Irrelevant speech does not interfere with serial recall in early blind ...

THE QUARTERLY JOURNAL OF EXPERIMENTAL PSYCHOLOGY, 2014 Vol. 67, No. 11, 2207–2217, http://dx.doi.org/10.1080/17470218.2014.910537

Irrelevant speech does not interfere with serial recall in early blind listeners Florian Kattner and Wolfgang Ellermeier Institute of Psychology, Technische Universität Darmstadt, Germany

Phonological working memory is known be (a) inversely related to the duration of the items to be learned (word-length effect), and (b) impaired by the presence of irrelevant speech-like sounds (irrelevant-speech effect). As it is discussed controversially whether these memory disruptions are subject to attentional control, both effects were studied in sighted participants and in a sample of early blind individuals who are expected to be superior in selectively attending to auditory stimuli. Results show that, while performance depended on word length in both groups, irrelevant speech interfered with recall only in the sighted group, but not in blind participants. This suggests that blind listeners may be able to effectively prevent irrelevant sound from being encoded in the phonological store, presumably due to superior auditory processing. The occurrence of a word-length effect, however, implies that blind and sighted listeners are utilizing the same phonological rehearsal mechanism in order to maintain information in the phonological store. Keywords: Irrelevant-sound effect; Working memory; Irrelevant speech; Blind; Sighted.

Working memory has been defined as a cognitive system that stores and manipulates information (e.g., Baddeley & Hitch, 1974). According to the most influential model during the last decades, working memory comprises a central executive (including an attentional control system) and separate subordinate storage systems that are responsible for the maintenance of verbal material on the one hand, and visuospatial information on the other (compare Baddeley, 2003; Baddeley & Hitch, 1974). Within the verbal subsystem (i.e., the phonological loop), a phonological store that keeps speech-based information for about 2 s is supposed to interact with an articulatory rehearsal process that can be used to actively maintain information in that store. Auditory verbal information is

supposed to gain obligatory access to the phonological store, whereas visually presented items have to be converted through subvocal articulatory rehearsal (grapheme-to-morpheme conversion). Several empirical phenomena in line with this model have been reported. Two of them (i.e., the wordlength effect and the irrelevant-speech effect) are in the focus of the present study. The word-length effect refers to the phenomenon that memory span is lower if the to-be-remembered list consists of long words (more syllables or longer duration) than if it consists of short words (Baddeley, Thomson, & Buchanan, 1975; Mackworth, 1963). The effect has been reported both with visual and auditory working-memory tasks (e.g., Caplan, Rochon, & Waters, 1992;

Correspondence should be addressed to Florian Kattner, Institute of Psychology, Technische Universität Darmstadt, Alexanderstr. 10, 64283 Darmstadt, Germany. E-mail: [email protected] We are indebted to Josephine Berger and Christopher-John Gawe for their assistance in recruiting the participants and collecting the data. © 2014 The Experimental Psychology Society

2207

KATTNER AND ELLERMEIER

Neath, Suprenant, & LeCompte, 1998). Moreover, the effect seems to be quite robust, being resistant to strategic learning effects (e.g., rehearsing only the initial syllables in long words), as reliable word-length effects have been obtained with the same words reoccurring on several trials in different orders (e.g., Avons, Wright, & Pammer, 1994; Campoy, 2008; Jacquemot, Dupoux, & Bachoud-Lévi, 2011). Theoretically, the effect provides empirical support for the temporal limitation of the phonological store, with verbal memorization depending on the phonological structure of the to-be-remembered words. Particularly, it has been shown that the memory span corresponds to the number of items that can be articulated in about 2 s (Baddeley et al., 1975). This indicates that memory span cannot be defined in terms of a constant number of items (Miller, 1956), but depends on a time-based rehearsal process. In line with this view, the word-length effect was reported to depend on the individual speed of articulation (e.g., Baddeley et al., 1975; Dosher & Ma, 1998). Moreover, having participants continuously articulate irrelevant words (e.g., repeatedly pronouncing the word “the”, a method referred to as “articulatory suppression”) has been shown to eliminate the word-length effect if the words are presented visually (Baddeley, Lewis, & Vallar, 1984). These findings suggest that the word-length effect is related to articulatory rehearsal of information in the phonological store, with longer words taking more time to rehearse than shorter words. The irrelevant-speech effect (ISE) refers to the impairment of working memory by the presence of irrelevant background speech, compared to silence or stationary noise (Colle & Welsh, 1976; Ellermeier & Zimmer, 1997; Salamé & Baddeley, 1982). The irrelevant-speech effect is a robust phenomenon, and increases in error rate by 10 to 20% have been reported (for reviews, see Banbury, Macken, Tremblay, & Jones, 2001; Ellermeier & Zimmer, 2014). Typical ISE experiments use immediate, or slightly delayed, serial recall tasks with short lists of visually presented words, letters or digits to be remembered while the irrelevant background sound must be ignored.

