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PubMed1994

Patterns of perceptual asymmetry in processing facial expression.

The paper reports four visual half-field experiments on the recognition of schematic faces whose emotional expression varied. Experiments I and II tested accuracy of recognition in a match-to-sample task. The results confirmed an overall left visual-field superiority in face recognition, but an analysis of a subset of the stimuli indicated that the direction and magnitude of the perceptual asymmetry depend upon the sign of the emotional expression. A replot of the results based on direct scaling of emotional expression (Experiment III) revealed an asymmetry gradient shifting from a left visual-field superiority for faces displaying hostile, aggressive emotions. When the stimuli are rotated 180 degrees the faces lose their emotional expression and no visual half-field asymmetry in recognition was observed in this condition (Experiment IV). It is concluded that emotional signals are processed independently of pattern, object and face recognition, and that the relative contribution of the left and right cerebral hemispheres to processing of emotional signals varies according to the type of emotion displayed.

Adult↗
PubMed2006

Insect vision: remembering the shape of things.

How does the nervous system store a newly experienced visual pattern, and how is that pattern subsequently made available for recognition? Recent work in Drosophila suggests that specific pattern features are stored separately in the nervous system.

Animals↗
PubMed2004

Neurodynamic studies on emotional and inverted faces in an oddball paradigm.

The detection of a change in a face stimulus was studied in an oddball paradigm. Event-related potentials (ERPs) and MEG responses to face stimuli were recorded in four conditions: 1) happy standard, neutral deviant; 2) neutral standard, neutral deviant; 3) inverted happy standard, inverted neutral deviant; 4) inverted neutral standard, inverted neutral deviant. In all conditions, the target was a face with glasses. Neutral deviants elicited a negative deflection (with a maximum around 280 ms) in ERP and MEG responses, an effect similar to auditory mismatch negativity. Face inversion diminished deviance-related negativity, implying an important role of face recognition in the observed effect. Emotional content and larger physical differences between stimuli in conditions 1 and 3 compared to conditions 2 and 4 did not show statistically significant effect on the neutral-deviant-related negativity.

Adult↗
PubMed2006

Event-related potential (ERP) indices of infants' recognition of familiar and unfamiliar objects in two and three dimensions.

We measured infants' recognition of familiar and unfamiliar 3-D objects and their 2-D representations using event-related potentials (ERPs). Infants differentiated familiar from unfamiliar objects when viewing them in both two and three dimensions. However, differentiation between the familiar and novel objects occurred more quickly when infants viewed the object in 3-D than when they viewed 2-D representations. The results are discussed with respect to infants' recognition abilities and their understanding of real objects and representations. This is the first study using 3-D objects in conjunction with ERPs in infants, and it introduces an interesting new methodology for assessing infants' electrophysiological responses to real objects.

Child Development↗
PubMed1989

Visual responses of sheep temporal cortex cells to moving and stationary human images.

Single-cell extracellular recordings were made from temporal cortical neurones in the conscious sheep. The visual responses of these cells to stationary or moving images of humans were investigated. Results from 6 animals showed that a small population of cells responded preferentially to the sight of humans as opposed to other objects or food. These cells did not respond to visual images of the human face, or to individual body parts (legs or arms) or to the smell of a human. The majority of cells showed direction selectivity, with the most effective stimulus being a human moving towards the animal. Cells did not respond differentially to the front and back view of a human although the side view was less effective. The posture adopted by the human was important, since responses were diminished or absent if the human adopted a quadrupedal as opposed to the normal bipedal posture. These results provide evidence for integrated neural processing of both visual recognition, movement and posture in the sheep temporal cortex.

Animals↗
PubMed1984

Global versus local processing: is there a hemispheric dichotomy?

A major dichotomy proposed for lateralized information processing is that the right and left cerebral hemispheres are "global" and "analytic" processors respectively. Here three experiments employed a tachistoscopic recognition paradigm with letter patterns varying in size and composition. No visual field asymmetries in RT were found in the first two experiments, although statistical power was high and a Stroop-like effect ("global precedence") was supported. Experiment 3 resulted in a right field advantage for vocal naming responses yet no asymmetry for manual responses, suggesting that both hemispheres can recognize global and local patterns, but that introduction of a laterally controlled response independently determines asymmetry.

