Attention in Psychology: I Historical Background

1
Attention in Psychology I Historical Background

• Attention was one of the first concepts to appear
  in Psychology texts (ca 1730) e.g., Ebbinghaus,
  Titchener,
• Early discussions (Hatfield, 1998) focused on
  properties such as
• Narrowing (Aristotle, 4th century BC)
• Active Directing (Lucretius, 1st century AD)
• Involuntary shifts (Hippo, 400 AD)
• Clarity (Buridan, 14th century)
• Fixation over time (Descartes, 17th century)
• Effector sensitivity (Descartes)
• All the above phenomena (William James, early
  1900s)
• More recent studies have been concerned with
• The view of attention as selection
• The analysis of attention as a process of
  resource allocation
• The study of the relation between voluntary and
  involuntary control of attention

2
Attention as Selection
?

• We will concentrate on the Selection or
  Filtering aspects of attention. We will ask
• Why do we need to select anyway?
• Because our processing capacity is limited?
• The Big Question In what way is it limited?
  (Miller, 1957)
• We will return to this core question after some
  preliminaries on the early study of attention as
  selection and the filter theory.
• On what basis do we select? Some alternatives
• We select according to what is important to us
  (e.g., affordances)
• We select what can be described physically (i.e.,
  channels)
• We select based on what can be encoded without
  accessing LTM
• We pick out things to which we subsequently
  attach concepts i.e., we pick out objects (or
  regions?)
• What happens to what we have not selected? A
  largely unsolved mystery (though in some cases
  there are plausible answers).

3
Big Question 1 Why do we need to select
information?
?

• Along which dimensions is human information
  processing capacity limited?
• Channel capacity Shannon-Hartley Theorem
• Capacity measured in some sort of chunks
  (Miller)
• Capacity measured in terms of the number of
  arguments that can be simultaneously bound to
  cognitive routines (Newell)
• To what things in the world can the arguments of
  visual predicates be bound?

4
Early studies Colin Cherrys Cocktail Party
Problem

• What determines how well you can select one
  conversation among several? Why are we so good
  at it?
• The more controlled version of this study used
  dichotic presentations one channel per ear.
• Cherry found that when attention is fully
  occupied in selecting information from one ear
  (through use of the shadowing task), almost
  nothing is noticed in the rejected ear (only if
  it was not speech).
• More careful observations shows this was not
  quite true
• Change in spectral properties (pitch) is noticed
• You are likely to notice your name spoken
• Even meaning is extracted, as shown by
  involuntary ear switching and disambiguating
  effect of rejected channel content

5
Visual analogues illustrating the two-channel
selection problem
In these examples you are to read only the text
in shadows and ignore the rest. Read as quickly
as you can and when you are finished, close your
eyes or look away from the text.
6
Visual analogue 1 illustrating the two-channel
selection problem
In performing an experiment like this one on man
attention car it house is boy critically hat
important she that candy the old material horse
that tree is pen being phone read cow by book the
hot subject tape for pin the stand relevant view
task sky be read cohesive man and car
gramatically house complete boy but hat without
shoe either candy being horse so tree easy pen
that phone full cow attention book is hot not
tape required pin in stand order view to sky read
red it nor too difficult.
7
Visual analogue 2 illustrating the two-channel
selection problem
It is important that the subject man be car
pushed slightly boy beyond hat his normal limits
horse of tree competence pen for be only in phone
this cow way book can hot one tape be pin certain
stand that snaps he with is his paying teeth
attention in to the the empty relevant air task
and hat minimal shoe attention candy to horse the
tree second or peripheral task.
8
Broadbents Filter Theory
Rehearsal loop
Effectors
Motor planner
Senses
Filter
Limited Capacity Channel
Very Short Term Store
Store of conditional probabilities of past events
(in LTM)
Broadbent, D. E. (1958). Perception and
Communication. London Pergamon Press.
9
Problems with the Filter Theory

• The filter leaks. Work by Treisman, Lackner,
  and many others shows that the filter could not
  be eliminating parts of the input using a
  physically-defined channel, because the
  properties on the basis of which the input is
  filtered require a high level of processing
  (e.g., determination of meaning). Consequently
  such information must have to have gotten through
  the filter!
• Many solutions to this conundrum have been
  proposed, ranging from replacing the filter with
  an attenuator, to various complex (and highly
  incomplete) proposals such as those of Deutsch
  Deutsch, (1963) and Norman (1968), Morton (1969)
  and Neisser(1967), none of which are
  satisfactory, but each of which embodies some
  ideas that may be part of the story.
• What all these alternatives do is assume that the
  filter is responsive to top-down expectancy and
  prediction effects. But the evidence is against
  this sort of knowledge-based selection as a
  general property of perception (Pylyshyn, 1999),
  although it is possible within such modular
  domains as language processing.

