Segregation of object and background
motion in the retina
Bence P. O
lveczky*†, Stephen A. Baccus‡ & Markus Meister‡
* Division of Health Sciences and Technology, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, Massachusetts 02138, USA
† Program in Neuroscience, Harvard University, 220 Longwood Avenue, Boston, Massachusetts 02115, USA
‡ Department of Molecular and Cellular Biology, Harvard University, 16 Divinity Avenue, Cambridge, Massachusetts 02138, USA
An important task in vision is to detect objects moving within a stationary scene. During normal viewing this is complicated
by the presence of eye movements that continually scan the image across the retina, even during ﬁxation. To detect moving
objects, the brain must distinguish local motion within the scene from the global retinal image drift due to ﬁxational eye
movements. We have found that this process begins in the retina: a subset of retinal ganglion cells responds to motion in the
receptive ﬁeld centre, but only if the wider surround moves with a different trajectory. This selectivity for differential motion is
independent of direction, and can be explained by a model of retinal circuitry that invokes pooling over nonlinear interneurons. The
suppression by global image motion is probably mediated by polyaxonal, wide-ﬁeld amacrine cells with transient responses. We
show how a population of ganglion cells selective for differential motion can rapidly ﬂag moving objects, and even segregate
multiple moving objects.
Movements of the eye are a fundamental component of vision, as
they directly inﬂuence the stimulus falling on the retina. There are
two main types of eye movement: the large and rapid saccades
or pursuit movements by which we redirect our gaze, and the
smaller ﬁxational eye movements that occur between saccades
Whereas ballistic gaze-shifting eye movements suppress vision
small ﬁxational eye movements are essential for seeing: if the retinal
image is stabilized, visual perception fades within a tenth of a
During ﬁxation, the retinal image drifts over about 0.58 of visual
angle, or about 60 cone receptive ﬁelds, at an average speed of
approximately 0.5 degrees s
, and any processing of visual infor-
mation must occur on the background of this drifting motion
Similar eye movements occur in other animals, including salaman-
. Despite their importance to vision, the effect of
these eye movements on retinal function has received rather limited
Given the presence of continuous eye movements, the funda-
mental task of detecting object motion within a scene becomes a
signiﬁcant computational problem. The task is not simply to detect
motion on the retina; rather, the visual system must discriminate
between local motion patterns speciﬁc to an object and global
motion induced by ﬁxational eye movements
. Humans perceive
this task as effortless: movements anywhere within a scene immedi-
ately ‘pop-out’ and attract our attention
, even if their velocity and
amplitude is only a fraction of the image motion caused by
Figure 1 Simulating local object motion on the retina in the presence of ﬁxational eye movements. a, Receptive ﬁeld proﬁle of a rabbit ON Brisk Transient retinal ganglion cell (left; see
Methods). A stripe grating representing an object was projected in and around the cell’s receptive ﬁeld centre, while the remainder of the retina was presented with a background grating
(right). b, Trajectory of vertical ﬁxational eye movements in an unrestrained rabbit, acquired using a scleral search coil
(left). The right panel shows a sample of the random walk
trajectory used to jitter the gratings.
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ﬁxational eye movements
. A neuron that subserves this function
should respond to local motion on the retina, but only if the motion
trajectory differs from that in a large surrounding region. Neurons
capable of such computations have been described in the visual
and superior colliculus
of mammals, and also in the
optic tectum of birds
. However, given that the ﬁxational eye
movements in the two eyes differ
, extraction of object motion
probably happens before the visual pathways from the two eyes
merge. Here we show that the segregation of object motion and
image motion induced by eye movements happens in the retina.
The retina senses differential motion
We recorded the spike trains of ganglion cells in the isolated retina of
salamander and rabbit. The stimulus display was divided into a
small ‘object’ region overlying the receptive ﬁeld centre of the
ganglion cell and a surrounding large ‘background’ region covering
the rest of the retina (Fig. 1a). Both object and background were
given a visual texture by a simple stripe grating. The background
grating jittered laterally with a random walk trajectory, similar to
that of ﬁxational eye movements (Fig. 1b). The object grating also
jittered in a random walk with the same statistics, either coherently
with the background, or incoherently with a different trajectory.
