Regular articleFocused and divided attention in a simulated cocktail-party situation: ERP evidence from younger and older adults
Introduction
Speech perception under so-called “cocktail-party” conditions usually becomes harder with increasing age, posing a severe problem for everyday communication. As recently demonstrated, the ability to understand speech under complex listening conditions with multiple speakers being simultaneously active declines already in midlife (Helfer, 2015). There is increasing evidence that these age-related difficulties in speech perception are not only based on changes in peripheral hearing (e.g., presbycusis) and in central auditory processing (Humes and Dubno, 2010) but also on changes in cognitive abilities. Declines in working memory capacity, for example, are associated with speech perception of older adults (e.g., Gygi and Shafiro, 2014, Lin and Carlile, 2015, Meister et al., 2013). Age-related changes in attentional and inhibitory control also appear to impact speech perception, especially in multispeaker listening environments. Accurate speech perception when multiple people are speaking depends on the ability to focus auditory attention to a speaker of interest while suppressing the concurrent speech of others (for review, see Schneider et al., 2010).
Attention and inhibitory control could be especially relevant for a conversation with 2 or more speakers, where a listener has to (1) attend to all involved speakers at once and (2) to focus on the verbal input of a single (relevant) speaker. In this regard, 2 aspects of auditory attention can be distinguished: focused and divided attention. Focused attention includes the selection of a relevant speaker of interest and the suppression of any irrelevant speech. Divided attention, on the other hand, refers to the spreading of attentional resources to different speakers and different spatial locations. Successful speech perception in multispeaker environments depends on both divided and focused attention, given that a listener may divide attention among several speakers before selectively focusing on a single one (Brungart et al., 2001). Since divided attention is more complex and requires more processing operations (Madden and Plude, 1993), it appears to be more prone to age-related decline than focused attention (e.g., Kok, 2000, McDowd and Craik, 1988, Wild-Wall and Falkenstein, 2010). In addition, although the selection of a relevant speaker may be preserved in aging (e.g., Talsma et al., 2006), suppressing irrelevant stimuli appears to decline, as has been discussed with respect to the inhibitory deficit hypothesis (Hasher and Zacks, 1988; for a recent review, see; Zanto and Gazzaley, 2014). Accordingly, older adults appear to have more difficulties under conditions of divided attention than in situations where auditory attention can be focused on one fixed source of interest (e.g., Drager and Reichle, 2001, Gygi and Shafiro, 2014, Meister et al., 2013, Wild-Wall and Falkenstein, 2010). Moreover, older adults have more difficulties with divided attention (Helfer et al., 2010, McDowd and Craik, 1988), which requires more processing resources than focused attention.
The interplay of divided and focused attention can be operationalized by an experimental design in which listeners first have to explicitly detect a target word presented by several alternative speakers (divided attention). If the target word is present, they would then identify specific information presented by this target speaker (selective attention). Using this “dual-task” design, it could be demonstrated that divided and focused attention are highly entangled in natural speech perception and that both aspects of attention draw on a shared pool of processing resources (e.g., Gygi and Shafiro, 2012, Shafiro and Gygi, 2007).
The aim of the present experiment was to test for cortical responses in a speech perception task that differ among younger and older adults. The design included 2 attention conditions and 2 speech conditions, in a crossed design. The 2 attention conditions were termed “focused” and “divided” attention and used the combination of a naturalistic speech comprehension paradigm and electrophysiological measures. We used a simulated “cocktail-party” environment in which the participants had to attend to relevant information that was presented either from a fixed position (focused attention) or, alternatively, from 2 different positions in space (divided attention). Although the focused attention condition allowed the listener to direct auditory attention to a single location, in the divided attention condition the listener first had to simultaneously monitor 2 locations, and then to select the relevant location. A modified version of the “stock-price monitoring” task was used (Getzmann and Falkenstein, 2011, Getzmann et al., 2014), in which sequences of short company names and simulated stock prices were presented (e.g., “Bosch—zwei” [“Bosch—two”]). The listener had to monitor a target company while ignoring all other concurrent information. The focus of attention toward the relevant target position was operationalized by a go-nogo task, in which the participants had to press a response button when the value of the target company was a specific number.
The stock-price monitoring task is a cued go-nogo task in which the company name is the cue (indicating the spatial position of the relevant information) and the company value is the target (indicating whether the listener has to respond or not). There were also 2 speech conditions. In the single-speech (baseline) condition, only the speaker of the target company was presented. In the multispeech condition, the target speech was embedded in a complex sound scape having 3 concurrent speakers of nontarget speech stimuli. It was expected that older participants would differ from the young in their ability to simultaneously attend to 2 different positions. We predict that age-related decreases in speech perception will be worse in the divided, relative to the focused, attention condition, and that these differences will be exacerbated in the multispeech situation.
