Attention and information storage in visual short-term memory

Schioldborg, P. Attention and information storage in visual short-term memory. Scand. J. Psychol., 1973, 14, 1–3.- Information retrieval from STM was examined with Sperling's (1960) method. Of nine letters displayed in rows of three, the number of letters correctly reported from each row differed significantly, the mean being 2.4, 2.2, and 1.6 letters for the middle, upper, and lower row, respectively. By increasing exposure time, number of correctly reported letters increased for each row at equal rate. However, by increasing the delay period of the selection signal, number of letters decreased at different rates, the reduction being 48%, 24%, and 10% for the lower, upper, and middle row respectively. The results are assumed to reflect differences in the initial attention level for the individual item; the smaller this level, the lower the level of information processing and the faster the erasure from STM.     

Developmental differences in intake and storage of visual information

A partial report technique was used to determine how much visual information subjects of four ages (ranging from 5-year-olds to adults) were capable of taking in and what the course of information loss was over a 1-sec time period. Subjects were tachistoscopically presented eight items followed by an indicator at variable intervals after array offset and were required to report that item in the indicated position. No reliable age differences were found at the earliest “memory point,” 50 msec. There were, however, age differences both before and after this point. Results suggested an absence of age differences in visual intake capacity, but important differences in other stages of processing.     

Task demands control acquisition and storage of visual information

Attention and working memory limitations set strict limits on visual representations, yet researchers have little appreciation of how these limits constrain the acquisition of information in ongoing visually guided behavior. Subjects performed a brick sorting task in a virtual environment. A change was made to 1 of the features of the brick being held on about 10% of trials. Rates of change detection for feature changes were generally low and depended on the pick-up and put-down relevance of the feature to the sorting task. Subjects' sorting decision suggests that changes may be missed because of a failure to update the changed feature. The authors also explore how hand and eye behavior are coordinated for strategic acquisition and storage of visual information throughout the task.     

Retinal location and string position as important variables in visual information processing

Three experiments were conducted to isolate the effects of retinal locus and string position in tachistoscopic letter recognition. Retinal locus proved to be an important variable even when its range was restricted to less than a degree from the center of the fovea. Performance was maximal at the center of the fovea, dropping off rapidly to about 1.5 deg from the center. From that distance on, the decline in performance was quite gradual. String position was also an important factor. Retinal locus and string position interacted in such a way that the end positions were less affected by retinal locus than the middle positions. It was also found that processing order, as distinct from report order, was a significant component of the string position effect.     

Retinal location and visual processing rate

Although previous studies have shown that the time required to process visual stimuli increases for presentations away from the fovea, the evidence concerning the exact nature of this increase is inconclusive. Three experiments were conducted using both reaction time and tachistoscopic masking tasks to generate time-accuracy functions for stimuli at different retinal locations. All results indicated that only the time intercept parameter of the time-accuracy function is affected by retinal location of stimulation. This finding suggests that it takes longer for information to become available to some decision mechanism with stimuli displaced away from the fovea, but that the actual rate of extracting information is not influenced by retinal locus of stimulation.     

Short-term visual storage

The delay between the offset of a briefly exposed array of letters and digits and the onset of an arrow pointing at one of the array positions was varied from 0 to 5000 msec. In addition, the luminance of the stimulus array was varied over three levels. The Ss reported the item in the position indicated by the arrow. Luminance, delay, and the luminance by delay interaction were all significant I Performance monotonically decreased from a delay of 0 msec to a delay of 250 msec, but the percent correct remained fairly constant from 250 msec to 5000 msec. With delays shorter than 250 msec, high luminance arrays showed better performance.     

Object-based representations govern both the storage of information in visual short-term memory and the retrieval of information from it

Interest is growing in how information is retained in visual short-term memory (VSTM). We describe an experiment that assesses VSTM within the context of multidimensional signal detection theory. On every trial, participants were presented with a 250-ms display containing four colored shapes. They were then probed 900 ms later with a colored shape and made separate old/new judgments about the color and the shape. In any particular trial, one, both, or neither of the probed features had been presented. Performance differed according to whether both probed features belonged to a single object or to two different objects. When both probed features belonged to the same object, featural retrieval was better than would be predicted by independent feature storage. When both probed features belonged to two different objects, featural retrieval was worse than would be predicted by independent feature storage. We conclude that storage in and retrieval from VSTM operate on the basis of object-based representations.     

Subjective pictorial information and visual search

The effects of a combination of variables previously studied in ordinary and dichotic immediate memory were examined in bisensory memory, wherein the visual and auditory modalities were employed. These variables. combined in a factorial design. were: (1) type of material; (2) rate of presentation of material; (3) order of recall for a modality. either first or second; (4) locus of instructions about order of report; and (5) overall differences in memory for each modality. The variables of instruction, order of report, and nature of materials yielded effects in the bisensory situation similar to those reported for the dichotic and ordinary immediate memory situations. On the other hand. interference effects due to the combination of materials in the two channels were practically nonexistent. Additionally, when the modalities were stimulated simultaneously each displayed curves predictable from data obtained when it was explored independently of the other modality.     

