Aristotle

1
Aristotles illusion and the enactive embodied
situated approach to perception

• Elena Pasquinelli
• PhD Student
• Elena.Pasquinelli_at_ehess.fr
• Institut Jean Nicod EHESS
• www.institutnicod.org
• EU Network of Excellence Enactive
• www.enactivenetwork.org

2

• New wave in cognitive sciences
• representationalist, computationalist,
  cognitivist view of mind (mainstream) vs
  enactive, situated, embodied view of mind
  (enactive view)
• 3 main criticisms of the enactive situated
  embodied view towards the mainstream
• No representations
• Embodied, situated, distributed processes
• Role of action and movement in perception and
  cognition
• Different claims
• Different theoretical frameworks
• Aristotles illusion
• Relation of the Aristotles illusion to motor
  possibilities
• Experiments by Benedetti on the role of motor
  skills in the occurrence of the illusion
• Merleau-Ponty on Aristotles illusion
• Implicit knowledge about sensorimotor skills
• ORegan theory of sensorimotor contingencies and
  sensorimotor knowledge
• Explanation of the Aristotles illusion in terms
  of sensorimotor knowledge

3
Enactive embodied situated approach

4

• cognitivist/
• computationalist/
• representationalist view of the mind
• Vs
• enactive/embodied/situated view of the mind

5
representationalist-computationalist mainstream

• The cognitivist/classicist research program can
  be defined as a rule-based, information-processing
  model of cognition that
• 1) characterizes problem-solving in terms of
  inputs and outputs,
• 2) assumes the existence of symbolic, encoded
  representations which enable the system to devise
  a solution by means of computation, and
• 3) maintains that cognition can be understood by
  focusing primarily on an organisms internal
  cognitive processes (i.e., specifically those
  involving computation and representation).

6
criticisms of the representationalist-computationa
list mainstream

• Cognition (knowledge and perception) is not
  (limited to) being the mirror of reality
  (representation of a pre-given world)
• criticism of symbolic processes and internal
  representations. Two possible positions are
  presented
• internal, symbolic representations are obsolete
  for explaining cognition (i.e. Brooks, 1991
  ORegan, 2001)
• internal symbolic representations are just not
  the whole story (i.e. Kirsh, 1995)

7

• Cognitive processes are not (necessarily)
  centralized, i.e. there is no gap between
  cognitive processes and their surrounds
• cognitive processes are not all in the brain ?
  study of the role of the body in cognition, of
  peripheral processes (such as the physical
  conditions of the body) in perception and action
  (i.e. Thelen, 1994 Brooks, 1991, Varela, 1991)
• cognitive processes are not all in the (one)
  subject ? study of the role of environment
  (social physical) (i.e. Hutchins, 1995)

8

• Perception and cognition cannot be considered
  outside the frame of action and movement
• the motor experience plays a significant position
  in the explanation of perceptual phenomena
• action and perception are conceived as directly
  linked as in the case of a sensory-motor loop,
  with no mediation of cognitive processes

9
two different claims within the assertion of a
key role played by action in perception

• The first claim is that action directs
  perception through the exploration of the
  environment and that perception guides action
  Lederman, 1987 Milner, 1995.
• The second claim is that motor competences and
  motor acts shape the perceptual content.

10
Action is for perception and perception is for
action

• Milner, 1995 affirms the existence of two
  perceptual systems one directed to the
  construction of representations of the world and
  the other to the guidance of action. The two
  systems would be anatomically and functionally
  separated.
• Lederman, Klatsky and colleagues (i.e. Lederman,
  1987) sustained that the hand system is an
  intelligent instrument in that it makes use of
  its motor capacities for ameliorating its
  sensitive abilities.
• Kirsh, 1995 Successful Tetris players make use
  of epistemic actions, that is they manipulate the
  pieces that are falling, changing their
  orientation to assess the fit instead of holding
  up the performance, epistemic actions seem to
  have the effect of saving time and of increasing
  the chances of success in the game. Epistemic
  actions in fact are supposed to improve cognition
  by reducing the memory and the number of steps
  involved in mental computation (space and time
  complexity) and reducing the probability of
  error.

