P300 habituation from auditory single-stimulus and oddball paradigms.

The habituation of auditory P300 event-related brain potential (ERP) from single-stimulus paradigm was evaluated and compared to that from oddball paradigm. Three task conditions were: oddball with a button press (oddball/press) response, single-stimulus with a button-press (single-stimulus/press) response and a silent count (single-stimulus/count) response. The oddball/press condition demonstrated larger P300 amplitude and longer latency overall than either single-stimulus condition, but P300 amplitude decreased and peak latency increased similarly over successive trial blocks for all three tasks. Thus, the oddball and single-stimulus ERP tasks produce analogous changes under repeated measurements and indicate that the single-stimulus task can serve as an alternative method for eliciting the P300 in applied and clinical settings.     

P300 from auditory and somatosensory stimuli: probability and inter-stimulus interval.

The P300 (P3) event-related brain potential (ERP) was elicited with auditory and somatosensory stimuli using an easy discrimination task in two experiments. Experiment 1 manipulated target stimulus probability (0.20 vs. 0.80). Experiment 2 manipulated inter-stimulus interval (2 s vs. 6 s) for both stimulus modalities in different conditions while keeping target probability constant. Probability and inter-stimulus interval had similar effects for auditory and somatosensory stimuli, with lower probability and longer inter-stimulus intervals producing larger P3 amplitudes. No statistically reliable differences in scalp distribution between modalities were obtained, with both modalities producing maximal amplitudes at Pz. The results suggest that auditory and somatosensory stimuli when used in a relatively easy discrimination task yield the same overall P3 values.     

Target-to-target interval, intensity, and P300 from an auditory single-stimulus task

Target-to-target interval (TTI) is a primary determinant of P300 amplitude, such that longer TTIs yield larger components than shorter intervals. Systematic manipulations of TTI affect component amplitude, latency, and associated response time in a fashion that suggests that the template update hypothesis can account for these outcomes. The present study examines whether manipulations of TTI (from 1 to 16 s) and stimulus intensity (soft and loud tones) produce outcomes consistent with this hypothesis. A single-stimulus task was employed in which only target stimuli were presented. P300 amplitude increased, peak latency decreased, and response time increased as TTI became longer, with less effect for soft compared to loud stimulus conditions on P300 amplitude at Pz. TTI increases also augmented N100 amplitude, with consistently smaller amplitudes obtained for soft relative to loud stimuli. Overall, P300 measures are sensitive to both temporal and physical stimulus factors. Theoretical implications are discussed.     

P300 topography and modality effects from a single-stimulus paradigm

The P300 event-related brain potential (ERP) was elicited with auditory and visual stimuli in two different tasks. The oddball paradigm presented both target and standard stimuli; the single-stimulus paradigm presented a target but no standard stimulus, with the intertarget interval the same as that for the oddball condition. Target probability was .20 for the oddball task, with target stimuli occurring at the same temporal frequency in the single-stimulus paradigm. Scalp topography was assessed with 15 electrode locations. P300 amplitude was larger and latency was longer for the oddball than for single-stimulus procedure. P300 from auditory stimuli was smaller and shorter in latency than that from the visual stimuli, and both modalities showed similar but not identical scalp topographies. The findings suggest that the single-stimulus paradigm may be useful in experimental and applied contexts that require very simple ERP task conditions.     

P300 hemispheric amplitude asymmetries from a visual oddball task

The P3(00) event-related potential (ERP) was elicited in 80 normal, right-handed male subjects using a simple visual discrimination task, with electroencephalographic (EEG) activity recorded at 19 electrodes. P3 amplitude was larger over the right than over the left hemisphere electrode sites primarily at anteromedial locations (F3/4, C3/4) for target, novel, and standard stimuli. The N1, P2, and N2 components also demonstrated hemispheric asymmetries. The strongest P3 hemispheric asymmetries for all stimuli were observed at anterior locations, suggesting a frontal right hemisphere localization for initial stimulus processing, although target stimuli produced larger P3 amplitudes at parietal locations than did novel stimuli. The relationships of hemispheric asymmetries to anatomical variables, background EEG activity, and neurocognitive factors are discussed.     

