Selective masking and processing strategy

A patterned masking stimulus was presented immediately following a 100-ms exposure of a centrally-fixated, eight-letter row. The bar-marker probe, indicating which letter to report, appeared either at onset (simultaneous cue), or at offset (delayed cue) of a letter row. A selective-masking effect--greater masking at the centre positions than at the ends of a row--was obtained with the delayed cue. With the simultaneous cue, all positions were masked and there was no selective-masking effect. These results indicate that the effects of a patterned masking stimulus are dependent upon the processing strategy, and they support previous interpretations of selective masking which state that it is produced by an ends-first processing strategy.     

Processing of information about location in brief visual displays

Within the context of the selective masking effect (Merikle, Coltheart, & Lowe, 1971), a series of five experiments investigated the utility of bar-marker probes as a poststimulus sampling procedure for partial report of brief visual displays. It was demonstrated that bar markers are inadequate as partial-report cues because subjects cannot properly locate the positions of the probes. An improved bar-marker procedure was developed which removed this problem of cue localization. Furthermore, it was shown that subjects, when given the opportunity, are able to report much more from brief visual displays than the bar-marker procedure typically permits. It was also suggested that subjects’ ability to employ bar-marker probes is governed by quite different factors than their capacity to report the contents of brief visual displays.     

Temporal aspects of selective masking

In two experiments, rows of random letter sequences were presented for 100 ms and were patterned masked at varying delays after display offset. In Experiment I recall was probed by visual partial report cues, while auditory probes were employed in Experiment II. Compared to no-masking control conditions, the masking stimulus had a selective effect at the different positions of the rows. The masking stimulus produced the largest decrements in recall of letters from the centre positions of the displays but had a minimal effect on performance at either end of the rows. Furthermore, it was demonstrated that improvements in recall were limited to the centre positions of the rows at increased delays of mask. Subsidiary analyses revealed that processing of the end letters of the displays terminates shortly after display offset while processing of the centre letters continues for at least 500 ms. The results are consistent with the notion that processing of multi-letter arrays commences at the ends of the rows and that the selective masking effect reflects the order of processing of the contents of iconic memory. However, these results were evident only in Experiment II which employed auditory partial report cues. When the partial report cues were visual, there were no effects of masking and minimal increases in performance at increased delays of mask. The discrepant results of the two experiments are discussed in terms of process interruption caused by obligatory attention to the partial report cues.     

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.     

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.     

Searching for a pre-specified target letter in briefly displayed words and unpronounceable non-words

Two experiments were designed in which subjects searched briefly displayed and masked arrays of letters for a single pre-specified target. The target was randomly located at one of twelve positions, its identity remained constant throughout, and it was embedded either in the context of words or in a context of unpronounceable strings of letters. In experiment 1 the letters were arranged in two six-item rows, and word and non-waord displays were mixed and presented to a single group of subjects. Accuracy of search was superior when the letters formed words, both for responses scored for correct position and for responses scored for correct row. In experiment 2 word and non-word displays were presented to different groups of subjects, and for both groups the twelve characters were either arranged as before in two rows or were positioned at loci representing the clock positions. Accuracy of search was again superior when the letters formed words and were arranged in rows, but there was no advantage for words when the letters formed a circle. These findings, firstly, indicated that the “word-superiority effect” obtained in experiment 1 was not a result of subjects adopting a word processing strategy for all stimuli, and secondly, they suggested that the word information could not be used to advantage in the absence of spatial cues delineating the words and/or when the letters were not positioned in the usual horizontal arrangement. It was concluded that the results of both studies were consistent with a perceptual account of the word superiority effect.     

Selective attention and target search with brief visual displays

In a series of four experiments, subjects were presented with eight item arrays tachistoscopically. In two tasks, the subject was required to recall a digit presented among seven letters or a letter among seven digits. The remaining tasks required the subject to detect the presence of a specific letter either in the context of seven random letters or seven digits. An examination of the effects of a masking stimulus for various target positions suggested that subjects could attend selectively when the target was a different category than its context but had to process the entire array when the target was the same category as the context. The effects of selective attention and masking are explained in terms of parallel and sequential identification processes.     

