P300 and Feedback Provided by Absence of the Stimulus

This experiment is concerned with the issue of functional equivalence of emitted (in response to ahsence of a stimulus) and evoked (in response to presentation of a stimulus) P300s. Subjects attempted to estimate a 600-msec time interval hy the method of reproduction. Subjects were informed whether the time interval was under- or overestimated and whether the estimation error magnitude was within a limit (“correct” estimate, positive feedback) or exceeded the limit (“incorrect,” negative feedback). This feedback was presented by means of either a single event or a combination of two events. Each event consisted of a pair of stimuli. Emitted, as well as evoked, early fronto-central and late parietal P3OOs were elicited by the feedback event regardless of whether positive or negative feedback was delivered, and regardless of whether feedback was delivered by a single event or by the combination of two events. In addition, what appears to be a positive Slow Wave was found following the first stimulus ofthe feedback event when this stimulus was low intensity indicating an underestimation. The other condition (high intensity, overestimation) was followed by a CNV. Since these slow wave findings were serendipitous, counterbalancing was not available to determine whether intensity (low vs high) or information (underestimation vs overestimation) was responsible for the difference.     

Relationship Between Stimulus Intensity and the P300

The effect of stimulus intensity on the P300 component of the averaged auditory evoked potential was examined in healthy young adults. Although no effect on P300 amplitude was present, increasing loudness was inversely related to P300 latency. These data demonstrate a partial dependence of P300 on stimulus parameters, and underscore the importance of determining the hearing ability of subjects and patients in studies employing P300 as an index of information processing speed.     

Effects of Stimulus Probability and Task-Relevance on Event-Related Potentials

Stimuli were delivered to 12 subjects in a sequence that included regularly occurring standard tone pips, random warning tone pips, and random while noise bursts. Half the noise bursts were preceded by warning tones (high probability), and half were not (low probability). There were four runs, each having one of two noise burst intensities, and each having the warning tone and noise bursts either both task-relevant to a reaction time task or both task irrelevant. Event-related potentials (ERPs) were obtained by signal averaging in F₂, C₂, P₂ and eye leads. The P₃ to the warning tone was largest in P, and was not affected by task relevance. CNV_s preceded all the high probability noise bursts. These CNV_s had an amplitude of 5μV even when the bursts were task irrelevant. Low probability noise bursts elicited larger P3_s in all leads for the task-irrelevant condition, but only in P_z for the task-relevant conditions. In C_z, the amplitudes of NI. P₂, and P₃ to the high probability. task-relevant noise bursts correlated with the amplitude of the preceding CNV.     

中国乒乓球听障奥运选手脑诱发电位特点的研究

探讨中国乒乓球听障奥运队员视觉诱发电位P100和事件相关电位P300的特点,为该项目运动员的选材和机能学评定提供参考。采用上海海神医疗电子仪器厂生产的NDI-200（海神号）神经电检诊仪,对参加2013年7月在保加利亚举行的第22届夏季听障奥林匹克运动会的8名中国乒乓球听障奥运选手和74名常人大学生的视觉诱发电位和视觉事件相关电位进行了记录、分析比较。奥运选手组和对照组之间视觉诱发电位P100波幅和潜伏期均无显著性差异（P＞0．05）。奥运选手组与对照组相比,视觉事件相关电位P300表现为：Cz点的波幅呈极显著性增加（P＜0．01）、Fz点的波幅呈显著性增加（P＜0．05）、Pz点的波幅有一定的增加（P＝0．061）;Pz点的潜伏期呈极显著性缩短（P＜0．01）;Pz、Cz、Fz点的反应时均呈极显著性缩短（P＜0．01）。听障乒乓球运动员和常人对照组之间视觉诱发电位P100波幅和潜伏期均无显著性差异;视觉事件相关电位P300表现为波幅增加、潜伏期缩短、反应时缩短的特点。     

Heart Rate, Contingent Negative Variation, and Evoked Potentials during Anticipation of Affective Stimulation

