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Posted-Date: Fri, 16 Oct 92 08:19:07 PDT
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Date:         Fri, 16 Oct 1992 08:19:07 PDT
From:         marken@AERO.ORG
Subject:      family man

Isaac

Here is the rejected paper. Enjoy.
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The Hierarchical Behavior of Perception


Richard S. Marken
RSM & Associates
Los Angeles, CA 90024


Abstract

	This paper argues that the coincidental development of
hierarchical models of perception and behavior is not a coincidence.
Perception and behavior are two sides of the same phenomenon -- control.
A hierarchical control system model shows that evidence of hierarchical
organization in behavior is also evidence of hierarchical organization in
perception. Studies of the temporal limitations of behavior, for example, are
shown to be consistent with studies of temporal limitations of perception. A
surprising implication of the control model is that  the perceptual limits are
the basis of the behavioral limits. Action systems cannot produce controlled
behavioral results faster than the rate at which these results can be
perceived. Behavioral skill turns on the ability to control a hierarchy of
perceptions, not actions.

 	Psychologists have developed hierarchical models of both
perception (eg. Bryan and Harter, 1899; Palmer, 1977; Simon, 1972;
Povel, 1981) and behavior (eg. Albus, 1981; Arbib, 1972; Greeno and
Simon, 1974; Lashley, 1951; Martin, 1972; Keele, Cohen and Ivry, 1990;
Rosenbaum, 1987). This could be a coincidence, a case of similar models
being applied to two very different kinds of phenomena. On the other hand,
it could reflect the existence of a common basis for both perception and
behavior. This paper argues for the latter possibility, suggesting that
perception and behavior are two sides of the same phenomenon -- control
(Marken, 1988).  Control is the means by which agents keep perceived
aspects of their external environment in goal states (Powers, 1973). It is
argued that the existence of hierarchical models of both perception and
behavior is a result of looking at control from two different perspectives;
that of the agent doing the controlling (the actor) and that of the agent
watching control (the observer). Depending on the perspective, control can
be seen as a perceptual or a behavioral phenomenon.

	 From the actor's perspective, control is a perceptual
phenomenon. The actor is controlling his or her own perceptual experience,
making it behave as desired. However, from the observer's perspective,
control is a behavioral phenomenon. The actor appears to be controlling
variable aspects of his or her behavior in relation to the environment. For
example, from the perspective of a typist (the actor), typing involves the
control of a dynamically changing set of kinesthetic, auditory and, perhaps,
visual perceptions. If there were no perceptions there would be no typing.
However, from the perspective of someone watching the typist (the
observer), perception is irrelevant; the typist appears to be controlling the
movements of his or her fingers in relation to the keys on a keyboard.

	These two views of control have one thing in common; in both
cases, control is seen in the behavior of perception. For the actor, control is
seen in the behavior of his or her own perceptions. For the observer,
control is seen in the behavior of his or her own perceptions of the actor's
actions. (The observer can see the means of control but can only infer their
perceptual consequences as experienced by the actor). If control is
hierarchical then it can be described as the behavior of a hierarchy of
perceptions. Hierarchical models of perception and behavior can then be
seen as attempts to describe control from two different perspectives, those
of the actor and observer, respectively. This paper presents evidence that
hierarchical models of perception and behavior reflect the hierarchical
structure of control.

A Perceptual Control Hierarchy

	The concept of control as the behavior of perception can be
understood in the context of a hierarchical control system model of
behavioral organization (Powers, 1973; 1989). The model is shown in
Figure 1. It consists of several levels of control systems (the figure shows
four levels) with many control systems at each level (the figure shows
seven). Each control system consists of an input transducer (I), comparator
(C) and output transducer (O). The input transducer converts inputs from
the environment or from systems lower in the hierarchy into a perceptual
signal,p. The comparator computes the difference between the perceptual
signal and a reference signal ,r. The output transducer amplifies and
converts this difference into actions which affect the environment or become
reference signals for lower level systems.
________________
Insert Figure 1 Here
 ________________

