Evidence for modality-independent order coding in working memory

The aim of the present study was to investigate the representation of serial order in working memory, more specifically whether serial order is coded by means of a modality-dependent or a modality-independent order code. This was investigated by means of a series of four experiments based on a dual-task methodology in which one short-term memory task was embedded between the presentation and recall of another short-term memory task. Two aspects were varied in these memory tasks—namely, the modality of the stimulus materials (verbal or visuo-spatial) and the presence of an order component in the task (an order or an item memory task). The results of this study showed impaired primary-task recognition performance when both the primary and the embedded task included an order component, irrespective of the modality of the stimulus materials. If one or both of the tasks did not contain an order component, less interference was found. The results of this study support the existence of a modality-independent order code.     

Cross-domain interference costs during concurrent verbal and spatial serial memory tasks are asymmetric

Some evidence suggests that memory for serial order is domain-general. Evidence also points to asymmetries in interference between verbal and visual–spatial tasks. We confirm that concurrently remembering verbal and spatial serial lists provokes substantial interference compared with remembering a single list, but we further investigate the impact of this interference throughout the serial position curve, where asymmetries are indeed apparent. A concurrent verbal order memory task affects spatial memory performance throughout the serial positions of the list, but performing a spatial order task affects memory for the verbal serial list only for early list items; in the verbal task only, the final items are unaffected by a concurrent task. Adding suffixes eliminates this asymmetry, resulting in impairment throughout the list for both tasks. These results suggest that domain-general working memory resources may be supplemented with resources specific to the verbal domain, but perhaps not with equivalent spatial resources.     

Short-term memory for serial order supports vocabulary development: New evidence from a novel word learning paradigm

Although recent studies suggest a strong association between short-term memory (STM) for serial order and lexical development, the precise mechanisms linking the two domains remain to be determined. This study explored the nature of these mechanisms via a microanalysis of performance on serial order STM and novel word learning tasks. In the experiment, 6- and 7-year-old children were administered tasks maximizing STM for either item or serial order information as well as paired-associate learning tasks involving the learning of novel words, visual symbols, or familiar word pair associations. Learning abilities for novel words were specifically predicted by serial order STM abilities. A measure estimating the precision of serial order coding predicted the rate of correct repetitions and the rate of phoneme migration errors during the novel word learning process. In line with recent theoretical accounts, these results suggest that serial order STM supports vocabulary development via ordered and detailed reactivation of the novel phonological sequences that characterize new words.     

Single-probe serial position recall: Evidence of modularity for olfactory,visual, and auditory short-term memory

The present study examined and compared order memory for a list of sequentially presented odours, unfamiliar faces, and pure tones. Employing single-probe serial position recall and following a correction for a response bias, qualitatively different serial position functions were observed across stimuli. Participants demonstrated an ability to perform absolute order memory judgments for odours. Furthermore, odours produced an absence of serial position effects, unfamiliar faces produced both primacy and recency, and pure tones produced recency but not primacy. Such a finding is contrary to the proposal by Ward, Avons, and Melling (2005) that the serial position function is task, rather than modality, dependent. In contrast, the observed functions support a modular conceptualization of short-term memory (e.g., Andrade & Donaldson, 2007; Baddeley & Hitch, 1974), whereby separate modality-specific memorial systems operate. An alternative amodal interpretation is also discussed wherein serial position function disparities are accommodated via differences in the psychological distinctiveness of stimuli (Hay, Smyth, Hitch, & Horton, 2007).     

Behavioural evidence for separating components within visuo-spatial working memory

Several different sources of evidence support the idea that visuo-spatial working memory can be segregated into separate cognitive subsystems. However, the nature of these systems remains unclear. Recently we reported data from neurological patients suggesting that information about visual appearance is retained in a different subsystem from information about spatial location. In this paper we report latency data from neurologically intact participants showing an experimental double dissociation between memory for appearance and memory for location. This was achieved by use of a selective dual task interference technique. This pattern provides evidence supporting the segregation of visuo-spatial memory between two systems, one of which supports memory for stimulus appearance and the other which supports memory for spatial location.     

