PubMed Health⌕ Search

Biomedical subjects

C Casco

Publications and source records attributed to C Casco.

At least 19 recordsLinked to original sources
PubMed2005

Long-term effects of MDMA (Ecstasy) on the human central nervous system revealed by visual evoked potentials.

Several studies indicate long-term cognitive impairment of MDMA (ecstasy) users. In the present study we attempted to establish whether electrophysiological correlates of low-level cognitive processes present a long-term alteration, dependent on the level of use of ecstasy. We addressed this issue by investigating amplitude and latency of VEPs related to a very simple discrimination task involving sustained attention (arousal). Eight heavy-MDMA users, eight moderate-MDMA users and 18 drug-free control subjects were asked to discriminate whether the digit at the centre of the screen was 1 or 2. None of the subjects (except one) had used MDMA in the 6 months previous testing. We measured psychophysical performance and EEG, recorded in Oz and Fz during task execution. The heavy-MDMA users made significantly more errors than the other two groups (p < .05). Moreover, they presented reduced amplitude but not latency of VEPs in both Oz and Fz. The effect in Oz is present in P200 (for heavy users only, p < .05) and in P300 components (for both MDMA groups; heavy users: p < .001, moderate users: p < .0.5). In Fz, the amplitude effect is present in N250 (for heavy users only, p < .05) and in P300 components (for both MDMA groups; heavy users: p < .05, moderate users: p < .05). The three groups do not differ in early components, reflecting low-level processing. These results provide evidence of long-term electrophysiological abnormality displayed by ecstasy users and agree with the suggestion that even typical recreational doses of ecstasy are sufficient to cause long-term altered cortical activity in humans.

Adult↗
PubMed2004

High prevalence of vitamin D insufficiency in healthy elderly people living at home in Argentina.

OBJECTIVE: To evaluate the nutritional status of vitamin D in urban populations of healthy elderly people living at home, in different regions of Argentina. DESIGN: Cross-sectional study. SUBJECTS: In total, 386 ambulatory subjects over 65 y of age from seven cities (between latitude 26 degrees S and 55 degrees S) were asked to participate between the end of winter and the beginning of spring. Of these, 369 accepted, 30 were excluded because of medical history or abnormal biochemical determinations. Finally, 339 subjects (226 women and 113 men) (X+/-s.d.) (71.3+/- 5.2 y) were included. RESULTS: Serum 25OHD levels were lowest in the South (latitude range: 41 degrees S-55 degrees S): 14.2+/-5.6 ng/ml (P<0.0001vs North and Mid regions); highest in the North (26 degrees S-27 degrees S): 20.7+/-7.4 ng/ml (P<0.03 vs Mid, P<0.0001vs South); and intermediate in the Mid region (33 degrees S-34 degrees S) 17.9+/-8.2 ng/ml. Serum mid-molecule PTH (mmPTH) and 25OHD were inversely related: (r=-0.24, P<0.001). A cutoff level of 25OHD at which serum mmPTH levels began to increase was established at 27 ng/ml. A high prevalence (87-52%) of subjects with 25OHD levels in the deficiency-insufficiency range (25OHD levels <20 ng/ml) was detected. CONCLUSION: This study shows that vitamin D deficiency/insufficiency in the elderly is a worldwide problem. Correction of this deficit would have a positive impact on bone health of elderly people.

Aged↗
PubMed2001

Discrimination of an orientation difference in dynamic textures.

We investigated whether the response of a motion sensor was related to the specificity of sensory information (orientation and direction of motion) used to compute motion energy. This was done in two ways. First, we assessed whether orientation discrimination of a target line, which segregated by an orientation difference from a textured background, was improved with two-frame apparent motion stimulation (as compared with static presentation). Second, we investigated whether the amount of improvement (in either orientation or direction of motion discrimination) depends on a particular combination of target orientation and direction of motion (either orthogonal or parallel). We found that the percentage of correct responses in the discrimination task (a) was higher for a moving target than for a static one; (b) was higher when the target was oriented more orthogonally to motion direction than background elements; (c) was little affected by background motion and (d) decreased with frame duration in the direction of motion task whereas it was largely unaffected by frame duration in the discrimination of orientation task. These results suggest that discrimination of moving texture boundaries is based on a motion sensor tuned to a particular combination of orientation and direction of motion, which is capable of signalling the orientation of a moving target more accurately than a static sensor.

