Presentation on theme: "Five Ways Sensory Content Can Be Conceptual (or Non-Conceptual) Mohan Matthen University of Toronto."— Presentation transcript:
Five Ways Sensory Content Can Be Conceptual (or Non-Conceptual) Mohan Matthen University of Toronto
Thesis Sensation is differently formatted than thought. Thought is linguistically coded; sensation is iconic and qualia-coded. Yet, like thought-content, sensory content is conceptual. A sensory state has propositional content: a Fregean concept (like a general “term”) predicated of an individual. We grasp this content in the very act of perception.
Outline 1.Show one way that sensory content is conceptual. 2.Address objections to this thesis: A.That sensation lacks logical form. B.That grasp of concepts is not a condition of sensation. C.That sensation is too “rich” to be conceptual. 3.Argue that in one way, sensation is not conceptual: its “reference” is not descriptively determined.
The First Problem Given a two- dimensional retinal display, how does the visual system construct a three-dimensional scene?
The Plurality of (Distal) Interpretations A line on the retina could be a projection of many scenes – two lines at different distances that happen to join, a flat object viewed from the side, etc. Why does the visual system reject some of these possibilities, and present this simply as a line? Cf. Hoffman Visual Intelligence 1998
The Second (Prior) Problem The retina consists of individual cells activated by the light that falls on them. These activated cells together constitute a line: but how is the multi-cell pattern registered? How does the system even know that there is a line on the retina?
The Tiger In this formation, each person knows that he is in his place,...... but only an observer who is standing across from the display can tell that together they form a picture of a tiger.
A Homunculus Similarly, only a homunculus observing this retinal display can determine that it forms a line. The information is simply not in the individual units.
II. How the Visual System Solves These Problems
a. Hierarchical Processing The visual system does indeed assign a homunculus, or monitor, to collections of cells in the retina (and other visual areas). The job of the monitor is to register the occurrence of a particular pattern in its “receptive field”.
b. Throwing Information Away The monitor registers a pattern despite detectable variations. For example, there is a type of monitor that will fire when a 60° line is present in its receptive field...... whether the line is dark against a light background or coloured against a dark background.
Digitality The information concerning specificities is “thrown away”. In linguistically encoded content, an utterance such as “There is a slanted line on the left” contains (as Dretske says) no non-nested information. In imagistically encoded content, by contrast, any slanted line has to be of some particular colour, and oriented at a particular angle. As with linguistic coding, the monitor-cell state encodes the proposition that the pattern is present, but does not contain information about colour, background, precise angle, etc.
c. Distal Processing The monitor/receptive field structure is repeated again and again. In each iteration, a monitor cell becomes a member of a receptive field for a further monitor cell. In early stages of visual processing, monitors responds to proximal (retinal) stimulation. The sequence of pattern-responses is so arranged that in later stages, neural states correspond (though with less than perfect fidelity) to distal (external) things and states of affairs: colours, shapes, movement, faces, objects, etc. (This design addresses the problem of reconstructing the distal environment.)
Characteristics of the monitor The “on”-state of the “monitor” cell: – contains less information than its receptive field – the receptive field contains an instance of the property registered by the monitor. This loss of information is not merely a blurring or loss of definition. It reflects sensitivity to a particular kind of pattern. – Can be assessed as accurate or inaccurate. In early stages of visual processing, it is so with respect to retinal or brain activation patterns. In later stages, the activation patterns to which these cells respond are surrogates for distal conditions, and accuracy must be assessed against them.
Fregean Concepts The on-state of the monitor is comparable to a Fregean concept. Each monitor cell encodes some condition. It signals that this condition holds of some target in its receptive field. It is true or false of its target according to whether the latter meets some condition.
Conceptual Content: Sense 1 Thesis: Sense features (proper sensibles) are the outcome of hierarchical monitor-cell processing. Every sensory state has Fregean concepts as constituents of its content.
Immediate question for my view: What are the subjects for Fregean concepts in sensory states? To what are these concepts attributed? Some say these questions have no proper answer.
The Generality Constraint Claim: Sensory states are not logically structured. Gareth Evans: If we hold that the subject’s understanding of Fa and Gb are structured, we are committed to the view that the subject will also be able to understand the sentences Fb and Ga. Richard Heck: Thoughts are conceptually articulated, but perceptual content is not.
Two Ideas The Generality Constraint denies logical structure in perceptual content: 1.A perception of a blue round thing is not the logical product of the perception of the thing as blue and as round. 2.No perception is decomposable into subject and predicate – a visual subject, its colour, its shape.
Binding Sensory processes are modular: the process that registers colour is separate from the one that registers form, or object identity, or faces. The seemingly integrated sensory image is the result of a process of integration known as “binding”. The apprehension of a blue, round thing is indeed a combination of these features separately registered and then conjoined. The separateness of these processes implies that one could not see something as blue and round if one were not able to see something as some other colour and round, and something (else) as blue and some other shape. Binding makes predicative structure. Above, vision attributes (predicates) blue and round of an object.
Subject, Predicate, and Iconic Coding Jerry Fodor has noted that the form of sensory presentation is iconic. Parts of an image of x are images of parts of x. In language, a complex representation breaks down into unique components. But an iconic presentation has no unique subject: – An image of a red square is equally two images of red half-squares.
