What do experiments on mental imagery tell us about consciousness?

• Rediscovery of mental imagery in the 1950s marked the return of cognitive concepts within a behaviorist context.

• The term mental image has been universally assumed to mean a conscious mental state, similar to a perceptual state. Thus it provides a way to examine the cortical embodiment of one of the most frequently studied conscious states.

Some empirical properties of mental images, together with assumptions about its connection with perception, has lead many people to search for a specific pictorial objects in the brain.

NB The question whether there are (or can be) unconscious mental images has, to my knowledge, never been raised. This is an interesting idea which runs counter to everyone’s assumption about images (and therefore worth exploring).

One of the strongest cases for the causal role of consciousness comes from the study of reasoning with mental images

● The ‘psychological reality’ of mental images is unquestioned because many experiments have shown that manipulating imagery instructions results in a large and reliable effect on behavior.

● For example, there are many demonstrations that in order to recall something you must first recall an image of something else, and then examine that image for the answer: On what side of your front door is the handle on? How many

windows are there in your kitchen? What is 6 feet behind you? What is in your pocket? Did any US president have a beard (or glasses)?

Imagine a cube on its corner and point and count its corners. What do you ‘see’ if you rotate a ‘D’ by 90° and put it on a ‘J’

DJ

Among the early experiments suggesting the causal role of consciousness comes from the use of mental images in learning and memory

● A good mnemonic for recalling a list of items is to combine an image of each item on the list with a place on the image of a familiar path (street, sidewalk...). Then imagine walking along the path and leaving items from your list at familiar places. To recall the list you reverse this walk and notice the items. E.g., items might be a shopping list, such as bread, milk, eggs, …

Then imagine walking along a path from the store to this room, dropping off the items on the list: the bread goes at the corner, the milk goes under the tree, the eggs go by the light, etc..

To recall the list imagine walking back along that path while looking for any objects you recognize as being on the list. You might see the eggs, then the milk, then the bread.This “Method of loci” is used by actors for obvious reasons.

● In order to remember pairs of words, do this: Imagine the objects denoted by each of the word pairs interacting in some way – the more bizarre the better. Imagine the pairs and remember the image of each pair. When its time to recall you will be given one of the pair. Then you must find the image that contains that object and see what other object is with it.

One of the strongest cases for the causal role of consciousness comes from the

study of reasoning using mental images● In the 1970’s most research on mental imagery studied the effect of imagery

(or “imigability rating of words”) on learning and memory. This research brought the idea of mental imagery back into mainstream psychology, but the next big thing in imagery research was to ask subjects to do things with their image – to derive conclusions by examining their image. This era was most visibly occupied by Steven Kosslyn (with whom I have debated often – see my paper “The Imagery Debate: …” in your reading list).

● Research in this period found more and more ways in which imagining something was like seeing a picture of that thing. It was a case study in the Stimulus Error or the Intentional Fallacy. Before describing some of the research and the way conclusions were drawn from them I will reiterate why this has something to do with the course theme: Consciousness, and will also give you a demonstration of the Intentional Fallacy at work.

On the difference between explanations that appeal to mental architecture and those that appeal to tacit knowledge

This difference is closely related to the intentional fallacy and so deserves a special aside.

Methodological aside:

Aside on the parable of the mystery box

● A Cognitive Scientist, out walking in a field, comes upon a black box which happens to have a meter and recorder that records the meter’s changes over time.

● The Cognitive Scientist examines lots of records generated by the box and finds the pattern to be quite systematic. It follows the following regular pattern:

An illustrative example: Mystery Code Box

What does this behavior pattern tell us about the nature of the box?

An illustrative example: Mystery Code Box

What does this behavior pattern tell us about the nature of the box?

Careful study revealed that pattern #2 only occurs in this special context when it is preceded by pattern A

The punch line:● The black box is transmitting International Morse Code

– in this case English messages in IMC.

● The Morse code for e is ▪, for i is ▪ ▪ , for c is ▬ ▪ ▬ ▪

● There is a spelling ‘rule’ in English; Roughly it’s i (▪ ▪)

before e (▪) except after c (▬ ▪ ▬ ▪).

