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Results for “Pattern Recognition, Visual”

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PubMed1984

Gender factor in longer P100 latency of elderly persons.

Monocular pattern-shift visual evoked potentials (PSVEPs) were obtained in 26 neurologically and ophthalmologically normal elderly community volunteers (mean age 59.4, males 15, females 11), and compared with similarly obtained data in 26 sex-matched young subjects (mean age 28.1). Elderly males were age-matched with elderly females, and young males were age-matched with young females. Data analyses at both the midoccipital-linked ears and midoccipital-midcentral derivations revealed that the combined-eye mean P100 latency in the elderly as a whole was significantly longer than the young sex-matched controls (P less than 0.02). However, the latency in the elderly males was not significantly different from that of sex-matched young males, or age-matched elderly females. The latency in young female subjects, on the other hand, was significantly shorter both when compared to that of age-matched young males (P less than 0.01) and sex-matched elderly females (P less than 0.01). The differences in other PSVEP variables, namely, interocular P100 latency differences, P100 amplitudes and interocular P100 amplitude ratios were not significant between the groups and subgroups studied. It is concluded that females account for the major contribution towards the longer P100 latency in the elderly.

Adult↗

PubMed1986

P100 amplitude variability of the pattern visual evoked potential.

This study quantifies the amplitude variability of the pattern visual evoked potential (P-VEP) and compares this variability between the two eyes and between individual runs recorded in the typical clinical laboratory. Cooperative adults were studied in order to obtain measurements under optimal conditions. Average P100 amplitudes of 10 runs for one eye were essentially equal to average P100 amplitudes of the other eye, as were the variances. Mean amplitude ratio (the smaller amplitude divided by the larger amplitude) was 0.91. With a group mean P100 amplitude of 10.06 microV, standard deviation for intrasubject data was 1.84, and for intersubject data was 3.75. Therefore, most of the amplitude variability between the two eyes is due to run-to-run variability. A minimum of 3 runs (100 stimuli each) and an optimum of 5 runs should be recorded before making an evaluation.

Adult↗

PubMedDate not supplied

Serial pattern evoked potential recording in a case of toxic optic neuropathy due to ethambutol.

Visual evoked potentials (VEPs) were studied in a patient who developed visual impairment during ethambutol treatment. The ERG and the flash VEP were normal at the time of maximal visual loss, whereas pattern reversal VEPs 2 and 5 months after onset revealed evidence of severe bilateral optic nerve involvement, especially affecting macular fibres. Seven months after onset paramacular PNP complexes with a late positivity (scotomatous response) were recorded after pattern reversal and half-field stimulation, suggesting involvement of fibres subserving central vision. At the time when visual acuity was normal there was still electrophysiological evidence of a mild involvement of the anterior visual pathway. The papillomacular bundle seems to be especially involved in ethambutol eye toxicity.

Aged↗

PubMedDate not supplied

Pattern visual evoked potentials recorded from human occipital cortex with chronic subdural electrodes.

Pattern evoked potentials to full- and partial-field stimulation were recorded simultaneously from scalp electrodes and from subdural electrodes located over the temporal and occipital cortex, including electrodes placed over or close to the lower lip of the calcarine fissure. High-amplitude pattern evoked potentials were recorded exclusively from electrodes localized in the vicinity of the calcarine fissure and showed a positive-negative deflection in phase with surface recordings, followed by a second negative peak phase reversed with respect to the major surface positive peak ("P100"). The findings suggest that the initial component is an expression of the afferent volley and that the second component (equivalent of the surface "P100") is most probably generated as a dipole strictly localized to the visual cortex in close proximity of the calcarine fissure (area 17 and/or area 18).

Adult↗

PubMed1995

Scalp-recorded oscillatory potentials evoked by transient pattern-reversal visual stimulation in man.

Replicable oscillatory potentials, time-locked to pattern stimuli (9.0 degrees central; counterphase reversal at 2.13 Hz) were dissociated from conventional, broad-band VEPs recorded in healthy volunteers at occipital scalp locations by high-pass digital filtering at 17.0-20.0 Hz. Nine consecutive wavelets were identified with a 56.4 +/- 8.4 msec mean latency of the first replicable wavelet and mean peak-to-peak amplitude varying between 0.9 and 2.0 muV. The first 2 wavelets had significantly shorter latencies than wave N70 of unfiltered VEP, whereas the last 2 wavelets had longer latencies than N145. Latency and amplitude values varied as a function of contrast and spatial frequency of the stimulus, with shorter latencies and larger amplitudes at 60-90% contrast level and tuning of amplitude at 5.0 c/deg. All wavelets were correlated with wave P100 of unfiltered VEP, while a correlation with N70 of VEP was observed only for those wavelets with latencies in the range of wave P100. Two patients with documented brain lesions involving the visual system are described as examples of oscillatory responses occurring irrespective of filter bandpass and instead of the expected conventional VEP when the generation of these is interfered with by brain pathology. A substantial cortical contribution to the origin of the oscillatory response is conceivable. It is suggested that the oscillatory response to pattern-reversal stimulation reflects events in the visual system that are parallel to, and partly independent of, the conventional VEP, with potential application in research or for clinical purposes.