The coherent condition simulated the global image motion on the
retina that results when viewing a stationary scene in the presence of
eye movements only (‘Eye Only’ condition). The incoherent con-
dition simulated, in addition, local motion of an object within that
scene (‘Eye þ Object’ condition).
In both the salamander and rabbit retina we found ganglion cells
that were highly selective for motion within the scene (Fig. 2): these
neurons responded vigorously to the Eye þ Object condition
(Fig. 2a), but were almost completely suppressed under the Eye
Only condition (Fig. 2b), even though their receptive ﬁeld centres
experienced the same stimulus under both conditions. When the
background region was uniformly grey (‘Object Only’, Fig. 2c), the
responses were similar to the Eye þ Object condition (Fig. 2a),
indicating that an incoherently moving background has little effect
on the centre response. Whereas the stimulus condition in Fig. 2a
simulated an object jittering within the scene, a steady drift of the
object relative to the background also elicited reliable responses
(‘Eye þ Object Drift’, Fig. 2d).
As these ganglion cells are selective for local object motion over
global motion, we will refer to them as OMS (object motion
sensitive) cells, noting that this class comprises several recognized
cell types (for example, ‘ON Brisk Transient’ cells and ‘ON–OFF
Direction Selective’ cells in rabbit, and ‘Fast OFF’ cells in salaman-
der; Fig. 2e). Both retinas contain other cell types that show much
Figure 2 Certain retinal ganglion cells are selective for object motion. a–d, Responses to
15 s of jitter from a rabbit ON Brisk Transient cell and a salamander Fast OFF cell. Each
panel shows a raster plot with spikes on eight identical stimulus trials (top) and a peri-
stimulus time histogram of the ﬁring rate averaged over all trials (bottom). The stimulus
conditions are: Eye þ Object (a), object and background gratings jittered incoherently;
Eye Only (b), object and background jittered coherently with same trajectory as the
object in a; Object Only (c), object jittered as in a, background grey; Eye þ Object Drift (d),
object and background jittered as in b with a steady drift (450
) added to the
object region. e, Ratio of ﬁring rates in the coherent (b) and incoherent (a) motion
condition. Data from 6 ON Brisk Transient (ON BT) cells, 11 ON–OFF Direction Selective
(ON–OFF DS) cells, 5 Local Edge Detector (LED) cells, and 7 OFF Brisk Transient (OFF BT)
cells in two rabbit retinas; 41 Fast OFF cells, 8 Weak OFF cells and 8 ON cells in nine
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smaller, if any, difference between the coherent and incoherent
motion conditions (for example, ‘OFF Brisk Transient’ cells in
rabbit and ‘ON’ cells in salamander, Fig. 2e). Thus, the selectivity
for object motion may be a special feature of a few of the parallel
pathways that convey retinal output to the brain.
Mechanism of suppression from coherent motion
OMS ganglion cells are excited by motion in or near the receptive
ﬁeld centre, but are suppressed if the same image motion extends
over the wider surround. We measured the extent of these antago-
nistic regions by gradually increasing the size of the object, while
keeping the trajectories in the object and background regions
different (Fig. 3a). For salamander Fast OFF cells, the ﬁring rate
increased up to an object radius of approximately 250
m: this is the
extent of the region excited by grating motion and corresponds very
well to the classic receptive ﬁeld centre as measured by ﬂashing spots
of increasing size (Fig. 3b). As the object grew in size, it began to
invade the suppressive surround region, and the response gradually
decreased out to radii of about 1,000
m. Thus, the suppressive
effect of coherent motion extends over at least 1 mm on the retina.
