Onset Of Target Stimulus Research Articles

Valence moderates the effect of stimulus-hand proximity on conflict processing and gaze-cueing.

An effective interaction with the environment requires adaptation of one's own behaviour to environmental demands. We do so by using cues from our environment and relating these cues to our body to predict the outcomes of events. The recent literature on embodied cognition suggests that task-relevant stimuli, presented near the hands, receive more attentional capacity and are processed differently than stimuli, presented spatially more distant to our body. It has also been proposed that near-hand processing is beneficial to conflict resolution. In the current study, we tested the assumption of an attentional bias towards the near hand space in the context of our previous work by combining a cueing paradigm (allocation of visual attention) with a conflict processing paradigm (Simon task) in the near vs far hand space. In addition, the relevance of processing was manipulated by using affective (angry vs neutral smileys) gaze cues (i.e., varying the valence of the cues). Our results indicate that (a) the interaction of valence × cue congruency × hand proximity was significant, indicating that the cueing effect was larger for negative valence in the proximal condition. (b) The interaction of valence × Simon compatibility × stimulus-hand proximity interaction was significant, indicating that for negative valence processing, the Simon effect was smaller in the proximal than in the distal stimulus-hand condition. This effect was at least numerically but not significantly reversed in the neutral valence condition. (c) Overall, cue congruency, indicating the correct vs incorrect attention allocation to the target stimulus onset, did not reveal any effect on Simon compatibility × stimulus-hand proximity. Our results suggest that valence, the allocation of attention, and conflict, seem to be decisive factors determining the direction and strength of hand proximity effects.

T63. TOWARDS A COMPREHENSIVE SEMANTIC MEMORY NETWORK IN SCHIZOPHRENIA: PRELIMINARY RESULTS USING MAGNETOENCEPHALOGRAPHY (MEG) IN SCHIZOTYPY

BackgroundSemantic memory (memory for facts, concepts, and knowledge of the external world) abnormalities are predicted to underlie disturbances in thought and language, deficits in cognitive domains, and the development and maintenance of delusions in patients with schizophrenia. Electroencephalographic (EEG) recordings have successfully identified the neural time course for the processing of semantic information as an electrophysiological response between 300 and 500ms post stimulus (i.e., the N400). The N400 is a remarkably consistent and highly sensitive neural response to semantic relationships, and is thought to index the binding of current stimuli into context by detecting whether meaning is shared with recently processed stimuli or items in memory. To date, the N400 appears to be amodal: an index of semantic processing irrespective of stimulus type (e.g., word/picture stimuli alike), and has shown mixed findings in schizophrenia. However, existing literature has largely relied on EEG or functional magnetic resonance imaging (fMRI) techniques, and these are constrained in spatial and temporal resolution, respectively. Comparatively, MEG provides excellent spatio-temporal resolution, not possible from other stand-alone neuroimaging techniques. We aimed to determine the neuromagnetic correlates of novel semantic triads in both lexical and picture form, and to determine N400m differences in high/low schizotypal samples.MethodsMEG was recorded (whole-head 306 channel Elekta Neuromag® TRIUX magnetometer system) in 35 nonclinical controls (18 male) while completing a novel explicit semantic association task. MEG data were continuously sampled at 1KHz (0.1Hz high pass filter). Following MaxFiltering, data was processed using MNE for Python. Data were filtered offline (40Hz lowpass) and epoched at -300ms to 800ms post- target stimulus onset. The largest peak was measured at sensor triplets at temporo-parietal sites in both hemispheres. High/low schizotypal samples were determined by a median split of the Oxford-Liverpool Inventory of Feelings and Experiences (cognitive disorganisation scale; high=17, low=18).ResultsPreliminary sensor level analyses demonstrated an N400m at temporo-parietal sites in response to both word and picture stimulus sets (with an earlier peak to pictures). Neither amplitude nor latency was significantly different between schizotypal samples, however a significant task x hemisphere x group interaction was found for N400m latency, F(1.00,33.00) = 6.18, p<.02.DiscussionAn N400m was confirmed in response to the novel lexical task. The earlier peak (~200ms) to picture stimuli suggests that pictorial semantic information may be processed more rapidly than lexical information. The significant schizotypal group latency interaction demonstrated that while individuals low in schizotypal traits process lexical stimuli first in the right hemisphere (followed by the left) and picture stimuli first in the left hemisphere (followed by the right), individuals high in schizotypal traits do not demonstrate hemispheric specificity/laterality according to stimulus type. The data is currently being analysed for (i) source localisation, (ii) deep source contributions (e.g., hippocampus), and (iii) de/synchronisation of neural oscillations (across six frequency bands; 1-8Hz, 8-30Hz, 30-50Hz, 70-120Hz, 120-200Hz, and 200-300Hz).

