Iconic memory is the name given to how we handle fleeting or temporary visual images. It's part of our sensory memory. Sensory memory is perhaps best considered as a filter, processing the huge amount of images, smells, sounds and physical feelings that we experience all the time. Our sensory memory is not controlled by us - providing our eyes are open we cannot stop an image being seen. However, we can decide, to an extent, which elements of sensory memory we decide to move further into our memory chain.
Images stored in iconic memory decay very quickly. It's commonly referred to as ultra-short storage and while it will vary from person to person and situation to situation, it's considered to be in the region of less than half a second. If you like, it's split-second memory storage.
Visual memory can be typically broken into three stages. The first of which is iconic memory which, as we know, lasts a fraction of second. Images that we decide to store are then moved to Visual Short-Term Memory (VSTM) which is generally regarding to last in the region of say half a minute. VSTM is essential for a whole range of functions but perhaps strangely, there's not much you can actually store in it. George Miller, an eminent cognitive psychologist calculated that only around seven pieces of information could be held in short term memory. In short, you must decide whether to keep the images by moving them into Long-Term memory (LTM) or get rid of them. Whether games like spot the difference are testing your Iconic, VSTM or LTM, we will leave to the experts to debate.
Eidetic memory is often called photographic memory. It's not exactly the same and in the instance of this memory test, photographic memory is likely to be more relevant. For the purposes here let's define it as the ability for someone to clearly recall an image (or the information the image represents, such as a number) even after a few brief moments of viewing.
It's been noted that as Eidetic memory only tends to exist in younger children and as they aren't likely to be taking this memory test, we'll leave it there !
By now, you should realise that iconic memory plays only a fleeting part in the memory test. The images that you see within the test are moved rapidly to VSTM and then to long term memory. While this is a slightly strange concept, in reality, your brain, rather than you (!) will decide over the course of the test the best way to hold the information required. Most people would argue that by taking the memory test here, you are working within your long term memory.
However, there's an important concept here of 'maintenance rehearsal' which is essentially the process repeating information that you know you only need for a short time but might not need later. For example, if someone tells you an address but you can't find a pen, you might say the address over and over again in your head until you find the pen. Then, it's gone. You didn't move that address to long term memory - you didn't bother - but you knew you needed to keep hold of it longer than it would stay in short term memory. But it's a little more complex. Firstly, how effective is maintenance rehearsal with visual short term memory ? Second, and more importantly perhaps, if the memory test shows you an image of a shoe, do you really remember the image or the fact that it was a shoe ? Are you therefore recalling or conducting maintenance rehearsal on the image itself or the concept/word that the image represented ?
And with that, we'll simply say, enjoy the test !