10
Stroop EffectBaseline Name the colors of the ink
??????????????????????????????????????????????????
??????????????????????????????????
11
Stroop Effect in Portuguese Name the colors of
the ink
VERMELHO VERDE AZUL MARROM ROSA ALARANJADO VERDE
ROSA VERMELHO AMARELO VERDE AMARELO VERMELHO
MARROM VERMELHO AZUL MARROM VERDE VERMELHO
ALARANJADO VERMELHO AZUL AMARELO ROSA ALARANJADO
VERDE AZUL MARROM ROSA VERMELHO AMARELO VERDE
AMARELO VERMELHO MARROM ROSA VERMELHO AMARELO
VERDE AMARELO VERMELHO ROSA ALARANJADO VERDE AZUL
MARROM ROSA VERMELHO AMARELO VERDE AMARELO
VERMELHO BROWN VERMELHO AZUL MARROM VERDE AMARELO
VERDE AMARELO VERMELHO ROSA ALARANJADO VERDE
VERMELHO AZUL MARROM VERDE VERMELHO ALARANJADO
VERMELHO AZUL
12
Stroop Effect in English Name the colors of the
ink
RED GREEN BLUE PINK BROWN ORANGE GREEN PINK RED
YELLOW GREEN YELLOW RED BROWN RED BLUE BROWN
GREEN RED ORANGE RED BLUE YELLOW PINK ORANGE
GREEN BLUE BROWN PINK RED YELLOW GREEN YELLOW RED
BROWN PINK RED YELLOW GREEN YELLOW RED PINK
ORANGE GREEN BLUE BROWN PINK RED YELLOW GREEN
YELLOW RED BROWN RED BLUE GREEN BROWN YELLOW
GREEN YELLOW RED PINK ORANGE GREEN RED BLUE BROWN
GREEN RED ORANGE RED BLUE YELLOW YELLOW GREEN
YELLOW RED BROWN PINK RED YELLOW GREEN PINK RED
YELLOW
13
Degree of Interference of the attended message,
as well as its interpretation, shows that the
rejected message was understood

• Moral Although the rejected channel appears to
  be rejected, it is being processed enough to
  understand the words!
• The semantic interpretation of attended message
  depends on the meaning content of the rejected
  message. Subjects were asked to paraphrase the
  attended message in
• Channel 1 (attended) I think I will go down to
  the bank but I will be back for dinner
• Channel 2 (rejected) The election results will
  depend on the value of the dollar against the
  Euro and on the state of the domestic economy
• OR Channel 2 (rejected) The rain has resulted
  in erosion by the overflowing riverLackner, J.
  R., Garrett, M. F. (1972). Resolving ambiguity
  Effects of biasing context in the unattended ear.
  Cognition, 1, 359-372.

14
Amount of information in terms of the
Information-theoretic measure (entropy)

• Amount of information in a signal depends on how
  much ones estimate of the probability of events
  is changed by the signal. H -?pi Log2 (pi)
  information in bits
• One of by land, two if by sea contains one bit
  of information if the two possibilities were
  equally likely, less if they were not (e.g., if
  one was twice as likely as the other the
  information in the message would be ? Log ? ?
  Log ? 0.92 bits)
• The amount of information transmitted depends on
  the potential amount of information in the
  message and the amount of correlation between
  message sent and message received. So information
  transmitted is a type of correlation measure.
• The information measure assumes an ideal
  receiver. It is the maximum information that
  could be transmitted, given the statistical
  properties of messages, assuming that the sender
  and receiver know the code. This maximum depends
  on physical properties of the channel its
  Channel Capacity.

