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.     

Modality independence of order coding in working memory: Evidence from cross-modal order interference at recall

Working memory researchers do not agree on whether order in serial recall is encoded by dedicated modality-specific systems or by a more general modality-independent system. Although previous research supports the existence of autonomous modality-specific systems, it has been shown that serial recognition memory is prone to cross-modal order interference by concurrent tasks. The present study used a serial recall task, which was performed in a single-task condition and in a dual-task condition with an embedded memory task in the retention interval. The modality of the serial task was either verbal or visuospatial, and the embedded tasks were in the other modality and required either serial or item recall. Care was taken to avoid modality overlaps during presentation and recall. In Experiment 1, visuospatial but not verbal serial recall was more impaired when the embedded task was an order than when it was an item task. Using a more difficult verbal serial recall task, verbal serial recall was also more impaired by another order recall task in Experiment 2. These findings are consistent with the hypothesis of modality-independent order coding. The implications for views on short-term recall and the multicomponent view of working memory are discussed.     

The effect of articulatory suppression and manual tapping on serial recall

Concurrent tasks, such as articulatory suppression and manual tapping, are used to understand the mechanisms underlying short-term memory by overloading domain-specific resources. The present study addresses the debate regarding the theoretical frameworks accounting for interference in serial recall by comparing the effects of both the modality of concurrent tasks (verbal vs. spatial) as well as the state of the tasks (steady vs. changing) in both verbal and spatial recall. The findings indicate that the verbal changing-state concurrent task significantly impaired digit recall, whereas the spatial changing-state concurrent task significantly impaired block recall. The theoretical implications are discussed in the context of a multimodal working memory model with domain-specific resources and a unitary approach to short-term memory.     

Short-term memory stages in sign vs. speech: the source of the serial span discrepancy

Speakers generally outperform signers when asked to recall a list of unrelated verbal items. This phenomenon is well established, but its source has remained unclear. In this study, we evaluate the relative contribution of the three main processing stages of short-term memory – perception, encoding, and recall – in this effect. The present study factorially manipulates whether American Sign Language (ASL) or English is used for perception, memory encoding, and recall in hearing ASL-English bilinguals. Results indicate that using ASL during both perception and encoding contributes to the serial span discrepancy. Interestingly, performing recall in ASL slightly increased span, ruling out the view that signing is in general a poor choice for short-term memory. These results suggest that despite the general equivalence of sign and speech in other memory domains, speech-based representations are better suited for the specific task of perception and memory encoding of a series of unrelated verbal items in serial order through the phonological loop. This work suggests that interpretation of performance on serial recall tasks in English may not translate straightforwardly to serial tasks in sign language.     

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.     

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.     

The development of visual and auditory selective attention using the central-incidental paradigm

Analogous auditory and visual central-incidental learning tasks were administered to 24 second-, fourth-, and sixth-grade and college-age subjects to study the effects of modality of presentation on memory for central and incidental stimulus materials. There was no strong evidence to indicate that modality of presentation was an important factor in the development of selective attention. Central task learning increased with age for both auditory and visual presentations; incidental learning declined at the oldest age level for both auditory and visual tasks. The serial position analysis revealed that the observed developmental increase in recall performance was due primarily to differences in the initial serial positions. The use of active strategies for focusing attention on the relevant stimulus materials seemed to be the crucial determinant of level of performance.     

Disruption of order information by irrelevant items: a serial recognition paradigm

Irrelevant speech effect (ISE) is defined as a decrement in visually presented digit-list short-term memory performance due to exposure to irrelevant auditory material. Perhaps the most successful theoretical explanation of the effect is the changing state hypothesis. This hypothesis explains the effect in terms of confusion between amodal serial order cues, and represents a view based on the interference caused by the processing of similar order information of the visual and auditory materials. An alternative view suggests that the interference occurs as a consequence of the similarity between the visual and auditory contents of the stimuli. An important argument for the former view is the observation that ISE is almost exclusively observed in tasks that require memory for serial order. However, most short-term memory tasks require that both item and order information be retained in memory. An ideal task to investigate the sensitivity of maintenance of serial order to irrelevant speech would be one that calls upon order information but not item information. One task that is particularly suited to address this issue is serial recognition. In a typical serial recognition task, a list of items is presented and then probed by the same list in which the order of two adjacent items has been transposed. Due to the re-presentation of the encoding string, serial recognition requires primarily the serial order to be maintained while the content of the presented items is deemphasized. In demonstrating a highly significant ISE of changing versus steady-state auditory items in a serial recognition task, the present finding lends support for and extends previous empirical findings suggesting that irrelevant speech has the potential to interfere with the coding of the order of the items to be memorized.     