Applying strychnine largely blocked the antagonistic effect of
coherent surround motion, suggesting that it is caused by long-
range glycine-mediated inhibition, presumably from wide-ﬁeld
Ganglion cells can be suppressed by peripheral motion
However, this alone does not explain our ﬁndings, as the amount
of motion in the background region was identical for both the
Eye þ Object and the Eye Only conditions, and for all the stimuli in
Fig. 3a. As seen in Fig. 2c, the OMS cells respond to a jittering object
over the receptive ﬁeld centre with brief bursts of spikes that are
precisely timed to the motion trajectory. We hypothesized that
inhibition from peripheral motion arrives in similar brief pulses
that have the same dependence on the motion trajectory as the
excitatory events from the centre (Fig. 4a). Under stimulation with
coherent motion, the peripheral inhibition would coincide with the
excitation from the centre and suppress the cell’s response. In
response to object motion, when the object and background regions
jitter incoherently, inhibition would arrive with random timing
Figure 3 Spatial interactions that produce the sensitivity to object motion. a, Relative
ﬁring rate of salamander Fast OFF cells (n ¼ 5) as a function of object size in the
Eye þ Object condition. b, Relative ﬁring rate of the same cells to a 1-Hz ﬂashing spot of
increasing size. The black trace shows the effect of 10
M strychnine (STR). Firing rates
were averaged over 2 min of stimulation and normalized to the maximum ﬁring rate of
Figure 4 Transient excitation and inhibition are synchronous during coherent motion,
causing suppression of ﬁring. a, Schematic proposal for the inputs to an OMS ganglion
cell: excitation from motion in the receptive ﬁeld centre, and inhibition from motion in the
periphery. Both consist of transient events and are triggered by the same motion features.
Under coherent motion they coincide in time, but under incoherent motion they are
uncorrelated. b, Average ﬁring rate of Fast OFF ganglion cells (GCs) as the jitter
trajectories of the object and background regions are shifted in time relative to each other
(thick red line). Firing rates were averaged over 5-min stimulus presentations, normalized
to the cell’s average ﬁring rate under the Object Only condition, then averaged over ﬁve
neurons. Average membrane potential of polyaxonal amacrine cells (AC V
) during global
(Eye Only) jitter, as a function of time before or after a ganglion cell spike in the Object Only
condition using the same trajectory (thin blue line). Each amacrine cell’s membrane
potential was normalized by subtracting its mean and dividing by its standard deviation,
which was 4 ^ 1 mV (mean ^ s.e.m.; n ¼ 3); note inverted axis, depolarization is
downward. c, Membrane potential of a polyaxonal amacrine cell in response to coherent
motion (top; Eye Only condition). Spiking response of a salamander Fast OFF cell to motion
in the Object Only condition, using the same trajectory as for the amacrine cell (bottom).
The amacrine and ganglion cells were recorded in different retinas. d, Vertical projection
of the confocal image of the amacrine cell in c, superimposed on its receptive ﬁeld (left).
Receptive ﬁeld of the ganglion cell in c, on the same scale (right).
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relative to the excitation and thus be ineffective. To test this idea, we
used the same jitter trajectory for the object and background
regions, but shifted them with respect to each other in time. As
predicted, the suppressive effect was limited to a very brief time
window around zero delay (Fig. 4b, thick red trace). This suggests
that peripheral inhibition indeed arrives in brief pulses approxi-
mately 100 ms wide, triggered by the same motion features as the
excitatory events from the centre.
We searched, using intracellular recordings in the salamander
retina, for interneurons that might mediate this long-range inhi-
bition. We encountered a type of amacrine cell that responded to
coherent jitter (Eye Only) with sharp depolarizations, about 100 ms
wide, often carrying action potentials (Fig. 4c). These depolarizing
events in amacrine cells aligned perfectly with the excitatory inputs
to OMS cells, as marked by the bursts of spikes produced in the
Object Only condition (Fig. 4c). If such amacrine cells inhibit the
OMS ganglion cells, this could explain the suppression of ﬁring
under coherent motion. By calculating the average amacrine cell
membrane potential relative to the time of a ganglion cell spike, we
predicted how this inhibition should depend on the time delay
between object and background motion. Figure 4b shows that the
time course of the amacrine cell membrane potential nicely predicts
the measured time course of ganglion cell suppression.
These amacrine cells had visual receptive ﬁelds of about 150
radius (Fig. 4d), probably mediated by inputs on a small ﬁeld of
dendrites near the soma
(see Supplementary Fig. S1). Several long
output processes extended .1 mm across the retina (Fig. 4d). A
ganglion cell collecting inhibitory input from these amacrine cell
processes will be suppressed whenever the motion in the distant
periphery matches the motion over the ganglion cell’s receptive ﬁeld
centre. Thus both the anatomy and the physiology of these amacrine
cells are consistent with their being the source of inhibition onto
OMS cells. Amacrine cells with a similar polyaxonal morphology are
found in other species including rabbit
Object motion selectivity is independent of spatial pattern
For a neuron to be selective for object motion under natural viewing
conditions, the timing of the excitation and inhibition should
ideally depend only on the motion trajectory, and be largely
independent of the spatial pattern of the stimulus. To test this we
changed both the spatial phase and frequency of the object grating,
while keeping the background uniformly grey. Indeed, the time
Figure 5 The response of OMS cells is largely independent of the spatial pattern.
