Zeman’s Visual Imagery Vividness

Adam Zeman et al, The neural correlates of visual imagery vividness – An fMRI study and literature review Cortex 105, 2018.

Abstract

Group comparison revealed that the low-vividness group activated a more widespread set of brain regions while visualising than the high-vividness group.

Introduction

   The ability to imagine is a defining feature of human cognition. It enables us to represent items and events in their absence, allowing us to escape from the limitations of our current perspective into a limitless range of virtual worlds.While we can simulate many aspects of our experience and behaviour, for most of us, visual imagery ‘visualisation’ is a particularly prominent component of our imaginative lives.

The current study is inspired by our previous report of a clinical case, MX. MX abruptly lost the ability to visualise following a cardiac procedure. His dreams became avisual. Unexpectedly, he performed normally on standard measures of visual imagery, but appeared to do so in the absence of any conscious experience of imagery. This combination of findings led us to describe his case in terms of blind imagination’ by analogy with ‘blindsight’. A functional MRI study revealed that while his brain activation during face perception was identical to that of controls, his brain activity during imagination of famous faces was markedly different. … Since our initial description of the case of MX, we have described a group of individuals with a lifelong absence of visualisation, a phenomenon we have termed ‘aphantasia’.

Discussion

… As discussed below ,the activations, in the low vividness group, in regions negatively correlated with vividness in the parametric analysis may be explained by either a failure to suppress activity that can interfere with vividness, for example in auditory cortex, or by consequential or compensatory activation of executive regions with potential to drive the imagery process: this possibility is consistent with the prominence of frontal regions.
In contrast to the more widespread regions that display increased activation in the low vividness group relative to the high vividness group, only two areas show increased activation in the high vividness group compared to the low vividness group. This is in keeping with evidence from other domains where greater task proficiency tends to be associated with reduced brain activation. [In keeping with the neural efficiency hypothesis.]

4.3. Parametric analysis of the neural correlates of imagery vividness

Positive correlations [with vividness] were seen in

  1.  Regions … associated with higher order visual and semantic processing,and are likely to be involved in mediation between the verbal stimuli used in our paradigm and the visual representations they excited.
  2. One of the key nodes of the default mode network.
  3. [A region which is] associated … with internally directed thought.
  4. A region strongly associated with face perception, and the visualisation of faces both as images and as hallucinations
  5. A region linked to memory, particularly spatial memory.

There were only two areas of positive correlation in the frontal lobe, in the right MFG and IFG: interestingly right IFG has been associated with ‘directing attention to or active selection of perceptual, rather than conceptual, representations during retrieval’.
In contrast, increased brain activity linked to decreasing vividness was seen distinctively:

  1. in … broadly executive regions, contributing, for example, to the frontoparietal control network
  2. [in] regions … associated with [the sense of hearing where] deactivation has been observed … during visual imagery in previous studies. Their involvement in semantic memory could also be relevant.
  3. [and other areas with less clear significance].

4.4. Literature review: i) current findings in relation to previous studies of visual imagery vividness

… Taken together these studies point to activation positively correlated with vividness in the occipital lobes, with more prominent involvement of higher than lower order visual association cortices; positively correlated activation in the MTLs, most likely related to memory retrieval; positively correlated activation in regions … which participate in internally directed cognition within the default mode network .

4.6. Blind imagination: current findings in relation to patient MX and ‘aphantasia’

The evidence from studies of hallucinogens, that vivid imagery occurs when posterior brain regions are unconstrained by anterior areas, is potentially relevant to this question. However, it is likely that there are two dissociable neural routes to vivid imagery: one involving spontaneous imagery occurring in an ‘unconstrained’ brain, the other involving deliberately generated imagery in a highly connected brain. It could be that the relationship between frontal activation and imagery vividness differs for these two types of imagery.

One estimate suggests that approximately 2% of the normal population lacks the ability deliberately to summon visual imagery to the mind’s eye. The current study did not include any individuals at the far extreme of the imagery vividness spectrum, but the studies of the neural correlates of visual imagery summarised here suggest a range of hypotheses for the neural basis of aphantasia.

Conclusion

We have shown that a group of individuals with high visual imagery vividness activate the brain more selectively than individuals with low vividness. … Many of the areas activated in the low but not the high imagery group displayed an inverse relationship with imagery vividness.

… Further work is required to elucidate the neural basis of lifelong ‘aphantasia’. The most general implication of our work, consistent with other recent findings, is that metacognition for the vividness of visual imagery, both on summary measures and on a trial by trial basis, is meaningful, and has observable neural correlates.