An analysis of immediate serial recall performance in a macaque

There has been considerable research into the ability of nonhuman primates to process sequential information, a topic that is of interest in part because of the extensive involvement of sequence processing in human language use. Surprisingly, no previous study has unambiguously tested the ability of nonhuman primates to encode and immediately reproduce a novel temporal sequence of perceptual events, the ability tapped in the immediate serial recall (ISR) task extensively studied in humans. We report here the performance of a rhesus macaque on a spatial ISR task, closely resembling tasks widely used in human memory research. Detailed analysis of the monkey’s recall performance indicates a number of important parallels with human ISR, consistent with the idea that a single mechanism for short-term serial order memory may be shared across species.     

The endurance of children's working memory: a recall time analysis

We analyze the timing of recall as a source of information about children’s performance in complex working memory tasks. A group of 8-year-olds performed a traditional operation span task in which sequence length increased across trials and an operation period task in which processing requirements were extended across trials of constant sequence length. Interword pauses were longer than are commonly found in immediate serial recall tasks yet shorter than for reading span. These pauses increased with the demands of recall, decreased across the output sequence, and were to some extent predictive of scholastic ability. Overall, timing data illustrate that recall in working memory tasks involves subtle processes of item access rather than simple readout of information from an immediate store.     

Encoding and representation of simultaneous and sequential arrays in visuospatial working memory

The effect of presentation type on organization in visuospatial working memory (VSWM) was examined. Stimuli were presented sequentially or simultaneously at study, and participants made same/different judgements at test. The test array varied in four different spatial configuration conditions: one featuring no changes from study, one in which two items switched, one in which the same array repeated but in a different location, and one in which a completely novel test stimulus appeared. Results indicated the use of a global configuration for both simultaneous and sequential presentations and showed increased impairment of item-level knowledge with sequential presentations. Overall, these results support the use of a global configuration organization as a fundamental aspect of VSWM processing.     

Differentiating between verbal and spatial encoding using eye-movement recordings

Visual information processing is guided by an active mechanism generating saccadic eye movements to salient stimuli. Here we investigate the specific contribution of saccades to memory encoding of verbal and spatial properties in a serial recall task. In the first experiment, participants moved their eyes freely without specific instruction. We demonstrate the existence of qualitative differences in eye-movement strategies during verbal and spatial memory encoding. While verbal memory encoding was characterized by shifting the gaze to the to-be-encoded stimuli, saccadic activity was suppressed during spatial encoding. In the second experiment, participants were required to suppress saccades by fixating centrally during encoding or to make precise saccades onto the memory items. Active suppression of saccades had no effect on memory performance, but tracking the upcoming stimuli decreased memory performance dramatically in both tasks, indicating a resource bottleneck between display-controlled saccadic control and memory encoding. We conclude that optimized encoding strategies for verbal and spatial features are underlying memory performance in serial recall, but such strategies work on an involuntary level only and do not support memory encoding when they are explicitly required by the task.     

A Bayesian hierarchical model for the measurement of working memory capacity

Working memory is the memory system that allows for conscious storage and manipulation of information. The capacity of working memory is extremely limited. Measurements of this limit, and what affects it, are critical to understanding working memory. Cowan (2001) and Pashler (1988) suggested applying multinomial tree models to data from change detection paradigms in order to estimate working memory capacity. Both Pashler and Cowan suggested simple formulas for estimating capacity with these models. However, in many cases, these simple formulas are inadequate, and may lead to inefficient or biased estimation of working memory capacity. I propose a Bayesian hierarchical alternative to the Pashler and Cowan formulas, and show that the hierarchical model outperforms the traditional formulas. The models are easy to use and appropriate for a wide range of experimental designs. An easy-to-use graphical user interface for fitting the hierarchical model to data is available.     