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).     

Impact of auditory selective attention on verbal short-term memory and vocabulary development

This study investigated the role of auditory selective attention capacities as a possible mediator of the well-established association between verbal short-term memory (STM) and vocabulary development. A total of 47 6- and 7-year-olds were administered verbal immediate serial recall and auditory attention tasks. Both task types probed processing of item and serial order information because recent studies have shown this distinction to be critical when exploring relations between STM and lexical development. Multiple regression and variance partitioning analyses highlighted two variables as determinants of vocabulary development: (a) a serial order processing variable shared by STM order recall and a selective attention task for sequence information and (b) an attentional variable shared by selective attention measures targeting item or sequence information. The current study highlights the need for integrative STM models, accounting for conjoined influences of attentional capacities and serial order processing capacities on STM performance and the establishment of the lexical language network.     

Musical and verbal memory in Alzheimer’s disease: A study of long-term and short-term memory

Musical memory was tested in Alzheimer patients and in healthy older adults using long-term and short-term memory tasks. Long-term memory (LTM) was tested with a recognition procedure using unfamiliar melodies. Short-term memory (STM) was evaluated with same/different judgment tasks on short series of notes. Musical memory was compared to verbal memory using a task that used pseudowords (LTM) or syllables (STM). Results indicated impaired musical memory in AD patients relative to healthy controls. The deficit was found for both long-term and short-term memory. Furthermore, it was of the same magnitude for both musical and verbal domains whether tested with short-term or long-term memory tasks. No correlation was found between musical and verbal LTM. However, there was a significant correlation between verbal and musical STM in AD participants and healthy older adults, which suggests that the two domains may share common mechanisms.     

A re-evaluation of the phonological similarity effect in adults' short-term memory of words and nonwords

The phonological similarity effect (PSE) was studied in two tasks of serial recall, in one task of serial recognition and one item identification task. PSE occurred only in the former three tasks involving memory of order when study items were words and nonwords with an associative connectedness to long-term memory. Nonwords that, according to a reaction time assessment of associative value, were less well connected to long-term memory mechanisms, were not sensitive to phonological similarity. These results are discussed in relation to contemporary models of short-term memory that explain the PSE as a result of confusions of items that are similarly encoded in a phonological layer. This layer is identified as a higher-level phonological space that is accessed by words and nonwords of high associative value and not by nonwords of low associative value.     

The phonological neighbourhood effect on short-term memory for order

There is a growing body of literature that suggests that long-term memory (LTM) and short-term memory (STM) structures that were once thought to be distinct are actually co-dependent, and that LTM can aid retrieval from STM. The mechanism behind this effect is commonly argued to act on item memory but not on order memory. The aim of the current study was to examine whether LTM could exert an influence on STM for order by examining an effect attributed to LTM, the phonological neighbourhood effect, in a task that reduced the requirement to retain item information. In Experiment 1, 18 participants completed a serial reconstruction task where neighbourhood density alternated within the lists. In Experiment 2, 22 participants completed a serial reconstruction task using pure lists of dense and sparse neighbourhood words. In Experiment 3, 22 participants completed a reconstruction task with both mixed and pure lists. There was a significant effect of neighbourhood density with better recall for dense than sparse neighbourhood words in pure lists but not in mixed lists. Results suggest that LTM exerts an influence prior to that proposed by many models of memory for order.     

