used to process and analyze the data. Prepro-
cessing of each functional scan involved head motion cor-
rection (absolute mean displacements per scan averaged
across participants were 0.48, 0.56, 0.46, E 0.58 mm),
slice-timing correction, nonbrain removal, spatial smooth-
ing (5 mm full width at half maximum Gaussian kernel),
intensity normalization and high-pass Gaussian-weighted
temporal filtering (sigma = 50 sec). Each participantʼs
functional dataset was registered with their anatomical im-
age and then transformed into MNI space. Unexpected
noise and artifacts were removed using Probabilistic Inde-
pendent Component Analysis (Beckmann & Smith, 2004)
implemented in MELODIC (Multivariate Exploratory Linear
Decomposition into Independent Components), part of
FMRIBʼs software library. Only 25 (of a total of 72) del
search scans required component removal, and of these
scans, an average 3.8% of components were removed.

fMRI Analysis

General linear modeling analysis was conducted for each
scan using FILM with local autocorrelation correction
(Woolrich, Ripley, Brady, & Smith, 2001). A design matrix
was created with 16 regressors representing each experi-
mental condition according to the following factorial de-

sign: 4 (trial type: preview search, preview only, full search,
and dummy) by 4 (quadrant: lower-left, lower-right, superiore-
left, and upper-right). Data were collapsed across set size.
Preview search and full search trial regressors were defined
as the duration from the onset of the first display to the
response time. Preview-only and dummy trial regressors
were the duration of the first display (cioè., 2 sec). Trials with
incorrect responses were modeled as regressors of no in-
terest as were the six movement parameters obtained dur-
ing motion correction. All regressors were convolved with
a gamma function.

Contrasts of interest included comparing preview-only
trials with dummy trials for each quadrant separately. Simi-
larly, contrasts were created to compare preview search
with full search trials for each quadrant. Contrasts were com-
bined across runs for each participant using fixed effects
analysis. Group analysis was conducted using FMRIBʼs Lo-
cal Analysis of Mixed Effects ( Woolrich, Behrens, Bedell,
Jenkinson, & Smith, 2004; Beckmann, Jenkinson, & Smith,
2003). Z (Gaussianized T/F) statistic images were thresh-
olded using clusters with Z > 2.1 and a (corrected) cluster
significance threshold of p < .05 (Worsley, Evans, Marrett, & Neelin, 1992) or an extent threshold of k > 50 and a
significance threshold of p = .05. Group analyses included
a prethreshold mask to limit results to the gray matter.
Time-course data were extracted from each run for each
participant using the Perl Event-related Average Time-
course Extraction tool (www.jonaskaplan.com/peate).

