Genevieve Z. Steiner

Pupillary responses and event-related potentials as indices of the orienting reflex

This study examined skin conductance responses, the late positive complex of the event-related potential, and pupillary dilation responses as autonomic and central correlates of the orienting reflex (OR) in the context of indifferent and significant stimuli. In particular, we aimed to clarify the inconsistencies surrounding the pupillary dilation response as an OR index. An auditory dishabituation paradigm was employed, and physiological measures were recorded from 24 participants. Response decrement to a repeated stimulus, response recovery to a change stimulus, and subsequent dishabituation were assessed. Findings confirmed expectations that the skin conductance response and the late positive complex are indices of the OR. The pupillary dilation response, however, demonstrated an unexpected sensitivity to stimulus novelty only, while the prestimulus measure of tonic pupil diameter showed the significance effect that was expected of the phasic measure. Together, these findings argue against the suggestion that the pupillary dilation response is an OR index. The diverse results obtained from this experiment contribute to our understanding of the OR, and provide impetus for further research with a variety of paradigm manipulations.

Comparing P300 modulations : target-to-target interval versus infrequent nontarget-to-nontarget interval in a three-stimulus task

This study examined temporal determinants of the P300 component of the ERP in a three-stimulus visual oddball task. Frequent standards, with equiprobable targets and infrequent nontargets, were utilized. We tested whether the infrequent nontarget-to-nontarget interval (infrequent NNI) influences P300 amplitudes and latencies analogously to the target-to-target interval (TTI). EEG was recorded from 27 participants, and response time and P300 effects of TTIs and infrequent NNIs were assessed. Increases in TTI augmented target P300 amplitudes and decreased latencies and response times. However, this modulation of P300 amplitude was weak for manipulations of infrequent NNI. P300 latencies increased initially before decreasing across infrequent NNI levels. Together, these findings support the notion that the P300 has an underlying temporal mechanism that is modulated by motivationally significant events. Theoretical implications are discussed.

Reinstating the Novelty P3

P300 (or P3) is a major positive complex in the human event-related potential, occurring some 300 ms after stimulus onset, and long thought to be the cortical correlate of the Orienting Reflex, our automatic attention-grabbing response to a novel stimulus. The Novelty P3 was the third P3 subcomponent discovered (after P3a and P3b) and appeared promising in its sensitivity to stimulus novelty, the defining characteristic of the Orienting Reflex. But some 15 years later it was claimed to be indistinguishable from the previously-discovered P3a. This led to a decline in interest in the field and confused nomenclature, with some studies using “P3a” and “Novelty P3” interchangeably. However, recent similar studies have again reported three subcomponents of the P3. Further, using single-stimulus habituation paradigms, in addition to P3a and P3b, a later decrementing P3 subcomponent has been reported, and recently labelled “HabP3” to avoid contention. We report three studies to resolve this chaotic situation, arguing for identification of the late subcomponent following the P3a and P3b as the Novelty P3. Reinstatement of the Novelty P3 as the central index of the Orienting Reflex will have widespread impact in a range of theoretical, practical, and clinical areas involving novelty processing and attention.

The mechanism of dishabituation

The dual-process theory of habituation attributes dishabituation, an increase in responding to a habituated stimulus after an interpolated deviant, to sensitization, a change in arousal. Our previous investigations into elicitation and habituation of the electrodermal orienting reflex (OR) showed that dishabituation is independent of sensitization for indifferent stimuli, arguing against dual-process theory’s explanation. However, this could not be tested for significant stimuli in that study, because sensitization was confounded with incomplete resolution of the preceding OR. This study aimed to clarify the mechanism of dishabituation for significant stimuli by extending the stimulus onset asynchrony (SOA) beyond the time required for the phasic response to resolve. Participants completed an auditory dishabituation task with a random SOA of 13–15 s while their electrodermal activity was recorded. The stimulus sequence was 10 standards, 1 deviant, 2–4 standards; counterbalanced innocuous tones. Two counterbalanced conditions were used: silently count all stimuli (significant) and no task (indifferent). Skin conductance responses (SCRs) and pre-stimulus skin conductance levels (SCLs) both decremented over trials 1–10. In both conditions, SCRs showed response recovery and dishabituation, indicating habituation, and post-deviant SCL sensitization was apparent. Across all trials, phasic ORs were dependent on the pre-stimulus SCL (arousal level); this did not differ with condition. Importantly, dishabituation was independent of sensitization for both conditions. Findings indicate that sensitization, the change in state, is a process separate from phasic response resolution, and that arousal consistently predicts OR magnitude, including the dishabituation response. This argues against dual-process theory’s explanation, and instead suggests that dishabituation is a disruption of the habituation process, with magnitude determined by the current arousal level.

