The phonological loop model of working memory: An ERP study of irrelevant speech and phonological similarity effects

The phonological loop model for retention of auditory verbal material in working memory, developed by Baddeley, assumes that irrelevant speech and phonological similarity influence only one and the same element of the system—that is, the phonological short-term store. We tested this idea by recording eventrelated potentials (ERPs) to auditorily presented letters that were phonologically similar or dissimilar and were to be memorized in the presence of more or less disturbing irrelevant speech. Irrelevant speech and phonological similarity caused ERP effects with clearly different scalp topographies, indicating that these factors influence different brain systems and hence probably different cognitive elements. Moreover, ERPs indicated that the phonological similarity effect might involve processes at the level of phonological analysis. Our data also support recent suggestions that the irrelevant speech effect is not based on the phonological similarity between relevant and irrelevant material, but on the phonological variability within the irrelevant stream.     

Duration estimation and the phonological loop: Articulatory suppression and irrelevant sounds

Clock-based theories of time estimation propose that clock pulses are accumulated in working memory. Although these theories do not constrain the form of the memory trace, evidence reported in the literature suggests that active manipulation of a verbal trace may be involved. Four experiments are reported in which participants reproduced or verbally estimated short durations (up to a few seconds) either in a single-task condition or in a condition with a phonological load. Experiments 1, 2 and 4 showed that both interval reproduction and verbal estimation were impaired under concurrent articulatory suppression in comparison to a timing only control condition. Neither irrelevant speech (Experiments 1-3) nor irrelevant tones and music (Experiment 3) impaired timing performance. These findings are taken to show that time estimation is mediated by phonological working memory and the involvement of an active articulatory rehearsal process.     

The phonological loop: Some answers and some questions

Jones, Hughes, and Macken (2007) claim that their data and our own are inconsistent with a multicomponent working-memory model. We explain in greater detail how the model can account for the data and can address their more specific criticisms. Both sides accept that data relating to the presence of a phonological similarity effect throughout the list depend on list length. We accept that, at this point, all explanations of their interaction are speculative and require further empirical investigation. We examine J, H, & M's interpretation of their and our results in terms of an auditory modality effect, observing that their interpretation of this effect is not well supported by the literature. We suggest that their account assumes a very narrow basis for a general theory of short-term retention, in contrast to a phonological loop interpretation, which forms part of a well-developed and articulated model of working memory.     

An irrelevant speech effect with repeated and continuous background speech

The irrelevant speech effect is the impairment of task performance by the presentation of to-be-ignored speech stimuli. Typically, the irrelevant speech comprises a variety of sounds, but previous research (e.g., Jones, Madden, & Miles, 1992) has suggested that the deleterious effect of background speech is virtually eliminated if the speech comprises repetitions of a sound (e.g., “be, be, be”) or a single continuous sound (e.g., “beeeeeee”). Four experiments are reported that challenge this finding. Experiments 1, 2, and 4 show a substantial impairment in serial recall performance in the presence of a repeated sound, and Experiments 3 and 4 show a similar impairment of serial recall in the presence of a continuous sound. The relevance of these findings to several explanations of the irrelevant speech effect is discussed.     

The importance of semantic similarity to the irrelevant speech effect

Irrelevant speech disrupts immediate recall of a short sequence of items. Salamé and Baddeley (1982) found a very small and nonsignificant increase in the irrelevant speech effect when the speech comprised items semantically identical to the to-be-remembered items, leading subsequent researchers to conclude that semantic similarity plays no role in the irrelevant speech effect. Experiment 1 showed that strong free associates of the to-be-remembered items disrupted serial recall to a greater extent than words that were dissimilar to the to-be-remembered items. Experiment 2 showed that this same pattern of disruption in a free recall task. Theoretical implications of these findings are discussed.     