11
perceptual content depends upon action

• Ecological perception tradition what we directly
  perceive is affordances
• Affordances are usually described as -ables, as
  a ball which is catch-able possibilities for
  action Turvey, 1981 Gibson, 1979 surfaces for
  walking, chairs for sitting, space for
  navigating, and so on. It is not the absolute
  size or shape of a ledge that determines whether
  the ledge is a stepping down or a falling off
  place it depends on the particular animal that
  is facing the ledge, including its size and style
  of locomotion.
• Theory of perception as simulated action
  Berthoz, 2002
• perceptual activity is not confined to the
  interpretation of sensory messages but
  anticipates the consequences of action, so it is
  internal simulation of action.
• Sensorimotor approach to perception O'Regan,
  2001
• perceiving is doing and the content of the
  perceptual experience is determined by the
  knowledge of sensorimotor contingencies

12
Sensorimotor contingencies

• As an exploratory activity, perception is related
  to the actions a perceiver performs and to the
  sensory consequences of his actions.
• Thus, perception is based on skills that are both
  motor and perceptual and that are called
  sensorimotor contingencies because perception is
  contingent to the exertion of motor explorations.
• Being a perceiver is an ability that consists in
  being able of keeping track of the
  interdependence of perception and action this
  ability comprises the capacity of keeping track
  of how what one does affects what one perceives.

13
Patterns of sensorimotor contingecies

• In the case of habitual movements and habitual
  perceptual conditions, the interdependence of
  perception and action takes the stable form of
  patterns of sensorimotor contingencies.
• Driving a car, for instance, is characterized,
  for the expert driver, by some stable connections
  between the actions that he performs on the wheel
  and the perceptual consequences that normally
  arise.
• In the same way, but involving patterns of
  sensorimotor contingencies that are more stable
  and general, seeing a circular surface from a
  certain point of view is related to the ability
  of keeping track of the fact that the surface
  will look more or less elliptic when changing the
  point of view.

14
Sensorimotor knowledge

• the patters of sensorimotor contingencies
  instantiate a form of understanding or knowledge,
  which is named by the authors sensorimotor or
  implicit knowledge, which is responsible for
  expectations and surprises
• This knowledge has the form of a mastery.

15
Implicit knowledge

• Implicit knowledge related to the
  motor-perceptual skills allows the subject to
  make (implicit) previsions about the perceptual
  consequences of the movements he accomplishes
• When an object as a cube is sensed only a part of
  it enters in contact with the organs of
  perception, for instance, only a face can be
  directly viewed.
• But all the faces of the cube are present in
  perception because of the knowledge about the
  perceptual consequences of the familiar action of
  making the tour of the object.
• When the body makes the tour of the object, all
  the faces of the cube are viewed one after the
  other.
• The faces are synchronously present in the
  possibility of seeing them by the same movement
  that makes them successively present and in the
  implicit knowledge of this possibility.

16
Enactive knowledge

• (Bruner, 1956) proposes the existence of 3 types
  of knowledge
• Symbolic knowledge, i.e. the one implied in
  language
• Iconic knowledge (i.e. the one implied in the use
  of iconic representations, as images)
• Enactive knowledge or knowledge by doing (i.e.
  the knowledge implied in skilled actions, such as
  riding a bycicle)

17
Praktognosie

• Merleau-Ponty (1945) describes an implicit form
  of knowledge or praktognosie
• Praktognosie is grounded on the motor and
  perceptual skills of the body
• The acquisition of new motor skills represents
  the acquisition of new knowledge about the body
  and the parts of the world that are committed
  with the bodily actions
• Praktognosie is related to concrete gestures and
  movements
• Indicating a body part, or reproducing a gesture
  without its context, are abstract gestures
  related to abstract knowledge tailoring a dress,
  driving a car, typing a letter are all concrete
  movements, related to motor habits and concrete
  knowledge
• In concrete movements the body and the objects
  and circustances that are committed with the
  bodily actions cannot be separated

