Biomedical subjects

Silvia Savazzi

Publications and source records attributed to Silvia Savazzi.

3 recordsLinked to original sources

PubMed2003

Object-based versus object-centred neglect in reading words.

Neglect dyslexia is a reading disorder which affects the identification of portions of words or sentences and is typically due to right-brain damage. Caramazza and Hillis (1990a, b) proposed a model of representation of words whereby various patterns of neglect dyslexia are attributed to selective impairment to the different forms of representation. According to the model, patients with first and second level deficits will "neglect" those parts of horizontally presented words that fall on one side of the retina, or on one side of the string centre, respectively, but will read vertically presented words without errors. A patient with a third level deficit will neglect letters at the beginning of the word irrespective of whether they fall on the right or left half of the retina, or on the right or the left of the word centre. In the present paper I describe an atypical pattern of neglect errors that is not easily explicable by this model and is better interpreted as an object-based neglect within an ego-centred frame of reference.

Dyslexia↗

PubMed2002

Speeding up reaction time with invisible stimuli.

Normal subjects react more quickly to a pair of visual stimuli than to a stimulus alone. This phenomenon is known as the redundant signal effect (RSE) and represents an example of divided visual attention in which signal processing is carried out in parallel to the advantage of response speed. A most interesting aspect of this phenomenon is that it can occur when one stimulus in a pair cannot be consciously detected because of hemianopia or unilateral extinction resulting from brain damage. Here, we report that a similar dissociation between visual awareness and visually guided behavior is present in normal subjects who show an RSE even when the luminance of one of a pair of stimuli is below detection threshold. The observed RSE cannot be attributed to probability summation because it violates Miller's race inequality and is likely to be related to neural summation between supra- and subthreshold stimuli. Given that a similar implicit RSE is present in hemispherectomy patients, we hypothesize that the site of this summation might be the superior colliculus (SC).

Adult↗

PubMed2002

Unilateral neglect and perceptual parsing: a large-group study.

Array-centred and subarray-centred neglect were disambiguated in a group of 116 patients with left neglect by means of a modified version of the Albert test in which the central column of segments was deleted so as to create two separate sets of targets grouped by proximity. The results indicated that neglect was more frequent in array- than subarray-centred coordinates and that, in a minority of cases, neglect co-occurred in both coordinate-systems. The two types of neglect were functionally but not anatomically dissociated. Presence of visual field defects was not prevalent in one type of neglect with respect to the other. These data contribute further evidence to previous single-case and small-group studies by showing that neglect can occur in single or multiple reference frames simultaneously, in agreement with current neuropsychological, neurophysiological and computational concepts of space representation.

Aged↗