2208

However, irrelevant speech has been shown to produce the same working-memory disruptions when participants are asked to remember spoken items (Hanley & Bakopoulou, 2003; Hanley & Broadbent, 1987; Hanley & Hayes, 2012). According to the “phonological-loop model” (e.g., Baddeley, 2003), speech is supposed to automatically gain access to the phonological store. The ISE is based on interference between the to-beremembered items and task-irrelevant speech within the phonological store. Consistent with the model, articulatory suppression has been shown to remove the ISE if the to-be-remembered items are presented visually (because concurrent articulation prevents phonological encoding of visual items; see Salamé & Baddeley, 1982), but not if the targets are presented auditorily (e.g., Hanley & Broadbent, 1987). It has been shown, however, that serial recall disruption can also be elicited by auditory nonspeech stimuli such as instrumental music, tones or traffic noise (Hygge, Boman, & Enmarker, 2003; Jones & Macken, 1993; Salamé & Baddeley, 1989). Moreover, the same background sounds do not seem to interfere with recall in nonserial memory tasks (Beaman & Jones, 1997). Based on these findings, Jones, Beaman, and Macken (1996) argued that the ISE may be due to fluctuations in the state of the background sounds (exhibiting irrelevant serial-order cues) competing with the memorization of serial order of the relevant items. According to this model (the “object-oriented episodic record model”; Jones et al., 1996), serial recall depends on the integrity of links (pointers) that maintain the order of distinct auditory events. As in the phonological-loop model, rehearsal is required to prevent the decay of these pointers. Common to both accounts is the assumption that perceptual characteristics of the unattended sound (i.e., speech-specific or changing-state properties) cause interference with the verbal information (whether presented visually or auditorily) that is being maintained in the short-term memory store. So far, it is rather unclear, exactly how background sounds gain access to working memory. As both models (Baddeley & Hitch, 1974; Jones et al., 1996) assume the memory disruption to occur via

THE QUARTERLY JOURNAL OF EXPERIMENTAL PSYCHOLOGY, 2014, 67 (11)

IRRELEVANT SPEECH AND BLIND LISTENERS

automatic access of the (irrelevant) auditory stimuli, the ISE is supposed to be independent of attention or cognitive abilities. In line with this assumption, it has been shown that people with higher working memory capacity (operation span) are not less susceptible to irrelevant speech (Beaman, 2004). Further, even loud bursts of noise were shown to have almost no effect on serial recall (Colle, 1980; Salamé & Baddeley, 1987), and it has been found that the ISE may not be affected by habituation to the irrelevant sound (Hellbrück, Kuwano, & Namba, 1996; Tremblay & Jones, 1998). More recent studies, however, reported less workingmemory impairment if participants had been preexposed to the irrelevant sound (Bell, Röer, Dentale, & Buchner, 2012), and found that the disruptive effects of the to-be-ignored speech or music are attenuated with repeated presentations of the same irrelevant streams (i.e., habituation to the distractors), suggesting that the maintenance of verbal information depends on attentional processes (Röer, Bell, & Buchner, in press). An alternative attentional account of the ISE has been proposed by Cowan (1995), namely the “embedded-processes model”. The key difference to the other two accounts is that irrelevant sound is assumed to capture the focus of attention (much like an orienting response), and thus to divert it from the rehearsal of relevant information in memory. New or suddenly changing sounds (e.g., speech or changing tones) are supposed to produce more attentional distraction than frequently occurring or stationary sounds. Similarly, referring to the “feature model” (Nairne, 1990), Neath (2000) compared the ISE to a dual-task situation where participants have to pay attention to the relevant information while disregarding irrelevant stimuli. These models can account for an attenuation of the memory disruptions through habituation of the attentional orienting response to the irrelevant sound (Röer et al., in press). Moreover, in line with an attentional account, there is some indication that the ISE is subject to developmental changes regarding the amount of attentional control (Elliott, 2002). The present study aims to investigate whether phonological memory disruptions (ISE and word-

