If a picture paints a thousand words, what can we say of the human memory with its remarkable power to store information visually? Most people have the ability to conjure up pictures from memory with extraordinary vividness. We often find that the images endure long after names, dates and circumstantial details have been forgotten.
How many doors do you have in your home? Most people are not able to answer this question straight away but have to retrieve an internal image of their house or flat and mentally travel from room to room, counting the doors. In accessing information of this kind, many psychologists would argue that we are using a distinct visual memory system.
According to this idea, long-term memory is housed in two separate systems: a verbal memory system that contains networks of stored facts, and a visual memory system akin to a photographic library where information is stored in the form of images. The visual memory system comes into play when we make Visual comparisons between one object and another. For example, is a garden pea a lighter or a darker reen than a Christmas tree? To answer this question, you retrieve an image of each object and compare them in your mind’s eye. The capacity of human memory for images is generally far greater than that for words, and this seems to support the idea of separate visual and verbal memory systems. We are quite poor at recalling all the specifics of a conversation, although we can usually remember the gist of what was said. In contrast, our memory for images is pretty impressive. In tests, it has been shown that people can recognise as many as 10,000 pictures with over 90 per cent accuracy after being shown each picture for just a few seconds. In addition, studies of people with specific problems of visual recognition suggest a separate visual system. For example, people with visual agnosia understand the names of objects but cannot recognise the objects themselves.
Are images stored or constructed?
However, not all researchers agree with this idea. Some think that the images we experience in our mind’s eye are not stored but are created as and when we need them. For example, imagine a tiger. No ware you retrieving an image of a specific tiger from memory? If so (and your mental image is clear), you should be able to see how many stripes the tiger has – but you probably find you cannot. US philosopher Daniel C. Dennett argues that mental images are more like descriptions than pictures: they do not specify every detail. So, to count the stripes on your mental image of a tiger, you would have to construct them.
This raises the question of how, we can ever separate ‘genuine’ images, which stem from actual experience and are retrieved from memory, from the made-up images of our imagination. Although schizophrenics, for example, have difficulty in distinguishing between imagined images and those that relate to real experience, most of us do not have this problem. However, psychologists know from their work on eyewitness testimony that what constitutes a true memory is not always straightforward. One of the current hot topics in psychology is whether retrieved images have fundamentally different properties from constructed images.
Picturing Words
Memory researcher Alan Paivio argues that easy-to-visualise words can be stored in two memory systems – one for language and the other for images.
- whereas abstract words can only be stored in the language system. Try his simple experiment:
- Read out this list of 30 words to someone else at a rate of about one word every tw o seconds.Then ask him or her to write down as many as possible from memory. Now take a look at which words were recalled. You will probably find that the list contains more concrete, easy-to visualise words such as house, dress and knife than abstract words such as through, similar and either. This may be because the easy- to-visualise words are stored in two ways, both visually and verbally , and are therefore easier to remember.
Visual Agnosia
This is a fault in visual memory that is brought about by brain damage – caused, for example, by a stroke or an accident. Visual agnosics can see the visual elements of an object, such as the colours and composite shapes, but they cannot put the pieces together to make a meaningful, recognisable ‘ whole’ .
Martha Farah, an American psychologist specialising in visual cognition, recorded one sufferer trying to make sense of the US flag: ‘I see a lot of lines. Now I see some stars. When I see things like this, I see a lot of parts. It’s like you have one part here and one part there, and you put them together to see what they make.
