The document discusses research on how the visual system assigns "indexes" to objects to track their locations over time. Three key points: 1. Assigning indexes to targets based on their color allows for as good or better tracking performance than flashing the targets, even when the color indication interval is reduced to as little as 50ms. 2. Using color as an indicator is a much stronger "index attractor" than flashing. Performance is largely unaffected even at very short color indication intervals. 3. This suggests the visual system can rapidly filter objects based on a pre-determined color top-down, faster than the automatic indexing process. However, more research is needed to understand how indexing works under these conditions and

1. Automatic Filtering for the
Assignment of Indexes
Multitons – Counting – locating and
various other things

2. ‘Filtering Out’
• “The visual system must be able to do the
equivalent of ‘filtering out’ some of the
potential false alarm causing signals … All
we can do in the filtering is attempt to
capitalize on some physically specifiable
detectable property that is …used to
distinguish those from other stimuli.”
(Is vision continuous with cognition? Brain Behavior Sciences 1999, 22, 341-423)

3. The First Stage
• A two-stage model has
been proposed for the
tracking task,
(McKeever, 1991,
Sears, 1991 and Sears
and Pylyshyn, 1995).
• The first stage can be
thought of as the
assignment of indexes,
which is automatic and
driven to objects via
primitive features

4. The Assignment of Indexes
• If the assignment of indexes is based on
what Muller & Findlay (1988) call the
automatic component of attention, then …

5. The Binding Problem
• Anne Treisman
– Some notes
• Features of surface-defining properties – luminance,
color, texture, motion, stereoscopic depth
• Features of shape-defining boundaries – orientation,
curvature, and closure
– She reviews the relevant research which seems
to be in conflict with the notion that binding
requires serial processing.
– Current Opinion in Neurobiology, 6, 171-178

6. Resolution
• “One resolution is that parallel search
reflects not preattentive processing but
global attention to the scene as a whole
with no individuation of separate
elements.”
• Therefore, a discrepant object is seen as a
break in the global structure of the three-
dimensional array..

7. Is Color-Change Primitive?
• Jacquie Burkell & Zenon Pylyshyn
– “It seems that when (a color change of any
kind) is in fact detected it can be perfectly
localized, even when the changed item is in
now different from its distracters.”

8. Location Encoding
• “If the indicated location did not match the
target location, but fell within one potential
display position of the actual target location
(i.e., .9 degrees of visual angle), the
response was recorded as ‘near’… if not
far.” (from Burkell and Pylyshyn)

9. Serial and parallel processing of
visual feature conjunctions
• “If one of the dimensions in a conjunctive
search is stereoscopic disparity, a second
dimension of either color or motion can be
searched in parallel … these conjunctive
tasks (were such that) the observer had the
distinct impression that each plane could be
search effortlessly, in turn.”
• Ken Nakayama & Gerald Silverman (Nature, V. 320 20 March 1986 264-265)

10. Color is Powerful 1
• Subjects could determine the orientation of
the target – i.e., a T amongst Ls when they
were cued symbolically by color, as when
cued by color at location, and a luminance
location cue.
– Efficiency of selective attention: selection by colour and location compared Jari Laarni
Mika Koski and Gote Nyman (Perception, 1996, V 25, 1401-1418)

11. Color is Powerful 2
• What is important here is that subjects could
selectively attend to a group of objects that
were one color, and perform better on the
discrimination and the orientation tasks,
when selectively attending to a subset of
items that were set apart via color.
– Can one pay attention to a particular color Peter Brawn and Robert Snowden
(Perception and Psychophysics V 61(5) July 1999, 860-873

12. Open Questions
• Can we extend the previous research that
involves the detection of single items to the
detection of multiple items
• Does location encoding requires serial
visitation?
• What is the duration of that initial
assignment?

13. Some More Questions
• What is the capacity of the assignment of indexes?
– What does it mean for an index to be assigned?
• Does that mean that it can be enumerated?
• Does it mean that it can be located?
• Conjunctions
– What is the influence of a conjunction of features on
the assignment of indexes?
– What about the search for multiple items in a
conjunction search?

14. Our results show that when the targets in an MOT task are
indicated by temporally making them a different color than
the non-targets, observers track just as well (or better) than when
they are indicated by flashing the targets.

15. This increase in performance holds even when the indication
interval is greatly reduced. In fact, in this case, color signaling
is noticeably better than flashing.
In fact, for the color signaling condition, performance remains
relatively unaffected when the indication interval is reduced from
900ms to 50ms!

16. This an outstanding, unexpected result.
The results clearly show that color signaling is a much
stronger INDEX ATTRACTOR than flashing the targets.

17. Points to consider:
The onset of the color on the targets cannot be useful to the observer
because all objects are colored. The only useful information is the color
of the targets versus the non-targets.
So how does the system assign indexes to the targets under
these conditions?
Two possibilities:
1. Particular colors automatically attract indexes. By coincidence,
we selected the right color.
2. The visual system is able to perform a fast top-down color
filtering for specific pre-determined colors.

18. Point 1:
Is not supported by data. Observers track both target (red or green) and
complement set (red or green) equally well.
Point 2:
How fast is this filtering process? It must be faster than automatic
indexing!!! At 50ms, tracking green is 87% as compared to the
flash case which is 65%.
But …