Iconic Memory Test (demo of a classic psychophysics experiment by George Sperling on VSTM)

This is a demonstration of the 'classical' psychophysics experiment examining the human iconic memory buffer. In 1960, Sperling performed an experiment using a matrix with three rows of three letters. Participants of the study were asked to look at the letters, for a brief period of time, and then recall them immediately afterwards. This technique, called free recall showed that participants were able to, on average, recall 4-5 letters of the 9 they were given. This however, was already generally accepted in the psychological community, because it was understandable that people simply could not retain all the letters in their mind in such a brief period of time. Sperling, on the other hand, felt that they had encoded all of the letters in their mind, but had simply forgotten them while trying to recall this information on what they had seen. He believed that all 9 letters were stored in the viewer's memory for a short period of time, but the memory failed leading to only 4 or 5 being recalled. Sperling called this iconic memory. This was exemplified through Sperling's Iconic Memory Test. This test involves having a grid of letters being flashed for 1/20th of a second. If individuals were prompted to recall a particular row immediately after the grid was shown, opposed to being asked to recall the entire grid, participants experienced higher accuracy. This procedure demonstrated that although iconic memory can store the whole grid, information tends to fade away too rapidly for a person to recall all of the information. Sperling also showed this with his experiment of cued recall. This trial was similar to free recall, however, instead of allowing participants to recall any of the letters, it would allow them to view the same matrix for the same amount of time, and then hear a pitch corresponding to a different row in the matrix. The viewer was to recall the letters in that corresponding row. On average, viewers were able to recall more during cued recall trials than free recall.
Sperling became the first to use a partial report paradigm to investigate the bipartite model of visual short term memory (VSTM). In Sperling's initial experiments in the 1960s, observers were presented with a tachistoscopic visual stimulus for a brief period of time (between 20-50 ms) consisting of either a 3x3 or 3x4 array of alphanumeric characters such as:
P Y F G
V J S A
D H B U
Recall was based on a cue which followed the offset of the stimulus and directed the subject to recall a specific line of letters from the initial display. Memory performance was compared under two conditions: whole report and partial report.
WHOLE REPORT
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The whole report condition required participants to recall as many elements from the original display in their proper spatial locations as possible. Participants were typically able to recall three to five characters from the twelve character display (~35%).[2] This suggests that whole report is limited by a memory system with a capacity of four-to-five items.
Partial report
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The partial report condition required participants to identify a subset of the characters from the visual display using cued recall. The cue was a tone which sounded at various time intervals (~50 ms) following the offset of the stimulus. The frequency of the tone (high, medium, or low) indicated which set of characters within the display were to be reported. Due to the fact that participants did not know which row would be cued for recall, performance in the partial report condition can be regarded as a random sample of an observer's memory for the entire display. This type of sampling revealed that immediately after stimulus offset, participants could recall a given row (from a 3x3 grid of 9 letters) on 75% of trials, suggesting that 75% of the entire visual display (75% of 9-letters) was accessible to memory. This is a dramatic increase in the hypothesized capacity of iconic memory derived from full-report trials.
See also:
Echoic Memory

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