Biomedical subjects

M Turatto

Publications and source records attributed to M Turatto.

11 recordsLinked to original sources

PubMed2001

Orienting of visual attention in dyslexia: evidence for asymmetric hemispheric control of attention.

The control of attentional orienting was studied in children with specific reading disorder (SRD) or dyslexia, and it was compared with that of normal readers. We used the covert orienting paradigm to measure subjects' reaction times for target detection both in valid and invalid cue conditions, either in the left or in the right visual fields. In experiment 1, we investigated exogenous orienting. The cue consisted of a peripheral abrupt onset and the cue-target delay was 350 ms. As compared with normal readers, in dyslexics the cue effect was absent in the right visual field, whereas in the left visual field a greater cue effect was observed. No visual field asymmetry was found in normal readers. In experiment 2, we investigated endogenous orienting. The cue was shown centrally and the cue-target delay was 750 ms. In dyslexics and normal readers, orienting of attention was present in both visual fields. However, in the invalid condition, dyslexic children showed significantly slower reaction times in the left visual field than in the right visual field. These results were interpreted as being due to an asymmetric control of visual spatial attention, possibly related with a posterior attention mechanism deficit in the right parietal cortex and/or an interhemispheric dysfunction and/or an impairment of cerebellar functions.

Adolescent↗

PubMed2001

Segmentation, attention and phenomenal visual objects.

Issues concerning selective attention provoke new questions about visual segmentation, and vice-versa. We illustrate this by describing our recent work on grouping under conditions of inattention, on change blindness for background events and the residual processing of undetected background changes, on modal versus amodal completion in visual search, and the differential effects of these two forms of completion on attentional processes, and on attentional modulation of lateral interactions thought to arise in early visual cortex. Many of these results indicate that segmentation processes substantially constrain attentional processes, but the reverse influence is also apparent, suggesting an interactive architecture. We discuss how the 'proto-objects' revealed by studies of segmentation and attention (i.e. the segmented perceptual units which constrain selectivity) may relate to other object-based notions in cognitive science, and we wrestle with their relation to phenomenal visual awareness.

Attention↗

PubMed2001

Four paradigms to study visual--spatial attention of myopic subjects.

We describe four protocols for evaluating the attentional skills of myopic and control subjects in target stimulus detection tasks; simple reaction times (RT) are recorded. Two protocols are designed to study both automatic and voluntary orienting of attention. Modified implicit orienting paradigms [Q. J. Exp. Psychol. 32A (1980) 2; J. Exp. Psychol. Gen. 109 (1980) 160] are used in which cues elicit a shift of attention but gaze is maintained on a central fixation point. A third paradigm is designed to study the time-course of focusing; two circles (focusing cues) of different diameters are randomly presented on a point of the visual space where attention has been previously shifted. Seven SOAs (stimulus onset asynchrony) are used. The fourth paradigm was designed to evaluate visual search; three circular arrays of four, eight and twelve stimuli are randomly presented around a fixation point and subjects have to detect the target stimulus inside one of the circles (the other circles are distracters). Since some attentional deficits are associated with myopia [Invest. Ophthalmol. Vis. Sci. 38 (1997) 1725; Cogn. Brain Res. 8 (1999) 369], these protocols could be useful both in the detection of deficits in subjects on the verge of becoming myopics and in the development of cognitive training programs to reduce attentional deficits.

Adolescent↗

PubMed2001

Cross-modal attentional deficits in processing tactile stimulation.

In order to substantiate recent theorization on the possible links between the causes of the attentional blink and the psychological refractory period phenomena (e.g., Jolicoeur, 1999a), four experiments are reported in which two target stimuli, T1 and T2, were presented in different modalities at varying stimulus onset asynchronies (SOAs), with each stimulus being associated with a distinct task, Task1 and Task2. In Experiment 1, T1 was a tone, and Task1 was a speeded vocal response based on pitch. T2 was a brief press applied to either of two distal fingerpads, and Task2 was a speeded manual response based on tactile stimulus location. In Experiment 2, the same T1 as that used in Experiment 1 was presented, and in Task1 the subject either made a speeded vocal response based on pitch or ignored T1. T2 was a masked tactile stimulation, and Task2 was an unspeeded manual discrimination of the tactile stimulation location. This Task2 was maintained in Experiments 3 and 4. The auditory T1 was replaced with a white digit embedded in a rapid serial visualization presentation of a stream of black letters, and in Task1 the subject either made an unspeeded decision based on T1 identity or ignored T1. In all the experiments, the results showed an SOA-locked impairment in Task2. As SOA was decreased, reaction times in the speeded Task2 of Experiment 1 increased, and accuracy in the unspeeded Task2 of Experiments 2-4 decreased. The SOA-locked impairment was almost eliminated when T1 could be ignored or was absent. The results are discussed in terms of central processing limitations as the cause of such effects.

Adult↗

PubMed2001

Attentional capture by color without any relevant attentional set.