Analysis of Variance↗
PubMed2000

Visual search for single and combined features by children and adults: possible developmental inferences.

Visual search time was measured in four groups of children 4 to 10 years of age and in young adults, as a function of display size for both target present and target-absent conditions. The slopes of regression lines in a simple search (search for \ within /) were compared with those obtained in within-dimension conjunction target searches, within either homogeneous (search for the inverted T within Ts) or heterogeneous distractors (search for arrow within Ys and inverted Ys). Analysis indicated that simple search was always preattentive (slopes near 0) after 5 years of age and serial (with positive slopes) before this age. Searching within heterogeneous distractors apparently involved element-by-element scrutiny and focal attention in all groups whereas searching within homogeneous distractors required distributed attention, perhaps based on parallel grouping of distractors in adults, though distractors were focally attended to by children.

Adult↗
PubMed1999

A visual evoked potential correlate of global figure-ground segmentation.

Human observers discriminated the global orientation of a texture-defined figure which segregated from a texture surround. Global figure discriminability was manipulated through within-figure collinearity, figure-surround interaction, and figure connectedness, while the local orientation contrast at edges between figure and surround was kept constant throughout all the experiments. Visual evoked potentials (VEPs) were recorded during onset-offset stimulation in which the figure cyclically appeared and disappeared from a uniform texture background. A difference component was obtained by subtraction of offset-from onset-VEP. Two negative peaks of the difference component are found with latencies around 140-160 and 200-260 ms, respectively. Enhanced discriminability of the global figure reduced (11-25 ms) the latency of the second peak, hence indicating that the 200-260 ms component was produced by global figure-ground segmentation.

Adult↗
PubMed1999

A new device for abrasive cytology sampling during upper gastrointestinal endoscopy: experience in infectious and neoplastic diseases.

BACKGROUND AND STUDY AIMS: The increase in infectious diseases of the gastrointestinal tract related to immunosuppression is becoming an important topic for the endoscopist. To improve the diagnostic efficacy of tissue acquisition while at the same time restricting costs, we have developed a new device for obtaining material from the upper gastrointestinal tract that can also be used in the diagnosis of neoplastic disease. PATIENTS AND METHODS: A total of 90 patients were examined and assigned to two groups according to indications. Group A consisted of 53 symptomatic patients with positive human immunodeficiency virus (HIV) serology with a suspicion of gastrointestinal infection. Group B included 37 patients in whom there was an endoscopic suspicion of neoplasia in the upper gastrointestinal tract. Cell fragments for cytological study were obtained using a device introduced through the endoscopic instrumentation channel (abrasive cytology). Different staining methods were used to isolate bacteria or diagnose tumors from cell fragments. The findings were compared with those obtained from conventional bioptic histology. RESULTS: Potentially responsible pathogens were isolated in 48 of the 53 patients in Group A, while bioptic histology provided a diagnosis in only 32 patients. In the 37 patients in group B, the cytological diagnosis matched the histological results. The costs of this new technique are similar to those for conventional cytological staining, and the time from sampling to obtaining a final diagnosis is less than one hour. CONCLUSIONS: This new device provides a fast and low-cost method of isolating pathogens and obtaining cell fragments from the gastrointestinal mucosa during routine upper gastrointestinal endoscopy.

AIDS-Related Opportunistic Infections↗
PubMed1999

Parallel search for conjunctions with stimuli in apparent motion.

