Contralateral White Noise Selectively Changes Left Human Auditory Cortex Activity in a Lexical Decision Task

Abstract

In a previous study, we hypothesized that the approach of presenting information-bearing stimuli to one ear and noise to the other ear may be a general strategy to determine hemispheric specialization in auditory cortex (AC). In that study, we confirmed the dominant role of the right AC in directional categorization of frequency modulations by showing that fMRI activation of right but not left AC was sharply emphasized when masking noise was presented to the contralateral ear. Here, we tested this hypothesis using a lexical decision task supposed to be mainly processed in the left hemisphere. Subjects had to distinguish between pseudowords and natural words presented monaurally to the left or right ear either with or without white noise to the other ear. According to our hypothesis, we expected a strong effect of contralateral noise on fMRI activity in left AC. For the control conditions without noise, we found that activation in both auditory cortices was stronger on contralateral than on ipsilateral word stimulation consistent with a more influential contralateral than ipsilateral auditory pathway. Additional presentation of contralateral noise did not significantly change activation in right AC, whereas it led to a significant increase of activation in left AC compared with the condition without noise. This is consistent with a left hemispheric specialization for lexical decisions. Thus our results support the hypothesis that activation by ipsilateral information-bearing stimuli is upregulated mainly in the hemisphere specialized for a given task when noise is presented to the more influential contralateral ear.

Aging Effects on the Activation of the Auditory Cortex during Binaural Speech Listening in White Noise: An fMRI Study

“…In addition, topdown influences appear to select the hemisphere specifically involved in the processing of stimuli depending on the task . During dichotic listening, the activation by ipsilateral information-bearing stimuli is upregulated mainly in the hemisphere specialized for a given task when noise is presented to the more influential contralateral ear [Behne et al, 2005[Behne et al, , 2006. To date, however, the activation patterns during binaural selective speech listening in white noise using both ears have seldom been examined.…”

“…In that of Scott et al [2004], subjects listened for the target speaker's meaning in unmodulated noise using both ears. In the study of Binder et al [2004], subjects were asked to press buttons during a sound identification task in different noisy conditions using both ears, and, in the reports of Behne et al [2005Behne et al [ , 2006, subjects actively did a frequency-modulat ed direction task or a lexical decision task and dichotic monosyllables in noise by pressing a button. In contrast, our instruction, except pressing a button at the end of each sentence, to our subjects was that they had to comprehend all sentences in white noise binaurally, but report the difficulty of sentence comprehension after scanning.…”

Auditory intensity processing: Categorization versus comparison

“…For the investigation, we used a method that is able to elucidate differential hemispheric contribution to the processing, based on an increase in activity by presenting additional noise contralateral to ipsilateral presented task-relevant stimuli (Angenstein and Brechmann, 2013a, b;Behne et al, 2005;Behne et al, 2006;Stefanatos et al, 2008). The task-relevant stimuli are presented monaurally with and without contralateral noise.…”

Hemispheric differences in specificity effects in talker identification

“…The presentation of noise in the opposite ear should increase competition between the hemispheres, which, in turn, should increase the likelihood of observing hemispheric asymmetries (Fecteau, Enns, & Kingstone, 2000;Kimura, 1961). Recent data provide evidence that presenting stimuli to one ear and noise to the other ear is an efficient strategy for examining hemispheric specialization in auditory cortical activity for both nonspeech (Behne, Scheich, & Brechmann, 2005) and speech (Behne, Wendt, Scheich, & Brechmann, 2006) stimuli. In order to test the robustness of this asymmetrical pattern in talker identification, we carried out an additional experiment under conditions less favorable to the emergence of hemispheric differences and more similar to natural conditions (i.e., conditions that would occur in daily life outside the laboratory).…”