The aim of the present study was to investigate mechanisms underlying attentional capture by color. Previous work has shown that a color singleton is able to summon attention only in the presence of a relevant attentional set, whereas when a color singleton is not useful for a task, evidence for purely stimulus-driven attentional capture is controversial. Three visual search experiments (T-L task) were conducted using a method different from that based on set sizes, consisting of monitoring target-singleton distance in a unique display size. In Experiment 1, we demonstrated that attention can be summoned in a real stimulus-driven manner by an irrelevant color singleton. Experiment 2A extended this observation, showing that the color singleton attracted attention even when capture was detrimental. However, Experiment 2B showed that such capture can be strategically prevented. Finally, in Experiment 3, we examined whether such a capture was due to a spatial shift or to a filtering cost, providing evidence supporting the shift hypothesis. Stimulus-driven capture was observed when color was neither the defining nor the reported target attribute (Yantis, 1993) and when subjects naive of visual search tasks were used. The present results give experimental support to many contemporary models of visual attention.

Adult↗

PubMed2000

Asymmetrical visual fields distribution of attention in dyslexic children: a neuropsychological study.

Visual spatial attention was evaluated in dyslexic and normally reading children by using a flanker task. When an irrelevant distractor is presented adjacent to a target stimulus, interference is observed when the two stimuli are associated with conflicting responses. In the present study the distractor flanked the target either to the right or to the left. Results showed an asymmetric flanker effect in dyslexics, whereas it was symmetrical in normal readers. Dyslexics exhibited a reduced flanker effect in the left visual field, concomitant with a strong flanker effect in the right visual field. These results give further support to the hypothesized left-side minineglect in dyslexics. Data also provide evidence for a reduced ability in suppressing distracting information in the right visual field. Such visual field asymmetry is thought to play a crucial role in reading disorders. Right over-distractibility and left inattention suggest an impairment of the right parietal functions as supported by the magnocellular theory of dyslexia.

Adolescent↗

PubMed2000

The Properties of Supernova 1997cy Associated with GRB 970514.

The extraordinary SN 1997cy associated with GRB 970514 has been observed photometrically and spectroscopically for nearly 2 yr. At the time of discovery, SN 1997cy was the brightest supernova (SN) ever observed (MV</=-20.1, vhel=19,140 km s-1, H0=65 km s-1 Mpc-1). Up to the last available observations (600 days after the gamma-ray burst), the total time-integrated flux was equal to or larger than that expected from the complete thermalization of the gamma-rays produced by 2.3 M middle dot in circle of 56Co. However, starting already on day 60 the luminosity decline is slower than the 56Co decay rate, indicating that the SN ejecta was interacting with circumstellar material (CSM). The interaction appeared to weaken around day 550. The spectra of SN 1997cy are dominated at all epochs by Halpha emission, which shows at least three components of different widths, as in SN 1988Z. Several other lines with different widths are also visible, especially at early epochs. The entire light curve of SN 1997cy is reproduced by a model of the interaction of the very energetic (E=3x1052 ergs) ejecta of a massive star (25 M middle dot in circle) with the CSM, with some contribution from radioactive decays. The CSM could have been ejected with a mass-loss rate of M&d2; approximately 4x10-4 M middle dot in circle yr-1 as the progenitor star evolved from a blue to a red supergiant about 104 yr before the explosion. The lack of oxygen and magnesium lines in the spectra at nebular phases poses a problem for models requiring high-mass progenitors. The possibility that most of the core material of the progenitor has fallen onto a massive black hole so that the reverse shock dies at the inner edge of the H/He envelope is discussed.

Journal Article↗

PubMed2000

Visual-spatial attention in developmental dyslexia.

Orienting and focusing of visual attention are two processes strictly involved in reading. They were studied in a group of dyslexic children and normal readers. Shifting of attention by both peripheral and central visual cues was studied by means of the covert orienting paradigm. Focusing, consisting in the ability to control the size of the attentional focus, was investigated using simple reaction times in central vision. Results showed that dyslexics had a specific disability in the shifting of attention caused by a peripheral cue at short SOAs, and were also able to maintain attention focused for short periods of time only, presumably not long enough for efficient visual processing. Our results support the suggestion that visual selective attention deficits in disabled readers may be due to a specific difficulty in orienting and focusing.

Adult↗

PubMed2000

Color, form and luminance capture attention in visual search.

Extant models of visual attention predict that a salient element should produce a bottom-up activation leading to a stimulus-driven attentional capture (e.g. Cave, 1999). However, apart from onset, previous works manipulating set-size in visual search failed to provide empirical evidence for this kind of capture. By varying target-singelton distance method, based on a single set-size, we explored whether, in a serial search task, an attentional capture is triggered by static discontinuities such as those generated through the manipulation of color, form, and luminance. The results suggest that those physical properties are indeed able to capture attention automatically.

Adult↗

PubMed2000

Automatic and voluntary focusing of attention.

In this study, we investigate whether attentional focusing, like attentional orienting, comprises two independent mechanisms. We provide direct empirical evidence in favor of the existence of two mechanisms--one exogenous, or automatic, and one endogenous, or voluntary--that play a role in adjusting the size of the focus of attention. When a new object suddenly occurs in the visual field, the focus is first automatically fitted to it, and then an endogenous effort has to be exerted to maintain attention in the focused mode. Also, we provide evidence that voluntary focusing needs a perceptual object in order to operate.

Adult↗

PubMed1999

Visuospatial attention in myopia.

Four experiments were conducted to ascertain whether myopia is associated with deficits of visuospatial attention. In myopic and emmetropic control subjects, we studied: (1) automatic and voluntary orienting of attention, (2) focusing of attention and (3) performance on a visual search task. The results indicated that automatic orienting was defective in myopics and their performance in visual search was less efficient than that of controls. By contrast, myopics showed no deficits in voluntary orienting and in focusing.

Analysis of Variance↗