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Early binding of feature pairs for visual perception

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Alex O Holcombe at The University of Sydney
Alex O Holcombe
Patrick Cavanagh at Glendon College
Patrick Cavanagh
  • Glendon College
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If features such as color and orientation are processed separately by the brain at early stages1, 2, how does the brain subsequently match the correct color and orientation? We found that spatially superposed pairings of orientation with either color or luminance could be reported even for extremely high rates of presentation, which suggests that these features are coded in combination explicitly by early stages, thus eliminating the need for any subsequent binding of information. In contrast, reporting the pairing of spatially separated features required rates an order of magnitude slower, suggesting that perceiving these pairs requires binding at a slow, attentional stage.
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nature neuroscience • volume 4 no 2 • february 2001 127
brief communications
Early binding of feature
pairs for visual perception
Alex O. Holcombe and Patrick Cavanagh
Vision Sciences Laboratory, Department of Psychology, Harvard University, 33
Kirkland Street, Cambridge, Massachusetts 02138, USA
Correspondence should be addressed to A.O.H. (aholcombe@psy.ucsd.edu)
If features such as color and orientation are processed sepa-
rately by the brain at early stages
1,2
, how does the brain sub-
sequently match the correct color and orientation? We found
that spatially superposed pairings of orientation with either
color or luminance could be reported even for extremely high
rates of presentation, which suggests that these features are
coded in combination explicitly by early stages, thus eliminat-
ing the need for any subsequent binding of information. In
contrast, reporting the pairing of spatially separated features
required rates an order of magnitude slower, suggesting that
perceiving these pairs requires binding at a slow, attentional
stage.
To determine the temporal resolution of the perception of
feature pairs, we combined color and orientation features,
either spatially superimposed or spatially separated (Fig. 1).
In the superimposed condition, half the trials consisted of a
display alternating between a red patch tilted leftward and a
green patch tilted rightward (semicircular windowed gratings
with a sinusoidal 45° tilt). In the other trials, the pairing of
color and orientation was reversed. Observers reported whether
the red was paired with rightward or with leftward tilt.
Observers fixated 0.2° away from the straight edge of the
semicircle windowed grating 8.5° in diameter. The red and
green stimuli were set to equiluminance separately for each
observer at each temporal frequency with a minimum motion
method
3
. Following this setting, the red and green
0.59 cycles/degree gratings had peaks of equal luminance and
troughs of equal luminance, and the luminance of the peak
and trough of each cycle differed by about 38 cd/m
2
. The
trough of the mean red grating was 16.4 cd/m
2
, CIE (x = 0.59,
y = 0.35), and its peak was 54.2 cd/m
2
(x = 0.41, y = 0.34). The
mean green grating had trough of 17.4 cd/m
2
(x = 0.30,
y = 0.55) and peak of 56 cd/m
2
(x = 0.32, y = 0.39). These val-
ues ensured that the sum of the bright red and dark green gave
the same yellow as the sum of the dark red and bright green,
thus camouflaging the orientations of the green and red grat-
ings in the sum. Perfect camouflage in the sum was verified
with each observer and, for one observer (AH), was tested over
a range of contrasts bracketing the critical values to determine
the sensitivity to possible unintended display deviations. These
control data showed that a deviation of greater than 5% con-
trast would be required to bring performance to the 75%
threshold, whereas the computed value fell within 2% of the
optimal value (producing chance performance). The first and
last pairing in the sequence was masked; the trial began with
extremely rapid presentation of the stimuli, and gradually
slowed to the intended temporal frequency (a few hundred
milliseconds), after which the presentation rate gradually
increased, ending the trial with a postmask.
In the spatially separated condition, the same pairings were
used, but the color was presented as a uniform patch of satu-
rated red or green, and the orientation was presented as an
adjacent achromatic patch of tilted bars. Another block of the
same experiment tested judgments of brightness and orienta-
tion pairings. A dark (30 cd/m
2
) semicircle windowed grating
alternated with a bright (86 cd/m
2
) grating on a noise back-
ground. The difference between the peak and trough of both
gratings was always 55 cd/m
2
, which ensured that the sum of
the two gratings was the same regardless of the brightness–ori-
entation pairing.
The critical rates for threshold accuracy (75%) in report-
ing the pairings were slower than 3 Hz for each observer in the
spatially separated condition (Fig. 1). In the spatially super-
imposed condition, thresholds were nearly ten times better.
The average for four observers in the color condition was
18.8 Hz, and the average in the brightness condition was a
remarkable 35.5 Hz. This latter value corresponded to ∼14 ms
for each feature pair.
Several studies suggest that features are more likely to be
processed together if they form part of a single object or
group
4
. The critical rates for the spatially separated conditions
may have been slower than rates for the superimposed condi-
tions because the separated features appeared to be part of sep-
arate objects or groups. To test this possibility, we devised
several variations that grouped the features together, based on
displays shown to have effects in earlier reaction
time studies
4
. However, even when the separated
features were linked into a common object or sur-
face, critical rates remained low (Fig. 2). These
results do not rule out the possibility that an
object context could provide a threshold advan-
tage in the region of a dozen milliseconds, but any
possible advantage (statistically insignificant in
this study) was small compared to that afforded
by superposition (300 ms).
