 |
 Previous Article | Next Article 
The Journal of Neuroscience, September 15, 1998, 18(18):7426-7435
Where and When to Pay Attention: The Neural Systems for Directing
Attention to Spatial Locations and to Time Intervals as Revealed by
Both PET and fMRI
Jennifer T.
Coull1 and
Anna C.
Nobre1, 2
1 Functional Imaging Laboratory, Wellcome Department of
Cognitive Neurology, Institute of Neurology, London WC1N 3BG, United
Kingdom, and 2 University of Oxford, Department of
Experimental Psychology, Oxford OX1 3UD, United Kingdom
 |
ABSTRACT |
Although attention is distributed across time as well as space, the
temporal allocation of attention has been less well researched than its
spatial counterpart. A temporal analog of the covert spatial
orientation task [Posner MI, Snyder CRR, Davidson BJ (1980) Attention
and the detection of signals. J Exp Psychol Gen 109:160-174] was
developed to compare the neural systems involved in directing attention
to spatial locations versus time intervals. We asked whether there
exists a general system for allocating attentional resources,
independent of stimulus dimension, or whether functionally specialized
brain regions are recruited for directing attention toward spatial
versus temporal aspects of the environment. We measured brain activity
in seven healthy volunteers by using positron emission tomography (PET)
and in eight healthy volunteers by using functional magnetic resonance
imaging (fMRI). The task manipulated cued attention to spatial
locations (S) and temporal intervals (T) in a factorial design.
Symbolic central cues oriented subjects toward S only (left or right),
toward T only (300 msec or 1500 msec), toward both S and T
simultaneously, or provided no information regarding S or T. Subjects
also were scanned during a resting baseline condition.
Behavioral data showed benefits and costs for performance during
temporal attention similar to those established for spatial attention.
Brain-imaging data revealed a partial overlap between neural systems
involved in the performance of spatial versus temporal orientation of
attention tasks. Additionally, hemispheric asymmetries revealed
preferential right and left parietal activation for spatial and
temporal attention, respectively. Parietal cortex was activated
bilaterally by attending to both dimensions simultaneously. This is the
first direct comparison of the neural correlates of attending to
spatial versus temporal cues.
Key words:
attention; space; time; orienting; parietal; lateralization; imaging
| |
INTRODUCTION |
Imagine waiting at traffic lights in
London that have just turned from red to amber. With this cue,
anticipation of the moment when the lights turn green begins. Common
experience tells us that focusing attention on the anticipated moment
will lead to quicker responses than if our mind is occupied elsewhere.
Similarly, within the spatial domain, attention must be directed toward
the light to respond efficiently. Focusing of attention within the spatial domain has been well investigated. The brain is capable of
directing attention dynamically across extrapersonal space on the basis
of expectations of where relevant events are likely to appear. Stimuli
appearing in predicted locations are detected more rapidly and
accurately than those that are not (Posner et al., 1980 ). Convergent
findings from neuropsychological (for review, see Mesulam, 1990) and
brain-imaging studies (Corbetta et al., 1993; Nobre et al., 1997) have
defined the neural network for spatial attention, the core elements of
which are posterior parietal cortex around intraparietal sulcus,
frontal eye fields in lateral and medial premotor cortex, anterior
cingulate, and subcortical areas.
By contrast, there has been little or no research investigating
attentional orienting to a particular point in time (but see Kingstone,
1992). Selective temporal attention is distinct from vigilance and from
the "attentional blink" in which target items occurring in close
temporal proximity compete for limited processing resources (Raymond et
al., 1992). Attentional orienting in time concerns whether and how
information about time intervals can be used to direct attention to a
point in time when a relevant event is expected, to optimize behavior.
Temporal orienting will depend on elementary time perception processes,
the neural correlates of which include the cerebellum (Ivry and Keele,
1989; Jueptner et al., 1995; Nichelli et al., 1996); basal ganglia (Rao
et al., 1997; Harrington et al., 1998), and frontal cortex (Nichelli et al., 1995; Harrington et al., 1998).
Our aim is to reveal the brain regions involved in directing attention
toward a particular time point once the time interval has
been estimated. Furthermore, we investigate the anatomical overlap
between the neural systems for spatial and temporal attention. We
developed a temporal analog of the spatial orienting of attention task
(Posner, 1980). In this task the subjects respond as quickly as
possible to visual targets appearing at peripheral locations. Immediately preceding the target is a visual cue that either correctly ("valid cue") or incorrectly ("invalid cue") predicts the
location of the upcoming target. Similarly, in our temporal orienting
task, we assessed whether stimuli that occurred at predictable cued intervals were detected more efficiently than those that did not occur
at the predicted moment. Brain imaging with PET and fMRI was used to
visualize the neural system involved in directing attention across
time, which was compared directly with that obtained during spatial
orienting. We ask whether there is a unitary system for allocating
limited-capacity attentional resources that is independent of the
stimulus dimension used to direct expectancies or whether functionally
specialized brain regions differentially deploy these resources toward
aspects of the extrapersonal world.
| |
MATERIALS AND METHODS |
Subjects
Seven healthy right-handed male volunteers (mean age 29) took
part in the PET experiment. Eight healthy right-handed volunteers (mean
age 30; 4 male, 4 female) took part in the fMRI experiment. Subjects
were physically fit, and none were taking medication. The study was
approved by the local hospital ethics committee, and written informed
consent was obtained before the study.
Experimental task
The basic visual display consisted of a central cueing stimulus
(1° eccentricity) and two peripheral boxes (7° eccentricity) inside
which the target ("x" or "+") appeared. The subjects' task was
to detect covertly the peripheral target stimuli as rapidly as possible
while avoiding mistakes. No discrimination was required. The reason for
using two types of stimulus was to enable compatibility with future
studies in which stimulus discriminations are involved.
The task manipulated subjects' expectations of where or
when target stimuli would appear within an experimental
display. A 2 × 2 factorial design was used in which the
experimental factors were spatial cueing (S) and temporal cueing (T).
Across runs there were four types of cues that predicted both spatial
location and onset time (ST), target location only (S), target onset
time only (T), and neutral cues that predicted neither target location
nor onset time (N).
The central cue was a compound stimulus consisting of a diamond and two
concentric circles. One part of the cue highlighted to inform the
subject whether to attend to the position of the target (left or right)
or to the time of the target (300 or 1500 msec from cue presentation)
(Fig. 1a). During the S
condition the left (or right) side of the diamond brightened to inform
the subject that the target is likely to appear in the left (or right) peripheral box. During the T condition a brightening of the inner circle indicated that the target would appear within a short time interval (300 msec), whereas a brightening of the outer circle represented a longer time interval (1500 msec). During the ST condition
one of the circles and one side of the diamond brightened, indicating
one of four combinations of spatial location and temporal interval (see
Fig. 1a). During the neutral cue (N) condition the entire
cue brightened, providing no spatial or temporal information.
