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Aphantasia is a relatively recent term coined by Adam Zeman and colleagues in 2015 to refer to the experience of lacking visual mental imagery. When people are asked to close their eyes and imagine a red apple, most people can conjure some mental image of a red apple, resembling one of the representations in the diagram below:
If your mental image resembles option #1, it suggests you have highly vivid visual mental imagery, or even hyperphantasia. Options #2, #3, and #4 likely reflect the typical range of mental imagery vividness, from a fairly vivid representation to a vague, fuzzy representation that might just contain the outline of the imagined apple. However, if you chose option #5, indicating that you see nothing but darkness when you close your eyes, you might have aphantasia.
Scientific debate on the nature of aphantasia
In the last decade of research on aphantasia, researchers and philosophers have disagreed about the nature of the phenomenon. Some have claimed that aphantasia is truly a lack of visual mental imagery. If that is the case, then people with aphantasia should find it challenging to accomplish certain cognitive tasks that are thought to be aided by mental imagery, for example, remembering details of a previously studied image or imagining specific aspects of a future interaction. Moreover, if people with aphantasia can’t imagine a visual image, then their brain activity during imagery tasks should show stark differences from the brain activity of people who report vivid imagery.
In a recent Letter in Trends in Cognitive Sciences, Matthias Michel and colleagues propose a different view: that aphantasia may be better characterized as a type of “imagery blindsight” rather than a lack of imagery altogether. In blindsight, individuals with damage to their primary visual cortex report being blind, but nevertheless show behaviors that suggest some access to visual information. For example, patients with blindsight can guess the motion of an object above chance levels, even if they report not being aware of the object itself. They can also navigate around obstacles, even without knowing how they do it.
The analogy to aphantasia is as follows: individuals with aphantasia may actually have neural representations and computations corresponding to visual imagery, but they lack conscious access to those representations. This view is supported by both neural and behavioral evidence. First, a recent neuroimaging study by Simon Weber and colleagues shows that it is possible to decode brain signals during working memory to reveal the contents of memory (such as the orientation of a grating) in both strong and weak mental imagers. Furthermore, in a study by Zoë Pounder and colleagues, participants with aphantasia performed similarly to controls when engaged in a mental rotation task. In this task, participants are asked to determine whether two 3D shapes shown from different angles are the same or not. A linear relationship between the angular distance of the shapes and people’s reaction time is taken as an indication that there is a rotation-like process happening in the brain. Since both aphantasics and controls show a similar linear relationship between angular distance and reaction time, it can be argued that aphantasics use similar mental rotation strategies to do the task, even though they do not report awareness of it.
Although more research is needed in this field, the blindsight analogy put forward by Matthias Michel and colleagues is an intriguing perspective that might also help explain other individual differences in cognition. For example, people differ greatly in whether and how often they remember dreams. As with aphantasia, could it be that people who report few or no dreams are actually dreaming but not conscious of it?
