Effects of Attention and Background Verbal Stimuli on Event-Related Potentials to Tone Pips in Humans

Abstract: The effects of attention and background verbal stimuli on event-related potentials (ERPs) following tone pips were assessed under four conditions: tone pips presented alone when attending and ignoring the tones and tone pips plus verbal stimuli when attending the tones and attending the verbal stimuli. The data were quantified in terms of the N1-P2 amplitude and the similarity (correlation) between ERPs in corresponding placements over the two hemispheres. The main results were that attention influenced the ERP amplitude only with the verbal stimuli, that interhemispheric similarity was greatest with the tones only, and that similarity was greater under the tone plus verbal stimuli condition during tone-attention instructions.     

Effects of attention and background verbal stimuli on event-related potentials to tone pips in humans

The effects of attention and background verbal stimuli on event-related potentials (ERPs) following tone pips were assessed under four conditions: tone pips presented alone when attending and ignoring the tones and tone pips plus verbal stimuli when attending the tones and attending the verbal stimuli. The data were quantified in terms of the N1-P2 amplitude and the similarity (correlation) between ERPs in corresponding placements over the two hemispheres. The main results were that attention influenced the ERP amplitude only with the verbal stimuli, that interhemispheric similarity was greatest with the tones only, and that similarity was greater under the tone plus verbal stimuli condition during tone-attention instructions.     

Endogenous event-related potentials in monkey: the role of task relevance, stimulus probability, and behavioral response

Monkeys were trained in auditory discrimination tasks resembling human paradigms in which long-latency endogenous components, such as P300, are typically recorded. Morphological, topographical, and functional properties of the monkey event-related potentials (ERPs) were analyzed to determine similarities and differences with human ERPs reported in the literature. ERPs were recorded from epidural electrodes in monkeys trained to produce operant responses. In a conditional discrimination (CD) task, tone pips (2 kHz or 6 kHz, 40 msec duration, and 60 dB above nHL) were presented every 4-8 sec. Target tones presented during 'time-in' (TI) were rewarded when followed by a response in the correct post-stimulus interval (400-3000 msec). In contrast, tones presented during 'time-out' (TO) were not rewarded. Under both conditions, tones elicited an initial frontally dominant triphasic complex (P56-N92-P157). Additionally, TI target tones followed by a response elicited a large negativity (N358) having maximal amplitude over mid-frontal regions and followed by a parietally distributed positivity (P658). The scalp distribution and covariation with task requirements of N358 resemble those reported for the human 'O' wave. ERPs were also recorded in an auditory oddball paradigm in which tone pips (2 kHz and 6 kHz, 40 msec duration, and 60 dB above nHL) were presented in random order every second. Monkeys trained in the CD paradigm, along with additional subjects, were trained to make delayed responses following target tones embedded in a background of different-pitch tones. Tone probabilities were varied in different sessions from 90-10, 70-30, to 50-50 to assess the effects of probability. Background and target tones elicited a triphasic complex (P52-N110-P159) similar in latency and distribution to that recorded in the CD task. Additionally, target tones in this paradigm elicited a long-latency positive component (LPC) that exhibited an inverse relationship with stimulus probability. LPC had an onset latency of approximately 150-200 msec, a duration of approximately 300 msec, and multiple peaks (P244 and P376). These data indicate the importance of stimulus context in eliciting long-latency endogenous activity. It further suggests that strong analogies exist between monkey and human potentials recorded under similar paradigms. The effects of task relevance, stimulus probability, and the act of producing behavioral responses are similar to the effects of these variables on analogous human potentials.(ABSTRACT TRUNCATED AT 400 WORDS)     

Long-latency event-related potentials in squirrel monkeys: further characterization of wave form morphology, topography, and functional properties