Asymmetric interference between domains: evidence from the stimulus order effect in complex span tasks

The stimulus order effect refers to the finding that recall in complex span tasks is better when span lists begin with a longer processing task and end with a shorter task than when these processing tasks are presented in the reverse order. This study independently manipulated processing time and processing difficulty between Long-final and Short-final lists. The processing task required participants to solve arithmetic problems with either verbal (Experiment 1) or visuospatial (Experiment 2) materials. The memory items used in the storage task were either digits (verbal material) or dots-in-matrices (visuospatial materials). Storage of both verbal and visuospatial materials was sensitive to the change in processing difficulty, but not processing time. Furthermore, this study provides further evidence for the asymmetry of domain interference in working memory. The similarities and differences between verbal and visuospatial storage in working memory are discussed.     

Short-term recognition memory for serial order and timing

Recent evidence suggests that a common temporal representation underlies memory for serial order of items in a sequence, and the timing of items in a sequence. This stands in contrast to other data suggesting a reliance on only ordinal information in short-term memory tasks. An experiment is reported here in which participants were post cued to perform a comparison between a probe and study list of items irregularly spaced in time, on the basis of order or temporal information.Participants' performance on theserial recognition task was notaffected by the temporal proximity of items, although participants were able to use temporal information to perform a temporal recognition task. Application of a temporal matching model of serial and temporal recognition suggests that although participants were able to remember the timing of items, this memory for timing was unlikely to determine serial recognition performance. The results suggest a dissociation between ordinal and temporal information in short-term memory.     

Hemispatial neglect and serial order in verbal working memory

Working memory refers to our ability to actively maintain and process a limited amount of information during a brief period of time. Often, not only the information itself but also its serial order is crucial for good task performance. It was recently proposed that serial order is grounded in spatial cognition. Here, we compared performance of a group of right hemisphere-damaged patients with hemispatial neglect to healthy controls in verbal working memory tasks. Participants memorized sequences of consonants at span level and had to judge whether a target consonant belonged to the memorized sequence (item task) or whether a pair of consonants were presented in the same order as in the memorized sequence (order task). In line with this idea that serial order is grounded in spatial cognition, we found that neglect patients made significantly more errors in the order task than in the item task compared to healthy controls. Furthermore, this deficit seemed functionally related to neglect severity and was more frequently observed following right posterior brain damage. Interestingly, this specific impairment for serial order in verbal working memory was not lateralized. We advance the hypotheses of a potential contribution to the deficit of serial order in neglect patients of either or both (1) reduced spatial working memory capacity that enables to keep track of the spatial codes that provide memorized items with a positional context, (2) a spatial compression of these codes in the intact representational space.     

The role of articulatory suppression in immediate false recognition

False memory for critical lures has been widely documented in long-term memory using the Deese/Roediger-McDermott paradigm. Recent evidence suggests that false memory effects can also be found in short-term memory (STM), supporting models that assume a strong relationship between short-term and long-term memory processes. However, no study has examined the role of articulatory suppression on immediate false memory, even though phono-articulatory factors are critically involved in STM performance and are an intrinsic part of all STM accounts. The current study proposes a novel paradigm to assess false memory effects in a STM task under both silent and articulatory suppression conditions. Using immediate serial recognition, in which participants had to judge whether two successive mixed lists of six associated and non-associated words were matched, we examined true recognition of matching lists and false recognition of mismatching lists comprising a critical lure or unrelated distractor in two experiments. Results from both experiments indicated reduced true recognition of matching lists and greater false serial recognition of mismatching lists comprising a critical lure under articulatory suppression relative to silence. These findings provide further support for some current models of verbal short-term memory, which posit a strong relationship between short-term and long-term memory processes.     

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.     

Fractionating the preview benefit in search: dual-task decomposition of visual marking by timing and modality

Providing participants with a preview of half the distractors in a visual search task facilitates performance. The present study examined the effects of secondary tasks on the preview benefit in search. Participants had to attend to a visual or an auditory stream of digits that began either (a) at the onset of the preview or (b) after the preview. Secondary tasks that onset with the preview disrupted the preview benefit irrespective of their modality. Only visual secondary tasks disrupted the benefit in the delayed condition. These selective interference effects suggest that the preview benefit can be fractionated into 2 components: an initialization component that involves modality-independent resources and a maintenance component that depends on visual resources. Results are discussed in relation to theoretical accounts of the preview benefit in search.