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PubMed2001

Attention and size in a global/local task.

Two-letter stimuli, consisting of one small letter inside a much larger one (in Experiments 1A, 1B, and 2) or inside a "blob" (in Experiment 3), were used to examine the role of size difference in global/local tasks. The small letter was placed at locations that avoided contour interactions. The results showed no identity interference, in that the specific identity of the large letter did not differentially affect identification of the small one. However, there was evidence of global advantage, in that the presence of a large letter hindered identification of the small one. The magnitude of the global advantage effect, as measured by the difference in performance between the small-single and small-embedded conditions, was largest (about 200 ms reaction time (RT) difference) when the large letters were the same as the small ones, lower (a 63 ms difference in Experiment IB, and 89 ms in Experiment 2) when the large letters were unrelated to the small ones, and lowest (a 25 ms difference) when the large stimuli were blobs. It is proposed that the amount of interference depends on the overlap between the features of the large stimuli, as a set, and those of the small ones, also as a set.

Adult↗
PubMed2002

Memory search instead of template matching? Representation-guided inference in same-different performance.

Data from two experiments using transformationally related patterns forming rotation/reflection equivalence sets of different size's are presented. In a same-different experiment, two successively presented patterns were judged as same when they belonged to the same equivalence set, and different otherwise. Reaction times depended on the size of the equivalence set to which the patterns belong. This was the case, even when they were physically identical. Results are interpreted within a framework of memory-guided inference which assumes that participants perform a memory search within the equivalence sets activated by the compared patterns instead of comparing these directly. In Experiment 2, goodness ratings were required which are shown to reflect a second component of information processing.

Adolescent↗
PubMed1997

Distorted visual feedback effects on drawing in Parkinson's disease.

We investigated the effects of distorted visual feedback on the drawing performance of a group with Parkinson's disease (PD) and a control group. Twenty older healthy adults and 20 PD patients copied figures onto a digitizer tablet with a pen under normal and distorted visual feedback conditions. PD patients were less able than controls to adjust the size of their drawing to compensate for distortions in visual feedback. The effect was particularly pronounced when patients were required to draw smaller than normal. Nevertheless, with practice. PD patients showed a similar degree of improvement in size as controls, although they did not match the control group's level of performance. Overall, these findings support the notion that PD may have specific difficulty adjusting to a change in gain (or discrepancy) between visual and kinesthetic feedback when they must alter the size of their drawing. These findings point to the putative role of the basal ganglia in adjusting for the intermodal discrepancy between sensory feedback, and re-scaling the size of movements.

Aged↗
PubMed1998

On the independence of modality effects and end-term and distance effects in episodic comparative judgement: dissociations of errors and reaction times.

The experiments reported in this paper explore the effect of modality variations on end-term and distance effects in an episodic comparative judgement task. In each experiment, subjects were to store serial orders of objects on a size dimension. Memory was tested after a brief retention interval by a comparative judgement task, in which subjects were presented with two elements of an order and had to point to the formerly larger one. Regarding the response times, we hypothesized that modality variations affect speed of stimulus identification and code access processes. We further hypothesized that distance variations and end-term variations affect processing components that are independent of the component affected by the modality variation. Finally, we assumed that end-term and distance effects interact in a predictable way, because they mirror competing response selection strategies. The latency data clearly support these hypotheses. As regards the accuracy data, we argued that modality and end-term effects, if they show up within the accuracy data, very likely have a different basis than the effects within the latency data. Again, the data support this assumption showing clear dissociations of accuracy and latency data. With respect to the stimulus modality variation, the whole data pattern shows that explanations which rely on modality-specific codings are not justifiable.

Adult↗
PubMed2003

Comparison of digital photography to weighed and visual estimation of portion sizes.

OBJECTIVE: The primary goal was to test the validity of digital photography for measuring food portion sizes compared with weighed foods and with direct visual estimation. SAMPLES: A total of 60 test meals consisting of 10 different portion sizes from six different university cafeteria menus were prepared and weighed. DESIGN: Food selections and plate waste, as estimated by digital photography and direct visual estimation, were compared with weighed foods. For each method, three observers independently estimated portion sizes of each food. Observers expressed the portion sizes as a percentage of a standard serving. These percentages were multiplied by the weight of the standard portion to yield estimated weights. Statistical analyses To test validity, the estimates of food weights derived from both methods were compared with weighed foods using correlations and were compared with each other using Bland-Altman regression analysis. RESULTS: For the digital photography and direct visual estimation methods, estimates of the portion sizes for food selections, plate waste, and food intake were highly correlated with weighed foods. Both methods tended to yield small overestimates or underestimates. Bland-Altman regression found the two estimation methods to yield comparable results (bias less than 1.5 g). APPLICATIONS/CONCLUSIONS: These findings support the validity of the digital photography method for measuring portion sizes. Digital photography may be most useful for measuring food intake in settings that allow for the direct observation of food selections and plate waste but require minimum disruption of the eating environment, and allow unhurried estimates of portion sizes.