When the superimposed features were alter-
Fig. 1. The critical rates for 75% accuracy in pairing
spatially superimposed features (depicted by the sec-
ond and fourth icons along the horizontal axis) are
nearly ten times faster than rates for pairing spatially
separated features (first and third icons). Each bar rep-
resents the mean of the same four observers. Small ver-
tical bars, 1 s.e.m.
© 2001 Nature Publishing Group http://neurosci.nature.com
© 2001 Nature Publishing Group http://neurosci.nature.com
128 nature neuroscience • volume 4 no 2 • february 2001
nated at rates above approximately 10 Hz, observers reported
that they did not experience the brief individual stimulus pre-
sentations separately. Instead, some observers reported that
the two feature pairings slowly alternated in their awareness,
or that one dominated. Others said that both seemed available
simultaneously, as if they had been presented transparently.
Still, underlying this percept is a high-speed process able to
read out the combined values of color (or brightness) and ori-
entation within the brief presentation of a single pairing. If this
process were not able to resolve each brief presentation, it
would be faced with the patterns summed across two or more
intervals. Because of the way the stimuli were constructed, the
pairings were camouflaged when the intervals were summed
(red right plus green left is indistinguishable from red left plus
green right). Although the alternate pairings had to be read
out separately in the consecutive intervals, the experience of
each pairing extended over time, as reflected in the reports of
transparency and slow rivalry. It seems that subsequent
processes before awareness integrate the paired representations
over a relatively long interval.
The high pairing rates for spatially superimposed feature
pairs suggest, among other possibilities, that some features may
be assessed in combination from early levels. In this case, there
is no binding problem. For example, nonlinear ON- and OFF-
channels as early as retinal ganglion cells separate stimuli
brighter and darker than the background, even at high flicker
rates
5,6
. Once the bright and dark stimuli are represented in
separate channels so that they do not cancel, orientation analy-
sis can proceed independently of the flicker. In the case of our
color–orientation pairings, color-opponent cells may have a
similar involvement by separating the red and green stimuli,
even at high presentation rates
7
. In contrast, in the case of the
spatially separated condition, it is unlikely that any one cell is
selective for the orientation at one location and the brightness
or color at another. Judging the pairings of spatially separate
features would therefore require a combination of the respons-
es of disparate neurons selected by later, slower and attentive
stages
8,9
.
A
CKNOWLEDGEMENTS
This work was supported by an NEI NRSA graduate fellowship to A.O.H. and
EY09258 to P.C.
RECEIVED 24 AUGUST; ACCEPTED 12 DECEMBER 2000
1. Zeki, S. M. Nature 274, 423–428 (1978).
2. Treisman, A. & Gelade, G. Cognit. Psychol. 12, 97–136 (1980).
3. Cavanagh, P., MacLeod, D. I. A. & Anstis, S. M. J. Opt. Soc. Am. 4,
1428–1438 (1987).
4. Scholl, B. Cognition(in press).
5. Kuffler, S. W. J. Neurophysiol. 16, 37–68 (1953).
6. Lee, B. B., Martin, P. R. & Valberg, A. J. Physiol. (Lond.) 414, 245–263
(1989).
7. Gur, M. & Snodderly, M. Vision Res. 37, 377–382 (1997).
8. Verstraten, F. A. J., Cavanagh, P. & Labianca, A. Vision Res. 40, 3651-3664
(2000).
9. Lu, Z. & Sperling, G. Vision Res. 35, 2697–2722 (1995).
brief communications
Fig. 2. The critical rates for 75% accuracy do not differ
significantly when spatially separated features are linked to
form a group or object (white bars, unlinked versions as
depicted by the left icon of each pair; black bars, linked
versions as depicted by the right icon of each pair. Small
vertical bars, 1 s.e.m. Averages of data from 25 observers
are shown, except middle conditions, which shows aver-
age of data from 7 observers. The feature pairings of the
dumbbell and lozenge-shaped stimuli alternated between
combinations of light or dark on one end and left- or right-
tilt on the other. The feature patches of the dumbbell
were sharp-edged as depicted, whereas those of the
lozenge stimulus were smoothly graded into their sur-
round. The left edge of the wedge stimulus alternated
between right- and left-tilted, whereas the right region
graded smoothly from the gray to, alternately, either red
or green.
© 2001 Nature Publishing Group http://neurosci.nature.com
© 2001 Nature Publishing Group http://neurosci.nature.com
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View
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Article
  • Feb 2000
  • VISION RES
The maximum speed for attentive tracking of targets was measured in three types of (radial) motion displays: ambiguous motion where only attentive tracking produced an impression of direction, apparent motion, and continuous motion. The upper limit for tracking (about 50 deg s-1) was an order of magnitude lower than the maximum speed at which motion can be perceived for some of these stimuli. In all cases but one, the ultimate limit appeared to be one of temporal frequency, 4-8 Hz, not retinal speed or rotation rate. It was argued that this rate reflects the temporal resolution of attention, the maximum rate at which events can be individuated from those that precede or follow them. In one condition, evidence was also found for a speed limit to attentive tracking, a maximum rate at which attention could follow a path around the display.
View
View
  • Jan 1997
  • 377-382
  • M Gur
  • M Snodderly
Gur, M. & Snodderly, M. Vision Res. 37, 377–382 (1997).
  • Jan 1995
  • 2697-2722
  • Z Lu
  • G Sperling
Lu, Z. & Sperling, G. Vision Res. 35, 2697–2722 (1995).