length effect) are related to acquired perceptual or attentional skills with regard to auditory processing. The reported working memory models differ with regard to whether they assume an attentional component (e.g., Cowan, 1995; Neath, 2000) or not (e.g., Baddeley, 2003; Jones, 1993). From the perspective of an attentional model of working memory, trained attentional and perceptual mechanisms could help (a) to prevent irrelevant sounds from entering the phonological store (through a selective-attention mechanism), or (b) to rehearse (and maintain) primarily the relevant rather than the irrelevant items (compare Cowan, 1995). Consequentially, the irrelevant-speech effect should either be eliminated or attenuated if attentional processing allows the listener to focus on the relevant information (and to ignore the irrelevant). The word-length effect, on the other hand, may be less controllable by attentional processing, as it is due to the articulatory rehearsal process (i.e., the speed of articulation). There is some indication of enhanced attentional processing in early blind people. It has been shown, for instance, that blind listeners are faster than sighted listeners in detecting auditory (and tactile) locations in selective-attention tasks (e.g., Collignon, Renier, Bruyer, Tranduy, & Veraart, 2006). Rokem and Ahissar (2009) reported that blind listeners perform better in a number of auditory tasks (e.g., verbal span, speech perception, and frequency discrimination), and the authors attributed these advantages to superior encoding of auditory information. Data from studies measuring event-related potentials further indicate that the encoding and processing of verbal information in memory is faster and more efficient in blind listeners than in sighted listeners (e.g., Röder, Rösler, & Neville, 2001). In addition, congenitally blind participants seem to be less susceptible to auditorytactile illusions (Höttig & Röder, 2004), indicating that task-irrelevant information (i.e., auditory distractors) produces less interference. We therefore decided to investigate whether blind listeners differ from sighted participants with regard to the interferences in verbal short-term memory. Particularly, if the blind listeners’ ability to attend to the relevant auditory items and to ignore the


2209


irrelevant ones is superior, then their recall performance for verbal materials should be less susceptible to irrelevant speech. That is, according to an attentional model of the ISE (e.g., Cowan, 1995), enhanced selective attention should reduce the degree of distraction by irrelevant speech. In contrast, the word-length effect is not assumed to be due to interference between two sources of information in the phonological store. Rather it is supposed to depend on the temporal capacity of the phonological store requiring an articulatory rehearsal mechanism to maintain verbal information. Thus, the word-length effect is expected to be a function of motor/articulatory skills, and it should not be attenuated by enhanced attention to the target stimuli. Only if blind listeners possess improved articulatory skills (the authors are not aware of any empirical evidence for this) might a reduced word-length effect then be expected. Thus, in the present study, the word-length effect served as a control condition against a non-attentional interpretation. Finding a reduced wordlength effect in blind listeners might suggest a more general superiority of verbal short-term storage in blind individuals (rather than an encoding advantage), potentially due to the use of a different (e.g., non-verbal) rehearsal strategy. According to the phonological-loop model (Baddeley & Hitch, 1974), the ISE should not interact with the word-length effect because these two effects are assumed to depend on separate memory processes (i.e., automatic access of auditory stimuli producing interference in the memory store vs. rehearsal of information). Thus, irrelevant sound and word length should be independent and exert additive, detrimental effects on memory performance. In line with this prediction, Jones (2000) showed that irrelevant sound (speech or changing sounds) had comparable disruptive effects on the recall of lists of short and long words (similar results have been reported by Longoni, Richardson, & Aiello, 1993). In contrast to these findings, however, Neath et al. (1998) found irrelevant speech (but not irrelevant tones) to eliminate word-length effects with both visual and auditory items to be remembered. As the reasons for these discrepancies are not yet fully understood, a

2210

further test of the interaction between word length and irrelevant sound is important and was a secondary objective of the present study.

METHOD Participants A total of 15 sighted blindfolded and 15 congenitally or early blind participants took part in the experiment. Sighted participants (13 female) had a mean age of 25.7 years (range: 20–49 years). Blind participants (8 female) had a mean age of 42.2 years (range: 20–71 years). In the blind group, there were 11 congenitally blind participants, 3 participants with total blindness starting at the age of 5, 11 and 20 years, respectively, and 1 participant with congenital high-grade visual impairment (less then 5% vision). All blind listeners had been blind (or high-grade visually impaired) for at least 23 years at the time of testing. Each participant was tested individually in an experimental session of about 1 hour.

Apparatus and stimuli The experiment was conducted in a single-walled sound-attenuated listening booth (International Acoustics Company). Sounds were D/A converted with 16 bits at 44.1 kHz by an external sound card (RME multiface II), passed through a Behringer HA 800 Powerplay PRO-8 headphone amplifier, and presented diotically via Beyerdynamics DT990 headphones (250 Ohm). The to-be-remembered words were selected from the Berlin Affective Word List (Vo, Jacobs, & Conrad, 2006). Two lists were selected, containing six neutral German words each having a length of either one syllable (“Zahl”, “Punkt”, “Mohn”, “Lift”, “Leim”, “Fracht”) or three syllables (“Tatsache”, “Plantage”, “Minute”, “Linie”, “Dokument”, “Dialekt”). Recordings of each word were generated by a male speaker. The durations of the utterances varied between 430 and 690 ms (M = 519 ms for short words, and M = 593 ms for long words).