Noise power associated with decreased task-induced variability of brain electrical activity in schizophrenia.

In schizophrenia, both increased baseline metabolic and electroencephalographic (EEG) activities as well as decreased task-related modulation of neural dynamics have been reported. Noise power (NP) can measure the background EEG activity during task performance, and Shannon entropy (SE) is useful for quantifying the global modulation of EEG activity with a high temporal resolution. In this study, we have assessed the possible relationship between increased NP in theta and gamma bands and decreased SE modulation in 24 patients with schizophrenia and 26 controls over the parietal and central regions during a P300 task. SE modulation was calculated as the change from baseline to the active epoch (i.e., 150-550 ms following the target stimulus onset). Patients with schizophrenia displayed statistically significant higher NP values and lower SE modulation than healthy controls. We found a significant association between gamma NP and SE in all of the participants. Specifically, a NP increase in the gamma band was followed by a decrease in SE change. These results support the notion that an excess of gamma activity, unlocked to the task being performed, is accompanied by a decreased modulation of EEG activity in schizophrenia.

Repetition in visual word identification: Benefits and costs

University students performed lexical tasks with visually presented target words after the presentation of an identical or unrelated prime, at short (80-120 ms) or longer (410-710 ms) prime-target stimulus onset asynchronies (SOAs). Experiment 1 showed perceptual identification benefits in vocal responding at a short SOA that were reduced (accuracy) or reversed (latency) at a longer SOA. Experiment 2 showed a transition from a repetition benefit to a cost over 3 SOAs in a target-masked version of the lexical decision task (LDT; target displayed for only 141 ms). In Experiment 3 the repetition cost was replicated at a 530-ms SOA in the LDT with masked targets, but a repetition benefit was observed in the conventional LDT (target displayed until response). The dependence of repetition costs on target masking is more consistent with biases based on episodic confusions than refractoriness of lexical representations.

Dynamic information flow analysis in Vascular Dementia patients during the performance of a visual oddball task

This study investigated the information flow in patients with Vascular Dementia (VaD). Twelve VaD patients and twelve age-matched controls participated in the study. EEG signal was recorded when subjects were performing a visual oddball task. Information flow was analyzed between 9 electrodes in frontal, central, and parietal lobes using short-window Directed Transfer Function (sDTF). VaD patients presented a significant decline in the information flow from parietal to frontal and central lobes, compared with the healthy elderly. This decline mainly occurred in delta, theta, and lower alpha bands, from about 200ms to 300ms after target stimulus onset. The findings indicated an impaired parietal-to-frontal and parietal-to-central connectivity in VaD patients, which may be one reason for the cognitive deficits in VaD patients.

Masked Priming of Conceptual Features Reveals Differential Brain Activation during Unconscious Access to Conceptual Action and Sound Information

Previous neuroimaging studies suggested an involvement of sensory-motor brain systems during conceptual processing in support of grounded cognition theories of conceptual memory. However, in these studies with visible stimuli, contributions of strategic imagery or semantic elaboration processes to observed sensory-motor activity cannot be entirely excluded. In the present study, we therefore investigated the electrophysiological correlates of unconscious feature-specific priming of action- and sound-related concepts within a novel feature-priming paradigm to specifically probe automatic processing of conceptual features without the contribution of possibly confounding factors such as orthographic similarity or response congruency. Participants were presented with a masked subliminal prime word and a subsequent visible target word. In the feature-priming conditions primes as well as targets belonged to the same conceptual feature dimension (action or sound, e.g., typewriter or radio) whereas in the two non-priming conditions, either the primes or the targets consisted of matched control words with low feature relevance (e.g., butterfly or candle). Event-related potential analyses revealed unconscious feature-specific priming effects at fronto-central electrodes within 100 to 180 ms after target stimulus onset that differed with regard to topography and underlying neural generators. In congruency with previous findings under visible stimulation conditions, these differential subliminal ERP feature-priming effects demonstrate an unconscious automatic access to action versus sound features of concepts. The present results therefore support grounded cognition theory suggesting that activity in sensory and motor areas during conceptual processing can also occur unconsciously and is not mandatorily accompanied by a vivid conscious experience of the conceptual content such as in imagery.