My comments

Wikipedia quotes Galton:

To my astonishment, I found that the great majority of the men of science to whom I first applied, protested that mental imagery was unknown to them, and they looked on me as fanciful and fantastic in supposing that the words ‘mental imagery’ really expressed what I believed everybody supposed them to mean. They had no more notion of its true nature than a colour-blind man who has not discerned his defect has of the nature of colour.

It also has:

The neural efficiency hypothesis is the phenomenon where smarter individuals show lower (more efficient) brain activation than less bright individuals on cognitive tests of low to moderate difficulty. For tasks of higher difficulty, however, smarter individuals show higher brain activation.

Zeman et al seem to suggest that the high-vividness  group are considered to be ‘smarter’ than the low-vividness group. So were “the great majority of the men of science” in Galton’s day were not so ‘smart’?

What if subjects were presented with a higher difficulty task? Would we now consider the ‘low-vividness group’, such as Galton’s scientists, to be smarter? Or would the high-vividness group split into two: those who retained their un-smart high-vividness and those who became less vivid and hence retained their ‘smartness’? Would these make better scientists that Galton’s?

Are there any low-vividness people who perform well (if inefficiently) on the tasks? If so, like galton’s scientists, perhaps their methods have some traction on the higher difficulty tasks, and perhaps they might perform better than the high vividness group? (If the high-vividness group routinely use imagery to solve easier tasks, their means to solve higher difficulty tasks will be less used and potentially less developed.)

Further, the high-vividness group are characterised as ‘summoning’ imagery as part of a controlled process, in contrast to hallucinations, which are un-bidden. But are there high-vividness people who continue to ‘summon’ images even when it is inappropriate? Perhaps they can only act on such imagery, appropriate or not? Possibly ‘mental imagery’ gets in the way of doing good science?

Aparently aphantasists (like Galton’s men of science) lack ‘the ability deliberately to summon visual imagery to the mind’s eye’, suggesting that aphantasia is a disability. But perhaps some of the high vividness group lack the ability to function effectively without relying on mental imagery? Maybe the high vividness group lack the ability to do good science? (Alternatively, maybe ‘normal’ people – and some good scientists –  can work with or without mental imagery as appropriate to the task at hand?)

Finally, while there is clearly evolutionary utility in being more able to utilise mental imagery, maybe there is also [in more difficult cases] utility in being able to work without it. So maybe this is an example where there is an evolutionary benefit to the poplation as a whole to have a mix of abilities. So is a lack of vivid imagery a neurological disorder?

More work required. Comments, anyone?

Addenda

Disability and disadvantage

Adam Zeman has commented:

I don’t think that aphantasia is a ‘disorder’ per se. It’s an intriguing variation in human experience, and work I hope we will soon publish indeed suggests that it had its advantages.

(personal correspondence)

Neural Efficiency

Adam’s work seems somehow inconsistent with the wikipedia version of the neural efficiency hypothesis, which I have critiqued here. But his own wording seems much less problematic.

See Also

New Scientist’s Inside the Mind’s Eye

8 June 2019.

Pearson thought this priming effect would be stronger in people who have a more vivid mind’s eye … . Sure enough, in 2011 he discovered that people [with] aphantasia, didn’t respond to image priming any more than you would expect by chance. At the other end of the spectrum, people who say they experience extremely vivid imagery were far more susceptible to priming than those who report being somewhere in the middle.

Those with stronger imagery than average had a smaller visual cortex – the region that processes information from the eyes – than the others. A similar study Pearson conducted found that people with stronger mental imagery also had lower neural activity in the visual cortex but higher activity in the prefrontal cortex, which is known as the brain’s command centre because it exerts control over other areas. “In terms of what determines the strength of your visual imagery, it seems to be partly about neural architecture and partly about activity,” says Pearson.

“The noise seems to disrupt the visual image.”

“You can’t hold two mental images in your mind at once,” says Holmes. “So if you do something that competes with the images from the traumatic event whilst these trauma memories are being laid down, you may be able to stop them intruding.”

Most recently, Holmes has shown that a suite of imagery-intervention techniques can help people with bipolar disorder, whose mood fluctuations are often driven by recurring mental images of what might happen in the future.

All of which has led Zeman and Pearson to wonder whether people with an extremely vivid mind’s eye are more susceptible to certain psychological disorders. And on the flip side, could aphantasics be to any extent immune?

Our brains are constantly predicting what we will see, generating signals from non-visual parts of the brain that feed into the visual cortex, where they are combined with information from the eyes to produce an image. That explains why we are so readily tricked by visual illusions. It also makes it very difficult to unpick which elements of consciousness come from expectations and which come from external stimuli.

Thus the ‘ability’ to visualise may have downsides. I speculate that as well as an impact on mental health, they may have a more broader impact on how people think and communicate, and hence a much broader social significance.

Mind’s Eye Project

Web site with a recent conference and exhibition.

 

 

Dave Marsay

 

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