View larger version (23K):
[in this window]
[in a new window]
|
Figure 1.
a, Attentional cues used to direct
subjects' attention to a particular target location or stimulus-onset
time. The neutral cue provides neither spatial nor temporal
information, the spatial (Space) cue directs the
subjects' attention to the left or right, the temporal
(Time) cue directs attention to a short or long
stimulus-onset time, and the spatiotemporal
(Space-Time) cue directs attention to both location and
stimulus-onset time. b, A typical trial, which in this
example directs the subjects' attention to a long stimulus-onset time,
with no information about the target's location. The attentional cue
is on for 100 msec, the cue-target interval is either
300 or 1500 msec (short/long cue), and finally the target appears for
50 msec in either the left or right
box.
|
|
The beginning of a trial was indicated by the brightening (100 msec) of
part of the central cue (Fig. 1b). Targets appeared for 50 msec in one of the two peripheral boxes and at one of two time periods,
according to the nature of the cue. Subjects indicated covert detection
of the target by pressing a response button with their right index
finger. The computer recorded reaction times (RTs) to target
stimuli.
Subjects performed two behavioral experimental sessions, one before and
one during the brain-imaging session. The behavioral session that
preceded scanning familiarized the subjects with the task and measured
each subject's attentional effects across experimental conditions. Two
hundred trials were presented for each of the four experimental
conditions. The proportion of trials with valid cues in the focused
attention conditions (ST, S, T) was 80%. Presentation order was
randomized both within and between subjects. During the PET session
each experimental run contained 60 trials and lasted ~2.5 min.
Subjects also were scanned during a resting baseline condition in which
they simply fixated on the static background display, which contained
cue, peripheral target boxes, and targets. There was an overall ratio
of 80:20 valid/invalid trials. During fMRI scanning, experimental
conditions were presented successively and in alternation with the
resting baseline condition. Only valid trials were imaged in the fMRI
scanning session.
PET scanning
Scans of the distribution of perfusion were obtained for each
subject, using a Siemens/CPS ECAT EXACT HR+ (model 962) PET scanner,
with septa retracted, to collect data in a three-dimensional mode. A
shielding insert was positioned at the front of the scanner to
attenuate the contribution of radioactivity from the rest of the body
to the recorded images. Radioactivity was administered as a
H215O bolus, infused over 20 sec,
followed by a 20 sec saline flush. The total effective dose equivalent
of radioactivity per subject was 5.0 mSv. Twelve PET emission scans
were collected over 96 min, with an 8 min interval between scans.
Integrated radioactivity counts over a 90 sec acquisition period,
beginning with the rising phase of radioactivity in the head, were used
as an index of local blood perfusion. A transmission scan was collected
before emission scans to check the position of subjects and to correct
for attenuation effects. Structural brain images also were obtained for
each subject, using T1-weighted MRI to coregister significant
functional PET activations with anatomy.
Of the 12 PET images that were obtained, 10 are relevant to the present
report. Two functional PET images were obtained for each of the four
experimental conditions of interest (ST, T, S, N). In addition, two
images were obtained during a resting baseline condition. Brain images
were collected after the subjects had been engaged in the task for 1 min. The order in which conditions were presented was randomized both
within and between subjects.
fMRI scanning
Scans were acquired by using a 2 Tesla Magnetom Vision (Siemens,
Erlangen, Germany) whole-body MRI system, which was equipped with a
head coil. Echo-planar imaging (EPI) was used to obtain T2*-weighted fMRI images in the axial plane. The acquired image volume consisted of 32 × 3-mm-thick slices, which allowed us to image the entire cortex, apart from the most ventral parts of the
temporal lobe. Two blocks of 350 images [with an interscan interval
(TR) of 3.5 sec] were acquired, with 70 images for each of the five
conditions, giving a total scanning time of ~41 min (2 × 20.5 min blocks). Each condition was presented for the duration of seven
scans (24.5 sec). Experimental conditions were presented 10 times each
in a counterbalanced manner (both within and between subjects). A
structural MRI image also was acquired (using a standard T1-weighted
scanning sequence) to allow for anatomically specific localization of
significant areas of brain activation.
Data analysis
Behavioral data. RT data for each of the attentional
tasks performed before scanning and during PET scanning were analyzed by repeated measures ANOVAs. The value of informative cues was assessed
in an ANOVA that compared the four task conditions (ST, S, T, N), of
which N provided noninformative cues, whereas all other conditions
provided valid cue information for 80% of the trials. The relative
advantage and disadvantage for valid and invalid cues was assessed with
an ANOVA on data from the two attention conditions in which cueing
information was provided along one dimension only (i.e., S and T). The
ANOVA tested for the effect of task condition (S, T), cue validity
(valid, invalid), target side (left, right), and interval duration
(short, long). A final ANOVA looked at data from the attention
condition that used both spatially and temporally informative cues
simultaneously (ST) and tested the effects of cue validity, target
side, and interval duration.
PET and fMRI data. All functional images (either PET images
or T2*-weighted fMRI images) for each subject were realigned to the
first image to correct for head movement between scans. Then the
structural MRI was coregistered to the functional images to put both
functional and structural images into the same space. All images were
spatially normalized into a standard space (Talairach and Tournoux,
1988) by matching each image to a standardized MNI template
(Montréal Neurological Institute, Québec, Canada), using
both linear and nonlinear three-dimensional transformations (Friston et
al., 1995a). Functional images were smoothed to accommodate intersubject differences in anatomy, using isotropic Gaussian kernels
of 16 and 8 mm for the PET and fMRI data, respectively, which yielded a
final resolution of 16 × 17 × 18 mm at full-width half-maximum for the PET data and 12 × 12 × 11 mm for the
fMRI data. The difference in degree of smoothing was reflective of the
anatomical resolution of each scanning technique.
Functional images were analyzed with statistical parametric mapping
(Friston et al., 1991) (SPM97d, Wellcome Department of Cognitive
Neurology, London, UK). Condition and subject effects were estimated
according to the general linear model at each voxel in brain space
(Friston et al., 1995b). For the PET data, indices of global blood flow
were modeled as a confounding covariate (normalized to 50 ml per 100 ml/min), using ANCOVA (Friston et al., 1990). For the fMRI data,
repeated measures (scans) were collapsed within subject (adjusting for
both global blood flow by using proportional scaling and low-frequency
physiological drifts by using a high-pass filter of 300 sec) to give
one scan per condition per subject. Then these conditions were compared
between subjects, thereby effecting a random effects model, allowing
inferences to be made about the general population. Analysis of single
subjects also was performed to aid anatomical localization of
significant activations from the group analysis.
For PET data, linear contrasts were used to test hypotheses about
regionally specific condition effects, which produced a statistical
parametric map of the t statistic generated for each voxel
(SPM{t}). The SPM{t} was transformed to a
map of corresponding Z values, thresholded at a Z
value of 3.09 (p = 0.001, uncorrected for
multiple comparisons), and the resulting foci were characterized in
terms of both spatial extent and peak height. The significance of each
region corrected for multiple comparisons was estimated by using
distributional approximations from the theory of Gaussian fields. For
the fMRI data, a Gaussian temporal smoothing kernel of 6 sec (at
full-width half-maximum) was applied to the data during statistical
analysis.
Statistical analysis was aimed at identifying common regions of
activation for both spatial and temporal orienting as well as regions
that were involved selectively in each type of attentional cueing.