Thirteen subjects low in fear of mutilation and 11 subjects high in this fear were exposed to repeated presentations of a 6-sec tone followed by slides depicting a mutilated body or a 6-sec tone of a different frequency paired with a slide of a neutral scene. For both groups, the N140 component of the evoked potential was larger following the signal for gruesome slides. Slow EEG activity displayed two negative waves. Notably, the late CNV wave was present even though a motor response was not required at the end of the foreperiod. Overall, high-fear subjects' early waves tended to be larger preceding neutral scenes than gruesome slides, whereas low-fear subjects showed a trend in the opposite direction. Similar but largely nonsignificant trends were present for the late wave. Heart rate reactions of both groups in the foreperiod included an early deceleration, acceleration, and a late deceleration. Among high-fear subjects both the acceleratory and late deceleratory limbs were greater preceding mutilation than neutral slides. In contrast, low-fear subjects' reactions lacked the acceleratory reaction and did not vary as a function of type of warning signal. These results, therefore, indicate differential autonomic patterns of anticipation of affective stimulation as a function of individual differences in fear.     

On the Dependence of P300 Latency on Stimulus Evaluation Processes

McCarthy and Donchin (1981) found that the latency of a late positive component of the event-related potential (ERP) was influenced by the presence of noise in a stimulus matrix but not by the compatibility between the stimulus presented and the response required. They concluded that this component is a P300 and that its latency was influenced by stimulus evaluation but not by response selection processes. The present experiments were designed to confirm that the component identified by McCarthy and Donchin was indeed a P300 and to determine if its latency varies systematically with increases in stimulus evaluation time produced by graded changes in noise level. In Experiment 1, subjects performed a standard oddball task in which they were required to count the rarer of two stimuli (the words RIGHT or LEFT) which were, or were not, embedded in a noise matrix (characters from the alphabet). The positive component of the ERP, whose amplitude was larger for rare target stimuli, was labeled a P300, and the latency of this component was longer when the stimuli were embedded in noise. In Experiment 2, subjects performed a choice reaction time task. Following the procedures used by McCarthy and Donchin, stimulus words RIGHT and LEFT required right or left hand responses depending on the presence of a cue word SAME or OPPOSITE which preceded the stimulus. Stimulus words were presented in four different degrees of noise, the levels of which were manipulated by varying the set size of the alphabetic characters which could surround the stimulus words. Reaction time increased both with noise (by 325 ms) and as a function of stimulus-response incompatibility (by 127 ms). In contrast, P300 latency increased substantially with noise (by 200 ms) but, to a much lesser extent (by 14 ms), with response incompatibility. These results indicate that the P300 is sensitive to the ease with which a target stimulus can be discriminated from noise. They confirm that P300 latency can be used as a measure of the timing of stimulus evaluation processes that is relatively independent of response selection and execution.     

The Effects of Stimulus Expectancy on Evoked Brain Potentials

The effects of self-generated expectancy of stimulus content on the visual evoked potential to physically identical stimuli were studied in college students. The subject set up his own internal expectant; by choosing to see either a bright or dim Hash. When a bright or dim Hash was anticipated, the potentials evoked by u medium stimulus intensity resembled the responses elicited by an actual bright or dim flash, respectively. Significant differences in visual evoked potential amplitude were obtained between identical medium intensity stimuli depending on the stimulus intensity expected, despite (he constant physical properties of the stimulus. 1 In1 results suggest that a subject's expectancy of certain physical parameters of a stimulus are as important In determining (he resultant visual evoked potential as the actual physical features of the stimulus.     