Finnish free-running speech (male speaker) and Gaussian noise were used as the irrelevant sounds. The duration of the irrelevant sounds was 10 s. Both the to-be-remembered words and the irrelevant sound were played diotically in each trial with both sounds overlapping during the first 6 s. All stimuli were played back at comfortable sound pressure levels of approximately 65 dB SPL. Stimulus presentation and response registration routines were programmed in Matlab utilizing the Psychophysics Toolbox extensions (Brainard, 1997; Pelli, 1997).

Design and procedure A mixed-factors 2 (Group: blind or sighted listeners) × 2 (Irrelevant Sound: speech or noise) × 2 (Word Length: 1 or 3 syllables) design was implemented with the last two factors being manipulated within subjects. At the beginning of the experiment, all participants were asked for informed consent and given a detailed description of how to respond. They were instructed that their task was to memorize the order of spoken word lists and to respond to a probe in each trial. After the oral instructions were understood, participants were seated in the listening booth. They were asked to put on the headphones and the blindfold. The experiment started with a training trial illustrating the procedure. If the participants had no further questions concerning the task, the experimenter left the booth and was present outside for the duration of the experiment. In each trial, a sequence of six target words was presented together with an irrelevant sound (Finnish speech or white noise). Both signals were played back simultaneously and diotically via headphones. The order of the six words was randomized in each trial. The words were presented at a constant rate of one word per second (irrespective of word length). During the subsequent retention interval of 4 s, only the irrelevant sound was continued. At the end of this interval, the irrelevant sound stopped, and the auditory probe was presented. The probe consisting of a randomly selected word from the presented list and number representing a serial position (e.g., “Leim 4”). In half of the

trials, the probe number corresponded to the actual position of the word (“correct” probe), in the other half of the trials the probe position was incorrect. Participants were asked to respond with a key press (right or left cursor key) to indicate whether the probe number corresponded to the true position of the word or not. There was an intertrial interval of 2 s before the next auditory presentation started. The experiment consisted of 192 trials in total (training trial not included). There were 48 repetitions of each experimental condition (Irrelevant Sound × Word Length), with the correct probe positions being tested 24 times, and 24 incorrectprobe trials. All serial positions were tested repeatedly within each condition, with the serial positions 2 to 5 being tested ten times, and the first and last serial position being tested four times. Unequal frequencies were used, because the first and last positions were expected to be less informative due to primacy and recency effects. Errors and response latencies were collected for each trial.

RESULTS Recall performance differed significantly between the serial positions tested (F (5, 140) = 14.67; p , .001), with more recall errors at positions 2 to 5 (30.0%, 29.4%, 29.4%, and 26.3%, respectively) than for the first (18.5%) and last (15.2%) words presented. However, as there were no significant interactions of Serial Position with Irrelevant Sound (F (5, 140) = 1.02; p = .41), Word Length (F (5, 140) = 0.56; p = .73) or Group (F (5, 140) = 0.95; p = .45), the data were collapsed across serial positions for further analysis. Figure 1 illustrates the mean proportion of response errors made in the four experimental conditions separately for the blind and for the sighted group. A 2 (Group) × 2 (Irrelevant Sound) × 2 (Word Length) mixed-factors analysis of variance on response accuracy revealed a significant main effect of Word Length (F (1, 28) = 17.60; p , .001; h2partial = 0.39), indicating that recall was better for short


2211


Figure 1. Mean percentage of recall errors for short (1 syllable) and long (3 syllables) words as a function of the irrelevant background sound (speech or noise) in blind and sighted individuals.

words than for long words. There was no Group × Word Length interaction (F (1, 28) = 0.01; p = .91; h2partial , 0.01), indicating that the word-length effect was evident in both groups. Additional within-group tests revealed that Word Length had a significant effect on recall performance in both the sighted group (F (1, 14) = 7.58; p = .01) and the blind group (F (1, 14) = 10.72; p = .005). There was also a significant main effect of Irrelevant Sound (F (1, 28) = 4.51; p = .04; h2partial = 0.14), indicating that speech produced more memory disruption than noise did. However, the irrelevantspeech effect differed between the sighted and the blind group, as indicated by a significant Group × Irrelevant Sound interaction h2partial = 0.16). (F (1, 28) = 5.18; p = .03; Additional comparisons showed that Irrelevant Sound had an effect on memory performance in the sighted group (F (1, 14) = 16.04; p = .001) but not in the blind group

