![]() As a consequence, speech stimuli presented in the right ear are processed more readily than similar information simultaneously presented in the left ear. The REA is considered to be a result of the anatomical fact that the contralateral neural pathways are more preponderant than the ipsilateral ones (Brodal, 1981), and that the left hemisphere is “programmed” to be superior to the right hemisphere for processing of linguistic auditory input (Kimura, 1961 1967). This is called a Right‐Ear Advantage (REA), and is one of the most frequently used indices of brain laterality within the auditory domain (see Hugdahl, 1988 for an overview). A common empirical finding with the DL technique is that more items are reported from the right compared to the left ear input, for speech stimuli (Bryden, 1988 Hugdahl, 1995). The dichotic listening (DL) situation means that two different auditory stimuli are presented at the same time, one in each ear (Kimura, 1961 Bryden, 1988). The observed activations in the parietal lobe during the focused attention conditions could be part of a modality non‐specific “attentional network”. An interpretation of the findings is that attention has a facilitating effect for auditory processing, causing reduced activation in the primary auditory cortex when attention is explicitly recruited. The musical instrument stimuli mainly activated areas in visual association cortex, cerebellum, and the hippocampus. The CV‐syllables activated areas corresponding to the classic language areas of Broca and Wernicke. Concentrating on either the right or left ear stimulus significantly decreased activity bilaterally in the temporal lobes compared to concentrating on both ear stimuli, at the expense of an increased activation in the right posterior and inferior superior parietal lobe. Brain activation was measured with 15O‐PET, and significant changes in regional normalized counts (rNC) were evaluated using statistical parametric mapping (SPM96) software. The subjects were instructed to either concentrate on the stimuli presented in both ears, or only on the left or right ear stimulus. The target stimulus appeared an equal number of times in the left and right ear. ![]() Twelve subjects listened to lists of consonant‐vowel syllables, or short musical instrument passages, with the task of detecting a “target” syllable or musical instrument by pressing a button. Two different stimuli were presented simultaneously, one in each ear. Dichotic listening is a technique to study laterality effects in the auditory sensory modality. The present study investigated the effect of attention on brain activation in a dichotic listening situation.
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