Common areas were defined by the statistical conjunction (Price and
Friston, 1997) of the comparisons between each attentional cueing
condition (S and T) to the resting baseline. Rest was chosen as an
appropriate baseline for two reasons. First, this comparison provides
the most compatibility with previous reports in the literature by using
visual fixation controls (Corbetta et al., 1993). Second, although the
neutral condition would seem like a superior alternative, this
condition in itself engages attention and orients it along two spatial
locations and two temporal intervals. The comparisons that use the
resting baseline therefore provide the fuller picture of brain areas
involved in attentional orienting. However, brain areas involved in
general perceptual and motor demands of the task also will be revealed
in these comparisons. Therefore, we also computed common areas for
spatial and temporal orienting, using the neutral condition (N) as a
baseline, to identify areas that were involved specifically in both
focused spatial and focused temporal orienting. Both of these
conjunctions were computed by showing only the significant areas of
activation for one comparison (spatial orienting vs baseline) that also
were activated significantly in the other comparison (temporal
orienting vs baseline). To preserve the orthogonality of these
comparisons, we divided the baseline scans equally between the
two contrasts. We used a significance threshold that was uncorrected
for multiple comparisons, because the neural correlates of attentional
orienting already have been well defined (Nobre et al., 1997), enabling
us to make clear predictions about the areas we expected to be
activated.
Brain regions selectively involved in spatial attention were obtained
by contrasting the two conditions in which the cues contained spatial
information (S and ST) with the two conditions that did not (T and N)
(i.e., the main effect of space in the factorial design). To avoid
potential contributions from deactivations linked to temporal
orienting, we interrogated only those brain regions that also were
activated significantly more by spatial orienting than by rest [i.e.,
the S minus Rest contrast (p < 0.001) was used
to mask the entire brain volume]. Brain regions selectively involved
in temporal orienting were obtained in an analogous manner [the main
effect of time masked by T minus Rest (p < 0.001)]. Brain regions preferentially engaged when attention was
oriented in both time and space simultaneously, as opposed to either
one separately, also were calculated (ST minus S and T, masked by ST
minus Rest).
| |
RESULTS |
Behavioral data
Behavioral results are reported from both PET and fMRI subjects
pooled together (n = 12). Data from two of the fMRI
subjects and one of the PET subjects were lost because of technical
difficulties. Separate analyses for PET and for fMRI subjects yielded
equivalent effects, suggesting that each of the subject samples is
representative of the larger group.
The comparison of RTs across all task conditions (Table
1) revealed that RTs were significantly
faster when informative cues were provided than when neutral cues were
used [F(3,33) = 5.25; p = 0.005; paired t test comparing N with all other
conditions t(11) = 2.68; p = 0.02]. RT data in the tasks with cues that were informative in one
dimension (S and T) showed a significant main effect of task
[F(1,11) = 11.23; p < 0.01],
such that the T task was performed significantly faster (320 msec) than
the S task (352 msec) (Table 2). There
was also a significant main effect of validity
[F(1,11) = 35.55; p < 0.001].
Responses were significantly faster in valid trials (319 msec) as
compared with invalid trials (363 msec). These validity effects were
confirmed in separate analyses of the S and T conditions individually
[condition S: F(1,11) = 26.60, p < 0.001; condition T: F(1,11) = 12.78, p < 0.005]. Significant interactions between
task and validity [F(1,11) = 5.78;
p < 0.05] and between task and duration
[F(1,11) = 15.41; p < 0.005]
also were observed. These were qualified by a three-way interaction
among task, validity, and duration [F(1,11) = 7.28; p < 0.05]. This reflected a large validity
effect in all conditions except those in which temporal cues in the T
condition incorrectly predicted the target's appearance at the long
time interval (i.e., there was very little deleterious effect when the
subject expected the target to occur at the short time interval, but it
actually occurred at the longer one) (see Table 2). In the condition
with informative cues along two dimensions (ST), a main effect of cue validity was obtained [F(1,11) = 29.26;
p < 0.001], with valid RTs (299 msec) being faster
than invalid ones (348 msec). Full behavioral data are summarized in
Table 2.
View this table:
[in this window]
[in a new window]
|
Table 1.
Reaction times (msec) (and SE) for validly cued targets in
the S, T, and ST conditions and for all targets in the N condition
|
|
View this table:
[in this window]
[in a new window]
|
Table 2.
Reaction times (msec) (and SE) to targets during spatial
(S), temporal (T), spatiotemporal (ST), or neutral (N) conditions
|
|
PET data
Common activations for spatial and temporal orienting
Resting baseline. The spatial and temporal orienting
tasks activated many brain regions in common. The common network of
brain regions was defined by the conjunction of the comparisons between each attentional cueing condition (S and T) to the resting baseline. Table 3 and Figure
2 present the brain areas that were
activated in common by the spatial and temporal orienting tasks.
Frontal areas of the network included the lateral premotor cortex
bilaterally (BA 6), which extended medially and dorsally toward the
supplementary motor area (BA 6). These locations are consistent with
previous reports of frontal eye fields (FEF) (Paus, 1996). Posterior
parietal activations also were obtained bilaterally. In both
hemispheres, activations occurred in the intraparietal sulcus and
extended into the inferior parietal lobule (BA 40). An additional
separate cluster of activation occurred in the right hemisphere only,
centered on the intraparietal sulcus at a more posterior and superior
location. Large clusters of activations were centered over ventral
visual cortical areas, particularly of the left hemisphere. Bilateral cerebellum also was activated.
View larger version (136K):
[in this window]
[in a new window]
|
Figure 2.
Areas commonly activated by spatial and
temporal orienting of attention, as measured by PET. Activations are
numbered according to Table 3.
|
|
Neutral condition baseline. There were fewer areas activated
in common when the neutral condition was used as a baseline. Of the
regions activated in common and using rest as the baseline, only the
left ventral posterior visual cortex (x, y,
z =  54, 74, 8; Z = 3.58;
p < 0.001) was common to both spatial and temporal orienting. A subthreshold activation in the left parietal cortex also
was observed (x, y, z = 58,
48, 46; Z = 2.85; p = 0.002).
Spatial orienting
Spatial orienting of attention was associated with significantly
more activation in the right posterior parietal cortex in the inferior
parietal lobule (Table 4a).
This focus was within the general area of common right parietal
activations across types of orienting (see Table 3). Activation in the
right inferior parietal lobule was, therefore, significantly higher in
the spatial cueing condition relative to temporal cueing but was not
involved exclusively in spatial cueing. Figure
3Aa shows the inferior
parietal activation rendered on a surface view of a standard brain and on a sagittal section of the averaged MRI of all seven subjects. Activations also were found in the left ventral visual cortex and
cerebellum.
View larger version (96K):
[in this window]
[in a new window]
|
Figure 3.
A, Areas preferentially activated
by (a) spatial orienting,
(b) temporal orienting, and
(c) spatiotemporal orienting of attention, as
measured by PET. B, Anatomical localization of the
preferential activation of (a) the right
intraparietal sulcus by spatial orienting (S),
(b) the left intraparietal sulcus by temporal
orienting (T), and (c) the
bilateral intraparietal sulcus by spatiotemporal orienting
(ST), as measured by fMRI. Coronal slices from
three separate individuals (S1, S2,
S3) are shown for each condition. The left
side of the figure corresponds to the left side
of the brain.
|
|
Temporal orienting
Brain regions specifically correlated with temporal orienting are
presented in Table 4b. Two brain areas within the common network of brain areas (see Table 3) were activated significantly more
for the temporal, than for the spatial, orienting condition: the left
intraparietal sulcus and the left cerebellum. In addition, the left
ventral premotor cortex in the general region of Broca's area (BA
6/44) was activated. The latter region was not part of the common
network and suggests a more exclusive relationship to aspects of
temporal orienting of attention. The location of the brain activations
selective for temporal orienting are shown in Figure 3Ab,
rendered on a surface view of a standard brain. The left premotor area
is shown on a sagittal section of the averaged MRI of all seven
subjects.