a, Responses of a salamander polyaxonal amacrine cell (top) and a Fast OFF ganglion cell
(bottom) to a jittering grating (08) and its contrast-reversed version (1808). b, Responses of
a different Fast OFF ganglion cell to a grating of varying spatial period. c, The average time
course of the retinal speed of the jittered grating before a spike for a salamander
polyaxonal amacrine cell (Eye Only condition) and three different types of OMS cells
(Object Only condition): the Fast OFF cell in salamander, and the ON Brisk Transient and
ON–OFF Direction Selective cells in rabbit. The time-averaged speed for the entire
stimulus is marked by the horizontal line.
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course of ﬁring of OMS cells did not depend on the spatial phase of
the grating: even a 1808 phase shift, corresponding to a complete
reversal of black and white bars, did not signiﬁcantly alter the cell’s
response (Fig. 5a). Nor did such a phase reversal alter the response
of polyaxonal amacrine cells (Fig. 5a). Varying the spatial fre-
quency of the grating also had little effect on the ﬁring pattern of
the ganglion cells (Fig. 5b), except for very ﬁne gratings with
m. In that limit, the ﬁring rate declined and the spike
bursts were triggered at different time points in the motion
trajectory. Polyaxonal amacrine cell responses were similarly
robust to changes in spatial frequency (data not shown). These
properties differed from those of other amacrine cell types. For
example, the responses of sustained OFF-type amacrine cells to
coherent motion (Eye Only) were uncorrelated with the excitatory
inputs to OMS ganglion cells, and strongly depended on the phase
and spatial frequency of the jittered grating (Supplementary
Whereas the response of OMS cells is largely independent of the
spatial pattern, it is almost completely determined by the motion
trajectory (Fig. 5a, b). We calculated the average image speed
before a spike for three types of OMS cells, and for salamander
polyaxonal amacrine cells, in response to a jittered object. The
average motion feature that triggered spikes was an acceleration of
the grating after a period of slower than average speed (Fig. 5c).
For most OMS cells this stimulus was effective regardless of the
direction of motion; however, the rabbit ON–OFF Direction
Selective cell responded only when the grating accelerated in its
Increasing or decreasing the speed of the jitter by a factor of two
did not signiﬁcantly alter the shape of the preferred speed proﬁle;
neither did it alter the OMS cells’ sensitivity to differential motion
(not shown). This suggests that the function of OMS cells is robust
to changes in the statistics of eye movements, which accompany
changes in the behavioural state of the animal
. Note also that the
preferred motion feature for the polyaxonal amacrine cell is
remarkably similar to that which excites the receptive ﬁeld centres
of OMS ganglion cells. This suggests that an inhibitory network
involving a single type of amacrine cell could serve to suppress
different types of OMS ganglion cells in the same retina.
A model explaining object motion selectivity
The fact that these cells respond to gratings much ﬁner than the
receptive ﬁeld centre, and independently of the phase of the grating,
is reminiscent of the Y-type ganglion cells found in cat
other mammals. It is thought that the Y-cell pools excitation from
many small subunits in its receptive ﬁeld, each of which contributes
a rectiﬁed response
. We implemented a concrete version of this
idea (Fig. 6a) and simulated how it would respond to the jittered
grating stimulus in the Object Only condition. With just two free
parameters, this simple model reproduced with good accuracy the
timing of ganglion cell ﬁring in both salamander and rabbit retina
The model’s response is independent of the direction of motion
and the phase of the grating, because the receptive ﬁeld centre
contains subunits arranged symmetrically in all directions and at all
possible phases relative to the grating. Similarly, the response is
largely independent of spatial frequency, as long as the bars of the
grating are larger than the subunit width. When the stripes become
smaller, the model’s output declines, and a comparison to the
observed responses (Fig. 5b) suggests a minimum subunit width
m. It has been proposed that bipolar cells form the
nonlinear subunits of ganglion cell receptive ﬁelds
. We recorded
intracellularly from bipolar cells in the salamander retina. Their
receptive ﬁeld centres measured 35–120
m(n ¼ 7) in width (data
not shown), in agreement with the dendritic ﬁeld size of salamander
, and consistent with their role as nonlinear subunits.