P300 and slow wave: the effects of reaction time quartile

Event-related potentials (ERPs) were recorded from 25 adolescents in a modification of the odd-ball paradigm. On alternate blocks subjects were required to detect either a missing stimulus or a change in pitch, each of which occurred 17% of the time and was embedded in a series of background tone pips (66% occurrence). The study was designed to assess the relationship between P300 and Slow Wave elicited by two infrequent targets which differed in the amount of temporal uncertainty (and thus, equivocation) associated with them. Principal components analyses (PCAs) were used in an attempt to reduce overlap among components. Stimulus-synchronized (SSA) and response-synchronized (RSA) averages were computed for correct trials only in association with the first (Q1) and fourth (Q4) reaction time (RT) quartiles. Measurement of the SSAs replicated the results of Roth, Ford and Kopell (1978): P300 amplitude was larger in Q1 than in Q4, while Slow Wave amplitude increased in Q4 relative to Q1. In the RSAs for Slow Wave, only the frontally negative aspect remained larger in Q4 than in Q1, while the parietally positive component did not differ between quartiles. The PCA basis waves showed that the major portions of P300 and Slow Wave followed response execution, thus precluding their involvement in the discrimination process per se. These results support the functional dissociation of P300 and Slow Wave and the functional independence of the frontal and parietal aspects of Slow Wave.     

Microsaccadic inhibition and P300 enhancement in a visual oddball task

It has recently been demonstrated that the presentation of visual oddballs induces a prolonged inhibition of microsaccades. The amplitude of the P300 component in event-related potentials (ERPs) has been shown to be sensitive to the category (target vs. nontarget) of the eliciting stimulus, its overall probability, and the preceding stimulus sequence. In the present study we further specify the functional underpinnings of the prolonged microsaccadic inhibition in the visual oddball task, showing that the stimulus category, the frequency of a stimulus, and the preceding stimulus sequence influence microsaccade rate. Furthermore, by co-recording ERPs and eye movements, we were able to demonstrate that, despite being largely sensitive to the same experimental manipulation, the amplitude of P300 and the microsaccadic inhibition predict each other only weakly.     

Target-to-target interval versus probability effects on P300 in one- and two-tone tasks

The P3(00) is an electrophysiological index of neural processing that varies with such stimulus parameters as interstimulus interval (ISI) and target probability, with a common view being that it reflects an endogenous form of memory update. Building on previous research, we argue that relations between P3 amplitude and both ISI and probability may be attributable to the target-to-target interval (TTI). Employing between-subject (Experiment 1; N = 24) and within-subject (Experiment 2; N = 10) designs, the present paper addresses this by testing subjects on a standard two-tone auditory oddball task as well as a one-tone task. In both studies, P3 amplitude increased and latency decreased linearly with TTI, and these relations were relatively unaffected by ISI or probability. This suggests that ISI and probability per se do not independently affect P3 amplitude, and that TTI offers a strong explanation of the reported relations between P3 amplitude and both ISI and probability.     

Wavelet analysis of oddball P300.

The comparative wavelet analysis presented in details by Demiralp et al. (1999), Ademoglu (1995) and by Ba?ar et al. (2001) will be now applied to oddball P300 results (see Ba?ar-Eroglu et al., 2001). The results obtained basically confirm those obtained by using adaptive digital filtering: The delta response dominates the P300 potential while the theta response is prolonged in a second late window.     

Comparison of P300 from passive and active tasks for auditory and visual stimuli.

The P300 event-related brain potential (ERP) was elicited with a stimulus-sequence paradigm for auditory and visual stimuli in separate active and passive task response conditions. Auditory stimuli in the passive task yielded P300 waveforms similar to those obtained from the active task condition. Visual stimuli in the passive task yielded much smaller P300 waveforms that were not morphologically consistent with those from the active task. The results suggest that auditory stimuli produce more robust P300 components than visual stimuli in passive task situations.     

With long intervals, inter-stimulus interval is the critical determinant of the human P300 amplitude

Previous research, using short inter-stimulus intervals (1-4 s), suggests that the P300 of the human event-related potential during oddball and single-stimulus tasks is mainly affected by target-to-target interval (TTI). The present study tested the validity of this claim at longer intervals in a learning task. Participants were assigned to either an oddball task with an inter-stimulus interval (ISI) of 9-20 s or a single-stimulus task with an ISI of 9-20 or 40-90 s and had to learn when to respond to the stimuli. In the oddball task, the target elicited larger amplitudes than did the standard. When comparing the stimuli from the short- and long-ISI conditions with the target from the oddball condition, it was found that the P300 was more positive at long-ISI stimuli than at short-ISI stimuli or oddball targets, and short-ISI stimuli and oddball targets elicited equally large P300 amplitudes. These results suggest that, in oddball tasks with long intervals, besides cognitive factors, ISI rather than TTI affects the P300 amplitude.     

