Mental images – what are they? How are they related to perception?

Mona Lisa Rasee is one of Marcel Duchamp's variations on the Mona Lisa.  This is a black and white photograph of the original painting.  The only difference between it and the original is the caption.  The caption "Mona Lisa Rasee" makes us see the painting differently, since it invokes the visual image of the Mona Lisa bearded and mustached.

Marcel Duchamp did create a bearded and mustached Mona Lisa before creating "Mona Lisa Rasee".  People who knew this version may have formed a visual image of the Mona Lisa with the specific beard and mustache that Duchamp painted on it.

What are mental images?  According to Prof.  Bence Nanay from Antwerp University, mental imagery is perceptual processing not triggered by corresponding sensory stimulation in the relevant sense modality.

What does this mean?  If the image is visual, for instance, it is not identical with a visual stimulus that we may concurrently see (we do not actually see the beard when we looked at the picture above and form the image of the bearded Mona Lisa).

This definition implies that a mental image is processed in the sensory processing systems.  When we form a mental image we activate the same brain areas that are activated when we process a perceptual stimulus.  When we form a visual image, we activate brain areas that are activated during visual processing.  When we form an auditory image, we activate brain areas that are activated during auditory processing, and so on. 

Mental images have five features:

1.  They can be formed in all modalities.  There are auditory images, olfactory images, flavor images tactile images.    We can play a song in our mind's ear, form an image of the scent of cinnamon or of the touch of a feather. 

2.  They can be involuntary.  A song we heard in the morning may involuntarily replay itself in our mind's ears throughout the day.   On a sadder note, people may have involuntary flashbacks of traumatic events that they've been through.

3.  They don't have to be placed in a specific spatial place.  If we see an apple in our mind's eye, it won't necessarily be "placed" anywhere specific in space.  We can manipulate an image from an egocentric point of view (imagining taking a different perspective in space) or from an allocentric point of view (mentally manipulating objects from a stationary point of view ).

4.  Usually they don't generate a sense of presence.  Usually we know that the mental image does not exist in reality.  But there are forms of mental image that do have a sense of presence, like dreams.

5.  They can be unconscious.  As defined above, a mental image is a perceptual process.  Since perceptual processes can be unconscious, mental images can also be unconscious.  Some people have a condition called Aphantasia.   These people can perform tasks that allegedly require the formation of mental images, but they do not report experiencing mental images.  Researchers have differing views on this:  some say these people have mental images that they are not aware of.  Others say they perform these tasks using other cognitive skills.

What cognitive tasks allegedly require the formation of mental images?

Tasks like this one:

In this task, the person is asked to decide which of the four stimuli on the right is identical to the stimulus on the left.  People usually solve this kind of problem by mental rotation – they mentally rotate the stimuli on the right until they are parallel (or not) with the stimulus on the left.

Prof. Nanay argues that mental images are an integral part of our perceptual processes.  We cannot perceive (almost) any stimulus without mental imagery taking a part in our perceptual process.  Why?  It's easy to explain with visual images.  Look around you.  Almost any object you see occludes other objects which lie behind it, and also occludes the back side of itself.  Using mental imagery we "complete" the background objects or the back side of objects.  Furthermore:  we experience everything in more than one sense modality.  But usually we don't get information about every object from all sense modalities.  We represent the information we don't get from our senses by forming multimodal mental images of objects.  For example, I can form a mental image of the tactile feeling of the tree trunk that is seen from my window.  If the window is closed, I can form an auditory image of the rustling of the tree's leaves in the wind.  The tactile and the auditory images are combined with the visual perception of the tree to create my experience of the tree.

Are you familiar with the phenomenon, that when you read an email written by someone you know, you read the message in that person's "voice"?  This is another example of the way a mental (auditory) image is involved in perceptual processes.

This is probably the reason visual processing (as a CHC ability) is defined this way:  "The ability to make use of simulated mental imagery (often in conjunction with currently perceived images) to solve problems".  Visual processing is what the mind does with the information coming from the eyes, sometimes a long time after the information arrived.  Likewise is the case with auditory processing.  Auditory processing is what the mind does with auditory information, sometimes a long time after it arrived.  That's why Beethoven managed to write such great music when he was already completely deaf.  He used auditory imagery.  And when he did that, he was engaged in auditory processing.

Reference:  video posts by Prof. Bence Nanay

http://philosophyofbrains.com/author/nanayb