What Is Sensory Memory?

Sensory memory is a very brief memory that allows people to retain impressions of sensory information after the original stimulus has ceased. It is often thought of as the first stage of memory that involves registering a tremendous amount of information about the environment, but only for a very brief period.

The purpose of sensory memory is to retain information long enough for it to be recognized.

Types of Sensory Memory

Experts 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, iconic 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, echoic 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, haptic involves the very brief memory of a touch. This type of sensory memory lasts for approximately two seconds.

How Does Sensory Memory Work?

During every moment of your existence, your senses are constantly taking in an enormous amount of information about what you see, feel, smell, 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.

While fleeting, sensory memory allows us to briefly retain an impression of an environmental stimulus even after the original information source has 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.

Characteristics of Sensory Memory

Sensory memory is an automatic process; it occurs automatically without conscious control:

• Sensory memory is limited in duration and capacity. It lasts very briefly and is almost immediately replaced by new information.
• Researchers have found that attention to the stimulus has only a weak impact on sensory memory.
• The type of memory stored is specific to the sensory modality; in other words, echoic memory stores auditory information, iconic memory stores only visual information, and haptic memory stores only tactile information.
• Information stored in sensory memory includes a great deal of detail.
  

Examples of Sensory Memory

Examples of iconic memory include situations where you briefly have an image in your head after the sight is gone. For instance, after turning off a flashlight, there is a brief image of the light in your memory. Or, after glimpsing an exit sign on the interstate, you can briefly see the image in your mind.

An example of echoic memory would be the brief memory of the blare of a car horn or the sound of an instrument, even after the noise has ended.

Haptic memory examples might include the brief memory of something brushing up against your skin.

In each instance, the very brief lingering memory you experience allows you to recognize and process the experience.

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 repeated as many of the letters as 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 1/20^th 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.

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 because the participants focused on the indicated row before their visual memory faded, they could recall the information. The recall was nearly impossible when the tone was sounded after sensory memory faded.