Concreteness effects revisited: The influence of dynamic visual noise on memory for concrete and abstract words

Two experiments are presented that investigate the effects of dynamic visual noise (DVN) on memory for concrete and abstract words. Memory for concrete words is typically superior to that of abstract words and is referred to as the concreteness effect. DVN is a procedure that has been demonstrated to interfere selectively with visual working memory and the generation of images from long-term memory. It was reasoned that if concreteness effects arise because of the ability of the latter to activate visual representations, then DVN should selectively impair memory for concrete words. Experiment 1 found DVN to selectively reduce free recall of concrete words. Experiment 2 investigated recognition memory and found DVN to reduce memory accuracy and remember responses, while increasing know responses to concrete words.     

Insensitivity of visual short-term memory to irrelevant visual information

Several authors have hypothesized that visuo-spatial working memory is functionally analogous to verbal working memory. Irrelevant background speech impairs verbal short-term memory. We investigated whether irrelevant visual information has an analogous effect on visual short-term memory, using a dynamic visual noise (DVN) technique known to disrupt visual imagery (Quinn & McConnell, 1996b). Experiment 1 replicated the effect of DVN on pegword imagery. Experiments 2 and 3 showed no effect of DVN on recall of static matrix patterns, despite a significant effect of a concurrent spatial tapping task. Experiment 4 showed no effect of DVN on encoding or maintenance of arrays of matrix patterns, despite testing memory by a recognition procedure to encourage visual rather than spatial processing. Serial position curves showed a one-item recency effect typical of visual short-term memory. Experiment 5 showed no effect of DVN on short-term recognition of Chinese characters, despite effects of visual similarity and a concurrent colour memory task that confirmed visual processing of the characters. We conclude that irrelevant visual noise does not impair visual short-term memory. Visual working memory may not be functionally analogous to verbal working memory, and different cognitive processes may underlie visual short-term memory and visual imagery.     

The interval for interference in conscious visual imagery

Three experiments are described that use dynamic visual noise (DVN) to interfere with words processed under visual and verbal processing instructions. In Experiment 1 DVN is presented to coincide with the encoding of the words or to coincide with the interval between encoding and recall. The results show that while DVN is a robust disruptor when it is applied during encoding to words processed under visual instruction, it has no effect during encoding when the words are processed under rote instruction. Moreover, DVN has no effect when it is applied during the retention interval, no matter what means are employed to encode the words. Experiment 2 extends these findings by again showing no effect of DVN during the retention interval, yet showing robust interference effects for visually processed words during recall. Finally, Experiment 3 demonstrates that the results of Experiments 1 and 2 cannot be explained by a difference in the time duration associated with application of DVN during the retention interval compared to during encoding and recall. Moreover, the differing decay functions for visually and verbally processed words during the intervals used in Experiment 3 suggest that any failure to cause interference is not because the two processing instructions resulted in words being retained in the same medium. The functions are consistent with word storage mechanisms reflecting appropriately verbal and visual properties. The results are discussed in terms of current models of visual working memory. It is argued that a full interpretation of the results requires a buffer mechanism as an important component of any model of visual working memory.     

The interval for interference in conscious visual imagery

Three experiments are described that use dynamic visual noise (DVN) to interfere with words processed under visual and verbal processing instructions. In Experiment 1 DVN is presented to coincide with the encoding of the words or to coincide with the interval between encoding and recall. The results show that while DVN is a robust disruptor when it is applied during encoding to words processed under visual instruction, it has no effect during encoding when the words are processed under rote instruction. Moreover, DVN has no effect when it is applied during the retention interval, no matter what means are employed to encode the words. Experiment 2 extends these findings by again showing no effect of DVN during the retention interval, yet showing robust interference effects for visually processed words during recall. Finally, Experiment 3 demonstrates that the results of Experiments 1 and 2 cannot be explained by a difference in the time duration associated with application of DVN during the retention interval compared to during encoding and recall. Moreover, the differing decay functions for visually and verbally processed words during the intervals used in Experiment 3 suggest that any failure to cause interference is not because the two processing instructions resulted in words being retained in the same medium. The functions are consistent with word storage mechanisms reflecting appropriately verbal and visual properties. The results are discussed in terms of current models of visual working memory. It is argued that a full interpretation of the results requires a buffer mechanism as an important component of any model of visual working memory.     