18
Aristotles illusion

• a case study for investigating the role of
  skilled actions in perception

19

• The phenomenon described as Aristotles illusion
  presents the following characteristics
• if one crosses two adjacent fingers one over the
  other and then touches the two crosses fingertips
  to a small ball, one will perceive touching two
  balls.
• A variant consists in the two crossed fingers
  touching ones nose, thus one perceiving two
  noses

20

• Aristotles illusion is one of the oldest
  observations about perception
• the phenomenon was first described in Aristotles
  Metaphysics and On Dreaming
• Successively, it was analyzed at the end of the
  XIX century and at the beginning of the XXth.
  Aristotles illusion is also taken into account
  by (Merleau-Ponty, 1945)
• More recently, the phenomenon has been
  investigated by (Benedetti, 1985 Benedetti,
  1986) who has described Aristotles illusion as a
  form of somesthetic or tactile diplopia. The
  doubling of the object perceived with crossed
  fingers reminds in fact the doubling of an image

21

• The phenomenon not only interests the fingertips,
  but has also been described at the level of lips,
  tongue, face, scrotum and ears
• when the skin is displaced from its resting
  position, and a small ball is touched with the
  displaced skin, the perception of a double ball
  arises.
• A different form of the phenomenon is described
  in 1855 by Czermak as inversion of the sensation
  when the fingers are crossed
• if one touches with crossed fingers an object
  which presents a sharp point on one side and a
  convex surface on the other, then one perceives
  the sharp point in the location where the convex
  surface is and viceversa.

22

• (Tastevin, 1937) has provided an explanation for
  the occurrence of the Aristotles illusion which
  is based on the activity of the neuromuscular
  apparatus
• When the fingers are passively crossed in an
  artificial position (beyond the limit of the
  voluntary movement) and stimulated, the sensation
  of the stimulus is referred back to the limiting
  position, that is to the position they would
  achieve with voluntary muscular effort beyond
  that limit, the neuromuscular apparatus does not
  provide any further information
• Thus, the spatial location of the stimulus is
  perceived in the natural limit position

23

• (Merleau-Ponty, 1945) Aristotles illusion is a
  trouble of the body schema
• The body schema is composed of the actual and
  potential motor habits and perceptual
  possibilities of the body
• Motor habits and perceptual possibilities are
  the actions a subject is able to perform and
  normally performs, and they can be expanded by
  new acquisitions, as when one learns to dance or,
  as a blind person, to use a stick
• Crossing the fingers is an artificial movement
  which goes beyond the motor possibilities of the
  fingers.
• For this reason, the body schema is not able to
  comprise the crossed fingers as one organ
  directed to one and the same motor project or
  intention.
• Thus, the crossed fingers act separately and give
  rise to separate sensations that cannot be
  unified in one percept.

24

• Benedetti, 1985 has provided an experimental
  setting for the explanation provided by Tastevin.
• Experiment 1 shows that tactile information with
  crossed fingers is processed as if the fingers
  were not crossed and that the information is
  processed differently when the third finger is
  crossed over or underneath the fourth
• Experiment 2 is directed to test the second part
  of the hypothesis emitted by Tastevin that
  beyond certain limits the perceived location of
  tactile stimuli does not vary
• Experiment 3 shows that the Aristotles illusion
  is susceptible of disappearing following
  sensorimotor training

25
Experiment 1

• Experimental setting
• Subjects are asked to identify the position of a
  small ball.
• The position is expressed as the angle between
  the ball and a sharp point which is equally
  contacted.
• In the uncrossed condition the third finger
  contacts the sharp point the sharp point is
  placed at the center of a circle and the ball is
  placed at 0 at the right of the sharp point.
• In the crossed condition the fourth finger
  contacts the sharp point and the third finger the
  ball, which is still in the same position, even
  if the subjects are informed that the ball may
  assume different positions.
• Results
• In the uncrossed position the ball is judged to
  be at an average angle of 3 with the point with
  the third finger crossed over the fourth, the
  perceived angle increases to 96 with the third
  finger crossed under, the perceived angle
  decreases to -115.
• Both 96 and -115 values are located on the left
  of the fourth finger touching the point, even if
  in the crossed position the third finger is on
  the right of the fourth one.
• Comments
• Thus, when the fingers are crossed, tactile
  spatial information seems to be processed as if
  fingers were uncrossed (third finger on the left
  of the fourth one).

