PCA and varimax rotation: some comments on Rösler and Manzey.
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Contingent Negative Variation↗
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On the correlated nature of evoked brain activity: biophysical and statistical considerations.
The contribution of EP research to the mind-brain problem is considered. The view is promoted that the scalp EP represents a macroscopic rescaling of patterns of activity in cortical columns, which are held by many workers to be the functional units of the neo-cortex. Implicit in re-scaling operations though is a loss of degrees of freedom. However, in reducing the dimensionality of the EP to a comparable order to that of the molar phenomena of behavior, it is argued that this loss may be regarded constructively as potentially facilitating the successful forging of mind-brain correlations. Various techniques are reviewed for extracting the dimensions of scalp activity, including those based on electric field theory which are argued to have high face validity. The multivariate approach is also surveyed. Principal components analysis, in particular, is evaluated using simulated data. The limitations of the method are pointed up. Caution is advised in the design of a PCA, and in the interpretation of factors. The use of discriminant analysis in combination with MANOVA is suggested as a more appropriate multivariate strategy.
Biophysical Phenomena↗
Anticipatory pleasure deficit in subjects reporting physical anhedonia: slow cortical evidence.
Slow cortical and heart rate responses were recorded from anhedonic and normal control subjects during a two-stimulus anticipation paradigm. Subjects were chosen for participation in the experiment based on their scores on the Physical Anhedonia Scale developed by Chapman, Chapman and Raulin (1976). During the procedure, auditory warning stimuli were delivered which informed subjects that a visual stimulus (color slide) would follow shortly and specified the category of the slide (neutral or high-interest) which was to be presented. Results of this investigation revealed that anhedonic subjects showed less differential physiological responsivity while anticipating high and low interest stimuli than did normal controls. This was most striking in the slow cortical response (CNV) which appears particularly sensitive to such motivational and/or attentional manipulations. The data are discussed with respect to emotion and psychopathology.
Adult↗
Attention-related negative brain potential for speech words and pure tones.
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Adult↗
The relation of P3b to prior events and future behavior.
A prediction paradigm was used to explore the relationship of the amplitude of the scalp-recorded event-related potential to the sequence of preceding signals and to preceding and subsequent behavior. P3b was found to be the only component which related systematically to prior sequence of signals. The CNV, P300E and Slow Wave were not affected by signal sequence. The P3b findings were the same for the emitted and evoked P3b, thus ruling out a sensory interpretation of the effect of signal sequence on P3b amplitude. Furthermore, it was found that signal sequence interacts with the subject's predictions in determining P3b amplitude. For signal discontinuations, P3b was large in amplitude regardless of what had been predicted. However, for signal continuations, P3b was small when continuations had been predicted, but large when discontinuations had been predicted. Finally, we found that for both correctly and incorrectly predicted signal continuations, larger P3bs were more likely than smaller P3bs to be followed by a prediction that the signal for the next trial would be different.
Adolescent↗
Hemispheric lateralization of event-related potentials in a cued reaction-time task.
Subjects were tested in a cued reaction-time task wherein warning stimuli (S1) of 5-letter words or dot patterns inter-mixed across trials were briefly presented. After 2 sec a second stimulus (S2) of th same category as the S1 appeared and the subject pressed a key with the left or right hand. The right key was pressed if S2 was a synonym of S1 or if the second dot pattern was the same as the first. The left key was pressed for antonyms or different patterns. It was predicted that CNVs would be larger over the left than right hemisphere on word trials and vice-versa on pattern trials in accordance with speculations concerning hemispheric specialization. The CNV was lateralized as expected, most prominently on pattern trials. In addition a negative transient evoked by S2, and a late negative post-imperative slow wave were similarly lateralized. P300 waves were very large and largest to the S2 when it differed from S1. Factor analysis confirmed these results and indicated, in addition, that P300 was larger in the hemisphere least relevant to the task.
Adult↗
The determinants of the non-motoric CNV in a complex, variable foreperiod, information processing paradigm.
The aim of the present study was to examine the determinants of the non-motoric CNV or E-wave elicited in a complex, variable foreperiod information processing task. Subjects were required to determine whether two sets of tones, one set presented back-to-back (S1/S2), the other separated by a variable foreperiod (S3/S4), were either matching or mismatching. Data were collected over two recording sessions; a baseline and an experimental run. The experimental session comprised three conditions; a match, a mismatch and no-response conditions. Mean amplitude and factor score comparisons showed the parietally-dominant E-wave to be dependent on the task relevance of the stimulus which it precedes. Differing midline distributions for the negative afterwave and the E-wave with increased processing requirements was taken to suggest that the two responses reflect functionally distinct phenomena.
