Proceedings Fonetik 2009 - Institutionen för lingvistik

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Proceedings, FONETIK 2009, Dept. of Linguistics, Stockholm UniversityAuditory white noise enhances cognitive performanceunder certain conditions: Examples from visuo-spatialworking memory and dichotic listening tasksGöran G. B. W. Söderlund, Ellen Marklund, and Francisco LacerdaDepartment of Linguistics, Stockholm University, StockholmAbstractThis study examines when external auditivenoise can enhance performance in a dichoticlistening and a visuo-spatial working memorytask. Noise is typically conceived of as beingdetrimental for cognitive performance; however,given the mechanism of stochastic resonance(SR), a certain amount of noise can benefitperformance. In particular we predict thatlow performers will be aided by noise whereashigh performers decline in performance duringthe same condition. Data from two experimentswill be presented; participants were students atStockholm University.IntroductionAimThe aim of this study is to further investigatethe effects of auditory white noise on attentionand cognitive performance in a normal population.Earlier research from our laboratory hasfound that noise exposure can, under certainprescribed settings, be beneficial for performancein cognitive tasks, in particular for individualswith attentional problems such as AttentionDeficit/Hyperactivity Disorder (ADHD)(Söderlund et al., 2007). Positive effects ofnoise was also found in a normal population ofschool children among inattentive or lowachieving children (Söderlund & Sikström,2008). The purpose of this study is to includetwo cognitive tasks that has not earlier beenperformed under noise exposure. The first taskis the dichotic listening paradigm that measuresattention and cognitive control. The secondtask is a visuo-spatial working memory test thatmeasures working memory performance.Participants were students at Stockholm University.BackgroundIt has long been known that, under most circumstances,cognitive processing is easily disturbedby environmental noise and non-taskcompatible distractors (Broadbent, 1958). Theeffects hold across a wide variety of tasks, distractorsand participant populations (e.g. Bomanet al., 2005; Hygge et al., 2003). In contrastto the main body of evidence regardingdistractors and noise, there has been a numberof reports of counterintuitive findings. ADHDchildren performed better on arithmetic’s whenexposed to rock music (Abikoff et al., 1996;Gerjets et al., 2002). Children with low socioeconomicstatus and from crowded householdsperformed better on memory test when exposedto road traffic noise (Stansfeld et al., 2005).These studies did not, however, provide satisfactorytheoretical account for the beneficialeffect of noise, only referring to general increaseof arousal and general appeal counteractingboredom.Signaling in the brain is noisy, but thebrain possesses a remarkable ability to distinguishthe information carrying signal from thesurrounding, irrelevant noise. A fundamentalmechanism that contributes to this process isthe phenomenon of stochastic resonance (SR).SR is the counterintuitive phenomenon ofnoise-improved detection of weak signals in thecentral nervous system. SR makes a weak signal,below the hearing threshold, detectablewhen external auditory noise is added (Moss etal., 2004). In humans, SR has also been foundin the sensory modalities of touch (Wells et al.,2005), hearing (Zeng et al., 2000), and vision(Simonotto et al., 1999), all in which moderatenoise has been shown to improve sensory discrimination.However, the effect is not restrictedto sensory processing as SR has alsobeen found in higher functions e.g., auditorynoise improved the speed of arithmetic computationsin a group of school children (Usher &Feingold, 2000). SR is usually quantified byplotting detection of a weak signal, or cognitiveperformance, as a function of noise intensity.This relation exhibits an inverted U-curve,where performance peaks at a moderate noiselevel. That is, moderate noise is beneficial forperformance whereas too much, or too littlenoise, attenuates performance.160
Proceedings, FONETIK 2009, Dept. of Linguistics, Stockholm UniversityAccording to the Moderate Brain Arousal(MBA) model (Sikström & Söderlund, 2007), aneurocomputational model of cognitive performancein ADHD, noise in the environment introducesinternal noise into the neural system tocompensate for reduced neural background activityin ADHD. This reduced neural activity isbelieved to depend on a hypo-functioning dopaminesystem in ADHD (Solanto, 2002). TheMBA model suggests that the amount of noiserequired for optimal cognitive performance ismodulated by dopamine levels and thereforediffers between individuals. Dopaminemodualtes neural responses and function byincreasing the signal-to-noise ratio throughenhanced differentiation between background,efferent firing and afferent stimulation (Cohenet al., 2002). Thus, persons with low levels ofdopamine will perform inferior in tasks thatdeserves a large signal-to-noise ratio. It isproposed that inattentive and/or low performingparticipants will benefit from noise whereasattentive or high performers will not.ExperimentsExperiment 1. Dichotic listeningDichotic literally means listening to two differentverbal signals (typically the syllables ba, da,ga, pa, ta, ka) presented at the same time, onepresented in the left ear and one in the right ear.The common finding is that participants aremore likely to report the syllable presented inthe right ear, a right ear advantage (REA)(Hugdahl & Davidson, 2003). During stimulusdriven bottom-up processing language stimuliare normally (in right-handers) perceived by theleft hemisphere that receive information fromthe contralateral right ear in a dichotic stimuluspresentation situation. If participants are instructedto attend to and report from the stimulipresented to the left ear, forced-left ear condition,this requires top-down processing to shiftattention from right to left ear. Abundant evidencefrom Hugdahl’s research group hasshown that this attentional shift is possible todo for healthy persons but not for clinicalgroups distinguished by attentional problemslike in: schizophrenia, depression, and ADHDwho generally fails to make this shift from rightto left ear (Hugdahl et al., 2003). The forcedleftsituation produces a conflict that requirescognitive control to be resolved.The purpose with present experiment is to findout whether noise exposure will facilitate cognitivecontrol in either forced-left ear, orforced-right ear condition in a group of students.Four noise levels will be used to determinethe most appropriate noise level.Experiment 2. Visuo-spatial memoryThe visuo-spatial working memory (vsWM)test is a sensitive measure of cognitive deficitsin ADHD (Westerberg et al., 2004). This testdetermines working memory capacity withoutbeing affected from previous skills or knowledge.Earlier research has shown that performingvsWM tasks mainly activates the right hemisphere,which indicates that the visou-spatialability is lateralized (Smith & Jonides, 1999).Research from our group has found that whitenoise exposure improve performance vsWM inboth ADHD and control children (Söderlund etal. manuscript). This finding rises the questionwhether lateralized noise (left or right ear) exposureduring vsWM encoding will affect performancedifferently.The purpose of the second experiment is tofind out if effects of noise exposure to the leftear will differ from exposure to the right ear.Control conditions will be noise exposure toboth ears and no noise. The prediction is thatnoise exposure to the left ear will affect performancein either positive or negative directionwhereas exposure to the right ear will be closeto the baseline condition, no noise.MethodsExperiment 1. Dichotic listeningParticipantsThirty-one students from Stockholm University,aged between 18 and 36 years (M=28,6), seventeenwomen and fourteen men. Twenty-ninewhere right-handed and two left-handed.Design and materialThe design was a 2 x 4, where attention (forcedleft vs. forced right ear) and noise level (nonoise, 50, 60, and 72 dB) were independentvariables (within subject manipulations). Dependentvariable was number of correct recalledsyllables. Speech signal was 64 dB. Interstimulusintervals were 4 seconds and 16 syllableswhere presented in each condition. Four161
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