Interaural intensity difference and ear advantage in listening to dichotic consonant-vowel syllable pairs.
The right-ear advantage (REA) is typically observed in verbal dichotic listening, indicating a left hemisphere superiority for speech processing. The REA could be thought of as a bottom-up, stimulus-driven laterality effect, caused by the preponderance of the contralateral neural fibers from the right ear to the auditory/speech processing areas in the left temporal lobe. The REA can, however, be modified by explicitly requiring the listeners to focus their attention alternatively on the left or right-ear stimuli, thus either countering or enhancing the bottom-up processes through top-down attentional control. In the present study, we manipulated the strength of the bottom-up REA by inducing an intensity difference between the right-ear and left-ear speech inputs in order to make the REA either weaker (left-ear input>right-ear input) or stronger (left-ear input<right-ear input) and also examined how this manipulation affected the top-down attention modulation effects. Twenty healthy participants listened to dichotic presentations of consonant-vowel syllable pairs with different attention instructions. The results showed that the interaural intensity difference significantly affected the ear advantage in the predicted way. It also interacted with the top-down control effects, attentional control having a stronger effect when attending to the ear that had a weaker sound intensity, as compared to when the intensities were equal.
Tallus
Jussi
J
Center for Cognitive Neuroscience, Department of Psychology, Publicum, Assistentinkatu 7, FIN-20014, University of Turku, Finland. jptall@utu.fi
Hugdahl
Kenneth
K
Alho
Kimmo
K
Medvedev
Svjatoslav
S
Hämäläinen
Heikki
H
D000161:Acoustic Stimulation; D000328:Adult; D000704:Analysis of Variance; D001288:Attention / Q000502:physiology*; D001307:Auditory Perception / Q000502:physiology*; D004007:Dichotic Listening Tests; D004307:Dose-Response Relationship, Radiation; D004423:Ear; D005260:Female; D007839:Functional Laterality / Q000502:physiology*; D006801:Humans; D008297:Male; D010700:Phonetics; D000091402:Prohibitins; D013061:Speech Acoustics; D013063:Speech Discrimination Tests