The effects of uncertainty and task-relevance on habituation and recovery of the electrodermal and visual orienting reaction

Habituation and recovery of the skin conductance reaction (SCR) and visual orienting reaction (VOR) were investigated. Half the subjects (total N = 48) were instructed to memorize a complex visual stimulus (TR), while the other half received a non task-relevant instruction (NTR). All subjects were exposed to two series of 16 identical stimuli. At trial 17 the location of the stimulus changed. Half the subjects in both groups received a priori information about the stimuli, the other half did not. Task-relevance led to slower SCR habituation and longer VORs. In the TR condition the VOR latency time rapidly decreased, indicating the development of a set. In terms of SCR frequency, but not in terms of SCR magnitude OR recovery was stronger in the task-relevant condition. However, all subjects oriented visually to the stimulus change. No habituation of the VOR was found using a drift-free technique for measuring eye-movements. It is concluded that the SCR and the VOR latency data supply evidence for a structural difference between task-relevant and task-irrelevant ORs.     

Habituation of early and late visual ERP components and the orienting reaction: the effect of stimulus information

Single trial event-related potentials at Fz, Cz, Pz and Oz were measured concurrently with pupil reactions and skin conductance reactions in a habituation paradigm. One group of subjects (n = 16) was given 36 simple visual stimuli and a second group (n = 16) 36 complex visual stimuli of equal duration, brightness and dimensions. No task-relevance was given to the stimuli. Under these circumstances we found rapid habituation (within 6 trials) of the vertex N1. Because we used long, variable interstimulus intervals, the N1 decrease could not be explained by refractory effects. Habituation rates of N1 and the concurrently measured SCR did not differ. Although the P3 showed significant habituation over the 12 trials (except at Oz), it habituated slower than the N1 and the SCR. The complex stimulus condition elicited larger P3b waves. No effect of stimulus complexity was found on the N1 and the SCR. The relevance of these results for the OR is discussed.     

Effects of task relevance on habituation of visual single-trial ERPs and the skin conductance orienting response

Single-trial event-related potentials were recorded at Oz, Pz, Cz, and Fz, concurrently with skin conductance reactions and fixation behavior in a habituation paradigm. A total of 48 subjects received 16 identical visual stimuli; 24 of them were instructed to pay attention, whereas the other half were given a neutral instruction. Two early negative components (N1 and N2), as well as a late positive component (P3) were identified. N1 and skin conductance reaction (SCR) showed fast decrement over trials, whereas N2 and P3 habituated slowly. Habituation of N1 and SCR was delayed by task instructions; N2 was hardly seen at all in the neutral condition. The task effects on N1 and N2 were observed only at Oz. It is concluded that the processing of relevant stimuli differs structurally from the processing of neutral stimuli; this difference may be observed even at a latency of 100 ms. The N1 appears to be related to the SCR, whereas this does not hold for P3; the N2 is related to selection negativities reported by other authors.     

Olfactory, auditory, and visual ERPs from single trials: no evidence for habituation.

Event-related potentials (ERPs) using olfactory, auditory, and visual stimuli were recorded from young adults to assess possible component habituation across single trials among modalities. A single-stimulus ERP paradigm was used that employed a 10-min inter-stimulus interval (ISI) to minimize possible sensory adaptation and three stimulus trials for each modality to assess initial habituation effects. The present findings were: (1) P3 amplitude does not habituate appreciably over the initial three trials but may increase from the first to second trial. (2) ERPs from a single-stimulus paradigm with a very long ISI produce significantly correlated component amplitudes for the olfactory, auditory, and visual modalities. (3) P3 amplitude from olfactory stimuli demonstrated scalp topography similar to that for auditory and visual ERPs. These findings suggest that the single-stimulus task using a long ISI produces highly comparable and stable P3 components from olfactory, auditory, and visual stimuli. Application of single-stimulus paradigm to olfactory ERP methods is supported.     

Visual stimulus change and the orienting reaction: event-related potential evidence for a two-stage process.

