On mental images

This being prompted by a perusal of the paper at reference 1 about mental imagery. This perusal prompting in turn a look at various other material, including the papers at references 2 and 3.

It seems that the idea of there being an image store in the brain is well established. Or at least something which functions as an image store, which can, at times, bring more or less vivid images into mind without needing input from the eyes. The image materials store in the sketch above. We note in passing the related phenomenon where the brain might jump to conclusions about input from the eyes, and overlay the new input from the eyes with old input from the store. As, for example, when one mistakes a bit of crumpled paper on the grass for a bird. But here the main interest is in the brain generating an image by itself, using just old input.

With this image store being different from the store of language orientated information about the world. The knowledge that cats usually have four legs and that the Congo is the name of a very long river in equatorial Africa. 

It is relatively easy to test when someone has lost the perceptual ability to name an object in front of them. This being the work usually done by the object identification box, top right. It is not so easy to test the strength of someone’s representational ability, their image generation capability, that is to say the combined efforts of the image generation and projection boxes. How do you test the strength of something which is subjective by definition? Then can the image be there without there being any subjective experience of same? When the projection of that otherwise satisfactory and sufficient image from working memory into consciousness has come unstuck?

The arrow from image generation to working memory is thinner than that from front end processing to working memory. This is intended to suggest that the latter is dominant. Input from the eyes tends to block input from memory, from storage - which is why we often shut our eyes when trying to imagine something. Note the ‘image’ root of the word ‘imagine’.

Lots of work has been done of all of this. First, there are questionnaires, designed to elicit information about the strength of the experience of internally generated images. There are a number of well known and widely used questionnaires of this sort, one of which, the VVIQ, is described at reference 4. One might worry that such questionnaires are terribly subjective and so unreliable – but they do seem to work.

Second, there are experiments with volunteers, experiments with experimental tasks designed to test different parts of the image processing complex. Reference 3 includes a lot of such tasks. One might, for example, be asked to take a capital letter apart and reassemble it to make something else: a visual version of mental arithmetic. Or to match an object seen from one angle with the same object seen from a different angle.

Over the years, all kinds of tricky tasks have been devised to test this image processing complex, with reference 3 listing nearly thirty of them. 

Third, one can look at the brain with scanners while various parts of the image processing complex are busy.

The upshot seems to be that there is a group of people who have an imagery deficit. People who can see stuff in the outside world well enough, but who have no subjective experience of internally generated images. Some such people are born, some are made, usually by their heads being damaged in some way. They have what is called aphantasia and they are called aphantasics.

Additional support for the concept of aphantasia is provided at reference 5, which offers a cunning test for same based on binocular rivalry, a test which uses the fact that the outcome of a binocular contest can be prejudiced by both real images and imagined images. Giving us a test for the strength of mental imagery which draws on clocks and binary choices rather than descriptions and five point Likert scales. Binocular rivalry more generally is described at reference 6.

Is aphantasia a problem? Reference 2 describes a man who reported losing all his mental imagery, that is to say he had become an aphantasic, which he was sorry about, but who performed OK on all the standard tests. The mental images must still have been there and his brain must have found a work-around.

Other people perform badly on perception, perhaps failing to recognise common objects by sight, but are able to recognise them by touch and are able to produce sketches of them. That is to say, representation seems OK. Reference 3 describes one such case.

Part of the interest here is using these differences to infer something about the architecture of the image processing complex. To infer something about its various modules, the idea of a module being that it has its task, which it can get on with independently, without needing to get all mixed up with other modules. Hence modularity, as sketched above. With the strength and effectiveness of these various modules varying from person to person, in much the same way as height or hair colour. Or from time to time, in the way of weight or blood pressure.

Another part of the interest here is trying to work out what this mental imaging capability is for. Is having subjective experience of these internally generated images needed in order to have that capability?

In which connection, the present paper, that is to say reference 1, seems to have found something. Aphantasics are not as frightened by scary stories without pictures as normals. It seems that their relative inability to generate scary pictures from scary stories dampens down their emotional response to them. While they are scared in the normal way if such pictures are added in. While normals get scared without needing actual pictures.

All very curious. All too tempting to follow in the footsteps of lots of other people and spend quality time on these matters!

PS: I have not been able to find either an ICD or a DSM code for aphantasia. Perhaps it is not yet respectable enough. Perhaps means that it is not yet claimable against a US medical insurance policy.

References

Reference 1: The critical role of mental imagery in human emotion: insights from fear-based imagery and aphantasia - Marcus Wicken, Rebecca Keogh, Joel Pearson – 2021. 

Reference 2: Loss of imagery phenomenology with intact visuo-spatial task performance: a case of 'blind imagination' – Zeman, A. Z., Della Sala, S., Torrens, L. A., Gountouna, V. E., McGonigle, D. J., & Logie, R. H. – 2010. 

Reference 3: Intact mental imagery and impaired visual perception: Dissociable processes in a patient with visual agnosia – Behrmann, M., Moscovitch, M., & Winocur, G. – 1994. 

Reference 4: https://en.wikipedia.org/wiki/Vividness_of_Visual_Imagery_Questionnaire. 

Reference 5: The blind mind: No sensory visual imagery in aphantasia – Keogh, R., & Pearson, J. – 2018.

Reference 6: https://en.wikipedia.org/wiki/Binocular_rivalry.