Event-related potentials (ERPs) were recorded from the brain surface of untrained monkeys exposed to sequences of auditory stimuli (2 kHz and 6 kHz tones of 40 msec duration). Stimulus probability and interstimulus interval (ISI) were systematically varied in different paradigms. In an oddball paradigm with a 1 sec ISI in which one stimulus constituted 90% of all trials and the other 10%, a 'monkey' late positive component (MLPC), characterized by two peaks (P248 and P369), was recorded prominently over lateral parietal areas in response to the unpredictable and infrequent shifts in pitch. The amplitude of this late positivity was found to be sensitive to stimulus probability and to exhibit trial-to-trial sequential dependencies similar to those described for the human P300. The amplitude of MLPC was also found to be larger following longer ISIs. In addition, a 'monkey' late negative component (MLNC), with characteristics similar to those of the human slow wave (SW), was recorded following the infrequent shifts in pitch and found to temporally overlap with MLPC. MLNC was recorded with maximal amplitude over frontal cortex and was sensitive to stimulus probability but not to trial-to-trial changes in stimulus sequence. Thus MLPC and MLNC which appear to reflect similar yet distinct processes exhibit several analogies to the human P3a and SW, respectively.     

EVALUATION OF AUDITORY EVOKED POTENTIALS FROM THE INFERIOR COLLICULUS IN RAT

This study aimed to investigate the usefulness of auditory evoked potentials (AEPs) in rats. To this end, N1, P2 latencies, and the N1 P2 amplitude of responses to different acoustic stimuli from rats, which were implanted with permanent electrodes in the inferior colliculus (IC), were evaluated and used to demonstrate the frequency characteristics of IC region. Permanent electrodes were implanted in IC regions of 7 male albino rats by the stereotaxic method. The animals were exposed to five tones series of stimuli (1000 Hz, 2000 Hz, 4000 Hz, 6000 Hz, and 8000 Hz tones with 1500 ms interstimulus intervals) of 70 dB with a duration of 1000 ms. AEPs)were recorded and analyzed with the Brain-Data Acquisition system. There were no statistically significant differences in N1, P2 latencies, and the N1-P2 amplitude of AEPs from IC regions of rats as a result of changes in the frequency of stimulus. It was determined that the dominant frequency activity of the IC to acoustic stimulus was theta-alpha band, with theta as the peak frequency. As a result it was concluded that there are similarities between the N1, P2 components of rat AEPs, and human AEPs. We have suggested that the rats may provide a useful model for investigating the generation of middle latency components of AEPs in humans.     

Auditory event-related potentials in schizophrenia and depression

Event-related potentials in two auditory target detection paradigms and two auditory paradigms without overt tasks were studied in 22 schizophrenic, 21 depressed, and 28 matched control subjects meeting Research Diagnostic Criteria. In the target detection paradigms, schizophrenics showed a pattern of reduced N120 amplitude and shorter P200 latency to frequently occuring tones, and reduced P300 and Slow Wave amplitude to infrequent target and nontarget tones. This pattern is consistent with impaired selective attention for stimuli. For depressed patients these variables were generally intermediate between those of schizophrenics and controls. In the other paradigms N120 latency was greater for schizophrenics, and P200 amplitude was less for depressed patients.     

Habituation of the auditory evoked potential in a short interstimulus interval paradigm

The present experiment was carried out to investigate elicitation and habituation of the auditory event related potentials with stimulus trains utilizing a short interstimulus intervals (ISI) of 1500 ms. Scalp event related potentials elicited by auditory stimuli were recorded in 10 male subjects. Thirty auditory stimuli were presented binaurally over headphones to every subject with a duration of 1000 ms, each with a constant ISI of 1500 ms. No task relevance was given to the stimuli. Wave-forms were collected using a Pentium 100 computer. All analyses were carried out over the 30 trials. In each single trial event related potentials, latencies and amplitudes of N1-P2 components were analyzed separately for four frequency bands (0.3-70, 0.3-4, 4-7, 7-13 Hz). Trend effects were tested with linear-regression analyses (N1-P2 amplitude x stimuli number). We found that the amplitude from the first stimulus decreased reliably across trial blocks of the N1-P2 components and that it was directly affected by ISI. The relevance of these results for the habituation is discussed.     