Dynamic visual noise reduces confidence in short-term memory for visual information

Previous research has shown effects of the visual interference technique, dynamic visual noise (DVN), on visual imagery, but not on visual short-term memory, unless retention of precise visual detail is required. This study tested the prediction that DVN does also affect retention of gross visual information, specifically by reducing confidence. Participants performed a matrix pattern memory task with three retention interval interference conditions (DVN, static visual noise and no interference control) that varied from trial to trial. At recall, participants indicated whether or not they were sure of their responses. As in previous research, DVN did not impair recall accuracy or latency on the task, but it did reduce recall confidence relative to static visual noise and no interference. We conclude that DVN does distort visual representations in short-term memory, but standard coarse-grained recall measures are insensitive to these distortions.     

The role of spatial working memory in visual search efficiency

Many theories have proposed that visual working memory plays an important role in visual search. In contrast, by showing that a nonspatial working memory load did not interfere with search efficiency, Woodman, Vogel, and Luck (2001) recently proposed that the role of working memory in visual search is insignificant. However, the visual search process may interfere with spatial working memory. In the present study, a visual search task was performed concurrently with either a spatial working memory task (Experiment 1) or a nonspatial working memory task (Experiment 2). We found that the visual search process interfered with a spatial working memory load, but not with a nonspatial working memory load. These results suggest that there is a distinction between spatial and nonspatial working memory in terms of interactions with visual search tasks. These results imply that the visual search process and spatial working memory storage require the same limited-capacity mechanisms.     

Reduced effects of pictorial distinctiveness on false memory following dynamic visual noise

High levels of false recognition for non-presented items typically occur following exposure to lists of associated words. These false recognition effects can be reduced by making the studied items more distinctive by the presentation of pictures during encoding. One explanation of this is that during recognition, participants expect or attempt to retrieve distinctive pictorial information in order to evaluate the study status of the test item. If this involves the retrieval and use of visual imagery, then interfering with imagery processing should reduce the effectiveness of pictorial information in false memory reduction. In the current experiment, visual-imagery processing was disrupted at retrieval by the use of dynamic visual noise (DVN). It was found that effects of DVN dissociated true from false memory. Memory for studied words was not influenced by the presence of an interfering noise field. However, false memory was increased and the effects of picture-induced distinctiveness was eliminated. DVN also increased false recollection and remember responses to unstudied items.     

Individual differences in visual imagery determine how event information is remembered

Individuals differ in how they mentally imagine past events. When reminiscing about a past experience, some individuals remember the event accompanied by rich visual images, while others will remember it with few of these images. In spite of the implications that these differences in the use of imagery have to the understanding of human memory, few studies have taken them into consideration. We examined how imagery interference affecting event memory retrieval was differently modulated by spatial and object imagery ability. We presented participants with a series of video-clips depicting complex events. Participants subsequently answered true/false questions related to event, spatial, or feature details contained in the videos, while simultaneously viewing stimuli that interfered with visual imagery processes (dynamic visual noise; DVN) or a control grey screen. The impact of DVN on memory accuracy was related to individual differences in spatial imagery ability. Individuals high in spatial imagery were less accurate at recalling details from the videos when simultaneously viewing the DVN stimuli compared to those low in spatial imagery ability. This finding held for questions related to the event and spatial details but not feature details. This study advocates for the inclusion of individual differences when studying memory processes.     

Selective interference with the use of visual images in the symbolic distance paradigm

Eight experiments investigated the effects of visual, spatial, auditory, and executive interference on the symbolic comparison of animal size and ferocity, semantic goodness of words, and numbers. Dynamic visual noise (DVN) and the reading of visually presented stimulus items were shown to selectively interfere with response times on the animal size comparison task, though the slope of the symbolic distance function remained unchanged. Increased change of DVN significantly increased interference, but interference was reduced by equiluminant DVN. Spatial tracking reduced the slope of the symbolic distance function in contrast to an executive task that only increased mean latency and errors for all comparisons. Results suggest that the generation of an image is necessary for size comparison, but neither imagery nor executive function is responsible for the frequently observed distance-time function.     