Precision of working memory for speech sounds

Memory for speech sounds is a key component of models of verbal working memory (WM). But how good is verbal WM? Most investigations assess this using binary report measures to derive a fixed number of items that can be stored. However, recent findings in visual WM have challenged such “quantized” views by employing measures of recall precision with an analogue response scale. WM for speech sounds might rely on both continuous and categorical storage mechanisms. Using a novel speech matching paradigm, we measured WM recall precision for phonemes. Vowel qualities were sampled from a formant space continuum. A probe vowel had to be adjusted to match the vowel quality of a target on a continuous, analogue response scale. Crucially, this provided an index of the variability of a memory representation around its true value and thus allowed us to estimate how memories were distorted from the original sounds. Memory load affected the quality of speech sound recall in two ways. First, there was a gradual decline in recall precision with increasing number of items, consistent with the view that WM representations of speech sounds become noisier with an increase in the number of items held in memory, just as for vision. Based on multidimensional scaling (MDS), the level of noise appeared to be reflected in distortions of the formant space. Second, as memory load increased, there was evidence of greater clustering of participants' responses around particular vowels. A mixture model captured both continuous and categorical responses, demonstrating a shift from continuous to categorical memory with increasing WM load. This suggests that direct acoustic storage can be used for single items, but when more items must be stored, categorical representations must be used.     

Processing of representations in declarative and procedural working memory

The article investigates the relation between declarative and procedural working memory (WM; Oberauer, 2009). Two experiments test the assumption that representations in the two subsystems are selected for processing in analogous ways. Participants carried out a series of decisions on memorized lists of digits. For each decision, they had to select declarative and procedural representations. Regarding declarative representations, participants selected a memory set and a digit within this set as the input to each decision. With respect to the procedural representations, they selected a task set to be applied to the selected digit and a response within that task set. We independently manipulated the number of lists and the number of tasks to be switched among (one, two, or three; Experiment 1) and preparation time for a list switch (Experiment 2). For three effects commonly observed in task-switch studies, analogues in declarative WM were found: list-switch costs, mixing costs, and residual switch costs. List- and task-switch costs were underadditive, suggesting that declarative and procedural representations are selected separately and in parallel. The findings support the hypothesis of two analogous WM subsystems.     

Reported serial positions of true and illusory memories in the Deese/Roediger/McDermott paradigm

One of the easiest ways to induce illusory memories in the laboratory is to use the Deese–Roediger–McDermott (DRM) word-list paradigm. Researchers have used this paradigm not only to study people's memories of stimuli that were not actually presented, but also to study the phenomenological qualities of these illusions. In four experiments, the current investigation explored a phenomenological quality of illusory memories that has received almost no attention, specifically, temporality. A serial position task was incorporated into the DRM paradigm to examine temporal attributes of participants' true and false memories. Effects of list strength, presentation order, and types of warnings were examined. Results showed consistent serial position responses for true and false memories. However, only responses for illusory memories were affected by manipulations at study. The current findings thus lend support to encoding-based explanations of false recollections.     

Individual differences in sentence memory

Results from an experiment with two parts are presented in this paper. In part one, participants listened to sentences containing two, three, four, or five clauses, and were asked questions about the content of the sentences. The results of part one demonstrate that an important unit of representation in sentence memory is the clause, and not some other component of discourse structure. In part two, the same group of participants performed eight different short-term storage/working memory tasks. A composite complex span score was computed for each participant based on three working memory tasks closely based on Daneman & Carpenter's (1980) reading span task. This working memory measure was significantly correlated with the participants' performance on the sentence memory task in part one. A second working memory measure—N-back—was also significantly correlated with the participants' performance on the sentence memory task, and there was no correlation between their performance on the complex span task and the N-back task. It is therefore concluded that (i) working memory consists of a number of dissociable components; and (ii) memory for sentences taps into more than one of these working memory components. Furthermore, the high correlations of sentence memory with the complex span and the N-back tasks (neither of which are language processing tasks) suggests that memory for sentences is not simply a result of linguistic experience; rather, it is likely that an independent working memory component contributes to participants' performance on the sentence memory task.     