● The pattern that was observed is due entirely to this rule of English spelling applied to Morse code.

● Because this box can presumably transmit any pattern of dots and dashes, the regularity will not be found in the way it is wired, but in what it (correctly) represents.

The Moral: Regularities in behavior may be due to either:

1. The inherent nature of the system (to its structure), or its Architecture

2. The nature of what the system represents (what it “knows”) or its Representations

Given this regularity, are we now in a position to figure out how the box works?

● Does the regularity itself place constraints on potential structural-functional properties of the black box?

● Will it help in inferring how the box works?

In general the behavioral repertoire does not determine the structure of the box

● That’s because the particular behavior of the box in the example is not constrained by its structure, but by its relation to its environment, and its function as described at a particular level– in an intentional vocabulary.

● To find out what vocabulary is the correct one a scientist must study the behavior of the box in special test situations (not in “ecologically valid” ones). Only rarely will the vocabulary be obvious, which is why science is hard.

Note the parallel with regularities attributed to the nature of mental images. In most cases it is attributable to what the subject knows about the imagined situation.

Before turning to the puzzle of conscious thoughts, here is a short detour to the intuitive

idea that we think in words or pictures● Recall the seductive idea behind the dual code theory of the mental.

We experience our conscious thoughts as either sensory or verbal (spoken)What else could they be? What would it be like to experience something consciously that we could not in principal have perceived?

How about pain (headache), dizziness, elation, fear, happiness? Are these basic, learned or inferred experiences? NB James-Lange theory of emotions.

● Consider first the intuitive idea that we think in our native language (e.g., English). This idea is so natural that most people do not even consider that it might need support!

● I claim the problem with either option in the dual code view is this: Neither words nor pictures have the right variable grain or specificity to represent the content of thought.

Inner speech is not thinking!

As I sit here, writing some text to go with the heading I just typed, I am aware of imagining saying (“thinking”) to myself:“I’d better hurry and finish this section or I will be late for my meeting.”

In “saying” that sentence to myself in my inner voice, I meant something more than what appears in the sequence of words. I knew which particular text I meant when I thought “this section”; I knew how much time would have to pass (roughly minutes rather than hours or days) in order for it to count as my being “late” for a meeting; I knew which meeting I had in mind even though I only thought “my meeting”; and I knew what counts as “hurrying” when typing a section of text, as opposed to running a race.

And for that matter I knew what “I” referred to, although the sentence did not specify who that was (“I” refers to different people on different occasions).

Imagined speaking is not thinking!

What is going on in my mind when I imagine speaking, is the same sort of thing that goes on when I am actually speaking to someone (or to myself, as I sometimes do). It involves deciding how best to communicate some idea to another person by uttering a sequence of words, and then using the resources of the grammar of my language, as well as principles of conversation, to construct a sentence that conveys that meaning when conjoined with my other beliefs, including what I believe my hearer already knows (or is in a position to infer in that context). The sentence I decide to speak or imagine speaking is the end product of such a thought process, it is not the thought.

Neither inner nor outer speech expresses all the thoughts behind them

Sentences alone never express all and only what their speakers mean or think. Because what we experience when we seem to be “thinking in words” is an imaginary dialogue, the sentences of this imagined dialogue follow rules of “discourse” such as those referred to as Gricean Maxims. These include principles of cooperation such as “make your statements as informative as required but not more informative than necessary” (i.e., don’t express what your hearer already knows). They include such principles as Truth (don’t say what you know to be false), Informativeness (only say what your hearer does not know), Relevance and Clarity (e.g., avoid ambiguity, vagueness, redundancy). Simple as these maxims are, they apply to all human dialogues, including imagined ones.

What we just saw is a case where much of the regularity does not reflect the nature of thoughts, but the constraints on discourse

● Like the case of the long-short dashes in the code-box example, much of the pattern is not caused by the nature of the intentional representations, but of the rules of discourse. The person determines the content by virtue of his thoughts but the rest of the regularities are determined by the constraints on discourse.

● The person controls the content of thoughts, just the way he does in a conversation, but this content is given prior to the sentences being formed.