Psychophysiological Interaction Analysis

We conducted psychophysiological interaction (PPI) anal-
yses to examine brain activity functionally connected to
activations identified with the main analyses. To create
the source regions for the PPI analysis, the most significant
voxel from each brain region was identified and a 6-mm
spherical ROI was centered on this voxel. The mean activ-
ity time courses were extracted from the source regions of
each of the participantʼs scans. The first level of an indi-
vidual PPI analysis was conducted on each scan separately
and included 16 regressors that represented the interac-
tion between the time course of the source region and
IL 16 experimental conditions. Contrasts of interest were
preview search–full search and preview only–dummy for
each quadrant (and vice versa). Contrast images were en-
tered into a fixed effects analysis to average data within
each participant and a group-level mixed effects analysis
Z > 1.7 and p < .05 was conducted (as above; Worsley et al., 1992). RESULTS Behavioral Data Data were collapsed across the separate search scans and analyses were performed on the preview search trials and full search trials separately for each set size. Payne and Allen 2049 D o w n l o a d e d l l / / / / j t t f / i t . : / / f r o m D h o t w t n p o : a / d / e m d i f t r o p m r c h . s p i l d v i e r e r c c t . h m a i r e . d u c o o m c / n j a o r c t i n c / e a - p r d t i 2 c 3 l 8 e - 2 p 0 d 4 f 6 / 1 2 9 3 4 / 1 8 5 / 8 2 7 0 o 4 c 6 n / 1 2 0 7 1 7 0 5 9 2 4 1 8 5 6 / 2 j o p c d n . b y 2 0 g 1 u 0 e . s t 2 o 1 n 5 6 0 2 7 . S p e d p f e m b y b e g r u 2 0 e 2 s 3 t / j f . / . t . o n 1 8 M a y 2 0 2 1 Table 1. Proportion of Correct Responses for Each Search Condition and Set Size Set Size Full Search Preview Search 0.84 0.77 0.89 0.86 6 10 Accuracy We recorded RTs and accuracy. All participants achieved 75% (or more) correct responses (Table 1). A repeated measures ANOVA with factors of condition (full search, preview search) and set size (6, 10 items) revealed sig- nificant main effects of condition [F(1, 17) = 27.7, p = .00006, partial η2 = 0.62] and set size [F(1, 17) = 15.8, p = .001, partial η2 = 0.48], and no significant interac- tion [F(1, 17) = 1.6, p = .22, partial η2 = 0.87]. Because there was a response deadline in the experiment (2 sec, after which responses were recorded as errors), the sig- nificant effects of condition and set size were not un- expected. RTs were longer in both the full condition and at the larger set size, thus there was a speed–accuracy tradeoff. Reaction Times We used an adjusted response time measure (RTadj) in- stead of RT as the dependent measure due to the re- stricted response period. We divided the average correct RT for each participant, condition, and set size combina- tion by the proportion correct for that combination. We used this adjustment in a recent study (Allen et al., 2008) where the error rates were also inflated by a response deadline. Figure 2A plots the RTadj against set size for the full search and preview search conditions. RTadj data for the correct trials were entered into a re- peated measures ANOVA with main factors of condition (preview search, full search) and set size (6, 10 items). De- spite there being no significant interaction between condi- tion and set size [F(1, 17) = 1.9, p = .19, partial η2 = 0.1], performance on full search was significantly slower than that in preview search [F(1, 17) = 54, p = .000001, partial η2 = 0.76], suggesting an advantage of the preview dis- play. Participants were slower with more display items [F(1, 17) = 33.6, p = .00002, partial η2 = 0.66]. Inspection of individual participant data revealed var- iations in preview benefit across participants, enabling us to categorize participants as “previewers” and “non- previewers.” A total of 12 of the 18 participants were classi- fied as previewers, identified strictly as those displaying the standard preview benefit ( Watson & Humphreys, 1997) measured in terms of an improvement of search efficiency (in terms of time per item) in the preview condition com- pared to the full condition. An ANOVA revealed a signifi- cant interaction between condition and set size for these participants [F(1, 11) = 15.4, p = .002, partial η2 = 0.58; Figure 2B]. There was also a significant interaction be- tween condition and set size for the non-previewers [F(1, 5) = 14.2, p = .013, partial η2 = 0.74], although the full and preview search slope functions did not conform to the standard preview benefit (Figure 2C). In a similar vein, we observed that there was considerable variation in preview benefit across quadrants (Figure 3A– D). For each participant, we calculated RTadj for each quadrant, set size, and search condition