Linking components of event-related potentials and autonomic measures of the orienting reflex.

This study examined autonomic measures and event-related potentials (ERPs) associated with elicitation and habituation of the basic Orienting Reflex (OR). Subjects received 16 innocuous tones with intensity alternating between 60 and 80 dB, at long inter-stimulus intervals. There was no stimulus-related task, so we could examine the effects of stimulus novelty and intensity in the absence of task demands. Cardiac, respiratory, peripheral vasoconstriction, and electrodermal measures were recorded, as well as continuous EEG. Single-trial ERPs were obtained, and components extracted by Principal Components Analysis were examined for potential response fractionation in the central indices of stimulus processing. The predicted fractionation of autonomic measures was obtained: cardiac deceleration showed no systematic change with intensity or trials, respiratory pause showed a substantial main effect of trials but no intensity effects, peripheral vasoconstriction showed intensity but no trials effects, and electrodermal responses showed substantial main effects of trials and intensity. A range of intensity and novelty effects were obtained in components identified as the N1, P3a, P3b, Novelty P3, and the classic Slow Wave. The different stimulus-response profiles of the ERP components are discussed in relation to the autonomic response profiles within the context of a sequential processing theory of OR elicitation.

Event‐related EEG time‐frequency PCA and the orienting reflex to auditory stimuli

We recently reported an auditory habituation series with counterbalanced indifferent and significant (counting) instructions. Time-frequency (t-f) analysis of electrooculogram-corrected EEG was used to explore event-related synchronization (ERS)/desynchronization (ERD) in four EEG bands using arbitrarily selected time epochs and traditional frequency ranges. ERS in delta, theta, and alpha, and subsequent ERD in theta, alpha, and beta, showed substantial decrement over trials, yet effects of stimulus significance (count vs. no-task) were minimal. Here, we used principal components analysis (PCA) of the t-f data to investigate the natural frequency and time combinations involved in such stimulus processing. We identified four ERS and four ERD t-f components: six showed decrement over trials, four showed count > no-task effects, and six showed Significance × Trial interactions. This increased sensitivity argues for the wider use of our data-driven t-f PCA approach.

Prestimulus EEG amplitude determinants of ERP responses in a habituation paradigm

Evidence for the nature and extent of the prestimulus EEG contributions to ERP determination has been mounting, and we have recently mapped these within an equiprobable auditory Go/NoGo task. Here we examined if the pattern of relationships in the Go/NoGo would generalise to an auditory habituation paradigm. Count and No-task conditions were assessed, and we predicted broadly corresponding effects between Go and Count, and NoGo and No-task conditions. Single-trial data were obtained at the midline sites (Fz, Cz, Pz). Prestimulus EEG in each of the traditional bands was quantified using a sliding FFT window, and five ERP components were manually identified. The corresponding EEG and ERP data were then correlated across subjects, sites, and trials, separately for each ERP component measure (amplitude, latency), task condition (Count, No-task), and EEG band (delta, theta, alpha, beta). Despite the substantial paradigm and methodological differences, 10 of the 17 expected prestimulus EEG-ERP directional relationships (i.e., direct or inverse effects) were confirmed across the traditional bands and ERP components, and only one was in the opposite direction. Importantly, 18 additional relationships reached significance here; these occurred across the EEG bands, and ERP components. Together these findings confirm the significant contributions of prestimulus EEG to subsequent ERP responses. These appear to be at least partially independent of the paradigm and EEG methodology employed, suggesting that there is merit in mapping these contributions further. Our findings also indicate the improved sensitivity of the statistical approach used here in detecting such EEG-ERP relationships.