Preview of what is to come…● Most, if not all the work on mental imagery in the past

40 or so years has been fueled by phenomenology and by the metaphor of mental space and mental pictures, which in turn has been used to explain empirical findings the way one might be tempted to explain the behavior of the black box – by looking for things inside instead of things outside the mind.

● In the case of mental imagery, much of the work has appealed to relevant spatial properties, but has done so by assuming that these properties are replicated inside the head!

Some writers have suggested that self-consciousness arises from the ability to distinguishing self from other on the basis of location.

So being conscious of oneself is being able to situate oneself apart from others in space.

If there is anything to this view of consciousness, the work on imagery could help place it in context since empirical findings concerning mental imagery have been essentially about how we mentally represent space.

Space and self-consciousness?Speculative aside concerning the role of space

What constraints does imagery impose on representations?

● Recalling the code-box example we might ask whether the regularities are due to the nature of our cognitive architecture or to what you we want or believe?

● As with the code-box example we should ask what constraints are imposed by the mental architecture. Can your image have any properties you choose? If not, ask; Why not? of examples; Can you imagine an object viewed from all directions at once, or from no

particular direction? Can you imagine a 4-dimensional object? Can you imagine a written character that is neither upper nor lower case?

Or a figure that does not have a particular size or shape (e.g. Berkeley asked: can you imagine a triangle that is neither equilateral nor isosceles, nor scalene, …etc)?

Can you imagine a 3x3 array of numbers and read them back in any order?

What constraints does imagery impose on representations?

Images are better at representing spatial layouts than temporal patterns

L M Q

G F S

E Y T

More on Consciousness of space and arguments from neuroscience

● The intuition that images are spatial (or, as some put it, that they “have space”) is deeper than most other questions about images. I have discussed this in mind-numbing detail in “Things and Places” (Chapter 4).

● According to Pictorialists (like Kosslyn), the argument over imagery is now in its third and final stage, where evidence from neuroscience has essentially put an end to the debate. I will look at some of this alleged debate-ending evidence and will show that it is characterized by the pervasive acceptance of the intentional fallacy.

One of the earliest and most-cited studies that have been interpreted as showing that images are laid out in space: Mental Scanning – a ‘window on the mind’

• The experiments seem to show that when you move your attention across a mental image, it takes longer (in real time) to move it a greater (imagined) distance – i.e. time & distance on the image appears to follow the same laws as it does in the real world – i.e. time increases linearly with distance when speed is constant.

Mental Scanning (“Window on the Mind”)

• Kosslyn (and many hundreds of researchers and students) showed that if you ask subjects to move their attention from one place on an imagined map, it takes longer to do so when the distance represented is greater.

• This series of studies was judged by the journal editor as an example of important new findings in psychology. It has become a classic.

• You might keep watch for possible cases of the intentional fallacy or the stimulus error!

Studies of mental scanningDoes it show that images have metrical space?

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(Pylyshyn & Bannon. Described in Pylyshyn, 1981)

Conclusion: The image scanning effect is Cognitively Penetrable i.e., it depends on Tacit Knowledge.

Does visual imagery use the visual system?• It depends on what you mean by use and visual system

To use vision can mean to visually perceive the image – a non-starter Only early vision is relevant to this use of “perceive”, since general

vision can involve all of cognition. This point requires a whole lecture! This question is of interest to picture theorists because if vision is

involved it would suggest that images are uninterpreted picture-like spatial displays. The visual module cannot be applied to already-interpreted data structures – we don’t see symbolic descriptions.

• Let’s assume that “the visual cortex” is “active” during mental imagery as some fMRI studies have suggested, What follows from that? Does it tell us what the image itself must be like?

• Why should we believe that vision is involved? In the last 15 years the main support for the assumption that the visual

system is involved has come from neuroscience.