Combined spatiotemporal orienting
The interaction between spatial and temporal orienting isolated
the areas that additionally were activated by attending to both spatial
and temporal cues simultaneously, as opposed to either one separately.
The resulting activations occurred within parietal cortex and are
summarized in Table 4c. Activations were obtained around the
intraparietal sulcus bilaterally in regions that overlapped with the
common network (see Table 3). In addition, the inferior region of the
right temporoparietal junction, which straddled both inferior parietal
and posterior superior temporal cortices, was activated exclusively by
combined spatial and temporal orienting. The locations of the brain
activations selective for combined spatial and temporal orienting are
shown in Figure 3Ac, rendered on a surface view of a
standard brain. The bilateral intraparietal sulcus activations are
shown on two coronal sections of the averaged MRI of all seven
subjects.
fMRI data
Common activations for spatial and temporal orienting
The spatial and temporal orienting tasks activated many brain
regions in common. The common network of brain regions was defined by
the conjunction of the comparisons between each attentional cueing
condition (S and T) to the resting baseline. Table
5 presents the brain areas that were
activated in common by the spatial and temporal orienting tasks and is
strikingly similar to those areas activated by the similar comparison
in the PET study. Frontal areas of the network included the lateral
premotor cortex bilaterally (BA 6), which extended medially and
dorsally toward the supplementary motor area (BA 6), and ventral
frontal cortex bilaterally. Intraparietal sulcus activations also were
obtained bilaterally. Large clusters of activations were centered over
ventral visual cortical areas, extending into the cerebellum in both
hemispheres.
Neutral condition baseline. There were fewer areas
activated in common when the neutral condition was used as a baseline. Of the regions activated in common and using rest as the baseline, only
the left parietal cortex (x, y, z = 45, 30, 39;
Z = 3.01; p = 0.001) was common to both
spatial and temporal orienting.
Spatial orienting
Spatial orienting of attention was associated with significant
activation of the right intraparietal sulcus, extending down toward the
temporoparietal junction, and a similar, although weaker, activation in
the left intraparietal sulcus (Table
6a). The right visual cortex
and bilateral cerebellum also were activated. Figure 3Ba
shows the precise location of the right intraparietal sulcus activation
in three of the eight subjects.
Temporal orienting
Temporal orienting of attention produced focal activation of the
left intraparietal sulcus and left cerebellum only (Table 6b). Figure 3Bb shows the location of the left
intraparietal sulcus activation in three of the eight subjects.
Combined spatiotemporal orienting
The interaction between spatial and temporal processing isolated
areas that were activated additionally by attending to both spatial and
temporal cues simultaneously, as opposed to either one separately. The
resulting activations occurred within the intraparietal sulcus
bilaterally and cerebellum bilaterally (Table 6c). Figure
3Bc shows the location of the bilateral intraparietal sulcus
activation in three of the eight subjects.
| |
DISCUSSION |
We have demonstrated a behavioral advantage of knowing
when to expect a stimulus to occur, which is qualitatively
similar to that for knowing where to expect it to occur.
Although the benefits of spatial cueing are well established, this is
the first demonstration that such benefits also can manifest themselves when attention is paid to moments in time. One exception is the study
by Kingstone (1992), which investigated the interaction between
attending to form and attending to temporal interval but did not
investigate temporal cueing per se. Convergent findings from our own
PET and fMRI studies indicated a considerable overlap between neural
networks for performing spatial or temporal orienting of attention
tasks but also showed functional specialization in certain brain
regions. The PET experiment defined the networks for spatial and
temporal orienting. The fMRI experiment replicated the results and
additionally improved anatomical localization by individual subject
analysis. Specifically, the left intraparietal sulcus (IPS) and the
left inferior premotor cortex (BA44/6) were involved in attention to
time intervals. In contrast, the right IPS was activated during spatial
orientation, confirming earlier functional imaging (Corbetta et al.,
1993; Nobre et al., 1997) and neuropsychological studies (Posner et
al., 1984).
Behavioral advantages of attending to time
Attention to temporal intervals is a relatively novel concept,
which represents how directing attentional resources to specific moments in time can influence behavior. This is directly analogous to
the concept of spatial orienting (Posner et al., 1980) whereby shifting
attention to a likely target location improves signal detection.
Indeed, subjects drawn from two independent samples demonstrated RT
benefits in all conditions when cues were spatially or temporally
informative, as compared with neutral cues. Furthermore, subjects
showed behavioral costs for invalid, as compared with valid, trials in
both spatial and temporal orienting. An interaction among task,
validity, and stimulus-onset time suggested that the behavioral cost
was smaller for targets presented at long intervals in the temporal
condition. Because of the bimodal nature of stimulus-onset times,
omission of the target at the short interval guaranteed it would occur
at the long interval (see also Kingstone, 1992). Subjects then could
reorient attention to the later time point.
Common neural network for spatial and temporal orienting
of attention
A number of brain regions were activated by both
spatial and temporal orienting tasks, as compared with a resting
baseline, suggesting the existence of a ubiquitous system for
allocating attentional resources in general, independent of stimulus
dimension. The areas were consistent with theoretical proposals of a
frontoparietal attentional network, based on neuropsychological
evidence (Mesulam, 1981, 1990; Kinsbourne, 1987; Rizzolatti et al.,
1987; Posner and Petersen, 1990). Our results extend these theories by
showing that these brain areas are recruited not just for the orienting of spatial attention but more generally for other stimulus dimensions as well. Furthermore, the specific areas recruited (IPS and FEF) were
consistent with those observed in oculomotor tasks, thus supporting a
strong relationship between oculomotor preparation and attentional
orienting (Rizzolatti et al., 1987; Corbetta, 1998; Nobre et
al., 1998). When the neutral cue was used as a baseline for determining
the overlap between the two attentional dimensions, very few brain
areas were revealed. This indicates that the selective
orienting of attention in time or space is subserved by
nonoverlapping brain areas.
Hemispheric lateralization for spatial and temporal orienting
The right hemisphere bias for spatial orienting in this study is
consistent with neuropsychological theories (Mesulam, 1981; Kinsbourne,
1987) and previous brain-imaging studies (Corbetta et al., 1993; Nobre
et al., 1997). The left hemisphere bias for temporal orienting was a
novel finding. This, coupled with the specific constellation of the
brain regions involved, helps constrain hypotheses regarding how
temporal orienting may be implemented in the brain and how it may
affect ongoing stimulus processing. Temporal orienting may affect
perceptual analysis of stimuli in a manner analogous to spatial
orienting (see Mangun, 1995), may affect motor preparation or timing,
or may affect both. Similar left-sided asymmetries have been reported
for the processing of fine temporal discriminations and during motor
preparation, suggesting that these processes may be involved in
temporal orienting.