Effects of Stimulus Repetition, Duration, and Rise Time on Startle Blink and Automatically Elicited P300

Intense auditory stimuli of sudden onset evoke not only startle blinks but also an event-related potential component resembling classic P300, even when subjects have no assigned task. To more closely examine the relationship of this P300 to startle, event-related potentials and eyeblink were recorded from 16 young adults in three paradigms designed to produce wide variation in startle amplitude: an Habituation series of 30-ms, 105dBA white noise bursts, a Duration paradigm which presented 105dB noise bursts for 3, 10, 30, or 90 ms, and a Rise Time paradigm which varied the rise/fall times (3, 15, 30, and 45 ms) of 110dBA, 1000-Hz tone bursts. Subjects received two runs of each paradigm. Only on the final Duration and Rise Time runs were stimuli explicitly task relevant; on those runs subjects rated verbally, midway in each 8.4-s interstimulus interval, the disturbingness of the prior sound. Although even the briefest noise bursts evoked parietal P300 as well as startle blink, P300 did not behave like startle. P300 habituated more slowly than did blink amplitude, was more responsive to sustained noise than were blink, N110, and P190, and most importantly, did not show the sensitivity to stimulus rise time manifested by these measures. These findings suggest that the amplitude of automatically elicited P300 is not governed by the same mechanisms as startle amplitude, but behaves more like a defense response.     

Amplitude and Latency Changes in the Visual Evoked Potential to Different Stimulus Intensities

Visual evoked potentials (VEPs) were recorded from five sites (T₃, T₄, C_z, O₁, O₂) to six intensities of light flashes. Peak-to-trough amplitudes were measured for the P100-N120 and N120-P200 waveforms as well as baseline (prestimulus)-to-peak amplitudes for each component (i.e. P100, N120, and P200). Different methods of defining augmenting/reducing were compared. These included subtracting the VEP epoch mean level from mean levels within a timeband corresponding to P100 and calculating slopes both for these values and for the P100-N120 amplitudes across intensities. The technique of using slopes to describe amplitude-intensity functions was found to be unjustified and misleading. The Augmenting/Reducing groups defined by the slopes of peak-to-trough amplitudes or slopes of the timeband “amplitudes” proved to be almost mutually exclusive. Results also showed that the frequency with which actual VEP peaks occur within the appropriate timeband is very low and differs topographically. Augmenting/Reducing was then defined by monotonic increases in the P100-N120 peak-to-trough amplitudes. Augmenters and Reducers differed from each other not only for amplitude-intensity patterns but on a number of latency measures. Hemisphere differences were also found between groups. An inverse relationship was found between occipital and vertex amplitude-intensity patterns such that vertex augmenting was accompanied by occipital reducing and vice versa. Temporal and vertex amplitude-intensity patterns were similar.     

Functional Differences Between Members of the P300 Complex: P3e and P3b

The main findings of this study bear upon differences in the functional roles of P3b and a shorter latency, more centrally distributed endogenous positive component denoted as P3e. At the present writing, we have observed P3e only in conjunction with P3b. As in the case of P3b, P3e is fully endogenous in that it can be- elicited by omission of a stimulus if stimulus omission conveys relevant information to the subject. It was found that P3e and P3b relate differently to information delivery. Information delivery was manipulated by varying event probabilities and the discriminability of the events. The well known properties of P3b, namely that its amplitude is large when elicited by low probability (high information content) events and is reduced by perceptual difficulty (information loss-equivocation), were replicated in the current study. In contrast to P3b, variation of event probability had no effect upon P3e amplitude, but increased perceptual difficulty markedly reduced P3e amplitude. In addition, two CNV-type negativities were observed in the epochs prior to presentation of the informative signal event: 1) A negativity that was maximal over central scalp related to the subject's prediction that a rare or frequent event would be presented; 2) A negativity that was maximal over occipital scalp related to a stimulus that informed the subject whether the subsequent discrimination of the signal would be easy or difficult. Finally, there was a serendipitous Hading of an apparently new short duration component, tentatively labeled Px, which is elicited by presentation of the signal that informs the subject whether the subsequent discrimination will be easy or difficult.     

