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S Aglioti

Publications and source records attributed to S Aglioti.

41 records · Page 3Linked to original sources
PubMed1990

Effectiveness of different task paradigms in revealing blindsight.

Four patients with hemianopia from posterior cerebral artery infarction were tested for residual unconscious vision ('blindsight') in their anopic hemifield. One task tested for spatial summation between the normal and the abnormal hemifields. A second task tested for temporal interactions between the two hemifields. A third task required a manual localization of the site of a brief flash in the hemianopic side. The last test was administered either in a condition of free gaze during pointing or in a condition in which the gaze was kept fixed throughout all phases of the task. The first two tasks differed from the third not only in the type of visual function, that is, detection vs spatial localization, but also in the response criterion. A forced-choice procedure was adopted in the localization task while in the spatial and temporal interfield interaction tasks a reaction time paradigm that did not require guessing was used. One patient showed unequivocal evidence of blindsight on all tasks, thus excluding the possibility that his blindsight depended on the nature of the response. An interesting dissociation was found in the localization task where 1 patient showed evidence of blindsight when tested under conditions of unrestrained gaze during pointing but not when tested under fixed gaze conditions.

Aged↗
PubMed1987

Distribution in the visual field of the costs of voluntarily allocated attention and of the inhibitory after-effects of covert orienting.

By using a simple reaction time (RT) paradigm we have investigated the spatial distribution of the benefits and costs of voluntarily directed attention and of the inhibitory after-effects of covert orienting. In the first experiment subjects deliberately allocated attention to each one of five stimulus positions disposed along the horizontal meridian, while at the same time fixing their eyes on the central position. The separation in visual angle between the central position and the two nearest positions, one on the left and the other on the right, was 10 degrees; that between the central position and the two most eccentric positions was 30 degrees. By comparing RT to brief flashes of light presented at each position during directed attention with RT to identical flashes at the same position during diffuse attention (i.e. in a condition in which subjects paid equal attention to all five positions), it was possible to determine that benefits, that is RT decreases relative to the diffuse-attention condition, were strictly limited to the attended position. Costs, i.e. RT increases relative to the diffuse-attention condition, showed a more diffuse and complex spatial pattern. When attention was directed to one of the noncentral positions, costs were apparent at the two contralateral positions and at the central position, but not at the ipsilateral position. When attention was directed to the central position, costs occurred at all other positions. This suggests a special role for the vertical meridian in delimiting the area of costs when one covertly orients towards the opposite right or left visual half field. Work of others and our preliminary evidence indicate that the area of costs is similarly limited by the horizontal meridian when one orients toward the opposite upper or lower visual field. In the second experiment we studied the inhibitory after-effect of covert orienting. Orienting to a light stimulus without moving the eyes to it may induce a short-lived facilitation of the speed of response to a second stimulus presented at the same position, but this facilitation is followed by a profound and prolonged RT retardation. By using a two-flashes paradigm we observed this RT retardation not only when the two stimuli appeared at the same position, but also when they occurred at different locations in the same altitudinal or lateral visual hemifield. There were no inhibitory after-effects when the two stimuli appeared on opposite sides of the vertical or horizontal meridian.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1986

Spatial summation across the vertical meridian in hemianopics: a test of blindsight.

Twenty hemianopic patients with retrochiasmatic lesions have been tested for spatial summation of pairs of flashes simultaneously presented either to the same hemifield or to opposite hemifields across the vertical meridian. In such a task normal subjects show summation, i.e. a faster reaction time in response to a pair of stimuli than in response to a single stimulus. Such an effect is present both for pairs of stimuli presented within the same hemifield and for pairs of stimuli in which the two flashes are presented one in the right and the other in the left hemifield. In contrast to normals, hemianopics as a group did not show interfield summation although, like normals, showed summation within one hemifield. A single-case analysis, however, revealed that in one patient there was a reliable overall interfield summation and that in three others there was evidence of summation in at least one testing session. The presence of interfield spatial summation between the normal and the affected hemifield of hemianopics thus provides further evidence of blindsight in a task paradigm in which guessing strategies and stimulus artefacts can be eliminated. The very small proportion of patients showing blindsight can be in part related to the relatively low stimulus intensity and the very brief stimulus exposure duration used.

Adolescent↗