combination, and separate ANOVAs for each quadrant (including all partici- pants) revealed a significant interaction between condition and display size for only the lower-left quadrant [F(1, 17) = 12, p = .003, partial η2 = 0.41]. Thus, the best preview benefit was found in the lower-left quadrant where search efficiency for the preview search condition was significantly better than the efficiency in the full search condition. Fur- thermore, 13 of the 18 participants displayed a clear pre- view benefit in terms of slope differences between the conditions in the lower-left quadrant. Nine participants previewed in the lower-right and upper-right quadrants, whereas only six participants previewed in the upper-left D o w n l o a d e d l l / / / / j f / t t i t . : / / f r o m D h o t w t n p o : a / d / e m d i f t r o p m r c h . s p i l d v i e r e r c c t . h m a i r e . d u c o o m c / n j a o r c t i n c / e a - p r d t i 2 c 3 l 8 e - 2 p 0 d 4 f 6 / 1 2 9 3 4 / 1 8 5 / 8 2 7 0 o 4 c 6 n / 1 2 0 7 1 7 0 5 9 2 4 1 8 5 6 / 2 j o p c d n . b y 2 0 g 1 u 0 e . s t 2 o 1 n 5 6 0 2 7 . S p e d p f e m b y b e g r u 2 0 e 2 s 3 t / j . t . . f / o n 1 8 M a y 2 0 2 1 Figure 2. Adjusted reaction times (RTadj) plotted against set size for the full (filled squares) and preview (unfilled circles) search conditions averaged across (A) all participants (n = 18), (B) previewers (n = 12), and (C) non-previewers (n = 6). RTadj is measured by RT/proportion correct. The slope function in terms of time (msec) per search item for each condition is reported. Vertical bars represent ±1 standard error. 2050 Journal of Cognitive Neuroscience Volume 23, Number 8 Figure 3. Adjusted reaction times (RTadj) plotted against set size for the full (filled squares) and preview (unfilled circles) search conditions averaged across all participants (n = 18). The search slopes are plotted for each quadrant separately: (A) upper-left quadrant, (B) upper-right quadrant, (C) lower-left quadrant, and (D) lower-right quadrant. The slope function in terms of time (msec) per search item for each condition is reported. Vertical bars represent ±1 standard error. quadrant. Note that the search slopes in the lower-right quadrant (Figure 3D) indicate a standard preview benefit for this quadrant, although this is not significant ( p = .26). It is unclear why there are stronger preview benefits in the lower visual field (although it is consistent with attention studies that report a lower visual field advantage for tasks in- volving attention, e.g., He, Cavanagh, & Intriligator, 1996). It is possible that the unusual viewing conditions made it easier (or more difficult) to direct attention to (or from) certain lo- cations. We used the differences in preview benefit between quadrants, as well as between previewing and nonpreview- ing participants, to search for BOLD activity specifically linked to successful preview by incorporating these behav- ioral variations into the fMRI analyses. Because the behav- ioral preview benefit was stronger in some quadrants and participants, this allows us to find the neural signature relat- ing to a successful preview benefit while removing activity relating to merely searching the stimuli or intent to preview. full search/dummy trials. Preview activity in behavioral non-previewers was deducted from preview activity in be- havioral previewers (Table 2). Supporting previous findings (Dent et al., in press; Allen et al., 2008; Olivers et al., 2005; Pollmann et al., 2003), we find activation in the precuneus and SPL that corresponds with ignoring the preview display. Regardless of what attentional task a participant intends to perform, they will only be successful if the correct neural messages are passed to earlier cortical stages. If the intent is to attend to a particular target, but the appropriate stimulus- specific neurons are not modulated, then the target will not be enhanced, for example. Here, only some of our par- ticipants and quadrants generated a preview benefit (see above). Thus, we can assume that the activation patterns that underlie the preview benefit will be stronger in the more successful preview trials. In our data, regions such as the SPL were more activated when previewers (as opposed to non-previewers) had greater preview benefit, which sug- gested that this was the case (Supplementary Figure). Imaging Data fMRI data from all scans from one participant and from two scans belonging to another participant were discarded due to excessive head movement. Preview-related Neural Activity First, we identified brain areas showing preview-related activity. Preview search/only trials were contrasted against Linking Preview-related Neural Activity with Behavioral Preview Benefit Here, the critical comparison is between