Visual stability based on remapping of
attention pointers
Patrick Cavanagh1,2, Amelia R. Hunt2,3, Arash Afraz2,4 and Martin Rolfs1
1 Laboratoire Psychologie de la Perception, Universite´ Paris Descartes, 45, rue des Saints Pe`res, 75006 Paris, France
2Vision Sciences Laboratory, Harvard University, 33 Kirkland St. Cambridge MA 02138, USA
3Department of Psychology, William Guild Building, University of Aberdeen, Aberdeen AB24 2UB, UK
4McGovern Institute for Brain Research, MIT, 43 Vassar Street, Cambridge MA 02142, USA
When we move our eyes, we easily keep track of where
relevant things are in the world. Recent proposals link
this stability to the shifting of receptive fields of neurons
in eye movement and attention control areas. Reports of
‘spatiotopic’ visual aftereffects have also been claimed
to support this shifting connectivity even at an early
level, but these results have been challenged. Here,
the process of updating visual location is described as
predictive shifts of location ‘pointers’ to attended tar-
gets, analogous to predictive activation seen cross-mod-
ally. We argue that these location pointers, the core
operators of spatial attention, are linked to identity
information and that such a link is necessary to establish
a workable visual architecture and to explain frequently
reported positive spatiotopic biases.
The challenge of eye movements
Because of our frequent eye and head movements, the
image of the world moves constantly on our retina. Despite
this instability, we know where things are around us, at
least well enough to get by. Hurrying down the stairs we
might slip but quickly grab hold of a handrail that we only
glimpsed briefly a moment earlier. This knowledge might
be represented in the brain as an explicit spatiotopic (see
Glossary) map of the scene, where object locations are
given in world-based coordinates that are independent of
the orientations of our eyes, head and body. This conjecture
of an explicit spatiotopic map has been proposed several
times [1–5], but has been vigorously challenged as
unnecessary and unsupported [6–12]. This long debate
has been completely transformed by two recent discov-
eries: remapping and spatiotopic visual aftereffects.
In remapping, a neuron in attention and saccade control
areas can be activated by a stimulus far outside its recep-
tive field, even in the opposite visual field, if an impending
saccade will bring that stimulus into the classical receptive
field of the cell [13–18] (Figure 1). This predictive transfer
of activation has been attributed to shifting receptive fields
and been proposed as a possible mechanism for visual
stability. In the case of visual aftereffects, adaptation to
a tilted grating, for example, causes a vertical test to seem
tilted away from vertical in the direction opposite to the
adaptation grating. This negative aftereffect is typically
seen at the same retinal location as the adapting stimulus,
but if an eyemovement intervenes between adaptation and
Opinion
Glossary
Aftereffects: Prolonged exposure to visual patterns causes adaptation in the
eye and brain. Aftereffects are the effects of this adaptation on subsequent
perception. For example, the aftereffect of staring at a leftward-tilted line is that
a vertical line will seem to tilt to the right.
Corollary discharge: See ‘efference copy’.
Efference copy: When a signal is sent from the brain to the muscles to generate
a movement (i.e. an efferent motor command), efference copy is the message
that is also sent to perceptual systems to predict or anticipate the sensory
consequences of the movement as it is occurring.
FINST: The FINST [61] was proposed to provide a continuously updated spatial
index of an object, allowing it to be tracked over time and space.
fMRI: A technique for detecting oxygen intake in specific regions of the brain.
Regions with more de-oxygenated blood are considered to have been recently
active.
FEF: An area of frontal cortex associated with eye movements and spatial
attention, and also with saccadic remapping.
Fovea: The center of the light-sensitive retina where the receptors are most
densely packed. With good lighting, the part of the visual scene falling on the
fovea is seen better than elsewhere and this location is normally taken to be
‘‘where we are looking.’’
Gain setting: The specific relationship between the input and the output of a
neuron or population or network of neurons. Gain settings can be modified by
adaptation.
LIP: An area of parietal cortex associated with eye movements and spatial
attention, and with saccadic remapping.
LO: A lateral area of the occipital lobe associated with object segmentation and
attention.
MT: (also known as V5). A small region of the occipital lobe that is part of the
dorsal stream and associated with processing of motion information.
Object files: A temporary representation combining an object’s identity,
location and characteristics that is updated whenever the object moves or
changes features [46].
Receptive field: A cell’s receptive field is the region of the retina where a visual
stimulus can modulate the firing rate of the cell. Early in the visual system
receptive fields are very small in size but grow increasingly large as the
information progresses through additional stages.