Eliminating the P300 rebound in short oddball paradigms.

In short oddball paradigms, the P3 (or P300) amplitude often shows a curvilinear "rebound" pattern, such that an initial drop during the first few trials is followed by an increase in later trials. While the initial attenuation has been attributed to habituation, no explanation has been offered for the later increase. Our hypothesis was that this curvilinear pattern is due to anticipation of the end of each fixed-length block. In study 1, a series of 16 short, fixed-length auditory oddball tests (with six targets each) replicated the rebound effect. In study 2, a further set of 16 variable-length blocks (7-10 targets) eliminated the rebound, and the P300 amplitude decreased linearly as expected. Results are interpreted in light of various constructs related to the P3: habituation, attentional salience, and updating in working memory.     

fMRI in an oddball task: effects of target-to-target interval

The amplitude of the P3 event-related potential (ERP) elicited by task-relevant target ("oddball") stimuli has been shown to vary in proportion to the length of time between targets. Here we use functional magnetic resonance imaging (fMRI) to identify neural systems modulated by target interval in a large sample of healthy adults (n=100) during performance of an auditory oddball task that included both target and novel stimuli. A positive relationship was found between target interval and hemodynamic activity in the anterior cingulate and in bilateral lateral prefrontal cortex, temporal-parietal junction, postcentral gryi, thalamus, and cerebellum. This modulation likely represents updating of the working memory template for the target stimuli. There was no such effect of novel interval, suggesting that neuronal modulation may only occur for task-relevant stimuli, possibly in the service of strategic resource allocation processes.     

Habituation of P300 from visual stimuli

The P300 event-related brain potential (ERP) was elicited with visual stimuli using an oddball task in which the subjects made button press responses to discriminate target and standard stimuli. Each stimulus occurred randomly with a 0.50 probability, and 10 trial blocks were presented at 10-min inter-block-intervals (IBIs). P300 amplitude declined reliably across trial blocks, and an interaction between trial block number and electrode site was observed. No habituation effects were found for P300 latency or for N100, P200, or N200 amplitude. The results suggest that P300 amplitude from visual stimuli habituates when short IBIs and a sufficient number of trial blocks are employed. Theoretical implications are discussed with respect to attentional resource allocation and context updating.     

Roll aftereffects: influence of tilt and inter-stimulus interval

A theme in sensory perception is that exposure to a stimulus causes perception of subsequent stimuli to be shifted in the opposite direction. Such phenomenon is known as aftereffect and has been extensively described in the visual system as well as recently described for the vestibular system during translation. It is known from aviation studies that after a maneuver in roll, pilots can experience a false perception of roll in the opposite direction. The magnitude and duration of this effect as well as the potential influence of the gravity vector have not previously been defined. In the current paper this roll aftereffect (RAE) is examined in response to whole-body roll about an earth-horizontal axis in eight healthy human subjects. The peak velocity of a 0.5-s-duration roll was varied based on previous responses to find the point where subjects perceived no motion. Without a preceding stimulus, the starting position (upright, 9° left, or 9° right) did not influence roll perception. The RAE was measured in a completely dark room using an adapting (first interval) stimulus consisting of 9° of roll over 1.5 s (peak velocity, 12°/s), delivered 0.5, 3, or 6 s prior to test (second interval) stimulus. A significant RAE was seen in all subjects. Half a second after the adapting stimulus, a test stimulus had to be on average 1.5 ± 0.4°/s in the opposite direction to be perceived as stationary. When the subject remained upright after the adapting stimulus, the RAE diminished with time, although it remained significantly larger at 3 and 6 s when the subject remained tilted after the adapting stimulus. These data demonstrate that roll perception can be influenced by small preceding stimuli and tilt causes a persistence of the RAE.     

Stimulus intensity effects on P300 amplitude across repetitions of a standard auditory oddball task

An evaluation was made of whether stimulus intensity affects changes of P300 amplitude in response to repeated presentation of the target stimulus in a standard auditory oddball task. P300 latency values were also evaluated. Three samples were selected, one for each intensity used: 65, 85 and 105 dB SPL (sound pressure level). Five hundred tones (5 subblocks, 100 tones each) were presented. P300 amplitude (1) increased from Fz to Pz, (2) was larger at 105 than 65 or 85 dB SPL, (3) increased from the first to second subblock and decreased from the second subblock onwards at the three intensities, replicating our previous findings at 85 dB SPL and demonstrating a consistent phenomenon, and (4) at 105 dB SPL, the decrease was less pronounced, which we attribute to the more intense stimuli capturing the attention in a sustained manner during the task and interfering with the possible automation of the context-updating process.     

