An interesting phenomenon regarding to event-related-potentials is noticeable during dichotic presentation. Overall, the ERP's for attended stimuli were larger in amplitude than when the same stimuli at the same ear were not being attended to. This N1 effect must have been caused by selective attention somehow acting on neural mechanisms to enhance processing of information from that ear. The prefix "N" refers to the negative voltage deflection of the event-related potential.

Johns Hopkins University

Dichotic presentation is where participants listen to two different streams of dialog delivered simultaneously to the left and right ears.

Dichotic Presentation

Gross potential changes in the electrical activity of the brain due to a sensory stimulus such as a flashing light. The location of recording, the type of stimulus, and the state of the subject are reflected in the properties of ERPs, such as the wave shape and the latency (i.e., time delay). 
With ERPs, researchers ask participants to do the same task over and over again and they average all the EEGs recorded during those repeated trials. The variation due to random firing averages out. ERP has become the favorite tool of neuroscientists studying moment-to-moment consequences of attention in the brain.

Event-Related Potentials (ERPs)

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

During the experimental task of dichotic presentation, subjects are asked to focus attention on one ear or the other while stimuli are being presented separately to both ears. Participants could accurately report what they were hearing in the attended ear, but they could report very little that had been presented to the nonattended ear. 

Dichotic Presentation: Shadowing

N1 Effect

This is another ERP , event-related-potential, finding based on the dichotic presentation studies. P3, a wave also called auditory P300, is believed to reflect higher-order cognitive processing of the stimulus (ie. semantic meaning of words, identification of the speaker, etc.). The P3 effect is an example of a late-selection effect of auditory attention. The prefix "P" refers to the positive voltage deflection of the event-related potential.

P3 Effect

In a task where a participant is told to identify/recall the different sounds coming through each ear, most people will identify sounds that come from the right ear more accurately than the right ear. (Note: 50%of left-handers experience the reverse, which is a left-ear advantage).



The Right-Ear Advantage in Dichotic Presentation

Latency is the time delay between the initiation of a stimulus and the electrical stimulation detected as a result of that stimulus. When latency is short, exogenous factors such as the intensity of the stimulus are primarily responsible for the latency. Longer-latency components, on the other hand, are primarily attributable to information-processing tasks that take a longer amount of time, such as attention, decision-making, and planning, among others. 

Timing of Latency

During visual search tasks, the N2pc appears over visual cortex contralateral to the location in space to which subjects are attending. Through experimentation, it has been proven that the N2pc component is associated with covert orientation towards an object when it is the target, rather than the suppression of a response towards distracters.

N2pc Component

On valid trials, electrodes measuring the activity of the occipital cortex show substantial enhancement of the event-related-potential component called P1, a positive wave that occurs over auditory cortex about 70-100 ms after stimulus onset. At longer intervals between the cue and target, the visual P1 effect may actually be reduced as an electrophysiological manifestation of inhibition of return. For invalid trials, where attention is directed elsewhere, the visual P1  effect isn't evident at all. 

Posner: Visual P1 Effect

The late positive potential (LPP) is a type of ERP that emerges during the processing of emotional stimuli, positive or negative, compared to more "neutral" stimuli. It is a positive-trending waveform that spikes around 200-300 ms after initial exposure to a stimulus.

Late Positive Potential (LPP)

Cultural neuroscience is an emerging field of research that joins social and biological sciences to explore the influences of culture on brain development. While cultural psychology historically has relied on observational studies and survey methods, neuroscience measures such as ERPs and fMRI enable researchers to study the underlying neural mechanisms responsible for observed behavioral differences across cultures.

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