26
Experiment 2

• Experimental setting
• The apparatus is analogous to the exp. 1 but
• the 0 is on the left, while in the first
  experiment it was on the right
• the range of normal position is between 90 and
  -90
• the range with the third finger crossed over the
  fourth is between 90 and 180 for the third
  finger crossed under is between -180 and -90),
• so that the limits are 84 (180 - 96) and 65
  (180 - 115) and saturation of tactile
  information (no variations in the perceived
  position) is expected at these points.
• The fourth finger of the subjects is immobilized
  and put in contact with a sharp point and the
  third finger is again passively moved over and
  under the fourth one and contacts a small ball.
• Results
• The results seem to confirm the expected
  saturation effect tactile sensations with
  crossed fingers are perceived at 80 and -70.
• Within this functional range of action the
  tactile spatial sensation follows and reproduces
  almost exactly the effective spatial position of
  the fingers beyond the indicated values, the
  experience does not change.
• Comments
• beyond certain limits of fingers location and
  movement, the perceived location of tactile
  stimuli does not vary

27
Experiment 3

• Experimental setting
• Tests whether the individuated range of action of
  the fingers can be modified by a long-lasting
  crossing.
• The subjects crossed the third finger over the
  second and conducted a normal life with crossed
  fingers for variable periods, from 60 to 183 days
  (with short periods of rest with uncrossed
  fingers)
• some of the subjects also underwent special
  training.
• Spatial perception with crossed and uncrossed
  fingers and the perception of the position of the
  fingers were tested at intervals in the modality
  adopted for the experiments 1 and 2
• Again, since the actual position of the ball is
  at 0, an error greater than 90 indicates that
  the ball is perceived as if the fingers were
  uncrossed, while an error smaller than 90
  indicates that the ball is perceived on the
  correct side.
• Results
• A decrease of the error from 90 is observed for
  all subjects. Hence, all the subjects learned to
  perceive the ball on the correct side with the
  second and third finger. A test performed over
  the non-trained third and fourth finger always
  elicited perception as if the fingers were
  uncrossed.
• Comments
• The results indicate that Aristotles illusion
  disappears after a period of training with
  crossed fingers.
• Even when perception with the crossed fingers
  became correct, perception with uncrossed fingers
  still remained correct too ? no adaptation has
  occurred, but an extension of the range of action
  of the fingers, which now includes the crossed
  position.
• The observed perceptual modifications (extension
  of the range within which perception varies
  following the variations of the stimuli) are
  accompanied by corresponding motor modifications.
  The percentage of correct movements ( the number
  of times a stimulus is rejoined correctly)
  greatly improve in correspondence with the
  dropping of perceptual errors. Thus motor and
  perceptual performances show a good
  correspondence.

28

• The experiments by Benedetti show that
• What mediates the perception of the object with
  crossed fingers is something related to the
  possible movement of the fingers
• (but not the representation of the position of
  the fingers, which is not altered by the fact of
  crossing the subject of the illusion describes
  his fingers as crossed).
• The configurations with uncrossed or crossed
  fingers include intertwined motor and perceptual
  components.

29

• We can consider the two configurations with
  crossed and uncrossed fingers as different
  sensorimotor configurations and the perceptual
  and motor abilities that are connected to the
  configurations as sensorimotor skills.
• A skilled perceiver with uncrossed fingers
  becomes an unskilled perceiver with crossed
  fingers because he lacks the proper skills
• The unskilled perceiver lacks the capacity of
  synthesizing the partial percepts in one
  perceptual unit
• Becoming a skilled perceiver with crossed fingers
  enlarges the capacity of synthesis