15
Information transmitted in a typical absolute
judgment experiment

• Information transmitted in an experiment in which
  subjects were presented with tones drawn from a
  known practiced set (of a given size, which
  determines the value of input information) and
  had to name the tones from a learned name set.
• The information transmitted was always around 2.5
  bits or an average of 6.25 equiprobable
  alternatives!

16
The channel capacity hypothesis implies that the
amount of information retained in STM is constant
and independent of the type of items

• But it turns out that much more information is
  retained when the items are drawn from a larger
  set (e.g., more information can be retained when
  the input is numerals rather then than binary
  digits, more for letters, more for words, etc).

17
Short term memory capacity is independent of the
amount of information per item!

• STM capacity (number of items) plotted as a
  function of the information content of individual
  items in each type of code. It seems that the
  number of items remains roughly constant but
  amount of information is highly dependent on
  information carried by each item.

18
Why can we retain vastly different amounts of
information just by using a different encoding
vocabulary?

• Answer The architecture of the cognitive system
  has the property that it can deal with a fixed
  maximum number of items, regardless of what the
  items are.
• This property can be exploited to get around the
  bottleneck of the short-term memory. We do this
  by recoding the input into a smaller number of
  discrete units, called chunks.
• There is also evidence that it takes additional
  time to encode and decode chunks, so the recoding
  technique is a case of time-capacity tradeoff or
  what is known in CS as a compute-vs-store
  tradeoff.
• Newell has a model of the time taken in the
  Sternberg memory scan experiment that attributes
  the observed RT to encoding or chunking.

19
Example of the use of chunking

• To recall a string of binary bits e.g.,
  00101110101110110101001
• People can recall a string of about 8 binary
  integers. If they learn a binary encoding rule
  (00?0, 01?1, 10?2, 11?3) they can recall about 8
  such chunks or 18 binary bits. If they learn a
  31 chunking rule (called the Octal number
  system) they can recall a 24 bit string, etc

20
Does the evidence support this idea?
Memory span can be greatly increased through
chunking! Yet chunking has also been used to
explain things it cannot explain. It is only
explanatory if you have an account of how
chunking occurs and what rules in LTM are being
used (and what counts as a chunk).
21
What does visual attention select? (What are the
bases for selection?)

• If attention is selection, what does visual
  attention select?
• An obvious answer is places. We can select
  places by moving our eyes so our gaze lands on
  different places.
• When places are selected, are they selected
  automatically?
• Must we always move our eyes to change what we
  attend to?
• Studies of Covert Attention-Movement Posner
  (1980).
• How does attention switch from one place to
  another?
• Is it always the case that we attend to places?
  Can we attend to any other property? Can we
  select on the basis of color, depth, spatial
  frequency, affordances, or the property a
  painting has of having been painted by Da Vinci
  (A property to which Bernard Berenson was able to
  attend extremely well). cf Gibson

22
How else can visual attention select?
?

• Can we control the size and shape of the region
  that is selected, or is selection always punctate
  and data-driven?
• Zoom Lens model of spatial attention (Eriksen
  St James, 1986).
• What controls where attention moves
• Is this automatic or voluntary?
• How do we know where to direct our attention?
  How do we specify a location prior to attending
  to it?
• We need a way to specify where or what prior to
  attending to it!
• Keep this conundrum in mind we will return to
  it later!
• How narrowly can we focus our attention? Can we
  make it pick out one out of several objects?
• Are there special conditions under which we are
  able to pick out individual things? We will
  return to attentional resolution or the minimum
  spacing for selecting individual things.

23
Covert movements of attention
Example of an experiment using a cue-validity
paradigm for showing that the locus of attention
moves without eye movements and for estimating
its speed. Posner, M. I. (1980). Orienting of
Attention. Quarterly Journal of Experimental
Psychology, 32, 3-25.
24
Extension of Posners demonstration of attention
switch
Does the improved detection in intermediate
locations entail that the spotlight of
attention moves continuously through empty space?
25
Exogenous vs endogenous control of attention

• In the Posner paradigm illustrated in the last
  slide, attention was automatically grabbed by the
  onset of a spot (exogenous attention allocation).
  Other experiments showed that this could be done
  under voluntary (endogenous) control e.g., by
  providing an arrow at fixation indicating what
  direction to move attention.
• Posner, Tsal and others showed that when
  attention goes from A to B, intermediate
  locations are maximally sensitive to detecting a
  signal at intermediate times.
• Both exogenous and endogenous control produces
  movement of attention, but they differ in some of
  their effects.
• Endogenously moved attention does not lead to
  Inhibition of Return (we will turn to this next)
• Endogenous controlled movement does not appear to
  affect detection sensitivity, but it does affect
  discrimination
• Endogenous controlled effects are stronger and
  appear earlier
• Although the evidence suggests a continuously
  moving spotlight of attention, there are other
  models that claim that this is a side-effect of
  an attentional activation that fades at the
  starting place and grows at the target place,
  creating an overlap in intermediate locations
  (Sperling).