Irrelevant speech,articulatory suppression,and phonological similarity: A test of the phonological loop model and the feature model

Two experiments tested competing predictions about the nature of the irrelevant speech effect that were derived from Neath's (2000) feature model and from Salamé and Baddeley's (1982) phonological loop model. The first experiment examined the combined effects of irrelevant speech and articulatory suppression when target items were presented auditorily. Contrary to the suggestions of Neath, but consistent with the phonological loop model, the effects of articulatory suppression and irrelevant speech were additive even when the irrelevant speech was presented during the retention interval The second experiment examined the combined effects of irrelevant speech and phonological similarity when target items were presented visually. Consistent with the phonological loop model, the effects of phonological similarity and irrelevant speech were additive when participants were specifically instructed to use articulatory/phonological rehearsal to remember the list items. The results therefore contradicted Neath's claim that irrelevant speech abolishes the phonological similarity effect when list items are presented visually. However, the effect of phonological similarity was abolished in the irrelevant speech conditions when no instructions were given concerning rehearsal. It is argued that the phonological similarity effect disappears in some experiments because participants sometimes employ a semantic rehearsal strategy, consistent with the views of Salamé and Baddeley (1986).     

Directly assessing the relationship between irrelevant speech and irrelevant tapping

The acoustic confusion effect is the finding that lists of to-be-remembered items that sound similar to one another are recalled worse than otherwise comparable lists of items that sound different. Previous work has shown that concurrent irrelevant speech and concurrent irrelevant tapping both reduce the size of this effect, suggesting similarities between the two manipulations. The authors assessed the relation between irrelevant speech and irrelevant tapping by correlating the disruption each causes to recall of similar- and dissimilar-sounding items. A significant correlation was obtained, indicating a relation between the two. The results indicate that researchers should be sensitive to changes in the magnitude of the effects rather than focusing exclusively on the presence or absence of particular effects. Implications for the 3 major explanations of the irrelevant speech effect are discussed. (PsycINFO Database Record (c) 2008 APA, all rights reserved).     

Organizational factors in the effect of irrelevant speech: The role of spatial location and timing

Typically, hearing a repeated syllable produces minimal disruption of serial recall of visual lists, but a sequence of different syllables impairs performance markedly. Two conditions for presenting anidentical sequence of three syllables are compared: one, in which, by means of stereophony, each syllable is assigned to the left, center, or right auditory locus (three streamsnot changing in state), and another, in which the same syllable sequence occurs in one location only (one streamwith changing state). Disruption was significantly less in the stereophonic than in the monophonic condition. There was a joint effect of changing state and location, not an effect of the number of locations alone. In Experiment 2, temporal predictability was used to manipulate changing state. The disruptive effect ofregular presentation of a repeated syllable was markedly increased when it was presentedirregularly. The results are discussed in the context of organizational factors in short-term memory.     

Investigating the role of attentional resources in the irrelevant speech effect

Irrelevant words can be disruptive to performance, and the frequency of usage of the irrelevant words has affected the magnitude of such disruption (Buchner &; Erdfelder, 2005). The finding of word frequency differences in the magnitude of the irrelevant speech effect (ISE) implicated a role for attentional processes. Using a different conceptualization of attention, researchers have found that individual differences in working memory capacity did not predict the magnitude of the ISE, which questioned the role of attentional control (Beaman, 2004; Sörqvist, 2010). The current study investigated aspects of the construct of attention and the ISE, using both individual and developmental difference approaches. Results showed no significant difference between serial recall performances in the presence of high or low word frequency distractors. Furthermore, effects of working memory capacity differences were not found, but children displayed a larger ISE than college students. The weight of the evidence appears against an attentional resource view of the ISE.     

Manipulations of irrelevant information: Suffix effects with articulatory suppression and irrelevant speech

Numerous studies have demonstrated impaired recall when the to-be-remembered information is accompanied or followed by irrelevant information. However, no current theory of immediate memory explains all three common methods of manipulating irrelevant information: requiring concurrent articulation, presenting irrelevant speech, and adding a stimulus suffix. Five experiments combined these manipulations to determine how they interact and which theoretical framework most accurately and completely accounts for the data. In Experiments 1 and 2, a list of auditory items was followed by an irrelevant speech sound (the suffix) while subjects engaged in articulatory suppression. Although articulatory suppression reduced overall recall compared to a control condition, comparable suffix effects were seen in both conditions. Experiments 3 and 4 found reliable suffix effects when list presentation was accompanied by irrelevant speech. Experiment 5 found a suffix effect even when the irrelevant speech was composed of a set of different items. Implications for working memory, pre-categorical acoustic store, the changing-state hypothesis, and the feature model are discussed.     

