Aristotle’s illusion and the enactive embodied situated approach to perception

1. Aristotle’s illusion and the enactive embodied situated approach to perception Elena Pasquinelli PhD Student Elena.Pasquinelli@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 • Aristotle’s illusion • Relation of the Aristotle’s illusion to motor possibilities • Experiments by Benedetti on the role of motor skills in the occurrence of the illusion • Merleau-Ponty on Aristotle’s illusion • Implicit knowledge about sensorimotor skills • O’Regan theory of sensorimotor contingencies and sensorimotor knowledge • Explanation of the Aristotle’s 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 organism’s internal cognitive processes (i.e., specifically those involving computation and representation).

6. criticisms of the representationalist-computationalist 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; O’Regan, 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. Aristotle’s illusion a case study for investigating the role of skilled actions in perception

19. The phenomenon described as Aristotle’s 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 one’s nose, thus one perceiving two noses

20. Aristotle’s illusion is one of the oldest observations about perception • the phenomenon was first described in Aristotle’s Metaphysics and On Dreaming • Successively, it was analyzed at the end of the XIX century and at the beginning of the XXth. Aristotle’s 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 Aristotle’s 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 Aristotle’s 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) : Aristotle’s 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 Aristotle’s 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 finger’s 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 Aristotle’s 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 surface’s 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 Aristotle’s 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.

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