(F (1, 14) = 0.01; p = .93). There was no significant interaction between Word Length and Irrelevant Sound (F (1, 28) = 2.02; p = .17; h2partial = 0.07), no main effect of Group (F (1, 28) = 0.002; p = .96; h2partial , 0.01) and no three-way interaction (F (1, 28) = 0.01; p = .91; h2partial , 0.01). The latencies of recall responses did not differ as a function of Irrelevant Sound or Word Length (F , 0.1). The main effect of Group on response times was not significant (F (1, 28) = 2.41; p = .13; M = 1045 and 1375 ms in the sighted and blind group, respectively). However, there was a significant Serial Position effect (F (5, 140) = 2.89; p = .02) with faster responses to the earlier positions, as well as a Serial Position × Group interaction (F (5, 140) = 3.11; p = .01), indicating that sighted and blind listeners differ with regard to the serial position curves of response latencies.1

Whereas sighted participants responded faster to the first (M = 840 ms) and last (M = 892 ms) words than to words in the middle of the list (M = 917, 1039, 1250, and 1333 ms, respectively), response times seemed to increase monotonically with the serial position in blind listeners (M = 1165, 1260, 1328, 1361, 1365, and 1768 ms, respectively). 1

2212



Table 1. Sensitivity (d ′ ) to discriminate between correct and incorrect probes as a function of word length and irrelevant sound (response criteria b in parentheses). Sighted group

Noise Speech

Blind group

Short

Long

Short

Long

1.56 (1.34) 1.28 (1.35)

1.32 (1.32) 0.85 (1.16)

1.32 (1.08) 1.46 (1.14)

1.13 (1.01) 1.03 (1.00)

To test whether the effects on recall performance were due to sensitivity or to a response bias, hit rates and false alarm rates were computed from the numbers of “yes” and “no” responses given that the probed position was correct (hit rate) or incorrect (false alarm rate). Sensitivity values d ′ and response criteria b were computed for each experimental condition (see Table 1). In the sighted group, sensitivity was higher for short words than for long words (Dd ′ = 0.34), and it was higher if noise was presented than if speech was presented (Dd ′ = 0.38). In the blind group, sensitivity was also higher for short words than for long words (Dd ′ = 0.31), but d ′ did not depend on the type of the irrelevant sound (Dd ′ = 0.02). In contrast, the response criterion (b) did not vary systematically with word length or irrelevant sound, but it differed between groups with the sighted participants demonstrating a more conservative response criterion (fewer “yes” responses) than the blind participants in all experimental conditions.

DISCUSSION The aim of the present study was to test whether phonological working memory mechanisms differ between blind and sighted participants. As (attentional) processing of auditory information has been shown to be more efficient in blind participants (e.g., Röder et al., 2001; Rokem & Ahissar, 2009), these individuals might be less susceptible to certain types of memory interference that are produced by irrelevant auditory information (Salamé & Baddeley, 1982).

Results show that irrelevant background speech produced impairments of serial recall performance in sighted listeners, but not in the blind sample. Sighted participants produced about 5–10% more errors if they were exposed to irrelevant speech than if they were exposed to irrelevant noise. The magnitude of the ISE is comparable to what has been reported in the research literature (Colle, 1980; Ellermeier & Zimmer, 1997; Salamé & Baddeley, 1982) though it is at its lower end, which is very likely due to the “probe” methodology employed (compare Hadlington, Bridges, & Darby, 2004, who reported an ISE of similar magnitude with that procedure). By contrast, the number of recall errors did not differ between speech and noise conditions in blind participants (see Figure 1). The same pattern of results has been obtained with the sensitivities to discriminate between “correct” and “incorrect” probes (but not for the response criteria, see Table 1), indicating that the crucial interaction is not due to different response biases under conditions of speech or noise masking. Moreover, the fact that the mean recall performance is equal in both groups of participants indicates that blind listeners were not simply better in memorizing verbal items. That is, blind listeners’ phonological working memory does not seem to be disrupted by the presence of irrelevant speech. Previous studies showed that blind listeners are superior in tasks that require distinguishing between relevant and irrelevant auditory information (Collignon et al., 2006), and it has been argued that they might benefit from more efficient ways of verbal stimulus encoding (Rokem & Ahissar, 2009). When confronted with irrelevant auditory information during a recall task, enhanced selective attention and stimulus encoding mechanisms might prevent the irrelevant information from gaining access to the phonological store. Thus, in contrast to the “automatic-access” assumption, the present results suggest that the working memory interferences produced by irrelevant auditory stimuli can be controlled by attention. The observation that blind listeners are resistant to irrelevant-speech distraction is in line with the embedded-processes account (Cowan, 1995). According to this model, unsteady sounds like speech are supposed to cause an orienting response, diverting attention