53. Joint position sense in the knee before and after partial meniscectomy

The aim of this study is to clarify the neurophysiological mechanism of cognitive impairments in migraine patients. We evaluated the relationships between event-related potentials (ERPs) and clinical parameters. Thirty-one migraine patients diagnosed by ICHD-II were submitted for this study. They were enrolled in headache-free periods. Clinical subtype (with/without aura), severity, duration, and preventative medicine use were evaluated as clinical parameters. We used 2 tones counting oddball paradigm to elicit P3 activities. EEG was recorded from 20 electrodes on the scalp according to international 10/20 system. We assessed the distribution of generator activity in the cortex by standardized low-resolution brain electromagnetic tomography (sLORETA). Regression analyzes of these clinical parameters and ERP source activities for the entire time frame was computed using sLORETA. sLORETA revealed a significant negative correlation in both attack frequency per a month and preventative medicine use in the cingulate gyrus and superior frontal gyrus 280 ms after the onset of target stimuli. Therefore, migraine patients might have impairment of cognitive function, such as executive dysfunction. The dysfunction is reflected by the attenuated activity of the frontal gyrus in sLORETA.

A P300 based online brain-computer interface system for virtual hand control

Brain-computer interface (BCI) is a communication system that can help lock-in patients to interact with the outside environment by translating brain signals into machine commands. The present work provides a design for a virtual reality (VR) based BCI system that allows human participants to control a virtual hand to make gestures by P300 signals, with a positive peak of potential about 300 ms posterior to the onset of target stimulus. In this virtual environment, the participants can obtain a more immersed experience with the BCI system, such as controlling a virtual hand or walking around in the virtual world. Methods of modeling the virtual hand and analyzing the P300 signals are also described in detail. Template matching and support vector machine were used as the P300 classifier and the experiment results showed that both algorithms perform well in the system. After a short time of practice, most participants could learn to control the virtual hand during the online experiment with greater than 70% accuracy.

Identifiable orthographically similar word primes interfere in visual word identification

University students participated in five experiments concerning the effects of unmasked, orthographically similar, primes on visual word recognition in the lexical decision task (LDT) and naming tasks. The modal prime–target stimulus onset asynchrony (SOA) was 350 ms. When primes were words that were orthographic neighbors of the targets, and relative to primes sharing no letters in position with the targets, interference with responses to targets was observed consistently in both tasks. Nonword primes did not consistently interfere except with high-frequency targets in the LDT. Phonological similarity and congruity and incongruity in spelling–sound connections did not account for the effects of orthographic similarity. The results are consistent with competition in lexical processing and suggest shared mechanisms of inhibition for masked and unmasked neighbor primes.

Attentive anticipation modulates phase-entrainment of human delta EEG oscillations – a single trial analyis