preview-only and dummy trials as this reveals processes involved with active ignoring without contamination from the search displays. For each participant and quadrant separately, dummy tri- als were deducted from preview-only trials. Because we were interested in trials where the intent to preview was Payne and Allen 2051 D o w n l o a d e d l l / / / / j f / t t i t . : / / f r o m D h o t w t n p o : a / d / e m d i f t r o p m r c h . s p i l d v i e r e r c c t . h m a i r e . d u c o o m c / n j a o r c t i n c / e a - p r d t i 2 c 3 l 8 e - 2 p 0 d 4 f 6 / 1 2 9 3 4 / 1 8 5 / 8 2 7 0 o 4 c 6 n / 1 2 0 7 1 7 0 5 9 2 4 1 8 5 6 / 2 j o p c d n . b y 2 0 g 1 u 0 e . s t 2 o 1 n 5 6 0 2 7 . S p e d p f e m b y b e g r u 2 0 e 2 s 3 t / j t . . / f . o n 1 8 M a y 2 0 2 1 Table 2. Areas of Significant Clusters of Preview-related Activity, Averaged across Quadrants, for Behavioral Previewers Compared to Non-previewers (Extent Threshold = 50, p = .05) Contrast Structure Location x, y, z (mm) Z Score Volume ( Voxels) Preview (search and only)–full L Lateral occipital cortex/precuneus (search and dummy) L Lateral occipital cortex L Precuneus L Precentral gyrus L Supramarginal gyrus L Superior frontal gyrus Preview only–dummy L Lateral occipital cortex/precuneus R Precentral gyrus R Lateral occipital cortex/SPL L Lateral occipital cortex L Cingulate gyrus R Cingulate gyrus Preview search–full search L Lateral occipital cortex/SPL L Postcentral gyrus L Lateral occipital cortex L Precentral gyrus R Middle temporal gyrus −24, −64, 32 −42, −74, 16 −12, −54, 56 −24, −6, 46 −54, −24, 26 0, 32, 52 −22, −64, 32 48, 4, 26 36, −62, 52 −42, −74, 16 −6, −28, 34 10, −42, 38 −28, −62, 60 −52, −26, 50 −40, −74, 16 −24, −6, 48 46, −46, 12 2.56 2.84 2.14 3 2.33 2.22 3.07 2.25 2.73 2.41 2.44 2.14 2.64 2.38 2.54 3.44 2.7 239 115 75 67 67 59 414 194 80 71 50 50 189 100 92 91 69 successfully carried out, quadrants that participants pre- viewed in were compared to those quadrants in which participants did not preview. There were three clusters where activity was greater for previewers compared to non- previewers (Table 3, Figure 4). Supporting previous findings (Dent et al., in press; Allen et al., 2008; Olivers et al., 2005; Pollmann et al., 2003), we found activation in the left and right precuneus corre- sponding to ignoring the preview display. Secondly, the results indicate that actively ignoring visual information leads to signal changes in early visual cortex. To investigate whether actively preparing to ignore in- creased activation in the precuneus and visual cortex, we extracted the mean BOLD activity from these areas for the preview only–dummy contrast for each quadrant and par- ticipant and correlated these signals with the magnitude of behavioral preview benefit (Figure 5A–D). We extracted the mean BOLD signal (using Featquery) from spherical ROIs of 6 mm radius centered on the maximally activated peak voxels in the left precuneus (−8, −78, 40), right pre- cuneus (14, −82, 42), left intracalcarine cortex (−10, −90, −2), and left occipital fusiform gyrus (−16, −88, −10). To calculate the magnitude of behavioral preview benefit for each participant and quadrant, we used Equation 1: Preview Benefit ¼ Efficiency : Full Search þ c Efficiency : Preview Search þ c ð1Þ where c is a constant added to reflect that slopes occasion- ally decreased with increasing set size in the preview con- dition. The behavioral preview benefit was significantly correlated with activation in left intracalcarine cortex and the left precuneus but not with the right precuneus and left occipital fusiform gyrus. We further examined the fMRI data in response to preview- only and dummy trials presented to the quadrant (lower- left) that showed the strongest benefit from preview. This contrast revealed significantly greater preview activ- ity for the behavioral previewers compared to the non- previewers in occipital cortex (Table 4). Importantly, the focus of activation in visual cortex is located above the calcarine sulcus in the right hemisphere, that is, contra- lateral to the visual field of stimulation, and thus, corre- sponds to the known retinotopic anatomy of early visual cortex. As predicted by the behavioral data, there was no signif- icant preview-related neural activity from the other presen- tation quadrants. However, with a threshold of p = .01 (uncorrected, k > 50), an area of early visual cortical activ-
ità (−18, −104, 0; 110 voxels) related to successful pre-
viewing was identified in the left hemisphere for the
lower-right quadrant (cioè., contralateral to the visual field
of stimulation). There were no (k > 50) areas of activation
in visual regions for the upper-left and upper-right quad-
rant analyses using the uncorrected threshold.