In a previous study it was found that infrequent deviant visual stimuli, in a series of standards, elicited event-related potentials (ERPs) with enhanced P2-N2s and P3 amplitudes, suggesting that these parameters reflect processes related to the orienting reaction (OR). In the present study a similar oddball series was presented against the background of a second class of stimuli. With respect to the latter stimuli, subjects had to perform either a very involved (hard) or an easy task. EEG was recorded to oddball (probe) stimuli from Oz, Pz, Cz, and Fz. Analysis of average ERPs revealed that, in the easy condition, deviant probes elicited both enhanced P2-N2s and enhanced P3s, relative to the standards. In contrast, in the hard condition P2-N2, but not P3, was enhanced by stimulus change. In addition, overall P3 amplitude to probes was smaller in the hard condition (sequence-independent load effect). Analysis of single-trial ERPs (SERPs) with orthogonal polynomial trend analysis largely replicated these effects. In addition, SERP analysis also revealed a sequence-independent load effect on P2, as well as a decreasing P3 to deviant stimuli in the Easy condition, which was observed at Cz and Fz, but not at Pz or Oz. The results are interpreted as suggesting that P2-N2 and P3 reflect different stages of the OR, one of automatic and one of capacity-limited processing.     

The effects of interstimulus interval on sensory gating and on preattentive auditory memory in the oddball paradigm: Can magnitude of the sensory gating affect preattentive auditory comparison process?

P50, and mismatch negativity (MMN) are components of event-related potentials (ERP) reflecting sensory gating and preattentive auditory memory, respectively. Interstimulus interval (ISI) is an important determinant of the amplitudes of these components and N1. In the present study the interrelation between stimulus gating and preattentive auditory sensory memory were investigated as a function of ISI in 1.5, 2.5 and 3.5 s in 15 healthy volunteered participants. ISI factor affected the N1 peak amplitude significantly. MMN amplitude in 2.5 s ISI was significantly smaller compared to 1.5 and 3.5 s ISI. ISI X stimuli interaction on P50 amplitude was statistically significant. P50 amplitudes to deviant stimuli in 2.5 s ISI were larger than the P50 amplitudes in other ISIs. P50 difference (P50d) waveform amplitude correlated significantly with MMN amplitude. The results suggest that: (i) auditory sensory gating could affect preattentive auditory sensory memory by supplying input to the comparator mechanism; (ii) 2.5 s ISI is important in displaying the sensory gating and preattentive auditory sensory memory relation.     

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.     

Habituation and the Orienting Response in the Auditory Cortical Evoked Potential

Habituation of the auditory cortical evoked potential, the GSR, and heart rate was measured in 100 male subjects. Stimuli were 31 tones of 1 sec duration with an ISI of 33 sec. All stimuli were sinusoidal, at a frequency of 1000 Hz, and at an intensity of 95 dB (re 20 N/cm²). The EEG was measured from bipolar electrode placement to the C_z and T₃ scalp locations. Evoked potentials were averaged over 3 successive blocks of 10 stimuli. The GSR habituation scores were the regression coefficients over trials of the response amplitude in square root conductance. Significant habituation of all evoked potential amplitude components was found. This was a rapid process occurring between the first and the second 10 stimuli. The habituation score for the most significant evoked potential variable (P200) was found to correlate significantly with the GSR and heart rate habituation scores. These results were interpreted as suggesting that the amplitude of the evoked potential was enhanced by the orienting reaction.     

Electrophysiological correlates of feature analysis during visual search

Event-related brain potentials (ERPs) were recorded from normal young adults during visual search tasks in which the stimulus arrays contained either eight identical items (homogeneous arrays) or seven identical items and one deviant item (pop-out arrays). Four experiments were conducted in which different classes of stimulus arrays were designated targets and the remaining stimulus arrays were designated nontargets. In Experiments 1 and 2, both target and nontarget pop-out stimuli elicited an enhanced anterior N2 wave and a contralaterally larger posterior P1 wave, but Experiments 3 and 4 demonstrated that these components do not reflect fully automatic pop-out detection processes. In all four experiments, target pop-outs elicited enlarged anterior P2, posterior N2, occipital P3, and parietal P3 waves. The target-elicited posterior N2 wave contained a contralateral subcomponent (N2pc) that exhibited a focus over occipital cortex in maps of current source density. The overall pattern of results was consistent with guided search models in which preattentive stimulus information is used to guide attention to task-relevant stimuli.     