Remapping: An eye movement will shift a stimulus from one location to
another on the retina. Remapping is the activation of neurons representing the
new retinal location of the stimulus and can be seen earlier than, or in the
absence of, the actual arrival of the stimulus in that location when the eye
movement occurs.
Retinotopy: The representation of spatial information in coordinates corre-
sponding to where a stimulus falls on the retina.
Saccade: Fast movements of the eye that shift the higher-acuity region of the
retina (the fovea) into alignment with a new location in space, allowing that
location to be inspected in greater detail.
Salience map: A representation of space with areas of activation corresponding
to locations that have some current or potential importance.
Spatiotopy: Representation of spatial information in world-based coordinates
(as opposed to retinotopic coordinates).
SC: Superior colliculus (also known as the optic tectum). A mid-brain structure
involved in eye movement control.
Transsaccadic memory: Visual information that is retained in short-term
memory buffer from one fixation to the next that allows for integration,
comparison and detection of changes.
Visual stability: When we shift our gaze the visual world does not seem to
move, even though the eye movement shifts the image across the retina.
Corresponding author: Cavanagh, P. (patrick.cavanagh@parisdescartes.fr).1364-6613/$ – see front matter  2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.tics.2010.01.007 Available online 26 February 2010 147

test, it is also reported at the same spatial location as the
adaptation [4,19–22]. These spatiotopic aftereffects have
Figure 1. Remapping (a) The ‘+’ indicates the fovea and a face is the target of an
impending saccade. (b) A second stimulus is flashed on immediately before the
saccade, activating a cell (in LIP) with a receptive field, RF 1, at the location of the
new stimulus. (c) The activation of the cell with classic receptive field on the right is
transferred to a new cell whose receptive field, RF 2, is on the left; critically, its
receptive field lies where the second stimulus will land after the saccade. This cell’s
predictive activation gives a head start for the processing of this stimulus when it
lands. (d) The saccade has landed on the face and the truck lands in the pre-
activated receptive field. In the physiological experiments (e.g. [13]) the second
stimulus is extinguished before the saccade lands so that any response from RF 2
can be attributed solely to the presaccadic activity at the remote location and to the
intended saccade and its corollary discharge or efference copy.been taken as evidence that remapping transfers low-level
feature information around the time of a saccade.
post-saccadic location of the target would respond even
when the target was turned off before the saccade landed.
148OpinionHowever, here we present evidence that challenges the
shifting receptive field notion and the finding of spatiotopic
aftereffects. We will argue that remapping is best seen as a
transfer of activation to prepare for a predictable incoming
stimulus, similar to that found in the somatosensory sys-
temwhen a stimulus is seen to be approaching a particular
location on the body [23] or in the auditory system when a
loud sound is anticipated [24]. In the visual system, in
preparation for a saccade, this transfer of activation to the
target’s upcoming location gives a head start for attention
benefits at, or programming a saccade to, that location. We
show that remapping does not require briefly rewiring the
receptive field to the new retinal location nor does it involve
the transfer of low-level features or gain settings. This
simplified view of remapping helps organize current
results in eye movements and attention within a common
framework, supporting our view that these maps are the
functional core of spatial attention. We begin with a brief
review of the remapping effect (see [7,11,12,25] for detailed
reviews).
Remapping: Shifting receptive fields or shifting
pointers?
The remapping of activity around the time of a saccade has
been attributed to the shifting of receptive fields (Figure 2)
[13–18] and has been proposed as the mechanism that
keeps track of locations in space when the eyes move
[11–18,24]. Wurtz [11] has provided an elegant argument
that corollary discharge of the impending eye movement
command (also known as efference copy) transfers activity
on a retinotopicmap to keep track of the locations of objects
in the world. Sommer and Wurtz [18] demonstrated that
this remapping is at least partially under the control of
signals from the superior colliculus (SC), closing the link
between eye movements, corollary discharge, and visual
stability. Wurtz [11] proposed that remapping does not
lead to an explicit spatiotopic map but instead underlies
the updating of the locations of targets of interest on a
retinotopic representation. Only the activity for a few,
relevant items are remapped [16] and Wurtz’s proposal
is a minimalist theory of visual stability – keep track of the
locations of currently attended items and nothing else is
required.