Age and inter-stimulus interval effects on event-related potentials to frequent and infrequent auditory stimuli.

The aim of this study was to investigate aging effects on non-attended changes of auditory stimulation, by using psychophysiological methods. Event-related potentials (ERPs) were recorded to frequent (standard; 950 Hz, p = 0.9) and infrequent (deviant; 1045 Hz, p = 0.1) auditory stimuli in older (mean age = 60.8 years) and younger (mean age = 21.3 years) subjects. In various blocks the inter-stimulus interval (ISI) was either 800, 2400 or 7200 ms. During the experimental sessions the subjects read books, and ignored the auditory stimuli. As a function of ISI, the amplitude of the N1 and the amplitude and latency of the P2 increased. The P2 amplitude was larger in the younger group. In the 120-180 ms latency range the deviant stimuli elicited more negative ERPs (mismatch negativity, MMN) than the standard stimuli. The amplitude of the MMN did not change as a function of ISI. MMN was larger in the younger group. Thus the younger subjects were more sensitive to the deviant stimuli. In the younger group, at the two shorter ISIs, the MMN was followed by a positive wave (P3a). The emergence of this component is an indication of the increased activity of the orienting system in the younger subjects, in comparison to the older age group.     

Somatosensory N250 and P300 during discrimination tasks.

We investigated the event-related potentials (N250 and P300) during three kinds of somatosensory discrimination tasks (oddball task). Strong (standard: 90%) and weak (deviant: 10%) electrical stimuli were randomly delivered to the right median nerve at the wrist with a 500-ms constant interstimulus interval. In a passive situation, subjects read a self-selected book, ignoring all stimuli (ignore condition). One of the active situations was a mental counting task (count condition), and another required pressing a button to deviant stimuli as quickly as possible (motor response condition). The N250-P300 complex was elicited by deviant stimuli in the active-attended situations, but not found in the ignore condition. The N250 peak amplitude was unchanged between the count and motor response conditions whereas P300 changed. In addition, the N250 latency significantly correlated with the reaction time, but the P300 latency did not. These results indicate that the somatosensory N250 reflects an attentive process which is related to the temporal aspect of behavioral response.     

P3 and delta band responses in visual oddball paradigm in schizophrenia

Amplitude reduction of the oddball P3 wave is a well-replicated but non-specific finding of schizophrenia. The time-frequency analysis of single-trial ERP data allows to specify in a reliable manner whether the P3 reduction in schizophrenia is due to the decreased P3 response in single trials or due to the inter-trial variability in the timing of the response. Since the delta response most strongly contributes to the P3 amplitude, we focused to the low frequency range of the time-frequency transformed data. EEG was recorded from chronic schizophrenia patients and matched healthy controls during a simple visual oddball task. The wavelet transforms of the averaged ERP and the single trials were computed to investigate the amplitudes of the evoked (phase-locked) and total (phase-locked+non-phase-locked) delta (1-3 Hz) responses, respectively. Evoked delta activity and P3 amplitude to target stimuli were both reduced significantly in patients with schizophrenia, whereas no such difference was obtained for the total delta activity. The significant reduction of the evoked delta response and the absence of such a difference in the total delta response of schizophrenia patients reveals that the delta band response is weakly phase-locked to stimulus in schizophrenia. This result suggests that the reduced P3 amplitudes in the averaged ERPs of schizophrenia patients result from a temporal jitter in the activation of neural circuits engaged in P3 generation.     

Effects of aging on the novelty P3 during attend and ignore oddball tasks

The effects of attention were assessed on novelty P3 amplitude and scalp distribution elicited by environmental sounds in young and elderly volunteers who participated in either actively attended or ignored oddball conditions. For the young, novelty P3 amplitude decreased with time on task during both attend and ignore sequences. Amplitude decrements were greatest at frontal sites during the attend condition, but at all sites during the ignore condition. A reliable amplitude decrement was not observed for the elderly in either the attend or ignore oddball series. The data suggest that attention differentially activates multiple generators that contribute to scalp-recorded novelty P3 activity. The lack of novelty P3 habituation seen in the elderly is consistent with changes in frontal lobe function as age increases.