So far this week I introduced the notion that most people can see with their “mind’s eye”, but some cannot. That does not depend on whether you are congenitally blind or not – there are forms of imagery that are spatial, rather than visual, and people without visual imagery can make use of that.  I also claimed that imagery has a lot to do with perception, since the brain areas involved in perception get activated through visual imagery as well.

How far do those parallels go? In some ways mental images are like pictures.

• Chronometric studies indicate that the pattern of what information is more available and what is less available in an image closely matches the pattern of what is available in an actual picture. Likewise, the times needed to scan across an image, to zoom in on an image to examine detail, or to imagine the form rotating, all correspond closely to the times needed for these operations with actual pictures.
• In many settings, visual imagery seems to involve mechanisms that overlap with those used for visual perception. This is reflected in the fact that imaging one thing can make it difficult to perceive something else, or that imaging the appropriate target can prime a subsequent perception. In other words, if I ask you to image something it makes it harder to perceive a weak visual stimulus at the same time. And if I ask you to to image something that resembles a visual stimulus you are faster to see it when it pops up on a screen. Further evidence comes from neuroimaging and studies of brain damage; this evidence confirms the considerable overlap between the biological basis for imagery and that for perception.
• Even when imagery is visual, mental images are picture-like—they are not actually pictures. Unlike pictures, mental images seem to be accompanied by a perceptual reference frame that guides the interpretation of the image and also influences what can be discovered about the image. For example if I ask you to image a simple ambiguous picture like the one below, you are not able to reverse it to its alternative interpretation, something that is very easy to do when you look at the actual picture.Duck/rabbitOld woman /young woman