2213


from the to-be-remembered items. Consistent with this assumption, it has been shown that memory disruption attenuates with repeated presentations of the irrelevant sound, indicating habituation of the orienting response (Röer et al., in press). In blind listeners the ISE might be absent because, for them, changing-state sounds cause less attentional distraction, potentially due to habituation to auditory distraction or more efficient ways of auditory processing. Working memory performance also depended on the length of the words to be remembered, with short words being recalled better than long words (demonstrating a typical word-length effect; Baddeley et al., 1975). Interestingly, the word-length effect was evident to the same degree in sighted and blind listeners, indicating that both groups of participants were recruiting the same phonological storage mechanisms. Particularly, the occurrence of a word-length effect suggests that the phonological store is temporally limited (to approximately 2 s of spoken information), and that the maintenance of information requires (subvocal) articulatory rehearsal. The data suggest that this mechanism is independent of attentional abilities or verbal encoding advantages. That is, though blind listeners seem to have an advantage with regard to the selective encoding of relevant auditory information (as indicated by the absence of an ISE), the maintenance of items that have been encoded in the store (i.e., through articulatory rehearsal) does not seem to benefit from these processing advantages. This dissociation between the ISE and the word-length effect suggests that the absence of an ISE in blind listeners is not due to their use of a different rehearsal strategy (or enhanced articulatory skills), but rather to an advantage that is specific to the selective encoding of relevant auditory information. As the to-be-remembered words were presented auditorily (for obvious reasons), concurrent irrelevant sound might have produced some degree of masking. Even though the signal-to-noise ratios used guaranteed 100% intelligibility for the to-beremembered words, it might be argued that some residual masking was stronger with speech than with continuous noise in the background. Thus,

2214

the absence of an ISE in blind listeners could potentially be interpreted in terms of their enhanced ability to identify speech under conditions of partial acoustic masking. However, it has been demonstrated that irrelevant speech interferes with the memorization of auditorily presented items even if speech is presented only in the retention interval (after presentation of the targets; e.g., Hanley & Bakopoulou, 2003), indicating that memory disruptions are not caused by degraded target identification. Thus, blind listeners’ speech identification performance alone cannot explain the absence of working memory disruptions. Moreover, if the present data were a result of masking then a smaller ISE would be expected for long target words (which should be easier to identify). By trend, however, speech produced even more recall disruption with long words than with short words in sighted participants. Replicating Longoni et al. (1993) and Tremblay et al. (2000), the word-length effect was not eliminated by the presence of irrelevant speech in either sighted or blind listeners. That is, lists of short words were always recalled better (by about 5– 10%) than lists of long words, irrespective of the type of background sound. This finding is consistent with the phonological loop account of the ISE (Baddeley, 2003), assuming independent effects of irrelevant speech and word length as they relate to separate components of phonological working memory (similar predictions are made by the object-oriented episodic record model; see Jones et al., 1996). Together with previous findings (Tremblay et al., 2000), the present results seem to disprove the interaction between word length and irrelevant sound reported by Tremblay and Jones (1998, see Tremblay et al., 2000, for a discussion of task variables that might account for this discrepancy). The analysis of the response latencies revealed an additional interesting finding, indicating that sighted and blind participants may have used different retrieval strategies. Whereas sighted participants responded fastest to the first and last words in the list (primacy and recency effects), the blind listeners’ retrieval times seem to increase monotonically with the serial position of the word



in the list. Thus, sighted participants may be retrieving the last item from an echoic buffer, whereas blind individuals seem to retrieve the list by strictly adhering to the serial order. As faster responses were not accompanied by lower accuracy, a speed–accuracy trade-off account is unlikely. Although an interpretation of this finding is rather speculative, it could also be explained by differences in the allocation of attentional resources. That is, the blind listeners’ enhanced attentional control may (a) have helped them to focus on the serial order during recall, and (b) have made them more resistant to irrelevant phonological information. Admittedly, a possible limitation concerns the unequal age ranges of the two groups of participants, with the blind listeners being older on average. It could thus be argued that the observed differences between groups (i.e., with regard to the susceptibility to irrelevant speech) may be due to age rather than to different auditory encoding mechanisms. However, as previous studies have convincingly demonstrated that the irrelevant-sound effect does not depend on the age of the participants (e.g., Beaman, 2005; Bell & Buchner, 2007; Rouleau & Belleville, 1996), we argue that an age-related account of the present results is highly unlikely. Even if one assumes the irrelevant-speech effect to be related to cognitive functions that decline with age, then greater memory disruptions would still be expected in older participants. In contrast to this prediction, however, the irrelevant-sound effect was shown to be restricted to the younger participants (sighted group) in the present study. Furthermore, an additional regression analysis showed that only group (b = 0.07; p , .05) but not age (b = 0.00; p = .77) was a significant predictor of the magnitude of the ISE (i.e., the difference in error rates between noise and speech trials). To sum up, the present study shows that serial recall of verbal information depends on word length in both sighted and blind listeners. In contrast, the presence of irrelevant speech interfered with serial recall only in sighted participants, but not in blind participants. This indicates that blind listeners are superior with regard to the selective encoding of relevant auditory information,

whereas there is no difference between sighted and blind listeners in the maintenance of phonological information in working memory (through articulatory rehearsal). In addition, there was no interaction between irrelevant sound and the word length on memory performance, suggesting that these two effects are due to distinct workingmemory components. Original manuscript received 27 November 2013 Accepted revision received 25 February 2014 First published online 6 May 2014