Adolescent↗

PubMed1994

Induced refractive errors and pattern electroretinograms and pattern visual evoked potentials: implications for clinical assessments.

Refractive errors were induced in normal subjects by means of positive dioptre lenses to reduce visual acuity (VA) from an initial level of 20/20 to 20/100 and then to 20/200. Pattern electroretinograms (PERGs) and pattern visual evoked potentials (PVEPs) were simultaneously recorded at each of these 3 levels of VA using high contrast checkerboard stimuli subtending 11' and 42' of visual arc. Attention was paid to PERG and PVEP variables used for clinical assessments. The findings confirmed the need to take refractive errors into account because, in some cases, latencies and particularly PERG amplitudes fell outside normal limits with decreased VA, especially when using smaller checks.

Adult↗

PubMed1994

Pattern reversal evoked potentials: gender differences and age-related changes in amplitude and latency.

This report is intended to complement the current body of literature by describing pattern reversal evoked potential (PREP) component amplitudes and latencies in a larger sample than has been previously studied and providing comparisons of males and females across the lifespan. Binocular PREPs were measured from 406 normal subjects, 6-80 years of age. In general, latencies were found to decrease during maturation, stabilize across early adulthood, then begin to increase sometime after the late 20s. There were minimal gender differences in latencies during development but males tended to have longer latencies than females during adulthood. Across the lifespan, amplitudes were larger for females. Results of regression analyses using the entire data set were compared to results of separate regression analyses for developmental years (6-20) and adulthood (21-80). Separate analyses appear to provide more useful descriptions of PREP latency and amplitude changes across the lifespan. It is clear that predicted normal values can vary depending on age range and relative proportion of males and females comprising a reference sample. Appropriate clinical values should be based on age- and sex-matched normal subjects and should be specific with regard to technical and methodological variables.

Adolescent↗

PubMed1990

The lateralization of language comprehension using event-related potentials.

Event-Related Potentials were recorded over occipital and parietal scalp from left- and right-handed adults presented with a language and a non-language visual stimulus using a divided field, "oddball" paradigm. The major finding of interest was that the P300 component was larger over the left than the right hemisphere of the right-handers when the language stimulus was presented to the left hemisphere; there were no hemispheric differences for the left-handers, regardless of field of presentation. These results are discussed in the context of developing noninvasive measures to lateralize language function.

Arousal↗

PubMed1980

Event-related brain potentials to semantically inappropriate and surprisingly large words.

Event-related brain potentials (ERPs) were recorded from young adult subjects as they silently read 160 different seven-word sentences, presented one work at a time. The sentences either ended normally or were completed by unexpected words that were either semantically inappropriate, physically deviant or both. These two types of deviations were associated with distinctly different ERP components - a late negative wave (N400) for semantic deviations and a late positive complex for physical deviations. A deviation along either one or these dimensions (semantic or physical) did not appear to alter the ERP effect of a concurrent deviation along the other. In addition, it was found that the ERPs elicited by the words during the reading condition were characterized by a left-greater-than-right asymmetry in a slow, positive component. This asymmetrical scalp distribution was most pronounced for right-handed subjects having not left-handers in their immediate family.

Adult↗

PubMedDate not supplied

Lateralization of visual cognitive potentials.

Pairs of stimuli containing either the same or different visual patterns were presented separately to the right and left brain hemispheres. Ten adult males were trained before the formal experiment to perform the task automatically and without verbal control. A verbal control task was arranged at the end of the experiment. Reaction times and P3P4, C3C4 brain evoked potentials were recorded. The N2 (180-290 msecs) and P3 (290-380 msecs) components were found to be lateralized over the right side of the scalp for nonverbal conditions. Slightly larger P3 was found over the left side for the verbal control test. The results are discussed in relation to the present evidence about the nature of N2 and P3 in the single act of perception and in the ontogenetic development.

Adult↗

PubMed1989

Stimulus probability and motor response in young and old adults: an ERP study.

