Visual Memory

By: Eric Hartwell

When it comes to studying vision, the focus is normally on VSTM (or visual short term memory.) The two other branches of memory are long term memory and sensory memory. VSTM is a type of short term memory, although it is strictly limited to the visual realm. We call short term memory the ability to recall something from several seconds to a minute ago. When we speak of “sensory memory,” we are referring to the few split seconds that follows the initial perception of an object. If you are able to briefly look at something and immediately memorize its details, then that is an instance of sensory memory. Usually, in these cases, when you are only able to see something for a few split seconds, you might feel like you saw a lot more than you are able to describe. Unlike short term and sensory memories, which disappear in a brief amount of time, long term refers to memories that can be stored for a period of up to several years. Psychologists disagree on how long term memory works. Some argue that a long term memory remains in the brain forever, but this is impossible to prove, as there has never been a human being who has lived forever!

Visual short term memories are memories containing visual data that are stored temporarily over an extended period. There is also a type of memory that is referred to as working memory. It can be viewed as a form of short term memory, in that it refers to the limited store that is needed in order for certain mental tasks to be performed. Whereas short term memory is rooted in duration, working memory is defined by purpose. Baddeley’s Model of Working Memory defines three components to this type of memory – the verbal store, the visuo-spatial sketchpad, and the central executive, which determines control and rehearsal.

Using a special experiment involving a “partial report paradigm,” the researcher George Sperling conducted some vital experiments in the realm of sensory memory. Sperling arranged a dozen letters in to three rows of four. He then played either a low, medium, or high tone, which would be their cue for what row of letters they were supposed to recite. The result of this experiment was that most humans can process at least twelve items with sensory memories, but that this begins to degrade at quite a rapid pace.

The main difference between a sensory memory and a visual short term memory is that, while the former are delicate, tend to decay very quickly, and are not able to be maintained, the latter respond to certain forms of stimuli and can remain alive in the mind for a period of more than a few seconds.

The study of visual short term memories was revolutionized in the 1970s. The experiment that took place in the early part of that decade involved asking participants to identify whether figures they had just seen a brief while before were the same or different. The result was that some visual information indeed had been stored. However, there were several questions left open by these experiments, namely whether only a subset of the visual stimulus’s perceptual dimensions are stored. Also unclear was whether or not some elements are better stored in the visual short term memory than others. It was also not resolved how exactly these aspects are encoded in the visual short term memory.

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