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PubMed1982

Visual neurones responsive to faces in the monkey temporal cortex.

Of 497 single neurones recorded in the cortex in the fundus of the superior temporal sulcus (STS) of three alert rhesus monkeys, a population of at least 48 cells which were selectively responsive to faces had the following response properties: (1) The cells' responses to faces (real or projected, human or rhesus monkey) were two to ten times as large as those to gratings, simple geometrical stimuli or complex 3-D objects. (2) Neuronal responses to faces were excitatory, sustained and were time-locked to the stimulus presentation with a latency of between 80 and 160 ms. (3) The cells were unresponsive to auditory or tactile stimuli and to the sight of arousing or aversive stimuli. (4) The magnitude of the responses of 28 cells tested was relatively constant despite transformations, such as rotation, so that the face was inverted or horizontal, and alterations of colour, size or distance. (5) Rotation to profile substantially reduced the responses of 21 cells (31 tested). (6) Masking out or presenting parts of the face (i.e. eyes, mouth or hair) in isolation revealed that different cells responded to different features or subsets of features. (7) For several cells, responses to the normal organisation of cut-out or line-drawn facial features were significantly larger than to jumbled controls. These findings indicate that explanations in terms of arousal, emotional or motor reactions, simple visual feature sensitivity or receptive fields are insufficient to account for the selective responses to faces and face features observed in this population of STS neurones. It appears that these neurones are part of a system specialised to code for faces or features present in faces, and it is suggested that damage to this system is related to prosopagnosia, or difficulty in face recognition, in man and to the tameness and social disturbances which follow temporal lobe damage and are part of the Klüver-Bucy syndrome in the monkey.

Animals↗

PubMed1995

Recognition potential latency and word image degradation.

Ten subjects viewed a stream of meaningless background images in which English words occasionally appeared. A subject indicated detection of a word by lifting the index finger of the preferred hand. He received payment based on his performance. A computer program degraded half of the word images, removing a fraction of the lit pixels and replacing them with others that resembled the background images. The recognition potential (RP) was recorded from occipital electrodes. Degrading the word images increased the peak latency of the RP from 231 to 266 msec. The 35 msec difference was comparable to the 36 msec reaction time (RT) difference. At 395 and 431 msec, RT occurred about 165 msec after the RP peak. The results indicated the RP is closely related to a recognition process. The study did not resolve whether it is concurrent with that process or immediately follows it. The RP's sensitivity to image degradation and its short latency make it unlikely that N2 and P3 are concurrent with the recognition process.

Adult↗

PubMed1990

Experimental and theoretical results for some models of random-dot-pattern discrimination.

The popular, but low-power, two-stimulus signal-detection paradigms are extended to generate response-criterion-dependent psychometric functions. Maximumlikelihood estimation within a sufficiently powerful experimental design is described, and theoretical conditions for the resulting psychometric functions to be monotonically increasing are presented. These results are applied to an experiment on the detection of spatial-density differences in briefly presented random-dot patterns. The results confirm, extend, and complement current notions put forth by H.B. Barlow and his co-workers on mechanisms of internal spatial-density representation and the efficiency of intermediate levels of visual processing.

Attention↗

PubMed1983

Visual masking by flickering surrounds.

Observers detected drifting sine-wave gratings presented in a circular 3 dia test field which was surrounded by a 3.25 degrees wide annulus. Forced choice contrast thresholds were measured with surrounds consisting of a steady field of light or uniform sinusoidal flicker. The flickering surround raised detection thresholds only for gratings with spatial frequencies below 2-4 c/deg. Variations on the basic experiment revealed that: (1) low spatial frequency gratings drifting through the surround masked detection of uniform flicker presented to the center; (2) masking did not depend greatly on the drift rate of the test grating but could not be obtained with stationary targets; (3) flicker restricted to either the top or side borders of the test field was a sufficient condition to produce masking; (4) the size of the masking effect decreased with center-surround separation. These results suggest a destructive interaction between transient mechanisms subserving neighboring regions of the visual field.

Form Perception↗

PubMed1991

Visual field asymmetries in pattern discrimination: a sign of asymmetry in cortical visual field representation?

