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PubMed1995

Pattern reversal visual evoked potentials in patients with hemineglect syndrome.

To investigate basic visual information processing in patients with hemineglect syndrome, pattern reversal visual evoked potentials (VEPs) were recorded in 21 brain-injured patients (10 with neglect symptoms) and 6 healthy subjects. The stimulus was a checkerboard which varied in check size or temporal frequency, presented to the left or right visual field. VEPs recorded in neglect patients to stimuli presented in the subjectively neglected left visual field were comparable in amplitude to those recorded to stimuli presented in the normal right visual field. For stimuli presented centrally, there was no difference in VEPs between neglect patients and brain-damaged patients without neglect. These results support neuropsychological theories that state that the neglect syndrome is more closely related to deficits at post-sensory levels than to impairments in basic visual processing. Some evidence, however, suggests that the nature of the interaction between the two visual hemi-fields may also be altered in neglect patients.

Aged↗
PubMed1997

The influence of center of mass effect on the distribution of spatial attention in the vertical and horizontal dimensions.

Normal subjects attend toward the middle of grouped items (center of mass effect). In order to learn if mass effect could influence performance on line bisection tasks and if the spatial orientation of the line (vertical vs. horizontal) could influence center of mass effect, we administered bisection tasks to 16 normal subjects using either lines composed of two unequal segments (one thick and one thin) or unsegmented lines. When the longer segment was to the right, left, up, or down, subjects erred by deviating their bisection toward the longer segment (center of mass effect). Our results demonstrate that the center of mass effect can be seen with bisection tasks and is greater in the vertical than in the horizontal dimension.

Adult↗
PubMed2002

Orthographic neighborhood effects in the right but not in the left cerebral hemisphere.

Two lexical decision experiments investigated orthographic neighborhood effects in the hemispheres. In the first experiment, lexical decision was affected by orthographic neighborhood size when stimuli were presented to the right hemisphere (RH) but not to the left hemisphere (LH). In a four-field masked-prime lexical decision task (Experiment 2), a larger shared orthographic neighborhood between prime and target facilitated lexical decision in the RH but not in the LH. The patterns of activation invoked in the two cerebral hemispheres by a written word and its orthographic neighbors may be qualitatively different.

Adolescent↗
PubMed2002

Word length and orthographic neighborhood size effects in the left and right cerebral hemispheres.

Previous studies have reported an interaction between visual field (VF) and word length such that word recognition is affected more by length in the left VF (LVF) than in the right VF (RVF). A reanalysis showed that the previously reported effects of length were confounded with orthographic neighborhood size (N). In three experiments we manipulated length and N in lateralized lexical decision tasks. Results showed that length and VF interacted even with N controlled (Experiment 1); that N affected responses to words in the LVF but not the RVF (Experiment 2); and that when length and N were combined, length only affected performance in the LVF for words with few neighbors.

Adolescent↗
PubMed1997

Metamemory Assessment and Memory Behavior in a Simulated Memory Professional Task

This study investigated metamemory knowledge related to a professional task and the relationships between metamemory knowledge and memory performance in a simulated professional task, which was a beverage-service job with memory constraints changes. Metamemory knowledge was assessed by interviewing student waiters about hypothetical recall tasks concerning lists of beverages. They then carried out a simulated beverage-service task, including a first paired-associate recall (beverage-customer), then a global recall (order to the bartender), followed by a second paired-associate recall (beverage-customer). Memory constraints were manipulated with table size and perceptive cues. Results revealed that in metamemory knowledge, task-strategy, and strategy were the only variables that were related. Metamemory knowledge produced an effect on all memory performance, whatever the constraints were. The implications of these findings for professional training are discussed in terms of strategy instruction for enhancing professional performance when memory demands change in the work environment. Copyright 1997Academic Press

Journal Article↗
PubMed1996

Developmental trends in haptic and visual free classifications: influence of stimulus structure and exploration on decisional processes.

This research explores whether the differences observed between the development of visual and haptic free classifications (Berger & Hatwell, 1995) depend from the nature of the information available at different levels of processing. Two experiments are reported, in which subjects were presented with a free classification task using tetrads in the haptic modality (Experiment 1) or in the visual modality (Experiment 2). The type of response elicited (dimensional vs global) was studied as a function of the nature of exploration in Experiment 1 and as a function of the stimulus components' presentation in Experiment 2. Results showed that both the characteristics of exploration and the presentation of the dimensions tended to modify the type to response elicited. The observed modifications, however, were shown to be of different nature in children and in adults. These results were discussed with reference to the development of the valued classification criteria, which could depend on low-level information in young children and on higher-level information in adults.

Adult↗
PubMed1997

Development of size modification of human figure drawings in spatial axes systems of varying complexity.

In the present study, intraindividual development of the ability to modify the size of the human figure drawing was investigated. In a longitudinal data set with repeated measurement at ages 7, 9, and 12 it was shown that size was reduced between 7 and 9 years. Three factors were found to be responsible for size variation of the human figure drawing: The larger the figure initially, the more complex the level of the spatial axes system and the more persons in the picture, the greater size reduction.