Visual and verbal working memory loads interfere with scene-viewing

Working memory is thought to be divided into distinct visual and verbal subsystems. Studies of visual working memory frequently use verbal working memory tasks as control conditions and/or use articulatory suppression to ensure that visual load is not transferred to verbal working memory. Using these verbal tasks relies on the assumption that the verbal working memory load will not interfere with the same processes as visual working memory. In the present study, participants maintained a visual or verbal working memory load as they simultaneously viewed scenes while their eye movements were recorded. Because eye movements and visual working memory are closely linked, we anticipated the visual load would interfere with scene-viewing (and vice versa), while the verbal load would not. Surprisingly, both visual and verbal memory loads interfered with scene-viewing behavior, while eye movements during scene-viewing did not significantly interfere with performance on either memory task. These results suggest that a verbal working memory load can interfere with eye movements in a visual task.

     

The (lack of) effect of dynamic visual noise on the concreteness effect in short-term memory

It has been suggested that the concreteness effect in short-term memory (STM) is a consequence of concrete words having more distinctive and richer semantic representations. The generation and storage of visual codes in STM could also play a crucial role on the effect because concrete words are more imaginable than abstract words. If this were the case, the introduction of a visual interference task would be expected to disrupt recall of concrete words. A Dynamic Visual Noise (DVN) display, which has been proven to eliminate the concreteness effect on long-term memory (LTM), was presented along encoding of concrete and abstract words in a STM serial recall task. Results showed a main effect of word type, with more item errors in abstract words, a main effect of DVN, which impaired global performance due to more order errors, but no interaction, suggesting that DVN did not have any impact on the concreteness effect. These findings are discussed in terms of LTM participation through redintegration processes and in terms of the language-based models of verbal STM.     

Masking of alphabetic character recognition by ultrahigh-density dynamic visual noise

In this paper the results of an experiment measuring the masking effects of ultrahigh-density dynamic visual noise (DVN) on character recognition are reported. It is shown that the period in which DVN acts as a mask is not extended beyond that measured with less dense DVN, even when the interval between the DVN dots is as small as 32 μsee. This result permits the rejection of the notion that there are sub threshold “tails” to the period of persistence of the visual store of the DVN dots. These results thus confirm the measurements made with less dense DVN of the duration of the period of persistence that allows confusion between sequential stimulus and mask dots to occur.     

Representations in mental imagery and working memory: Evidence from different types of visual masks

Although few studies have systematically investigated the relationship between visual mental imagery and visual working memory, work on the effects of passive visual interference has generally demonstrated a dissociation between the two functions. In four experiments, we investigated a possible commonality between the two functions: We asked whether both rely on depictive representations. Participants judged the visual properties of letters using visual mental images or pictures of unfamiliar letters stored in short-term memory. Participants performed both tasks with two different types of interference: sequences of unstructured visual masks (consisting of randomly changing white and black dots) or sequences of structured visual masks (consisting of fragments of letters). The structured visual noise contained elements of depictive representations (i.e., shape fragments arrayed in space), and hence should interfere with stored depictive representations; the unstructured visual noise did not contain such elements, and thus should not interfere as much with such stored representations. Participants did in fact make more errors in both tasks with sequences of structured visual masks. Various controls converged in demonstrating that in both tasks participants used representations that depicted the shapes of the letters. These findings not only constrain theories of visual mental imagery and visual working memory, but also have direct implications for why some studies have failed to find that dynamic visual noise interferes with visual working memory.     

Strategic and automatic effects of visual working memory on attention in visual search

Previous research indicates that visual attention can be automatically captured by sensory inputs that match the contents of visual working memory. However, Woodman and Luck (2007) showed that information in working memory can be used flexibly as a template for either selection or rejection according to task demands. We report two experiments that extend their work. Participants performed a visual search task while maintaining items in visual working memory. Memory items were presented for either a short or long exposure duration immediately prior to the search task. Memory was tested by a change-detection task immediately afterwards. On a random half of trials items in memory matched either one distractor in the search task (Experiment 1) or three (Experiment 2). The main result was that matching distractors speeded or slowed target detection depending on whether memory items were presented for a long or short duration. These effects were more in evidence with three matching distractors than one. We conclude that the influence of visual working memory on visual search is indeed flexible but is not solely a function of task demands. Our results suggest that attentional capture by perceptual inputs matching information in visual working memory involves a fast automatic process that can be overridden by a slower top-down process of attentional avoidance.     

