Sensory memory is actually the ‘ultra-short-term memory’ of our brain. It runs much like a train terminal where it enters and gets routed to where it needs to go. From the initial impression made upon your senses the sensory memory carries the information and puts it on the right track to your working memory, where it is processed and then sent off to the short-term memory – where it is stored for a day or so, or on to the long-term memory. For example, the ability to look at something and remember what it looked like with just a second of observation is an example of sensory memory. 
Because this portion of your brain takes everything you get through your senses is pretty much everything, it is not possible to let it remain there for any length of time or it would have a massive congestion problem so it is just sent along to another destination without having to do any processing of its own.
Think about a certain scent that reminds you of someone special – say your grandmother. Every time you smell that scent you think of her. That is sensory memory. When you use one of your senses – taste, touch, smell, sight, and hearing – there is a signal sent to your brain. The impression left after the feeling, sight, noise, taste or fragrance has gone is called your ‘sensory memory’.
The sensory memory pays attention to the signals the information sends out so it is able to route the message to the appropriate connection for further processing. Obviously, any problem with the impression, or the processing, would cause the connection to derail and problems to occur.
The three primary forms of sensory memory are:
§        Iconic – Visual stimulation forms a picture in your mind, or mental forms of stimulation. A common, and good example of iconic memory would be to watch a child making images with a sparkler. They spin the sparkler fast and it makes designs with the ‘light trail.’ The continuous images of the letters or designs forms stimulate your visual senses. Visual information is found by the photoreceptor cells in the eyes and is sent to the occipital lobe in the brain.
§        Echoic – Auditory information is sound waves that are sensed by the hair cells in your ears and travels to the temporal lobe of the brain. Here it is able to detect changes in the environment. This has been the key to survival of any organism. These changes could be as simple as a language difference, or as the detection of some unusual activity in your surroundings that could prove to be dangerous – such as a lion in the jungle. A reduced duration of echoic memory would be delayed development in learning language skills.
§        Haptic – Haptic memory comes from touch, and has to do with the sensations our body feels (pain, stimulation, itching, etc.). We have sensory receptors all over our bodies, and any touch sends off signals that travel through different neurons in the spinal cord to the ‘post central gyrus’ of the parietal lobe in the brain. Studies have found that specific neurons in the prefrontal cortex are involved in haptic memory with regards to reaction to motor response.
Since there is no processing of information in the sensory memory you cannot consciously store memory. Your sensory memory provides the details, and allows other brain connections to determine what to do with them. But, just because if is not a conscious part of your memory doesn’t mean it is not essential for keeping your memory system ‘on track.’
This is Ron White, and I am a two-time USA Memory Champion. I am intrigued with the different parts of the brain that makes memory work, and hope you have found something interesting in this information.
Sources:
Oracle Think Press – Cognitive Processes: http://library.thinkquest.org/26618/en-5.2.2=sensory%20memory.htm
Wikipedia: – Sensory Memory: http://en.wikipedia.org/wiki/Sensory_memory