Iconic memory, location information, and partial report

It has been suggested that the systematic decline of partial report as the delay of the partial-report cue increases is due to a time-related loss of location information. Moreover, the backward masking effect is said to be precipitated by the disruption of location information before and after identification. Results from three experiments do not support these claims when new indices of location information and of item information are used. Instead, it was found that the systematic decline in partial report was due to a time-related loss of item information, and location information was affected neither by the delay of the partial-report cue nor by the delay of backward masking. Subjects adopted the "select-then-identify" mode of processing.     

Iconic memory of dot patterns: preliminary report.

Pairs of complementary dot-pattern stimuli whereby each stimulus pair forms a bigram were used in an iconic memory paradigm. The variables of stimulus duration, interstimulus interval, dot density, and letter field were all shown to affect recognition performance of 15 naive college students.     

Iconic memory and visible persistence

There are three senses in which a visual stimulus may be said to persist psychologically for some time after its physical offset. First, neural activity in the visual system evoked by the stimulus may continue after stimulus offset (“neural persistence”). Second, the stimulus may continue to be visible for some time after its offset (“visible persistence”). Finally, information about visual properties of the stimulus may continue to be available to an observer for some time after stimulus offset (“informational persistence”). These three forms of visual persistence are widely assumed to reflect a single underlying process: a decaying visual trace that (1) consists of afteractivity in the visual system, (2) is visible, and (3) is the source of visual information in experiments on decaying visual memory. It is argued here that this assumption is incorrect. Studies of visible persistence are reviewed; seven different techniques that have been used for investigating visible persistence are identified, and it is pointed out that numerous studies using a variety of techniques have demonstrated two fundamental properties of visible persistence: theinverse duration effect (the longer a stimulus lasts, the shorter is its persistence after stimulus offset) and theinverse intensity effect (the more intense the stimulus, the briefer its persistence). Only when stimuli are so intense as to produce afterimages do these two effects fail to occur. Work on neural persistences is briefly reviewed; such persistences exist at the photoreceptor level and at various stages in the visual pathways. It is proposed that visible persistence depends upon both of these types of neural persistence; furthermore, there must be an additional neural locus, since a purely stereoscopic (and hence cortical) form of visible persistence exists. It is argued that informational persistence is defined by the use of the partial report methods introduced by Averbach and Coriell (1961) and Sperling (1960), and the term “iconic memory” is used to describe this form of persistence. Several studies of the effects of stimulus duration and stimulus intensity upon the duration of iconic memory have been carried out. Their results demonstrate that the duration of iconic memory is not inversely related to stimulus duration or stimulus intensity. It follows that informational persistence or iconic memory cannot be identified with visible persistence, since they have fundamentally different properties. One implication of this claim that one cannot investigate iconic memory by tasks that require the subject to make phenomenological judgments about the duration of a visual display. In other words, the so-called “direct methods” for studying iconic memory do not provide information about iconic memory. Another implication is that iconic memory is not intimately tied to processes going on in the visual system (as visible persistence is); provided a stimulus is adequately legible, its physical parameters have little influence upon its iconic memory. The paper concludes by pointing out that there exists an alternative to the usual view of iconic memory as a precategorical sensory buffer. According to this alternative, iconic memory is post-categorical, occurring subsequent to stimulus identification. Here, stimulus identification is considered to be a rapid automatic process which does not require buffer storage, but which provides no information about episodic properties of a visual stimulus. Information about these physical stimulus properties must, in some way, be temporarily attached to a representation of the stimulus in semantic memory; and it is this temporarily attached physical information which constitutes iconic memory.     

Iconic memory and central processing capacity

Three experiments were conducted to assess whether or not iconic memory is influenced by demands placed upon central processing capacity. In Experiment 1 S was required to store material in short-term memory while performing an iconic memory task. In Experiments 2 and 3 S performed an auditory classification task concurrently with iconic storage. The three experiments did not reveal any significant impairment of iconic memory as a function of performing a subsidiary task. Similarly, performance on the subsidiary tasks did not suffer as a result of the concurrent iconic memory task.     

