Evoked potentials (Electrophysiology)

Racial bias remains a prevalent issue in society. Clues to the cognitive basis for such biases have been found in EEG studies of the ‘Other Race Effect’ (ORE) in relation to the P100 and N170 event related potentials (ERPs). Previous research in this area has focused on adults, and only one such study has looked at implicit racial biases (He et al., 2009), while only a few have looked at experience with own- and other-race persons (Herzmann et al., 2011; Stahl et al., 2008; Walker et al., 2008). The present study is the first to examine how race might modulate ERP responses in children, and the first to relate these responses with both implicit racial biases and race contact experience. We examined EEG responses in 5- to 10-year-old children and adults, and whether such responses were associated with implicit racial biases and own- and other-race experience. Results showed that both children and adults displayed larger P100 and N170 responses to other-race faces, greater implicit racial biases related to larger N170 responses to other- than own-race faces, and greater other-race experience related to larger P100 responses to other- than own-race faces. In terms of age differences, we found that compared with adults, children displayed larger and more delayed P100 and N170 responses, and that in children but not in adults, greater experience with own- and other-races were associated with more delayed N170 responses to other- than own-race faces. These findings suggest that age, experience with own- and other-race persons, and implicit racial biases all influence early ERP responses to own- and other-race individuals.

The P300 component of the auditory event-related potential waveform was investigated in control children and two groups of HIV-infected children (asymptomatic and symptomatic), aged five to seven, under combinations of two interstimulus interval (ISI) rates (1 and 2 sec) and two target probability rates (.2 and.5). No group differences were found under the different combinations of ISI and target probability, for either P3a amplitude and latency, or P3b amplitude and latency. Although the present study was not able to distinguish between-groups by manipulating the target presentation rate, there were several within-group effects on P3a latency that were dependant upon the specific clinical or control group. The general findings for the study were that as the target presentation rates increased, P3a latencies increased.

The P300 component of the auditory event-related potential waveform was investigated in two groups of HIV positive children (symptomatic and asymptomatic) who were compared to HIV negative relatives. Results demonstrated the expected increased latencies of the P3b component in the symptomatic group, but no P3a latency differences. Amplitude measures of P3a and P3b showed no group differences. However, the symptomatic children had relatively larger P3a amplitudes whereas the asymptomatic children had a larger P3b. Difference measures (P3b minus P3a) revealed a significant difference across groups. Discussion focuses on three interrelated issues: (1) the cognitive mechanisms which could account for the current findings, (2) the relevance of a symptomatic/asymptomatic distinction and a P3a/P3b distinction for the purposes of clinical research, and (3) the clinical implications of these findings.

This research investigated whether choice reaction time (RT) measures and the P300 component of the event-related brain potential (ERP) could be employed to index the attentional resources associated with performing two near-simultaneous tasks. Specifically, this study investigated the effects of auditory tones on the ERPs and RTs associated with a visual stimulus when the stimuli in both modalities were presented in close temporal proximity. The hypothesis that the ERPs and RTs elicited by the deviant visual stimulus would index the processing demands associated with the auditory modality was confirmed. In general, greater P300 amplitude associated with one task indicates diminished P300 and poorer performance on a second task. The results indicate that P300 may be a sensitive indicator of shared processing resources when two tasks are performed near simultaneously.

The P3 and slow wave measures were examined in a simultaneous oddball task in a clinical population of alcoholics and multiple-drug addicted patients. Standard and Deviant tones and lights were used in a counting task in single modality trials in two separate test sessions and tones and lights were used simultaneously but independently in a counting task in which tones were to be ignored and deviant lights were to be counted. Differences between clinical subjects and control subjects and between test sessions were examined. While there were no significant results between test sessions, there were significant differences between controls and clinical subjects in the P3 component. Amplitude of the P3 was smaller for the clinical subjects in all three conditions and in the bimodal task there was evidence in the P3 EP measure that the clinical group had difficulty ignoring the tones, although there were no significant differences in accuracy of count possibly due to a temporal deficiency on the part of the clinical subjects.