Modeling the effects of irrelevant speech on memory

The feature model (Nairne, 1990) is extended to account for the effects of irrelevant speech and concomitant interactions in immediate serial recall. In the feature model, both articulatory suppression and irrelevant speech are seen as adding noise to the memory representation, the difference being that articulatory suppression diverts more resources than does irrelevant speech. The addition of noise impairs recall because it reduces the probability of successful redintegration. When a competitor is incorrectly recalled, rather than the correct item, this competitor is recalled out of order, producing an increase in order errors. Six simulations are reported that show that the model accounts for (1) the impairment by both irrelevant speech and articulatory suppression, (2) the irrelevance of the phonological and semantic composition of the irrelevant speech, (3) greater disruption when the irrelevant speech tokens vary, (4) the abolition of the phonological similarity effect for visual, but not for auditory, items, (5) the abolition of the word length effect for both visual and auditory items, and (6) the abolition of the irrelevant speech effect under articulatory suppression for both visual and auditory items. The feature model is compared with the two other major views of irrelevant speech, the phonological store hypothesis and the changing state hypothesis.     

Phonological similarity and the irrelevant speech effect: implications for models of short-term verbal memory

Three experiments studied the interaction between irrelevant speech and phonological similarity within both the remembered and the irrelevant auditory material. Phonological similarity within the remembered list impaired performance in both baseline and irrelevant speech conditions, whereas phonological similarity between the remembered and ignored irrelevant items did not influence performance. Although there was a tendency for similarity within the irrelevant items to reduce interference, this proved to be a less robust finding. Implications for the theoretical interpretation of the irrelevant speech effect are discussed.     

Phonological similarity and the irrelevant speech effect: Implications for models of short-term verbal memory

Three experiments studied the interaction between irrelevant speech and phonological similarity within both the remembered and the irrelevant auditory material. Phonological similarity within the remembered list impaired performance in both baseline and irrelevant speech conditions, whereas phonological similarity between the remembered and ignored irrelevant items did not influence performance. Although there was a tendency for similarity within the irrelevant items to reduce interference, this proved to be a less robust finding. Implications for the theoretical interpretation of the irrelevant speech effect are discussed.     

The influence of phonological similarity neighborhoods on speech production

The influence of phonological similarity neighborhoods on the speed and accuracy of speech production was investigated with speech-error elicitation and picture-naming tasks. The results from 2 speech-error elicitation techniques-the spoonerisms of laboratory induced predisposition technique (B. J. Baars, 1992; B. J. Baars & M. T. Motley, 1974; M. T. Motley & B. J. Baars, 1976) and tongue twisters-showed that more errors were elicited for words with few similar sounding words (i.e., a sparse neighborhood) than for words with many similar sounding words (i.e., a dense neighborhood). The results from 3 picture-naming tasks showed that words with sparse neighborhoods were also named more slowly than words with dense neighborhoods. These findings demonstrate that multiple word forms are activated simultaneously and influence the speed and accuracy of speech production. The implications of these findings for current models of speech production are discussed.     

The phonological loop in task alternation and task repetition

It has recently been proposed that task repetition is easier than task alternation because the appropriate task settings are already present in working memory, whereas during task alternation task settings must be retrieved from long-term memory (Mayr & Kliegl, 2000). The present study tested whether the phonological loop is involved in keeping the relevant task settings active in working memory. It may then be expected that concurrent articulatory suppression would diminish the facilitation associated with task repetition because the phonological loop could no longer maintain the appropriate task settings active in working memory. Both during task repetition and task alternation the relevant task settings should then be retrieved from long-term memory. Three dual-task experiments were conducted. The results of Experiment 1 were in support of our prediction. Experiment 2 replicated the findings of Experiment 1 and showed that the task settings probably represent the adequate response mappings. Experiment 3 ruled out the involvement of the visuo-spatial sketchpad and more general coordination demands during dual tasking.     