P300, Probability, and Interstimulus Interval

The relationship between target stimulus probability and interstimulus interval on the P300 (P3) component of the event-related potential was assessed in three experiments. In each study an auditory discrimination paradigm was employed wherein subjects indicated with a finger tap response the occurrence of a randomly presented 2000 Hz target tone embedded in a series of 1,000 Hz tones. Target stimuli were presented with a probability of either .20 or .80 in different conditions which were combined factorially with different interstimulus intervals. Experiment 1 presented stimuli at 2.0, 2.5, or 3.0 second intervals; Experiment 2 presented stimuli at 2.0, 3.0, or 4.0 second intervals; Experiment 3 presented stimuli at 4.0, 6.0, or 10.0 second intervals. P3 amplitude was larger for the .20 relative to the .80 target probability conditions for the shorter interstimulus intervals but not for the longer intervals. P3 latency was consistently longer for the .20 relative to the .80 target probability conditions, with generally little effect observed for interstimulus interval changes. The results suggest that interstimulus interval affects component amplitude by determining the amount of processing resources available when the P3 is produced.     

Parietal P3 Response as an Indicator of Stimulus Categorization: Increased P3 Amplitude to Categorically Deviant Target and Nontarget Stimuli

Two experiments were performed in which we compared the effects of selected non-deviant versus categorically deviant stimuli on parietal P3 under a variety of conditions in which one, both, or neither stimulus was a target of an experimental task. Subjects were repeatedly presented with series of 8 numeric stimuli and 1 alphabetic (Deviant) stimulus. P3 amplitudes to target and nontarget Deviant stimuli were consistently and significantly larger than to other, non-deviant targets and nontargets, respectively. Nontarget Deviant stimuli evoked P3 amplitudes comparable to those evoked by low-probability non-deviant targets. The observed differences indicate that P3 amplitude is a sensitive indicator of perceived category differences, and that the effect of category deviance on parietal P3 amplitude is independent of task response classification (target or nontarget) and of response probability.     

Evaluation of Nonspecific Brain Systems in Patients with Panic Disorders by the Method of P300 Cognitive Evoked Potentials

Measuring of the amplitude of auditory cognitive evoked potentials P300 showed its changes (decrease and increase) in patients with panic disorders compared to healthy individuals. The authors hypothesize that the decrease in P300 amplitude reflects increased activity of the cerebral reticulothalamic structures, while its increase is associated with activation of the septohippocampal limbic system in patients with panic disorders. P300 recording can serve as a valuable diagnostic method.     

P300 wave elicited by a stimulus-change paradigm in acutely prepared rats

Presentation of a long sequence of stimuli in one modality followed by infrequent substitution of stimuli in a different modality produced a very large P300 wave in the evoked potential to the infrequent stimulus. The P300 wave was never observed in a repetitive train of stimuli in one modality or to the background stimuli during the stimulus-change procedure. This phenomenon was observed in cortical recordings from anesthetized rats. This P300 wave corresponds in latency to that observed in human cognitive studies, and the use of this paradigm in animal studies could greatly facilitate work to determine the neural basis of the P300 wave.     

Subjective and objective probability effects on P300 amplitude revisited

Does objective probability affect P300 size independently and in addition to subjective probability? The latter was manipulated by the number of stimuli presented and classification task. Five groups saw target and frequent stimuli. Two saw these with p=.2 or .067, with two different button presses. Three groups saw two additional nontarget stimuli each with p=.067. One group pressed a different button for each stimulus. A second group pressed one button for the three oddballs, another for the frequent. A third critical group pressed one button for the target and another for other stimuli. In this group, P300 was larger for targets versus nontargets, and larger for nontargets versus frequents. Although nontargets were classified with frequents, their actual low probability distinguished them from frequents, and their subjective probability distinguished them from targets. Therefore, actual and subjective probability effects were independently found.     

P300 Latency and Digit Span

The relationship betweeen P300 latency and digit span reported by Polich, Howard, and Starr (1983) is re-examined. Evidence is presented which shows that these authors' use of partial correlation to correct for age differences in their sample of subjects is erroneous because the assumption of linear regression is clearly not satisfied. This finding seriously questions Polich et al.'s conclusion that P300 latency and digit span covary irrespective of any relationship of the variables to age.     