Adult↗
PubMed1998

ERPs and chronometry of face recognition: following-up Seeck et al. and George et al.

Seeck et al. found that event-related potentials (ERPs) evoked by repeated and non-repeated face photographs differ as early as 50-70ms post-onset. They thus suggested that faces are recognized at these latencies, in contrast with current opinions in ERP literature. However, the similar latencies obtained by George et al. for stimuli not perceived as faces suggest that Seeck et al.'s differences could index repetition rather than face recognition per se. To address this issue, we used matched faces of known and unknown persons. We found the earliest differences between the ERPs to these faces between 76 and 130 ms. These results, which are consistent with other data, suggest that the differentiation of faces takes approximately 100 ms of processing time in humans.

Adult↗
PubMed2000

Visual priming: the ups and downs of familiarity.

A dynamic picture of the neural processes underlying the 'priming' effects on the visual system of repeated object presentation has been obtained by combining functional magnetic resonance imaging with a gradual 'unmasking' procedure that slows down the process of visual recognition.

Brain↗
PubMed1984

Neurophysiological correlates of visual stimulus recognition in man.

This study investigated the components of evoked impulse activity of neurons and neuronal populations (NIA) in the human brain. Subjects were 5 parkinsonian patients, two patients with skull trauma and an epileptic, diagnosed and treated with implanted electrodes. NIA was recorded during the following psychological tests: (1) identification of letters and digits presented at near-threshold exposures; (2) recognition of polygonal shapes with and without semantic meaning. Peri-stimulus time histograms (PSTHs) for the cases of recognition and non-recognition in the first test and for cases of presentation of familiar and unfamiliar patterns in the second test were computed and compared with each other. PSTH components in the stimulus-response interval were classified into 3 groups: the earliest components with the latency 60-200 ms; the late components with latency 300-400 ms; and slow count rate shifts revealed 300-500 ms after stimulus presentation. No significant differences were found between the short-latency components for cases of recognition and non-recognition in the first test and for cases of presentation of familiar and unfamiliar patterns in the second test, while late components depended upon subjective estimation by the patient of the stimulus. Early components are supposed to be related to physical characteristics of the stimulus, while the late components with semantic meaning.

Adult↗
PubMed1998

Neural plasticity in the dynamics of human visual word recognition.

Repeated exposure to words leads to plastic changes in the nervous system throughout the lifespan, with the consequence that common words are processed more rapidly and accurately than rare words. Most behavior time measures correlate highly with the logarithm of a stimulus word's experiential frequency. Here, we demonstrate similar but earlier changes in the latency of a brain-generated evoked potential recorded over the left anterior scalp as individuals silently read sentences. We conclude that experience can speed the processing of some words by at least 50 ms within the first 335 ms of visual processing.

Brain↗
PubMed2003

Functional magnetic resonance imaging (fMRI) "brain reading": detecting and classifying distributed patterns of fMRI activity in human visual cortex.

Traditional (univariate) analysis of functional MRI (fMRI) data relies exclusively on the information contained in the time course of individual voxels. Multivariate analyses can take advantage of the information contained in activity patterns across space, from multiple voxels. Such analyses have the potential to greatly expand the amount of information extracted from fMRI data sets. In the present study, multivariate statistical pattern recognition methods, including linear discriminant analysis and support vector machines, were used to classify patterns of fMRI activation evoked by the visual presentation of various categories of objects. Classifiers were trained using data from voxels in predefined regions of interest during a subset of trials for each subject individually. Classification of subsequently collected fMRI data was attempted according to the similarity of activation patterns to prior training examples. Classification was done using only small amounts of data (20 s worth) at a time, so such a technique could, in principle, be used to extract information about a subject's percept on a near real-time basis. Classifiers trained on data acquired during one session were equally accurate in classifying data collected within the same session and across sessions separated by more than a week, in the same subject. Although the highest classification accuracies were obtained using patterns of activity including lower visual areas as input, classification accuracies well above chance were achieved using regions of interest restricted to higher-order object-selective visual areas. In contrast to typical fMRI data analysis, in which hours of data across many subjects are averaged to reveal slight differences in activation, the use of pattern recognition methods allows a subtle 10-way discrimination to be performed on an essentially trial-by-trial basis within individuals, demonstrating that fMRI data contain far more information than is typically appreciated.