	 The control  systems at each level of the hierarchy control
perceptions of different aspects of the external environment. However,  all
systems control perceptions in the same way; by producing actions that
reduce the discrepancy between actual and intended perceptions. Intended
perceptions are specified by the reference signals to the control systems.
The actions of the control systems coax perceptual signals into a match with
reference signals via direct or indirect effects on the external environment.
The actions of the lowest level control systems affect perceptions directly
through the environment. The actions of higher level control systems affect
perceptions indirectly by adjusting the reference inputs to lower level
systems.

	The hierarchy of control systems is a working model of
purposeful behavior (Marken, 1986; 1990). The behavior of the hierarchy is
purposeful inasmuch as each control system in the hierarchy works against
any opposing forces in order to produce intended results. Opposing forces
come from disturbances created by the environment as well as interfering
effects caused by the actions of other control systems. The existence of
disturbances means that a control system cannot reliably produce an
intended result by selecting a particular action. Actions must vary to
compensate for varying disturbances. Control systems solve this problem
by specifying what results are to be perceived, not how these results are to
be achieved. Control systems control perceptions, not actions. When set up
correctly the control systems in the hierarchy vary their actions as
necessary, compensating for unpredictable (and, often, undetectable)
disturbances, in order to produce intended perceptions. Indeed, the term
"control" refers to this process of producing intended perceptions in a
disturbance prone environment.

Levels of Perception.

	Powers (1990) has proposed that each level of the hierarchy of
control systems controls a different class of perception. These classes
represent progressively more abstract aspects of the external environment.
The lowest level systems control perceptions that represent the intensity of
environmental input. The next level controls sensations (such as a colors),
which are functions of several different intensities. Going up from
sensations there is control of configurations (combinations of sensations),
transitions (temporal changes in configurations), events (sequences of
changing configurations), relationships (logical, statistical, or causal co-
variation between independent events), categories (class membership),
sequences (unique orderings of lower order perceptions), programs (if-then
contingencies between lower level perceptions), principles (a general rule
that exists in the behavior of lower level perceptions) and system concepts
(a particular set of principles exemplified by the states of many lower level
perceptions; see Powers, 1989, pp. 190-208).  These eleven classes of
perception correspond to eleven levels of control systems in the hierarchical
control model. All control systems at a particular level of the hierarchy
control the same class of perception, though each system controls a slightly
different exemplar of the class. Thus, all systems at a particular level may
control configuration perceptions but each system controls a different
configuration.

	The rationale for hierarchical classes of perceptual control is
based on the observation that certain types of perception depend on the
existence of others. Higher level perceptions depend on (and, thus, are a
function of) lower level perceptions. For example, the perception of a
configuration, such as a face, depends on the existence of sensation (color)
or intensity (black/white) perceptions. The face is a function of these
sensations and intensities. The lower level perceptions are the independent
variables in the function that computes the higher level perception. Their
status as independent variables is confirmed by the fact that lower level
perceptions can exist in the absence of the higher level perceptions, but not
vice versa. Color and intensity perceptions can exist without the perception
of a face (or any other configuration, for that matter) but there is no face
without perceptions of intensity and/or color.

The Behavior of Perceptions. From the point of view of the hierarchical
control model, "behaving" is a process of controlling perceptual experience.
Any reasonably complex behavior involves the control of several levels of
perception simultaneously . For example, when typing the word "hello",
one controlled perception is the sequence of letters "h", "e", "l" ,"l" and
"o". The perception of this sequence is controlled by producing a sequence
of keypress event perceptions. Each keypress event is controlled by
producing a particular set of transitions between finger configuration
perceptions. Each finger configuration is controlled by a different set of
force sensations which are themselves controlled by producing different
combinations of intensities of tensions in a set of muscles.