Reflection of an Orienting Reflex in the Phases of Evoked Potentials in the Rabbit Visual Cortex and Hippocampus during Substitution of Stimulus Intensity

Experiments on conscious rabbits were performed using the oddball paradigm, in which a rare (deviant) and common (standard) stimuli were of the same color but different intensities. Deviant stimuli were of lesser intensity. Recordings were made of evoked potentials induced by series of uniform deviant stimuli (without using standard stimuli), which were presented at the beginning and end of stimulation. Visual evoked potentials recorded in response to deviant stimuli in the visual cortex and hippocampus showed increases in the amplitudes of phases, shifted towards positivity as compared with responses to standard stimuli and uniform deviant stimuli at the beginning and end of stimulus blocks. Significant changes affected phases P1 and P2 of visual evoked potentials in the cortex and phases P1, N1, and P2 in the hippocampus. The most significant increase in evoked potentials in the cortex was seen for the P2 peak (P130). It is suggested that changes in responses to oddball-deviant stimuli result from an orienting reflex to rare, unexpected stimuli and that the P2 (P130) peak in the cortex is associated with transmission of information regarding changes in the intensity of the light. The amplitude of this peak was shown to be decreased in responses to uniform deviant stimuli at the beginning and end of stimulus blocks. It was also demonstrated that the clearest and most contrasting changes in visual evoked potentials in responses to deviant and standard stimuli were seen with the smallest differences in intensity between these types of stimulus, this reflecting increases in the orienting reflex at threshold differences.     

Voluntary stimulus production enhances deviance processing in the brain.

Humans often get information by voluntary action. However, little is known about how stimulus processing is modulated by self-production of stimuli. In the present study, event-related brain potentials were recorded from 16 student volunteers performing an auditory three-stimulus oddball task in two conditions. In the self condition, the stimuli were triggered by participants' voluntary button presses. In the auto condition, the same stimuli were presented automatically by a computer with the same interstimulus intervals as those in the self condition. Perceptually deviant nontarget stimuli elicited a larger P3 and a larger subsequent positivity in the self condition than in the auto condition, whereas low-deviant target stimuli elicited a P3 with equally high amplitude in both conditions. The findings suggest that voluntary stimulus production enhances orienting of attention (reflected in the P3a component) and subsequent memory updating (reflected in the P3b component) for deviant stimuli, but does not affect the response to task-relevant stimuli. Voluntary action may activate the perceptual representation of its most frequent outcomes and this anticipatory activation may make deviant stimuli more salient in the context.     

Different Effects of Uncertainty and Complexity on Single Trial Visual ERPs and the SCR-OR in Non-Signal Conditions

Single trial event-related potentials at F_z, C_Z, P₇, and O_Z were measured concurrently with the skin conductance response (SCR) in a habituation paradigm. Half the subjects (26) were told that the same stimulus would be presented a number of times in the middle of a TV screen (“certain condition”), and the other half were not informed about the stimuli (“uncertain condition”). Within each of these groups, half of the subjects received 32 stimuli of 4 bits of information and the other half received 32 stimuli of 60 bits of information. No task-relevance was given to the stimuli. Larger vertex P300 waves were associated with more complex stimuli, but uncertainty had no effect on the P300. A significant complexity × uncertainty × trials interaction was found on a sustained late positive activity, called the Slow Wave (SW), which was maximal at P_z and habituated rapidly. As before, we found that both the SCR and the vertex P300 habituated. No effect of uncertainty or complexity was found on the SCR. The results suggest that the SW is a useful index of information processing, and that the SCR and P300 must be considered to index different aspects of information processing.     

Single-trial event-related potentials to significant stimuli

The stimulus–response pattern of the skin conductance response (SCR) was used as a model of the Orienting Reflex (OR) to assess the P1, N1, P2, N2 and late positive complex (LPC/P300) components of the ERP in a simple habituation paradigm, in which a single series of 12 innocuous tones were presented at a very long interstimulus interval (2 min). To maintain their waking state during this boring task, participants were instructed to alternately close or open their eyes to each stimulus. None of the baseline-to-peak ERP measures showed trials effects comparable with the marked habituation over trials shown by the SCRs. Principal Components Analysis was used to decompose the ERP, yielding factors identified as the N1, N2, P3a, P3b and Novelty P3 components. An additional factor represented later eye-movement activity. No trial effects were apparent for the N1, N2, P3a or P3b components. The Novelty P3 showed marked response decrement over trials. These results are discussed in relation to current conceptualisations of the OR.     