Event Abstract Back to Event Attentive anticipation modulates phase-entrainment of human delta EEG oscillations – a single trial analyis Gabor Stefanics1, 2*, Balazs Hangya3, Istvan Ulbert1, 4, Peter Lakatos1, 5, Istvan Winkler1, 4 and Istvan Hernadi2 1 Institute for Psychology, HAS, Hungary 2 Department of Experimental Zoology and Neurobiology, University of Pecs, Hungary 3 Department of Cellular and Network Neurobiology, Institute of Exp. Med., HAS, Hungary 4 Institute of Psychology, University of Szeged, Hungary 5 Cognitive Neuroscience and Schizophrenia Program, Nathan Kline Institute, United States Dynamic modulation of neuronal excitability via oscillatory activity has been suggested to play a key role in attentional mechanisms by phase-locking oscillations to expected events. We investigated the effect of attention toward an acoustic target stimulus on the phase of delta oscillations while systematically manipulating the amount of expectancy of target events. To this end, we applied an auditory target detection paradigm, where four cue tones of different frequencies predicted the probability (p=0.1, p=0.37, p=0.64, p=0.9) of the next stimulus to be the target event while EEG was recorded. Reaction times were significantly faster as expectancy increased, whereas the latency of the delta (0.5-3 Hz) component of P300 ERP peak decreased as a function of target probability. In order to investigate the effect of expectancy on the phase of delta activity, we computed the phase of delta-band filtered EEG using Hilbert-transform and sorted single trials from −pi to pi according to the phase at target stimulus onset. We found a shift in phase of delta activity preceding stimulus processing, which was significantly different between expectancy conditions (Figure 1) at Fz, Cz and Pz leads. We found that higher expectancy shifted delta oscillations remarkably toward the negative peak to coincide with target events. We observed fastest reaction times around −pi/pi, whereas slowest responses were around 0 phase, indicating that delta-band oscillations play a functional role in human attentional mechanisms by modulating rhythmic excitability fluctuations of neuronal groups and thus facilitate efficacious neuronal communication. tn_fig-Stefanics fig-Stefanics Conference: 12th Meeting of the Hungarian Neuroscience Society, Budapest, Hungary, 22 Jan - 24 Jan, 2009. Presentation Type: Poster Presentation Topic: Behavioural neuroscience Citation: Stefanics G, Hangya B, Ulbert I, Lakatos P, Winkler I and Hernadi I (2009). Attentive anticipation modulates phase-entrainment of human delta EEG oscillations – a single trial analyis. Front. Syst. Neurosci. Conference Abstract: 12th Meeting of the Hungarian Neuroscience Society. doi: 10.3389/conf.neuro.01.2009.04.128 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 04 Mar 2009; Published Online: 04 Mar 2009. * Correspondence: Gabor Stefanics, Institute for Psychology, HAS, Budapest, Hungary, gstefanics@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Gabor Stefanics Balazs Hangya Istvan Ulbert Peter Lakatos Istvan Winkler Istvan Hernadi Google Gabor Stefanics Balazs Hangya Istvan Ulbert Peter Lakatos Istvan Winkler Istvan Hernadi Google Scholar Gabor Stefanics Balazs Hangya Istvan Ulbert Peter Lakatos Istvan Winkler Istvan Hernadi PubMed Gabor Stefanics Balazs Hangya Istvan Ulbert Peter Lakatos Istvan Winkler Istvan Hernadi Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

Inhibition of return is unimpressed by emotional cues

Inhibition of return (IOR) is a phenomenon observed when a target unexpectedly appears in the place of a preceding cue: With long cue–target stimulus onset asynchronies, reaction times are longer than for targets that appear in an alternative location. Cognitive theories of anxiety suppose that the IOR effect diminishes with threatening, biologically relevant cues because these catch and hold attention. To test this hypothesis, we conducted three experiments, in which emotional valence of cues (animals or facial expressions) had no influence on the strength of the IOR effect, neither in an unselected sample of students nor in highly spider-fearful or socially anxious participants. Inhibition of return appears to be a robust effect, blind to cue valence.

Configural and contextual prioritization in object-based attention

When attention is directed to a location within an object, other locations within that object also enjoy an attentional advantage. Recently we demonstrated that this object-based advantage is mediated by increased attentional priority assigned to locations within an already attended object and not to early sensory enhancement due to the "spread" of attention within the attended object (Shomstein & Yantis, 2002). At least two factors might contribute to the assignment of attentional priority, one related to the configuration of objects in a scene and the other related to the probability of target appearance in each location imposed by task contingencies. We investigated the relative contribution of these factors by cuing one end of one of a pair of rectangles; a subsequent target appeared most often in the cued location. We manipulated attentional priority setting by varying (1) the probability that a target would appear in each of two uncued locations and (2) the cue to target stimulus onset asynchrony (SOA). On invalidly cued trials, the target appeared in the high-probability location (defined by an absolute spatial location, e.g., upper right) 83% of the time and in the low-probability location (e.g., lower left) 17% of the time. In both conditions, uncued targets appeared in the cued object half the time and in the uncued object half the time. At short SOAs, the same-object and probability effects were approximately additive. However, at longer SOAs, the same-object effects disappeared, and reaction times depended exclusively on location probability. These results suggest that observers adopt an implicit configural scanning strategy (in which unattended locations within an attended object have high priority) or an implicit contextual scanning strategy (in which objectively high-probability locations have high priority) depending on task contingencies and the amount of time that is available to deploy attention.