To clarify the neurophysiological basis of age-related differences in performance, electrophysiological correlates of speech processing were compared for the 2 attention conditions. Here, we focused on the so-called contingent negative variation (CNV) that is derived from the electroencephalogram (e.g., Chennu et al., 2013, Wild-Wall and Falkenstein, 2010, Zanto et al., 2011). The CNV is a central negative potential that is linked to expectancy (Walter et al., 1964) and—more generally—to the processes of preparation (Brunia and van Boxtel, 2001). The CNV usually occurs in the time interval between a cue signaling a subsequent target and an imperative stimulus triggering a (motor) response. It increases amplitude with task difficulty (e.g., Lorist et al., 2000, Wild-Wall et al., 2007) and effort (Falkenstein et al., 2003). The CNV has also been related to preparatory allocation of attentional resources (for recent evidence, see Wöstmann et al., 2015), possibly through an enhancement of excitability in task-relevant cortical neural networks (Raichle, 2011). Thus, CNV amplitude is reduced when selective attention to task-relevant stimuli is impaired by distractors (Tecce and Scheff, 1969, Travis and Tecce, 1998), whereas a larger CNV amplitude is associated with improved target detection (e.g., O'Connell et al., 2009, Rockstroh et al., 1993).
There is some evidence of age-related effects on CNV (for a review, see Zanto and Gazzaley, 2014), but previous results are rather inconsistent: Although in a previous study older adults showed a greater CNV, suggesting more preparation and higher effort than younger ones (Wild-Wall et al., 2007), other studies did not find consistent age-related differences in CNV (e.g., Wöstmann et al., 2015), or even a smaller CNV of older adults, especially under divided-attention conditions (Wild-Wall and Falkenstein, 2010). The latter effect could reflect an age-based decline in attention allocation in time, as has been found for several types of tasks (Zanto et al., 2011). CNV differences between young, young-old (60–69), and oldest-old adults (>85 years) also depend on the motor requirements of the task (Golob et al., 2005).
To clarify the role of preparatory activity for speech perception in a “cocktail-party” environment, we analyzed the CNV under divided and focused attention conditions. In the current paradigm, the CNV should occur between the onsets of the company name and company value. It should reflect the preparatory activity triggered by the company name that will influence processing of the subsequent target by allocation of attentional resources. A higher CNV amplitude was expected to be related to more efficient preparation, which should, consequently, be associated with better speech recognition performance. The time course of the CNV was also analyzed in the focused and divided attention conditions to reveal potential age-related differences in preparation. Finally, the cortical sources of potential CNV differences between the 2 age groups were investigated using standardized low-resolution brain electromagnetic tomography (sLORETA; Pascual-Marqui, 2002). Besides the CNV, we analyzed the event-related potentials (ERPs) to the onset of the company name to test whether older and younger adults differ in the processing of the cue information. We focused on the P1 and N1 components, which index, respectively, basic stimulus processing and early processes of attention allocation (e.g., Schneider et al., 2012, Wascher and Beste, 2010; for review, Eimer, 2014), and stimulus evaluation and classification (Potts, 2004).
Section snippets
Subjects
A total of 53 volunteers took part in the study, consisting of 30 young (16 female; mean age, 25.2 years; age range, 19–32 years) and 23 middle-aged and old (11 female; mean age, 62.2 years; age range, 55–69 years) adults. The young participants were recruited from local colleges, whereas the older participants were recruited through newspaper advertisements and flyers distributed in the city of Dortmund (Germany). All participants reported to be right handed and healthy, free of medication
Behavioural data
Results from the ANOVA tests of behavioral data are presented in Table 1. There was a main effect of listening condition, indicated by more hits with single-speech than multispeech stimuli (96.2% vs. 73.0%, respectively). There was also an age group × listening condition interaction, which indicated that the decrease in hit rates with multispeech stimuli was more pronounced in the older group (29.6% decrease) relative to the young (16.6% decrease; Fig. 2). There was no clear main effect of
Discussion
In the stock-price monitoring task, older participants showed the most pronounced decline in performance when they had to monitor 2 alternative speakers at once, and when the target speech information interfered with concurrent speech input. In contrast, while the performance of the younger participants also decreased in the presence of concurrent speech, there was no significant difference when attending to 1 versus 2 target speakers. Thus, the present speech perception task provided
Disclosure statement
All authors disclose no actual or potential conflicts of interest including any financial, personal, or other relationships with other people or organizations that could inappropriately influence (bias) their work.
Acknowledgements
The authors are grateful to Peter Dillmann for technical assistance, to Christina Hanenberg and Lukas Labisch for their help in running the experiments, and to 3 anonymous reviewers for valuable comments on an earlier draft of the article. This work was funded by a grant from the Deutsche Forschungsgemeinschaft (DFG GE 1920/3-1).
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