	The perceptions involved in typing "hello" are all being controlled
simultaneously. Transitions between finger configurations are being
controlled while the force sensations that produce the configuration
perceptions are being controlled.  However, the typist is usually not  aware
of the behavior of all these levels of perception. People ordinarily attend to
the behavior of their perceptions at a high level of abstraction, ignoring the
details. We attend to the fact that we are driving down the road and ignore
the changing muscle tensions, arm configurations and steering wheel
movements that produce this result. Paying attention to the details leads to a
deterioration of performance; it is the opposite of "zen" behavior, where you
just attend to the (perceptual) results that you intend to produce and let the
required lower level perceptions take care of themselves (Herrigal, 1971).
However, while it violates the principles of zen, attention to the detailed
perceptions involved in the production of behavioral results can provide
interesting hints about the nature of the perceptual control hierarchy.

The Perception of Behavior. The behavior of an actor who is organized like
the hierarchical control model consists of changes in the values of variables
in the actor's environment. An observer cannot see what is going on inside
the actor; he or she can only see the actor's actions and the effect of these
actions on the external environment. The effect of these actions is to cause
purposeful behavior of certain variables in the environment; the variables
that correspond to perceptions that the actor is actually controlling. The
purposefulness of the behavior of these variables is evidenced by the fact
that consistent behaviors are produced in the context of randomly changing
environmental disturbances. Thus, a typist can consistently type the word
"hello" despite changes in the position of the fingers relative to the
keyboard, variations in the push-back force of the keys or even a shift from
one keyboard arrangement to another (from QWERTY to Dvorak, for
example).

	Since the actor controls his or her own perceptions, the observer
cannot actually see what the actor is "doing"; the actor's "doings" consist of
changing the intended states of his or her own perceptions. All the observer
sees is variable results of the actor's actions; results that may or may not be
under control. For example, the observer, might notice that a click occurs
each time the typist presses a key. The click is a result produced by the
typist and the observer is likely to conclude that the typist is controlling the
occurrence of the click. In fact, the click may be nothing more than a side
effect of the typist's efforts to make the key feel like it has hit bottom.
 There
are methods that make it possible for the observer to tell whether or not his
or her perceptions of the actor's behavior correspond to the perceptions that
are being controlled by the actor (Marken, 1989). These methods make it
possible for the observer to determine what the actor is actually doing (i.e.
controlling).

 Hierarchical Control

	 The hierarchical nature of the processes that generate behavior
would not be obvious to the observer of a hierarchical control system. The
observer could tell that the system is controlling many variables
simultaneously but he or she would find it difficult to demonstrate that some
of these variables are being controlled in order to control others. For
example, the observer could tell that a typist is controlling letter sequences,
keypress events, finger movements and finger configurations. But the
observer would have a hard time showing that these variables are
hierarchically related. The observer could make up a plausible hierarchical
description of these behaviors; for example, finger positions seem to be
used to produce finger movements which are used to produce keypresses
which are used to produce letter sequences. But finding a hierarchical
description of behavior does not prove that the behavior is actually produced
by a hierarchical process (Davis, 1976; Kline, 1983).

 Hierarchical Invariance

	Hierarchical production of behavior implies that the commands
required to produce a lower level behavior are nested within the commands
required to produce a higher level behavior. For example, the commands
that produce a particular finger configuration would be nested within the
commands that produce a movement from one configuration to another.
Sternberg, Knoll and Turlock (1990) refer to this nesting as an invariance
property of hierarchical control. Lower level commands are like a
subprogram that is invoked by a program of higher level commands. The
invariance of hierarchical control refers to the assumption that the course of
such a subprogram does not depend on how it was invoked from the
program (low level invariance); similarly, the course of the program does
not depend on the nature of the commands carried out by the subprograms
(high level invariance).