A functional MRI study of visual oddball: evidence for frontoparietal dysfunction in subjects at risk for alcoholism

Attending to rare stimuli interspersed among repetitive frequent stimuli produces a positive scalp potential at 300 to 600 ms after the target stimulus onset; this potential is known as the P300 wave. Although there is clear evidence of low visual P300 in subjects at high risk (HR) for developing alcoholism, the functional neuroanatomical correlates have not been studied. Functional and high-resolution anatomical magnetic resonance images were collected during the performance of a visual oddball task, from six control (low risk—LR) subjects with high P300s and eight HR subjects with low P300s. All the HR subjects were offspring of male alcoholics. The data were analyzed using a randomization-based statistical method that accounts for multiple comparisons, requires no assumptions about the noise structure of the data, and does not require spatial or temporal smoothing. Target counts showed that all subjects performed the task comparably. Analysis of the functional magnetic resonance imaging (fMRI) data revealed two areas with significantly lower activation in the HR group when compared to the LR group: the bilateral inferior parietal lobule (BA 40), and the bilateral inferior frontal gyrus (BA 44). Inferior parietal lobule showed significantly lower activation in the HR group in contrast to the LR group, and inferior frontal gyrus was not activated in the HR group but was only activated in the LR group. This finding indicates that a dysfunctional frontoparietal circuit may underlie the low P300 responses seen in HR subjects. This perhaps implies a deficiency in the rehearsal component of the working memory system.

Repetition priming effects from attended vs. ignored single words in a semantic categorization task

The present research examines priming effects from a centrally presented single-prime word to which participants were instructed to either attend or ignore. The prime word was followed by a single central target word to which participants made a semantic categorization (animate vs. inanimate) task. The main variables manipulated across experiments were attentional instructions (attend vs. ignore the prime word), presentation duration of the prime word (20, 50, 80 or 100 ms), prime–target stimulus onset asynchrony (SOA; 300 vs. 800 ms), and temporal presentation of instructions (before vs. after the prime word). The results showed (a) a consistent interaction between attentional instructions and repetition priming and (b) a qualitatively different ignored priming pattern as a function of prime duration: reduced positive priming (relative to the attend instruction) for prime exposures of 80 and 100 ms, and reliable negative priming for the shorter prime exposures of 20 and 50 ms. In addition (c), the differential priming pattern for attend and ignore trials was observed at a prime–target SOA of 800 ms (but not at a shorter 300-ms SOA) and only when instructions were presented before the prime word. Methodological and theoretical implications of the present findings for the extant negative priming literature are discussed.

Priming of strong semantic relations in the left and right visual fields: a time-course investigation

Prior time-course investigations of cerebral asymmetries in word processing have sometimes reported hemisphere differences in the onset and duration of semantic priming. In the current study, very strongly related word pairs (categorical associates such as arm– leg) were employed in a low relatedness proportion lexical decision priming paradigm. A range of prime–target stimulus onset asynchronies (SOAs: 150–800 ms) was included. Only very weak evidence was obtained for a LVF priming lag at the briefest SOA, while priming was bilateral at moderately long SOAs. We consider these data in the context of previous time-course studies and suggest that, when highly semantically similar word pairs are used, a right hemisphere priming lag is, at best, a very small effect.

Eliminating the cost of task set reconfiguration.

With insufficient time to fully prepare for a switch in task, a deterioration in performance on the first trial of a new task would be expected. The interest of researchers has been captured by the residual switch costs that, surprisingly, remain despite sufficient time to prepare. We used avery simple task to investigate the costs to reaction time and accuracy associated with changing between two different instructional sets every eight trials. Subjects responded to left and right visual targets by making either spatially compatible or incompatible eye movements (Experiment 1) or buttonpress responses (Experiment 2). The subjects were cued as to whether to make the compatible or the incompatible response by the color of a border appearing on the perimeter of the display. In cases in which the subject alternated between making pro- and antisaccades, the large costs to reaction time and accuracy at the short cue-target stimulus onset asynchrony were completely eliminated when sufficient time was provided to prepare for the switch. This complete elimination of residual switch costs was not obtained when the same alternation was applied to manual responses. This pattern of results links residual costs to response selection processes and suggests that they are not a necessary component of the switch process. We propose that the elimination of "stubborn" residual switch costs is rooted in our use of a hypercompatible task (making saccades toward targets) that places minimal demands on response selection.