A visual field asymmetry is described relative to the discrimination of mirror symmetric bars with ramp-like luminance profiles. Along the vertical meridian the discrimination is better performed for patterns oriented parallel to the meridian than for patterns oriented orthogonally at all eccentricities tested (2-8 deg). Along the horizontal meridian, the preference for radially oriented stimuli is present at 2 deg from the fovea, but vanishes at larger eccentricities. The meridional asymmetry thus revealed psychophysically may reflect asymmetries in the representation of the vertical and horizontal meridians in the human visual cortex.

Discrimination, Psychological↗

PubMed1996

The coherence of subjective gratings.

Two differently oriented moving gratings when superimposed, are often seen to move coherently in a direction quite different from that of either grating's. By varying the characteristics of the component gratings researchers have been able to study specific aspects of the motion processing mechanisms in the primate visual system. Here we report the results of experiments performed with a class of subjective gratings. We find that observers perceive coherence and are able to accurately report pattern velocity with our stimuli. These results have implications for some key issues concerning strategies and mechanisms for motion estimation in the human visual system.

Discrimination, Psychological↗

PubMedDate not supplied

The neurogeometry of pinwheels as a sub-Riemannian contact structure.

We present a geometrical model of the functional architecture of the primary visual cortex (V1) and, more precisely, of its pinwheel structure. The problem is to understand from within how the internal "imminent" geometry of the visual cortex can produce the "transcendent" geometry of the external space. We use first the concept of blowing up to model V1 as a discrete approximation of a continuous fibration pi: R x P --> P with base space the space of the retina R and fiber the projective line P of the orientations of the plane. The core of the paper consists first in showing that the horizontal cortico-cortical connections of V1 implement what the geometers call the contact structure of the fibration pi, and secondly in introducing an integrability condition and the integral curves associated with it. The paper develops then three applications: (i) to Field's, Hayes', and Hess' psychophysical concept of association field, (ii) to a variational model of curved modal illusory contours (in the spirit of previous models due to Ullman, Horn, and Mumford), (iii) to Ermentrout's, Cowan's, Bressloff's, Golubitsky's models of visual hallucinations.

Animals↗

PubMed1999

Searching for face-specific long latency ERPs: a topographic study of effects associated with mismatching features.

In a previous study [E. Olivares, M.A. Bobes, E. Aubert, M. Valdés-Sosa, Associative ERPs effects with memories of artificial faces, Cogn. Brain Res. 2 (1994) 39-48] we reported the presence of a negativity associated with mismatching features when subjects carried out a face-feature matching task whilst their evoked potentials were recorded. Since the stimuli used were learned faces (realistic drawings), for which the subjects possessed no semantic information or associated verbal labels, the mismatch negativity obtained was considered a face-specific N400. In this work we present a new experiment to study the topographic distribution of these mismatch effects. As in the above-mentioned study, in each trial the subjects observed previously an incomplete (without the eyes/eyebrows fragment) familiar face, which served as a structural context for the face recognition. The face was then completed by grafting either matching (learned) features or mismatching features (from another face). In line with neuropsychological studies on prosopagnosia and electrophysiological findings in humans and non-human primates, we found as one of the most relevant items of data that the most-posterior (principally, left occipital) cortices appear to be a region in which are located the possible neural generators of the negativity associated with the detection of incongruencies in the structure of familiar faces. We also reported a late positivity, distributed in more anterior regions, which follows the mismatch negativity. This complex N-P is interpreted as reflecting a dual process of retrieval and integration of information in memory.

Adult↗

PubMed1996

The CODE theory of visual attention: an integration of space-based and object-based attention.

This article presents a theory that integrates space-based and object-based approaches to visual attention. The theory puts together M.P. van Oeffelen and P.G. Vos's (1982, 1983) COntour DEtector (CODE) theory of perceptual grouping by proximity with C. Bundesen's (1990) theory of visual attention (TVA). CODE provides input to TVA, accounting for spatially based between-object selection, and TVA converts the input to output, accounting for feature- and category-based within-object selection. CODE clusters nearby items into perceptual groups that are both perceptual objects and regions of space, thereby integrating object-based and space-based approaches to attention. The combined theory provides a quantitative account of the effects of grouping by proximity and distance between items on reaction time and accuracy data in 7 empirical situations that shaped the current literature on visual spatial attention.