Intensity-amplitude relationships in monkey event-related potentials: parallels to human augmenting-reducing responses.

In human, the amplitudes of specific event-related potential (ERP) components can increase or decrease in response to increasing stimulus intensity depending on the location of the recording site. Large increases characterize components presumably generated by modality-specific sites, while smaller increases or even decreases are associated with those originating in associational areas. Comparable data from non-human primates, which would permit invasive studies of the neural substrates underlying these intensity-amplitude differences, are limited. To more fully characterize these relationships, auditory ERPs were recorded from chronically implanted epidural electrodes in 5 squirrel monkeys (Saimiri sciureus) in response to tones (500 Hz, 300 msec duration) of varying intensities (50, 60, 70, 80 dB SPL). Squirrel monkey ERPs recorded at Fz exhibited 3 peaks during the 200 msec post-stimulus interval. These peaks included a positivity (P1), followed by a negativity (N1), and then another positivity (P2). At posterior sites, the frontal P1-N1 configuration was recorded as an N1-P1 complex. At these sites, a small negativity (N2) preceded the last positive peak (P2). Changes in polarity were independent of reference site and posterior N1-P1 peaks exhibited latencies similar to those of the frontal P1-N1 components. Amplitudes at Fz, Cz, and Pz increased substantially with increasing stimulus intensity ('augmenting'). In contrast, only small increases or even decreases in amplitude ('reducing') were evident at T3 and T4. On the other hand, peak latencies decreased with higher stimulus intensities at most sites. The site-specific amplitude responses exhibited considerable temporal stability. In one subject, for example, similar 'augmenting' profiles were recorded at Fz in 8 sessions over a 6-month period. The topography of monkey intensity-amplitude response profiles, their temporal stability, and peak latency shifts resemble observations made in humans. The data show that 'augmenting' characterizes monkey vertex potentials, which, like the analogous human potentials, may originate in primary auditory cortex. In contrast, potentials recorded over temporal cortex, which may originate in auditory association cortex, exhibit 'reducing.' Thus, the data support the hypothesis that differences in amplitude with increasing intensity may reflect differences in cortical origin.     

The mismatch negativity and the P3a components of the auditory event-related potentials in autistic low-functioning subjects.

OBJECTIVE: In order to understand better the psychophysiological basis of auditory processing abnormalities in autism, we decided to study two automatic components of the auditory event-related potentials (ERPs): the mismatch negativity (MMN)--a component of the ERP which is recorded when, during repetitive auditory stimulation, rare changes are introduced--and the novelty-related P3a which is recorded as a response to unexpected novel events occurring in a sequence of repetitive stimuli. METHODS: Ten male subjects, mean age 12.3 years (SD 4.95), affected by autism and mental retardation were admitted to this study. All patients were also mentally retarded. Ten normal male subjects, mean age 12.2 years (SD 3.94), were used as controls. Auditory evoked potentials were recorded from 19 scalp electrodes (10-20 system), and stimuli were presented in sequences consisting of 2000 tones (70 dB, ISI=800 ms). Three types of stimuli were presented: (1) standard stimuli (1000 Hz tones, 80% of total stimuli), (2) deviant stimuli (1300 Hz tones, 10% of total stimuli), and (3) novel stimuli (complex and non-monotonal, 10% of total stimuli). To quantify the MMN, the evoked response to the standard tones was subtracted from the corresponding deviant stimulus response and its amplitude and latency at peak were measured over Fz, Cz and Pz; similarly, the P3a component of the ERP was obtained by subtracting the response to the standard tone from that to the novel stimuli and its amplitude and latency at peak were measured over Fz, Cz and Pz. Also, the amplitude and latency at peak for the N1 component of the auditory evoked potential obtained with the standard stimuli were measured over Fz, Cz and Pz. The correlation between age and MMN and P3a amplitude was also analyzed. RESULTS: N1 showed significantly shorter latencies in the autistic groups. MMN elicited by deviant stimuli, but not that elicited by novel stimuli, was found to be significantly larger in autistic children than in normal controls. P3a showed higher amplitude in autistic subjects than in normal controls during childhood; the opposite was observed during young adulthood. DISCUSSION: Our findings indicate that significant changes in ERPs can also be seen in non-cooperative individuals with autism and mental retardation, which might be different from the changes already reported for high-functioning autistic subjects and deserve further insight. These changes show developmental modifications that should be taken into consideration when analyzing data from autistic subjects.     