Reasons for thinking that images are interpreted by the visual system

• Similar phenomenology of imagining & seeing This reason actually overshadows all others

• Re-perceiving and novel construals A large but very problematic literature

• Superposition & interference studies• Visual illusions with projected images

The ubiquitous role of attention

Reasons for thinking that images are interpreted by the visual system

• Similar phenomenology of imagining & seeing This phenomenology is what leads to the intentional

fallacy as shown in the next cartoons from Kliban

This is what our conscious experience suggests goes on in vision…

Kliban

This is what the demands of explanation suggests must be going on in vision…

Conceptual representation – not a picture or icon

More demonstrations of the relation between vision and imagery

• Images constructed from descriptions The two-parallelogram example

• “Seeing” mental images lacks the critical signature properties of vision Involuntary properties of vision such as amodal

completion, automatic 3D & apparent motion, different off-retina analysis, sensitivity to hints, …

• Reconstruals: Slezak

Do this imagery exercise:Imagine a parallelogram like this one

Now imagine an identical parallelogram directly below this one

Connect each corner of the top parallelogram with the corresponding corner of the bottom parallelogram:

What do you see?

What do you see when you imagine the connections?Did the imagined shape look (and change) like the one you see now?

Viewing Mental Images lacks signature properties of vision

• No ‘Amodal Completion’ of partly-occluded objects.• Off-retina figures do not combine.• Superposition not as common as thought – does not

occur in general (so assumed independent motivation for an internal screen not supported).

• Most psychophysical phenomena do not occur in viewing mental images (notwithstanding some bad published studies)

“Amodal completion” in images?

Is this what you saw?

Off-retinal information is different from foveal info

Off-retinal information is different from retinal info(which itself suggests that all mental information is different from visual inputs)

Standard view of saccadic integration by superposition

Is it plausible? It is one of the arguments given in support of the view that mental imagery is like vision except it enters higher up in the ‘visual pathway’.

Superposition does not work (O’regan 1983)

More questions about the relation between vision and imagery

• Conceptual information is never iconic or graphic, as picture theorists must assume.

• Images constructed from descriptions The D-J example(s) The two-parallelogram example

• Amodal completion• Reconstruals: Slezak

Labels propagate over picture

Visual-Motor adaptation and image-motor adaptation

● The basic prism adaptation setup: arm movement towards a target while wearing prism glasses

● Now repeat with arm unseen but subject told where it is (actually where it would have been in the prism case)

● Get adaptation {Finke, R. A. (1979). The Functional Equivalence of Mental Images and Errors of Movement. Cognitive Psychology, 11, 235-264.}

● But in the original experiment it has been shown that you don’t need to see a hand, any indicator of where the hand is will do as long as the subject believes his hand is where indicated: Being your hand is irrelevant.

Can images be visually reinterpreted?• There have been many claims that people can visually

reinterpret images These have all been cases where one could easily figure out

what the combined image would look like without actually seeing it (e.g., the J – D superposition). (This example was mentioned earlier)

• Peterson’s careful examination of visual “reconstruals” showed (contrary to her own conclusion) that images are never bistable (no Necker cube or figure-ground reversals) and when new construals were achieved from images they were quite different from the ones achieved in vision (more variable, more guessing from cues, etc).

• The best evidence comes from a philosopher (Slezak, 1992, 1995)

Slezak figures

Pick one (or two) of these animals and memorize what they look like. Now rotate it in your mind by 90 degrees clockwise and see what it looks like.

Slezak figures rotated 90o

What do parallels between seeing and imaging show?

Phenomenology is ambiguous between: 1. Showing that imagery uses vision to examine

an internal picture, or2. Showing that vision does not involve an

internal picture either!There is little doubt that (2) is the correct option. Why do we need a second (internal) image when we have the original to look at!

As Nelson Goodman said, ‘One of the damn things is enough’!

Neuroscience: The picture-theory’s last hope

Are there pictures in the brain?

There is no evidence of cortical displays of the right kind to explain imagery phenomena.

Here is what there is that gives hope to picture-theorists:

Neuroscience has shown that the retinal pattern of activation is displayed on the surface of the cortex

Tootell, R. B., Silverman, M. S., Switkes, E., & de Valois, R. L. (1982). Deoxyglucose analysis of retinotopic organization in primate striate cortex. Science, 218, 902-904.

There is a topographical projection of retinal activity on the visual cortex of the cat and monkey.