Visual Objects Phenomenology contradicts Fodor. The visual field contains objects and it is hard to switch attention from one to another even when they are of the same color, but not within an object even when color changes. This fact about attention is best explained by object-feature structure
Object Organization Reflected objects overlap with objects seen through window. Cannot attend to overlapping objects simultaneously.
Appearance of Motion In the phi-phenomenon, alternate flashes of light give the appearance of one object moving. Slower alternations give the appearance of two separate objects flashing. There is no difference in terms of colours, locations, and durations of flashing. Only in interval between flashes – and this creates a difference of subject-predicate structure.
Subject-predicate structure is even more marked in the case of audition, where temporally extended sounds are subjects. (Phonemes, melodies.)
Conceptual Content: Sense 2 Sensory content displays logical componency.
Seeing Without Understanding Evans and Fred Dretske point out that it is possible to see something – a daffodil or a spotted quail – without recognizing what kind of thing it is. – Infants and animals see, but they lack recognitional concepts. – A person with less visual acuity than another may see less than a sharper sighted person; nevertheless, she may recognize what she sees while the sharper sighted person fails to do so. They take this as evidence that visual content may be non-conceptual (or analogue, as opposed to digital).
Content vs. State (Non)- Conceptualism The Evans/Dretske argument is challenged by the thesis that monitor cells in the visual system encode Fregean concepts. The visual system might nevertheless possess proprietary concepts that are present in visual content. However, Evans argues that these states are non- conceptual in the sense that we can have sensory experience without grasping the constituent concepts. This is an observation about the state, not its content.
Testing for Possession of a Sensory Concept How do psychologists test for the possession of a sensory idea? They set experimental subjects a task that depends on sensing something as an instance of that idea. With humans, this may be verbal report: “Can you discriminate a from b?”
Discrimination Not Enough Discrimination does not (by itself) imply anything about content. An iron filing may move in one direction under gravitation, in another under a simultaneous magnetic field. It discriminates, but it doesn’t possess any kind of concept of GRAVITY or MAGNETIC FIELD.
Retention Suppose, by contrast, an animal is trained (by operant conditioning) to respond differently to blue and to yellow objects. When it responds differently to such objects, it is not merely being acted upon by them. It is being acted upon in virtue of a retained trace.
Using a Concept To perform a sensory task – do X if the target is blue – a subject has to bring the target under a sensory concept. This gives us a notion of perceptual or sensory grasp of concepts – that we should be able to respond differentially to instances. Conditioning and other instinctive reactions show that we are able to respond differentially to different sensory features. That an animal can be conditioned to respond to blue demonstrates its perceptual grasp of blue. – A colour blind animal cannot be trained on blue (differentially).
Perceptual Exploration There are instinctual procedures associated with sensing different perceptual properties: – Color: Look more closely, turn object around, view in different illuminations. – Shape: move relative to object, look at it more closely – Smell: sniff and move around – Sound location: move along volume gradient – Sound identity: turn ear toward source, cup ears, (for phonemes) look at speaker’s mouth These procedures also show a form of perceptual grasp of the nature of sense features.
Knowing Proper Sensibles Putting properties such as daffodil aside, consider proper sensibles. What more is there to grasping a color or taste or smell than to experience it? Do we not know many things about this color by looking at it? Is it reddish? Bright?
Conceptual Content: Sense 3 We grasp proper sensibles, but in a way that is peculiar to sensory knowledge.
Sensation Too Rich? Richard Heck: My desk exhibits a whole host of shades of brown for which I have no names... The problem is not lack of time, but lack of descriptive resources. Gareth Evans: Do we really understand the proposal that we have as many colour concepts as there are shades of colour that we can sensibly discriminate?
Descriptive Resources First, these philosophers seem simply to be mistaken. Munsell charts and paint sample books provide descriptive resources of precisely the kind that they deny. There are also similarity descriptors: ‘that shade but more yellow’, ‘that shape but a bit rounder’.
In any case... Even if sensory experience is rich beyond description, its usable content may be conceptually articulable. – Discrimination vs recall.
Conceptual Content Sense 4 Though sensation may be rich, it does not follow that it is not conceptual.
Visual Objects I have been discussing concepts in vision. These are attributed to objects. How are the objects of vision determined? – The things which are seem to be the bearers of visual features.
Non-Descriptive Reference It’s clear that these objects are not whatever bears visual features. That is, the visual object of blue-to-the-left isn’t necessarily whatever is blue and to the left. After all, there is perceptual error. It seems as if our awareness of visual objects is independent of our awareness of the features they possess.
Theories of Visual Reference Evans: an informational link between perceiver and object that gives the perceiver a demonstrative Idea of that object – Perceiver cannot misidentify the object to which she is attributing features. (Shoemaker, Evans) Campbell: thing to which we attend Matthen: thing (x) such that we are able visually to track x, point to x, manipulate x, and move relative to x. (cf. Evans: “perceptual skills”) – On the “two visual streams” theory, these abilities are visually guided independently of feature-placing.
Visual Reference is Concept Independent On all of these theories, the object of vision is determined independently of visual features. Object processing is independent from processing for sensory features – the latter are actively bound to the former in visual awareness. Visual reference is “non-conceptual”. It is a non-visual component of visual content.
Non-conceptual content: sense 5 Sensory states contain feature content (which are concepts in the Fregean sense) attributed to objects. The sensory object is determined independently of these features.