The effects of auditory attention measured from human electrocorticograms.

OBJECTIVE: A central question in auditory electrophysiology has been whether selective attention can modulate exogenous components of the scalp-recorded N1 (the 'N1 effect'). Intracranial electrocorticograms were used in the current work to investigate this issue in greater anatomical detail. METHODS: Data were recorded from subdural electrodes placed across temporal cortex in 6 patient-volunteers undergoing diagnostic procedures for medically intractable epilepsy. Patients performed a dichotic listening task in which they alternately attended to a series of tones presented to both ears (mean ISI 800 ms) by responding to rare frequency deviants. RESULTS: Effects of attention were measured on the largest negative and positive waveform deflections observed between 70 and 220 ms post-stimulus for stimuli presented contralateral to grid location. Peak deflections were most often recorded from the upper bank of the posterior superior temporal gyrus at approximately 89 and 173 ms on average (labeled N90stg and P170stg, respectively). Selective attention had little effect on peak latencies but significantly increased the N90stg for 3 subjects, increased the P170stg for two subjects, and decreased the P170stg for two other subjects. CONCLUSIONS: Selective auditory attention can modulate neural response in auditory cortex. SIGNIFICANCE: The effects of attention on the scalp-recorded N1 component may arise in part from the enhancement of exogenous responses in temporal cortex.     

Anatomical substrates of auditory selective attention: behavioral and electrophysiological effects of posterior association cortex lesions

Even-related brain potentials (ERPs) and reaction times (RTs) were recorded in an auditory selective attention task in control subjects and two groups of patients with lesions centered in (1) the temporal/parietal junction (T/P, n = 9); and (2) the inferior parietal lobe (IPL, n = 7). High pitched tones were presented to one ear and low pitched tones to the other in random sequences that included infrequent longer-duration tones and occasional novel sounds. Subjects attended to a specified ear and pressed a button to the longer-duration tones in that ear. IPL and T/P lesions slowed reaction times (RTs) and increased error rates, but improved one aspect of performance — patients showed less distraction than controls when targets followed novel sounds. T/P lesions reduced the amplitude of early sensory ERPs, initially over the damaged hemisphere (N1a, 70–110 ms) and then bilaterally (N1b, 110–130 ms, and N1c 130–160 ms). The reduction was accentuated for tones presented contralateral to the lesion, suggesting that N1 generators receive excitatory input primarily from the contralateral ear. IPL lesions reduced N1 amplitudes to both low frequency tones and novel sounds. Nd components associated with attentional selection were diminished over both hemispheres in the T/P group and over the lesioned hemisphere in the IPL group independent of ear of stimulation. Target and novel N2s tended to be diminished by IPL lesions but were unaffected by T/P lesions. The mismatch negativity was unaffected by either T/P or IPL lesions. The results support different roles of T/P and IPL cortex in auditory selective attention.     