Convergent and Divergent Control. The hierarchical control model satisfies
both the low and high level invariance properties of hierarchical control. The
commands issued by higher level systems have no effect on the commands
issued by lower level systems and vice versa. It is important to remember,
however, that the commands in the control hierarchy are requests for input,
not output. Higher level systems tell lower level systems what to perceive,
not what to do. This aspect of control system operation solves a problem
that is either ignored or glossed over in most hierarchical models of
behavior: How does a high level command get turned into the the lower
level commands that produce results that satisfy the high level command? If
commands specify outputs then the result of the same command is always
different due to varying environmental disturbances. The high level
command to press a key, for example, cannot know which lower level
outputs will produce this result on different occasions. This problem is
solved by the hierarchical control model because intended results are
represented as a convergent function rather than a divergent network.

	Most hierarchical models of behavior require that a high level
command be decomposed into the many lower level commands that produce
the intended result. In the hierarchical control model, both the high level
command and the intended result of the command are represented by a
single, unidimensional signal. The signal that represents the intended result
is a function of results produced by many lower level commands. But the
high level command does not need to be decomposed into all the appropriate
lower level commands (Powers, 1979). The difference between the high
level command and the perceptual result of that command is sufficient to
produce the lower level commands that keep the perceptual result at the
commanded value (Marken, 1990).

Levels of Behavior

	The hierarchical invariance properties of the control hierarchy
provide a basis for determining whether its behavior is actually generated by
hierarchical processes. Hierarchical control can be seen in the relative timing
of control actions. In a control hierarchy, lower level systems must operate
faster than higher level systems. Higher level systems cannot produce a
complex perceptual result before the lower level systems have produced the
component perceptions on which it depends. This nesting of control actions
can be seen in the differential speed of operation of control systems at
different levels of the control hierarchy. Lower level systems not only
correct for disturbances faster than higher level ones; they carry out this
correction process during the higher level correction process. The lower
level control process is temporally nested within the higher level control
process.

Arm Movement. Powers, Clark and McFarland (1960) describe a simple
demonstration of nested control based on relative timing of control system
operation. A subject holds one hand extended straight ahead while the
experimenter maintains a light downward pressure on it. The subject is to
move his or her arm downward as quickly as possible when the
experimenter signals with a brief, downward push on the subject's extended
hand. The result of this simple experiment is always the same: the subject
responds to the downward signal push with a brief upward push followed
by downward movement of the arm. An electromyograph shows that the
initial upward push is an active response and not the result of muscle
elasticity.

	The arm movement demonstration reveals one level of control
nested within another. The subject's initial upward push (which cannot be
suppressed) is the fast response of a lower level control system that is
maintaining the perception of arm position in a particular reference state
(extended forward). The behavior of this system is nested within the
response time of a higher level system that moves the arm downward. The
higher level system operates by changing the reference for the arm position
control system. The downward signal push causes the brief upward reaction
because the signal is treated as a disturbance to arm position. This is
particularly interesting because the signal is pushing the arm in the direction
it should move; the lower level reaction is "counter productive" with respect
to the goal of the higher level system (which wants to perceive the arm
down at the side). The reaction occurs because the lower level system starts
pushing against the disturbance to arm position before the higher level
system can start changing the reference for this position.

Polarity Reversal. More precise tests of nested control were carried out in a
series of experiments by Marken and Powers (1989). In one of these
experiments, subjects performed a standard pursuit tracking task, using a
mouse controller to keep a cursor aligned with a moving target. At intervals
during the experiment the polarity of the connection between mouse and
cursor movement was reversed in a way that did not disturb the cursor
position. Mouse movements that had moved the cursor to the right now
moved it to the left; mouse movements that had moved the cursor to the left
now moved it to the right.

