Prolonging the Present: Sensory Memory 425Figure 15.1 Percent correct identification performance in a simple audi-
tory backward masking experiment, plotted as a function of the delay of the
masking tone. The data are shown separately for three individual subject
(after Massaro, 1970). Reprinted with permission.
Many researchers find it compelling that similar masking
functions are found for visual and auditory stimuli (Cowan,
1995; Massaro, 1975); furthermore, the estimated duration
derived from backward masking—250 ms—roughly corre-
sponds to the phenomenological duration tapped by the syn-
chrony judgment task. Other persistence tasks yield similar
duration estimates. For example, in a temporal integration
task,subjects are asked to identify a missing element in an
array of elements (e.g., Di Lollo, Hogben, & Dixon, 1994).
Presentation of the array unfolds over time: Subjects receive
a random half of the elements at Time 1 and the second half
after a brief, but variable, delay. Successful performance re-
quires perceptual integration of the two halves, which seems
to occur only if the two halves are separated by fewer than
100–200 ms.
The Partial Report Technique
The measurement technique most commonly associated with
sensory memory, particularly visual sensory memory, is the
partial report procedure developed by Sperling (1960; see
also Averbach & Coriell, 1961). When people are presented
with a visual display of letters—for example, a three-by-four
array of 12 letters—for a very brief duration—say, around
50 ms—roughly 3 or 4 letters can be reported correctly. Peo-
ple can presumably process only a limited amount of infor-
mation in 50 ms, so this result may not seem surprising.
However, people report the clear sensation of seeing the
entire display, with all 12 letters, but the display fades before
all the letters can be reported. Sperling (1960) set out to mea-
sure the persistence of the display, which he believed tapped
a form of visual sensory memory.
Sperling’s first challenge was to document that people
do, in fact, have more than three or four letters available
following the offset of the display. He devised a partial report
condition, which required the reporting of only part of the
display rather than all 12 letters (hence the name partial
report). After the display was turned off, one of three audi-
tory cues sounded—a high-, medium-, or low-pitched tone—
which signaled the subject to recall only one of the three rows
of letters. Because the cue was presented after the display
was physically terminated, average row performance could
be used to estimate availability of the display as a whole.
Sperling discovered that, indeed, people have much more
display information available than the three to four letters
tapped by whole report.
The partial over whole report advantage is important, but
it does not, by itself, establish the presence of sensory mem-
ory. For one thing, fewer items need to be recalled under par-
tial report (4 instead of 12 letters), so some kind of recall (or
output) interference could be contributing to the condition
differences. Of main interest is the finding that the partial re-
port advantage declines rapidly with the insertion of a delay
between display offset and the occurrence of the recall cue.
Sperling found that the advantage was eliminated if the recall
cue was delayed for 1 s after offset of the display, and it was
sharply reduced after a few hundred milliseconds. The infer-
ence is that the visual display persists, as a sensory or iconic
memory, for a brief period following offset, allowing the sub-
ject to continue processing its contents. Note that the estimate
of duration derived from the partial report technique is
slightly longer than, but in the same ballpark as, the estimates
of persistence derived from the other procedures described
previously.
Considerable work has been conducted using the partial re-
port task over the past 40 years (see Greene, 1992; Massaro,
1975; Neath, 1998, for general reviews). Auditory versions of
the task indicated initially that auditory sensory memory
might last considerably longer than visual sensory memory
(on the order of seconds rather than milliseconds; e.g.,
Darwin, Turvey, & Crowder, 1973), but methodological con-
cerns cloud this conclusion (see Massaro, 1975). Other influ-
ential work has studied the particulars of the errors that occur
in the task as the recall cue is delayed. It turns out that people
primarily make location errors with delay: That is, the identi-
ties of the letter are not lost, but, rather, people become con-
fused about the row the letters occupied (Mewhort, Campbell,
Marchetti, & Campbell, 1981).The Characteristics of Sensory PersistenceIt is not yet certain whether each of the tasks just described
really measures the same psychological construct—that is, a
decaying sensory memory. Each has somewhat different task