Event-related EEG time-frequency analysis and the Orienting Reflex to auditory stimuli: EEG time-frequency analysis and the OR

Sokolovs classic works discussed electroencephalogram (EEG) alpha desynchronization as a measure of the Orienting Reflex (OR). Early studies confirmed that this reduced with repeated auditory stimulation, but without reliable stimulus-significance effects. We presented an auditory habituation series with counterbalanced indifferent and significant (counting) instructions. Time-frequency analysis of electrooculogram (EOG)-corrected EEG was used to explore prestimulus levels and the timing and amplitude of event-related increases and decreases in 4 classic EEG bands. Decrement over trials and response recovery were substantial for the transient increase (in delta, theta, and alpha) and subsequent desynchronization (in theta, alpha, and beta). There was little evidence of dishabituation and few effects of counting. Expected effects in stimulus-induced alpha desynchronization were confirmed. Two EEG response patterns over trials and conditions, distinct from the full OR pattern, warrant further research.

Exploring the mechanism of dishabituation

In this study we explored elicitation and habituation of the orienting reflex (OR) in the context of indifferent and significant stimuli, particularly aiming to clarify the mechanism driving dishabituation. An in-depth analysis of the mechanisms of electrodermal habituation and dishabituation was conducted, focusing on the role of state measures as determinants of the phasic response profile. Twenty-four young adult participants completed an auditory dishabituation task while electrodermal activity was recorded. Participants listened to a series of 10 innocuous tones of the same frequency (standards), followed by a deviant tone of a different frequency, and succeeded by 2-4 tones of the same frequency as the initial 10 stimuli. All stimuli had a random stimulus onset asynchrony of 5-7 s. Participants completed an indifferent condition in which there was no task in relation to the stimuli, and a significant condition where instruction was given to count the stimuli silently; order was counterbalanced between participants. As predicted, both skin conductance responses (SCRs) and skin conductance levels (SCLs) were larger for the significant than the indifferent condition. The initial phasic ORs were dependent on pre-stimulus arousal level, and there were significant decreases in both SCR and SCL over the first 10 standards in both conditions. Phasic response recovery was apparent to the deviant stimulus, and dishabituation to the following standard stimulus; both effects were enhanced in the significant condition. Sensitisation was apparent in SCL following the initial and deviant stimuli, but the extent of this was confounded with incomplete resolution of the preceding phasic OR in the significant condition. In the indifferent condition, dishabituation was independent of deviant-related sensitisation; this could not be tested in the significant condition. These findings suggest that dishabituation is not a process of sensitisation, but rather, a disruption of the habituation process.

Stimulus-to-matching-stimulus interval influences N1, P2, and P3b in an equiprobable Go/NoGo task

Previous research has shown that as the stimulus-to-matching-stimulus interval (including the target-to-target interval, TTI, and nontarget-to-nontarget interval, NNI) increases, the amplitude of the P300 ERP component increases systematically. Here, we extended previous P300 research and explored TTI and NNI effects on the various ERP components elicited in an auditory equiprobable Go/NoGo task. We also examined whether a similar mechanism was underpinning interval effects in early ERP components (e.g., N1). Thirty participants completed a specially-designed variable-ISI equiprobable task whilst their EEG activity was recorded. Component amplitudes were extracted using temporal PCA with unrestricted Varimax rotation. As expected, N1, P2, and P3b amplitudes increased as TTI and NNI increased, however, Processing Negativity (PN) and Slow Wave (SW) did not show the same systematic change with interval increments. To determine the origin of interval effects in sequential processing, a multiple regression analysis was conducted on each ERP component including stimulus type, interval, and all preceding components as predictors. These analyses showed that matching-stimulus interval predicted N1, P3b, and weakly predicted P2, but not PN or SW; SW was determined by P3b only. These results suggest that N1, P3b, and to some extent, P2, are affected by a similar temporal mechanism. However, the dissimilar pattern of results obtained for sequential ERP components indicates that matching-stimulus intervals are not affecting all aspects of stimulus processing. This argues against a global mechanism, such as a pathway-specific refractory effect, and suggests that stimulus processing is occurring in parallel pathways, some of which are not affected by temporal manipulations of matching-stimulus interval.