The effects of responding hand and stimulus probability were investigated in young and old subjects in an RT task in which both rare and frequent stimuli required a response. It was found that the effect of stimulus probability was less pronounced in old subjects than in young, and that the latency of P3 was longer in the elderly, although their RTs were not different from young subjects. ERPs for right hand responses were larger than for left hand responses; this difference was discernible already in the P2 and N2 peaks of the ERP. A tentative explanation is offered for these large and unexpected hand differences. An interpretation in terms of an age-related decrease in resources is proposed for the increased P3 latency and the decreased probability effect on P3 amplitude in old subjects.

Adolescent↗

PubMed1994

Associative ERP effects with memories of artificial faces.

A previous study (Valdes-Sosa and Bobes, 1990) described a negative ERP component evoked by mis-matches in a face-feature matching task, using photographs of real faces. This component could be N400 (or an analogue), elicited by associative priming within a non-linguistic domain: that of face structure. To confirm this it is necessary to demonstrate that semantic/linguistic recoding was not a necessary condition in triggering the negativity. This means falsifying what we call the 'priming by proxy' hypothesis, and locating the triggering mis-match within face structure. In this paper subjects studied artificial schematic faces over several sessions, and 1 week later were presented with a face-feature matching task with simultaneous ERP recording. Since no semantic information or verbal labels were available, eliciting a mis-match negativity with these faces contradicts the 'priming by proxy' hypothesis. In a first experiment, in which the subjects learning was controlled through a face familiarity decision task, no significant mis-match negativity was found. However, in a second experiment in which learning was controlled through a forced-choice face-feature match, a significant mis-match negativity was found in the subsequent recording session. This result supports the idea that a component similar to N400 can be elicited by an associative mis-match restricted to the face-structural domain.

Adolescent↗

PubMed2006

Response-time corrected averaging of event-related potentials.

OBJECTIVE: The present study presents a novel approach to averaging of event-related potentials (ERPs). Acknowledging latency variability of late ERP components as related to performance fluctuations across trials should improve the assessment of late portions of the ERP. METHODS: Prior to the averaging procedure stimulus-to-response epochs in the electroencephalogram (EEG) were expanded/compressed in time to match mean RT in a certain condition and participant. By means of several mathematical functions RT variability was differentially distributed over late vs. early portions of the ERP. Data from 20 participants from two conditions of an identity-based priming task were analyzed using traditional stimulus- and response-locked averaging, as well as four different RT-corrected averaging procedures. RESULTS: Area under the curve as an index of precision of LPC assessment was reliably enhanced for certain RT-corrected procedures relative to traditional ERP averaging. Moreover, a priming effect on amplitude of a distinct LPC subcomponent which could not be confirmed with traditional stimulus-locked averaging was reliably born out using a cubic RT-correction procedure. CONCLUSIONS: RT-corrected ERP averaging can outperform traditional ERP averaging in the assessment of late portions of the ERP, and experimental effects upon. SIGNIFICANCE: Cognitive ERP researchers may take advantage of the improved capability of RT-corrected averaging to establish experimental effects on amplitudes in the late ERP range.

Adult↗

PubMed2004

Texture segmentation and visual search for pop-out targets. An ERP study.

"Parallel" visual search and effortless texture segmentation were believed to rely on similar mechanisms until Wolfe [Vis. Res. 32 (1992) 757] demonstrated that efficient visual search and effortless texture segmentation are not always the same thing. In a recent study, Meinecke and Donk [Perception 31 (2002) 591] varied display size in a pop-out task and found that, albeit stimulus elements and the task remained the same, different set sizes led to different processing modes. These findings indicate that it may suffice to vary set size in an otherwise unchanged pop-out task to initiate different processing which may be similar to the processing in efficient visual search and in effortless texture segmentation. In four experiments, we further investigated this issue by presenting stimulus arrays of different set sizes while recording event-related brain potentials (ERPs). We found that when display size was increased, detection performance first decreased slightly before it then increased. ERP effects were observed for the posterior N2 (N2p), the N2pc and the P3 component. All three components showed variations with set size; N2p differential amplitude effects were confined to large set sizes, whereas an N2pc was obtained for a broader set size range except for very small set sizes and the largest set size (121 elements). We interpret both the non-monotonic relationship between set size and response data and the variations of ERP components with set size as evidence in favor of different processing occurring for stimulus arrays with small and large set sizes.

Adult↗

PubMed2005

Electrophysiological correlates of forming memories for faces, names, and face-name associations.