	A sample of the behavior that occurs in the vicinity of a polarity
reversal is shown in Figure 2. The upper traces show the behavior of a
control system model and the lower traces show the behavior of a human
subject. When the reversal occurs, both the model and the subject respond
to error (the deviation of the cursor from the target) in the wrong direction,
making it larger instead of smaller (any deviation of the error trace from the
zero line represents an increase in error). The larger error leads to faster
mouse movement which causes the error to increase still more rapidly. A
runaway condition ensues with error increasing exponentially.
_____________
Figure 2 Here
______________

	About 1/2 second after the polarity reversal the subject's behavior
departs abruptly from that of the model. The subject adjusts to the polarity
reversal and the error returns to a small value. The model cannot alter its
characteristics and the error trace quickly goes off the graph. These results
provide evidence of two nested levels of control operating at different
speeds. The faster, lower level system control the distance between cursor
and target. This system continues to operate as usual even when, due to the
polarity reversal, this causes an increase in perceptual error. Normal
operation is restored only after a slower, higher level system has time to
control the relationship between mouse and cursor movement.

Levels of Perception

	The arm movement and polarity shift experiments reveal the
hierarchical organization of control from the point of view of the observer.
The hierarchical control model suggests that it should also be possible to
view hierarchical organization from the point of view of the actor. From the
actor's point of view, hierarchical control would be seen as a hierarchy of
changing perceptions. One way to get a look at this hierarchy is again in
terms of relative timing; in this case, however, in terms of the relative timing
of the perceptual results of control actions rather of the actions themselves.

Computation Time Window. The hierarchical control model represents the
results of control actions as unidimensional perceptual signals. A
configuration, such as the letter "h", is a possible result of control actions,
as is a sequence of letters, such as the word "hello". The model represents
these results as perceptual input signals, the intensity of a signal being
proportional to the degree to which a particular result is produced. This
concept is consistent with the physiological work of Hubel and Wiesel
(1979) who found that the firing rate of an afferent neuron is proportional to
the degree to which a particular environmental event occurs in the "receptive
field" of the neuron.

	Many of the higher level classes of perception in the control
hierarchy depend on environmental events that vary over time. Examples are
transitions, events, and sequences. The neural signals that represent these
variables must integrate several lower level perceptual signals that occur at
different times. Hubel and Weisel found evidence of a computation time
window for integrating perceptual signals. Certain cells respond maximally
to configurations (such as "lines") that move across a particular area of the
retina at a particular rate. These are "motion detector" neurons. The neuron
responds maximally to movement of a configuration that occurs within a
particular time window. Movement that occurs outside of this time window
is not included in the computation of the perceptual signal that represents
motion.

Levels by Time The hierarchical control model implies that the duration of
the computation time window increases as you go up the hierarchy. The
minimum computation time window for the perception of configurations
should be shorter than the minimum computation time window for the
perception of transitions which should be shorter than the minimum
computation time window for the perception of sequences. I have developed
a version of the psychophysical method of adjustment which makes it
possible to see at least four distinct levels of perception by varying the rate
at which items occur on a computer display. A computer program presents a
sequence of numbers at two different positions on the display. The
presentation positions are vertically adjacent and horizontally separated by 2
cm. The numbers are presented alternately to the two positions. The subject
can adjust the rate at which the numbers occur in each position by varying
the position of a mouse controller 1.

	The results of this study are shown schematically in Figure 3. At
the fastest rate of number presentation subjects report that the numbers
appear to occur in two simultaneous streams. The fact that the numbers are
presented to the two positions alternately is completely undetectable.
However, even at the fastest rate of number presentation subjects can make
out the individual numbers in each stream. At the fastest rate, there are
approximately 20 numbers per second in each stream. This means that there
is a 50 msec period available for detecting each number. This duration is
apparently sufficient for number recognition suggesting that the computation
time window for perception of configuration is less than 50 msec. Studies
of the "span of apprehension" for sets of letters suggest that the duration of
the computation time window for perception of visual configuration may be
even less less than 50 msec, possibly as short as 15 msec (Sperling, 1960).
_____________
Figure 3 Here
______________

	As the rate of number presentation slows, the alternation between
numbers in the two positions becomes apparent. Subjects report perception
of alternation or movement between numbers in the two positions when the
numbers in each stream are presented at the rate of about 7 per second. At
this rate, an alternation from a number in one stream to a number in another
occurs in 160 msec. This duration is sufficient for perception of the
alternation as a transition or movement from one position to the other
suggesting that the computation time window for transition perception is on
the order of 160 msec. This duration is compatible with estimates of the
time to experience optimal apparent motion when configurations are
alternately presented in two different positions (Kolers, 1972).

