Brett MacDonald

Single-trial event-related potentials and the orienting reflex to monaural tones.

We aimed to clarify the event-related potentials (ERPs) involved in elicitation and habituation of the orienting reflex (OR), seeking parallels with two autonomic measures reflecting different stages in OR-related processing. Participants were presented with 8 unexpected innocuous novel tones to one ear at long variable inter-stimulus intervals, and horizontal eye movement in the direction of the ear of stimulation was taken as a behavioural measure of the OR. Skin conductance, heart rate, and 19 EEG channels were also recorded. Single-trial ERPs were decomposed using principal components analysis for intervals covering the early N1 complex and the late positive complex (LPC). Eye movements at trial 1 showed significant directional differences with ear of stimulation, and this difference reduced over trials, providing behavioural evidence of OR elicitation and habituation. Electrodermal responses, Processing Negativity, and the Novelty P3 showed substantial main effects of trials, suggesting their close links to the OR. Cardiac deceleration and Component 1 of the N1 complex showed no change over trials, suggesting their association in marking the transient onset of each stimulus. Component 3 of the N1 complex, P3a, P3b, and early and late Slow Waves showed only topographic changes over trials, and their dominant continuation over the stimulus sequence rules them out as OR markers. Theory development is required to clarify the non-OR role of the LPC. These results point to the usefulness of a sequential-processing approach to the OR in accommodating the range of subcomponents in the ERP. These data also illustrate the value of single-trial ERP analysis in simple paradigms with very long inter-stimulus intervals.

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.

Caffeine effects on resting-state electrodermal levels in AD/HD suggest an anomalous arousal mechanism.

The effect of a single oral dose of caffeine was examined in a randomised double-blind placebo-controlled repeated-measures cross-over study. Eighteen children with AD/HD, aged between 8 and 13 years, were individually age- and gender-matched with a control group. All children participated in two sessions, one week apart. Skin conductance level (SCL) from a 3 min eyes-closed epoch, commencing 30 min after ingestion of caffeine or placebo, was examined. Across conditions, mean SCL was lower in the AD/HD group than controls, confirming hypoarousal in AD/HD. Caffeine produced an increase in SCL, and this increase did not differ between the groups. However, arousal increases were dose-dependent in controls, but not in AD/HD. Rather, caffeine-induced arousal increases in the AD/HD group were positively related to their hyperactivity/impulsivity levels. This suggests an anomalous arousal mechanism in AD/HD functionally related to impairment in one symptom dimension.

Single-trial event-related potentials and autonomic measures of the orienting reflex

We aimed to clarify the event-related potentials (ERPs) associated with elicitation and habituation of the basic Orienting Reflex (OR). Participants were presented with 16 innocuous tones, alternating in intensity, at long variable inter-stimulus intervals, with no task. This allowed us to examine stimulus novelty and intensity effects in the absence of stimulus-related task demands. Single-trial ERPs were extracted to obtain estimates of the early N1 and the late positive complex (LPC) to each stimulus. Electrodermal responses showed substantial main effects of trials and intensity, supporting their functionality as an OR index. Cardiac deceleration showed no systematic change with intensity or trials, suggesting that it marks the transient onset of each stimulus, early in the stimulus-processing sequence. Respiratory pause showed a substantial main effect of trials but no intensity effect, suggesting that it reflects an intermediate processing stage. A main effect of intensity, but no simple trial effect, was apparent in the N1, suggesting that it reflects a different intermediate processing stage. The subsequent LPC showed only a topographic interaction with trials and intensity, failing to support any substantive role in OR processing. These different stimulus-response profiles are discussed in the context of a sequential processing model of the OR.

Trial effects in single-trial ERP components and autonomic responses at very long ISIs

Single-trial data from autonomic and ERP measures were used to capture the rapidly decreasing initial responses characteristic of the orienting reflex (OR) to repeated stimuli. Stimulus-response patterns were compared to determine central analogues of autonomic indices of processes leading to the OR, and the OR itself. Participants were presented with 12 indifferent tones in an auditory dishabituation paradigm. Temporal principal component analysis (PCA) decomposed EOG-corrected ERP data for 16 subjects. Response patterns of ERPs, cardiac, and respiratory responses were compared to the phasic skin conductance response (SCR). SCR decremented over trials, recovered on the change trial, and dishabituated to the representation of the standard, meeting the formal definition of habituation required of the OR. The evoked cardiac response showed no trial effects. Respiratory pause (RP) decreased linearly over trials, recovering marginally on the change trial. Nine identifiable ERP components were extracted: P1, N1-3, N1-1, processing negativity (PN), P2, P3a, P3b, a novelty-sensitive P3 component (labelled HabP3), and the slow wave (SW). P3b and SW showed decrement over trials, but with no recovery, HabP3 showed decrement and increased response on the change trial, while the P1, N1 subcomponents, P2 and P3a were insensitive to novelty. Stimulus-response patterns of the RP and HabP3 suggest sensitivity to novelty processing, while the P1, N1-3, N-1, PN, P2, P3a and cardiac deceleration appear to mark processing prior to novelty, such as stimulus transient detection (cardiac deceleration) and/or intensity processing. This study supports predictions of preliminary process theory, demonstrating fractionation of 3 autonomic and 9 ERP components to novelty, and disconfirming the unitary nature of the OR.