REFERENCES Avons, S. E., Wright, K. L., & Pammer, K. (1994). The word-length effect in probed and serial recall. The Quarterly Journal of Experimental Psychology, 47A, 207–231. Baddeley, A. D. (2003). Working memory - looking back and looking foward. Nature Reviews Neuroscience, 4, 830–839. Baddeley, A. D., & Hitch, G. J. (1974). Working memory. In G. H. Bower (Ed.), The psychology of learning and motivation (Vol. 8, pp. 47–90). New York, NY: Academic Press. Baddeley, A. D., Lewis, V., & Vallar, G. (1984). Exploring the articulatory loop. The Quarterly Journal of Experimental Psychology, 36A, 233–252. Baddeley, A. D., Thomson, N., & Buchanan, M. (1975). Word length and the structure of working memory. Journal of Verbal Learning and Verbal Behavior, 14, 575–589. Banbury, S., Macken, W. J., Tremblay, S., & Jones, D. M. (2001). Auditory distraction and short-term memory: Phenomena and practical implications. Human Factors, 43, 12–29. Beaman, C. P. (2004). The irrelevant sound phenomenon revisited: What role for working memory capacity? Journal of Experimental Psychology: Learning, Memory, and Cognition, 30, 1106–1118. Beaman, C. P. (2005). Irrelevant sound effects amongst younger and older adults: Objective findings and subjective insights. European Journal of Cognitive Psychology, 17, 241–265. Beaman, C. P., & Jones, D. M. (1997). Role of serial order in the irrelevant speech effect: Tests of the changing-state hypothesis. Journal of Experimental


2215


Psychology: Learning, Memory, and Cognition, 23, 459–471. Bell, R., & Buchner, A. (2007). Equivalent irrelevantsound effects for old and young adults. Memory & Cognition, 35, 352–364. Bell, R., Roer, J. P., Dentale, S., & Buchner, A. (2012). Habituation of the irrelevant sound effect: Evidence for an attentional theory of short-term memory disruption. Journal of Experimental Psychology: Learning, Memory, and Cognition, 38, 1542–1557. Brainard, D. H. (1997). The Psychophysics Toolbox. Spatial Vision, 10, 443–446. Campoy, G. (2008). The effect of word length in shortterm memory: Is rehearsal necessary? The Quarterly Journal of Experimental Psychology, 61, 724–734. Caplan, D., Rochon, E., & Waters, G. S. (1992). Articulatory and phonological determinants of word length effects in span tasks. The Quarterly Journal of Experimental Psychology, 45A, 177–192. Colle, H. A. (1980). Auditory encoding in visual shortterm recall: Effects of noise intensity and spatial location. Journal of Verbal Learning and Verbal Behavior, 19, 722–735. Colle, H. A., & Welsh, A. (1976). Acoustic masking in primary memory. Journal of Verbal Learning and Verbal Behavior, 15, 17–31. Collignon, O., Renier, L., Bruyer, R., Tranduy, D., & Veraart, C. (2006). Improved selective and divided spatial attention in early blind subjects. Brain Research, 1075, 175–182. Cowan, N. (1995). Attention and memory: An integrated framework. New York, NY: Oxford University Press. Dosher, B., & Ma, J.-J. (1998). Output loss or rehearsal loop? Output-time versus pronunciation-time limits in immediate recall for forgetting-matched materials. Journal of Experimental Psychology: Learning, Memory, and Cognition, 24, 316–335. Ellermeier, W., & Zimmer, K. (1997). Individual differences in susceptibility to the ‘irrelevant speech’ effect. Journal of the Acoustical Society of America, 102, 2191– 2199. Ellermeier, W., & Zimmer, K. (2014). The psychoacoustics of the irrevelant sound effect. Acoustical Science and Technology, 35, 10–16. Elliott, E. M. (2002). The irrelevant-speech effect and children: Theoretical implications of developmental change. Memory & Cognition, 30, 478–487. Hadlington, L., Bridges, A. M., & Darby, R. J. (2004). Auditory location in the irrelevant sound effect: The effects of presenting auditory stimuli to either the