Diet Records↗
PubMed1999

Reduced P300 responses in criminal psychopaths during a visual oddball task.

BACKGROUND: Clinicians have long recognized that psychopaths show deficits in cognitive function, but there have been few experimental studies exploring these deficits. We present here the first in a series of event-related potential (ERP) experiments designed to elucidate and characterize the neural correlates of cognitive processes of psychopaths. METHODS: We recorded ERPs from a topographic array from 11 psychopathic and 10 nonpsychopathic prison inmates, assessed with the Hare Psychopathy Checklist-Revised, during performance of a visual oddball task. ERPs to target (25% of trials) and nontarget (75% of trials) visual stimuli were analyzed. RESULTS: Consistent with previous research, there were no group differences in the latency or amplitude of the ERPs for the nontarget stimuli. For nonpsychopaths, the P300 amplitude was larger when elicited by the target stimuli than when elicited by the nontarget stimuli. In contrast, psychopaths failed to show reliable P300 amplitude differences between the target and nontarget conditions. Psychopaths had a smaller amplitude P300 to target stimuli than did nonpsychopaths. In addition, the amplitude of the P300 was less lateralized in psychopaths than in nonpsychopaths. Psychopaths also had a larger centrofrontal negative wave (N550) during the target condition than did nonpsychopaths. CONCLUSIONS: The results of this study indicate that there are substantial differences between psychopaths and others in the processing of even simple cognitive tasks and provide support for information processing models of psychopathy.

Adult↗
PubMedDate not supplied

Visual and tactile length matching in spatial neglect.

Previous studies have shown that many patients with spatial neglect underestimate the horizontal extent of leftwardly located shapes (presented on screen or on paper) relative to rightwardly located shapes. This has been used to help explain their leftward biases in line bisection. In the present study we have tested patients with right hemisphere damage, either with or without neglect, on a comparable length matching task, but using 3-dimensional objects. The task was executed first visually without tactile contact, and second through touch without vision. In both sense modalities, we found that patients with neglect, but not those without, tended to underestimate leftward located objects relative to rightward located objects, differing significantly in this regard from healthy subjects. However these lateral biases were not as frequent or as pronounced as in previous studies using 2-D visual shapes. Despite the similar asymmetries in the two sense modalities, we found only a small correlation between them, and clear double dissociations were observed among our patients. We conclude that leftward length underestimation cannot be attributed to any one single cause. First it cannot be entirely due to impairments in the visual pathways, such as hemianopia and/or processing biases, since the disorder is also seen in the tactile modality. At the same time, however, length underestimation phenomena cannot be fully explained as a disruption of a supramodal central size processor, since they can occur in either vision or touch alone. Our data would fit best with a multiple-factor model in which some patients show leftward length underestimation for modality-specific reasons, while others do so due to a more high-level disruption of size judgements.

Aged↗
PubMedDate not supplied

Comparison of the Milner and Bisiach Landmark Tasks: can neglect patients be classified consistently?

The aim of the presented studies was to investigate whether classifications of neglect patients into perceptual (i.e. identifying a patient as suffering from mainly attentional/space representation deficits) and premotor (judging the main impairment to be related towards actions into contralesional space) categories are consistent across similar Landmark techniques that have, in the past, been designed to tease these potentially overlapping aspects of hemispatial neglect apart. Thirteen patients with hemispatial neglect were tested both with the Landmark Test, adapted from Milner et al. (1992; 1993) in which they had to manually point to the half of a centrally pre-bisected line that, to them, appeared shorter and the motor version of the Bisiach Landmark Test (Bisiach et al., 1998) in which, rather than just judging a centrally prebisected line, they had to judge asymmetrically bisected lines as well. The specific question was whether these two tasks, which are very similar, would categorise the same set of patients in the same way. Most patients could be classified into either the premotor or perceptual category in each task, but no consistent categorisation emerged across the two tests. Just three out of the thirteen patients were consistently classified across both tests. Despite the apparent similarity of the two tests the Milner Landmark Test proved to be much more sensitive to identifying even a slight perceptual bias and seems therefore the test of choice if identification of perceptual bias is the major interest.

Aged↗
PubMed1999

Mechanisms of spatial attention revealed by hemispatial neglect.

We report performance by a patient, NG, with hemispatial neglect after nondominant stroke, in detecting briefly (200 msec) presented visual targets. NG's detection of targets (gaps in circles) was determined by the location of the target in the space in which stimuli appeared. Gaps on the neglected side of a circle at fixation were rarely detected when circles of uniform size were always presented at fixation. The same targets in the same location were detected far more often in blocks that also included targets presented on each side of the central circle, or in blocks that included larger target stimuli. In these blocks, the window of space in which stimuli appeared was larger, such that the target fell closer to the center of this "window". These results indicate that the spatial extent of attention, and of hemispatial neglect, can be modified on the the basis of expectations and task requirements.

