Electrophysiologic correlates of attention versus stimulus competition in young male and female listeners.

The effects of attention and stimulus competition on the late auditory-evoked potential (LAEP) were compared in 10 young males and 10 young females. Listeners attended to discriminably different oddball tonal sequences presented binaurally or monaurally. Peak amplitudes in response to the frequent tones were measured for N1, P2, and early and late N2 (N2e and N21) components of the LAEP Whereas N1 amplitudes increased, the amplitudes of P2 decreased when listeners attended to, rather than ignored, the tones. Competition effects for both N1 and P2 resulted in reduced amplitudes in the presence of contralateral competition. Although findings with N2e and N21 suggested possible attention and competition effects, as well as gender differences, the data were inconsistent and will need further experimental verification. The present findings with the N1 and P2 components provide evidence that different neural processes underlie the attention and competition effects in the human brain.

Effects of monaural versus binaural stimulation on P300 scalp topography in elderly listeners.

The P300 event-related potential was recorded from groups of young and elderly listeners in response to monaural and binaural stimulation. An oddball stimulus paradigm was used to record responses from 19 scalp locations. When listening to binaural stimuli, the young group showed midline and central P300 amplitude maxima, whereas the elderly group exhibited maximal responses in the midline and parietal regions. With monaural stimulation, the young group's responses were similar to those obtained with binaural stimulation. The elderly group, however, showed evidence of a greater contralateral hemisphere response to monaural stimulation during the early part of the P300 response. These findings support the possibility that the P300 neural generators may change with age with respect to temporal onset characteristics or their orientation and strength.

Electrophysiologic signs of auditory competition in the human brain.

The present project investigated the electrophysiologic effects of auditory competition on components of the late auditory evoked potential (LAEP). A group of 12 young female listeners attended to deviant tones interspersed among frequent tones in one ear while trains of deviant and frequent tones of a different frequency were either present or absent at the opposite ear. Comparison of event-related potential (ERP) waveforms with competition- and attention-related difference waves revealed evidence that the neural effects of competition were not simply a moderation of the effects of selective attention (i.e. the processing negativity). The two difference waves exhibited amplitude peaks that were not mirror-images with respect to polarity. This suggests the existence of a unique underlying neural process that is responsible for the effects of competition on the LAEP.

Electrophysiologic signs of auditory distraction in elderly listeners.

Brain mapping was used to investigate the ability of young and elderly female listeners to attend to /ga/ syllabic events at one ear in the presence of speech babble competition at the opposite ear. An oddball stimulus presentation paradigm was used to record the N1 and P2 components of the late auditory evoked potential (LAEP) from 19 scalp locations. With speech competition, elderly listeners exhibited significantly larger reductions in P2 amplitude than did young listeners. The competition produced no changes in N1 amplitude in either group. These findings contrast with those of an earlier study in which age-related reductions in N1 but not P2 amplitude were found when listeners attended to tones rather than speech stimuli in the presence of speech competition. These studies suggest that amplitude reductions in different LAEP components may provide electrophysiologic indices of age-related breakdowns in processing sounds in the presence of competition. Which LAEP components are affected may depend on experimental variables such as task difficulty or the nature of the stimuli (e.g., speech vs nonspeech).

Effects of contralateral speech competition on auditory event-related potentials recorded from elderly listeners: brain map study.

Topographic brain mapping was used to investigate the ability of young and elderly female listeners to attend to tones at one ear in the presence of speech competition at the opposite ear. An oddball stimulus presentation paradigm was used to record the N1, P2, and P300 components of the late auditory evoked potential from 19 scalp locations. With speech competition, elderly listeners exhibited significantly larger reductions in N1 amplitude than did young listeners. This suggests that N1 may provide an electrophysiologic index of age-related breakdowns in processing sounds in the presence of background competition. An unexpected difference was also found between young and elderly listeners in P300 scalp topography. While the young listeners' P300 response was centered at midline for both left and right ear stimulation, the elderly participants had P300 maxima centered in the parietal area of the hemisphere located contralateral to the test ear. This suggests that some of the functional properties (e.g., timing, strength, orientation) of the P300 neural generators may change with age or, alternatively, that different generators may be operative in elderly listeners.