We believe this proposal has great promise as it relies on
activity in these areas to act as pointers to the locations of
the targets, a role that fits with the characterization of the
lateral intraparietal area (LIP), frontal eye fields (FEF),
and SC as salience maps for spatial attention and maps of
potential saccade targets [26–28]. We adapt Wurtz’s pro-
posal here by linking remapping to the transfer of activity,
rather than shifting receptive fields (Box 1), and by claim-
ing that it is the updating of attentional ‘pointers’
(Figure 3) that does the work: attended locations are all
that need to be tracked because feature information, which
remains unchanged, can be dealt with independently
(Box 2).
In their original paper [13], Duhamel et al. presented a
target immediately before a saccade and discovered that
some cells with a classical receptive field at the anticipated,
Trends in Cognitive Sciences Vol.14 No.4

The authors claimed that ‘the location of the receptive field
Figure 2. Simplified examples of two remapping mechanisms (a) An upcoming saccad
some cells with classic receptive fields at 208 even though the secondary target does n
(shown as LIP here) is connected to all locations on the retina through interneurons
correspond to the default location when fixating (saccade of 08) or the appropriately
activated depends on the cell and the saccade. The cell shown with its classical receptiv
connections link all cells on a salience map (LIP here). An upcoming saccade will open a
presaccadic targets to locations where those targets will fall after the saccade. These co
receptive field at 308 and this activity is transferred to the 208 cell through the active in
Opinionis shown to shift transiently before an eye movement.’ (p.
90) They concluded that parietal neurons have access not
only to information in the fixation field but also to infor-Box 1. Mechanisms of remapping
Weoutline two current proposals for the remapping process. First, the
shifting receptive field model, as proposed by Duhamel et al. [13] and
Sommer andWurtz [18], requires broad input from all locations on the
retina to each cell (Figure 2b). A level of interneurons allows these
inputs to be gated by the current saccade target, shifting all receptive
fields from their default location to a location offset by the saccade
vector. The default location of each cell is its classic receptive field
location (which can be considered to be switched on by a saccade
vector of 08). This shift would maintain the stimulus specificity of the
cell, if any, as it processed input from other retinal sites. Could this
remapped receptive field mediate the transfer of visual adaptation
from pre- to postsaccadic locations [4,19–22] – the spatiotopic
aftereffects reported by several authors? Melcher and Colby [25]
point out that this is improbable. The remapped connection is brief,
perhaps from 50 to 100 msec, replaced shortly after the saccade lands
with the cell’s default connection to its classical receptive field. Once
the connection reverts to the default receptive field, stimulus
information is arriving over unadapted connections.
Second, two neural models propose that learned horizontal
connections in, for example LIP, FEF or other salience map sites,
determine which cell will be at a target’s postsaccadic location
[30,31]. The connection activates that cell without passing stimulus
information (Figure 3b). To accomplish this, all cells in LIP must be
connected together and the link between currently active cell, the
efference copy (from FEF), and the predicted cell is learned across
exposure to the pairings of pre- and postsaccadic activations that
occur in LIP for each of the multitude of saccades occurring in our
visual experience. Could this remapped activation mediate the
transfer of visual adaptation from pre- to postsaccadic locations?
Improbable, because the learned connections only transfer activa-
tion, they are not specific to stimulus features nor to change in the
sensitivity to those features.mation at other retinal locations. This characterization of
shifting fields has persisted across the years, both for LIP
neurons [17] and FEF neurons [18].
With remapping, a stimulus evokes a response from a
cell whose receptive field is normally elsewhere and this
e to a target at 108 with a briefly presented second target at 308. This will activate
ot land there until after the saccade. (b) Shifting field. Each cell in a salience map
. Input from an oculomotor center (FEF here) turns on subsets of the input that
offset location when a saccade is imminent (108 here). The shifted location to be
e field at 208 will now respond to the input at 308. (c) Activation transfer. Horizontal
ll connections of the appropriate offset, transferring any activation from cells with
nnections must be learned [30,31]. Here the secondary target activates the cell with
terneuron.