The effect of alternating primary task stimulus modality on event-related brain potentials and secondary signal detection performance was examined in a dual-task paradigm. An odd-ball paradigm with alternating pairs of auditory tones and visual lights was employed as the primary counting task. Primary task stimuli were classified by previous trial modality (same vs different), previous trial stimulus type (standard vs deviant), and current trial stimulus type. A signal detection task in which an auditory tone followed the primary task stimuli by 120 ms on 50 percent of the trials served as the secondary task. For all but one condition, deviant stimuli produced large P300 and decreased signal detection performance. When a deviant stimulus preceded a deviant in the same modality, however, signal detection performance was better than on standard trials preceded by a deviant. These results were interpreted using a two-parameter model of stimulus probability and subjective value of the stimulus sequence. Also examined were other effects of alternating modality of the primary task stimulus and the sequences defined by the modality and stimulus type of the current and previous trial on the event-related potentials elicited by the primary task stimuli.

The relationship between P300 elicited on a primary counting task
and performance on a secondary signal detection task was examined in a
dual-task paradigm in which the secondary task followed the primary
task by 120 ms. An odd-ball paradigm, utilizing two auditory tones
(Standard and Deviant) was employed as the primary counting task in
order to elicit two states characterized by differences in P300
amplitudes. The standard trials were further categorized according to
their serial position in each series of trials. A signal detection
task in which an auditory tone followed the primary task tones on 50
percent of the trials served as the secondary task. The principal
hypothesis was that a decrease in sensitivity on secondary signal
detection task accompanied Deviant trials in which a P300 was elicited.
Results were consistent with the hypothesis and provided support for
both neural inhibition and cognitive resource allocation models.

The relationship between P300 elicited on a primary
counting task and performance on a secondary signal
detection task was studied in a dual task paradigm where
the secondary task followed the primary task by 300 msec.
A modified ("count both tones") oddball paradigm, utilizing
two auditory tones (Frequent and Rare) was used as the
primary counting task to elicit two states characterized by
differences in P300 amplitudes. An auditory signal detection
task presented on 50 percent of the trials following
the primary task tones served as the secondary task. Predictions
about performance on the secondary task were based
on a neural inhibition model of P300. It was hypothesized
that signal detection performance, as measured by detection
sensitivity (d') would be less on Rare tone trials than on
Frequent tone trials. Results were consistent with the
hypothesis and provided support for the neural inhibition
model of the P300.

Evoked potentials elicited by tones of high and low probability of
presentation requiring the suppression of a frequent response (counting
or not-counting) or its maintenance were studied. Low probability
(Novel) tones requiring response (counting) suppression elicited P300
amplitudes of the event-related potential comparable to those elicited
by low probability tones (Target) which did not require suppression of
an ongoing frequent response. This finding was not in agreement with
those reported in a similar study by Karlin and Martz (1973). It was
advanced that situations in which subjects maintain a high level of
response readiness enhance the effects of stimulus probability and
response probability on P300 amplitude values. In agreement with the
current literature, low probability stimuli (Novel and Target) were
found to consistently elicit larger P300 amplitudes than high
probability (Background) stimuli regardless of response frequency. N100
amplitudes were also larger for low probability tones than for high
probability Background tones. These results were attributed to either
habituation, attention or a combination of both. P200-N250 peak-to-peak
amplitude values were also shown to be larger in response to Target and
Novel tones than in response to Background tones.

Sokolov's (1963) hypothesis of selective extinction of the
orienting response accounts for the phenomenon of dishabituation by a
discrepancy between immediate sensory input and a stored template of a
habituated stimulus. The "oddball" stimulus procedure often used to
elicit the P300 evoked potential waveform bears resemblance to a
habituation-dishabituation paradigm. In the present experiment
subjects were habituated to a 70 dB tone burst which was then occasionally
replaced by 50, 60, 80 or 90 dB stimuli. According to a selective
extinction model of the P300, equal absolute amounts of stimulus change
should evoke equal amplitude waveforms. While the decreased intensity
stimuli did evoke a P300, the largest P300s were associated with an
intensity increase. The N200 component was seen to be largest with
intensity decrease. It is suggested that the N200 is the evoked
potential correlate of discrepancy detection which can be obscured by
an intensity-driven P300.