Neural correlates of perceptual priming of visual motion

In two experiments, the temporal dynamics of neural activity underlying perceptual priming of visual motion was examined using event-related potentials (ERPs) during directional judgments of the apparent motion of two-dimensional sine-wave gratings. Compared to perceptually ambiguous motion, unambiguous left- or rightward motion was associated with enhanced ERP activity about 300 ms after the onset of apparent motion. In the second experiment, ERPs were recorded to two successive motion jumps in which an unambiguous motion jump served as a prime for a subsequent target motion that was ambiguous. The prime-target time interval was varied between 200, 400, and 1000 ms. In a control (motion reversal) condition, the two motion jumps were both unambiguous but in opposite directions. Compared to the motion reversal condition, motion priming was associated with an enhancement of ERP amplitudes at 100 ms and 350 ms following target stimulus onset. ERP enhancement was greatest at a short prime-target interval of 200 ms, which was also associated behaviorally with the strongest priming. The ERP enhancement and behavioral priming were both eliminated at the long 1000 ms prime-target interval. Functional magnetic resonance imaging (fMRI) data from a subset of subjects supported the view that motion priming involves modulation of neural responses both in early visual cortex and in later stages of visual processing.

The role of fixation point and subjects' readiness in the occurrence of express saccades as revealed by the self-initiation paradigm.

The role of fixation and the subjects' response preparedness in producing express saccades were explored in seven human subjects. The occurrence frequencies of the express saccades were compared in the overlap (continuous presentation of fixation point), gap (fixation point offset 0-400 ms prior to target onset) and no-fixation tasks under the conventional and self-initiation paradigms. In the latter paradigm, the subjects, when ready, touched a sensor in order to ignite the target lamp with a delay time of 0-400 ms (target onset delay time). Therefore, the subjects' response preparedness might be expected to be higher than that in the normal paradigm and equated in each subject at the time when the subjects touched a sensor regardless of the paradigms. Although express saccades were produced neither in the normal overlap nor in the normal no-fixation tasks, they could be produced at the rate of 24 and 48% in the overlap and no-fixation tasks under the self-initiation paradigm, respectively. The highest occurrence frequency of express saccades was obtained when the gap paradigm was combined with the self-initiation paradigm with a delay time of 100 ms (62%). The value was higher by 20% than in the normal gap task. At a target onset delay time of 0 ms under the self-initiation paradigm, the occurrence frequency of express saccades was higher in the overlap task than in the gap task. These results suggest that the subjects' response preparedness has a potentiality to produce express saccades without fixation point offset and that fixation point offset at the same time of the target stimulus onset has an interference, rather than facilitatory, influence on the generation of express saccades.

Event-related brain potentials elicited by rhyming and non-rhyming pictures differentiate subgroups of reading disabled adolescents.

Event-related brain potentials were recorded while disabled adolescent subjects read and judged whether two sequentially presented pictures had names that rhymed. Subjects with relatively good phonetic skills displayed an N400 priming effect, i.e., a significant reduction in the amplitude of the negative peak, occurring approximately 400 msec post-stimulus, for pictures with names that rhymed with preceding pictures as compared with pictures that had names that did not rhyme with the prime. No such effect was evident for subjects with relatively poor phonetic skills. This lack of an N400 priming effect provides evidence for a reduction in neural capacity and/or activation during phonological processing in the subjects with poor phonological skills. Demonstrating the N400 priming effect to be stronger in one group of reading disabled subjects, compared to another, supports the position that specific subtypes of reading disability exist. In addition to the stronger N400 priming effect, the phonetically stronger group also exhibited an enhanced negativity, from 700 to 1,000 msec after target stimulus onset, compared to phonetically inferior subjects. This finding replicates earlier work and possibly reflects a higher level of confidence in the group with better phonetic skills.

Visual ‘cognitive’ evoked potentials in the behaving monkey

Using a visual ‘oddball’ paradigm we studied ERPs in monkeys trained in a ‘go’ ‘no-go’ discrimination task. The stimuli were 2.5 cpd sinusoidal gratings differing only in orientation (0° or 25°). Monkeys released a lever during 1 of 2 response windows (RW), 480–1762 or 740–1672 msec, following target stimulus onset. Target stimulus presentation probabilities were 1.0, 0.5 and 0.3. The primary evoked potentials recorded to either the target or non-target stimulus were similar in all monkeys. P 3 signals progressively emerged in the monkeys only to the target stimulus. P 3 recorded at Cz, P3, and P4 had similar mean latencies and amplitudes. Eye movements showed no relationship to P 3 potentials. Neither the primary visual potentials nor P 3 changed significantly as a function of RW. P 3 amplitude was inversely related to target probability. When the target stimulus was presented 100% of the time ( P = 1.0) P 3 disappeared over 4–5 blocks of trials, while the primary evoked potentials remained consistent.