	The numbers presented in each stream are always changing.
However, subjects find it impossible to perceive the order of the numbers as
they alternate from one position to another even though it is possible to
clearly perceive the individual numbers and the fact that they are alternating
and changing across positions. The rate of number presentation must be
slowed considerably, so that each stream of numbers is presented at the rate
of about two per second, before it is possible to perceive the order in which
the numbers occur. At this rate numbers in the sequence occur at the rate of
four per second. These results suggest that the duration of computation time
window for the perception of sequence is about 0.5 seconds. This is the
time it takes for two elements of the sequence to occurQ the minimum
number that can constitute a sequence.

	The numbers in the rate adjustment study did not occur in a fixed,
repeating sequence. Rather, they were generated by a set of rulesQ a
program. The sequence of numbers was unpredictable unless the subject
could perceive the rule underlying the sequence. The rule was as follows: if
the number on the right was even then the number on the left was greater
than 5, otherwise the number on the left was less than 5. (Numbers in the
sequence were also constrained to be between 0 and 9). Subjects could not
perceive the program underlying the sequence of numbers until the speed of
the two streams of numbers was about .25 numbers per second so that the
numbers in the program occurred once every two seconds. The perception
of a program in a sequence of numbers requires considerably more time
then it takes to perceive the order of numbers in the same sequence.

	The perception of a sequence or a program seems to involve more
mental effort than the perception of a configuration or a transition. Higher
level perceptions, like programs, seem to represent subjective rather than
objective aspects of external reality; they seem more like interpretations than
representations. These higher level perceptions are typically called
"cognitions". Of course, all perceptions represent subjective aspects of
whatever is "out there"; from the point of view of the hierarchical control
model, the location of the line separating perceptual from cognitive
representations of reality is rather arbitrary.  Behavior is the control of
perceptions which range from the simple (intensities) to the complex
(programs).

Perceptual Speed Limits.The hierarchical control model says that all
perceptions of a particular type are controlled by systems at the same level in
the hierarchy. This implies that the speed limit for a particular type of
perception should be about the same for all perceptions of that type. The
160 msec computation time window for perception of transition, for
example, should apply to both visual and auditory transition. There is
evidence that supports this proposition. Miller & Heise (1950) studied the
ability to perceive an auditory transition called a "trill". A trill is the
perception of a temporal alternation from one sound sensation or
configuration to another.  The speed limit for trill perception is nearly the
same as the speed limit for visual transition perception found in the number
rate adjustment study -- about 15 per second. As in the visual case, when
the rate of alternation of the elements of the auditory trill exceeds the
computation time window the elements "break" into two simultaneous
streams of sound; the perception of transition (trill) disappears even though
the sounds continue to alternate.

	There is also evidence that the four per second speed limit for
sequence perception found in the number rate adjustment study applies
across sensory modalities. Warren, Obusek, Farmer, & Warren (1969)
studied subjects' ability to determine the order of the components sounds in
a sound sequence. They found that subjects could not perceive the order of
the components until the rate of presentation of the sequence was less than
or equal to four per second. This was a surprising result because it is well
known that people can discriminate sequences of sounds that occur at rates
much faster than four per second. In words, for example,  the duration of
the typical phoneme is 80 msec so people can discriminate sequences of
phoneme sounds that occur at the rate of about 10 phonemes per second.
But there is reason to believe that the phonemes in a word are not heard as a
sequence; that is, the order of the phonemes cannot be perceived. Warren
(1974) showed that subjects can learn to tell the difference between
sequences of unrelated sounds that occur at rates of 10 per second.
However, the subjects could not report the order of the sounds in each
sequence; only that one sound event differed from another. A word seems
to be a lower order perception -- an event perception -- which is recognized
on the basis of its overall sound pattern. There is no need to perceive the
order in which the phonemes occur; just that the temporal pattern of
phonemes (sound configurations) for one word differs from that for other
words.

