PubMed Health⌕ Search

Biomedical subjects

P J Benson

Publications and source records attributed to P J Benson.

At least 19 recordsLinked to original sources
PubMed2001

Recognizing one's own face.

We report two studies of facial self-perception using individually tailored, standardized facial photographs of a group of volunteers and their partners. A computerized morphing procedure was used to merge each target face with an unknown control face. In the first set of experiments, a discrimination task revealed a delayed response time for the more extensively morphed self-face stimuli. In a second set of experiments, functional magnetic resonance imaging (fMRI) was used to measure brain activation while subjects viewed morphed versions of either their own or their partner's face, alternating in blocks with presentation of an unknown face. When subjects viewed themselves (minus activation for viewing an unknown face), increased blood oxygenation was detected in right limbic (hippocampal formation, insula, anterior cingulate), left prefrontal cortex and superior temporal cortex. In the partner (versus unknown) experiment, only the right insula was activated. We suggest that a neural network involving the right hemisphere in conjunction with left-sided associative and executive regions underlies the process of visual self-recognition. Together, this combination produces the unique experience of self-awareness.

Adult↗
PubMed2001

Web alert. Development.

A selection of World Wide Web sites relevant to papers published in this issue of Current Opinion in Neurobiology.

Internet↗
PubMed2001

New-onset absence status epilepsy presenting as altered mental status in a pediatric patient.

Absence status epilepsy (ASE) is an uncommon seizure disorder in children. The primary presentation of new-onset ASE in a pediatric patient is an unusual cause of altered mental status in the emergency department. We describe a previously healthy 8-year-old child who presented with an acutely altered mental state. The patient was awake but confused, with a fluctuating level of alertness and an inability to perform simple routine tasks. The results of general physical and neurologic examination, with the exception of mental status, were normal. Head computed tomography and laboratory test results were normal. Electroencephalographic testing revealed seizure activity consistent with ASE. Administration of intravenous diazepam caused cessation of seizure activity and a return to the patient's baseline mental function. Although rare, ASE should be considered in the differential diagnosis of altered mental status in children.

Anticonvulsants↗
PubMed2000

Towards a functional neuroanatomy of self processing: effects of faces and words.

We studied the neural correlates of self vs. non-self judgements using functional magnetic resonance imaging (fMRI). Individually tailored faces and personality trait words were used as stimuli in three experiments (exp.). In the first two experiments, brain activation was measured while subjects viewed morphed versions of either their own (self face exp.) or their partner's face (partner's face exp.), alternating in blocks with presentation of an unknown face. In the self face exp. right limbic areas (hippocampal formation, insula, anterior cingulate), the right middle temporal lobe, left inferior parietal and left prefrontal regions showed signal changes. In the partner's face exp., only the right insula was activated. In the third exp., subjects made decisions about psychological trait adjectives previously categorized as describing their own attributes. Activation was present in the precuneus, the left parietal lobe, left insula/inferior frontal gyrus and the left anterior cingulate. A reaction time advantage was present when subjects responded to self-relevant words. The main area with signal changes during self-reference processing, regardless of the type of stimulus, was the left fusiform gyrus. The self-relevant stimuli engaged to a differential extent long term and working memory, semantic and emotional processes. We suggest that regions activated by these stimuli are engaged in self-processing.

Adult↗
PubMed1999

Stages in motion processing revealed by the ocular following response.

Motion perception and associated involuntary eye movements depend on factors such as the physical attributes of the stimulus and visual attention. Cues from spatial changes in luminance (first-order motion in the Fourier domain) or more complicated transitions involving two-dimensional patterns (second-order, non-Fourier) require rather different kinds of analyses to detect their net motion. During a fixation task we monitored eye movements induced by the onset of motion to examine the functional properties of the monkey cortical motion processing system. Eye movement velocity was indistinguishable to first- and second-order motion; concomitant response latency confirmed an additional calculation is required to detect the direction and velocity of second-order motion.

Analysis of Variance↗
PubMed1999

Cortical evoked potentials due to motion contrast in the blind hemifield.

Subcortical visual inputs to motion-selective cortex in primates survive after damage to the primary visual cortex (area 17/V1). Activation of human motion cortex was examined using scalp electrodes in a V1-damaged hemianope. Blind field motion-onset visual evoked potentials (VEPs) shared many of the characteristics associated with sighted vision but were smaller in amplitude and had longer latencies. The representative negative wave (C(II) peak) showed typical dependency on stimulus contrast, its peak latency increased and amplitude decreased as contrast decreased, reflecting the difficulty with which directional information could be detected. VEPs were present at contrasts below 25% when blind field motion was imperceptible even though direction guessing was paradoxically accurate. Subcortical inputs to motion cortex contribute to visual experience but not to conscious perception.

Adult↗
PubMed1999

Grating and plaid chrominance motion influences the suppressed ocular following response.

Involuntary eye movements to foveal stimulation were measured in a monkey while it performed a fixation task. Second-order plaid motion generated higher velocities of eye movements than did first-order gratings, yet the latency of the early following response was no different for grating or plaid motion. Nevertheless, early suppressed ocular following responses to isoluminant motion continue to be titrated by stimulus velocity and spatial frequency. Motion defined by 60% luminance contrast gratings and plaids generated a motion signal gain of 60% over chrominance motion. The 20% longer latency of eye movements to chrominance motion may reflect the longer conduction latency of the parvocellular channel and an additional stage in cortical processing en route to motion areas and eye movement control.