Problems with drawing conclusions about the nature of mental images from neuroscience data

1. The capacity for imagery and for vision are known to be independent. Also all imagery results are observed in the blind.

2. Cortical topography is 2-D, but mental images are 3-D – all phenomena (e.g. rotation) occur in depth as well as in the plane.

3. Patterns in the visual cortex are in retinal coordinates whereas images are in world-coordinates Your image stays fixed in the room when you move your eyes or turn your

head or even walk around the room

4. Accessing information from an image is very different from accessing it from the perceived world. Order of access from images is highly constrained. Conceptual rather than graphical properties are relevant to image

complexity (e.g., mental rotation).

Problems with drawing conclusions about mental images from the neuroscience evidence

5. Retinal and cortical images are subject to Emmert’s Law, whereas mental images are not;

6. The signature properties of vision (e.g. spontaneous 3D interpretation, automatic reversals, apparent motion, motion aftereffects, and many other phenomena) are absent in images;

7. A cortical display account of most imagery findings is incompatible with the cognitive penetrability of mental imagery phenomena, such as scanning and image size effects;

8. The fact that the Mind’s Eye is so much like a real eye (e.g., oblique effect, resolution fall-off) should serve to warn us that we may be studying what observers know about how the world looks to them, rather than what form their images take.

Problems with drawing conclusions about mental images from the neuroscience evidence

9. Many clinical cases can be explained by appeal to tacit knowledge and attention The ‘tunnel effect’ found in vision and imagery (Farah) is likely due to

the patient knowing what things now looked like to her post-surgery Hemispatial neglect seems to be a deficit in attention, which also

explains the “representational neglect” in imagery reported by Bisiach. A recent study shows that imaginal neglect does not appear if patients

have their eyes closed. This fits well in the account I have offered in which the spatial character of a mental images derives from concurrently perceived space.

10. What if colored three-dimensional images were found in visual cortex? What would that tell you about the role of mental images in reasoning? Would this require a homunculus?

This is MORE than enough for now!

So why does it not feel like we are doing computations?

The content of our conscious experience is a very poor guide to what is actually going on that causes both our experiences and our behavior. Science is concerned with causes, not just correlations.

We have learned (since Galileo) that we can’t assume that the way things seem has much to do with how it works (consider the example of language understanding) As in most sciences, the essential causes are far from obvious

(e.g., How can the moon exert a pull on the earth without contacting it? What is this table made of? etc.).

In the case of cognition, what is going on is a delicate mixture of the obvious (what Granny or Shakespeare knew about people, and why they do what they do) and the incredible.

Is there very short-lasting iconic storage?

● Although the idea of pictorial long-term memory has been known to be false ever since Sir Fredrick Bartlett’s book on memory (and Hebb’s work on neural basis of memory), there is some provisional evidence that sensory information may outlast the duration of the stimulus. Many people have studied these “sensory buffers” including George Sperling and Michael Posner. But the story remains murky even there. Visual information loses its spatiality very soon after the retina.

Sperling’s partial report method for showing an iconic memory

Mental Scanning

● Some hundreds of experiments have now been done demonstrating that it takes longer to scan attention between places that are further apart in the imagined scene. In fact the relation is linear between time and distance.

● These have been reviewed and described in: Denis, M., & Kosslyn, S. M. (1999). Scanning visual mental

images: A window on the mind. Cahiers de Psychologie Cognitive / Current Psychology of Cognition, 18(4), 409-465.

Rarely cited are experiments by Pylyshyn & Bannon which I will summarize for you.

Studies of mental scanningDoes it show that images have metrical space?

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(Pylyshyn & Bannon. Described in Pylyshyn, 1981)

Conclusion: The image scanning effect is Cognitively Penetrable i.e., it depends on Tacit Knowledge.

What is assumed in imagist explanations of mental scanning?

● In actual vision, it takes longer to scan a longer distance because real distance, real motion, and real time is involved, therefore this equation holds due to natural law:

Time = distance

speed

But what ensures that a corresponding relation holds in an image?

The obvious answer is: Because the image is laid out in space!