The influence of visual information on habituation of the electrodermal and the visual orienting reaction.

In this study the influence of the information value of visual stimuli on habituation of the visual orienting reaction (VOR) and the skin conductance reaction (SCR) was investigated. 28 subjects received two blocks of 14 trials. Half the subjects received the higher information condition first and then the lower information, the other half received the conditions in the reversed order. Subjects fixated the stimuli with the higher information value longer than the stimuli with the lower information value during the 14 trials and habituated slower. This effect of information was absent in the second block and VOR habituation was also faster in this block. There was no difference in SCR amplitudes nor in SCR habituation scores between the two information conditions, neither in block 1 nor in block 2. The results of this study are discussed in relation with a two-stage model of the OR.     

The influence of task relevance and stimulus information on habituation of the visual and the skin conductance orienting reaction

This study investigated the hypothesis that task-relevant stimuli induce orienting reactions (ORs) that are stronger and more resistant to habituation when their information content is high than when it is low. Task-relevance was given to the stimuli by rewarding the subjects for correct recognition at the end of the experiment. The dependent variables in this study were the visual orienting reaction (VOR), the skin conductance reaction (SCR), their habituation scores and the number of spontaneous fluctuations in skin conductance (SFs). 28 subjects received two blocks of 14 trials. Half the subjects received the higher information condition first and then the lower information condition, while the other half received the reversed order. The VOR habituated quickly and was not significantly influenced by information value. SCR amplitudes were larger and SCR-habituation slower to stimuli containing more information. The results were interpreted as supporting the hypothesis that the SCR is associated with a secondary phase of the orienting process.     

Effects of "Below-Zero" Habituation on the Electrodermal Orienting Response to a Test Stimulus

Two experiments were designed to investigate the effect of below-zero habituation training on skin conductance response (SCR) amplitude to a change in auditory stimulus frequency. In both experiments, subjects were trained with a 1000 Hz tone until zero responding and then received 5, 10, or IS further training trials. In Experiment 1 (N=45), subjects then received 1 presentation of a test stimulus of 1400 Hz, while in Experiment 2 (N=45), the test stimulus was a tone of 670 Hz. On the basis of dual-process theory, it was hypothesized that response amplitude to the test stimulus would be inversely related to amount of below-zero training. However, the results of both experiments indicate that SCR amplitude was positively related to amount of below-zero training. These results suggest that in situations of extended habituation training, an expectancy or subjective probability of stimulus occurrence gradient is important in determining response amplitude to a test stimulus.     

Potentials evoked by temporal deviance

Infrequent stimuli deviating qualitatively from a train of standard stimuli appear to evoke two 'N2' potentials: A modality-specific 'mismatch negativity' (N2a), and a sharp peak forming part of a biphasic vertex response (N2b/P3a). Previous investigations leave it uncertain whether the same pattern of potentials is elicited by temporal deviance. In the present experiment a chequerboard was flashed at a standard ISI of 2000 msec, with occasional flashes occurring early at ISIs of 500, 1000 or 1500 msec. Detected deviants evoked N2b/P3a at an amplitude which increased with degree of deviance, but it was also evoked, at lower amplitude, by missed deviants and by standards. Its amplitude seems to depend upon the discriminability of the deviant stimuli, rather than upon whether they are actually detected. Moreover deviance from a repetitive background does not appear to be a necessary condition, since the complex can be elicited by isolated stimuli presented at irregular intervals. These considerations suggest that temporal uncertainty is an important factor. Temporal deviance produced no discernible mismatch negativity, modality-specific or otherwise, suggesting that it may involve processes different from those engaged in qualitative deviance.     