Trends in Cognitive Sciences Vol.14 No.4remote activation is not unreasonably labeled a shifted
receptive field. However, this characterization is inap-
propriate and we give two examples to explain why. First,
there are analogous cross-modal anticipatory responses
where no shifting receptive fields can be invoked. For
example, some cells in area 5 of posterior parietal cortex,
a somatosensory processing area [23], that respond to
stimulation of a specific body part (e.g. the hand or
shoulder) also show a change in firing rate when the
experimenter is seen approaching that body part as though
contact would be made. In this case, the somatosenory
neuron is responding to a visual stimulus that is not only
outside its receptive field, but also outside itsmodality. Not
only would the rewiring have to be from each somatosen-
sory neuron to all possible retinal locations, but also the
predicted contact location does not even correspond to the
current location of the visual stimulus, but to its eventual
contact point with the animal’s body. This anticipatory
activation for cells with receptive fields at the location of
future contact rules out all notions of a ‘shifting receptive
field’. Second, remapping has also been seen in the case of
FEF units that show short-term spatial memory responses
[29]. Stimuli were flashed for 50 ms, from 200 to 1000 ms
before a saccade. A significant proportion of cells that did
not respond to the flashed stimulus alone (the stimulus
location was outside the cells’ receptive fields) did respond
if the saccade would have brought the stimulus onto their
receptive fields, as in the classic remapping case. However,
in this case there can be no rewiring of the receptive fields
149

serv
targ
e fovFigure 3. Remapping and attention A network of areas form a target map that sub
index the locations of targets and specify the retinotopic coordinates at which the
simplified, as a stack of aligned areas divided into right and left hemifields with th
Opinionto earlier input streams to produce this remapping because
the stimulus is long gone: there is no activity on the retina
or in earlier cortices at the time of the remapping. The only
source for the remapping is a transfer of activity from the
currently active cells, holding thememory of its location, to
its predicted postsaccadic location, maintaining a pointer
to that remembered location in the world.
If, as these two examples indicate, receptive fields do not
shift, how is the activation transfer produced? It might be
generated by learned horizontal connections (Figure 2) or
by some more flexible mechanism yet to be discovered,
analogous to the computation of expected touch location
seen in the somatosensory system. Two separate groups
[30,31] have presented models in which horizontal connec-
tions in a salience map (e.g. LIP) can transfer activation to
the appropriate postsaccadic location (Box 1). With the
transfer of activation as the mechanism of remapping, it is
clear that location counts, rather than content, because
locations and not features are the critical properties
represented in these particular parietal, frontal and sub-
cortical regions. Once the activation shifts to the new
location on the attention and saccade target maps
(Figure 3), its downward projections can rapidly begin to
facilitate processing at the expected postsaccadic locations
in earlier retinotopic cortices.
Attention-based spatiotopy
The remapping hypothesis of spatiotopy proposed by
Wurtz [11] and others underlines the potential of remap-
(heavy black outline) and depend on attention to bias input [67] in favor of the target an
field at any one time. (b) Around the time of a saccade, the activations for the three atten
and, following the saccade, what had been the saccade target, at the right, now lands
150es spatial attention as well as eye movements [26–28]. (a) Peaks of activity (in red)
et’s feature data are to be found in earlier visual cortices which are shown, highly
ea in the center. In object recognition areas, cells have very large receptive fields
Trends in Cognitive Sciences Vol.14 No.4ping to keep track of targets as the eyes move and so to
derive a working spatiotopy of locations (Figure 3) and, in
particular, a working spatiotopy for spatial attention.
Spatial attention shares spatial maps with saccade control
centers in areas such as SC, LIP and FEF [32] and the
activity peaks on thesemaps domore than indicate or point
at each target’s location for purposes of programming a
saccade. Each of the activations also indexes the location of
that target’s feature information on other similarly orga-
nized retinotopic maps throughout the brain. Activity in
these attention/saccade maps can project to corresponding
locations in other regions, enhancing the processing of
information from the corresponding target location in
these areas. The attentional benefits of the projections
from these maps to other retinotopic visual cortices have
been demonstrated in microstimulation studies (see [33]
for a review). When stimulating cells in FEF or SC with a
movement field, for example in the lower right quadrant, a
high stimulating current triggers a saccade to that
location, but a slightly weaker stimulation that does not
trigger a saccade generates either enhanced neural
response for cells with receptive fields at that location
[33] or lowered visual thresholds for visual tests at that
location [33].
Duhamel et al. [13] had originally argued that the
remapping phenomenon was unrelated to attention
because it did not occur when the monkey shifted attention
to the saccade target but then withheld an eye movement.
However, as Berman and Colby [12] point out, with an
d suppress surrounding distractors so that only a single item falls in the receptive
ded targets shift to the locations the targets will have at the end of the saccade, (c)
in the fovea.

Box 2. Object identity and remapping – the hard binding
problem
Attention has been characterized in a variety of ways but here we
focus on the target or salience map [16,26–28]. In this approach, the
array of activations on areas involved in eye movement and
attention control (LIP, FEF and SC) specify the location of the
target’s features in early retinotopic visual cortices enhancing
processing at those locations and suppressing surrounding fea-
tures, a proposal similar to the master map of Treisman and
Gormican [59]. The suppression of distractors surrounding the
target is critical – if a distractor is also present in the receptive field
and is not suppressed, its features are unavoidably mixed with
those of the target producing crowding [60].