Second Thoughts: Multiple P300s Elicited by a Single Stimulus

In a previous report (Johnson & Donchin, 1978), we manipulated the discriminability of tone pairs that delivered feedback information in a time-estimation paradigm. As in other experiments using feedback stimuli, the event-related potentials elicited by these stimuli did not return to baseline in the 800-ms poststimulus interval. Since we were interested in this “Slow Wave'’activity, the poststimulus interval was lengthened to 1500 ms. Averages revealed that a second positive peak was present for some of the individual subjects. To investigate this activity further, the filtered singletrial waveforms were inspected visually. These data were characterized by the presence of one, and occasionally two, positive peaks, with highly variable latencies, following the P300. These peaks were indistinguishable in frequency and general appearance from the P300s elicited by the feedback stimuli. After latency adjusting the waveforms on the peak of the second positive wave, amplitude and latency were quantified. Whereas P300 amplitude was directly related to stimulus discriminability and positive feedback elicited larger P300s than negative feedback, the amplitude of the second positive wave was constant across levels of discriminability and the same for both types of feedback. In contrast, the latencies of both waves were inversely related to stimulus discriminability and shorter following positive feedback than negative feedback. Evidence is presented to support our contention that these additional positive peaks represent P300 activity. The data are discussed in terms of what these multiple P300s reveal about human information processing.     

精神分裂症事件相关电位P300与心理症状的相关性研究

目的探讨精神分裂症患者的事件相关电位P300与其心理症状之间的相关性。方法对51例精神分裂症患者(研究组)和29例正常人(对照组)进行脑诱发电位仪听觉Oddball范式检测,记录靶P300波的潜伏期与波幅;运用心理疾病预测量表(MDPS)进行心理症状评定。结果 1研究组靶P300潜伏期、波幅较对照组延长、降低(P0.05);2与对照组相比,除家族及既往史、成长经历因子外,研究组的MDPS预测总分及心理症状各因子分均有明显差异性(P0.01);3研究组靶P300潜伏期与MDPS预测总分及心理症状各因子分(精神病性、抑郁、躁狂、神经症以及人格偏移)呈明显的正相关(r=0.443～0.593,P0.001),而P300波幅与其没有相关性(P0.05)。结论事件相关电位P300可辅助评价精神分裂症患者心理症状的严重程度。P300与MDPS有明显的相关性。     

Taking Attention to Task: P300, Task Response Probability, and Within-Category Deviation Detection

Previously, we reported enhanced P3 amplitudes to between-category deviations among high and low probability events. Here, we tested the effects of a within-category difference. Subjects performed a go/no-go button press task as they viewed repeated, randomly-ordered presentations of nine double-digit numbers. Eight numbers fell within a prescribed range (42-49, standards); prior to testing, subjects selected one standard number for later recall. A ninth, out-of-range (91, deviant) number was also included. Subjects were tested under two conditions, in which they responded either to one (low response probability) or to seven (high response probability) standard nonselected numbers, designated as targets. Relatively larger P3s were consistently apparent only when the deviant nontarget was associated with a low probability response to a nontarget. There was a selective effect of nontarget response probability on P3 amplitude to the deviant nontarget. Our results indicate that within-category deviation detection is facilitated by "controlled" attention to the structure of the stimulus field.     

Stimulus artefact in somatosensory evoked potential measurement

When an electrical stimulus is used to evoke action potentials in peripheral nerves or the spinal cord, the stimulus causes an artefact which may interfere with measurement of the evoked potentials. This artefact, unlike all other sources of noise in the measurement, cannot be reduced by ensemble averaging. Confusion about the origin and transmission of stimulus artefact has led to considerable frustration in spinal somatosensory evoked potential (SSEP) measurements. The three mechanisms by which stimulus artefact is coupled into the measuring system are identified, and means for their reduction are discussed.