... is now up in draft on my homepage.
Here's an abstract:
In the 1870s, Francis Galton asked people to describe their visual imagery experiences when recalling their breakfast table as they sat at it in that morning. Apparently ordinary people gave very different reports, spanning the full range from claiming that imagery was entirely unknown to them to saying that their imagery was as clear and detailed, or even more so, than ordinary vision. Since then, a long history of attempts to correlate differences in subjective report of imagery experience with performance on presumably imagery-facilitated tasks (like mental rotation, mental unfolding, visual memory, and visual creativity) has largely failed. Given the ease with which most people can be brought to uncertainty about the character of their imagery experience (its richness of detail, its stability, its coloration, etc.), and given the history of debates in psychology and philosophy about the phenomenal character of imagery (e.g., the "imageless thought" debate, the Locke-Berkeley debate about abstract ideas), it shouldn't be too surprising that people's reports about their imagery experience don't reliably reflect real differences in their underlying experience. Hence, the disaster of Galton's subjective methodology.As always, comments warmly welcomed (here on this post or by email). The title and framing around Galton are new. (Previously it was "How Well Do You Know Your Own Visual Imagery?", without section i and with less focus on Galton throughout.) I'm inclined, today at least, to think the shift makes the chapter livelier; but I could easily see changing my mind about that.
20 comments:
Sorry but I do not understand properly. The idea is that they want to prove that imagery is related to "imagery enhanced abilities"(1). I did not even know there was such think as (1). Why do they even relate those to mental functions? which other kind of (1) exists?
I am really intrested onthe subject but excuse me cause I do not get it properly
Consider "mental rotation" tasks. You're presented with two line-drawings of three-dimensional abtract objects and asked to make a quick judgment about whether one is a simple rotation of the other of whether, instead, they are configurationally different. Most psychologists, following Shepard, have assuming that this sort of task is enhanced by imagery. (You visually imagine rotating one until it matches in orientation with the other.) The problem is: There seems to be no relationship between performance on such mental rotation tasks and any sort of subjective self-report about mental imagery.
Probably the lack of correlation is because imagery involves mainly the visual area of the brain and the other area related to what the imagery is about, like the area that recognizes faces. But the task of rotating involves other mental areas, for example the part of the brain that handles geometric abstraction.
Do you think it might make sense to distinguish phenomenal imagery from functional imagery? If I ask you to draw a map from your office to the nearest bus stop, you must recall some kind of stored (remembered) internal representation of the relevant environmental features/affordances. But do you necessarily have to have a phenomenal experience of these features to draw the map? If not, a person who denies experiencing visual imagery might perform just as well as a person with vivid imagery in the map-drawing task. A crucial question to ask would be what kinds of tasks *require* phenomenal images for their successful completion. See, for example, pp.276-277 and Fig. 15.1 in *The Cognitive Brain*.
Have yet to read the chapter, but
"Author: Muddy Tree Frogs" (in the PDF properties) ??
Curious.
Thanks for the comments, folks!
Mariana and Arnold: I agree that any one task may not crucially involve (phenomenal) visual imagery -- not even (despite widespread assumption) "mental rotation" tasks. I think it's the failure to find any objective task that correlates with subjective report that's troubling. (Arnold I do briefly discuss what you call the difference between functional and phenomenal imagery in the penultimate section of the chapter (with reference to Paivio).
Tsmithe: Well, who doesn't like tree frogs? We decided not to share my real name with Microsoft on my home computer (though I do on my work computer). But of course one must enter something.
