For the vast majority of you, if I asked you, right now, to imagine a beach – all golden sands and blue sky then I doubt it would be a problem. We ‘see’ the beach with our mind’s eye, even though there is no beach in front of us, and it’s most likely still grey and raining outside. The fact that our mind can generate images this lifelike is extraordinary, and something which I will explore more in this week’s post.
Something also interesting about our ability to generate these mental images, is that we can manipulate them in our minds. We do not see a flat, 2D object, but something we can move, or interact with. This was investigated in one study by Shepard & Metzler (1971) which used novel shapes so that previous experiences could not affect the results. Participants were shown pairs of shapes like the ones in the image below, and were asked to decide whether they were the same shape, or mirror images of each other, as quickly as possible.
As you can see, this requires some concentration! The researchers found that there was a strong linear relationship between the time it took for participants to respond and the angle of rotation. From this, they concluded that people rotate mental images at about 60º per second.
Interestingly, other studies have shown that this rotation speed of mental imagery is affected by the laws of physics – which at first glance seems improbable. I mean if you’re imagining something, why can’t you move it however you’d like? Parsons (1987) found that people find it difficult to rotate a mental image if it is physically difficult for this to happen – they used the example of imagining a foot rotating from someone’s ankle.
This effect is thought to occur as mental imagery, such as the examples above, rely on motor imagery – neuroimaging studies have shown that the motor cortex is active when we perform mental image rotation. As physical movement is constrained by the laws of physics, so are our transformations of mental images.
Mental imagery is also strongly related to visual perception, as shown in this early experiment by Perky (1910). Participants were asked to imagine the image of a given object on the dark screen in front of them, however they didn’t know that a faint picture of that object was also projected onto the screen. They found that although the participants do not notice the projected picture, they report that the image they’re imagining has the same properties as this picture e.g. the same rotation and size. This result suggests there must be some overlap between our mental imagery and our perceptions. More recent studies have also shown our mental imagery has some of the same properties as our visual perception, such as increased sensitively to the lower visual field.
Now, go back to your mental image of the beach, and try to imagine what life would be like if you kept really trying to conjure up that image, but were always unable to. Although most of us take our ability to have mental imagery for granted, a small percentage of people are unable to visualise mental images. This is known as aphantasia, and people with this condition are unable to visualise aspects of a memory, although they will be able to describe it. Scientists who have studied this condition believe that there is a spectrum of the vividness of which people experience mental imagery, with aphantasia being at the bottom.
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