Attention↗

PubMed1991

A microgenetic study of the Müller-Lyer illusion.

In two experiments a decomposed Müller-Lyer pattern was used to measure the time course of the illusion. A partial report procedure was used to prevent the subjects from focusing only on parts of the pattern and to maximize visual processing. The Müller-Lyer figure was decomposed into two parts, its angles and its line. A configuration of three pairs of angles, each corresponding to a row in the usual partial report arrangement, was used. A line that did or did not fit the gap was shown with a variable delay (interstimulus interval, ISI). By this procedure the relevant row (line gap) was cued. The subject had to decide whether the line fitted or was too short/long. Two exposure times for the angles were used, 50 or 200 ms in one experiment and 50 or 500 ms in the other. The result of the first experiment, with outward-pointing fins, was a stable illusion for all values of ISI (25-400 ms) and all exposure times, with one significant exception: exposure for 50 ms with an ISI of 50 ms yielded an illusion peak. It was shown that this was not caused by a reduction in length-discrimination performance. In the second experiment, with inward-pointing fins, no such peak occurred. There was only a tendency for the illusion to vanish with zero ISI. The results are discussed with respect to 'global to local' theories of visual processing.

Distance Perception↗

PubMed2006

Effect of colour pop-out on the recognition of letters in crowding conditions.

The crowding effect of adjacent objects on the recognition of a target can be reduced when target and flankers differ in some feature, that is irrelevant to the recognition task. In this study, the mechanisms of this effect were explored using targets and flankers of the same and different colours. It was found that facilitation nearly equal to that of differently coloured targets and flankers can be observed with a differently coloured background blob in the location of the target. The different-colour effect does not require advance knowledge of the target and flanker colours, but the effect increases in the course of three trials with constant mapping of colours. The results are consistent with the notion of exogenous attention that facilitates the processing at the most salient locations in the visual field.

Color Perception↗

PubMed1996

Laboratory studies of antipredator behavior in the Mongolian gerbil (Meriones unguiculatus): factors affecting response attenuation with repeated presentations.

A series of experiments was conducted to study the properties of the attenuation of responding to repeated presentation of overhead visual transients in the gerbil (Meriones unguiculatus). Results suggest that this attenuation consists of habituation to the repeated association of a potentially threatening sensory stimulus with an increasingly familiar spatial context. The results of these experiments further suggest that the likelihood of eliciting fleeing is a conjoint function of the degree of risk posed by an overhead sensory transient and the degree of safety that is to be gained by fleeing. Results are discussed in the context of the ecology of predator recognition and the structural organization of the rodent visual system.

Animals↗

PubMed2002

[Visual representation for object recognition and visuomotor control: an evaluation using two orientation matching tasks].

This study examined effects of binocular information on visual orientation perception and visuomotor control of a hand using two tasks in which observers matched the orientation of two rods. On the perceptual matching task, they were asked to make a visual judgment of the orientation of two rods. On the motor (preshaping) task, they were asked to move a rod which they can not see by their hands so as to match the orientation of the presented rod. Decrement in availability of binocular cues produced considerable disruptions on the motor task, while did less disruptions on the perceptual matching task. Hence binocular information seemed to play a critical role on the motor task. These results are consistent with recent suggestions that visual perception and visually guided motor control should be mediated by separate visual pathways.

Adult↗

PubMed1991

Event-related brain potentials as indicators of visual recognition and detection of criminals by their use.

An event-related potential (ERP) was recorded, using photographs as stimuli, in 12 subjects for attended, 9 subjects for non-attended conditions and 14 subjects for a simulated criminal investigation. An ERP was detected only when a subject recognized a familiar image (target) mixed with other, unfamiliar images (non-target), regardless of whether he was asked to attend to or neglect the target image. ERPs in the subject who watched each picture but tried to ignore the relevant picture (non-attended) were more activated at the parietal region than at the central region, in contrast with ERPs in the subjects who paid attention to each picture without trying to ignore the relevant picture (attended). In the simulated criminal investigation, only a simulated thief, but not a simulated innocent subject elicited ERP only after the picture of a criminal site or thing was intermingled with pictures bearing no relationship to the crime. These findings indicate that the ERP using photographs as stimuli is useful as an objective indicator of crime-relevance.