Adult↗
PubMed2002

Priming visual face-processing mechanisms: electrophysiological evidence.

Accumulated evidence from electrophysiology and neuroimaging suggests that face perception involves extrastriate visual mechanisms specialized in processing physiognomic features and building a perceptual representation that is categorically distinct and can be identified by face-recognition units. In the present experiment, we recorded event-related brain potentials in order to explore possible contextual influences on the activity of this perceptual mechanism. Subjects werefirst exposed to pairs of small shapes, which did not elicit any face-specific brain activity. The same stimuli, however, elicitedface-specific brain activity after subjects saw them embedded in schematic faces, which probably primed the subjects to interpret the shapes as schematic eyes. No face-specific activity was observed when objects rather than faces were used to form the context. We conclude that the activity of face-specific extrastriate perceptual mechanisms can be modulated by contextual constraints that determine the significance of the visual input.

Adult↗
PubMed1986

Detection performance of normal cats and those lacking areas 17 and 18: a behavioral approach to analyse pattern recognition deficits.

The ability of cats to discriminate between two geometrical outline patterns in the presence of superimposed Gaussian visual noise was tested before and after bilateral removal of cortical area 17 and parts of area 18. The detection probability PD was measured as a function of the signal-to-noise ratio for the parameters: noise bandwidth, spatial frequency content and rate of movement of patterns. In both normal and lesioned cats a broadband noise was found to be most effective in masking the large patterns while two other types of noise, a medium frequency noise and a high frequency noise had little or no masking effect. For recognition of the smaller patterns in normal cats the medium frequency noise was found to be more effective than the broadband noise. The performance of the lesional cats was disturbed severely at low signal-to-noise ratios and was significantly inferior to that of normal cats-especially for small patterns. However, at high S/N ratios and for large patterns the performance of the lesioned cats was comparable to that of normals while for the small patterns they reached PD values inferior to those of normal cats. It is concluded that although pattern recognition can be performed successfully by cats lacking areas 17 and 18, these cortical areas probably make an essential contribution to this function under natural conditions in two ways: because of the X-type input of area 17, they increase the acuity of the system by making it more sensitive to higher spatial frequencies, and they permit detection of patterns at much lower S/N ratios i.e. they lower the signal-to-noise ratio at which the system is able to detect the presence of a pattern in a background of statistical visual noise. The latter effect is not limited to the higher spatial frequencies but also affects the very low spatial frequencies which are normally used for pattern detection. Previous failures to demonstrate clear deficits in pattern discrimination after 17/18 lesions in cats may be attributed to the fact that the patterns presented for discrimination were not masked by visual noise. Movement of patterns led to a slight, but not significant improvement of the performance in both normal and lesioned cats, but the deficits found for stationary and moving patterns were more or less equal.

Animals↗
PubMed2005

ERP components reflecting stimulus identification: contrasting the recognition potential and the early repetition effect (N250r).

The recognition potential component (RP) in the event-related brain potential (ERP) appears during rapid stream stimulation and has been related to the activation of word form or word meaning. The early repetition effect (ERE/N250r) is observed in repetition priming designs and has been linked to the access to stored representations of the structure of familiar faces and names. Because of the apparent similarities in latency, topography and theoretical interpretation we compared the RP and ERE/N250r within the same rapid stream stimulation design and for the same type of stimulus material: names and faces of famous persons and names and pictures of common objects. Contrasting with RP, the ERE/N250r occurred later and differed in both scalp topography and amplitude patterns across stimulus conditions. Therefore, the ERE/N250r seems to reflect a separate and content-specific stage of information processing, following the RP, which appears to reflect domain-general processes of structural analyses.

Adolescent↗