The model in Fig. 6a includes an inhibitory network that pools
over many nonlinear subunits in the periphery. The fact that the
excitatory and inhibitory networks receive input from the same type
of subunits results in a selectivity for differential motion between
Figure 6 A model of retinal processing that accounts for differential motion sensitivity.
a, The OMS ganglion cell (G) receives additive excitatory input from many nonlinear
subunits underlying the object region. It is also inhibited by amacrine cells (A) that pool
over similar nonlinear subunits underlying the background. Each subunit (right) pools light
over a small receptive ﬁeld, passes the result through a temporal ﬁlter, and rectiﬁes the
result above a threshold (arrow). b, Simulated responses to a jittered grating using the
model in a, compared to the responses of real OMS cells to the same jitter (see Methods).
The stimulus trajectory was the same for both salamander and rabbit cells.
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the receptive ﬁeld centre and the surround. This is accomplished
without explicitly computing and comparing the motion vectors in
the two regions, contrary to what was found for motion contrast
sensors in higher visual centres
. In fact, the behaviour of this
model is not in any way dependent on the direction of motion, only
on the speed. To test this prediction, we performed an experiment in
which the object and background regions jittered with exactly
opposite trajectories, and found that the recorded responses from
OMS cells were indeed suppressed, just as under the coherent
motion condition (Supplementary Fig. S3). Although this situation
represents a departure from the ideal of differential motion detec-
tion, it rarely arises in nature, because the relative motion of an
object within the scene would have to mimic the observer’s eye
Among the rabbit Brisk Transient cells, only the ON-type is
suppressed by global motion (Fig. 2e); presumably the OFF-type
receives different inhibitory input. For the purpose of detecting
object motion it is not essential to have OMS properties in both
ON- and OFF-type Brisk Transient cells. Owing to the nonlinear
spatial summation, the model of Fig. 6a predicts that an OMS cell
would have the same response to a moving pattern whether its
subunits are ON-type or OFF-type. This prediction was conﬁrmed
experimentally, as the rabbit ON-type OMS cell and the salamander
OFF-type OMS cell ﬁred at similar times during the motion
trajectory (see Figs 2a–d, 5c and 6b).
Motion pop-out and binding
Finally, we consider how a population of OMS cells represents a
visual scene composed of several objects. For this, the stimulus
included two objects moving with different trajectories on an
incoherently jittering background (Fig. 7a). We recorded the
response of many Fast OFF ganglion cells in the salamander retina
at more than 200 positions relative to the stimulus display. Figure 7b
shows a map of the ﬁring rate in this population. In the region
covered by the two moving objects, ganglion cells ﬁred vigorously.
In the background region, the cells were suppressed, because they
experienced coherent motion between their receptive ﬁeld centres
and the wider periphery. Thus, a population of OMS cells could
support the perceptual ‘motion pop-out’ effect, which ﬂags local
motion within the scene and attracts our visual attention. This pop-
out would involve only a short delay: in salamander, the median
spike latency of these cells from the onset of object motion was
about 230 ms (data not shown).
Sudden movement of an image on the retina is known to
synchronize ﬁring in multiple ganglion cells
. Inspection of the
spike trains in the two-object experiment showed that OMS cells
covering the same object indeed ﬁred in synchrony (Fig. 7c, d),
whereas OMS cells seeing differently moving objects were uncorre-
lated (Fig. 7d). This is expected from the model of Fig. 6a, as the
receptive ﬁeld centres of cells covering the same object experience
the same trajectory, and consequently the same speed time course.
Because the ﬁring responses are sparse, two neurons belonging to
differently moving objects will only rarely ﬁre together by chance.
Thus, a group of OMS cells with persistent coincident activity can
deﬁne a moving object, regardless of its visual pattern or its exact
motion trajectory. Segregation of objects based on motion cues is a
well-described perceptual phenomenon
. It has been suggested that
synchronous ﬁring is the tag that ‘binds’ neurons together in an
assembly to represent a visual object
. The circuitry of Fig. 6a is a
candidate for the underlying neural mechanism.