Two types of short-term visual storage

Seven-letter words were flashed repetitively at various durations above and below the recognition threshold for single flashes. One form of a short-term storage effect was studied by measuring the interstimulus interval between flashes at which S reported that the stimulus became phenomenally discontinuous in time. Storage times reached a maximum of about 300 msec in this task. A second form of storage effect was measured by decreasing the interstimulus interval until S could correctly recognize a repeated stimulus whose duration was below the single-flash recognition threshold; this effect extended to 900 msec in some cases. Each of these effects was reliably obtained for both rare and frequent words. Both forms of storage were increased by providing a dark rather than a lighted adapting field between presentations of the test stimulus. Implications for Information processing of brief displays are discussed.     

Dynamic visual noise interferes with storage in visual working memory

Several studies have demonstrated that dynamic visual noise (DVN) does not interfere with memory for random matrices. This has led to suggestions that (a) visual working memory is distinct from imagery, and (b) visual working memory is not a gateway between sensory input and long-term storage. A comparison of the interference effects of DVN with memory for matrices and colored textures shows that DVN can interfere with visual working memory, probably at a level of visual detail not easily supported by long-term memory structures or the recoding of the visual pattern elements. The results support a gateway model of visuospatial working memory and raise questions about the most appropriate ways to measure and model the different levels of representation of information that can be held in visual working memory.     

Depth of visual information processing

The depth of visual information processing is identified with the longest randomly-generated binary-encoded spatial pattern whose partial repetitions can be detected. In contrast with the auditory detection of sequentially-presented constraints, the depth of perceptible visual encoding of spatially-presented constraints is sharply limited. Depths of about 35 were achieved for one-dimensional constraints; depths of perhaps 3 or 4 were achieved for two-dimensional constraints imposed in only one direction and depths of perhaps 2 for two-dimensional constraints imposed in two directions. With one-dimensional constraints, it is shown that the inferred depth of processing is partially determined by the number of pattern representations and by the spatial distance between successive representation for visual displays of fixed size.     

Direct measures of short-term visual storage

Two experiments, involving seven conditions, explored the use of direct measures of visual persistence. In each, the subject was asked to judge if an intermittent stimulus appeared perceptually continuous, or whether it completely faded before the next presentation occurred. The first experiment showed that visual persistence was set at approximately 250 msec. for a recycling presentation of a circle in a tachistoscope; in another task employing a moving opaque slit passing back and forth over a circle, persistence times averaged 50 msec. longer. Reducing luminance by 2 log units increased persistence only slightly, though removing the adapting field increased it by over 100 msec. The second experiment, using the repeating circle, varied the duration of the stimulus, and compared monoptic with dichoptic presentations. Visual persistence was found to be independent of stimulus duration over a range of 4 to 200 msec., where all durations were above recognition threshold for the stimulus. Persistence was unaffected whether the stimulus was repeatedly presented in the same eye or alternated between eyes, strongly suggesting that the storage is central. Finally, a re-analysis of Dodwell and Engel's paper on stereopsis suggests that their effects can be adequately explained by visual persistence of the asynchronous stereo pairs, rather than a more complex fusion model. All of these results strongly support the use of visual persistence as a direct measure of short-term visual storage.     

How owls structure visual information

Recent studies on perceptual organization in humans claim that the ability to represent a visual scene as a set of coherent surfaces is of central importance for visual cognition. We examined whether this surface representation hypothesis generalizes to a non-mammalian species, the barn owl (Tyto alba). Discrimination transfer combined with random-dot stimuli provided the appropriate means for a series of two behavioural experiments with the specific aims of (1) obtaining psychophysical measurements of figure–ground segmentation in the owl, and (2) determining the nature of the information involved. In experiment 1, two owls were trained to indicate the presence or absence of a central planar surface (figure) among a larger region of random dots (ground) based on differences in texture. Without additional training, the owls could make the same discrimination when figure and ground had reversed luminance, or were camouflaged by the use of uniformly textured random-dot stereograms. In the latter case, the figure stands out in depth from the ground when positional differences of the figure in two retinal images are combined (binocular disparity). In experiment 2, two new owls were trained to distinguish three-dimensional objects from holes using random-dot kinematograms. These birds could make the same discrimination when information on surface segmentation was unexpectedly switched from relative motion to half-occlusion. In the latter case, stereograms were used that provide the impression of stratified surfaces to humans by giving unpairable image features to the eyes. The ability to use image features such as texture, binocular disparity, relative motion, and half-occlusion interchangeably to determine figure–ground relationships suggests that in owls, as in humans, the structuring of the visual scene critically depends on how indirect image information (depth order, occlusion contours) is allocated between different surfaces. Electronic Publication