Iconic gestures prime words

Using a cross-modal semantic priming paradigm, both experiments of the present study investigated the link between the mental representations of iconic gestures and words. Two groups of the participants performed a primed lexical decision task where they had to discriminate between visually presented words and nonwords (e.g., flirp). Word targets (e.g., bird) were preceded by video clips depicting either semantically related (e.g., pair of hands flapping) or semantically unrelated (e.g., drawing a square with both hands) gestures. The duration of gestures was on average 3,500 ms in Experiment 1 but only 1,000 ms in Experiment 2. Significant priming effects were observed in both experiments, with faster response latencies for related gesture-word pairs than unrelated pairs. These results are consistent with the idea of interactions between the gestural and lexical representational systems, such that mere exposure to iconic gestures facilitates the recognition of semantically related words.     

Iconic storage in the two hemispheres

Three experiments have tested for the existence of laterality effects in iconic storage by employing a Sperling partial-report paradigm and lateralized presentations of alphabetical or pattern material. Even though an overall laterality effect was found in favor of the right visual field for the alphabetical material and in favor of the left visual field for the pattern material, the amount and time decay of partial-report advantage was similar in the two visual fields. These results indicate that hemispheric asymmetries occur beyond the iconic stage of visual information processing.     

Stimulus duration may affect partial report performance

Townsend, and Di Lollo and Moscovitch investigated the retention of item information in nearly identical variations of the partial report task. Whereas Townsend found a slight decrement in performance as the interval increased, Di Lollo and Moscovitch found a substantial increment. An experimental study of procedural differences that may have led to this discrepancy is reported. The results suggest that stimulus duration may have been responsible: Di Lollo and Moscovitch used extremely short durations (2 ms), while Townsend used longer durations (50 ms). This difference in durations may be important when the stimulus array and the partial report probe occur in close temporal contiguity.     

Inverse duration effects in partial report.

In partial-report experiments, an array of stimuli is displayed briefly, followed by a probe indicating the items to be reported. When exposure duration of the array is increased, 2 contrasting outcomes have been found: Some experiments find that performance improves (direct-duration effect); others find that it deteriorates (inverse-duration effect). The objective here was to identify the reasons for the discrepant results. This was done by investigating the roles played by 5 factors that differed between the 2 sets of contrasting studies. An inverse-duration effect was obtained in each of 6 experiments; its magnitude was affected by retinal eccentricity and by the number of items denoted by the probe. The effect was independent of array configuration and of number of items in the array. The direct-duration effect was shown to arise from a confounding of exposure duration and brightness.     

Iconic memory: A reply to Professor Holding

Professor Holding has argued that the partial report superiority normally taken as evidence for the existence of iconic memory might instead be due to cue anticipation or output interference. I have suggested that both of these alternative explanations are inconsistent with the finding that the partial report superiority diminishes rapidly with increasing cue delay. In addition, Sperling’s original partial report experiment was designed in such a way that cue anticipation could not have occurred; and both his results with selection by letter vs number and Averbach and Coriell’s bar-marker results indicate that output interference effects are absent or negligible in tachistoscopic experiments. Consequently, I have concluded that the partial report superiority, and especially its decline with increasing delay, remains as strong evidence in favor of the conventional view of iconic memory. Furthermore, if this view were wrong, there would remain no way of giving a satisfactory account of (a) Averbach and Coriell’s results, (b) “direct” investigations of visual persistence, or (c) integration and interruption effects in backward visual masking.     

Task requirement and hemifield asymmetry in tachistoscopic partial report performance

It was hypothesized that the amount and direction of differences in tachistoscopic recognition accuracy for the right and the left visual hemifield should depend on the degree to which a partial report task requires exhaustive processing of the test stimulus. Position curves for single-item report were examined using four different tasks. In the Arrow task, Ss had to report a letter which was designated by a bar marker. In the Number task, the position of the critical letter was indicated by the digits 1–8. In the Letter task, the cue stimulus was a letter, and Ss were required to report its position in the test stimulus. In the Alphabetic task, a report on the alphabetically first letter of the test stimulus was required. The tasks were designated to encourage either selective processing (Arrow and Number tasks) or exhaustive processing (Letter and Alphabetic tasks). Right-hemifield superiority was predicted for selective processing, and left-hemifield superiority for exhaustive processing. The predictions were confirmed for the Arrow and Alphabetic tasks. A complete account of the position curves in the Number and Letter tasks required a consideration of the effects of the semantic nature of the cue stimulus and/or the spatial arrangement of cue stimulus and test stimulus. It was concluded that the processing operations underlying partial report are more complex than had been assumed previously.     