Eric,
What do you make of the seeing-more-than-is-there (SMTT) phenomenon. I think this is a particularly important and revealing phenomenal event where there is a vivid visual experience that seems to be neither an instance of direct visual perception nor an instance of visual imagery. Here is a summary of my experiment (Trehub 1991):
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If a narrow vertically oriented aperture in an otherwise occluding screen is fixated while a visual pattern is moved back and forth behind it, the entire pattern may be seen even though at any instant only a small fragment of the pattern is exposed within the aperture. This phenomenon of anorthoscopic perception was reported as long ago as 1862. More recently, Parks (1965), McCloskey and Watkins (1978), and Shimojo and Richards (1986) have published work on this striking visual effect. McCloskey and Watkins introduced the term seeing-more-than-is-there to describe the phenomenon and I have adopted it in abbreviated form as SMTT. The following experiment was based on the SMTT paradigm:
1. Subjects sit in front of an opaque screen having a long vertical slit with a very narrow width, as an apeture in the middle of the screen. Directly behind the slit is a computer screen, on which any kind of figure can be displayed and set in motion. A triangular-shaped figure in a contour with a width much longer than its height is displayed on the computer. Subjects fixate the center of the aperture and report that they see two tiny line segments, one above the other on the vertical meridian. This perception corresponds to the actual stimulus falling on the retinas (the veridical optical projection of the state of the world as it appears to the observer).
2. The subject is given a control device which can set the triangle on the computer screen behind the aperture in horizontal reciprocating motion (horizontal oscillation) so that the triangle passes beyond the slit in a sequence of alternating directions. A clockwise turn of the controller increases the frequency of the horizontal oscillation. A counter-clockwise turn of the controller decreases the frequency of the oscillation. The subject starts the hidden triangle in motion and gradually increases its frequency of horizontal oscillation.
Results:
As soon as the figure is in motion, subjects report that they see, near the bottom of the slit, a tiny line segment which remains stable, and another line segment in vertical oscillation above it. As subjects continue to increase the frequency of horizontal oscillation of the almost completely occluded figure there is a profound change in their experience of the visual stimulus. At an oscillation of ~ 2 cycles/s (~ 250 ms/sweep), subjects report that they suddenly see a complete triangle moving horizontally back and forth instead of the vertically oscillating line segment they had previously seen. This perception of a complete triangle in horizontal motion is strikingly different from the tiny line segment oscillating up and down above a fixed line segment which is the real visual stimulus on the retinas.
As subjects increase the frequency of oscillation of the hidden figure, they observe that the length of the base of the perceived triangle decreases while its height remains constant. Using the rate controller, the subject reports that he can enlarge or reduce the base of the triangle he sees, by turning the knob counter-clockwise (slower) or clockwise (faster).
3. The experimenter asks the subject to adjust the base of the perceived triangle so that the length of its base appears equal to its height.
Results:
As the experimenter varies the actual height of the hidden triangle, subjects successfully vary its oscillation rate to maintain approximate base–height equality, i.e., lowering its rate as its height increases, and increasing its rate as its height decreases.
This experiment demonstrates that the human brain has internal mechanisms that can construct accurate analog representations of the external world. Notice that when the hidden figure oscillated at less than ~ 2 cycles/s, the observer experienced an event (the vertically oscillating line segment) that corresponded to the visible event on the plane of the opaque screen. But when the hidden figure oscillated at a rate greater than 2 cycles/s, the observer experienced an internally constructed event (the horizontally oscillating triangle) that corresponded to the almost totally occluded event behind the screen.
This experiment also demonstrates that the human brain has internal mechanisms that can accurately track relational properties of the external world in an analog fashion. Notice that the observer was able to maintain an approximately fixed one-to-one ratio of height to width of the perceived triangle as the height of the hidden triangle was independently varied by the experimenter.
These and other empirical findings obtained by this experimental paradigm were predicted by the neuronal structure and dynamics of a putative brain system (the retinoid system) that was originally proposed to explain our basic phenomenal experience and adaptive behavior in 3D egocentric space (Trehub, 1991). It seems to me that these experimental findings provide conclusive evidence that the human brain does indeed construct analog representations of the external world within a coherent and perspectival egocentric neuronal space.
