Brain Event‐Related Potentials as Indicators of Early Selective Processes in Auditory Target Localization

Abstract

To establish the stages of brain processing in an auditory stimulus localization task, event‐related potentials (ERPs) were recorded from 24 normal subjects listening to brief white noise stimuli in a free‐field situation from front, back, left and right loudspeakers. The subject's task was to respond to ‘target’ stimuli from one designated speaker. Performance varied as a function of sound location, stimuli in the front/back dimension being more difficult to localize than those in the left/right. ERP results, based on averaged waveforms, difference waveforms and the factors derived from a principal components analysis, revealed a series of task related components. Some were relatively transient, others more sustained in character. One brain component showed task related amplitude changes with an onset as early as 15 msec. These changes were target specific for sounds in the easier left/right dimension only. Later components, such as the P300, also varied in amplitude between targets and non‐targets, but showed no significant amplitude or latency differences to target stimuli as a function of location, despite the significant performance differences.

Knowledge of Stimulus Repetition Affects the Magnitude and Spatial Distribution of Low-Frequency Event-Related Brain Potentials

“…The present findings demonstrate that there are effects of stimulus expectancies or attentional biases [McCallum et al, 1983] on mid-latency AERs. Subjects who knew how many stimuli were to be presented had a larger rate effect than those who did not possess such information.…”

“…Apparently, when subjects had knowledge of repetition configuration in this paradigm, the first event provided all the relevant information for adequately processing the impending stimuli. This is strong evidence that stimulus expectancies or attentional biases [McCallum et al, 1983;Schafer and Marcus, 1973] can have a profound impact on the rate effect, even for early AERs that have been thought to index preattentive sensory gating [Freedman et al, 1991].…”

“…A series of other investigations, however, suggest that there are effects of 304 Audiol Neurootol 2002;7:303-314 Clementz/Barber/Dzau selective attention [McCallum et al, 1983;Woldorff et al, 1993;Woldorff and Hillyard, 1991] and predictability of stimulus timing [Schafer and Marcus, 1973;Schafer et al, 1981] on AERs as early as 25 ms after stimulus onset. Additionally, Erwin et al [1998] reported correlations between measures of attention and rate effects among schizophrenia patients, a clinical population in which AER gating studies have played an important theoretical role.…”

Focused auditory attention and frequency selectivity

“…Electrophysiological evidence shows that in cats (Oatman & Anderson, 1977) and in humans (Lukas, 1980(Lukas, , 1981 attention to a visual task reduces and delays the neural potentials evoked by sound in the cochlear nucleus and inferior colliculus. In humans, attention to a targeted auditory locus has been shown to enhance evoked potentials from the periphery of the auditory nervous system (McCallum, Curry, Cooper, Pocock, & Papakostopoulos, 1983). These results revive the possibility that efferent input under attentional control may attenuate the responsiveness of the auditory system to sound.…”

Brain cortical organization in entrepreneurs during a visual Stroop decision task

“…Their topography and amplitude are strongly task-dependent. The amplitude of ERPs varies with the amount of neuronal activation 8 and the amount of mental effort. 9,10 ERP topography varies with the underlying cognitive process [11][12][13] and is correlated with the brain location of the underlying neural generators.…”