26
It also appears that we can to some extent
control the shape of our attended region
Farah, M. J. (1989). Mechanisms of
imagery-perception interaction. Journal of
Experimental Psychology Human Perception and
Performance, 15, 203-211.
27
We can select a shape even when it is intertwined
among other similar shapes
Are the green items the same? On a surprise test
at the end, subjects were not able to recognize
recall shapes that had been present but had not
appeared in green.
28
The time-course of attentionInhibition of return

• If we vary the time between the cue and target in
  a modified Posner paradigm, we find that when the
  Cue-Target-Onset-Asynchrony (CTOA) gets to
  around 300-900 ms, reaction time to the target
  begins to increase. This is called
  Inhibition-of-return (Klein, 2000).
• To get this effect we actually have to attract
  attention to the target location and then attract
  it back to the origin. IOR is one of many
  examples of an inhibition effect being produced
  by attention.

29
Other examples of attentionally induced inhibition

• Negative Priming (Treisman DeShepper, 1996).

• Is there a figure on the right that is the same
  as the figure on the left?
• When the figure on the left is one that had
  appeared as an ignored figure on the right, RT is
  long and accuracy poor.
• This negative priming effect persisted over 200
  intervening trials and lasted for a month!

30
Another negative attention effect Inattentional
Blindness
31
Inattentional Blindness

• The background task is to report which of two
  arms of the is longer. One critical trial per
  subject, after about 3,4 background trials.
  Another critical trial presented as a divided
  attention control.
• 25 of subjects failed to see the square when it
  was presented in the parafovea (2 from
  fixation).
• But 65 failed to see it when it was at fixation!
  
• When the background task cross was made 10 as
  large, Inattentional Blindness increased from 25
  to 66.
• It is not known whether this IB is due to
  concentration of attention at the primary task,
  or whether there is inhibition of outside regions.

32
In what other ways might our information
capacity be limited?

• We have limitations on the input side that depend
  on the acuity of the sensors and the range of
  physical properties to which they respond.
• But there is a limitation beyond that of acuity
  The perceptual system is limited in what it can
  individuate and how many of these individuals it
  can deal with at one time. The capacity to
  individuate is different from the capacity to
  discriminate.
• This notion of individuating and of individuals
  may be related to Millers chunks, but it has a
  special role in vision which we will explore in
  the next lecture
• First some reason for thinking that individuating
  is a distinct process

33
Individuating is different from discriminating
34
Individuating as a distinct process

• Individuating has its own psychometric function
  The minimum distance for individuating is much
  larger than for discriminating.
• It may be that in vision our attention is limited
  in the number of things we can individuate and
  simultaneously access (more on this later). But
  how do you determine what counts as a thing?
  See next lecture.
• Individuating is a prerequisite for recognition
  of patterns and other properties defined among a
  number of individual parts
• An example of how we can easily detect patterns
  if they are defined over a small enough number of
  parts is in subitizing
• Another area where the concept of an individual
  has become important is in cognitive development,
  where it is clear that babies are sensitive to
  the numerosity of individual things in a way that
  is distinct from their perceptual abilities but
  is limited in its capacity

35
Pick out 3 dots and keep track of them

• You can follow instructions to move one up or
  Move 2 right etc so long as at no time do you
  have to hold on to more than 4 dots
• You can pick out 4 dots and then search through
  those 4 locations if all dots change to search
  items (Burkell Pylyshyn, 1997)
• You can count up to 4 dots without error (Trick
  Pylyshyn, 1994)
• You can keep track of 4 dots through saccades
  (Irwin, 1996)
• You can detect such basic patterns as inside(dot,
  contour), Collinear(x1,x2,x3,x4), or Online(dot,
  contour) so long as there are a small number of
  the relevant arguments to hold on to at one time.