A series of experiments was conducted to determine whether apparent motion tends to follow the similarity rule (i.e. is attribute-specific) and to investigate the underlying mechanism. Stimulus duration thresholds were measured during a two-alternative forced-choice task in which observers detected either the location or the motion direction of target groups defined by the conjunction of size and orientation. Target element positions were randomly chosen within a nominally defined rectangular subregion of the display (target region). The target region was presented either statically (followed by a 250 ms duration mask) or dynamically, displaced by a small distance (18 min of arc) from frame to frame. In the motion display, the position of both target and background elements was changed randomly from frame to frame within the respective areas to abolish spatial correspondence over time. Stimulus duration thresholds were lower in the motion than in the static task, indicating that target detection in the dynamic condition does not rely on the explicit identification of target elements in each static frame. Increasing the distractor-to-target ratio was found to reduce detectability in the static, but not in the motion task. This indicates that the perceptual segregation of the target is effortless and parallel with motion but not with static displays. The pattern of results holds regardless of the task or search paradigm employed. The detectability in the motion condition can be improved by increasing the number of frames and/or by reducing the width of the target area. Furthermore, parallel search in the dynamic condition can be conducted with both short-range and long-range motion stimuli. Finally, apparent motion of conjunctions is insufficient on its own to support location decision and is disrupted by random visual noise. Overall, these findings show that (i) the mechanism underlying apparent motion is attribute-specific; (ii) the motion system mediates temporal integration of feature conjunctions before they are identified by the static system; and (iii) target detectability in these stimuli relies upon a nonattentive, cooperative, directionally selective motion mechanism that responds to high-level attributes (conjunction of size and orientation).

Adult↗
PubMed1999

Spatial interactions in simple and combined-feature visual search.

To isolate the mechanisms responsible for spatial interactions in visual search, we investigated the effects of inter-element distance and positional jittering in both simple (in/s) and combined-feature (inverted V in Vs) search tasks in which the observer had to find a target in a background of similar nontargets. Thresholds, defined as the stimulus duration for 75% correct, were measured for 'present' and 'absent' target conditions as a function of background numerosity (ranging from 4 to 64 background elements), independently for four inter-element distances and three positional jittering conditions. Results show: (1) both simple and combined-feature search involve a parallel, capacity limited process, (2) thresholds for parallel search of simple features are directly related to inter-element distance whereas this has little effect on thresholds in combined-feature search, and (3) positional jittering has a direct effect on thresholds in combined-feature search and an inverse effect in simple-feature search. These results indicate that two different mechanisms of spatial interactions are involved in parallel search. The activation of each of the two mechanisms depends on the stimulus used. In parallel search for simple and dissimilar features, the underlying mechanism is a short-range one, based on lateral inhibition, whereas the parallel search for combined and similar features is based on a nontarget grouping mechanism which relies on facilitatory interactions between regular elements.

Computer Terminals↗
PubMed1998

Visual selective attention and reading efficiency are related in children.

We investigated the relationship between visual selective attention and linguistic performance. Subjects were classified in four categories according to their accuracy in a letter cancellation task involving selective attention. The task consisted in searching a target letter in a set of background letters and accuracy was measured as a function of set size. We found that children with the lowest performance in the cancellation task present a significantly slower reading rate and a higher number of reading visual errors than children with highest performance. Results also show that these groups of searchers present significant differences in a lexical search task whereas their performance did not differ in lexical decision and syllables control task. The relationship between letter search and reading, as well as the finding that poor readers-searchers perform poorly lexical search tasks also involving selective attention, suggest that the relationship between letter search and reading difficulty may reflect a deficit in a visual selective attention mechanisms which is involved in all these tasks. A deficit in visual attention can be linked to the problems that disabled readers present in the function of magnocellular stream which culminates in posterior parietal cortex, an area which plays an important role in guiding visual attention.

Attention↗
PubMed1996

Visual search of good and poor readers: effects with targets having single and combined features.

This study examined differences between normal and poor readers in the visual-search strategy used to detect a target shape in a background of similar shapes. No differences between the two groups occur in search for simple features (Exps. 1 and 3) and conjunction of features (Exp. 2). However, the performance of the two groups differ on search tasks with multifeatured shapes, in which targets and nontargets differ in both the identity of features and their spatial relationship or in the spatial relationship of features alone. Results suggest that, rather than a problem in searching complex stimuli, poor searchers have difficulty within stimuli like letters and geometrical shapes which require integration of features within a module of the visual system.

Attention↗
PubMed1993

Rigid and non-rigid kinetic depth effect with rotating discrete helices.