2052

Journal of Cognitive Neuroscience

Volume 23, Numero 8

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Tavolo 3. Three Clusters of Significant Activations for the Preview-only–Dummy Contrast for Quadrants in Which Participants
Behaviorally Previewed Compared to Quadrants in Which Participants Did Not Preview (Cluster Threshold Z = 2.1, P < .05) Structure Left Occipital Location x, y, z (mm) Z Score Volume ( Voxels) L Occipital fusiform gyrus extending to: −16, −88, −10 3.45 1556 –L Intracalcarine cortex –L Lateral occipital cortex –L Lingual gyrus Left Medial −10, −90, −2; 0, −94, 4 −44, −72, −10; −36, −86, 2 −6, −76, −8 L Occipital cortex extending to: −30, −92, 24 3.76 645 –L Precuneus −8, −78, 40; −10, −76, 54; −6, −70, 56; −6, −80, 52 –L Lateral occipital cortex −16, −86, 42 Right Medial R Lateral occipital cortex extending to: 44, −58, 54 3.64 1199 –R Angular gyrus –R Precuneus –R Lateral occipital cortex 42, −54, 56; 50, −52, 56 14, −82, 42 50, −58, 52; 26, −70, 46 Psychophysiological Interaction We performed functional connectivity analyses to identify the contribution of the precuneus to activity in other brain regions. We examined whether the coupling between the precuneus and other brain areas differed depending on whether the observers were actively ignoring items in the first display (i.e., preview condition) compared to when Figure 4. Preview-related group activation revealed from the preview only–dummy contrast for quadrants in which participants behaviorally previewed compared to those quadrants in which participants did not preview (presented on the MNI template brain). D o w n l o a d e d l l / / / / j f / t t i t . : / / f r o m D h o t w t n p o : a / d / e m d i f t r o p m r c h . s p i l d v i e r e r c c t . h m a i r e . d u c o o m c / n j a o r c t i n c / e a - p r d t i 2 c 3 l 8 e - 2 p 0 d 4 f 6 / 1 2 9 3 4 / 1 8 5 / 8 2 7 0 o 4 c 6 n / 1 2 0 7 1 7 0 5 9 2 4 1 8 5 6 / 2 j o p c d n . b y 2 0 g 1 u 0 e . s t 2 o 1 n 5 6 0 2 7 . S p e d p f e m b y b e g r u 2 0 e 2 s 3 t / j / f t . . . o n 1 8 M a y 2 0 2 1 Payne and Allen 2053 Figure 5. The magnitude of behavioral preview benefit plotted against mean BOLD signal extracted from the (A) left precuneus, (B) right precuneus, (C) left intracalcarine cortex, and (D) left occipital fusiform gyrus for the preview only–dummy contrast for each participant and quadrant. One-tailed Pearsonʼs R2 and p values are indicated for each area. Each point represents data from each quadrant for each participant (n = 68). *p < .05. they were not (i.e., full condition). We seeded the separate PPI analyses in the left (centered at −8, −78, 40) and right precuneus (centered at 14, −82, 42). The PPI analysis using the right precuneus as the source region revealed that there was differential activation within regions of the fronto-parietal attention network depending on whether participants were undertaking the dummy condition or the preview-only condition and whether participants were previewers or non-previewers. We found that for those par- ticipants who benefited from the preview, the right pre- cuneus interacted significantly with the postcentral and the precentral gyri when participants were completing the dummy condition in comparison to the preview-only condition (see Table 5 and Figure 6). Similar clusters of ac- tivation (R precentral gyrus = 14, −30, 70; L postcentral gyrus = −56, −18, 34) were found for the left precuneus source region with a threshold of p = .01 (uncorrected, k > 50). Precuneus activity during preview-only trials,
relative to dummy trials, was thus related to a decrease
in preview-related activation in attentional control areas
(Corbetta & Shulman, 2002).