The Relationship Between Behavior and Perception

	Configurations, transitions, events, sequences and programs are
potentially controllable perceptions. An actor can produce a desired
sequence of sounds, for example, by speaking sound events (phonemes) in
some order. An observer will see the production of this sequence as a
behavior of the actor.  The hierarchical control model suggests that the
actor's ability to produce this behavior turns on his or her ability to perceive
the intended result. Since perception depends on speed, it should be
impossible for the actor to produce an intended result faster than the result
can be perceived. The observer will see this speed limit as a behavioral
limit. An example of this can be seen in the arm movement experiment
described above. In that experiment it appears that the time to respond to the
signal push is a result of a behavioral speed limit; the inability to generate
 an
output faster than a certain rate. But a closer look indicates that the
neuromuscular "output" system is perfectly capable of responding to a
signal push almost immediately, as evidenced by the immediate upward
response to the downward signal push. The same muscles that produce this
immediate reaction must wait to produce the perception of the arm moving
downward. The speed limit is not in the muscles. It is in the results that the
muscles are asked to produce; a static position of the arm (a configuration
perception) or a movement of the arm in response to the signal push (a
relationship perception).

Sequence Production and Perception. Some of the most interesting things
people do involve the production of a sequence of behaviors. Some recent
studies of temporal aspects of sequence production are directly relevant to
the hierarchical control model. In one study, Rosenbaum (1989) asked
subjects to speak the first letters of the alphabet as quickly as possible.
When speed of letter production exceeded four per second the number of
errors (producing letters out of sequence) increased dramatically, indicating
a loss of control of the sequence. The speed limit for sequence production
corresponds to the speed limit for sequence perception -- four per second.

	The letter sequence study does not prove that the speed limit for
letter sequence production is caused by the speed limit for letter sequence
perception. It may be that the speed limit is imposed by characteristics of the
vocal apparatus. However, in another study Rosenbaum (1987) found the
same four per second speed limit for production of errorless finger tap
sequences. The speed limit for finger tap sequence production is likely to be
a perceptual rather than a motor limit because we know that people can
produce finger taps at rates much higher than four per second. Pianists, for
example, can do trills (alternating finger taps) at rates which are far faster
than four per second. Further evidence of the perceptual basis of the finger
tap sequence speed limit would be provided by studies of finger tap
sequence perception.  When a subject produces a sequence of finger taps he
or she is producing a sequence of perceptions of pressure at the finger tips.
A perceptual experiment where a pressure is applied to the tip of different
fingers in sequence should show the four per second speed limit. Subjects
should have difficulty identifying the order of finger tip pressures when the
sequence occurs at a rate faster than four per second.

Confounding Levels. It is not always easy to find clear-cut cases of
behavioral speed limits that correspond to equivalent perceptual speed
limits. Most behavior involves the control of many levels of perception
simultaneously. People control higher level perceptions (like sequences)
while they are controlling lower level perceptions (like transitions). This can
lead to problems when interpreting behavioral speed limits.  For example,
Rosenbaum (1983) presents some finger tapping results that seem to violate
the four per second speed limit for sequence perception. When subjects tap
with two hands they can produce a sequence of at least 8 finger taps per
second. But each tap is not necessarily a separate event in a sequence. Some
pairs of taps seem to occur at the rate at which sequences are experienced as
events. A sequence of finger taps is an event in the same sense that the
sequence of muscle tensions that produce a finger tap is an event; the order
of the components of the sequence cannot be perceived. These finger tap
events are then unitary components of the sequence of finger tap
perceptions.