Adult↗

PubMed1994

Stability from variation: the case of face recognition. The M.D. Vernon Memorial Lecture.

A theme running through M.D. Vernon's discussions of visual perception was the key question of how we perceive a stable world despite continuous variation. The central problem in face identification is how we build stable representations from exemplars that vary, both rigidly and non-rigidly, from instant to instant and from encounter to encounter. Experiments reveal that people are rather poor at generalizing from one exemplar of a face to another (e.g. from one photograph to another showing a different view or expression) yet highly accurate at encoding precise details of faces within the range shown by several slightly different exemplars. Moreover, provided instructions do not encourage subjects explicitly to attend to the way that different exemplars vary, faces are retained in a way that enhances familiarity of the prototype of the set, even if this was not presented for study. It is suggested that our usual encounters with continuous variations of facial expressions, angles, and lightings provide the conditions necessary to establish stable representations of individuals within an overall category (the face) where all members share the same overall structure. These observations about face recognition would probably not have come as any great surprise to Maggie Vernon, many of whose more general observations about visual perception anticipated such conclusions.

Attention↗

PubMed1991

Perception and action in 'visual form agnosia'.

A single case study of a patient with 'visual form agnosia' is presented. A severe visual recognition deficit was accompanied by impairments in discriminating shape, reflectance, and orientation, although visual acuity and colour vision, along with tactile recognition and intelligence, were largely preserved. Neuropsychological and behavioural investigations have indicated that the patient is able to utilize visual pattern information surprisingly well for the control of hand movements during reaching, and can even read many whole words, despite being unable to make simple discriminative judgements of shape or orientation. She seems to have no awareness of shape primitives through Gestalt grouping by similarity, continuity or symmetry. It is proposed that many of these perceptual disorders might be the combined result of (1) a selective loss of the cortical elaboration of the magnocellular visual processing stream, and (2) a selective output disconnection from a central processor of visual boundaries and shape primitives in the occipital cortex.

Adult↗

PubMed2005

Dynamic brain activation patterns for face recognition: a magnetoencephalography study.

The present study used magnetoencephalography (MEG) to investigate the spatiotemporal profile of neurophysiological activity associated with recognition of recently encountered human faces in seventeen healthy right-handed adults. Activity sources modeled as instantaneous equivalent current dipoles were found in ventral occipito-temporal regions during the early stages of stimulus processing and in lateral temporal cortices during later stages. Hemispheric asymmetries in regional activity were restricted to ventral occipitotemporal areas. The magnitude of magnetic flux originating in these regions was greater in the right hemisphere during the first 350 ms post-stimulus onset. In addition, the duration of neurophysiological activity was greater in the right hemisphere after 600 ms post-stimulus onset. The results indicate right hemisphere predominance in the degree of engagement of neurophysiological processes involved in both the pre- and post-recognition phases of face processing.

Adolescent↗

PubMed2000

Developmental and lesion effects in brain activation during sentence comprehension and mental rotation.

The development of neurocognitive networks was examined in 2 cognitive paradigms: auditory sentence comprehension and mental rotation of alphanumeric stimuli. Patterns of brain activation were measured with whole brain echoplanar functional magnetic resonance imaging at 3 Tesla in 5 adults (20-28 years old), 7 children (9-12 years old), and 6 pediatric patients (9-12 years old) with perinatal strokes or periventricular hemorrhages. Healthy children and adults activated similar neurocognitive networks, but there were developmental differences in the distribution of activity across these networks. In the sentence task, children showed more activation in the inferior visual area suggesting an imagery strategy rather than a linguistic strategy for sentence processing. Furthermore, consistent use of a sentence comprehension strategy, whether correct or incorrect as compared to chance performance, was associated with greater activation in the inferior frontal area (Broca's) in both children and pediatric patients. In the mental rotation task, healthy adults showed more activation in the superior parietal and middle frontal areas and less activation in the supramarginal gyrus, suggesting adults were primarily engaged in visual-spatial manipulation and less engaged in the recognition of noncanonical views of stimuli. The pediatric patients showed patterns of activation consistent with organization of cognitive processing into homologous areas of the contralateral hemisphere.

Adult↗