426 Sensory and Working Memory
requirements, so it is reasonable to expect differences. For
example, a synchrony judgment task does not require one to
extract meaningful information from the display, such as let-
ter identities, and the partial report technique requires one to
allocate attention selectively to the cued location in the visual
display (Dixon, Gordon, Leung, & Di Lollo, 1997). Few
studies have attempted to compare the different techniques
directly, but there is some indication that the partial report
technique may be measuring something qualitatively differ-
ent from what is tapped by the other techniques (Loftus &
Irwin, 1998).
Inverse Effects
Most forms of sensory persistence, at least as studied by the
majority of measurement techniques, do show common char-
acteristics. For example, the duration of persistence is in-
versely related to target stimulus duration and intensity.
Efron (1970) found that people were quite accurate at judging
stimulus offset as long as the target stimulus was presented
for at least 150 ms. In general, as the duration of the target
stimulus increases, people experience less persistence. The
duration of persistence also shortens as the intensity of the
target stimulus increases: For example, brighter stimuli lead
to shorter persistence effects. One interpretation of these
results is that the target stimulus, at onset, initiates a period of
neural activity that lasts for a few hundred milliseconds. If
the physical stimulus is removed prior to the completion
of this neural response, the stimulus will appear to persist
until the response function is complete. If the duration of the
stimulus itself exceeds the neural response time, or if some
other factor, such as intensity, effectively shortens the neural
response time, then no persistence effects will be found.
Neural Dynamics
At present, there is no consensus on the proper interpretation
of these persistence effects. However, the idea that people
have special sensory memory stores, designed to maintain lit-
eral copies of sensory input as an aid to subsequent percep-
tual processing, is losing favor among researchers. Instead,
persistence effects are widely believed to result from the dy-
namics of neural processing, perhaps simply as an artifact of
systems that are designed to accomplish more general ends.
For example, Francis (1999) has proposed that visual persis-
tence effects accrue from a general mechanism of excitatory
feedback in cortical neural circuits; the duration of persis-
tence, in turn, is driven by cortical “reset” signals that
dampen, or inhibit, the feedback. Increases in stimulus dura-
tion or intensity increase the strength of the reset signals,
thereby affecting the perceived duration of persistence (see
also Grossberg, 1994).
To the extent that persistence effects are caused by general
neural mechanisms, one might expect to find similar effects
across all modalities. As discussed, there do indeed appear to
be common performance characteristics across modalities,
but more research needs to be conducted. Moreover, for
methodological reasons, it is difficult to investigate persis-
tence effects in some modalities; consider, for example, the
inherent difficulties involved in controlling the presentation
duration of an olfactory or gustatory stimulus. For this rea-
son, little work has been conducted on modalities other than
vision and audition. New techniques are in development,
particularly techniques designed to tap neural processing
(see Näätänen & Winkler, 1999), so answers may be on the
horizon.Modality and Suffix EffectsThe evidence gleaned from the partial report technique, as
well as the other measures of persistence, was used in the
1960s and 1970s to support the proposal of specialized sen-
sory memory stores—that is, iconic memory for visual stim-
uli and echoic memory for auditory memory. These memory
stores, in turn, were widely believed to contribute to perfor-
mance in a number of perceptual and mnemonic tasks. In im-
mediate serial recall, for example, a persisting auditory, or
echoic, trace was thought to underlie the modality effect,
which is the large recency advantage that one typically sees
for lists presented aloud (Corballis, 1966). An extensive liter-
ature developed to explain how factors influenced the size of
the modality effect, purportedly for the reason of understand-
ing the characteristics of auditory sensory memory.Precategorical Acoustic StorageCrowder and Morton (1969) proposed that lingering echoic
information was held in precategorical acoustic storage
(PAS), a limited-capacity sensory store capable of holding a
few auditory items. Unlike visual sensory memory, which
decayed very rapidly, the contents of PAS were believed to
last for several seconds, allowing a subject time to give the
last one or two items in a memory list a kind of once-over
prior to recall. This provided an end-of-the list advantage for
aurally presented items because the subject could use the
echoic information in PAS to correct selective information in
short-term (or working) memory (see Crowder, 1976). A re-
lated empirical phenomenon, the suffix effect, provided sup-
porting evidence: If an auditory list is followed by another
redundant spoken item, such as the word recall,the auditory