Dual-task interference in visual working memory: A limitation in storage capacity but not in encoding or retrieval

The concurrent maintenance of two visual working memory (VWM) arrays can lead to profound interference. It is unclear, however, whether these costs arise from limitations in VWM storage capacity (Fougnie & Maro is, 2006) or from interference between the storage of one visual array and encoding or retrieval of another visual array (Cowan & Morey, 2007). Here, we show that encoding a VWM array does not interfere with maintenance of another VWM array unless the two displays exceed maintenance capacity (Experiments 1 and 2). Moreover, manipulating the extent to which encoding and maintenance can interfere with one another had no discernable effect on dual-task performance (Experiment 2). Finally, maintenance of a VWM array was not affected by retrieval of information from another VWM array (Experiment 3). Taken together, these findings demonstrate that dual-task interference between two concurrent VWM tasks is due to a capacity-limited store that is independent from encoding and retrieval processes.     

Picture span test: Measuring visual working memory capacity involved in remembering and comprehension

The working memory system is assumed to operate with domain-specific (verbal and visuospatial) resources that support cognitive activities. However, in research on visuospatial working memory, an appropriate visual working memory task has not been established. For the present study, a novel task was developed: the picture span test (PST). This test requires memorizing parts of scene images while comprehending various scene situations simultaneously. Results of correlation analyses and a factor analysis among college students (n=52) validated that PST can predict visuospatial cognitive skills whereas a simple visual storage task and a verbal working memory task cannot. Furthermore, an error analysis indicated that inhibition is important for visuospatial working memory. Additionally, PST is considered to reflect individual differences in the visual working memory capacity. These findings suggest that the PST is appropriate for measuring visual working memory capacity and can elucidate its relationship to higher cognition.     

Selective interference with image retention and generation: Evidence for the workspace model

We address three types of model of the relationship between working memory (WM) and long-term memory (LTM): (a) the gateway model, in which WM acts as a gateway between perceptual input and LTM; (b) the unitary model, in which WM is seen as the currently activated areas of LTM; and (c) the workspace model, in which perceptual input activates LTM, and WM acts as a separate workspace for processing and temporary retention of these activated traces. Predictions of these models were tested, focusing on visuospatial working memory and using dual-task methodology to combine two main tasks (visual short-term retention and image generation) with two interference tasks (irrelevant pictures and spatial tapping). The pictures selectively disrupted performance on the generation task, whereas the tapping selectively interfered with the retention task. Results are consistent with the predictions of the workspace model.     

Visual cognition influences early vision: the role of visual short-term memory in amodal completion

A partly occluded visual object is perceptually filled in behind the occluding surface, a process known as amodal completion or visual interpolation. Previous research focused on the image-based properties that lead to amodal completion. In the present experiments, we examined the role of a higher-level visual process-visual short-term memory (VSTM)-in amodal completion. We measured the degree of amodal completion by asking participants to perform an object-based attention task on occluded objects while maintaining either zero or four items in visual working memory. When no items were stored in VSTM, participants completed the occluded objects; when four items were stored in VSTM, amodal completion was halted (Experiment 1). These results were not caused by the influence of VSTM on object-based attention per se (Experiment 2) or by the specific location of to-be-remembered items (Experiment 3). Items held in VSTM interfere with amodal completion, which suggests that amodal completion may not be an informationally encapsulated process, but rather can be affected by high-level visual processes.     

Expertise for upright faces improves the precision but not the capacity of visual working memory

Considerable research has focused on how basic visual features are maintained in working memory, but little is currently known about the precision or capacity of visual working memory for complex objects. How precisely can an object be remembered, and to what extent might familiarity or perceptual expertise contribute to working memory performance? To address these questions, we developed a set of computer-generated face stimuli that varied continuously along the dimensions of age and gender, and we probed participants’ memories using a method-of-adjustment reporting procedure. This paradigm allowed us to separately estimate the precision and capacity of working memory for individual faces, on the basis of the assumptions of a discrete capacity model, and to assess the impact of face inversion on memory performance. We found that observers could maintain up to four to five items on average, with equally good memory capacity for upright and upside-down faces. In contrast, memory precision was significantly impaired by face inversion at every set size tested. Our results demonstrate that the precision of visual working memory for a complex stimulus is not strictly fixed but, instead, can be modified by learning and experience. We find that perceptual expertise for upright faces leads to significant improvements in visual precision, without modifying the capacity of working memory.