Presaccadic attention allocation and express saccades

Express saccades are visually-guided saccades that are characterized by an extremely short latency of about 100 ms. The present experiments tested the hypothesis that a disengagement of visual attention is necessary for the generation of express saccades. All subjects produced large numbers of express saccades in the gap paradigm, in which the fixation stimulus is removed 200 ms before target onset (Exp. 1), but not in the overlap paradigm, in which the fixation stimulus remained on during the entire trial (Exp. 2). By means of peripheral cues (Exps. 3-5) and central cues (Exps. 6-7), visual attention was directed at the target location for the saccade before the actual appearance of the saccade target. In all experiments, the location cues facilitated rather than abolished express saccades. The generation of express saccades was facilitated even when the currently fixated visual stimulus was not removed before target onset (fixation-overlap; Exps. 5-7). The results are explained by the hypothesis that a disengagement of a separate fixation system is necessary for the generation of express saccades, a hypothesis that is in line with current neurobiological findings.     

Prolonged P300 latency in attention deficit hyperactivity disorder predicts poor response to imipramine

P300 is a cognitive evoked potential that evaluates attention and information processing. This study uses auditory and visual P300 topography to develop a classification of attention deficit hyperactivity disorder (ADHD), and find predictors of treatment response. Of 45 ADHD children ages 6 to 15 treated with pemoline in a previous study, 25 were poor responders. Of these 25, 17 participated in an imipramine treatment protocol. Auditory and visual P300 testing was performed before and after treatment using 31 scalp electrodes. Good and poor responders to imipramine were clinically identical. Poor imipramine responders had longer auditory and visual P300 latencies than good responders. Treatment with imipramine decreased auditory P300 latencies and increased auditory P300 amplitudes. We have previously reported that ADHD patients with small right frontocentral auditory P300 amplitudes respond poorly to pemoline. Thus, P300 topography and latency classifies ADHD into three groups: group 1 with normal P300 topography, and good response to pemoline; group 2 with small right frontocentral auditory P300 amplitudes, poor response to pemoline, and good response to imipramine; and group 3 with long auditory and visual P300 latencies and small right frontocentral auditory P300 amplitudes, and poor response to pemoline and imipramine.     

Causality and the allocation of attention during comprehension.

Recent research has suggested that each statement in a narrative text is understood by relating it to its causal antecedents and consequences and that the text as a whole is understood by finding a causal path linking its opening to its final outcome. C. R. Fletcher and C. P. Bloom (see record 1989-10829-001) have proposed that in order to accomplish this goal, while minimizing the number of times long-term memory has to be searched, readers focus their attention on the last clause of a narrative that has causal antecedents but no consequences in the preceding text. As a result, a statement that is followed by a causal antecedent should remain the focus of attention, while the same statement followed by a consequence should not. This prediction was tested and confirmed in three experiments which show that when a target statement is followed by a sentence that includes only causal antecedents (a) continuation sentences related to it are read more quickly, (b) target words drawn from it are easier to recognize, and (c) subject-generated continuations are more likely to be causally related to it. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Psychophysiology of P300.

The P300 component of the human average evoked potential has been associated with a host of stimulus and S variables, such as information delivery and stimulus salience. P300 is emitted by the brain in response to either attended events that are surprising or to unattended events that produce orienting. P300 does not appear to be a real-time index of signal (target) selection, since attended low-probability nonsignals also result in P300 and its latency is too long. P300 further appears to be independent of response selection; its latency therefore may or may not correlate with RT, depending on the experimental context. P300 latency does appear to index stimulus evaluation time in that it is not emitted until the stimulus has been cognitively evaluated. P300 amplitude appears sensitive to manipulations of perceptual limited capacity but not sensitive to manipulations of motor limited capacity. It has been proposed that P300's functional role in human information processing is the updating of neurocognitive models concerning future events, although other functions have also been proposed. (5 p ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Postperceptual effects and P300 latency