Deficits in verbal long-term memory and learning in children with poor phonological short-term memory skills

Possible links between phonological short-term memory and both longer term memory and learning in 8-year-old children were investigated in this study. Performance on a range of tests of long-term memory and learning was compared for a group of 16 children with poor phonological short-term memory skills and a comparison group of children of the same age with matched nonverbal reasoning abilities but memory scores in the average range. The low-phonological-memory group were impaired on longer term memory and learning tasks that taxed memory for arbitrary verbal material such as names and nonwords. However, the two groups performed at comparable levels on tasks requiring the retention of visuo-spatial information and of meaningful material and at carrying out prospective memory tasks in which the children were asked to carry out actions at a future point in time. The results are consistent with the view that poor short-term memory function impairs the longer term retention and ease of learning of novel verbal material.     

Working memory capacity and retrieval limitations from long-term memory: An examination of differences in accessibility

In two experiments, the locus of individual differences in working memory capacity and long-term memory recall was examined. Participants performed categorical cued and free recall tasks, and individual differences in the dynamics of recall were interpreted in terms of a hierarchical-search framework. The results from this study are in accordance with recent theorizing suggesting a strong relation between working memory capacity and retrieval from long-term memory. Furthermore, the results also indicate that individual differences in categorical recall are partially due to differences in accessibility. In terms of accessibility of target information, two important factors drive the difference between high- and low-working-memory-capacity participants. Low-working-memory-capacity participants fail to utilize appropriate retrieval strategies to access cues, and they also have difficulty resolving cue overload. Thus, when low-working-memory-capacity participants were given specific cues that activated a smaller set of potential targets, their recall performance was the same as that of high-working-memory-capacity participants.     

Activation and binding in verbal working memory: a dual-process model for the recognition of nonwords

The article presents a mathematical model of short-term recognition based on dual-process models and the three-component theory of working memory [Oberauer, K. (2002). Access to information in working memory: Exploring the focus of attention. Journal of Experimental Psychology: Learning, Memory, and Cognition, 28, 411-421]. Familiarity arises from activated representations in long-term memory, ignoring their relations; recollection retrieves bindings in the capacity-limited component of working memory. In three experiments participants encoded two short lists of nonwords for immediate recognition, one of which was then cued as irrelevant. Probes from the irrelevant list were rejected more slowly than new probes; this was also found with probes recombining letters of irrelevant nonwords, suggesting that familiarity arises from individual letters independent of their relations. When asked to accept probes whose letters were all in the relevant list, regardless of their conjunction, participants accepted probes preserving the original conjunctions faster than recombinations, showing that recollection accessed feature bindings automatically. The model fit the data best when familiarity depended only on matching letters, whereas recollection used binding information.     

A working memory account for spatial-numerical associations

Several psychophysical and neuropsychological investigations have suggested that the mental representation of numbers takes the form of a number line along which magnitude is positioned in ascending order according to our reading habits. A longstanding debate is whether this spatial frame is triggered automatically as intrinsic part of the number semantics or whether it constitutes a short-term representation constructed during task execution. Although several observations clearly favor the working memory account, its causal involvement has not yet been demonstrated. In two experiments we show that information stored in working memory get spatially coded in function of its ordinal position in the sequence and that the spatial–numerical associations typically observed in number categorization tasks draw upon this mechanism.     

Syntax and serial recall: How language supports short-term memory for order

The extent to which familiar syntax supports short-term serial recall of visually presented six-item sequences was shown by the superior recall of lists in which item pairs appeared in the order of “adjective–noun” (items 1–2, 3–4, 5–6)—congruent with English syntax—compared to when the order of items within pairs was reversed. The findings complement other evidence suggesting that short-term memory is an assemblage of language processing and production processes more than it is a bespoke short-term memory storage system.