Abstract
We used event-related brain potentials (ERPs) to study effects of selective attention on the processing of attended and unattended spoken syllables and letters. Participants were presented with syllables randomly occurring in the left or right ear and spoken by different voices and with a concurrent foveal stream of consonant letters written in darker or lighter fonts. During auditory phonological (AP) and non-phonological tasks, they responded to syllables in a designated ear starting with a vowel and spoken by female voices, respectively. These syllables occurred infrequently among standard syllables starting with a consonant and spoken by male voices. During visual phonological and non-phonological tasks, they responded to consonant letters with names starting with a vowel and to letters written in dark fonts, respectively. These letters occurred infrequently among standard letters with names starting with a consonant and written in light fonts. To examine genuine effects of attention and task on ERPs not overlapped by ERPs associated with target processing or deviance detection, these effects were studied only in ERPs to auditory and visual standards. During selective listening to syllables in a designated ear, ERPs to the attended syllables were negatively displaced during both phonological and non-phonological auditory tasks. Selective attention to letters elicited an early negative displacement and a subsequent positive displacement (Pd) of ERPs to attended letters being larger during the visual phonological than non-phonological task suggesting a higher demand for attention during the visual phonological task. Active suppression of unattended speech during the AP and non-phonological tasks and during the visual phonological tasks was suggested by a rejection positivity (RP) to unattended syllables. We also found evidence for suppression of the processing of task-irrelevant visual stimuli in visual ERPs during auditory tasks involving left-ear syllables.
Highlights
In everyday situations, our sensory systems receive much more information than we can consciously and actively process
Most previous event-related potential (ERP) studies on auditory selective attention examined the effects of attention on the processing of simple tones during auditory non-linguistic tasks (e.g., Hillyard et al, 1973; Näätänen et al, 1978; Hari et al, 1989; Woldorff et al, 1993) or the processing of speech sounds during auditory linguistic tasks (e.g., Woods et al, 1984; Teder et al, 1993)
Inspired by the suppression effect found for unattended speech in our previous study (Salo et al, 2013), we investigated in the present study whether ERPs to task-irrelevant spoken syllables during a visual phonological task would show an rejection positivity (RP) in relation to ERPs to task-irrelevant spoken syllables during a visual nonphonological task
Summary
Our sensory systems receive much more information than we can consciously and actively process. Most previous event-related potential (ERP) studies on auditory selective attention examined the effects of attention on the processing of simple tones during auditory non-linguistic tasks (e.g., Hillyard et al, 1973; Näätänen et al, 1978; Hari et al, 1989; Woldorff et al, 1993) or the processing of speech sounds during auditory linguistic tasks (e.g., Woods et al, 1984; Teder et al, 1993). In the present ERP study, we compared effects of selective attention on the processing of attended and ignored spoken syllables during auditory phonological (AP) and non-phonological tasks. Since the visual stimuli attended during the visual tasks and ignored during the auditory tasks were written letters, the present experiment allowed us to study possible effects of auditory and visual attention and tasks on the processing of visually presented linguistic material
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