30

• Deviations from the laws of sensorimotor
  contingency extracted by the brain can cause
  modifications in the resulting percept or
  illusions
• Nevertheless, our brains have extracted such
  laws, and any deviation from the laws will cause
  the percept of the surfaces shape to be
  modified. Thus, for example, our brains register
  the fact that the laws associated with normal
  seeing are not being obeyed when, for example, we
  put on a new pair of glasses with a different
  prescription for a while, distortions are seen
  when the head moves (because eye movements
  provoke displacements of unusual amplitudes) or
  when we look into a fish tank (now moving the
  head produces unusual kinds of distortions), or
  dream or hallucinate (now blinking, for instance,
  has no effect). Our impression in such cases is
  that, then, something unusual is happening.
  O'Regan, 2001, pp. 944-945

31

• Illusory phenomena as the Aristotles illusion
  might be ascribed to some form of deviation from
  the laws of sensorimotor contingency, that is
  from the habitual sensorimotor skills
• inconsistency between expectations based on
  sensorimotor knowledge and actually gained
  sensorimotor information.

32

• Berthoz, A. (2002). The brain's sense of
  movement. Harvard University Press.
• Brooks, R. A. (1991). Intelligence Without
  Representation. Artificial Intelligence
  Journal(47), 139-159.
• Bruner, J., Goodnow, J., Austin, A. (1956). A
  Study of Thinking. New York Wiley.
• Clark, A. (1997). Being there. Cambridge, MA The
  MIT Press.
• Hutchins, E. (1995). Cognition in the Wild.
  Cambridge, MA MIT Press.
• Kirsh, D., Maglio, P. (1995). On Distinguishing
  Epistemic from Pragmatic
• Actions. Cognitive Science, 18, 513-549.
• Lederman, S. J., Klatzky, R. L. (1987). Hand
  movements A window into haptic object
  recognition. Cognitive Psychology, 19(3),
  342-368.
• Merleau-Ponty, M. (1945). Phénoménologie de la
  perception. Paris Gallimard.
• Milner, A. D., Goodale, M. A. (1995). The
  Visual Brain in Action. Oxford Oxford Univ.
• Press.
• O'Regan, K. J., Noë, A. (2001). A sensorimotor
  account of vision and visual consciousness.
  Behavioral and Brain Sciences, 24(5), 939-1011.
• Thelen, E., Smith, L. B. (1994). A Dynamic
  Systems Approach to the Development of Cognition
  and Action. Cambridge, MA MIT Press.
• Varela, F., Thompson, E., Rosch, E. (1991). The
  Embodied Mind. Cambridge, MA MIT Press.
• Gibson, J. J. (1979). The ecological approach to
  visual perception. Houghton Mifflin Co.
• Turvey, M. (1981). Ecological Laws of Perceiving
  and Acting In Reply to Fodor and Pylyshyn.
  Cognition, 9, 237-304.
• Viviani, P. (1990). Motor-perceptual
  interactions the evolution of an idea. In M.
  Piattelli Palmarini (Ed.), Cognitive Sciences in
  Europe Issues and trends (pp. 11-39) Golem.

33

• Bendetti, F. (1991). Perceptual learning
  following a long-lasting tactile reversal.
  Journal of experimental psychology Human
  perception performance, 17(1), 267-277.
• Benedetti, F. (1985). Processing of tactile
  spatial information with crossed fingers. Journal
  of Experimental Psychology Human Perception and
  Performance, 11(4), 517-525.
• Benedetti, F. (1985). Tactile diplopia
  (diplesthesia) on the human fingers. Perception
  Psychophysics, 15(83-91).
• Benedetti, F. (1988). Exploration of a rod with
  crossed fingers. Perception Psychophysics, 44,
  281-284.
• Benedetti, F. (1988). Localization of tactile
  stimuli and body parts in space two dissociated
  perceptual experiences revealed by a lack of
  constancy in the presence of position sense and
  motor activity. Journal of Experimental
  Psychology Human Perception and Performance,
  14(1), 69-76.
• Benedetti, F. (1990). Goal directed motor
  behavior and its adaptation following reversed
  tactile perception in man. Experimental brain
  research, 81, 70-76.