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It can be argued that the triangle vividly experienced in this experiment is not an instance of perception because the retina is not exposed to a triangular stimulus, and at no time is there an image of a triangle on the retina. On the other hand, it can be argued that the experienced triangle is not an instance of imagery because there is no evidence that the subject recalls an image of a triangle before it suddenly appears to S in his "visual field".
Would you agree, Eric, that this is an objective task that clearly correlates with subjective reports?
Hi Arnold! That's a pretty neat little experiment which I confess I was unaware of before.
It seems to me that it fits generally with the finding that very briefly displayed stimuli can be retained and experienced for some fraction of a second after their presentation has ceased, as long as they are not "masked". However, this experiment strikes me as a very nice dynamic presentation of that result.
I'll buy the subjective reports, especially if they're fairly similar between people. My claim is not that there are *no* correlations between subjective report and objective behavior but just that with some kinds of reports, even about seemingly fairly large and basic aspects of our experience (such as the coloration of dreams, the vividness of imagery, planar perspectival distortion) fail to show such a relationship; and such reports don't deserve much credit. Where there is a nice relationship between the objective and the subjective, I think the default view should be to credit the reports.
Where do we tend to see such nice objective/subjective relationships? Generally, I think, when the subjective reports pertain to how something is experienced as being, objectively, in the world. Subjective reports with more of an inward turn tend to be more problematic.
Eric,
Suppose a detailed theoretical model of the brain predicts that under certain conditions a person should have a particular phenomenal experience that is significantly different in a predicted way from what he objectively sees. If the subject's report corresponds to what the theory predicts, would you say that his subjective report is objectively confirmed?
It depends on how good the theory is! But in principle, yes.
Eric,
Two dimensional drawings in 3D perspective pose an interesting case. Perspectival drawings of converging railroad tracks, for example, induce a phenomenal experience of tracks in a 3D space receding in the distance. As you know, if objects of equal size are placed in the foreground and background of the drawing, we experience the background object as larger than the object in the foreground. One explanation of this subjective experience is based on a process of logical inference; that is, if two objects are seen to be of equal size, experience tells us that the more distant object must actually be larger than the nearer object, *therefore* the distant object looks bigger to us. A fundamentally different explanation holds that there is an innate mechanism in the visual brain that enlarges a brain representation of an object in accordance with its distance from the observer. But how can this explain the enlargement of an object in a 2D perspective drawing when that object is not really more distant from the observer than the "nearer" object?
The retinoid model explains how this can happen. The theory predicts that there really is an expansion of the neuronal image of the "distant" object in the 2D rendition, and that this enlarged neuronal representation is the basis for our corresponding phenomenal experience. Significantly, a beautiful recent fMRI experiment by Murray et all reported in *Nature Neuroscience* (2006) demonstrates that when subjects are shown a 2D perspectival scene, "A distant object that appears to occupy a larger portion of the visual field activates a larger area in V1 than an object of equal angular size that is perceived to be closer and smaller."
Isn't this another example of a nice objective/subjective relationship. And doesn't this finding lend strong support to the theoretical model that predicts and explains the result?
What do you think would happen if the visual presentation were not of a scene projected on a flat surface but rather of a scene projected on a concave surface (with the corresponding projective size and shape distortions; maybe it could even structure the light going to the retina in exactly the same way for a motionless eye)?
My guess is: Same thing. So why think of the 2D presentation as privileged?
Eric,
Does your thought experiment assume that a scene identical to the 2D perspective scene is optically projected onto a concave surface? If this were the case, then the actual physical size of the image of the background object might be larger than that of the foreground object if it were in fact farther away from the projection source. Also, the perspectival cues would be distorted by the curved projection surface. This case is unlike the 2D perspective case where the foreground object and the background object are on the same depth plane and are exactly the same size, but one's phenomenal experience is that of a 3D scene in which the background object appears larger than an identical foreground object.
Here's another case of a nice subjective/objective relationship predicted and explained by a theoretical model of the visual-cognitive brain:
1. Form an after-image of a square.
2. Hold a poster-board as a fixation surface in front of you.
3. If you tilt the fixation surface away from you on a horizontal axis, your square after-image appears to change into a rectangle elongated on its vertical axis .