Platel et al. (1997) found activation of the left inferior frontal
gyrus (BA 44/6) for attention to rhythm of sequences of notes. Rhythm
perception requires the ability to process the temporal characteristics
of sequential stimuli. Similarly, Fiez et al. (1995) found activation
of the left frontal operculum in conditions that required perception of
rapid temporal modulations, whether the stimuli were linguistic or not,
as compared with stimuli without rapid temporal transitions. In a
companion experiment that used visually displayed letter stimuli, the
left frontal opercular activity was increased for tasks requiring
temporal, as compared with orthographic, judgments. Thus, forming
internal representations of temporal duration is sufficient to activate
this area. These results support a theoretical framework (Tallal et
al., 1993) that explains the left hemisphere dominance for language as
originating from the specialization of the left hemisphere for rapid
temporal integration (Merzenich et al., 1996). In accordance with this view, we find preferential activation of the left hemisphere for temporal orienting. This may reflect fine discrimination of temporal intervals, necessary for focusing attention at specific moments in
time.
Hammond (1982) suggested that low-level cognitive processes, such as
timing, may be common to several higher-order ones such as language or
motor preparation. Examination of these more elemental functions may be
a profitable line of research for characterizing the functional
specializations of the two hemispheres. A recent study has demonstrated
that areas traditionally associated with speech also are associated
with the internal representation of movement, specifically the left
inferior premotor and left inferior parietal cortex (M. F. S. Rushworth, M. Krams, R. E. Passingham, unpublished observations).
Preparation to make either right or left finger movements activated the
left inferior premotor cortex (Broca's area), which is the same area
recruited for speech preparation (Krams et al., 1998; M. F. S. Rushworth, M. Krams, R. E. Passingham, unpublished
observations). This study used fixed intervals between cue and
response, allowing the subjects to anticipate the moment at which they
had to respond. A previous study by Deiber et al. (1996) found only
left parietal cortex activations when the interval between cue and
response was random. It may be that the left parietal activation
relates to the type of movement to be made (see also Rushworth et al.,
1997), whereas the left frontal activation relates more to when the
movement should be made. This raises the possibility of a distinction
between attention to a motor act and attention to a moment in time per
se. Motor anticipation and preparation are likely to have played an
important role in the attention effects in the temporal orienting
condition of our own study. Further experiments are required to
distinguish between anticipation of a motor act and attention to
temporal intervals per se.
Recently, studies have begun to investigate nonspatial aspects of
attention, using tasks with rapid, successive, foveal stimuli. Brain
imaging (Coull et al., 1996; Wojciulik and Kanwisher, 1998) and
neuropsychological studies (Harrington et al., 1998) have identified
areas that overlap with those for spatial attention, such as the right
posterior parietal cortex. Harrington et al. (1998) concluded from
impairments in nonspatial attentional orienting in patients with right
or left parietal lesions that "parietal cortex is essential for
covert shifts of attention to temporal stimuli." Our results agree
with findings from studies that used nonspatial attention tasks by
demonstrating a general bilateral frontoparietal attentional orienting
network across different stimulus dimensions. However, these nonspatial
tasks are more likely to have measured short-term aspects of vigilance
than to have measured attentional orientation to temporal intervals
explicitly. Our own temporal orienting task measures selective
attention to temporal intervals, and although both hemispheres were
activated by the performance of this task, we demonstrated preferential activation of the left parietal (and inferior premotor) cortex. By
contrast, using the attentional blink paradigm, Husain et al. (1997)
have observed lapses in temporal attention in neglect patients with
lesions of the right inferior parietal cortex (patients with left-sided
lesions were not tested). However, this paradigm indexes the time
course of the attentional process itself, whereas our own task
represents the orienting of attention in time.
We note that temporal processing is not a unitary phenomenon and that
it can be decomposed into many constituent parts. Hazeltine et al.
(1997) suggest that this functional heterogeneity is reflected neuroanatomically, with different brain areas being involved in different aspects of timing. Our results suggest that a left
frontoparietal network is recruited particularly for directing
attention toward a particular moment in time.
Parietal cortex and combined spatiotemporal orienting
Simultaneous spatial and temporal attention activated mainly
parietal areas. Parietal cortex, particularly on the right, was activated to an even greater extent when subjects directed their attention across both space and time together, as compared with either
dimension alone. This area has been implicated in many aspects of
attentional processing, such as spatial attention (Corbetta et al.,
1993; Nobre et al., 1997) and sustained attention (Pardo et al., 1991).
A recent PET study showed the right parietal cortex to be the main site
of interaction between selective responding to nonspatial targets and
sustained attention (Coull et al., 1998). Together, all of these
findings raise the important possibility that the right parietal cortex
not only is implicated in discrete forms of attention but also provides
a site for one attentional process to influence, or interact with,
another. Also notable was activation of the inferior parietal cortex,
including the temporoparietal junction. This area has been implicated
most consistently in clinical neglect (Rafal and Robertson, 1995) and
may highlight the importance of temporal as well as spatial orienting
to guide purposeful behavior.
In conclusion, we gathered behavioral and neuroimaging evidence
supporting the existence of a ubiquitous neural network for attentional
orienting. However, a striking hemispheric lateralization for attention
to spatial location versus temporal interval also exists, with
preferential activation of the right and left parietal areas for
spatial versus temporal cues, respectively. Furthermore, modulation of
different foci within parietal cortex across experimental conditions
suggests functional heterogeneity of this region. Finally, we have
found equivalent results by using both PET and fMRI scanning methodologies. This demonstrates the reliability of the task-specific activations and also cross-validates the sensitivity of each scanning technique.
| |
FOOTNOTES |
Received March 25, 1998; revised June 29, 1998; accepted June 30, 1998.
J.T.C. was funded by the Medical Research Council during the
acquisition of these data and is now funded by The Wellcome Trust. The
experiments were partially supported by a project grant to A.C.N. by
The Wellcome Trust. We thank Professors Dick Passingham and Chris Frith
for invaluable discussion and comments, and Dr. Christian Buechel for
advice on analysis of fMRI data.
Correspondence should be addressed to Drs. J.T. Coull or A.C. Nobre,
Functional Imaging Laboratory, Wellcome Department of Cognitive
Neurology, Institute of Neurology, 12 Queen Square, London WC1N 3BG,
UK.
| |
REFERENCES |
-
Corbetta M
(1998)
Frontoparietal cortical networks for directing attention and the eye to visual locations: identical, independent, or overlapping neural systems?
Proc Natl Acad Sci USA
95:831-838[Abstract/Free Full Text].
-
Corbetta M,
Miezin F,
Shulman G,
Petersen SE
(1993)
A PET study of visuospatial attention.
J Neurosci
13:1202-1226[Abstract].
-
Coull JT,
Frith CD,
Frackowiak RSJ,
Grasby PM
(1996)
A fronto-parietal network for rapid visual information processing: a PET study of sustained attention and working memory.
Neuropsychologia
34:1085-1095[Web of Science][Medline].
-
Coull JT, Frackowiak RSJ, Frith CD (1998) Monitoring for
target objects: activation of right frontal and parietal cortices with
increasing time on task. Neuropsychologia, in press.
-
Deiber M-P,
Ibanez V,
Sadato N,
Hallett M
(1996)
Cerebral structures participating in motor preparation in humans: a positron emission tomography study.
J Neurophysiol
75:233-247[Abstract/Free Full Text].
-
Fiez JA,
Raichle ME,
Miezin FM,
Petersen SE,
Tallal P,
Katz WF
(1995)
PET studies of auditory and phonological processing effects of stimulus characteristics and task demands.
J Cogn Neurosci
7:357-375.
-
Friston KJ,
Frith CD,
Liddle PF,
Dolan RJ,
Lammertsma AA,
Frackowiak RSJ
(1990)
The relationship between global and local changes in PET scans.