36
Next Objects and Attention
37
Are there collinear items (ngt3)?
38
Several objects must be picked out at once in
making relational judgments

• The same is true for other relational judgments
  like inside or on-the-same-contour etc. We must
  pick out the relevant individual objects first.

39
When items cannot be individuated, predicates
over them cannot be evaluated? Do these figures
contain one or two distinct curves? ?
Individuating these curves requires a curve
tracing operation, so Number_of_curves (C1, C2,
) takes time proportional to the length of the
shortest curve.
40
The figure on the left is one continuous curve,
the one on the right is two distinct curves as
shown in color.
41
Another example Subitizing vs Counting. How
many squares are there? Subitizing is fast,
accurate and only slightly dependent on how many
items there are. Only the squares on the right
can be subitized.
Concentric squares cannot be subitized because
individuating them requires curve tracing, just
as it did in the spiral example.
42
Signature subitizing phenomena only appear when
objects are automatically individuated and indexed
Counting slope
subitizing slope
Trick, L. M., Pylyshyn, Z. W. (1994). Why are
small and large numbers enumerated differently? A
limited capacity preattentive stage in vision.
Psychological Review, 101(1), 80-102.
43
Example of subitizing popout and non-popout
features(Count Pink vs. Count Online)
44
What is attention is for? Treismans Attention
as Glue Hypothesis

• The purpose of visual attention is to Bind
  properties together in order to recognize objects

45
How are conjunctions of features detected?
Read the vertical line of digits in the following
display
Under these conditions Conjunction Errors are
very frequent
46
Rapid visual search (Treisman)
Find the following simple figure in the next
slide
47
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48
(No Transcript)
49
Rapid visual search (conjunction)
Find the following simple figure in the next
slide
50
(No Transcript)
51
Find the unique item in this slide
52
Serial vs parallel search?

• Finding an object that differs from all others in
  a scene by a single feature called a
  single-feature search is fast, error-free and
  almost independent of how many nontargets there
  are
• Finding an object that differs from all others by
  a conjunction of two or more features (and that
  shares at least one feature with each object in
  the scene) called a conjunction search is
  usually slow, error-prone, and is worse the more
  nontargets there are in the scene.
• These results suggest that in order to find a
  conjunction, which requires solving the binding
  problem, attention has to be scanned serially to
  all objects.

This way of putting is simplifies things.
Under certain conditions the serial-parallel
distinction breaks down
53
The attention-as-glue hypothesis has a converse
In addition to requiring attention to recognize
objectsAttention is primarily directed at Objects

• Instead of being like a spotlight beam that can
  be scanned around a scene and can be zoomed to
  cover a larger or smaller area, perhaps attention
  can only be directed towards occupied places
  i.e., to visual objects. (This is compatible
  with both kinds of attention allocation
  occurring).

54
Evidence for attentional selection based on
Objects

• Single Object Advantage pairs of judgments are
  faster when both apply to the same perceived
  object
• Entire objects acquire enhanced sensitivity from
  focal attention to a part of the object
• Single-Object advantage occurs even with
  generalized objects defined in feature space
• Simultanagnosia and hemispatial neglect show
  object-based effect
• Studies with Moving Objects
• IOR
• Object Files
• MOT

55
Some single-object superiority studies
Duncan (1984) showed that two judgments made
about the same objects are faster even when the
distances and areas are controlled. He concluded
Findings support a view in which parallel,
preattentive processes serve to segment the field
into separate objects, followed by a process of
focal attention that deals with only 1 object at
a time.
56
Single-object superiority even when the shapes
are controlled
57
More controls for the Baylis study (Baylis, 1994)
Controls for separability, convexity, area
58
Objects endure over time

• Several studies have shown that what counts as an
  object (as the same object) endures over time and
  over changes in location
• Certain forms of disappearances in time and
  changes in location preserve objecthood.
• This gives what we have been calling a visual
  object a real physical-object character and
  partly justifies our calling it an object.

