375: Visual Imagery

Visual Imagery

MENTAL MODELS

We construct mental models of situations.  When we read a sentence, for example, we create a mental picture of what we are reading.  Dr. Kirwan used a specific example of a fantasy novel describing a group of people walking in single file then suddenly talking to each other side by side.  These were two contradicting mental models.

Early on it was thought that these types of mental models were remembered in semantic categories.  Usually these semantic mental models were be explained in sentences.  A type of abstract representation of this is shown in an analog vs proposition of "a ball is on a box."  In proposition you have a relation, syntax, a truth value, it is abstract and it is not spatial.  Another possibility is an analog presentation (e.g., a picture of a ball on a box) and this analog presentation has no distinct relation, no syntax, no truth value until it is described, it is concrete and it is represented in a spatial medium as a picture.  We took a got in the class as to how we experience this sentence (a ball is on a box) and we all agreed that we imagine a picture instead of a proposition.  This was controversial in the 70's but it is becoming clear that this type of analog imagery is more correct.

MEMORIES AND MENTAL MODELS

If you have hippocampal damage how do you do at these types of imagining tasks?  It turns out that people with this type of damage cannot do this very well because we draw on memories to create these imagined scenarios.  So damage to the hippocampus means you will have damage to your memory system which makes it difficult to draw on memories in order to create a mental image/model.  This could be part of the reason why our memories are so susceptible to change based on new information.  We are usually pretty good at keeping imagination and memory separate but it can create some confusion.

PROPERTIES OF MENTAL MODELS

Property 1: Rotation

This is a type of spatial rotation.  There are also sex effects for this where men are slightly quicker and more effective with this than women.  It turns out that the further degree of rotation the two objects are different from each other the longer it takes to do this mental rotation.  This seems to indicate that people are actually visually imagining this mental rotation.  If people were doing this propositionally then it wouldn't take extra time.

Property 2: Size Zooming

A task that exemplifies this property is asking people to imagine a tiger in a small pink square and then tell me what color the tigers nose is.  The smaller the box is the longer it takes to answer this question.  This indicates that we are doing a sort of zooming in to determine what the color of the nose is.  Again this is in opposition to proposition.

Property 3: Scanning

Your task is to view an island with some fictitious landmarks such as a well, a tree, etc.  Then you take the map away and are asked to imagine going from one landmark to another.  If those landmarks are close together your response is faster than if you are asked to go from landmarks that are somewhat further away.  This indicates that people are scanning across the map and is again in opposition to proposition.

Property 4: Brain Locus

If these mental models are represented by language then as you do these tasks your language centers should be activated or if it is visual your visual centers should be activated.  It turns out that the dorsal stream, a visual center, is activated when a person is asked to do these tasks.  Language centers remain inactive.  

THE PIAZZA EXPERIMENT

Imagine that you are in the city square sitting on the cathedral steps looking south, tell me what you see.  Now imagine you are on the other side, now what do you see.  Undamaged people can do this task with little difficulty.  With unilaterally left neglect patients they could only focus their attention on half of the visual scene even for internally generated scenes.  The point is that mental images require you to focus attention on them and that mental images are intact in neglect but there is an attentional problem.