· But what if that option is closed for empirical reasons?● Imagists appeal to a “Functional Space” which they liken to a

matrix data structure in which some cells are adjacent to other cells, some are closer and others further away, and to move from one to another it is natural that you pass through intermediate cells

● Question: What makes these sorts of properties “natural” in a matrix data structure?

Thou shalt not cheat● There is no natural law that requires the representations of

time, distance and speed to be related according to the motion equation. You could equally easily imagine an object moving instantly or according to any motion relation you like, since it is your image!

● There are two possible answers why the relation

Time = Representation of distance

Representation of speed

typically holds in an image-scanning task:

1. Because subjects have tacit knowledge that this is what would happen if they viewed a real display, or

2. Because the matrix is taken to be a simulation of a real-world display, as it often is in computer science, we are tempted to think of the 2D display, whose presence is only heuristic: There is no 2D surface anywhere!!

Mental Rotation has been one of the most cited demonstrations of all

● Look at the following 3D figures and judge which pairs are the same except for orientation. The other pair are enantiomorphs – 3D mirror images so they can’t be put into correspondence by 3D rotation only.

Mental rotation

Time to judge whether (a)-(b) or (b)-(c) are the same except for orientation increases linearly with the angle between them (Shepard & Metzler, 1971)

What do you do to judge whether these two figures are the same shape?

When you make it rotate in your mind, does it seem to retain its rigid 3D shape without re-computing it?

Is this how the process looked to you?

Thou shalt not cheat● What happens in ALL imagist accounts of

phenomena from mental scanning to mental rotation is that they assume the properties of real space in order to provide a principled explanation, then retreat to something not-quite-real space when it is pointed out that they are assuming that images are laid out in real space-in-the-head.

● This happens with mental rotation as well, even though the tacit knowledge account is not plausible there (it is an involuntary and universal way of solving the rotated-figure task so long as the task involves tokens of enantiomorphs).

The missing bit of logic:

● According to Prinz (2002) p 118,“If visual-image rotation uses a spatial medium of the kind Kosslyn envisions, then images must traverse intermediate positions when they rotate from one position to another. The propositional system can be designed represent intermediate positions during rotation, but that is not obligatory.”

● Given that this happens in 3D so that it can’t be a literal brain space, the question arises: What makes this obligatory in “functional Space”?

Sources of obligatory constraint● It could be that there is a medium or a set of analog

properties that together happen to simulate a virtual space, and the physical properties of this medium enforce the continuity of motion through it. This is very unlikely.

● It could be that the constraint comes from the fact that it holds in the world. Then its transfer from the real to the mental world occurs either ; Voluntarily, because we know how it would happen and we can

use that fact to solve the problem Naturally, because the constraint got built in over time through

evolutionary pressures Naturally, but not because the constraint is built in, but because

of other properties of the architecture that make it more efficient to compute the rotated shape incrementally until there is a match

Do images have low-level psychophysical properties?

● Bring the bars closer and closer together. In which can you see the bars when the spacing is closest?

● In experiments, it was shown that the oblique effect occurs in mental images just as it does in vision Kosslyn, Thompson & Ganis (2006) argued that this is

because there are more vertical and horizontally tuned cells than obliquely tuned cells in visual cortex. Does this explain the finding?

Do images have low-level visual properties?● Imagine a grating in which the bars are:

1. Vertical2. Horizontal3. Oblique (45°)

● Which of these (identical) gratings can continue to be discriminated as the figure becomes smaller?

A final point…● In Kosslyn, Thompson & Ganis (2007) the authors cite

Ned Block to the effect that one does not need an actual 2D surface, so long as the connections upstream from the cortical surface can decode certain pairs of neurons in terms of their imagined distance. Imagine long stretchy axons going from a 2D surface to subsequent processes. Now imagine that the neurons are randomly moved around so they are no long on a 2D layout. As long as the connections remain fixed it will still behave as though there was a 2D surface.

● Call this the “encrypted 2D layout” version of literal space.

