Biomedical subjects

Alessio Toraldo

Publications and source records attributed to Alessio Toraldo.

5 recordsLinked to original sources

PubMed2005

Canceling out both the real and the spectral lines.

Neglect patients typically show motor perseveration while canceling targets on the ipsilesional side. This behavior can be influenced by the presence vs. absence of targets on the (neglected) contralesional side (). As alternative explanations, the authors proposed (i) directional hypokinesia--the patient cannot perform reaching movements towards detected left-sided targets, and thus carries on canceling on the right side, and (ii) allochiria--the patient misperceives left-sided targets as located on the right side, and cancels them there. We report here data from a patient (EZ) that might confirm the second hypothesis. EZ was presented with 19 displays in which the number and position of cancellation targets on both sides were varied systematically. EZ showed motor perseveration while canceling, but this tendency did not vary across conditions. Interestingly though, EZ also drew cancellation marks in the empty space between the ipsilesional targets, and this phenomenon was significantly more intense when there were more targets on the neglected side. As EZ's comments suggested, such a behavior might reflect the attempt to cancel out delusional targets. Our speculation is that those objects were generated by allochiria.

Aged↗

PubMed2005

Tachistoscopic treatment of dyslexia changes the distribution of visual-spatial attention.

Twelve children with developmental dyslexia underwent a four-month treatment with tachistoscopic presentation of words, according to Bakker's methodology. One group received standard lateral presentation of words on a PC screen, while the other group received the same stimuli in random lateral position. The spatial distribution of visual attention was measured by means of the Form-Resolving Field (FRF; ), which was administered along with reading tests, before and after treatment. The FRF of children who received random presentation widened at -12.5 degrees on the left side, while the FRF in the group that received standard lateral presentation narrowed at that position. Both groups significantly improved in reading accuracy for both words and nonwords. Some hypotheses are proposed concerning the mechanisms responsible for the changes in the FRF and their correlation with improvements in word and nonword reading. The results of the present study are also compared with data suggesting a left "minineglect" in dyslexia.

Adolescent↗

PubMed2004

Misprojection of landmarks onto the spatial map.

It has been suggested that neglect patients misrepresent the metric spatial relations along the horizontal axis (anisometry). The "fabric" of their internal spatial medium would be distorted in such a way that physically equal distances appear relatively shorter on the contralesional side (canonical anisometry). The case of GL, a 76-year-old lady with left neglect on visual search tasks, is presented. GL showed severe relative overestimation on the left (contralesional) side on two independent tasks evaluating the metrics of her internal representation. A qualitatively similar pattern was found in two out of 10 other neglect patients who performed the second task. This behavior cannot be accounted for by the canonical anisometry hypothesis. Nevertheless, GL produced a relative left overextension (underestimation) when trying to set the endpoints of a virtual line given its midpoint (Endpoints Task). An interpretation of these results is offered in terms of a misprojection of relevant landmarks onto the internal representation without assuming distortion of its "fabric."

Aged↗

PubMed2004

A revised method for analysing neglect using the landmark task.

In order to better disentangle 'perceptual' and 'response' biases in neglect patients, Bisiach and his co-workers developed a new version of the 'landmark task'. In their version, subjects are required to choose which is the longer (first condition) or the shorter (second condition) of the two portions of a pre-bisected horizontal line. Two indices were proposed, for the purpose of measuring perceptual and response bias respectively. The perceptual bias index (PB) is the constant error across conditions, while the response bias index (RB) is the degree of response consistency between conditions. Although valuable in a clinical context, these indices are not mathematically independent of one another. Furthermore, they do not exploit all of the information available in a given set of landmark data, since the responses made at the different landmark locations are all averaged together. To overcome these problems, we propose two new indices that can be derived from the revised landmark task. Our perceptual bias index is the Point of Subjective Equality (PSE)--the mean landmark location that appears to be halfway along the line. The response bias index, M, is the mean probability of making a response that opposes the patient's subjective midpoint. PSE and M are mathematically independent of each other and use most of the landmark information. The method and its theoretical foundation are summarized, and illustrative data obtained from brain damaged patients and control subjects are presented. Finally, computational procedures are provided for both PSE and M.

Brain↗

PubMed2003

Dissociation between the mental rotation of visual images and motor images in unilateral brain-damaged patients.

Deficits in the mental rotation of body parts and of external objects can be doubly dissociated (Rumiati, Tomasino, Vorano, Umiltà, & De Luce, 2001; Sirigu & Duhamel, 2001; Tomasino, Rumiati, & Umità, in press). The aim of this study was to replicate this finding and to then investigate the relevance of the specific hemispheres in these deficits. Nine patients with unilateral lesions (five in the Left Hemisphere and four in the Right) and 20 control subjects, performed a single task requiring mental rotation of hands, and two tasks requiring mental rotation of external objects. RH patients were impaired in the rotation of external objects, but showed intact performance on the rotation of hands; the opposite pattern was found for LH patients. These results support the view that the LH contributes to the mental rotation of hands, recruiting processes specific to motor preparation, while the RH is specialized for mental rotation of external objects.

Adult↗