PROCEEDINGS of the23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Effects of task-irrelevant background speech on verbal working
memory tasks
Maria KLATTE1; Kirstin BERGSTRÖM1; Thomas LACHMANN1,2,31

University of Kaiserslautern, Germany
2

3

University of Leuven, Belgium

Facultad de Lenguas y Educación de la Universidad Antonio de Nebrija, Spain

ABSTRACT
Immediate serial recall of visually presented verbal items is impaired by task-irrelevant background speechthat the participants are instructed to ignore. This so-called “irrelevant speech effect” (ISE) has been
attributed to interference with phonological representations, interference with representations of serial order,
or attentional capture away from the focal task.
In order to learn more about the task characteristics necessary for ISE evocation, we designed 3 verbal
working memory tasks that were comparable with respect to task structure, but differed in the cognitive
processes involved. In each task, sequences of 7 German nouns were presented pictorially. In Task 1,participants had to reconstruct the serial order of the items. In Task 2, participants had to decide which of the7 words represented by the pictures had no “partner” with the same initial phoneme. In Task 3, participants
had to decide which of the 7 items had no “partner” with respect to semantic category. Serial orderreconstruction of verbal items and phonological categorization were significantly impaired by irrelevant
speech, whereas semantic categorization was unaffected. Implications for theoretical accounts of the ISE arediscussed.
Keywords: Irrelevant speech effect, irrelevant sound effect, working memory, noise effects on cognitive
performance1. INTRODUCTION
Whether and to what extent task-irrelevant background sounds of moderate intensity disrupt
performance in non-auditory tasks (i.e., tasks that require processing of visually presentedinformation) depends on characteristics of the tasks and the sounds. The duplex-model proposed byHughes et al. [1] provides a general framework for noise effects on performance. This model assumes
two independent mechanisms of sound-induced disruption, i.e., “attentional capture” (involuntary
diversion of attention away from the focal task after an unexpected deviation from the recent auditorypast) and “interference-by-process” (specific interference between processes involved in thepre-attentive, obligatory processing of the irrelevant sound, and intentional processes involved in thefocal task).
Research in this field focused on verbal short-term memory, assessed by a standard task in which
participants have to recall a sequence of visually presented verbal items, e .g., digits, consonants, orwords, in the correct serial order. Performance in this “immediate serial recall”-task is reliably
impaired when task-irrelevant background sound is presented during item presentation, or during
presentation and recall. This so-called “irrelevant sound effect” (ISE) is especially pronounced withspeech sounds [2]. The ISE has been attributed to (i) interference between phonologicalrepresentations in the phonological store component of the phonological loop [3], (ii) interference
between serial order representations resulting from obligatory auditory perceptual organization of the
speech stream and serial order representations of the list items (“changing state effect”, [4]), and (iii)1

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mere attention capture due to speech [5].
In a series of experiments, we aim to elucidate the role of phonological processing, serial orderretention, and attention capture in the detrimental effect of speech sounds on working memory tasks.
In the experiment reported here, we assessed the effects of irrelevant speech on performance in threeverbal working memory tasks that were comparable with respect to task structure, but differed in thecognitive processes involved (serial order retention, phoneme comparison, and semantic
categorization).

2. Methods
2.1 ParticipantsParticipants were 74 students and junior researchers (51 male), aged between 19 and 34 years(M=23.5 years; SD 2 years), with German as first language. Participants were assigned to one of 3
experimental groups. One group (n=24, 19 male) performed the serial order reconstruction task, one
group (n=25; 16 male) performed the phonological processing task and one group (n=25, 16 male)
performed the semantic processing task.
2.2 Tasks and Sounds
In each of the three tasks, 7 easy-to-name pictures representing German nouns were presented oneafter another in the center of the computer screen, with a presentation time of 1100 msec and a 1000
interval between stimuli. After presentation of the seventh picture, all 7 pictures were shown
simultaneously in a random arrangement on the screen.
In the serial order task, participants had to reconstruct the serial order by clicking with the mouseon the pictures in the order they had been presented. For the phoneme comparison task, sequences werecomposed of 3 pairs of items with the same initial sound, and an “odd” item with a different initialsound. In the semantic categorization task, sequences were composed of 3 pairs of items from the same
semantic category (e.g., furnitures, vehicles), and one “odd” item representing a different category. In
both tasks, participants had to decide which of the 7 items is the “odd” one.
As task-irrelevant speech, we used a recording of narrative speech produced a male speaker readinga textbook in Korean language.
2.3 Procedure
Participants were tested individually in a sound-attenuated booth. After instruction, 3 practice trials
were performed, followed by 24 experimental trials. In half of the trials, irrelevant speech was played
through headphones at a comfortable sound level of about 60 dB. The remaining trials were performedin silence. Sound conditions (silence vs. speech) were varied quasi-randomly from trial to trial, so thatat most two successive trials were performed under the same sound condition.
2.4 Results
Mean performance (proportion correct) in the control condition was significantly lower in thesemantic categorization task (M = 0.56, SD = 0.18) when compared to serial order reconstruction(M=0.78; SD=0.12) and phoneme comparison (M = 0.68; SD = 0.22), with p < .01 and p = .06,
respectively. Serial order reconstruction and phoneme comparison did not differ with respect tocontrol performance (p > .20). Separate t-tests for paired samples revealed significant effects ofirrelevant speech in the serial order reconstruction task (p < .001) and in the phoneme comparison task
(p < 0.05). Semantic categorization was unaffected by irrelevant speech (p = .65).

3. Discussion
3.1 Mechanisms underlying the irrelevant speech effect
The current findings indicate that serial order retention is not a necessary condition for ISE
evocation. The phoneme comparison task does not require serial order retention, but evoked an ISE
similar to that observed in the serial order reconstruction task. Furthermore, the null effect found in thesemantic categorization task contradicts the attention capture account of the ISE. If irrelevant speech
impairs performance merely through diversion of attention, each of the three tasks should have been3680

affected. Thus, the results found here indicate that irrelevant speech evokes specific interference withphonological processing, which is involved in both serial order retention and phoneme comparison.
3.2 Limitations
Even though pilot studies were performed in order to verify comparable task difficulty, it turned outthat performance in the semantic categorization task was lower when compared to the other tasks. So,
the possibility that the difference in task difficulty is responsible for the differential effects ofbackground speech cannot be ruled out. However, this seems unlikely, as performance was well above
chance and below ceiling in each of the tasks, and prior findings argue against an impact of taskdifficulty on the ISE [6]. A further limitation is a lack of statistical power. Even though separate t-tests
indicate differential effects of irrelevant speech on the three tasks, the interaction could not be verified
statistically in a 2 (Sound condition) x 3 (Task) ANOVA (p >.20). Currently, we are performing furtherexperiments, aiming to confirm the current findings with increased sample sizes and trials percondition, the latter aiming to increase the reliability of the performance measures.

REFERENCES
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