J Cereb Blood Flow Metab
10:458-466[Web of Science][Medline].
-
Friston KJ,
Frith C,
Liddle P,
Frackowiak R
(1991)
Comparing functional (PET) images: the assessment of significant change.
J Cereb Blood Flow Metab
11:690-699[Web of Science][Medline].
-
Friston KJ,
Ashburner J,
Poline J-B,
Frith CD,
Heather JD,
Frackowiak RSJ
(1995a)
Spatial registration and normalisation of images.
Hum Brain Mapp
2:165-189.
-
Friston KJ,
Holmes AP,
Worsley KJ,
Poline J-P,
Frith CD,
Frackowiak RSJ
(1995b)
Statistical parametric maps in functional imaging: a general linear approach.
Hum Brain Mapp
2:189-210.
-
Hammond GR
(1982)
Hemispheric differences in temporal resolution.
Brain Cogn
1:95-118[Medline].
-
Harrington DL,
Haaland KY,
Knight RT
(1998)
Cortical networks underlying mechanisms of time perception.
J Neurosci
18:1085-1095[Abstract/Free Full Text].
-
Hazeltine E,
Helmuth LL,
Ivry RB
(1997)
Neural mechanisms of timing.
Trends Cognit Sci
1:163-169.
-
Husain M,
Shapiro K,
Martin J,
Kennard C
(1997)
Abnormal temporal dynamics of visual attention in spatial neglect patients.
Nature
385:154-156[Medline].
-
Ivry RB,
Keele SW
(1989)
Timing functions of the cerebellum.
J Cogn Neurosci
1:136-152.
-
Jueptner IH,
Rijntes M,
Weiller C,
Faiss JH,
Timmann D,
Mueller SP,
Diener HC
(1995)
Localization of a cerebellar timing process using PET.
Neurology
45:1540-1545[Abstract/Free Full Text].
-
Kingstone A (1992) Combining expectancies. Q J Exp Psychol
44[A]:69-104.
-
Kinsbourne M
(1987)
Mechanisms of unilateral neglect.
In: Neurophysiological and neuropsychological aspects of spatial attention (Jeannerod M,
ed). Amsterdam: Elsevier.
-
Krams M,
Rushworth MFS,
Deiber M-P,
Frackowiak RSJ,
Passingham RE
(1998)
The preparation, execution, and suppression of copied movements in the human brain.
Exp Brain Res
120:386-398[Web of Science][Medline].
-
Mangun GR
(1995)
Neural mechanisms of visual selective attention.
Psychophysiology
32:4-18[Web of Science][Medline].
-
Merzenich MM,
Jenkins WM,
Johnston P,
Schreiber C,
Miller SL,
Tallal P
(1996)
Temporal processing deficits of language-learning impaired children ameliorated by training.
Science
271:77-81[Abstract].
-
Mesulam MM
(1981)
A cortical network for directed attention and unilateral neglect.
Arch Neurol
10:304-325.
-
Mesulam MM
(1990)
Large scale neurocognitive networks and distributed processing for attention, language, and memory.
Ann Neurol
28:597-613[Web of Science][Medline].
-
Nichelli P,
Clark K,
Hollnagel C,
Grafman J
(1995)
Duration processing after frontal lobe lesions.
Ann NY Acad Sci
769:183-190[Web of Science][Medline].
-
Nichelli P,
Alway D,
Grafman J
(1996)
Perceptual timing in cerebellar degeneration.
Neuropsychologia
34:863-871[Web of Science][Medline].
-
Nobre AC,
Gitelman DR,
Sebestyen GN,
Meyer J,
Frackowiak RSJ,
Frith CD,
Mesulam MM
(1997)
Functional localisation of the system for visuospatial attention using positron emission tomography.
Brain
120:515-533[Abstract/Free Full Text].
-
Nobre AC,
Dias EC,
Gitelman DR,
Mesulam MM
(1998)
The overlap of brain regions that control saccades and covert visual spatial attention revealed by fMRI.
Neuroimage
7:59.
-
Pardo JV,
Fox PT,
Raichle ME
(1991)
Localization of a human system for sustained attention by positron emission tomography.
Nature
349:61-64[Medline].
-
Paus T
(1996)
Location and function of the human frontal eye field: a selective review.
Neuropsychologia
34:475-483[Web of Science][Medline].
-
Platel H,
Price C,
Baron J-C,
Wise R,
Lambert J,
Frackowiak RSJ,
Lechevalier B,
Eustache F
(1997)
The structural components of music perception: a functional anatomical study.
Brain
120:229-243[Abstract/Free Full Text].
-
Posner MI,
Petersen SE
(1990)
The attention system of the human brain.
Annu Rev Neurosci
13:25-42[Web of Science][Medline].
-
Posner MI,
Snyder CRR,
Davidson BJ
(1980)
Attention and the detection of signals.
J Exp Psychol Gen
109:160-174[Web of Science][Medline].
-
Posner MI,
Walker JA,
Friedrich FJ,
Rafal RD
(1984)
Effects of parietal injury on covert orienting of attention.
J Neurosci
4:1863-1874[Abstract].
-
Price CJ,
Friston KJ
(1997)
Cognitive conjunction: a new approach to brain activation experiments.
NeuroImage
5:261-270[Web of Science][Medline].
-
Rafal R,
Robertson L
(1995)
The neurology of visual attention.
In: The cognitive neurosciences (Gazzaniga MS,
ed), pp 625-648. Cambridge, MA: MIT.
-
Rao SM,
Harrington DL,
Haaland KY,
Bobholz JA,
Cox RW,
Binder JR
(1997)
Distributed neural systems underlying the timing of movements.
J Neurosci
17:5528-5535[Abstract/Free Full Text].
-
Raymond JE,
Shapiro KL,
Arnell KM
(1992)
Temporary suppression of visual processing in an RSVP task: an attentional blink?
J Exp Psychol Hum Percept Perform
18:849-860[Web of Science][Medline].
-
Rizzolatti G,
Riggio L,
Dascola I,
Umilta C
(1987)
Reorienting attention across the horizontal and vertical meridians
 evidence in favor of a premotor theory of attention.
Neuropsychologia
25:31-40[Web of Science][Medline]. -
Rushworth MFS,
Nixon PD,
Renowden S,
Wade DT,
Passingham RE
(1997)
The left parietal cortex and motor attention.
Neuropsychologia
35:1261-1273[Web of Science][Medline].
-
Talairach J,
Tournoux
(1988)
In: A co-planar stereotaxic atlas of the human brain. Stuttgart: Thieme.
-
Tallal P,
Miller S,
Fitch R
(1993)
Neurobiological basis of speech: a case for the preeminence of temporal processing.
Ann NY Acad Sci
682:27-47[Web of Science][Medline].
-
Wojciulik E,
Kanwisher N
(1998)
A general visual attention mechanism in the human brain: evidence from fMRI.
Neuroimage
7:578.
Copyright © 1998 Society for Neuroscience 0270-6474/98/18187426-10$05.00/0
This article has been cited by other articles:
|
|
|
|
 
M. Esterman and S. Yantis
Perceptual Expectation Evokes Category-Selective Cortical Activity
Cereb Cortex,
September 16, 2009;
(2009)
bhp188v1.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
C. A. Dickinson and H. Intraub
Spatial asymmetries in viewing and remembering scenes: Consequences of an attentional bias?