For the PPI analyses contrasting full search with pre-
view search, for those participants who benefited from
the preview, both the left and right precuneus interacted
significantly with visual cortical regions when participants
were completing the full search condition in comparison
to the preview search condition (Tavolo 5, Figura 6). Pre-
cuneus activity during preview search trials was thus re-
lated to a decrease in search-related activation in visual
cortex (relative to full search trials). Of particular interest
here is that there is significant activation in early visual
cortex, specifically in intracalcarine cortex (−16, −70,
4). Other areas of activation that overlap across the two
analyses include left lateral occipital cortex and right cu-
neal cortex.

DISCUSSION

Extending previous studies, we found that (Dent et al., In
press; Allen et al., 2008; Olivers et al., 2005; Pollmann
et al., 2003) precuneus activation was associated with suc-
cessfully ignoring distractors. Secondo, preparatory-related

Tavolo 4. Areas of Significant Activations for the Preview Only–Dummy Contrast in the Lower-left Quadrant for Behavioral
Previewers Compared to Non-previewers (Cluster Threshold Z = 2.1, P < .05) Structure Location x, y, z (mm) R Intracalcarine cortex extending to: –R Occipital pole –R Lingual gyrus –L Lingual gyrus 6, −82, 10 8, −92, 20 8, −74, −4; 4, −82, −8 −4, −74, −6 Z Score 3.33 Volume ( Voxels) 901 2054 Journal of Cognitive Neuroscience Volume 23, Number 8 D o w n l o a d e d l l / / / / j t t f / i t . : / / f r o m D h o t w t n p o : a / d / e m d i f t r o p m r c h . s p i l d v i e r e r c c t . h m a i r e . d u c o o m c / n j a o r c t i n c / e a - p r d t i 2 c 3 l 8 e - 2 p 0 d 4 f 6 / 1 2 9 3 4 / 1 8 5 / 8 2 7 0 o 4 c 6 n / 1 2 0 7 1 7 0 5 9 2 4 1 8 5 6 / 2 j o p c d n . b y 2 0 g 1 u 0 e . s t 2 o 1 n 5 6 0 2 7 . S p e d p f e m b y b e g r u 2 0 e 2 s 3 t / j . / t f . . o n 1 8 M a y 2 0 2 1 Table 5. Areas That Significantly Interact with the L Precuneus and the R Precuneus for the Dummy/Full Search–Preview-only/ Preview Search Contrasts for Quadrants in Which Participants Behaviorally Previewed Compared to Quadrants in Which Participants Did Not Preview (Cluster Threshold Z = 1.7, p < .05) Contrast Structure Location x, y, z (mm) Z Score Volume ( Voxels) Dummy–preview Source region: R Precuneus only L Postcentral gyrus extending to: −32, −36, 70 3.45 1466 –R Precentral gyrus 24, −22, 62; 10, −30, 74; –R Postcentral gyrus Full search– preview search Source region: L Precuneus L Cuneal cortex extending to: –L Intracalcarine cortex –L Lateral occipital cortex –R Cuneal cortex Source region: R Precuneus 22, −26, 74 16, −30, 70 −8, −88, 24 −16, −70, 4 −22, −82, 36; −28, −72, 20 8, −84, 40; 18, −72, 24 3.58 4712 L Lateral occipital cortex extending to: −24, −82, 38 4.13 5628 –L Intracalcarine cortex –R Cuneal cortex –R Lateral occipital cortex −16, −78, 2; −16, −70, 4 18, −70, 22 16, −84, 38 activity also increased neural activity in early visual cortex during this active ignoring process. Third, precentral and postcentral gyri activation (part of the fronto-parietal atten- tion network), driven by the precuneus, was reduced when successful previewers were preparing to ignore distracters. Fourth, search-related activation in early visual cortex, driven by the precuneus, was reduced when participants were able to successfully ignore early presented distracters. Figure 6. Results of PPI analyses. Yellow: BOLD activity driven by the right precuneus when previewing participants (relative to non-previewers) completed the dummy trials relative to the preview-only trials. Green: BOLD activity driven by both the left precuneus and the right precuneus when previewing participants (relative to non-previewers) completed the full search trials relative to the preview search trials. Activations are presented on the MNI template brain. D o w n l o a d e d l l / / / / j f / t t i t . : / / f r o m D h o t w t n p o : a / d / e m d i f t r o p m r c h . s p i l d v i e r e r c c t . h m a i r e . d u c o o m c / n j a o r c t i n c / e a - p r d t i 2 c 3 l 8 e - 2 p 0 d 4 f 6 / 1 2 9 3 4 / 1 8 5 / 8 2 7 0 o 4 c 6 n / 1 2 0 7 1 7 0 5 9 2 4 1 8 5 6 / 2 j o p c d n . b y 2 0 g 1 u 0 e . s t 2 o 1 n 5 6 