An activation peak on the target or salience map is the temporary
pointer or location token [61,62] for the target, but it does not specify
which target nor provide any link to the target’s identity. Several
studies point to parietal and frontal areas for visual short-term
memory that might preserve location information [29,63,64], but
feature information might be stored globally in earlier visual
cortices [48,49]. There is little information yet on the mechanism
that links the representation of locations in the saccade and
attention areas to these temporary memories let alone to the ventral
regions that would establish those identities. Many have proposed
temporary data structures that would manage all these connections
between location and identity – object files for example, or ‘Fingers
of Instantiation’ (FINSTs) – and recent work suggests some
structures that could underlie these functions [47]. However these
links are established, whenever corollary discharge remaps the
activation peak in saccade and attention areas sending it on to its
predicted postsaccadic location, it needs to take the link to the
target’s identity with it so that the same identity will be continuously
attributed to this target as the eyes move. Remapping does not
solve this hard binding problem; it only adds additional challenges
Opinionattentional shift alone, nothing will move on the retina and
there is no need to remap anything. The shifting of atten-
tion to the saccade target that occurs immediately before
the saccade [34,35] is essential for acquiring information
about the target but it is not the same as the shift of activity
that accompanies the actual execution of the saccade.
Interestingly, for the saccade target itself, the remapping
must return the attentional ‘pointer’ from the saccade
target to the fovea, which is the future location of the
target. This return of attention to the fovea (or nearby
[36]) should occur only if the saccade execution is imminent
and it should be synchronous with the shift of attention
from the current locations of other targets of interest, such
as recent transient flashes, to their predicted postsaccadic
locations.
What is the evidence that attention remaps to its
expected postsaccadic location? Direct evidence comes
from studies of apparent motion: the perception of motion
between two successive flashes. Apparent motion has been
described as the consequence of dragging attention from an
initial stimulus to the displaced location of a second [37],
linking the two locations together as the changing location
of a single target. If a saccade occurs between the first and
second stimuli, apparent motion is seen in spatiotopic, not
retinotopic coordinates ([38]; see the supplementary
material online for a demonstration video) indicating that
the attention pointer to the presaccadic location is correctly
shifted to the target’s expected postsaccadic location,
enabling the detection of the target displacement as appar-
ent motion in world coordinates. Relative location infor-
to it.mation can be accumulated across saccades but only for up
to about three locations [39], as would be expected for a
capacity-limited, attention-based mechanism. Additional
evidence of attention remapping has also come from cueing
experiments where benefits of a cue presented before a
saccade have been found in both retinotopic and spatioto-
pic locations following the saccade [40,41].
Shifting attention pointers can keep track of target
locations but what about target identities? There is no
mechanism built into attention remapping that represents
or tracks identity and yet, it is obvious that we do know
what is where after an eye movement, at least for attended
targets. Change blindness, for example, has shown that
changes across saccades are detected for attended items
but not for unattended items [42,43]. There is, as well,
evidence for transsaccadic spatiotopic memory [9,44],
priming [45] and integration [5]. These instances of trans-
saccadic maintenance of information might require mech-
anisms such as object files [9,46,47] or non-spatial memory
stores [48,49] but there is no indication as yet how these
mechanisms are linked to the location tracking processes
described here (Box 2). Next, we review the nature of
feature or identity information that might be maintained
across saccades.
Feature-specific spatiotopy
A great deal of earlier research demonstrated that little
information is retained in world coordinates across sac-
cades [9]. However, recent studies in brain imaging and
visual psychophysics have claimed to find spatiotopic
representations and link them to the remapping of visual
feature information from presaccadic to postsaccadic tar-
get locations [4,19–22,50,51]. In the case of functional brain
imaging, two studies reported spatiotopic responses in
extrastriate regions of occipital cortex that indicated a
remapping of featural information. D’Avossa et al. [50]
found that activation in the classically retinotopic portion
of middle temporal visual area (MT) was invariant in a
spatiotopic reference frame and not in a retinotopic frame.
McKyton and Zohary [51], in a functional Magnetic Reson-
ance Imaging (fMRI) study in the lateral occipital complex
(LO), showed that object-specific adaptation was largely
dependent on the position of objects on the screen and not
their position on the retina.