Intracranial identification of an electric frontal-cortex response to auditory stimulus change: a case study

The aim of the present study was to clarify whether ERPs recorded directly from the human frontal cortex contributed to the auditory N1 and mismatch negativity (MMN) elicited by changes in non-phonetic and phonetic sounds. We examined the role of prefrontal cortex in the processing of stimulus repetition and change in a 6-year-old child undergoing presurgical evaluation for epilepsy. EEG was recorded from three bilateral sub-dural electrode strips located over lateral prefrontal areas during unattended auditory stimulation. EEG epochs were averaged to obtain event-related potentials (ERPs) to repeating (standard) tones and to infrequent (deviant) shorter duration tones and complex sounds (telephone buzz). In another condition, ERPs were recorded to standard and deviant syllables, /ba/ and /da/, respectively. ERPs to vibration stimuli delivered to the fingertips were not observed at any of the sub-dural electrodes, confirming modality specificity of the auditory responses. Focal auditory ERPs consisting of P100 and N150 deflections were recorded to both tones and phonemes over the right lateral prefrontal cortex. These responses were insensitive to the serial position of the repeating sound in the stimulus train. Deviant tones evoked an MMN peaking at around 128 ms. Deviant complex sounds evoked ERPs with a similar onset latency and morphology but with an approximately two-fold increase in peak-to-peak amplitude. We conclude that right lateral prefrontal cortex (Brodmann's area 45) is involved in early stages of processing repeating sounds and sound changes.     

Evaluation of auditory evoked potentials from the inferior colliculus in rat

This study aimed to investigate the usefulness of auditory evoked potentials (AEPs) in rats. To this end, N1, P2 latencies, and the N1-P2 amplitude of responses to different acoustic stimuli from rats, which were implanted with permanent electrodes in the inferior colliculus (IC), were evaluated and used to demonstrate the frequency characteristics of IC region. Permanent electrodes were implanted in IC regions of 7 male albino rats by the stereotaxic method. The animals were exposed to five tones series of stimuli (1000 Hz, 2000 Hz, 4000 Hz, 6000 Hz, and 8000 Hz tones with 1500 ms interstimulus intervals) of 70 dB with a duration of 1000 ms. AEPs) were recorded and analyzed with the Brain-Data Acquisition system. There were no statistically significant differences in N1, P2 latencies, and the N1-P2 amplitude of AEPs from IC regions of rats as a result of changes in the frequency of stimulus. It was determined that the dominant frequency activity of the IC to acoustic stimulus was theta-alpha band, with theta as the peak frequency.     

Luminance and spatial attention effects on early visual processing

Event-related potentials (ERPs) were recorded from healthy subjects in response to unilaterally flashed high and low luminance bar stimuli presented randomly to left and right field locations. Their task was to covertly and selectively attend to either the left or right stimulus locations (separate blocks) in order to detect infrequent shorter target bars of either luminance. Independent of attention, higher stimulus luminance resulted in higher ERP amplitudes for the posterior N95 (80–110 ms), occipital P1 (110–140 ms), and parietal N1 (130–180 ms). Brighter stimuli also resulted in shorter peak latency for the occipital N1 component (135–220 ms); this effect was not observed for the N1 components over parietal, central or frontal regions. Significant attention-related amplitude modulations were obtained for the occipital P1, occipital, parietal and central N1, the occipital and parietal P2, and the parietal N2 components; these components were larger to stimuli at the attended location. In contrast to the relatively short latencies of both spatial attention and luminance effects, the first interaction between luminance and spatial attention effects was observed for the P3 component to the target stimuli (350–750 ms). This suggests that interactions of spatial attention and stimulus luminance previously reported for reaction time measures may not reflect the earliest stages of sensory/perceptual processing. Differences in the way in which luminance and attention affected the occipital P1, occipital N1 and parietal N1 components suggest dissociations among these ERPs in the mechanisms of visual and attentional processing they reflect. Nonetheless, scalp current density mappings of the attention effects throughout the latency ranges of the P1 and N1 components show the most prominent attention-related activity to be in lateral occipital scalp areas. Such a pattern is consistent with the spatially selective filtering of information into the ventral stream of visual processing which is reponsible for complex feature analysis and object identification.     