BACKGROUND: Structural and functional brain changes have been described in elderly patients with unipolar affective disorder. Changes appear to be more marked in patients with late-onset depression, but the reversibility of such changes after clinical recovery is not known. METHODS: Magnetic resonance imaging, electroencephalography (EEG), and cognitive tests were performed in 23 elderly patients (mean age 66.5 years) clinically recovered from major depression. Twelve had late-onset depression (first episode over 55 years of age); 11 had early onset (first episode before 50 years). EEG and cognitive testing were also performed on 15 control subjects. RESULTS: Patients with late-onset depression had larger third and lateral ventricles, increased ventricular-brain ratio, and greater frequency and severity of subcortical white matter lesions than those with early onset. There was no difference between early- and late-onset patients in EEG and cognitive measures, but compared with controls patients showed significant changes in EEG evoked potentials and increased slow-wave activity, slowed reaction times, and global impairments in cognitive function. CONCLUSIONS: These results suggest that structural changes are greater in patients with late-onset depression, and that EEG and cognitive impairments persist after recovery, regardless of age of onset of depression, and are independent of structural changes.     

P300 event-related potentials in stutterers and nonstutterers

This study investigated possible differences between adult stutterers and nonstutterers in the P300 event-related potential. Responses to tonal stimuli were recorded from electrodes placed over the left (C3) and righ (C4) hemispheres. The two groups exhibited different patterns of interhemispheric activity. Although all 8 participants in the fluent group exhibited P300s that were higher in amplitude over the right hemisphere, 5 of the 8 disfluent participants had higher amplitude activity over the left hemisphere. These results provide evidence that stutterers and nonstutterers may exhibit differences between hemispheres in the processing of some types of nonlinguistic (tonal) stimuli.     

P300 response: habituation

This study used the "oddball" counting paradigm to examine the possible habituation of the auditory P300 response. Twenty subjects kept a mental record of the number of rarely occurring tone pips presented in a series of more frequently occurring tone pips. Data were collected continuously until responses to 150 rare tone pips were obtained. Findings indicated that the P300 complex decreased in amplitude as a result of repeated stimulation. The decline was logarithmic, not linear, which suggests a stabilization of the amplitude over time. We suggest that the attenuation of amplitude was habituation and not a result of a recovery cycle.     

Auditory P300 and self-reported impulsive aggression

1. The purpose of the present study was to determine the cognitive psychophysiological correlates of impulsive aggression in a population considered "normal" by societal standards: college students. 2. Auditory event-related potentials were acquired on all subjects during a standard oddball task. The stimuli consisted of a random sequence of two tones, a frequent 1,000 Hz tone and a rare 2,000 Hz tone. Tones were presented in a ratio of 80/20. 3. Results of the study demonstrated that impulsive aggressive subjects show significantly lower P300 amplitude at frontal electrode sites when compared to nonaggressive controls. 4. These findings are consistent with the psychophysiological findings in impulsive aggressive incarcerated criminals and support the notion of a specific behavioral syndrome associated with spontaneous aggressive outbursts.     

P300 clinical utility and control of variability

The P300 event-related brain potential (ERP) has been used to study normal aging as well as patient populations with a variety of neurologic and psychiatric disorders. The P300 has demonstrated reasonable success as a means to assess disturbances in cognitive function, and its clinical utility has been enhanced by the identification of factors that contribute to the variability of ERP measurements. In this article, the neuropsychological theory of P300 is reviewed, ways in which this brain potential can be used as a measure of cognitive efficiency are defined, and methodologic issues that must be considered for successful clinical ERP applications are outlined. This approach is then extended to specific recommendations concerning the technical and practical aspects of P300 recording, so that a well-defined normative database can be developed for evaluating individual patients. When appropriate procedures are used, the P300 can provide a highly useful means to quantify human cognitive capability.     