The phonological store abandoned

Baddeley and Larsen (2007) argue that a number of key findings reported by Jones, Macken, and Nicholls (2004) and Jones, Hughes, and Macken (2006) pointing to shortcomings of the phonological store construct arise from the store being abandoned with long lists. In our rejoinder we point out that Baddeley and Larsen use a procedure in which retrieval from the supposed phonological storage would not—according to their own theory—have been possible, and we present theoretical, empirical, and logical problems with their “store abandonment” argument and highlight a number of difficulties associated with the interpretation of suffix and prefix effects. We conclude that our data are still problematic for the phonological store construct and suggest that a reformulation of short-term memory theory needs to embody (or indeed focus exclusively upon) perceptual and effector systems rather than bespoke storage modules.     

The phonological store abandoned

Baddeley and Larsen (2007) argue that a number of key findings reported by Jones, Macken, and Nicholls (2004) and Jones, Hughes, and Macken (2006) pointing to shortcomings of the phonological store construct arise from the store being abandoned with long lists. In our rejoinder we point out that Baddeley and Larsen use a procedure in which retrieval from the supposed phonological storage would not—according to their own theory—have been possible, and we present theoretical, empirical, and logical problems with their “store abandonment” argument and highlight a number of difficulties associated with the interpretation of suffix and prefix effects. We conclude that our data are still problematic for the phonological store construct and suggest that a reformulation of short-term memory theory needs to embody (or indeed focus exclusively upon) perceptual and effector systems rather than bespoke storage modules.     

Iconic gestures prime related concepts: An ERP study

To assess priming by iconic gestures, we recorded EEG (at 29 scalp sites) in two experiments while adults watched short, soundless videos of spontaneously produced, cospeech iconic gestures followed by related or unrelated probe words. In Experiment 1, participants classified the relatedness between gestures and words. In Experiment 2, they attended to stimuli, and performed an incidental recognition memory test on words presented during the EEG recording session. Event-related potentials (ERPs) time-locked to the onset of probe words were measured, along with response latencies and word recognition rates. Although word relatedness did not affect reaction times or recognition rates, contextually related probe words elicited less-negative ERPs than did unrelated ones between 300 and 500 msec after stimulus onset (N400) in both experiments. These findings demonstrate sensitivity to semantic relations between iconic gestures and words in brain activity engendered during word comprehension.     

Iconic and non-iconic stages in number development: the role of language

Is language the key to number? This article argues that the human language faculty provides the cognitive equipment that enables humans to develop a systematic number concept. Importantly, the number concept is based on non-iconic representations that involve relations between relations: relations between numbers are linked with relations between objects. In contrast to this, language-independent numerosity concepts provide only iconic representations. The pattern of forming relations between relations lies at the heart of our language faculty, suggesting that it is language that enables humans to make the step from these iconic representations, which we share with other species, to a generalized concept of number.     

Two visual stores and two processing operations in tachistoscopic partial report

A two-stage interpretation of the processes underlying tachistoscopic partial report performance is suggested. It is assumed that partial report is mediated by two kinds of visual store (a sensory store and a short-term store) and by two processing operations (selection and naming). In Experiment I, the accuracy and latency of two types of partial report (report by location and report by colour) were compared for cue stimulus-test stimulus intervals ranging from --500 ms to + 500 ms. It was concluded that selection by colour takes longer than selection by location; an explanation in terms of differential decay of attributes in the sensory store was rejected. In Experiment II, cue stimulus delays of 0, 150 and 300 ms were employed, and a backward masking stimulus followed the cue stimulus with a delay of 200, 300, 400 or 600 ms. The amount of masking depended on the cue stimulus-masking stimulus interval, rather than on the test stimulus-masking stimulus interval. It was concluded that selection operates on the sensory store and that backward masking can affect the naming of a stimulus representation which is residing in the visual short-term store.     

Iconic memory and its relation to perceptual processing and other memory mechanisms

Research on iconic memory is reviewed. Specific issues discussed include the duration of the icon, effects of stimulus variables, types of information lost, selection, processing capacity, and scanning. More general issues include the level of encoding in the icon and its relation to short-term memory. It is also argued that a number of experiments do not show what they were intended to show because of possible methodological problems. The view is developed that iconic memory is postretinal but uncoded; nor is it influenced directly by strategies or subsequent mechanisms.