Age Factors↗
PubMed1998

Developmental changes in the effect of dimensional salience on the discriminability of object relations.

Two experiments explored three issues regarding the nature of perceptual development in 5- and 10-year-old children and adults: (a) the role of featural discriminability, (b) the facilitatory role of identity relations, and (c) the role of salience in a task context designed to minimize the likelihood of attention-switching between dimensions during perceptual processing. In Experiment 1, perceptual salience for size and achromatic color dimensions was determined for each participant based on their best-fitting triad classification task response pattern. These same persons participated in Experiment 2, which employed a speeded visual discrimination task. The primary finding was that preassessed salience significantly influenced the 5-year-olds' ability to discriminate between two objects, while salience did not affect 10-year-olds' or adults' response times. The results of both experiments support Odom & Cook's (1992) differential-sensitivity view of perceptual development, but these data contribute important information by showing that salience effects in perceptual processing occur even when the observer is selectively attending to a particular dimension, likely during early component processes prior to classification.

Adult↗
PubMed1999

Developmental patterns in the understanding of social and physical transitivity.

Transitive inferences using both a linear dimension (A is longer than B) and a nonlinear dimension (A and B are friends) were examined. In Study 1, 6- to 9-year-old children received two problems of each kind. Performance showed similar developmental progressions but nonsignificant correlations between the two tasks. Study 2 extended these results by modifying the linear transitivity problem and adding variation in both context and type of social relation. Children 7, 9, and 11 years of age were given problems requiring judgments about friendship and about nonfriends (children who were quarreling with each other) in two different social contexts. No correlations were found between social judgments and judgments concerning length. Both type of relation and context influenced judgments about social relations. These results suggest that children possess two distinct strategies for making transitive judgments that correspond to the logical structure of the underlying relations.

Child↗
PubMed2002

Hemispheric asymmetry in global/local processing: effects of stimulus position and spatial frequency.

We examined the neural mechanisms of functional asymmetry between hemispheres in the processing of global and local information of hierarchical stimuli by measuring hemodynamic responses with functional magnetic resonance imaging (fMRI). In a selective attention task, subjects responded to targets at the global or local level of compound letters that were (1) broadband in spatial-frequency spectrum and presented at fixation; (2) broadband and presented randomly to the left or the right of fixation; or (3) contrast balanced (CB) to remove low spatial frequencies (SFs) and presented at fixation. Central broadband stimuli induced stronger activation in the right middle occipital cortex under global relative to local attention conditions but in the left inferior occipital cortex, stronger activation was induced under local relative to global attention conditions. The asymmetry over the occipital cortex was weakened by unilateral presentation and by contrast balancing. The results indicate that the lateralization of global and local processing is modulated by the position and SF spectrum of the compound stimuli. The global attention also produced stronger activation over the medial occipital cortex relative to the local attention under all the stimulus conditions. The nature of these effects is discussed.

Adult↗
PubMed2002

Functional imaging of visuospatial processing in Alzheimer's disease.

Alzheimer's disease (AD) is known to cause a variety of disturbances of higher visual functions that are closely related to the neuropathological changes. Visual association areas are more affected than primary visual cortex. Additionally, there is evidence from neuropsychological and imaging studies during rest or passive visual stimulation that the occipitotemporal pathway is less affected than the parietal pathway. Our goal was to investigate functional activation patterns during active visuospatial processing in AD patients and the impact of local cerebral atrophy on the strength of functional activation. Fourteen AD patients and fourteen age-matched controls were measured with functional magnetic resonance imaging (fMRI) while they performed an angle discrimination task. Both groups revealed overlapping networks engaged in angle discrimination including the superior parietal lobule (SPL), frontal and occipitotemporal (OTC) cortical regions, primary visual cortex, basal ganglia, and thalamus. The most pronounced differences between the two groups were found in the SPL (more activity in controls) and OTC (more activity in patients). The differences in functional activation between the AD patients and controls were partly explained by the differences in individual SPL atrophy. These results indicate that parietal dysfunction in mild to moderate AD is compensated by recruitment of the ventral visual pathway. We furthermore suggest that local cerebral atrophy should be considered as a covariate in functional imaging studies of neurodegenerative disorders.

Aged↗
PubMed2000

Regulatory action criteria for filth and other extraneous materials. .IV. Visual detection of hair in food.

