Sensory memory refers to the memories which are brought on and retained by the senses. This kind of memory is extremely short-term and, since it’s gathered by our senses, you have different types of sensory memories, such as olfactory, tactile, visual, etc.
Many experiences were held in which the goal was to demonstrate how this specific kind of memory actually works, but the most studied and researched types were, without a doubt, the iconic memory and the echoic memory.
One of the most famous experiments was performed by George Sperling in the 1960’s and it was a study on the field of iconic memory. The experiment consisted of presenting a group of letters (with no particular meaning) to the subjects for a short period of time (less than a second) and then asking the subjects to state back the letters they remember. The results were similar every time the experiment was conducted: the subjects can remember about 3 or 4 of them.
There were many variations made to this experiment. Sperling himself tried to add some sound to each row of letters, others tried to manipulate the number of stimuli or asked the subjects to recall one specific part of the stimuli, pointing out its position. The more senses the stimuli affected, the easier is became for the subject to remember it. However, in all experiments, one very important conclusion was made: this type of memory has a really short lifespan, or timeframe.
Still in the 60’s, experiments based on echoic memory were conducted as well. They consisted in telling a test subject a list of numbers and he or she should recall them immediately after they were recited to him. The word immediately is quite important here, because some variations were tried as well, and if the subject waited a couple seconds more, the memory of the numbers would fade, because that’s how long the sensory memory lasts: about 1 or 2 seconds.
Sensory memory is often confused with short-term memory, but in reality, they’re quite different, not only because sensory memory lasts for such little time, while short-term memory lasts for approximately 20 to 30 seconds, but also because sensory memory cannot be controlled by the conscious mind. The brain processes the information and stores it automatically and Sensory Memory cannot be prolonged or made to live on for longer, as Short-term or Long-term memory.