MaskingA series of images is presented below; the speed and fidelity of your experience will depend on your computer system. Each of the first two images has a sequenced display of a centered "X", a 4 x 3 array of letters, a circular mask surrounding the area in which one of the letters was previously displayed, a bar marker, and a blank, textured field. The sequence in the third image is the same, except for the omission of the mask from the sequence. Read the information for an image, look at the center of the image, stare at the X that appears in the middle of the figure area, and recall from memory the contents of the row indicated by the bar marker cues. Masked and metacontrast masked stimuli will be difficult or impossible to recall if you hold your fixation on the "X". You may experience the erasure phenomenon. You may also experience the commonly reported experience that you saw a lot more than you can recall. | |
 Metacontrast example - Fixate on the "X" and recall the row of stimuli to the left of the "red" bar marker. |
 The mask is displaced relative to the recall cue. These examples help to illustrate that STSM is spatially organized. Fixate on the "X" and recall the row of stimuli to the left of the "red" bar marker. |
 Example without masking - Fixate on the "X" and recall the row of stimuli to the left of the "red" bar marker. |
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Sperling (1960) and Averbach & Coriell (1961) reported phenomena that were later studied extensively as indications of STSM (Short Term Sensory Memory). STSM has been demonstrated to persist for a briefer duration (about .25 to .3 seconds) than STM (Short Term Memory - about 30 seconds without rehearsal). STSM has also been demonstrated to be richer in content and capacity than STM. Phenomena related to STSM can be classified as illusory in that a) there is a discrepancy between the physical stimulus and experience, b) people often report surprise at seeing a greater richness of content in brief visual displays than they are able to report, and c) people can experience a surprising erasure phenomenon when the contents in some regions of STSM are selectively masked. Masking occurs when two stimuli are presented in sequence and the presentation of the latter stimulus interferes with processing and consolidation of the first stimulus. A category of masking, called metacontrast masking, can be defined as interference to processing of the first stimulus by presentation of the second stimulus in conditions where there is no contour overlap between the stimuli. | |
| The figures below present a sequence of images that are the same, except for the row indicated for your recall by the bar marker. The sequences contain a plain white field, an "X" overlay on the white field, a 3 x 4 array of pictures, a nonuniform black mask that is displayed in the location previously occupied by one of the 12 pictures, a white field with a bar marker, and a plain white field. | |
 The bar marker points to a row other than one in which a stimulus is masked. If you keep your gaze on the center, you will be able to report all of the stimuli in the row by name. |
 The bar marker points to a row in which a stimulus is masked. If you keep your gaze on the center, it will be difficult to see the stimulus masked by the black overlay. |
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If you have access to a research database or research journals, you can find thousands of articles related to masking and metacontrast phenomena. Two foundation articles include: Averbach, E. & Coriell, A. S. (1961). Short-term memory in vision. Bell System Technical Journal, 40, 309-328. and Sperling, G. (1960). The information available in brief visual presentations. Psychological Monographs, 74, (Whole No. 498). On the WWW, some of the publicly available resurces include: Sperling brief note George Sperling publications Greg Francis simulations Greg Francis article Greg Francis article
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