59
Inhibition of return appears to be object-based
(as well as location-based)

• Recall that Inhibition-of-return is the
  phenomenon whereby an object that has been
  attended (and then attention is moved away from
  it) is less likely to attract attention again in
  a period of 300 ms to 900 ms after it is first
  attended. The attended item is said to be
  inhibited.
• This is thought to help in visual search since it
  prevents previously visited objects from being
  revisited
• The original study used static objects. Then
  (Tipper, Driver Weaver, 1991) showed that IOR
  moves with the inhibited object.

60
Object Based Inhibition of Return
61
Objects appear to carry their history with
themObject-specific priming of objects and
contents
Object File Theory Kahneman, Treisman
Gibbs(1992)
Letters are faster to read if they appear in the
same box where they appeared initially. Priming
travels with the object. According to the
theory, when an object first appears, a file is
created for it and the properties of the object
are encoded and subsequently accessed through
this object-file.
62
Tracking objects not defined by distinct spatial
locations and spatial trajectories
Blaser, E., Pylyshyn, Z. W., Holcombe, A. O.
(2000). Tracking an object through feature-space.
Nature, 408(Nov 9), 196-199.
63
Visual neglect syndrome is object-based
When a right neglect patient is shown a dumbbell
that rotates, the patient continues to neglect
the object that had been on the right, even
though It is now on the left (Behrmann Tipper,
1999).
64
Simultanagnosic (Balint Syndrome) patients only
attend to one object at a time
Simultanagnosic patients cannot judge the
relative length of two lines, but they can tell
that a figure made by connecting the ends of the
lines is not a rectangle but a trapezoid (Holmes
Horax, 1919).
65
Balint patients can only attend to one object at
a time even if they are overlapping
Luria, 1959
66
End ? (for now)

• Multiple Object Tracking is a methodology for
  studying Object-Based attention.

67
Multiple Object Tracking

• One of the clearest cases illustrating
  object-based attention is Multiple Object
  Tracking
• Keeping track of individual scene objects
  requires a mechanism for individuating,
  selecting, accessing and maintaining the identity
  of individuals over time
• These are the functions we have proposed are
  carried out by the mechanism of visual indexes
  (FINSTs)
• We have been using a variety of methods for
  studying visual indexing, including subitizing,
  subset selection for search, and Multiple Object
  Tracking (MOT).

68
Multiple Object Tracking

• In a typical experiment, 8 simple identical
  objects are presented on a screen and 4 of them
  are briefly distinguished in some visual manner
  usually by flashing them on and off.
• After these 4 targets have been briefly
  identified, all objects resume their identical
  appearance and move randomly. The subjects task
  is to keep track of which ones had earlier been
  designated as targets.
• After a period of 5-10 seconds the motion stops
  and subjects must indicate, using a mouse, which
  objects were the targets.
• People are very good at this task (80-98
  correct). The question is How do they do it?

69
Keep track of the objects that flash
70
How do we do it? What properties of individual
objects do we use?
71
Keep track of the objects that flash
72
How do we do it? What properties of individual
objects do we use?
73
Explaining Multiple Object Tracking

• Basic finding People (even 5 year old children,
  though not most senior professors!) can track 4
  to 5 individual objects that have no unique
  visual properties
• How is it done?
• We have shown that it is unlikely that the
  tracking is done by keeping a record of target
  locations, and updating them while serially
  visiting the objects.
• I have proposed that individuating and keeping
  track of certain kinds of individuals is a
  primitive visual operation and uses the mechanism
  of visual indexes or FINSTs.
• Tracking is preconceptual and preattentive (
  explanation is left for another occasion)

74
A possible location-based tracking algorithm

1. While the targets are visually distinct, scan
   attention to each target in turn and encode its
   location on a list.
2. When targets begin to move, check the nth
   position in the list and go to the location
   encoded there Call it Loc(n).
3. Find the closest element to Loc(n).
4. Update the actual location of the element found
   in 3 in position n in the list this becomes the
   new value of Loc(n).
5. Move attention to the location encoded in the
   next list position, Loc(n1).
6. Repeat from 3 until elements stop moving.
7. Report elements whose locations are on the list.

Use of the above algorithm assumes (1) focal
attention is required to encode locations (i.e.,
encoding is not parallel), (2) focal attention is
unitary and has to be scanned continuously from
location to location. It assumes no encoding (or
dwell) time at each element.
75
Predicted performance for the serial tracking
algorithm as a function of the speed of movement
of attention
76
If we are not using and updating objects
locations, then how are we tracking them?