Effects of locus coeruleus lesions on auditory, long-latency, event-related potentials in monkey

It has previously been demonstrated that monkeys exhibit certain event-related potential (ERP) components showing latency, polarity, and contingency similarities to those observed in humans. In the present study, monkey P300-like components were studied in order to evaluate the hypothesis that the noradrenergic locus coeruleus (LC) system participates in their generation or modulation. ERPs were recorded from untrained squirrel monkeys (Saimiri sciureus) twice a week for 4 weeks before and after bilateral LC lesions and interruption of dorsal bundle (DB) fibers. Stimuli consisted of 2 and 6 kHz tone pips (40 msec duration, 60 dB above nHL) presented once a second in random order. In most sessions, one tone constituted 90% of the stimuli and the other tone 10%, while in some sessions tones were made equiprobable to test the effects of manipulating stimulus probability. LC and DB lesions were made by first localizing the nucleus and creating an electrolytic lesion. Then, the electrode was placed at the anterior pole of the nucleus and a knife cut effected. The extent of damage to LC perikarya and ascending axons was assessed by reconstructing lesions from Nissl-stained sagittal sections through the brain stems. The effect of lesions on cortical noradrenergic axons was immunohistochemically verified utilizing antisera directed against dopamine-B-hydroxylase and tyrosine hydroxylase to label noradrenergic and dopaminergic axons, respectively. The prelesion ERP results replicated previous findings of P300-like components recorded in response to low-probability tones. The postlesion ERP data indicated that following damage to LC cell bodies, combined with interruption of histochemically detectable ascending noradrenergic axons, monkey P300-like potentials exhibited decreased areas, altered brain-surface distribution, and reduced sensitivity to stimulus probability. The correlation between the extent of cell body lesions and percentage reduction in the magnitude of P300-like responses was significant. However, interruption of DB fibers alone did not have similar effects. Neither type of lesion had any effect on amplitudes, latencies, or brain-surface distributions of P52, P172, or N250-900. There was, however, a significant effect on N106. Stimulus probability effects on the frontally distributed P52 and N106 were not altered by the lesions. These data support the hypothesis that the integrity of the LC nucleus and its ascending fibers is important in the generation and modulation of surface-recorded P300-like activity.     

Event-related potentials as a tool in the evaluation of cognitive functions in young subjects through the execution of a simple task

Event-related potentials (ERPs) were recorded in 20 student volunteers. Three recordings were performed using aural stimuli of 4,000 (rare tones) and 250 Hz. In the target recording subjects were asked to count the rare tones. Endogenous and exogenous components of ERP recordings were analyzed. During the target recording N2 and P3 components were observed at 200 ms and approximately 300 ms, respectively, in addition to N1 (100 ms) and P2 (180 ms). The N2 and P3 waves are indicative of analysis at a higher cognitive level and have been termed the 'response set'. The P3 wave appeared to be stable in all subjects and may represent a useful electrophysiological method to explore mnemonic and cognitive functions in man.     

P300 event-related potential in epileptic children and adolescents

P300 is a manifestation of activity in a limited capacity system "whose use in the service of different tasks is under relative control by instruction". It is accepted as an objective correlate of mental processing involved in the allocation of attentional resources when immediate memory is engaged. The aim of this study was to evaluate cognitive function in epileptic children and adolescents. We applied the "auditory oddball" paradigm to elicit event-related potentials (ERPs) according to the IFCN recommendation standards. ERPs were studied in fifteen patients with generalized epileptic seizures at matched age (8-18 years) (mean 13.8 +/- 2.4 y). 50 neurologically normal children were used as a control group. ERP were averaged with a Multiliner (Toennies, Germany) equipment. The method included two different tones for frequent and for rare stimuli generated at random. The tones were presented binaurally through headphones. ERPs were recorded at Fz, Cz and Pz according to the International 10-20 system. ERPs for target and non-target stimuli were averaged separately. The major positive peak between 250 and 500 ms for the rare tones was regarded as the cognitive evoked potential (P300). Latency values were obtained from the intersection of extrapolated lines from the ascending and descending slopes of each peak. The latencies of the N1, P2, N2 and P300 waves were determined for each subject, as well as peak to peak amplitudes of N1-P2, P2-N2, N2-P300. Auditory event related potential may be helpful procedures used in objective evaluation of cognitive function in patients with epilepsy.     