Adult↗
The true P3 is hard to see: some comments on Kok's (1986) paper on degraded stimuli.
Kok (1986) investigated why P3 amplitudes are reduced when stimuli are degraded. He proposed that a positive moment-related component might overlap P3 after intact stimuli and a negative one after degraded stimuli ("MRP overlap" hypothesis). Discussing his findings, it is suggested that MRP overlap can only account for the result if another overlap hypothesis ("nogo overlap") is added. But even this combined hypothesis cannot explain reducing effects of degradation found in other paradigms. While other overlap hypotheses have been proposed in the literature, the most parsimonious hypothesis is to assume that P3 itself gets smaller after degraded stimuli.
Arousal↗
Overlap between P300 and movement-related-potentials: a response to Verleger.
In reply to Verleger's commentary, I first clarify what the term "MRP overlap" implies; by means of a simple additive simulation it is shown that overlap between a stable P300 and a MRP that moves in time with reaction-time, may cause two types of artefacts--amplitude reduction and double peaking of P300. Following Verleger's suggestion, it is then argued that the effects of stimulus-degradation on P300 amplitude in our experiments was, at least in part, due to overlap with negative components of the MRP (in the go-intact condition), and with positive CNV return (in the nogo-intact condition). It is concluded that MRP overlap is not only an artefact but also a useful index of motor-preparation in reaction tasks, and that more refined methods should be developed in future research for accurate estimation of MRP overlap in stimulus-locked ERP waveforms.
Arousal↗
Event-related potential indices of speech motor programming in stutterers and non-stutterers.
CNVs were recorded from stutterers and non-stutterers prior to spoken words which varied according to the number of syllables, whether the words were the same or different on each trial, and the degree of repetition within the word. The effects of these response parameters on slow potential activity recorded over the speech motor area were evident both prior to, and also during, the response, suggesting that the slow potentials were reflecting both speech pre-programming and ongoing programmed control. Differences between groups were only evident prior to the response, particularly when words were familiar and therefore likely to be entirely pre-programmed. This suggests that stutterers have difficulty in setting up the parameters of the response, rather than in ongoing programmed control.
Adult↗
Doubts on the adequacy of the principal component varimax analysis for the identification of event-related brain potential components: a commentary on Glaser and Ruchkin, and Donchin and Heffley.
Glaser and Ruchkin (1976) as well as Donchin and Heffley (1978) have proposed principal component varimax analysis (PCVA) for identification of event-related potential (ERP) components. In the present commentary, the assumptions on the ERP data structure of this procedure are considered. They are formalized and compared with a simpler and more restrictive hypothesized ERP data structure containing autoregressive properties. Referring to the principle of parsimony, the comparison of the two models shows the superiority of the hypothesized autoregressive structure: to fit a set of ERP data equally well, the autoregressive structure does so with considerably more parsimonious assumptions, i.e. with fewer parameters to be estimated, than the structure induced by PCVA. It is concluded that an appropriate model for the ERP data structure should take the autocorrelated nature of the ERP into account.
Contingent Negative Variation↗
Temporal integration of auditory information in sensory memory as reflected by the mismatch negativity.
Event-related potentials (ERPs) to different types of infrequent change in a tone pair composed of two closely spaced tones of different frequencies were recorded. The mismatch negativity (MMN), a change-specific component of the ERP, was elicited by reversing the order of the two tones, by repeating the first tone, by replacing the first tone with the second tone, or by omitting the second tone. The omission of the second tone, however, elicited the MMN only when the interval between the two tones was very short (offset to onset 40 or 140 ms) but did not when this interval was somewhat longer (240 or 340 ms). The pattern of the present results suggests that sensory-memory traces, as reflected by the MMN, integrate information about two closely spaced stimuli into a unitary sensory event.
Adult↗
Strongly focused attention and auditory event-related potentials.
Effects of selective attention on the auditory event-related potential were studied by delivering two tones in a rapid, randomized sequence. One of the tones was designated as relevant and the other as irrelevant, the subject's task being to discriminate occasional softer tones within the relevant tones. Relevant and irrelevant tones differed from each other either in location (left vs. right ear) or pitch (300 vs. 6000 Hz). In both conditions, relevant tones elicited a larger N1 deflection (peak latency about 120 ms) than did irrelevant tones. In contrast to the exogenous N1 elicited by unattended tones, the scalp distribution of this attentional "N1 effect" did not depend on the stimulated ear and, further, its amplitude was not affected by the frequency of attended tones. These results suggest that the present attention effect was caused, at least mainly, by an endogenous processing negativity rather than by an enhancement of exogenous N1 components.
Adult↗
Event-related potentials as indices of display-monitoring performance.