• Since objects are identical, location is the only
  unique object property, yet we do not appear to
  be using locations to track.
• Other ideas of how we track (e.g., that we view
  objects as vertices of a deforming polygon), even
  if in some sense a true description, does not
  explain how we do it (e.g. polygon strategy).
• We could be splitting attention, with each
  attentional beam moving independently (but if so
  they act differently from focal attention e.g.,
  subjects do not notice properties of targets).
• The explanation we prefer, which is independently
  motivated, is that there are a small number of
  primitive indexes or pointers, each of which can
  pick out a particular individual object qua
  object and keeps providing access to the object
  as it changes its properties and its location.

77
Additional examples of MOT

• MOT with occlusion
• MOT with virtual occluders
• "Rubber band" displays

78
Summary of some properties of indexing revealed
by our recent experiments

1. Targets can be tracked even when they disappear
   behind an occluder and, under certain conditions,
   even when all objects disappear from view (Scholl
   Pylyshyn, 1999 Keane Pylyshyn, VSS2003).
   Demo MOT with occlusion
2. Properties of targets are not encoded during MOT
   nor are they used in tracking. Changes in target
   properties are not even noticed (Scholl, Pylyshyn
   Franconeri, 1999).
3. Not all well-defined clusters of features can be
   tracked Only ones that correspond to objects
   (Scholl, Pylyshyn Feldman, 2001). Demo
   "Rubber band" displays

79
Summary of some properties of indexing revealed
by our recent experiments

1. Indexes are assigned primarily exogenously
   (involuntarily). They can also be assigned
   endogenously (voluntarily) but only by moving
   focal attention to each target serially (Annon
   Pylyshyn, VSS2003).
2. Index maintenance in tracking appears to be
   non-predictive and non-attentive (Keane
   Pylyshyn, VSS2003 Leonard Pylyshyn, VSS2003).
3. Target-target confusions are much more numerous
   than target-nontarget confusions. The reason
   appears to be that nontargets are inhibited,
   which may prevent them from being swapped with
   nontargets (Pylyshyn Leonard, VSS2003).

80
So what are FINSTs?

• They are a primitive reference mechanism that
  refer to individual objects in the world (FINGs?)
• Objects are picked out and referred to without
  using any encoding of their properties, including
  their location. Picking out objects is prior to
  encoding their locations!
• Indexing is nonconceptual because it does not
  represent the individuals as members of some
  conceptual category.
• FINSTs serve as visual demonstratives, much like
  the terms this or that do in language, by picking
  out and referring to individuals without using
  their properties.
• The central function of FINST indexes is to bind
  arguments of visual predicates or of motor
  commands to things in the world to which they
  must refer. Only predicates with bound arguments
  can be evaluated.

81
Schema for how FINSTs function in visual-motor
control
82
The binding hypothesis of the visual-cognitive
bottleneck

• Going back to Newells binding hypothesis we are
  hypothesizing that the bottleneck between vision
  and cognition is in the number of objects that
  can be simultaneously bound to the arguments of
  cognitive routines
• Another way to put this is that visual cognition
  can simultaneously attend to only about 4
  objects.
• There is direct evidence for the limit of about 4
  visual objects in visual working memory
• Luck, S. and E. Vogel (1997). "The capacity
  of visual working memory for features and
  conjunctions." Nature 390 279-281.

83
Information processing capacity appears to be
limited to 7 2 chunks rather than to a number
of bits or baud

• Experiments on short term memory STM (or
  working memory)
• Miller, G. A. (1956). The magical number seven,
  plus or minus two Some limits on our capacity
  for processing information. Psychological Review,
  63, 81-97.
• Experiments on the capacity of Visual Working
  Memory (Luck Vogel, 1997)

84
Studies of the capacity of Visual Working Memory
(Luck Vogel, 1997)

• People appear to be able to retain about 4
  properties of an object (4 colors, 4 shapes, 4
  orientations, etc) over a short time
• People can also retain the identity of 4 objects
  for a short time.
• Luck and Vogel found that as long as there are
  not more than 4 properties per object, people can
  retain large numbers of properties (a phenomenon
  that is reminiscent of Millers chunking
  hypothesis except the chunks are objects).