P300 and stress in mild head injury patients

OBJECTIVE: The P300 component of event-related potentials is affected by personal meaningfulness of the stimulus to the subject. Thus, the P300 component could provide an objective parameter in the emotional assessment of road accident mild head injury patients, when exposed to relevant stimuli. METHODS: Thirteen patients with post-traumatic symptoms and 14 healthy controls were evaluated in this study. Two word types, distinguished by color, were presented on a computer screen in active 'oddball' paradigm conditions. In the first subtest, the targets were accident-related (stressful) words; in the second subtest, the targets were non-accident-related (neutral) words. Target (20%) and non-target (80%) were defined by word color. Data recorded from Pz were analyzed for P300 parameters. RESULTS: Patients and controls differed in their reaction to word types (group x word main effect P = 0.0089), regardless of the oddball presentation. Overall, accident-related words produced a significantly larger P300 wave than neutral words in patients (P = 0.0001), but not in controls (P = 0.5741). Significant correlation was found between combined P300 amplitude difference (all stressful words vs. all neutral words) and the patient's Zung state anxiety score (r = 0.68, P = 0.01). CONCLUSION: We suggest the P300 component can provide a useful, objective tool in the assessment of mild head injury patients.     

Extremely selective attention: Eye-tracking studies of the dynamic allocation of attention to stimulus features in categorization.

Humans have an extremely flexible ability to categorize regularities in their environment, in part because of attentional systems that allow them to focus on important perceptual information. In formal theories of categorization, attention is typically modeled with weights that selectively bias the processing of stimulus features. These theories make differing predictions about the degree of flexibility with which attention can be deployed in response to stimulus properties. Results from 2 eye-tracking studies show that humans can rapidly learn to differently allocate attention to members of different categories. These results provide the first unequivocal demonstration of stimulus-responsive attention in a categorization task. Furthermore, the authors found clear temporal patterns in the shifting of attention within trials that follow from the informativeness of particular stimulus features. These data provide new insights into the attention processes involved in categorization. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex differences in seasonal variations in P300

Previous reports of seasonal variations in P300 were based on cross-sectional observations of subjects tested at different times of the year. In this study, we tested three groups of subjects in each of two seasons: winter and spring, spring and summer, and summer and winter. We found winter or spring maxima in auditory and visual P300 and visual slow wave. This pattern of results, with the amplitude of P300 being inversely related to the amount of sunlight in a season, supports the hypothesis that the allocation of processing resources varies across the seasons. Our results also suggest a trend for an increased sensitivity of women, as compared with men, to seasonal influences on P300. Although our findings do not provide strong evidence that P300 varies systematically as a function of season, seasonal factors appear to affect cognitive processing (as indexed by P300) differentially in men and women.     

P300 latency and memory span development.

The rapid increase of memory span with development has been attributed to increases in the efficiency with which children can process the items to be remembered. To test this hypothesis, WAIS Digit Span and latency from the P300 component of the event-related brain potential—a measure of stimulus evaluation time independent of response production—were obtained from 24 5–14 yr olds and 24 20–40 yr olds. Increases in digit span were associated with decreases in peak latency for children but not for adults. This finding was obtained even when S age was statistically removed, and it suggests that immediate memory development is tightly coupled with decreases in speed of stimulus identification. Implications for theories of memory development are discussed. (42 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of age on P300 wave

A case of unicystic ameloblastoma which recurred after 15 years showing unusual histological features is reported. The prominent pseudo-glandular features present are described. This case highlights the importance of extensive histological examination for more characteristic features of ameloblastoma to reach a correct diagnosis.     

Meta-analysis of P300 normative aging studies

The theoretical and empirical backgrounds for the utility of the P300 event-related potential (ERP) as a measure of cognitive aging are summarized. P300 latency data from 32 different normative aging studies are then reviewed and assessed with meta-analytic procedures. Evaluation of moderator variables indicates that sample characteristics, stimulus factors, and task conditions contribute significantly to the "normal" change in peak latency that occurs with aging. These findings are critiqued in the context of previous reports, and implications are outlined for future applications of ERPs to normative aging. It is concluded that P300 latency can provide useful information about cognitive aging but that specific variables must be considered to obtain more precise results.     