The ability to put a name to a face is a vital aspect of human interaction, but many people find this extremely difficult, especially after being introduced to someone for the first time. Creating enduring associations between arbitrary stimuli in this manner is also a prime example of what patients with amnesia find most difficult. To help develop a better understanding of this type of memory, we sought to obtain measures of the neural events responsible for successfully forming a new face-name association. We used event-related potentials (ERPs) extracted from high-density scalp EEG recordings in order to compare (1) memory for faces, (2) memory for names, and (3) memory for face-name associations. Each visual face appeared simultaneously with a unique spoken name. Signals observed 200-800 ms after the onset of face-name pairs predicted subsequent memory for faces, names, or face-name associations. Difference potentials observed as a function of subsequent memory performance were not identical for these three memory tests, nor were potentials predicting associative memory equivalent to the sum of potentials predicting item memory, suggesting that different neural events at the time of encoding are relevant for these distinct aspects of remembering people.

Adolescent↗

PubMed2005

The relationship between local and global processing and the processing of high and low spatial frequencies studied by event-related potentials and source modeling.

The processing of global and local elements and of low- and high-spatial frequencies are thought to be interrelated. Evidence for this stems from findings showing that brain localizations for global/local elements and for low/high spatial frequencies seem to overlap. The present study aimed to provide direct evidence that topographical differences between the processing of global and local visual elements can directly be explained by their spatial frequency content, and to study at which point in time this relation is present. This was done by studying the event-related potentials (ERPs) and source models elicited by unfiltered, low- or high-pass filtered hierarchical stimuli. Results showed that performance for global and local targets was affected by removing low and high spatial frequencies, respectively. ERP data indicated that at 250 ms, there was an interaction between the processing of global/local targets and of spatial frequencies because at this time-point removal of low spatial frequencies decreased activity associated with the processing of global targets. When localizing this effect, we found evidence implying that spatial frequency content indeed affected the brain region in which local/global targets were processed. Results implicated that the processing of global information depended on its low spatial frequency content, which was processed more laterally. Instead, processing of local information seemed to depend on its high spatial frequency content, which was processed more medially. Thereby, present results extend former results showing that global and local processing is dependent on spatial frequency and mapped retinotopically in the visual cortex.

Adolescent↗

PubMed2005

Appearing and disappearing stimuli trigger a reflexive modulation of visual cortical activity.

From the vast array of stimuli continually inundating our senses, only a very small portion is selected for higher-order processing. This selection is influenced by voluntary and reflexive mechanisms that may act at multiple stages of analysis. Extensive research has revealed that top-down voluntary mechanisms modulate information processing at both "early" (e.g., perceptual) and "late" (e.g., semantic) stages. Bottom-up sensory-driven mechanisms, however, are less well understood. Previous investigations of bottom-up mechanisms may have been influenced by top-down mechanisms because the stimuli were task-relevant and required overt responses. Here, we directly measured bottom-up influences on visual information processing by recording event-related brain potentials (ERP) to sequences of task-irrelevant visual stimuli. We found that abrupt visual events triggered an automatic enhancement of extrastriate visual activity (the P1 ERP component) to subsequent visual stimuli occurring at the same location. In contrast to theories suggesting that the abrupt appearance of a new object is unique in being able to trigger bottom-up effects, we found that disappearing objects triggered the same enhancement of subsequent stimulus processing as did appearing objects. The present data, however, also provide new electrophysiological evidence for a level of analysis in the brain that may be specific to the appearance of new objects. These data thus provide evidence that abruptly appearing objects may evoke specialized processing at certain stages of analysis in the brain but that, despite this difference, appearing and disappearing objects both trigger reflexive mechanisms that bias neural activity in human extrastriate visual cortex.

Adolescent↗

PubMed2005

The role of spatial frequency information for ERP components sensitive to faces and emotional facial expression.

To investigate the impact of spatial frequency on emotional facial expression analysis, ERPs were recorded in response to low spatial frequency (LSF), high spatial frequency (HSF), and unfiltered broad spatial frequency (BSF) faces with fearful or neutral expressions, houses, and chairs. In line with previous findings, BSF fearful facial expressions elicited a greater frontal positivity than BSF neutral facial expressions, starting at about 150 ms after stimulus onset. In contrast, this emotional expression effect was absent for HSF and LSF faces. Given that some brain regions involved in emotion processing, such as amygdala and connected structures, are selectively tuned to LSF visual inputs, these data suggest that ERP effects of emotional facial expression do not directly reflect activity in these regions. It is argued that higher order neocortical brain systems are involved in the generation of emotion-specific waveform modulations. The face-sensitive N170 component was neither affected by emotional facial expression nor by spatial frequency information.

Adult↗