Sensory memory is the very first stage of memory that involves registering a tremendous amount of information about the environment, but only for a very brief period. During every moment of your existence, your senses are constantly taking in an enormous amount of information about what you see, feel, hear and taste.
While this information is important, there is simply no way to remember each and every detail about what you experience at every moment.
Instead, your sensory memory creates something of a quick “snapshot” of the world around you, allowing you to briefly focus your attention on relevant details.
So just how brief is a sensory memory? Experts suggest that these memories last for three seconds or less.
While fleeting, sensory memory allows us to briefly retain an impression of an environmental stimulus even after the original source of information has ended or vanished. By attending to this information, we can then transfer important details into the next stage of memory, which is known as short-term memory.
Sperling’s Sensory Memory Experiments
The duration of sensory memory was first investigated during the 1960s by psychologist George Sperling.
In a classic experiment, participants stared at a screen and rows of letters were flashed very briefly – for just 1/20th of a second. Then, the screen went blank. The participants then immediately said as many of the letters that they could remember seeing.
While most of the participants were only able to report about four or five letters, some insisted that they had seen all the letters but that the information faded too quickly as they reported them.
Inspired by this, Sperling then performed a slightly varied version of the same experiment. Participants were shown the three rows of four letters per row letters for 1/20th of a second, but immediately after the screen went blank, participants heard either a high-pitched, medium-pitched or low-pitched tone. If subjects heard the high-pitched tone, they were to report the top row, those who heard the medium-pitched were to report the middle row and those who heard the low-pitched were to report the bottom row.
Sperling found that participants were able to recall the letters as long as the tone was sounded within one-third of a second of the letter display.
When the interval was extended to over one-third of a second, the accuracy of the letter reports declined significantly, and anything over one-second made it virtually impossible to recall the letters. Sperling suggested that since the participants were focusing their attention on the indicated row before their visual memory faded, they were able to recall the information. When the tone was sounded after sensory memory faded, recall was nearly impossible.
Types of Sensory Memory
Experts also believe that different senses have different types of sensory memory. The different types of sensory memory have also been shown to have slightly different durations.
- Iconic memory, also known as visual sensory memory, involves a very brief image. This type of sensory memory typically lasts for about one-quarter to one-half of a second.
- Echoic memory, also known as auditory sensory memory, involves a very brief memory of sound a bit like an echo. This type of sensory memory can last for up to three to four seconds.
- Haptic memory, also known as tactile memory, involves the very brief memory of a touch. This type of sensory memory lasts for approximately two seconds.
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