0 2 7 . S p e d p f e m b y b e g r u 2 0 e 2 s 3 t / j . / f . t . o n 1 8 M a y 2 0 2 1 Payne and Allen 2055 Preview-related Preparatory Activity in Early Visual Cortex Previous studies have demonstrated preparatory activity in visual cortex for targets (Macaluso et al., 2003; Hopfinger et al., 2000; Kastner et al., 1999) and distracters (Ruff & Driver, 2006; Serences et al., 2004). Here, preparatory activity associated with previewing irrelevant distracters occurred in early visual cortex and could be easily sepa- rated from target-related activity. Our results demonstrate increased neural activity in primary visual cortex (in likely V1 identified using WFU PickAtlas: Maldjian, Laurienti, Kraft, & Burdette, 2003) that was quadrant specific. Con- sistent with the finding that increased preview-related BOLD activation in early visual cortex is correlated with the magnitude of behavioral preview benefit, the trials presented to the upper visual quadrants did not display a behavioral preview benefit or enhanced neural activity. The asymmetry of preview performance between upper and lower visual quadrants may be explained by a com- monly reported behavioral finding that visual processing is enhanced in the lower visual field compared to the upper visual field (e.g., Danckert & Goodale, 2001; Rubin, Nakayama, & Shapley, 1996). In particular, it has been re- ported that there is an advantage for attentional process- ing in the lower visual field (He et al., 1996). The portion of visual cortex in the macaque monkey brain that repre- sents the lower visual field projects considerably more to posterior parietal cortex, an area involved with spatial at- tention, than does the portion that represents the upper visual field (Maunsell & Newsome, 1987). This may explain the lower visual field advantage with attentional tasks in humans. However, the asymmetry seen here is weak with only the lower-left quadrant showing a significant advan- tage for the preview condition. Further research is re- quired to assess the specificity of the preview benefit to visual field location. Precuneus Activity There was a bilateral increase in precuneus neural activity for the preview-only trials relative to the dummy trials. The precuneus is consistently activated (Dent et al., in press; Allen et al., 2008; Olivers et al., 2005; Pollmann et al., 2003) in response to preview trials, suggesting this region plays a critical role in visual marking. This brain area is thought to be involved with a variety of higher-level cognitive func- tions including episodic memory, consciousness, and visual– spatial imagery (see Cavanna & Trimble, 2006 for a review). Allen et al. (2008) found that the precuneus was activated both by a visual working memory task and by a preview search task, and that the former could interfere with the latter. This provides evidence that the precuneus is in- volved with encoding the spatial representations of the old, to-be-inhibited, items in memory. Indeed, a second- ary auditory task did not interfere with the preview task if it was presented 1 sec after the presentation of the pre- view, whereas a secondary visual task did interfere, imply- ing that the visual memory representation of the old distracter items is critical (Humphreys et al., 2002). Functional Connectivity Analysis We report that activity in the precuneus is more con- nected with fronto-parietal activation for the dummy con- dition relative to the preview-only condition in successful previewers. The pre/postcentral cortical activation we dis- cerned has been implicated in several functional imaging studies that have used spatial attention tasks (Donner et al., 2000; Culham et al., 1998; see Corbetta & Shulman, 2002 for a review). Although often considered to be pas- sively viewed, the dummy trials informed observers as to the location of the subsequent stimulus and to prepare for a relatively difficult search task. It seems reasonable, therefore, that there is a strong connection with areas in- volved in attentional control and orienting in these trials. In support, a visual search study by Weidner, Krummenacher, Reimann, Müller, and Fink (2008) found that decreased target saliency increased BOLD activation in several areas of the fronto-parietal attention