Schizophrenia-like deficits in auditory P1 and N1 refractoriness induced by the psychomimetic agent phencyclidine (PCP).

OBJECTIVES: The amplitude of the cortically generated auditory event-related potential (ERP) components P1 and N1 decreases as the interval between successive stimuli (ISI) decreases. Although the phenomenon of P1 and N1 refractoriness is well established, the underlying mechanisms are poorly understood. The present study investigates P1 and N1 refractoriness in the awake monkey in order to investigate underlying mechanisms. METHODS: Auditory ERP were obtained in response to repetitive auditory stimuli presented at 5 levels of ISI between 150 ms and 9 s, prior to and following administration of the selective N-methyl-D-aspartate (NMDA) antagonist phencyclidine (PCP). RESULTS: P1 and N1 amplitude declined in monkeys with decreasing ISI, with similar temporal characteristics to that observed in humans. PCP inhibited P1 and N1 generation at long, but not short, ISI producing a pattern similar to that recently observed in schizophrenic subjects. CONCLUSIONS: The present findings suggest that the primate P1/N1 model may be useful for investigating mechanisms underlying impaired information processing in schizophrenia, and that NMDA receptor dysfunction may play a key role in information processing dysfunction associated with schizophrenia.     

Differential modulation of temporal and frontal components of the somatosensory N140 and the effect of interstimulus interval in a selective attention task

The modulation of the somatosensory N140 was examined in a selective attention task where a control condition was applied and the interstimulus interval (ISI) was varied. Electrical stimuli were randomly presented to the left index (p=0.4) and middle fingers (p=0.1), and right index (p=0.4) and middle fingers (p=0.1). In the attend-right condition, subjects were instructed to count silently the number of infrequent target stimuli presented to the right middle finger, and to the left middle finger in the attend-left condition. They had no task in the control condition. Each condition was performed with two different sets of ISI (mean 400 vs. 800 ms). The somatosensory N140 elicited by frequent standard stimuli was analyzed. The N140 amplitude was larger for the attended ERP compared to the control and unattended ERPs. This attention effect was more marked at the frontal electrodes compared to the temporal electrodes contralateral to the stimulation side. Furthermore, the attention effect at the frontal electrode was larger when the ISI was 800 ms than when it was 400 ms. The N140 amplitude did not differ between the control and unattended ERPs, which might show that a small processing negativity (PN) occurred during the control condition or difference in vigilance level between them. In conclusion, the early lateral ("temporal") and late midline ("frontal") components of the N1 (N140) show different behavior, and thus may have different functional significance. Enhancement of the attention effect at the frontal electrode in the longer ISI condition supports the hypothesis that it is related to stronger, voluntary maintenance of the attentional trace.     

Developmental changes of awareness during passive and active attentions: evaluation of serial event-related potentials (N130, N180, P250)

Serial event-related potentials (ERPs), especially the negative components before P300, were recorded to evaluate the developmental changes of awareness, or intentional attention. In this study, 36 healthy children (5-16 years of age) and eight healthy adults (19-37 years) were told to perform two attentive paradigms: passive and active. Each test condition consisted of 16 electrical stimuli. Four trials were averaged in sequence and then evaluated as serial four blocks. With repetition in both passive and active attentive paradigms the amplitude of N130 was not attenuated until six years old. During active attention, N180 remained undiminished in adolescents and adults. The amplitude of P250 decreased with repetition during passive attention in children over seven years old, but was not attenuated during active attention in adults. These results suggest that N130 reflects the orienting reflex, and that N180 is associated with the process to maintain awareness.