Psychophysical adaptation experiments also showed
spatiotopic aftereffects for tilt, shape and face adaptation
[4], motion aftereffects [20], duration adaptation [21], and
for binocular rivalry adaptation [22]. According to these
studies, after adapting to a particular stimulus at one
location and then making an eye movement, feature-
specific negative aftereffects (a bias away from the adapt-
ing feature) are found at the spatial location where the
adaptation took place, far removed from the location on the
retina where adaptation took place. Because the classic
literature on visual aftereffects had shown that effects are
overwhelmingly centered at the same retinal location as
the adaptation [52–53], these findings of aftereffects at
spatiotopic locations attracted enormous attention and
the importance of the findings was amplified by their
Trends in Cognitive Sciences Vol.14 No.4potential link to the physiological findings of remapping.
A subsequent study showed a tilt aftereffect in the
151

Acknowledgements
This research was supported by grants from an ANR Chaire d’Excellence
and NIH EY002958 to PC, a Harvard Dissertation Award to SRA, and
NSERC postdoctoral award to ARH.
Appendix A. Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.tics.
2010.01.007.
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small (about 20% of the retinotopic effect) and is not
significant until 10 seconds or more following adaptation,
properties that do not seem in line with the rapid and
reliable oculomotor remapping processes.
This absence of reliable transfer of low-level feature
information (specifically the feature gain settings that
underlie adaptation) across saccades weakens the claims
for a link between the transsaccadic transfer of visual
features and the oculomotor process of remapping in LIP
and FEF. Physiological remapping that putatively
underlies the stability of the visual world needs to be
robust, rapid and reliable. The pattern of spatiotopy
reported for aftereffects is too variable to attribute these
effects to oculomotor remapping. The properties that do
transfer across saccades [5,9,44,45] could be related to
maintenance of a link between the target’s identity and
its locations. This transsaccadic memory [47] must call on
other mechanisms beyond the updating of location (Box 2).
Summary
Spatiotopy as an explicit representation for world coordi-
nates in the visual system had been abandoned for many
years due to the failure of almost all tests of transsaccadic
fusion [55,56]. The discovery of remapping in LIP [13], SC
[15] and then FEF [14] and its characterization as shifting
receptive fields led to a reawakening of interest in this topic
and to explorations of spatiotopy in visual aftereffects and
brain imaging. Reports of spatiotopic aftereffects added
momentum to this new interpretation of visual stability by
implicating a shifting of connections even through early
levels of the visual system. However, as we showed here,
remapping is more likely to be limited to the predictive
transfer of activation for attended targets, a process that
does not shift receptive fields or transfer low-level feature
information such as changes in gain control settings that
underlie adaptation effects [4,19–22]. The small spatioto-
pic aftereffects that might exist are probably only super-
ficially related to oculomotor processes, if at all.
OpinionNevertheless, as pointed out by Wurtz [11] and others,
remapping, however it is produced, can update target
152locations on a retinotopic map to keep track of targets as
the eyes move. This activation transfer serves as an early
warning to cells whose receptive fields are about to receive
an attended target and indicates that these maps on which
the transfer operates are the functional core of spatial
attention. Additional mechanisms are needed to maintain
target identity and link it to these location pointers as they
are updated [47] (see also Box 3 for a list of outstanding
questions).
Box 3. Outstanding questions
 Some cells show responses to a target outside their classical
receptive field if an imminent saccade will bring that target into
their receptive field. Do these remapped, anticipatory responses
show selectivity for the features of that target? Although cells in
LIP, SC and FEF show little feature specificity, those in LIP do
show a weak directional selectivity [65]. Cells in V3A and other
areas of visual cortex, which also show remapping responses [66],
have a wider range of feature specificity. No experiments have yet
tested whether the remapped responses of cells in LIP or these
other visual areas show specificity to the features of the target. If
the remapped responses do reflect rewired connections to the
retina, they should maintain the feature specificity of their
classical receptive field. By contrast, if only a predictive activation
is involved, there is no requirement for feature specificity in the
remapped response.
 Is unsupervised learning possible in Keith and Crawford’s [30]
model for activation transfer (Box 1)? In their model, there is an
expected outcome that drives learning to the appropriate
connections. To be realistic, however, the learning in this model
must be unsupervised, as it is in real brains.
 What is the physiology underlying the temporary links, ‘object
files’, that combine location and identity information of each
target. Is the object file the same as visual short-term memory
[48,49,63,64] and if so, how is it linked to object recognition areas
[47]?
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