Analysis of Variance↗
PubMed1999

A means of measuring facial expressions and a method for predicting emotion categories in clinical disorders of affect.

In a radical departure from traditional approaches, it was found that only seven measures of facial expression are required to accurately distinguish between normal displays of happiness, sadness, fear, disgust, surprise and anger. Using these prototypical emotion categories it has been shown that particular facial areas in Parkinson's disease (PD) are responsible for communication of blended, rather than the intended expressions. We consider how assessment of facial expressions made in this way can be used to quantify progress of therapeutic intervention in PD. We also show that in gaining a better understanding of the structure of emotion categories, advances in understanding need not be overshadowed by methodological complexity. The simplicity of the approach presented here leads us to propose that the perceptual and behavioural aspects of affective disorders can now be tackled in a unified manner.

Adult↗
PubMed1999

More about brows: how poses that change brow position affect perceptions of gender.

The speeded categorisation of gender from photographs of men's and women's faces under conditions of vertical brow and vertical head movement was explored in two sets of experiments. These studies were guided by the suggestion that a simple cue to gender in faces, the vertical distance between the eyelid and brow, could support such decisions. In men this distance is smaller than in women, and can be further reduced by lowering the brows and also by lowering the head and raising the eyes to camera. How does the gender-classification mechanism take changes in pose into account? Male faces with lowered brows (experiment 1) were more quickly and accurately categorised (there was little corresponding 'feminisation' of raised-brow faces). Lowering gaze had a similar effect, but failed to interact with head lowering in a simple manner (experiment 2). We conclude that the initial classification of gender from the facial image may not involve normalisation of the face image to a canonical state (the 'mug-shot view') for expressive pose (brow movement and direction of gaze). For head pose (relative position of the features when the face is not viewed head-on), normalisation cannot be ruled out. Some perceptual mechanisms for these effects, and their functional implications, are discussed.

Adolescent↗
PubMed1999

Categorical perception of face actions: their role in sign language and in communicative facial displays.

Can face actions that carry significance within language be perceived categorically? We used continua produced by computational morphing of face-action images to explore this question in a controlled fashion. In Experiment 1 we showed that question--type--a syntactic distinction in British Sign Language (BSL)--can be perceived categorically, but only when it is also identified as a question marker. A few hearing non-signers were sensitive to this distinction; among those who used sign, late sign learners were no less sensitive than early sign users. A very similar facial-display continuum between "surprise" and "puzzlement" was perceived categorically by deaf and hearing participants, irrespective of their sign experience (Experiment 2). The categorical processing of facial displays can be demonstrated for sign, but may be grounded in universally perceived distinctions between communicative face actions. Moreover, the categorical perception of facial actions is not confined to the six universal facial expressions.

Adult↗
PubMed1999

A computer-graphic technique for the study of body size perception and body types.

We present a novel approach for measuring body size estimation in normal and eating-disordered women and men. Clinical categories of body types were used as prototypes. By comparing the subjective appearance of a person's body with prototypes, we can understand how different attributes of his or her body shape contribute to perception of body size. After lifelike random distortions have been applied to parts of their body image, individuals adjust their body shapes until they converge on their perceived veridical appearance. Exaggeration and minimization of particular body areas measured with respect to their true shape and with different prototypes can be expressed as numerical deviations. In this way, perceived body size and body attractiveness can be appraised during the course of diagnosis and treatment of eating disorders.

Body Constitution↗
PubMed1999

Enhancing images of facial expressions.

Facial images can be enhanced by application of an algorithm--the caricature algorithm--that systematically manipulates their distinctiveness (Benson & Perrett, 1991c; Brennan, 1985). In this study, we first produced a composite facial image from natural images of the six facial expressions of fear, sadness, surprise, happiness, disgust, and anger shown on a number of different individual faces (Ekman & Friesen, 1975). We then caricatured the composite images with respect to a neutral (resting) expression. Experiment 1 showed that rated strength of the target expression was directly related to the degree of enhancement for all the expressions. Experiment 2, which used a free rating procedure, found that, although caricature enhanced the strength of the target expression (more extreme ratings), it did not necessarily enhance its purity, inasmuch as the attributes of nontarget expressions were also enhanced. Naming of prototypes, of original exemplar images, and of caricatures was explored in Experiment 3 and followed the pattern suggested by the free rating conditions of Experiment 2, with no overall naming advantage to caricatures under these conditions. Overall, the experiments suggested that computational methods of compositing and caricature can be usefully applied to facial images of expression. Their utility in enhancing the distinctiveness of the expression depends on the purity of expression in the source image.

Adult↗
PubMed1998

Short-latency ocular following of motion by monkeys during a fixation task.

Short-latency ocular following responses in monkeys, induced by first- and second-order motion during a fixation task, were sensitive to stimulus size, retinal eccentricity and motion duration. Latency of eye movements was no different for first- or second-order motion and simply marked the occurrence of movement in the visual field. Second-order motion produced higher velocity eye movements than did first-order motion. The velocity of eye movements was influenced by the orientation of second-order pattern components as well as their conspicuous energy. Even when partially suppressed by a fixation task, involuntary eye movements during the initial pursuit remain sensitive to several properties of visual motion.

Analysis of Variance↗