Influence of questions on the allocation of attention during reading.

77 undergraduate readers were asked a question after every 4 pages of a 48-page oceanography text. Text information relevant to questions was learned better than text information irrelevant to questions. Reading times and probe RTs on a secondary task were longer when Ss were processing text segments containing information of the type addressed by questions. Results are discussed in the light of a theory that readers selectively allocate a greater volume of attention to question-relevant information and that a process supported by the additional attention causes more of the information to be learned. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Abrupt visual onsets and selective attention: Voluntary versus automatic allocation.

The hypothesis that abrupt visual onsets capture attention automatically, as suggested by S. Yantis and J. Jonides (see record 1985-19225-001), was tested in four experiments. A centrally located cue directed attention to one of several stimulus positions in preparation for the identification of a target letter embedded in an array of distractor letters. In all experiments, one stimulus (either the target or one of the distractors) had an abrupt onset; the remaining letters did not. The effectiveness of the cue was manipulated (varying either its duration or its predictive validity) to test whether abrupt onsets capture attention even when subjects are in a highly focused attentional state. Results showed that onsets do not necessarily capture attention in violation of an observer's intentions. A mechanism for partially automatic attentional capture by abrupt onset is proposed, and the diagnosticity of the intentionality criterion for automaticity is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

P300 habituation from visual stimuli?

The P3(00) event-related brain potential (ERP) was elicited with visual stimuli using an oddball task in which the subject indicated with a finger tap response the occurrence of a target stimulus that occurred randomly on 20% of the trials and refrained from responding to a standard stimulus. A total of six trial blocks were collected, with an equal number of artifact-free epochs averaged for both stimulus types. P3 amplitude from the target stimuli did not decrease across trial blocks; P3 amplitude from the standard stimuli did decrease across trial blocks. P3 latency from both the target and standard stimuli increased across trial blocks. No changes in amplitude or latency independent of the P3 effects were obtained for the other ERP components with trial block. The results suggest that P3 components elicited by visual stimuli do not readily habituate for actively discriminated target stimuli. The theoretical implications are discussed in the context of previous findings.     

Parallel allocation of attention prior to the execution of saccade sequences.

In a series of 5 experiments, the allocation of attention prior to the execution of saccade sequences was examined by using a dual-task paradigm. In the primary task, participants were required to execute a sequence of 2 endogenous saccades. The secondary task was a forced-choice letter identification task. During the programming of the saccade sequences, letters were briefly presented at the saccade goals and at no-saccade locations. The results showed that performance was better for letters presented at any of the saccade goals than for letters presented at any of the no-saccade locations. The results support a spatial model that assumes that prior to the execution of a saccade sequence, attention is allocated in parallel to all saccade goals. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

P300 potentials evoked by visual stimulation

INTRODUCTION: The P300 potential is a long-latency endogenous component of the event-related potentials to low-probability target stimuli. The same stimulus delivered without cognitive process does not provoke endogenous components; moreover event-related potentials are not dependent of the sensory pathways used for stimulating the subjects. P300 potential is a biological parameter used in scientific investigations in Clinical Neurophysiology, Neurology, Psychophysiology and Psychiatry. The most frequent methodology for obtaining P300 event-related potential is based on the 'odd-ball' paradigm using auditory stimulation. In this revision we analyzed the difficulties of this methodology and we propose to use the visual stimulation in order to obtain well defined P300 potential, based on a better signal to noise ratio and minor overlapping of exogenous and endogenous components of the evoked potentials. The improvement in the quality of the results obtained when comparing with auditory stimulation, it is supposed to facilitate that the use of P300 potential overflows the field of the investigation and permits their extensive use in the clinical practice.