Proceedings Fonetik 2009 - Institutionen för lingvistik

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Proceedings, FONETIK 2009, Dept. of Linguistics, Stockholm Universitycontrol syllables (same in both ears) where presentedin each trial so maximum score was 12syllables. Participants were divided into twogroups after their aggregate performance in themost demanding, forced left ear condition, inthe four noise levels.ProcedureParticipants sat in a silent room in front of acomputer screen and responded by pressing thefirst letter of the perceived syllable on a keyboard.Syllables and noise where presentedthrough earphones. Conditions and syllableswere presented in random order and the experimentwas programmed in E-prime 1.2 (Psychologysoftware). Nine trials of stimuli werepresented; the first time was the non-forcedbaseline condition. The remaining eight trialswhere either forced left ear or forced right earpresented under the four noise conditions. Thetesting session lasted for approximately 20 minutes.Experiment 2. Visuo-Spatial WM taskParticipantsTwenty students at Stockholm University aged18-44 years (M=32,3), 9 men and 11 women. 3where left-handed and 17 right handed.Design and materialThe design was a 4 x 2, where noise (no noise,noise left ear, noise right ear, noise both ears)were the within subject manipulation and performancelevel (high vs. low performers) werethe between group manipulation. The noise levelwas set in accordance with earlier studies to77 dB. The visuo-spatial WM task (Spanboard2009) consists of red dots (memory stimuli)that are presented one at a time at a computerscreen in a four by four grid. Inter-stimulus intervalswere 4 seconds, target is shown 2 secand a 2 sec pause before next target turns up.Participants are asked to recall location, and theorder in which the red dots appear. The workingmemory load increases after every secondtrial and the WM capacity is estimated based onthe number of correctly recalled dots. Participantswere divided into two groups after theirperformance in the spanboard task, an aggregatemeasure of their result in all four conditions.The results for high performers wherebetween 197-247 points (n=9) and low performersbetween 109-177 points (n=11).yProcedureParticipants sat in a silent room in front of acomputer screen and responded by using themouse pointer. The noise was presented in headphones. Recall time is not limited and participantsclick on a green arrow when they decideto continue. Every participant performs the testfour times, one time in each noise condition.Order of noise conditions were randomized.ResultsExperiment 1. Dichotic listeningIn the non-forced baseline condition a significantright ear advantage was shown. A maineffect of attention was found in favor for theright ear, more syllables were recalled in theforced right ear condition in comparison withthe forced left ear, (Figure 1). There was nomain effect of noise while noise affected conditionsdifferently. An interaction between attentionand noise was found (F(28,3) = 5.66, p =.004) In the forced left condition noise exposuredid not affect performance at all, the small increasein the lowest noise condition was nonsignificant.A facilitating effect of noise wasfound in the forced right ear condition, themore noise the better performance (F(30,1) =5.63, p = .024).8.07.57.06.56.05.55.04.54.0Recall as a Function of Attention and NoiseNoise, p = .024Left EarRight earN1 N2 N3 N4Noise LevelsNoise x attention, p = .004Figure 1. Number correct recalled syllables as afunction of noise. Noise levels were N1= no noise,N2 = 50 dB, N3 = 60 dB, and N4 = 72 dB.When participants where divided according toperformance in the dichotic listening task, noiseimproved performance for both groups in theforced-right ear condition. A trend was found inns.162
Proceedings, FONETIK 2009, Dept. of Linguistics, Stockholm UniversityNumber correct recalled dotsthe forced-left condition where high performersdeteriorated by noise and there was no changefor low performers (p = .094)Experiment 2. Visuo-spatial WM taskNo effect of noise was present when the entiresample was investigated. However, when participantswere divided into two groups based ontheir test performance a two way ANOVA revealeda trend towards interaction between lateralizednoise and group (F(16,3)=2.95,p=.065). When noise exposure to both ears wasexcluded from the ANOVA it did reach significance(F(17,2)=4.13, p=.024). Further interactionswere found between group and nonoise vs. noise left ear (F(18,1)= 8.76, p=.008)and between left ear and right ear(F(18,1)=4.59, p=.046). No interaction wasfound between group and noise right ear vs.noise both ears (Figure 2).6055504540353025Recall as a Function of Noise and Groupoverall: noise x group p = .065p = .008 p = .046 ns.High PerformersLow PerformersNo noise Noise left Noise right Noise bothFigure 2. Number correct recalled dots as a functionof laterlized noise. (77 dB, left ear, right ear, bothears, or no noise)Noteworthy is that the low performing groupconsisted nine women and two men whereasthe high performing group consisted of twowomen and seven men. However the genderand noise interaction did not reach significancebut indicated a trend (p= .096).Paired samples t-test showed that the noiseincrement in left ear for the low performinggroup was significant (t(10)=2.25, p=.024 onetailed) and the decrement for the high performinggroup in the same condition significant aswell (t(8)=1.98, p=.042 one tailed).ConclusionsThe rationale behind these two studies was toinvestigate effects of noise in two cognitivetasks that put high demands on executive functionsand working memory in a normal population.Results showed that there was an effect ofnoise in both experiments. In the dichotic listeningexperiment there was a main effect ofnoise derived from the forced-right ear condition.In the visuo-spatial working memory taskthere was no main effect of noise. However,when you split the group in two, high and lowperformers, you get significant results in accordancewith predictions.The most intriguing result in the presentstudy is the lateralization effect of noise exposurein the visuo-spatial working memory task.Firstly, we have shown that the noise effect iscross modal, auditory noise exerted an effect ona visual task. Secondly, the pattern of high andlow performers was inverted (in all conditions).The lateralization effect could have two possibleexplanations; the noise exposure to the righthemisphere either interacts with the rightdominantlateralized task specific activation inthe visuo-spatial task, or it activates crucial attentionalnetworks like the right dorsolateralpre-frontal cortex (Corbetta & Shulman, 2002).In the dichotic listening experiment we onlygot effects in the easy, forced-right ear condition,that owes a large signal-to-noise ratio. Themore demanding forced-left ear condition mayget improved by noise exposure when exposedto inattentive, ADHD participants, this will betested in upcoming experiments.To gain such prominent group effects despitethe homogeneity of the group consistingof university students demonstrates a large potentialfor future studies on participants withattentional problems, such as in ADHD.AcknowledgementsData collection was made by students from theDepartment of Linguistics and from students atthe speech therapist program. This research wasfunded by a grant from Swedish ResearchCouncil (VR 421-2007-2479).163
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