Aged↗
PubMed1992

Categorical-semantic and spatial-imagery judgements of non-verbal stimuli in the cerebral hemispheres.

A divided visual field task was given to two groups of normal subjects to investigate hemisphere differences in the processing of standardised pictorial stimuli. There were two conditions: subjects were asked to decide whether an entity represented by a picture was living or non-living, a task involving a categorical judgement based on semantic information, or, in the second condition, whether these depictions represented entities which were bigger or smaller than a cat. This latter task, it is suggested, requires visual imagery to compare spatial dimensions. The first, categorical task produced an LH advantage in reaction time. The second, imagery task, produced an RH advantage provided the comparison involved items whose sizes were relatively close to that of a cat. Furthermore, the size difference was inversely related to reaction time, only when items were presented to the RH. The data obtained are consistent with the notion that there are at least two systems for processing visual information, one specializing in categorical and semantic distinctions related to LH functions, and the other, specialized in spatial coordinates, an aspect of visual imagery, related to the RH.

Adult↗
PubMed1992

Visual agnosia: a case of reduced attentional "spotlight"?

A case study is presented of a patient with presenile dementia, for whom the dominant clinical feature from onset was a visual agnosia. The characteristics of the patient's visual agnosia were investigated in light of her apparent use of a "feature-by-feature" strategy to identify objects. Results from various tasks showed that the patient was unable to use global shape information or other grossly defined property cues characteristic of a "wide angle" attentional processing stage (Treisman, 1988) in object recognition. The patient appeared instead to rely on 'parts' or identifying features of the objects for object recognition. The patient showed significant improvement when the size of the drawing was reduced in size, thus suggesting that the disorder may be functionally localized to a reduction of the patient's attentional "spotlight".

Agnosia↗
PubMed1994

Pure dysgraphia with relative sparing of lower-case writing.

We describe the cognitive analysis of a patient with acquired pure dysgraphia. She presented a peculiar dissociation between lower- and upper-case handwriting: lower-case writing was relatively spared and showed a significant superiority of words versus nonwords. Upper-case writing and oral spelling did not show lexical effects, but were affected by item length. In all modalities errors consisted mainly of single graphemic substitutions, deletions, insertions and transpositions, resulting in legal or illegal nonwords, and showed a similar distribution across letter positions. These findings were suggestive of an impairment of the graphemic output buffer, which however revealed itself to different degrees in the two handwriting styles.

Aged↗
PubMed1984

Sorting of hemifield presented temporal and spatial stimuli.

An experiment was performed, using a sorting task (choice reaction-time), to study the processing of stimuli, which differed along a temporal or a spatial dimension, presented to the right or to the left visual hemifield. The results indicate more accurate responses and shorter reaction times to a temporal stimulus when it appears in the right-visual-field than when it appears in the left-visual-field. Conversely, more accurate responses and shorter reaction times are found to a spatial stimulus when it appears in the left-visual-field than when it appears in the right-visual-field. In addition to this major interaction, three more interactions are found, all of which involve response direction and one or two other stimulus variables. The results are consistent with the hypothesized hemispheric functional specificity, i.e., that the initial processing of the temporal dimension of visual stimuli is performed better by the left hemisphere than by the right hemisphere and that the converse is true for the initial processing of the spatial dimension of visual stimuli.

Discrimination Learning↗
PubMed1985

Individual use of judgmental dimensions and hemispheric specificity.

The present study investigated the relationship of hemispheric functional specificity to a subject's use of judgmental dimensions when discriminating temporal and spatial visual stimuli using a multidimensional scaling (MDS) paired-comparison paradigm. The major purposes of the study were: To identify the judgmental dimensions used in discriminating unidimensional (temporal or spatial) and multidimensional (combinations of temporal and spatial parameters) stimuli presented to the two visual hemifields; to study the relationship of the use of judgmental dimensions to the visual hemifields; to investigate whether the use of judgmental dimensions in discriminating unidimensional stimuli can be used to predict their use in discriminating multidimensional stimuli. Subjects used two dimensions in discriminating the spatial and temporal unidimensional stimuli: A dimension whose scaling paralleled the physically interval-scaled stimuli; a dimension, in which the extreme values were located on one end of the scale, while the mid-values are located at the other end of the scale. There is significantly greater use of the spatial dimension when spatial stimuli are presented to the left visual field (LVF) then when presented to the right visual field (RVF). Conversely, there is significantly greater use of the temporal dimension when temporal stimuli are presented to the RVF then when they are presented to the LVF. Three perceptual dimensions were used to judge multidimensional stimuli: Spatial-to-temporal; stimulus quality; apparent movement. Two groups of subjects were identified who differed in their relative use of the temporally and spatially scaled unidimensional stimuli presented to the RVF. These two groups differed with respect to their relative use of a spatial-to-temporal dimension when multidimensional stimuli were presented to the RVF.

Cues↗