Under Section 402(a)(3) of the Food, Drug and Cosmetic Act the distribution of foods which may contain repulsive or offensive matter, considered as filth, is prohibited. Filth includes contaminants such as rat, mouse, and other animal hairs and excreta; whole insects, insect parts, and excreta; and other extraneous materials which, because of their repulsiveness, would not knowingly be eaten or used. The presence of such filth renders food adulterated. Some foods, even when produced under good manufacturing practice, contain low levels of natural or unavoidable defects such as dirt, insect parts, and hair that are not hazardous to health. Although the health hazard is eliminated, most consumers find the presence of "any" visible filth contaminant such as hair in a food product objectionable. The objective of this study was to determine when a defect (hair) in a food (mushrooms) is visible to a consumer by testing the visual acuity of a consumer panel under controlled laboratory conditions. Of the panelists participating in the study, when presented with a single hair on a flat surface with a solid-colored background, 27% were able to detect a 1-mm hair, 58% were able to detect a 3-mm hair, and 75% were able to detect a 10-mm hair. Twenty-five percent of the panelists surveyed were able to detect a 5- or 10-mm hair on sliced, canned mushrooms. The experimental design and results of this study are discussed.

Adult↗
PubMed1992

Development of human precision grip. III. Integration of visual size cues during the programming of isometric forces.

Recent evidence has shown that visual and haptical size information can be used by adults to estimate the weight of the object, forming the basis of the force programming during precision grip (Gordon et al. 1991a, b,). The present study examined the development of the capacity to use visual size information. In the first experiment, 30 children (age 1-7 years) and 10 adults performed a series of lifts with two boxes presented in an unpredictable order. The boxes were equal in weight but unequal in size and were attached to an instrumented grip handle which measured the employed grip force, load force, position and their corresponding time derivatives. The isometric force development was not influenced by the box size before the age of 3. However, the children aged 3 years and older demonstrated greater visual influences on the force programming than adults. To determine more precisely when children began to use visual size information, a second experiment in which the size and weight covaried was performed on 15 children. Children still did not use the size information during the force programming until the later half of the third year. It is concluded that this ability, probably involving associative transformations between the size and weight of objects, emerges around one year after anticipatory control based on somatosensory information pertaining to the weight of the object.

Adolescent↗
PubMed1996

Size illusion influences how we lift but not how we grasp an object.

Reaching out for an object is often described as consisting of two components that are based on different visual information. Information on the object's position and orientation guides the hand to the object, while information on the object's shape and size determines how the fingers move relative to the thumb to grasp it. We propose an alternative description, which consists of determining suitable positions on the object-on the basis of its shape, surface texture, and so on- and then moving one's thumb and fingers to these positions. This could lead to the same performance without requiring distinct visual information on the object's orientation or size. If so, an illusory change in size need not influence the distance between thumb and fingers when reaching out for an object. However, as the object's size is used to estimate its weight, the illusory change in size should influence the force that is exerted to lift the object. To find out whether this is so, eight subjects were asked to pick up brass disks from a fixed position straight in front of them. The illusory change in size was brought about by presenting five converging lines in two different configurations under the disks. As predicted, the illusion influenced the force used to lift the disks, but not the distance between the subjects' thumbs and fingers when reaching for the disks.

Hand Strength↗
PubMed1993

Reach to grasp: the natural response to perturbation of object size.

This study assessed the reach to grasp movement and its adaptive response to a perturbation of object size. In blocked trials, subjects (n = 12) were instructed to reach 35 cm to grasp and lift a small- (0.7 cm) or large-diameter (8 cm) cylinder. Under an unconstrained condition (condition 1), no instructions as to the type of grasp to adopt were given. Subjects thus naturally used a precision grip (PG) for the small cylinder and whole hand prehension (WHP) for the large cylinder. Under condition 2, subjects were instructed to utilize a PG for grasps of both the large and small cylinders. For condition 3, the instruction was to use WHP irrespective of object size. Kinematic organization was determined with analysis of the recordings of active markers placed on the wrist, thumb, and three fingers. For condition 1 the results showed a temporal arrangement of both components (transport and manipulation) which differed from that of conditions 2 and 3. In perturbed trials, illumination shifted from the small to large cylinder or vice versa. With condition 1, subjects automatically switched from one grasp to another with no or little increase of movement duration. This was generally achieved by an earlier temporal setting of peak wrist deceleration. For conditions 2 and 3, where a change of aperture was required, movement duration was prolonged without adaptation of earlier transport component parameters. It is concluded that the adaptive responses to a change of distal patterning also affect the organization of the proximal component. Assessment of grasps constrained by instructions may lead to interpretations of central control of the reach to grasp movement which differ from those obtained by assessing more natural prehensile patterns.

Adolescent↗
PubMed1984

Effect of target size on spatial and temporal characteristics of a pointing movement in man.

The effects of constraints related to movement accuracy on the spatial and temporal characteristics of pointing movements of the arm to a target were investigated. It was found that movement time increased, even at slow speeds, when target size decreased. Spatial variability of the trajectory of the index finger was also reduced, but only in proximity to the target, when higher accuracy was demanded while variability of motion at the wrist showed little change. The effect of varying the angular orientation of the target on the trajectories of the wrist and finger was also investigated. The data support the hypothesis that motion at the shoulder and elbow joints, which is closely linked, is determined primarily by target position while motion at the wrist joint, which is only loosely coupled to the motion at the more proximal joints, is related principally to the angular orientation of the target in space. The data also suggest that wrist motion is controlled separately from motion at the more proximal joints.

Adult↗