4. If you tilt the poster-board away from you on a vertical axis, your square after-image appears to change into a rectangle elongated on its horizontal axis.
This relates to planar perspectival distortions. See *The Cognitive Brain*, p. 92.
Why don't you say the perspectival cues are also distorted by the 2D surface? With either the concave projection or the flat projection I suspect we can get cases where optically identical objects (whether at the eye or on the surface, and it could matter which one has in mind, especially the farther one gets from the point of fixation) are experienced as different sizes.
The question (in my mind) is, why privilege the 2D projection over the concave projection or some other projection?
The afterimage illusion you mention is a cool one. I certainly don't want to deny the existence of illusions!
Eric,
You ask:
"The question (in my mind) is, why privilege the 2D projection over the concave projection or some other projection?"
The flat 2D plane is very special because it is humanity's default surface for written communication and pictorial representation. A sheet of paper, a canvas surface, a computer display screen are ubiquitous 2D media for conveying information in our interpersonal world.
The fact that a rendition of a scene in 3D perspective on a 2D surface induces a phenomenal experience of pictorial depth leads us to ask what kind of neuronal mechanisms in the human brain can account for this important phenomenon. It turns out that the same mechanisms that give us our transparent experience of the world from an egocentric perspective (the retinoid system) provide the brain machinery competent to transform a 2D display into a 3D phenomenal experience. This is a very important finding for the theory of mind.
I agree, Arnold, that 2D surfaces are special in being a common medium for visual presentation, and so studying their relationship to visual experience is important. Of course, it doesn't follow (at least not in any way that I can see) that 2D projections are somehow implicit in our everday experience of the 3D world, which is the "flattist" view I attack in the chapter. But perhaps you are not in fact endorsing that view.
Eric,
I don't endorse the "flattist" view. Quite the opposite. I agree with Price that the degree of perspectival distortion (e.g., the obliquely-viewed penny) varies with distance. This is explained and predicted by the neuronal structure and dynamics of the retinoid system. See *The Cognitive Brain* Fig. 4.8, p. 70.
Recall the example of the square after-image changing into a rectangle when a slanted surface was viewed. This happens because our visual system's innate mechanism for size constancy as a function of viewing distance generates an inverse of the size-constancy effect when we view an unnaturally unchanging after-image while fixating a surface that varies in depth. If, instead of an after-image, we looked at a real square drawn on the tilted poster board, it would still appear square in a near view because of the compensatory enlargement along the axis of tilt by the size-constancy mechanism in the retinoid system. But if we view the same square from a much greater distance, it would appear distorted into a rectangular form because discrimination of the relative depth of the opposite edges of the square diminishes with distance, and so must the size-constancy compensation that conserves intrinsic shape in a nearby view. The same principles hold true when you look at a tilted penny.
Thanks for clarifying, Arnold. I see some of the appeal in that view. Apart from you and Price, do you know if anyone else advocates the view? -- advocates the view, that is, explicitly as a view about conscious experience (not just neural processing)?
Eric,
I think most psychophysicists today would subscribe to the view that perceptual distortions in visual perspective vary with the distance between the observer and the object seen. But, to my knowledge, the retinoid model (Trehub 1991) is the only theoretical model that explains how the neuronal mechanisms in our brain actually cause the phenomenal perspectival distortions.
I'm not so sure about your characterization of "most psychophysicists", Arnold. Remember that the issue is not (1.) illusion or (2.) judgment about external objects but rather (3.) veridical but perspectivally-distorted phenomenal experience. (Well, at least that's the issue that *I* mean to be talking about!) Not a lot of psychophysists cleanly enough distinguish these issues to have a clear take on them, at least in print. But maybe you have someone in mind who is particularly clear on the topic? Besides yourself, I mean. (I promise to get to the relevant parts of your own book soon.)
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