We evaluated event-related potentials (ERP) as indices of performance in three visual display-monitoring tasks: (a) signal detection, (b) running memory and (c) computation. Using factor analysis, we developed a global measure of performance (PFI) for each task. Task-relevant and irrelevant-probe stimuli elicited ERPs, which included components P1, N1, P2, P300, slow waves, and fronto-central negativities. In tasks (a) and (b), P300 amplitude in the task-relevant ERPs increased when the task was engaged, and was greater for accurate-than for inaccurate-response trials. In tasks (a) and (c), the irrelevant-probe ERPs also differed among task and performance conditions. To relate ERP measures to PF1, we developed linear regression models distinguished by three factors: general versus individual-subject, stimulus relevance, and signal-to-noise ratio (SNR). Model accuracy and reliability were highest for individual-subject, relevant-stimulus and high-SNR models, where average R2 values for the three tasks were 0.44, 0.46, and 0.38, respectively. We discuss implications of the models for performance monitoring and implications of the ERP effects for human information processing.
Adult↗
Aging, stimulus identification and the effect of probability: an event-related potential study.
Event-related potentials (ERPs) of younger and older subjects were compared in a simple reaction time (SRT) and in two GoNogo (20% and 80% target probability) tasks. At the T5 location, the NA component (the difference between the ERPs elicited by the frequent stimuli in the GoNogo tasks on the one hand, and the ERPs in the SRT task on the other hand) emerged earlier in the younger group. The N2b was larger in the younger group, and in this group the rare stimuli of the 80% GoNogo task elicited an enlarged N2. When compared to the older group, the stimulus probability in the younger group had a larger effect on the amplitude of the late positivity. The results show age-related changes at an early stage of the information processing activity, and larger sensitivity of the orienting system in the younger subjects.
Adolescent↗
Mismatch negativity subcomponents and ethyl alcohol.
Effects of ethanol (0.55 and 0.85 g/kg) on event-related potentials were investigated by presenting 50-ms standard and 25-ms deviant pure tones to 9 social drinkers during a reading task, in a single-blind, placebo-controlled paradigm. Whereas the lower ethanol dose had no impact on ERPs with an 0.8-s inter-stimulus interval (ISI), it attenuated the N1, P2, and mismatch negativity (MMN) amplitudes with a longer ISI of 2.4 s. The higher alcohol dose increased the N1 peak latency with both ISIs. It also suppressed the N1 and MMN amplitudes with the longer ISI. The MMN suppression did not, however, occur at scalp sites below the Sylvian fissure, thus suggesting that ethanol affected only the frontal MMN subgenerator. Moreover, the different dose responses of the N1, P2, and MMN (subcomponents) to ethanol may indicate that the neurotransmitter systems underlying their generation are, to some extent, different.
Adult↗
Focussing on aging: an electrophysiological exploration of spatial and attentional processing during reading.
Three types of selective attention tasks were presented to 24 young (20.5 years) and 24 middle-aged (57.5 years) participants. The major aim of the experiment was to explore three different aspects of selective attention, namely a pre-attentive level (i.e. auditory passive oddball task), an attentive level using spatial attention in a memory search task (i.e. selective search task) and an attentive level using a spatial cue to select a word in a reading-like situation (i.e. selective language task). The data showed that the mismatch negativity was not affected by aging although the ERPs indicated that the younger participants were paying more attention to the tones than the middle-aged. The selective search task data showed that spatial selective attention is only mildly affected by aging. The ERP-data seemed to indicate that irrelevant stimuli had a smaller impact in the middle-aged. The selective language data showed a look-a-like effect of flanker words for both age groups although the effect in the middle-aged was delayed by 30 ms and smaller. It was theorized that flankers might have smaller impact in the middle-aged. N400 was found to be smaller and delayed (90 ms) in the middle-aged participants. The overall conclusion on the basis of the three experiments is that the selectivity of processing was preserved or even enhanced in our particular group of middle-aged participants.
Adult↗
The locus of interference in the Simon effect: an ERP study.
The Simon effect was studied using ERPs and the lateralized readiness potential (LRP). In Experiment 1, visual stimuli requiring left or right hand responses were presented at either side of fixation. In Experiment 2, the empty side was occupied by a distractor. Spatial S-R incompatibility delayed P300 latency in both experiments, as predicted by perceptual interference accounts of the Simon effect. However, the LRP results were not conclusive. The lateralized presentation of visual stimuli (Experiment 1) or targets (Experiment 2) produced a posterior ERP hemispheric asymmetry that spread to central electrodes and obscured the early development of the LRP. Experiment 3 avoided the problem by presenting the stimuli in the vertical meridian, and the LRP showed signs of incorrect response preparation in incompatible trials, in agreement with response-interference models. Both perceptual and response interference may be present in the Simon effect.
Adult↗