Active attention modulates passive attention-related neural responses to sudden somatosensory input against a silent background

To reveal whether active attention modulates neuronal responses related to passive attention to somatosensory stimuli presented suddenly against a silent background, we examined the passive attention-related change in amplitude of the event-related brain potentials (ERPs), caused by temporal infrequency of stimuli. Eighteen healthy subjects performed passive and active attention tasks in two stimulus conditions. In the oddball condition, frequent (80%, standard) and infrequent (20%, deviant) electrical stimuli were randomly delivered to the second and third digits of the left hand. In the deviant-alone condition, the deviant stimulus (deviant-alone stimulus) was delivered with the same timing and sequence as in the oddball condition without standard stimuli. The P100, N140, and P200 elicited by the deviant-alone stimulus were enhanced in amplitude compared to those evoked by the oddball deviant stimulus in both the active and passive tasks. Moreover, active attention increased the enhancement of P100 and N140. The difference waveform (deviant-alone minus oddball deviant) provided similar findings. In conclusion, active attention enhances neural responses related to passive shifts of attention to somatosensory signals suddenly presented against a silent background. The results indicate that top-down signals for detecting target stimuli interact with passive shifts of attention caused by bottom-up signals.     

Effects of inter-stimulus interval (ISI) duration on the N1 and P2 components of the auditory event-related potential

The N1 and P2 components of the event-related potential are relevant markers in the processing of auditory information, indicating the presence of several acoustic phenomena, such as pure tones or speech sounds. In addition, the expression of these components seems to be sensitive to diverse experimental variations. The main purpose of the present investigation was to explore the role of inter-stimulus interval (ISI) on the N1 and P2 responses, considering two widely used experimental paradigms: a single tone task (1000 Hz sound repeated in a fixed rhythm) and an auditory oddball (80% of the stimuli were equal to the sound used in the single tone and the remaining were a 1500 Hz tone). Both tasks had four different conditions, and each one tested a fixed value of ISI (600, 1000, 3000, or 6000 ms). A sample of 22 participants performed these tasks, while an EEG was recorded, in order to examine the maximum amplitude of the N1 and P2 components. Analysis of the stimuli in the single tone task and the frequent tones in the oddball task revealed a similar outcome for both tasks and for both components: N1 and P2 amplitudes were enhanced in conditions with longer ISIs regardless of task. This response pattern emphasizes the dependence of both the N1 and P2 components on the ISI, especially in a scenario of repetitive and regular stimulation. The absence of task effects suggests that the ISI effect reported may depend on refractory mechanisms rather than being due to habituation effects.     

Auditory Evoked Potentials and Impairments to Psychomotor Activity Evoked by Falling Asleep

Sounds provide the most suitable stimuli for studies of information processes occurring in the brain during falling asleep and at different stages of sleep. The widely used analysis of evoked potentials averaged for groups of subjects has a number of disadvantages associated with their individual variability. Thus, in the present study, measures of the individual components of auditory evoked potentials were determined and selectively summed for individual subjects, with subsequent analysis by group. The aim of the present work was to identify measures of auditory evoked potentials providing quantitative assessment of the dynamics of the brain’s functional state during the appearance of errors in activity associated with decreases in the level of waking and falling asleep. A monotonous psychomotor test was performed in the lying position with the eyes closed; this consisted of two alternating parts: the first was counting auditory stimuli from 1 to 10 with simultaneous pressing of a button, and the second was counting stimuli from 1 to 5 silently without pressing the button, and so on. Computer-generated sound stimuli (duration 50 msec, envelope filling frequency 1000 Hz, intensity 60 dB) were presented binaurally with interstimulus intervals of 2.4–2.7 sec. A total of 41 subjects took part (both genders, mean age 25 years), of which only 23 fell asleep; data for 14 subjects with sufficient episodes of falling asleep were analyzed. Comparison of measures of auditory evoked potentials (the latencies and amplitudes of the N1, P2, N2, and P3 components) during correct and erroneous psychomotor test trials showed that decreases in the level of consciousness elicited significant increases in the amplitudes of the components of the vertex N1-P2-N2 complex in series without button pressing. The greatest changes in auditory evoked potentials in both series were seen in the N2 component, with latency 330–360 msec, which has a common origin with the EEG theta rhythm and is characteristic of the first stage of sleep.