The encrypted-spatial layout alternative● By itself the encrypted-layout alternative will not do because

without referring to the original 2D locations, the relation between pairs of neurons and scan time is not principled. In the end the only principle we have is Time=distance/speed so unless the upstream system decrypts the neuron locations into their original 2D surface locations the explanation for the increase in time with increased imagined distance remains a mere stipulation. It stipulates, but does not explain why, when two points are further away in the imagined layout it takes longer to scan between them or why scanning between them requires that one visit intermediate locations along the way.

● But this is what we needed to explain! One can apply such a mere stipulation to any form of representation. What was a principled explanation with the literal 2D display has now been given up for a mere statement of how it shall be.

The ‘Imagery Debate’ Redux

● According to Kosslyn there have been 3 stages in the debate over the nature of mental images:1. The role of images in learning and memory (Paivio’s

Dual Code theory). Influential at the time but now abandoned except for a few recidivists like Barsalou.

2. Spatial properties of images and their role in dynamic processes, as assessed by reaction time measures (Kosslyn’s research on ‘metric properties of images’)

3. Discovery of brain mechanisms underlying visual imagining, which led to ‘the resolution of the imagery debate’.

Mental imagery and neuroscience● Neuroanatomical evidence for a retinotopic display in

the earliest visual area of the brain (V1)● Neural imaging data showing V1 is more active during

mental imagery than during other forms of thought The form of activity differs for small vs large images in the

way that it differs when viewing small and large displays● Transcranial magnetic stimulation of visual areas

interferes more with imagery than other forms of thought● Clinical cases show that visual and image impairment

tend to be similar (Bisiach, Farah)● More recently psychophysical measures of images shows

parallels with comparable measures of vision, and these can be related to the receptive cells in V1

Neuroscience has shown that the retinal pattern of activation is displayed on the surface of the cortex

Tootell, R. B., Silverman, M. S., Switkes, E., & de Valois, R. L. (1982). Deoxyglucose analysis of retinotopic organization in primate striate cortex. Science, 218, 902-904.

There is a topographical projection of retinal activity on the visual cortex of the cat and monkey.

Problems with drawing conclusions about the nature of mental images from neuroscience data

1. The capacity for imagery and for vision are known to be independent. Also all imagery results are observed in the blind.

2. Cortical topography is 2-D, but mental images are 3-D – all phenomena (e.g. rotation) occur in depth as well as in the plane.

3. Patterns in the visual cortex are in retinal coordinates whereas images are in world-coordinates Your image stays fixed in the room when you move your eyes or turn

your head or even walk around the room

4. Accessing information from an image is very different from accessing it from the perceived world. Order of access from images is highly constrained. Conceptual rather than graphical properties are relevant to image

complexity (e.g., mental rotation).

Problems with drawing conclusions about mental images from the neuroscience evidence

5. Retinal and cortical images are subject to Emmert’s Law, whereas mental images are not;

6. The signature properties of vision (e.g. spontaneous 3D interpretation, automatic reversals, apparent motion, motion aftereffects, and many other phenomena) are absent in images;

7. A cortical display account of most imagery findings is incompatible with the cognitive penetrability of mental imagery phenomena, such as scanning and image size effects;

8. The fact that the Mind’s Eye is so much like a real eye (e.g., oblique effect, resolution fall-off) should serve to warn us that we may be studying what observers know about how the world looks to them, rather than what form their images take.

Problems with drawing conclusions about mental images from the neuroscience evidence

9. Many clinical cases can be explained by appeal to tacit knowledge and attention The ‘tunnel effect’ found in vision and imagery (Farah) is likely due to

the patient knowing what things now looked like to her post-surgery Hemispatial neglect seems to be a deficit in attention, which also

explains the “representational neglect” in imagery reported by Bisiach A recent study shows that imaginal neglect does not appear if patients

have their eyes closed. This fits well in the account I will offer in which the spatial character of a mental images derives from concurrently perceived space.

10. What if colored three-dimensional images were found in visual cortex? What would that tell you about the role of mental images in reasoning? Would this require a homunculus?

This is MORE than enough for now!

Should we welcome back the homunculus?