Identification,localization, and “iconic memory”: An evaluation of the bar-probe task

The partial report tachistoscopic task has been used to define “iconic memory,” a labile image-like precategorical visual store. Six interrelated partial report studies are reported that challenge the construct. On each trial, subjects were shown an eight-letter pseudoword (representing one of four orders of approximation to English) and a bar probe indicating which letter to report. The probe was delayed systematically, and the experiments included both mask and no-mask conditions. All three variables-familiarity of the material, masking, and delay of the probe-affected accuracy of report. Delaying the probe, for example, reduced accuracy by increasing location errors. Delaying the mask increased accuracy by reducing both location and item errors, but it did not reduce the location errors until its effect on item errors had reached asymptote. Across the stimulus array, however, masking reduced accuracy at all delays by increasing location errors. Finally, the greater accuracy associated with higher orders of approximation to English was complemented by a decrease in item errors, but the familiarity factor had no effect on location errors. Taken together, even though the task has been used to define the idea, the results indicate that the bar-probe task cannot be explained in terms of a simple iconic memory concept. Instead of a simple image-like buffer, the explanation requires a feature buffer, an “intelligent” letter identification process, and a postidentification character buffer. Iconic memory is a construct that oversimplifies the information processing system used in the bar-probe task.     

Perceptual processing in dichotic listening.

Subjects heard two lists of 4 items each presented simultaneously to the two ears at a rate of four pairs of items per sec. A recall cue presented immediately after the test list signalled report of 4 of the 8 items. In recall by spatial location, the cue indicated whether the items on the right ear on left ear should be recalled. In recall by category name, the cue indicated the superset category (e.g., letters or words) of the items to be recalled. Recall by spatial location was not significantly different than recall by category name. This results argues against the idea of a preperceptual auditory storage that holds information along spatial channels for 1 or 2 sec. The final experiment showed that recall by spatial location is significantly better than recall by category name when the report cue is given before, not after, the list presentation. These results show that spatial location can be used to enhance semantic processing and/or memory of 1 of 2 simultaneous items, but only if the relevant location is known at the time of the item presentation.     

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.     

Processing order in visual perception

Initial increases in the availability of items for report following tachistoscopic presentation of centrally-fixated rows of seven random letters were directly evaluated by measuring report accuracy following exposure durations of 10, 20, 40, 80 and 160 ms. A partial-report technique was used, and each presentation of a letter row was immediately followed by the presentation of a masking stimulus. Each of 10 subjects received 840 trials which reflected 24 trials for each exposure-duration by position-probed combination. The letters at both ends of a row became available for report prior to the centre letters. In addition, report of the left-most letter was consistently better than report of the right-most letter, and report of the centre item at fixation improved at a more rapid rate with increased exposure duration than report of the other centre letters. This pattern of results provides support for certain components of several different previous proposals concerning the order in which individual items from multi-element displays become available for report.     

Components of the laterality effect in letter recognition: Asymmetries in iconic storage

A partial report procedure and a backward masking paradigm were employed to explore lateral asymmetries in components of letter recognition. Stimulus displays were displaced off-centre into the left visual field (LVF) or the right visual field (RVF). Visual field differences in the effect of a delayed backward mask indicated an RVF superiority in the rate of read-out or encoding. Comparison of masked and unmasked full report also yielded estimates of iconic persistence. The persistence of these peripheral displays was surprisingly brief, although it was significantly longer in the LVF (₅₇ ms) than in the RVF (₃₄ ms). Precueing by colour and by location produced a larger partial report advantage in the RVF, reflecting a superiority in selective sampling. With postcueing no partial report effect was obtained at any delay, and this failure was attributed to the briefness of the iconic persistence.     

Attentional factors in iconic memory and visible persistence

Arrays of 12 fragmentary letters were followed, at various intervals, by one randomly selected complementary letter fragment. On half the trials a partial-report cue (a vertical bar-marker) coincided with the second completion fragment. In Experiment 1 subjects fixated the centre of the to-be-identified letter location, whereas in Experiment 2 subjects fixated the centre of the array. In Experiment 1, the degree of integration and time between successive fragments were inversely related. Integration of fragmentary letters in Experiment 2, however, was uniformly low in the experimental and guessing control conditions. The results were discussed in terms of recent non-traditional accounts of iconic storage that emphasize post-categorical processing.     