Our experiments involved the retinas of rabbit and salamander, but
the essential building blocks required for OMS cells are present in
many other species, including primates. Approximately 20% of the
magnocellular ganglion cells in the primate retina show nonlinear
spatial summation similar to that of our model (Fig. 6a)
Transient, polyaxonal amacrine cells as in Fig. 4d with narrow
dendritic and receptive ﬁelds and large axonal aborizations have
also been found in the macaque retina
. Thus, it is probable that
ganglion cells with OMS properties exist in many species, including
humans. These cells serve as an information channel for object
motion and may support diverse functions such as segregating
object from background, and directing the gaze towards moving
One would predict that inadvertent stimulation of OMS neurons
Figure 7 Pop-out of moving objects in a population of OMS ganglion cells. a, Schematic of
the stimulus: two object regions (red and green, each 800
m in diameter) are moving
with different trajectories on an incoherently jittering background. Encircled numbers
denote the receptive ﬁeld positions of the cells in c. b, Map of the ﬁring rate in a population
of salamander Fast OFF ganglion cells responding to the stimulus in a (see Methods).
c, Segment of the spike trains from two pairs of cells covering two differently moving
objects: 1 and 2 respond to the object on the left (red), whereas 3 and 4 respond to the
object on the right (green). d, Cross-correlation function between the spike trains of two
cells responding to either the same object (1,2; thick brown line), or differently moving
objects (1,3; thin line), normalized by the product of the two cells’ mean ﬁring rates.
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should evoke an erroneous perception of object motion. We
propose that this happens when viewing certain geometrical pat-
terns, such as the Ouchi illusion
(Fig. 8). Owing to the unusual
geometry of the display, retinal motion of the pattern is mainly
governed by vertical eye movements in the periphery, and by
horizontal eye movements in the centre. Because the eye executes
horizontal and vertical eye movements independently
, centre and
periphery experience different image motion
analogous to the
Eye þ Object stimulus (Fig. 2a). This triggers the OMS cells to
signal an apparent movement of the circle. Although this is an
example of a spatial pattern inﬂuencing the response of OMS cells, it
should be noted that the geometric peculiarities required for this
effect are rare in the natural environment, where retinal function
We have shown that certain retinal ganglion cells with nonlinear
spatial summation have a special role in the presence of ﬁxational
eye movements: such a neuron signals when an object in its
receptive ﬁeld centre moves relative to the background, but is
almost completely suppressed when the object moves together
with the background. This selectivity for object motion in any
direction is accomplished by a rather simple mechanism with three
crucial ingredients: excitation from many rectiﬁed subunits in the
receptive ﬁeld centre; inhibition from the same type of subunits in a
wide surround; and the random nature of ﬁxational eye movements
that produces transient and sparse activation of both the excitatory
and inhibitory networks. A
Retinas of larval tiger salamanders, and Dutch belted and New Zealand white rabbits were
isolated in darkness and superfused with oxygenated Ringer’s medium at room
temperature (salamander) or Ames’ solution at 36 8C (rabbit). A piece of retina, 6–8 mm
on a side, was placed with the ganglion cell layer facing down on a multi-electrode array,
which recorded spike trains simultaneously from many ganglion cells, as described
. For intracellular recordings from salamander
, sharp microelectrodes were
ﬁlled with 2 M potassium acetate and 4% neurobiotin, having a ﬁnal impedance of
150–250 MQ. Polyaxonal amacrine cell resting membrane potentials ranged from 250 to
275 mV, and their peak responses to jittered gratings were 17 ^ 4 mV (mean ^ s.e.m.;
n ¼ 7) in amplitude. To analyse amacrine cell spiking (Fig. 5c), the action potentials were
detected by setting a threshold for the derivative of the membrane potential. After
recording, cells were ﬁlled iontophoretically (1–5 nA pulses, about 10–15 min), stained
streptavidin Alexa-488 (Molecular Probes), and imaged using a confocal
microscope with a £40 oil immersion objective.