	The fact that certain pairs of finger taps are produced as events
rather than ordered sequences is suggested by the errors made at each point
in the finger tap sequence. Errors occur most frequently at the point in the
sequence at which a fast pair is being initiated. Errors rarely occur for the
second element of a fast pair. This suggests that the errors occur at the
sequence level rather than the event level. The subject's attempts to produce
a keypress sequence too rapidly apparently interferes with sequence rather
than event production. Events are already produced at a fast enough rate and
an increase in the speed of sequence production has little effect on the ability
to control the component events.

Changing Perception Can Change Behavior:SGoing Up A LevelS.  The
relationship between perception and behavior can be seen when a person
learns to perform a task by controlling a new perceptual variable.  An
example of this can be seen in simple pursuit tracking tasks. In the typical
tracking task the target moves randomly. When, however, a segment of
target movement is repeated regularly the subject's tracking performance
improves markedly with respect to that segment (Pew, 1966). According to
the hierarchical control model, control is improved because the repeated
segment of target movement can be perceived as a predictable event. With
the random target the subject must wait to determine target position at each
instant in order to keep the cursor on target. With the repeated target, the
subject controls at a higher level. keeping a cursor movement event
matching a target movement event. The fact that the subject is now
controlling a higher level perception (an event rather than a configuration) is
evidenced by the longer reaction time when responding to a change in target
movement. When controlling the target-cursor configuration the subject
responds almost immediately to changes in target position. When
controlling target-cursor movement events it takes nearly 1/2 second to
respond to a change to the same change in  target movement pattern.

	An experiment by Robertson and Glines (1985) also shows
improved performance resulting from changed perception. Subjects in the
Robertson and Glines study performed a learning task where the solution to
a computerized game could be perceived at several different levels. Subjects
who were able to solve the game showed three distinct plateaus in their
performance. The level of performance, as indicated by reaction time
measurements, improved at each succeeding plateau.  Because the same
outputs (keypresses) were produced at each level of performance, each
performance plateau was taken as evidence that the subject was controlling a
different perceptual variable.

Behavior/Perception Correlations. Few psychologists would be surprised
by the main contention of this paper: that there is an intimate relationship
between perception and behavior. However, most models of behavior
assume that the nature of this relationship is causal: behavior is guided by
perception. This causal model provides no reason to expect a relationship
between the structure of perception and behavior: no more than there is to
expect a relationship between the structure of computer input and output.
This does not mean that there might not be such a relationship; it is just not
demanded by the causal model.

	The control model integrates perception and behavior with a
vengeance. Behavior is no longer an output but, rather, a perceptual input
created by the combined effects of the actor and the environment. Behavior
is perception in action. From this point of view, behavioral skills are
perceptual skills. Thus, it is not surprising to find some indication of a
correlation between behavioral and perceptual ability. For example, Keele
and his colleagues (Keele, Pokorny, Corcos and Ivry, 1985) have found
that the ability to produce regular time intervals between actions is correlated
with with ability to perceive these intervals. These correlations were fairly
low by control theory standards but they are expected if the production of
regular time intervals involves control of the perception of these intervals.

Conclusion

	This report has presented evidence that human behavior involves
control of a hierarchy of perceptual variables. There is evidence that the
behavior of non-human agents, such as chimpanzees, also involves the
control of a similar hierarchy of perceptions (Plooij and van de Rijt-Plooij,
1990). A model of hierarchical control shows how studies of perception and
behavior provide evidence about the nature of control from two different
perspectives. Perceptual studies provide information about the ability to
perceive potentially controllable consequences of actions. Behavioral studies
provide information about the ability to produce desired consequences.  The
factors that influence the ability to perceive the consequences of action
should also influence the ability to produce them. In both cases we learn
something about how agents control their own perceptions.

	The hierarchical control model shows that limitations on the
ability to produce behavior may reflect limitations on the ability to perceive
intended results. The speed at which a person can produce an errorless
sequence of events, for example, is limited by the
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