The phonological loop in task alternation and task repetition

It has recently been proposed that task repetition is easier than task alternation because the appropriate task settings are already present in working memory, whereas during task alternation task settings must be retrieved from long-term memory (Mayr & Kliegl, 2000). The present study tested whether the phonological loop is involved in keeping the relevant task settings active in working memory. It may then be expected that concurrent articulatory suppression would diminish the facilitation associated with task repetition because the phonological loop could no longer maintain the appropriate task settings active in working memory. Both during task repetition and task alternation the relevant task settings should then be retrieved from long-term memory. Three dual-task experiments were conducted. The results of Experiment 1 were in support of our prediction. Experiment 2 replicated the findings of Experiment 1 and showed that the task settings probably represent the adequate response mappings. Experiment 3 ruled out the involvement of the visuo-spatial sketchpad and more general coordination demands during dual tasking.     

Brain activation and the phonological loop: the impact of rehearsal

Brain activation studies offer valuable techniques for exploring human cognition to complement behavioral measures and several studies report a wide range of neuroanatomical networks activated during verbal immediate memory. Behavioral investigations have shown use of multiple cognitive strategies across and within individuals, although aggregate data appear to reflect a common cognitive function. Variation in cognitive strategies could result in aggregate activation patterns that are relatively widespread and difficult to interpret. Imaging data (fMRI) from six participants instructed to use subvocal rehearsal showed significant left hemisphere activation in the inferior parietal gyrus and inferior and middle frontal gyri, a pattern of activation more clearly focused than in previous brain activation studies of immediate verbal serial ordered recall. Our results should be relatively free of the influence of other mental operations, and emphasise the importance of considering which cognitive strategies might give rise to focused or to diverse patterns of brain activation.     

Issues with the SIMPLE model: comment on Brown, Neath, and Chater (2007)

SIMPLE (G. D. A. Brown, I. Neath, & N. Chater, 2007) attempts to explain data from serial recall and free recall in the same theoretical framework. While it can fit the free-recall serial-position curves that are the cornerstone of the 2-store buffer model, it does not address 2 classic issues in short-term memory research: similarity effects and presentation-rate effects. Similarity effects in free recall led to important work on organization in free recall, whereas similarity effects in serial recall led to the phonological basis of short-term memory. Presentation-rate effects operate quite differently in free and serial recall. The model also does not consider recall order effects or interresponse times in free recall, which may be problematic.     

The phonological loop and memory for rhythms: an individual differences approach

The purpose of the current study was to examine the relationship between short-term memory for rhythm and the phonological loop in working memory. Results showed that digit span scores significantly correlated with the scores on the rhythmic memory task, and that the correlation between the two scores remained significant even after the common variance with reading speed was partialled out. Partial correlation and regression analyses indicated that the relation between memory for rhythm and digit span scores is mediated by the third component in the phonological loop, the component that is responsible for regulation of timing mechanisms in immediate memory tasks.     

Directly assessing the relationship between irrelevant speech and articulatory suppression

Larsen and Baddeley (2003) examine whether the disruption caused by articulatory suppression on immediate memory tasks is similar to or different from the disruption caused by irrelevant speech. Based on experiments in which they test whether the phonological similarity effect is present or absent, they conclude that articulatory suppression and irrelevant speech are different. We assessed whether articulatory suppression and irrelevant speech are similar or different by correlating the disruption each causes. A significant correlation obtained, indicating a relation between the two. These apparently different conclusions can be readily resolved by adopting the view that articulatory suppression, irrelevant speech, and many other factors vary in the degree to which they are likely to cause subjects to abandon reliance on phonological/acoustic cues in particular tasks.