● In the limit if the visual cortex contained the contents of ones conscious experience in imagery we would need an interpreter to “see” this display in visual cortex

● But we will never have to face this prospect because many experiments (including ones by Kosslyn) show that the contents of mental images are conceptual (or, as Kosslyn puts it, contain “predigested information”).

● And finally, it is clear to anyone who thinks about it for a few seconds that you can make your image do whatever you want and to have whatever properties you wish. There are no known constraints on mental images that cannot be attributed

to lack of knowledge of the imagined situation (e.g., imagining a 4D cube). All currently claimed properties of mental images are cognitively

penetrable.

Explaining mental scanning, mental rotation and image size effects in terms of “functional space”

● When people are faced with the natural conclusion that the “iconic” position entails space (as in scanning and size effects) they appeal to “functional space”

● A Matrix in a computer are often cited as an example● Consider a functional space account of scanning or of

mental rotation: Why does it take longer to scan a greater distance in a

functional space? Why does it take longer to rotate a mental image a greater

angle?

But there are examples of solving geometry problems easily with imagery

• There are many problems that you can solve much more easily when you imagine a layout than when you do not.

• In fact many instances of solving problems by imagining a layout that seem very similar to how would solve them if one had pencil-and-paper.

• The question of how pictures, graphs, diagrams, etc help in reasoning is very closely related to the question of how imagined layouts function in reasoning. That is not in question. What is in question is what happens in either the visual or imagined cases and how images can benefit from this processes even though there is no real diagram.

How do real visual displays help thinking? Why do diagrams, graphs, charts, maps, icons and other visual

objects help us to reason and to solve problems? The question why visual aids help is nontrivial and Seeing &

Visualizing, chapter 8 contains some speculative discussion, e.g., they allow the visual system to:• make certain kinds of visual inferences• make use of visual demonstratives to offload some of the memory load• Capitalize on the fact that the displays embody the axioms of measure

theory and of geometry (which are then inherited by thought) The big question is whether any of these advantages carry over to

imaginal thinking! Do mental images have some (or any) of the critical properties that make diagrams helpful in reasoning?

Visual inferences?● If we recall a visual display it is because we have encoded

enough information about its visual-geometrical properties that we can meet some criteria, e.g., we can draw it. But there are innumerably many ways to encode this information that are sufficient for the task (e.g. by encoding pairwise spatial relations, global spatial relations, and so on). For many properties the task of translating from one form to another is much more difficult than the task of visually encoding it – the translation constitutes visual inference.

● The visual system generalizes from particular instances as part of its object-recognition skill (all recognition is recognition-as and therefore assumes generalization from tokens to types). It is also very good at noticing certain properties (e.g., relative sizes, deviations from square or circle, collinearity, inside, and so on). These capabilities can be exploited in graphical layouts.

Memorize this map so you can draw it accurately

From your memory:• Which groups of 3 or more locations are collinear?• Which locations are midway between two others?• Which locations are closest to the center of the island?• Which pairs of locations are at the same latitude?• Which is the top-most (bottom-most) location?

If you could draw the map from memory using whatever properties you noticed and encoded, you could easily answer the questions by looking at your drawing – even if you had not encoded the relations in the queries.

Draw a rectangle. Draw a line from the bottom corners to a point on the opposite vertical side. Do these two lines intersect? Is the point of intersection of the two lines below or above the midpoint? Does it depend on the particular rectangle you drew?

A B

CD

m m’

y

x

Which properties of a real diagram also hold for a mental diagram?

● A mental “diagram” does not have any of the properties that a real diagram gets from being on a rigid 2D surface.

● When you imagine 3 points on a line, labeled A, B, and C, must B be between A and C? What makes that so? Is the distance AC greater than the distance AB or BC?

● When you imagine drawing point C after having drawn points A and B, must the relation between A and B remain unchanged (e.g., the distance between them, their qualitative relation such as above or below). Why?

● These questions raise what is known as the frame problem in Artificial Intelligence. If you plan a sequence of actions, how do you know which properties of the world a particular action will change and which it will not, given that there are an unlimited number of properties and connections in the world?

If all else fails there is always parsimony and generality…(they worked well in physics and linguistics!)