Atten Percept Psychophys,
August 1, 2009;
71(6):
1251 - 1262.
[Abstract]
[PDF]
|
|
|
|
|
|
|
V. van Wassenhove
Minding time in an amodal representational space
Phil Trans R Soc B,
July 12, 2009;
364(1525):
1815 - 1830.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
D. Bueti and V. Walsh
The parietal cortex and the representation of time, space, number and other magnitudes
Phil Trans R Soc B,
July 12, 2009;
364(1525):
1831 - 1840.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
K. A. MacLean, S. R. Aichele, D. A. Bridwell, G. R. Mangun, E. Wojciulik, and C. D. Saron
Interactions between endogenous and exogenous attention during vigilance
Atten Percept Psychophys,
July 1, 2009;
71(5):
1042 - 1058.
[Abstract]
[PDF]
|
|
|
|
|
|
|
M. J. Yates and M. E. R. Nicholls
Somatosensory prior entry
Atten Percept Psychophys,
May 1, 2009;
71(4):
847 - 859.
[Abstract]
[PDF]
|
|
|
|
|
|
|
G. L. Shulman, S. V. Astafiev, D. Franke, D. L. W. Pope, A. Z. Snyder, M. P. McAvoy, and M. Corbetta
Interaction of Stimulus-Driven Reorienting and Expectation in Ventral and Dorsal Frontoparietal and Basal Ganglia-Cortical Networks
J. Neurosci.,
April 8, 2009;
29(14):
4392 - 4407.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A.M. C. Kelly, A. Di Martino, L. Q. Uddin, Z. Shehzad, D. G. Gee, P. T. Reiss, D. S. Margulies, F. X. Castellanos, and M. P. Milham
Development of Anterior Cingulate Functional Connectivity from Late Childhood to Early Adulthood
Cereb Cortex,
March 1, 2009;
19(3):
640 - 657.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
C. N. Boehler, T. F. Munte, R. M. Krebs, H. -J. Heinze, M. A. Schoenfeld, and J. -M. Hopf
Sensory MEG Responses Predict Successful and Failed Inhibition in a Stop-Signal Task
Cereb Cortex,
January 1, 2009;
19(1):
134 - 145.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
K. M. BAUSENHART, B. ROLKE, and R. ULRICH
Temporal preparation improves temporal resolution: Evidence from constant foreperiods
Atten Percept Psychophys,
November 1, 2008;
70(8):
1504 - 1514.
[Abstract]
[PDF]
|
|
|
|
|
|
|
B. ROLKE
Temporal preparation facilitates perceptual identification of letters
Atten Percept Psychophys,
October 1, 2008;
70(7):
1305 - 1313.
[Abstract]
[PDF]
|
|
|
|
|
|
|
F. M. Carvalho and N. Kriegeskorte
The Arrow of Time: How Does the Brain Represent Natural Temporal Structure?
J. Neurosci.,
August 6, 2008;
28(32):
7933 - 7935.
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. Arzy, I. Molnar-Szakacs, and O. Blanke
Self in Time: Imagined Self-Location Influences Neural Activity Related to Mental Time Travel
J. Neurosci.,
June 18, 2008;
28(25):
6502 - 6507.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
L. D. SANDERS and L. B. ASTHEIMER
Temporally selective attention modulates early perceptual processing: Event-related potential evidence
Atten Percept Psychophys,
May 1, 2008;
70(4):
732 - 742.
[Abstract]
[PDF]
|
|
|
|
|
|
|
P. H. Weiss, N. N. Rahbari, M. D. Hesse, and G. R. Fink
Deficient sequencing of pantomimes in apraxia
Neurology,
March 11, 2008;
70(11):
834 - 840.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
L. A. Newman and J. McGaughy
Cholinergic Deafferentation of Prefrontal Cortex Increases Sensitivity to Cross-Modal Distractors during a Sustained Attention Task
J. Neurosci.,
March 5, 2008;
28(10):
2642 - 2650.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. X. O'Reilly, M. M. Mesulam, and A. C. Nobre
The Cerebellum Predicts the Timing of Perceptual Events
J. Neurosci.,
February 27, 2008;
28(9):
2252 - 2260.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. Bhat and K. Rockwood
Delirium as a disorder of consciousness
J. Neurol. Neurosurg. Psychiatry,
November 1, 2007;
78(11):
1167 - 1170.
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. A. Stevens, M. Snodgrass, D. Schwartz, and K. Weaver
Preparatory Activity in Occipital Cortex in Early Blind Humans Predicts Auditory Perceptual Performance
J. Neurosci.,
October 3, 2007;
27(40):
10734 - 10741.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
I. Indovina and E. Macaluso
Dissociation of Stimulus Relevance and Saliency Factors during Shifts of Visuospatial Attention
Cereb Cortex,
July 1, 2007;
17(7):
1701 - 1711.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. R. Lehky and K. Tanaka
Enhancement of Object Representations in Primate Perirhinal Cortex During a Visual Working-Memory Task
J Neurophysiol,
February 1, 2007;
97(2):
1298 - 1310.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. H. Fecteau and D. P. Munoz
Warning Signals Influence Motor Processing
J Neurophysiol,
February 1, 2007;
97(2):
1600 - 1609.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
D. S. Bassett, A. Meyer-Lindenberg, S. Achard, T. Duke, and E. Bullmore
From the Cover: Adaptive reconfiguration of fractal small-world human brain functional networks
PNAS,
December 19, 2006;
103(51):
19518 - 19523.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. B. Postuma and A. Dagher
Basal Ganglia Functional Connectivity Based on a Meta-Analysis of 126 Positron Emission Tomography and Functional Magnetic Resonance Imaging Publications
Cereb Cortex,
October 1, 2006;
16(10):
1508 - 1521.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
E. Rounis, K. E. Stephan, L. Lee, H. R. Siebner, A. Pesenti, K. J. Friston, J. C. Rothwell, and R. S. J. Frackowiak
Acute changes in frontoparietal activity after repetitive transcranial magnetic stimulation over the dorsolateral prefrontal cortex in a cued reaction time task.
J. Neurosci.,
September 20, 2006;
26(38):
9629 - 9638.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. Quickfall and D. Crockford
Brain Neuroimaging in Cannabis Use: A Review
J Neuropsychiatry Clin Neurosci,
August 1, 2006;
18(3):
318 - 332.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. Shomstein and S. Yantis
Parietal Cortex Mediates Voluntary Control of Spatial and Nonspatial Auditory Attention
J. Neurosci.,
January 11, 2006;
26(2):
435 - 439.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
D. M. Eagleman, P. U. Tse, D. Buonomano, P. Janssen, A. C. Nobre, and A. O. Holcombe
Time and the Brain: How Subjective Time Relates to Neural Time
J. Neurosci.,
November 9, 2005;
25(45):
10369 - 10371.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. R. Doherty, A. Rao, M. M. Mesulam, and A. C. Nobre
Synergistic Effect of Combined Temporal and Spatial Expectations on Visual Attention
J. Neurosci.,
September 7, 2005;
25(36):
8259 - 8266.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. Haller and E. W. Radue
What Is Different about a Radiologist's Brain?