2216

left ear, right ear or both ears. Brain and Cognition, 55, 545–557. Hanley, J. R., & Bakopoulou, E. (2003). Irrelevant speech, articulatory suppression, and phonological similarity: A test of the phonological loop model and the feature model. Psychonomic Bulletin & Review, 10, 435–444. Hanley, J. R., & Broadbent, C. (1987). The effects of unattended speech on serial recall following auditory presentation. British Journal of Psychology, 78, 287–297. Hanley, J. R., & Hayes, A. (2012). The irrelevant sound effect under articulatory suppression: Is it a suffix effect? Journal of Experimental Psychology: Learning, Memory, and Cognition, 38, 482–487. Hellbrück, J., Kuwano, S., & Namba, S. (1996). Irrelevant background speech and human performance: Is there long-term habituation? Journal of the Acoustical Society of Japan, 17, 239–247. Höttig, K., & Röder, B. (2004). Hearing cheats touch, but less in congenitally blind than in sighted individuals. Psychological Science, 15, 60–64. Hygge, S., Boman, E., & Enmarker, I. (2003). The effect of road traffic and meaningful irrelevant speech on different memory systems. Scandinavian Journal of Psychology, 44, 13–21. Jacquemot, C., Dupoux, E., & Bachoud-Lévi, A.-C. (2011). Is the word-length effect linked to subvocal rehearsal?. Cortex, 47, 484–493. Jones, D. M. (1993). Objects, streams, and threads of auditory attention. In A. D. Baddeley & L. Weiskrantz (Eds.), Attention: Selection, awareness and control (pp. 167–198). Oxford: Clarendon Press. Jones, D. M., Beaman, C. P., & Macken, W. J. (1996). The Object-Oriented Episodic Record Model. In S. E. Gathercole (Ed.), Models of short-term memory (pp. 209–238). Hove: Psychology Press. Jones, D. M., & Macken, W. J. (1993). Irrelevant tones produce an irrelevant speech effect: Implications for phonological coding in working memory. Journal of Experimental Psychology: Learning, Memory, and Cognition, 19, 369–381. Longoni, A. M., Richardson, J. T. E., & Aiello, A. (1993). Articulatory rehearsal and phonological storage in working memory. Memory & Cognition, 21, 11–22. Mackworth, J. F. (1963). The duration of the visual image. Canadian Journal of Psychology, 17, 62–81. Miller, G. (1956). The magical number seven, plus or minus two: Some limits to our capacity for processing information. Psychological Review, 63, 81–97. Nairne, J. S. (1990). A feature model of immediate memory. Memory & Cognition, 18, 251–269.



Neath, I. (2000). Modeling the effects of irrelevant speech on memory. Psychonomic Bulletin & Review, 7, 403–423. Neath, I., Suprenant, A. N., & LeCompte, D. C. (1998). Irrelevant speech eliminates the word length effect. Memory & Cognition, 4, 343–354. Pelli, D. G. (1997). The VideoToolbox software for visual psychophysics: Transforming numbers into movies. Spatial Vision, 10, 437–442. Roder, B., Rosler, F., & Neville, H. J. (2001). Auditory memory in congenitally blind adults: A behavioralelectrophysiological investigation. Cognitive Brain Research, 11, 289–303. Roer, J., Bell, R., & Buchner, A. (in press). Evidence for habituation of the irrelevant-sound effect on serial recall. Memory & Cognition. Advance online publication. doi:10.3758/s13421-013-0381-y. Rokem, A., & Ahissar, M. (2009). Interactions of cognitive and auditory abilities in congenitally blind individuals. Neuropsychologia, 47, 843–848. Rouleau, N., & Belleville, S. (1996). Irrelevant speech effect in aging: An assessment of inhibitory processes in working memory. Journal of Gerontology, 51B, 356–363.

Salame, P., & Baddeley, A. (1982). Disruption of short-term memory by unattended speech: Implications for the structure of working memory. Journal of Verbal Learning and Verbal Behavior, 21, 150–164. Salame, P., & Baddeley, A. D. (1987). Noise, unattended speech and short-term memory. Ergonomics, 30, 1185–1194. Salamé, P., & Baddeley, A. D. (1989). Effects of background music on phonological short-term memory. The Quarterly Journal of Experimental Psychology, 41A, 107–122. Tremblay, S., & Jones, D. M. (1998). Role of habituation in the irrelevant-sound effect: Evidence from the effects of token set size and rate of transition. Journal of Experimental Psychology: Learning, Memory, and Cognition, 24, 659–671. Tremblay, S., Macken, W. J., & Jones, D. M. (2000). Elimination of the word length effect by irrelevant sound revisited. Memory & Cognition, 28, 841–846. Vo, M.-L., Jacobs, A., & Conrad, M. (2006). Crossvalidating the Berlin Affective Word List (BAWL). Behavior Research Methods, 38, 606–609.


2217