1,721,004 research outputs found
Steady-state VEPs in neglect patients have longer latencies for luminance but not equiluminant patterns
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Professor Adriana Fiorentini: 1/11/1926-29/2/2016
No full textAdriana Fiorentini was for many decades a pillar of the CNR Institute for Neurophysiology (then Neuroscience). On February 29, 2016, she passed away peacefully in her sleep, with a smile. A whole generation of vision scientists remembers her with love and respect. Her wisdom, intelligence, dedication to science, enthusiasm for research, and love of knowledge set an example to us all. She was a role model of respect, generosity, patience, collaboration, and true humility: discrete and reserved, always there for her students and colleagues
Rhythmic modulation of visual contrast discrimination triggered by action
No full textRecent evidence suggests that ongoing brain oscillations may be instrumental in binding and integrating multisensory signals. In this experiment, we investigated the temporal dynamics of visual-motor integration processes. We show that action modulates sensitivity to visual contrast discrimination in a rhythmic fashion at frequencies of about 5 Hz (in the theta range), for up to 1 s after execution of action. To understand the origin of the oscillations, we measured oscillations in contrast sensitivity at different levels of luminance, which is known to affect the endogenous brain rhythms, boosting the power of alpha-frequencies. We found that the frequency of oscillation in sensitivity increased at low luminance, probably reflecting the shift in mean endogenous brain rhythm towards higher frequencies. Importantly, both at high and at low luminance, contrast discrimination showed a rhythmic motor-induced suppression effect, with the suppression occurring earlier at low luminance. We suggest that oscillations play a key role in sensory-motor integration, and that the motor-induced suppression may reflect the first manifestation of a rhythmic oscillation
Contrast sensitivity loss in the neglected hemifield
No full textContrast sensitivity to gratings of various spatial frequencies displayed in the left and right visual hemifield was measured in a group of ten right brain-damaged patients with unilateral visuospatial neglect. Two groups of ten left brain-damaged (LBD) and ten right brain-damaged (RBD) patients without neglect served as controls. All patients had normal visual fields according to standard clinical procedure. Stimuli were patches of sinusoidal gratings of 1, 2, 4 and 8 c/deg spatial frequency. The patches subtended 6 deg and were displayed at 3 deg of eccentricity. A two-alternative forced-choice technique was employed. Results showed a reduction in contrast sensitivity for stimuli presented to the contralesional hemifield with respect to the ipsilesional hemifield in patients with neglect. No difference in contrast sensitivity between hemifields was found for LBD and RBD groups. These findings indicate a basic visual impairment in the contralesional hemifield in patients with neglec
Characteristics of writing disorders in Italian dyslexic children
No full textObjective: This study characterizes the spelling impairment of Italian dyslexic children and evaluates the relationship between reading and spelling disorders. Background: Developmental spelling deficits are much less investigated than reading deficits. Based on the dual-model approach, studies of English speaking subjects describe a surface and a phonological syndrome. In languages with shallow orthographies, there is evidence of surface and phonological dyslexia, but no data are available for dysgraphia. Methods: Eighteen dyslexic children were studied. Writing was investigated by means of a spelling test that included regular words with one-sound-to-one-letter correspondence, regular words requiring syllabic conversion rules, words with unpredictable transcription and non-words with one-sound-to-one-letter correspondence. The dyslexics' spelling errors were compared to those of 30 age-matched proficient readers. Results: The dyslexic participants were very slow readers. Their errors were compatible with the hypothesis of a prevalent use of the sub-lexical reading procedure (i.e., surface dyslexia). They were also generally impaired with respect to the control children in all sub-sections of the spelling test. However, multivariate and single case analyses as well as qualitative analysis of errors indicated that their major problem was writing words with unpredictable transcription. This failure was consistent with the view of prevalent sub-word level processing in writing. Conclusion: The pattern of the spelling impairment mirrors the children’s reading impairment, with most children suffering from surface dysgraphia
Frame-of-reference and hierarchical-organization effects in the rod-and-frame Illusion.
No full textTwo hypotheses proposed as alternatives by Rock -- frame of reference and hierarchical organisation of perception -- were tested in a series of experiments with the use of the rod-and-frame illusion. This illusion produces errors in the apparent vertical due to the presence of a tilted frame surrounding the test rod. The apparent vertical is shifted in the direction of the frame tilt. When an upright square was added inside the tilted frame, rod-setting errors varied according to the visual characteristics of the display. In the case of a large display presented in the dark (experiment 1), there continued to be large errors in the direction of the outer-square tilt. This finding supports the frame-of-reference hypothesis, which proposes that the orientation of all objects in the visual field is dominated by the most peripheral reference. In the case of a small display presented in a lit environment (experiments 2 and 3), the direction of errors was the opposite. This latter finding was taken to indicate that the rod was set with reference to the perceived tilt of the inner upright square. Thus, according to a hierarchical - organisation hypothesis, the orientation of an object in the visual field is influenced by objects in the immediate surroundings not by outermost reference.
Overall, the results confirm the presence of two qualitatively different classes of orientational phenomena: one is concerned with the definition of egocentric coordinates and one with an object-centred visual representation
VEPs in neglect patients have longer latencies for luminance but not for chromatic patterns
No full textLarge errors in the perception of verticality are generated by luminance borders (integrated across space) not by subjective borders
No full textThe rod-and-frame illusion shows large errors in the judgment of visual vertical in the dark if the frame is large and there are no other visible cues (Witkin and Asch, 1948 Journal of Experimental Psychology 38 762-782). Three experiments were performed to investigate other characteristics of the frame critical for generating these large errors. In the first experiment, the illusion produced by an 11 degrees tilted frame made by luminance borders (standard condition) was considerably larger than that produced by a subjective-contour frame. In the second experiment, with a 33 degrees frame tilt, the illusion was in the direction of frame tilt with a luminance-border frame but in the opposite direction in the subjective-contour condition. In the third experiment, to contrast the role of local and global orientation, the sides of the frame were made of short separate luminous segments. The segments could be oriented in the same direction as the frame sides, in the opposite direction, or could be vertical. The orientation of the global frame dominated the illusion while local orientation produced much smaller effects. Overall, to generate a large rod-and-frame illusion in the dark, the tilted frame must have luminance, not subjective, contours. Luminance borders do not need to be continuous: a frame made of sparse segments is also effective. The mechanism responsible for the large orientation illusion is driven by integrators of orientation across large areas, not by figural operators extracting shape orientation in the absence of oriented contours
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