Radiology,
September 1, 2005;
236(3):
983 - 989.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
N. Alahyane and D. Pelisson
Long-lasting modifications of saccadic eye movements following adaptation induced in the double-step target paradigm
Learn. Mem.,
July 1, 2005;
12(4):
433 - 443.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
G. Garraux, C. McKinney, T. Wu, K. Kansaku, G. Nolte, and M. Hallett
Shared Brain Areas But Not Functional Connections Controlling Movement Timing and Order
J. Neurosci.,
June 1, 2005;
25(22):
5290 - 5297.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. Molholm, A. Martinez, W. Ritter, D. C. Javitt, and J. J. Foxe
The Neural Circuitry of Pre-attentive Auditory Change-detection: An fMRI Study of Pitch and Duration Mismatch Negativity generators
Cereb Cortex,
May 1, 2005;
15(5):
545 - 551.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. T. Coull, F. Vidal, B. Nazarian, and F. Macar
Functional Anatomy of the Attentional Modulation of Time Estimation
Science,
March 5, 2004;
303(5663):
1506 - 1508.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
D. A. Crowe, M. V. Chafee, B. B. Averbeck, and A. P. Georgopoulos
Neural Activity in Primate Parietal Area 7a Related to Spatial Analysis of Visual Mazes
Cereb Cortex,
January 1, 2004;
14(1):
23 - 34.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
G. L. Shulman, M. P. McAvoy, M. C. Cowan, S. V. Astafiev, A. P. Tansy, G. d'Avossa, and M. Corbetta
Quantitative Analysis of Attention and Detection Signals During Visual Search
J Neurophysiol,
November 1, 2003;
90(5):
3384 - 3397.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
V. Kavcic and C. J. Duffy
Attentional dynamics and visual perception: mechanisms of spatial disorientation in Alzheimer's disease
Brain,
May 1, 2003;
126(5):
1173 - 1181.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
T. Wolbers, C. Weiller, and C. Buchel
Contralateral Coding of Imagined Body Parts in the Superior Parietal Lobe
Cereb Cortex,
April 1, 2003;
13(4):
392 - 399.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. R. Friedman-Hill, L. C. Robertson, R. Desimone, and L. G. Ungerleider
Posterior parietal cortex and the filtering of distractors
PNAS,
April 1, 2003;
100(7):
4263 - 4268.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
G. Allen and E. Courchesne
Differential Effects of Developmental Cerebellar Abnormality on Cognitive and Motor Functions in the Cerebellum: An fMRI Study of Autism
Am J Psychiatry,
February 1, 2003;
160(2):
262 - 273.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. R. Simon, M. Meunier, L. Piettre, A. M. Berardi, C. M. Segebarth, and D. Boussaoud
Spatial Attention and Memory Versus Motor Preparation: Premotor Cortex Involvement as Revealed by fMRI
J Neurophysiol,
October 1, 2002;
88(4):
2047 - 2057.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
K. M. Shafritz, J. C. Gore, and R. Marois
The role of the parietal cortex in visual feature binding
PNAS,
August 6, 2002;
99(16):
10917 - 10922.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
Y. Laufer, L. Gattenio, E. Parnas, D. Sinai, Y. Sorek, and R. Dickstein
Time-Related Changes in Motor Performance of the Upper Extremity Ipsilateral to the Side of the Lesion in Stroke Survivors
Neurorehabil Neural Repair,
September 1, 2001;
15(3):
167 - 172.
[Abstract]
[PDF]
|
|
|
|
|
|
|
M. F. S. Rushworth, T. Paus, and P. K. Sipila
Attention Systems and the Organization of the Human Parietal Cortex
J. Neurosci.,
July 15, 2001;
21(14):
5262 - 5271.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. L. Giraud, C. J. Price, J. M. Graham, and R. S. J. Frackowiak
Functional plasticity of language-related brain areas after cochlear implantation
Brain,
July 1, 2001;
124(7):
1307 - 1316.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. C. Coghill, I. Gilron, and M. J. Iadarola
Hemispheric Lateralization of Somatosensory Processing
J Neurophysiol,
June 1, 2001;
85(6):
2602 - 2612.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
P. C. Fletcher and R. N. A. Henson
Frontal lobes and human memory: Insights from functional neuroimaging
Brain,
May 1, 2001;
124(5):
849 - 881.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. I. Schubotz and D. Y. von Cramon
Interval and Ordinal Properties of Sequences Are Associated with Distinct Premotor Areas
Cereb Cortex,
March 1, 2001;
11(3):
210 - 222.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J.T. Coull, A.C. Nobre, and C.D. Frith
The Noradrenergic {{alpha}}2 Agonist Clonidine Modulates Behavioural and Neuroanatomical Correlates of Human Attentional Orienting and Alerting
Cereb Cortex,
January 1, 2001;
11(1):
73 - 84.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. A. Sperling, C. R. G. Guttmann, M. J. Hohol, S. K. Warfield, M. Jakab, M. Parente, E. L. Diamond, K. R. Daffner, M. J. Olek, E. J. Orav, et al.
Regional Magnetic Resonance Imaging Lesion Burden and Cognitive Function in Multiple Sclerosis: A Longitudinal Study
Arch Neurol,
January 1, 2001;
58(1):
115 - 121.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. Gevins and M. E. Smith
Neurophysiological Measures of Working Memory and Individual Differences in Cognitive Ability and Cognitive Style
Cereb Cortex,
September 1, 2000;
10(9):
829 - 839.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
B. J. Casey, K. M. Thomas, T. F. Welsh, R. D. Badgaiyan, C. H. Eccard, J. R. Jennings, and E. A. Crone
Dissociation of response conflict, attentional selection, and expectancy with functional magnetic resonance imaging
PNAS,
July 18, 2000;
97(15):
8728 - 8733.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A.-L. Giraud, E. Truy, R. S. J. Frackowiak, M.-C. Gregoire, J.-F. Pujol, and L. Collet
Differential recruitment of the speech processing system in healthy subjects and rehabilitated cochlear implant patients
Brain,
July 1, 2000;
123(7):
1391 - 1402.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
K. R. Thulborn, C. Martin, and J. T. Voyvodic
Functional MR Imaging Using a Visually Guided Saccade Paradigm for Comparing Activation Patterns in Patients with Probable Alzheimer's Disease and in Cognitively Able Elderly Volunteers
AJNR Am. J. Neuroradiol.,
March 1, 2000;
21(3):
524 - 531.
[Abstract]
[Full Text]
|
|
|
|
|
|
|
J. E. Holden and B. Therrien
The Effect of Familiarity on Distraction and Single Cue Use after Hippocampal Damage
Biol Res Nurs,
January 1, 2000;
1(3):
165 - 178.
[Abstract]
[PDF]
|
|
|
|
|
|
|
C. Miniussi, E. L. Wilding, J. T. Coull, and A. C. Nobre
Orienting attention in time: Modulation of brain potentials
Brain,
August 1, 1999;
122(8):
1507 - 1518.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. N. A. Henson, T. Shallice, and R. J. Dolan
Right prefrontal cortex and episodic memory retrieval: a functional MRI test of the monitoring hypothesis
Brain,
July 1, 1999;
122(7):
1367 - 1381.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. Townsend, E. Courchesne, J. Covington, M. Westerfield, N. S. Harris, P. Lyden, T. P. Lowry, and G. A. Press
Spatial Attention Deficits in Patients with Acquired or Developmental Cerebellar Abnormality
J. Neurosci.,
July 1, 1999;
19(13):
5632 - 5643.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
Top
Abstract
Introduction