Visual stimuli were projected from a computer monitor onto the photoreceptor layer, as
. All experiments used a mean photopic intensity of 8 mWm
otherwise stated, the jittered grating consisted of black and white bars with a periodicity of
m. The jitter trajectory was generated by stepping the grating randomly in one
dimension every 15 ms with a step size of 6.7
m. The seeds for generating the random
walk in the object and background regions were the same or different for the Eye Only and
Eye þ Object conditions, respectively. The object region, 800
m in diameter, was
separated from the background region, measuring 4,300 £ 3,200
m, by a 67-
annulus, except for the experiment in Fig. 3a, where no annulus was present. For Fig. 3b
the stimulus was a spot of varying size ﬂashing from black to white at 1 Hz on a grey
background. In experiments with different stimulus conditions, the trials were interleaved.
Receptive ﬁeld mapping
The spatio-temporal receptive ﬁelds of all neurons were measured by reverse correlation to
a ﬂickering black-and-white checkerboard stimulus
. The spatio-temporal receptive ﬁeld
was approximated as the product of a spatial proﬁle and a temporal ﬁlter. The receptive
ﬁeld centre of a ganglion cell was estimated as the region where the spatial proﬁle was
larger than one-third of its maximum value. The diameter of the receptive ﬁeld centre of
amacrine and bipolar cells was approximated by the full-width at half-maximum of the
two-dimensional gaussian function that best ﬁt the spatial proﬁle.
Retinal ganglion cells appear in distinct functional types. For salamander, we classiﬁed
them on the basis of their spatio-temporal receptive ﬁelds
. We report on the responses of
the Fast OFF (,60% of recorded cells), Weak OFF (,12%) and ON cells (,12%). Rabbit
ganglion cells were classiﬁed on the basis of the spatio-temporal receptive ﬁeld and the
spike train’s autocorrelation function, following the criteria of ref. 42. For rabbit, we report
on data from ON–OFF Direction Selective cells (,30% of recorded cells), OFF Brisk
Transient cells (,20%), ON Brisk Transient cells (,15%) and Local Edge Detectors
(,15%). Other cell types in rabbit were encountered rarely, and are not reported.
Only ganglion cells with receptive ﬁeld centres enclosed by the object region were included
in the analyses, except for Fig. 3, where only cells with receptive ﬁelds concentric with the
object region were included. Error bars in ﬁgures denote standard error, derived from
variation among cells. For calculating the average speed proﬁles in Fig. 5c, the jitter
trajectory was smoothed using a 30-ms box ﬁlter. During the experiments for Fig. 7b, the
object regions were shifted in increments of 530
m along both the horizontal and vertical
dimensions. Responses from 11 salamander Fast OFF cells were analysed, each sampled at
20 independent positions of the stimulus. Each cell’s ﬁring rate was normalized with
respect to its ﬁring rate under the Eye Only condition. In Fig. 7b, the image value at a given
point is the average normalized ﬁring rate of all cells whose receptive ﬁeld centre contained
that point. The results were mirrored on the axis of symmetry in the stimulus, and
smoothed using a two-dimensional gaussian ﬁlter (standard deviation of 70
For the simulations in Fig. 6, the subunit width (full width at half maximum of a parabolic
proﬁle) was chosen as 42
m for both salamander and rabbit, within the measured range of
bipolar cell receptive ﬁelds; simulations were robust to changes in this parameter. The
waveform of the temporal ﬁlter was measured by reverse correlation of ganglion cell spikes
to a ﬂicker stimulus
. The threshold was set so that the subunit outputs were non-zero
2.5% (salamander) or 3.5% (rabbit) of the time. The subunits were centred 6.7
effectively sampling all possible phases relative to the stimulus grating. The region covered
by the excitatory subunits was chosen larger than one grating period.
Received 20 December 2002; accepted 18 March 2003; doi:10.1038/nature01652.
Published online 11 May 2003.
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Supplementary Information accompanies the paper on www.nature.com/nature.
Acknowledgements We thank members of the Meister laboratory for advice; P. Cavanagh,
F. Engert, V. Murthy and K. Nakayama for comments on the manuscript; and H. van der Steen for
providing the eye movement data in Fig. 1b. This work was supported by a grant from NEI
(M.M.) and NRSA (S.A.B.).
Competing interests statement The authors declare that they have no competing ﬁnancial
Correspondence and requests for materials should be addressed to M.M.
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