Trials and intensity effects in single-trial ERP components and autonomic responses in a dishabituation paradigm with very long ISIs

The phasic orienting reflex (OR) was investigated using single-trial data collected concurrently from 4 autonomic measures and event-related potentials (ERPs). In an auditory dishabituation paradigm, twelve indifferent tones of two intensities (60 or 80 dB, intensity change on trial 11, counterbalanced between subjects) were presented at very long interstimulus intervals (ISIs). Novelty and intensity based stimulus-response patterns were examined seeking ERP analogues of autonomic measures representing pre-OR and OR processing. Skin conductance response (SCR) represented the phasic OR index. EOG-corrected ERP data for 16 subjects were decomposed by a temporal Principal Components Analysis (PCA). SCR diminished over 10 standard trials, recovered on change trial 11, dishabituated to the re-presentation of the standard tone on trial 12, and showed intensity effects at the change - formal requirements for an OR index. The evoked cardiac response (HR) showed no trial or intensity effects. Respiratory pause (RP) decreased linearly over trials and showed recovery but no dishabituation or intensity effect. Peripheral vasoconstriction (PVC) failed to decrement but exhibited an intensity effect. Ten identifiable ERP components were extracted: Na, P1, N1-1, PN, P2, P3a, P3b, a novelty-sensitive HabP3, an intensity-sensitive IntP3, and the Slow Wave (SW). Pattern 1 showed no trial or intensity effects (HR, P1, PN, P2); Pattern 2 showed no trial effect but an intensity effect (PVC, Na, N1-1, P3a); and Pattern 3 demonstrated habituation and an intensity effect (SCR, RP, P3b, HabP3, IntP3, SW). The observed fractionation of autonomic and central measures is consistent with Preliminary Process Theory (PPT) rather than the notion of a unitary OR.

Significance and Novelty effects in single-trial ERP components and autonomic responses

The phasic orienting reflex (OR) was investigated in two counterbalanced blocks of an auditory dishabituation paradigm differing in stimulus Significance (operationalised as tone counting). Twelve tones were presented at very long, randomly-varying interstimulus intervals (ISIs). Novelty and Significance were varied within subjects. Stimulus-response patterns were assessed to find ERP matches for autonomic measures. The phasic OR index was represented by the skin conductance response (SCR). SCR decremented over 10 standard trials, showed recovery on trial 11 (change trial), enhancement to re-presentation of the standard tone (trial 12: dishabituation), and a main effect of Significance over the first 10 trials - demonstrating the formal criteria for an OR index. The evoked cardiac response (HR) subcomponents ECR1 (deceleration) and ECR2 (acceleration) showed no trial effects, but ECR2 showed a Significance effect. Respiratory pause (RP) decreased linearly over trials, and showed recovery, but no dishabituation or Significance effect. Temporal PCA was applied to single-trial EOG-corrected data. Ten ERP components were extracted: P1, N1-3, N1-1, PN, P2, P3a, P3b, HabP3, a Frontal Slow Wave (FSW), and the Classic SW. The dependent measures showed 4 distinct patterns. Pattern 1: No trial or Significance effects (ECR1, P1, N1-3, P3a, FSW); Pattern 2: No trial effect but a Significance effect (ECR2, N1-1, P2); Pattern 3: Trial but not Significance effects (RP, PN, P3b, HabP3); Pattern 4: Both trial and Significance effects (SCR and Classic SW). The evidenced fractionation of autonomic and central measures is compatible with Preliminary Process Theory (PPT), contrary to the notion of a unitary OR.

Intensity and trial effects from simple auditory stimuli in a dishabituation paradigm

Abstract presented at the 23rd Australasian Society for Psychophysiology Conference, 20-22 Nov 2013, Wollongong, Australia