To examine the conditions in which human observers fail to recover the rigid structure of a three-dimensional object in motion we used simulations of discrete helices with various pitches undergoing either pure rotation in depth (rigid stimuli) or rotation plus stretching (non-rigid stimuli). Subjects had either to rate stimuli on a rigidity scale (Experiments 1 and 2) or to judge the amount of rotation of the helices (Experiments 3 and 4). We found that perceived rigidity depended on the pitch of the helix rather than on objective non-rigidity. Furthermore, we found that helices with a large pitch/radius ratio were perceived as highly non-rigid and that their rotation was underestimated. Experiment 5 showed that the detection of a pair of dots rigidly related (located on the helix) against a background of randomly moving dots is easier at small phases in which the change of orientation across frames is also small. We suggest that this is because at small phases the grouping of dots in virtual lines does occur and that this may be an important factor in the perceived nonrigidity of the helices.

Adult↗
PubMed1993

Perceived rigidity and nonrigidity in the kinetic depth effect.

Stroboscopic simulations of three-dimensional rotating rigid structures can be perceived as highly nonrigid. To investigate this nonrigidity effect a sequence of either three (experiment 2 and 3) or thirty six frames (experiment 4) was used, each consisting of a set of dots with location on the horizontal axis corresponding to the parallel projection of a nominally defined helix. Observers were asked to judge the angle of rotation of eighty helices defined by the factorial combination of eight phase (phi) values (ie difference between the sinusoidal path of one dot and its neighbours) and ten different angular displacement values (alpha). When in each static frame the dots can be organized into curved dotted line (small values of phi), the perceived 3-D helices are highly nonrigid. But when shape information is not available in each static frame (high values of phi), the helices are perceived as rigid and rotation judgement is possible providing that alpha < 15 degrees. It appears that at small values of phi observers fail to recover the rigid structure of the helices since the input to the structure from the motion process may be distorted.

Adult↗
PubMed1990

Spatial filtering and spatial primitives in early vision: an explanation of the Zöllner-Judd class of geometrical illusion.

The apparent length and orientation of short lines is altered when they abut against oblique lines (the Zöllner and Judd illusions). Here we present evidence that the length and orientation biases are geometrically related and probably depend upon the same underlying mechanism. Measurements were done with an 'H' figure, in which the apparent length and orientation of the cross-bar was assessed by the method of adjustment while the orientation of the outer flanking lines was varied. When the flanking lines are oblique the apparent length of the central line is reduced and its orientation is shifted so that it appears more nearly at right-angles to the obliques than is in fact the case. Measurements of the orientation and length effects were made in three observers, over a range of flanking-line angles (90, 63, 45, 34 and 27 deg) and central line lengths (9, 17, 33 and 67 arc min). The biases increased with the tilt of the flanking-lines, and decreased with central line length. The extent of the length bias could be accurately predicted from the angular shift by simple trigonometry. We describe physiological and computational models to account for the relation between the orientation and length biases.

Humans↗
PubMed1990

The relationship between visual persistence and event perception in bistable motion display.

Observers viewed two alternating frames, each consisting of three rectangular bars displaced laterally by one cycle in one frame with respect to the other. At long interframe intervals (IFIs) observers perceived a group of three bars moving as a whole (group motion), and at short IFIs the overlapping elements in the two frames appeared stationary, while the third element appeared to move from one end of the display to the other (element motion). The upper temporal limit for perceiving element motion was reduced when bars with blurred edges were used and when either frame duration or bar size was increased. However, when inner and outer elements had different sizes, the element motion percept was dominant up to 230 ms IFI. These findings may be interpreted in terms of spatial tuning of motion mechanisms involved in the perception of bistable apparent motion.

Attention↗
PubMed1989

Spatial properties of mechanisms for detection of moving dot targets in dynamic visual noise.

The maximum displacement threshold for direction discrimination (dmax) was determined for single or paired dot targets moving discretely against a background of dynamic visual noise. dmax rose as the spatial density of noise was reduced, or when the interframe interval was decreased. dmax was greater for dot pairs than for single dots, and rose progressively as the distance between the dots was reduced. dmax was also greater if the orientation of the target dot pairs differed from the orientation of paired dots in the background noise. Dichoptic presentation of the target and background noise allowed the target to be detected with an accuracy that did not depend on displacement.

Female↗