Efficient visual search by category: Specifying the features that mark the difference between artifacts and animals in preattentive vision

In this report, we explored the features that support visual search for broadly inclusive natural categories. We used a paradigm in which subjects searched for a randomly selected target from one category (e.g., one of 32 line drawings of artifacts or animals in displays ranging from three to nine items) among a mixed set of distractors from the other. We found that search was surprisingly fast. Target-present slopes for animal targets among artifacts ranged from 10.8 to 16.0 msec/item, and slopes for artifact targets ranged from 5.5 to 6.2 msec/item. Experiments 2–5 tested factors that affect both the speed of the search and the search asymmetry favoring detection of artifacts among animals. They converge on the conclusion that target-distractor differences in global contour shape (e.g., rectilinearity/curvilinearity) and visual typicality of parts and form facilitate search by category. We argue that existing theories are helpful in understanding these findings but that they need to be supplemented to account for the specific features that specify categories and to account for subjects’ ability to quickly locate targets representing heterogeneous and formally complex categories.     

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.     

Selective Masking and The “Lamp-Phosphor” Problem

Mollon and Polden (1978) have suggested that selective backward masking, the greater masking of central than peripheral items in briefly-presented letter rows by a patterned stimulus, may be due to an advantage conveyed to the peripheral items by the more rapid onset of the short wavelengths emitted by tachistoscope lamps. This suggestion was evaluated by comparing report accuracy under mask and no mask conditions when the tachistoscope fields were viewed through yellow or red filters that eliminated all wavelengths below 510 and 590 nm, respectively. The results showed similar selective-masking effects with both filters. Since selective masking occurs even when the short wavelength emissions are eliminated, Mollon and Polden's suggested explanation for selective masking must be rejected.     

Phonemic and semantic generation norms

Independent groups of subjects generated restricted free associations that either rhymed with the cue or were members of the semantic category designated by the cue. The data include both a listing of the responses to each cue and a cross-index of all words appearing as responses to more than one cue. These data will permit researchers to take into account the a priori associative strength between cues and targets at these two levels of processing.     

Task probability and report of feature information: What you know about what you ‘see’ depends on what you expect to need

We investigated the influence of dimensional set on report of object feature information using an immediate memory probe task. Participants viewed displays containing up to 36 coloured geometric shapes which were presented for several hundred milliseconds before one item was abruptly occluded by a probe. A cue presented simultaneously with the probe instructed participants to report either about the colour or shape of the probe item. A dimensional set towards the colour or shape of the presented items was induced by manipulating task probability — the relative probability with which the two feature dimensions required report. This was done across two participant groups: One group was given trials where there was a higher report probability of colour, the other a higher report probability of shape. Two experiments showed that features were reported most accurately when they were of high task probability, though in both cases the effect was largely driven by the colour dimension. Importantly the task probability effect did not interact with display set size. This is interpreted as tentative evidence that this manipulation influences feature processing in a global manner and at a stage prior to visual short term memory.     

Family resemblances: Studies in the internal structure of categories

Six experiments explored the hypothesis that the members of categories which are considered most prototypical are those with most attributes in common with other members of the category and least attributes in common with other categories. In probabilistic terms, the hypothesis is that prototypicality is a function of the total cue validity of the attributes of items. In Experiments 1 and 3, subjects listed attributes for members of semantic categories which had been previously rated for degree of prototypicality. High positive correlations were obtained between those ratings and the extent of distribution of an item's attributes among the other items of the category. In Experiments 2 and 4, subjects listed superordinates of category members and listed attributes of members of contrasting categories. Negative correlations were obtained between prototypicality and superordinates other than the category in question and between prototypicality and an item's possession of attributes possessed by members of contrasting categories. Experiments 5 and 6 used artificial categories and showed that family resemblance within categories and lack of overlap of elements with contrasting categories were correlated with ease of learning, reaction time in identifying an item after learning, and rating of prototypicality of an item. It is argued that family resemblance offers an alternative to criterial features in defining categories.     

Efficient visual search by category: specifying the features that mark the difference between artifacts and animals in preattentive vision.

In this report, we explored the features that support visual search for broadly inclusive natural categories. We used a paradigm in which subjects searched for a randomly selected target from one category (e.g., one of 32 line drawings of artifacts or animals in displays ranging from three to nine items) among a mixed set of distractors from the other. We found that search was surprisingly fast. Target-present slopes for animal targets among artifacts ranged from 10.8 to 16.0 msec/item, and slopes for artifact targets ranged from 5.5 to 6.2 msec/item. Experiments 2-5 tested factors that affect both the speed of the search and the search asymmetry favoring detection of artifacts among animals. They converge on the conclusion that target-distractor differences in global contour shape (e.g., rectilinearity/curvilinearity) and visual typicality of parts and form facilitate search by category. We argue that existing theories are helpful in understanding these findings but that they need to be supplemented to account for the specific features that specify categories and to account for subjects' ability to quickly locate targets representing heterogeneous and formally complex categories.