network, including pre/ postcentral cortex. For preview search, it seems that these orienting signals are comparatively weak in comparison to the preview-related activity. We also report that activity in the precuneus is related to decreases in early visual cortex activation for the pre- view search condition relative to the full search condition in successful previewers. This is in contrast to the increase in early visual activation for the preview-only condition rel- ative to the dummy. Thus, it seems that in early visual cor- tex, successful ignoring of the previewed distracters is related to, first, an increase in activity but also an overall down modulation of activity by the precuneus. This is con- sistent with recent studies comparing distracter encoding during the preview display that also show an increase in activity associated with the preview benefit (Allen et al., 2008; Pollmann et al., 2003). Similarly, Humphreys et al. (2004) presented probe dots early (200 msec) and late (800 msec) in a preview display. As with previous probe- dot detection studies (Olivers & Humphreys, 2002; Watson & Humphreys, 2000), late probes gave rise to longer RTs when they appeared at the locations of the old distracters than when they occurred at the location of the new dis- tracters, suggesting inhibition of the old distracters. How- ever, detection of early probes was actually facilitated, suggesting that participants initially attend to the old dis- tracters before inhibiting them. Similarly, results from an event-related potential study (Belopolsky, Peterson, & Kramer, 2005) suggest that the inhibition of old distracters is applied toward the end of the preview interval. Of course, such an explanation requires that a decrease in BOLD signal means a decrease in neural activity (see Shmuel, Augath, Oeltermann, & Logothetis, 2006). The processes underlying the preview benefit can be separated into two components (Humphreys et al., 2002). 2056 Journal of Cognitive Neuroscience Volume 23, Number 8 D o w n l o a d e d l l / / / / j t t f / i t . : / / f r o m D h o t w t n p o : a / d / e m d i f t r o p m r c h . s p i l d v i e r e r c c t . h m a i r e . d u c o o m c / n j a o r c t i n c / e a - p r d t i 2 c 3 l 8 e - 2 p 0 d 4 f 6 / 1 2 9 3 4 / 1 8 5 / 8 2 7 0 o 4 c 6 n / 1 2 0 7 1 7 0 5 9 2 4 1 8 5 6 / 2 j o p c d n . b y 2 0 g 1 u 0 e . s t 2 o 1 n 5 6 0 2 7 . S p e d p f e m b y b e g r u 2 0 e 2 s 3 t / j / f . t . . o n 1 8 M a y 2 0 2 1 First, observers attend and encode the previewed dis- tracters to form a representation of the items in memory. Second, this representation is inhibited and the new items are prioritized. Thus, the increased activation for pre- view during the first display is likely to represent active attentional encoding of the distracters. The decreased activation for preview (relative to full search) is likely to reflect that in the full search condition there were effec- tively more items to search through. It is important to note, however, that the data cannot tell us whether activation in the preview search condition was suppressed relative to the full search condition or whether activation in the full search condition was increased relative to the preview search condition. Conclusion We used the preview search paradigm to investigate whether there are neural signatures relating to ignoring known distracters. We found that in order to benefit from the preview, observers must prepare to inhibit old dis- tracters, leading to an increase in activation in visual and parietal regions. Subsequently, further processing of these items is suppressed. 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Vision Research, 39, 293–306. 2058 Journal of Cognitive Neuroscience Volume 23, Number 8 D o w n l o a d e d l l / / / / j f / t t i t . : / / f r o m D h o t w t n p o : a / d / e m d i f t r o p m r c h . s p i l d v i e r e r c c t . h m a i r e . d u c o o m c / n j a o r c t i n c / e a - p r d t i 2 c 3 l 8 e - 2 p 0 d 4 f 6 / 1 2 9 3 4 / 1 8 5 / 8 2 7 0 o 4 c 6 n / 1 2 0 7 1 7 0 5 9 2 4 1 8 5 6 / 2 j o p c d n . b y 2 0 g 1 u 0 e . s t 2 o 1 n 5 6 0 2 7 . S p e d p f e m b y b e g r u 2 0 e 2 s 3 t / j . f . / t . o n 1 8 M a y 2 0 2 1

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