Biomedical subjects

P Zoccolotti

Publications and source records attributed to P Zoccolotti.

At least 19 recordsLinked to original sources

PubMed2005

Abnormal motor preparation in severe traumatic brain injury with good recovery.

Movement-related cortical potentials (MRCPs) were examined in seven patients with severe traumatic brain injury (TBI) and 12 matched control subjects. All patients had clinically established good recovery by the time of testing. Flexion movements of the index finger of the left or right hand were recorded in two (alternating and repetitive) self-paced conditions and in one externally triggered condition. In control subjects, the bereitschaftspotential (BP) component of MRCP was detected approximately 2000 msec prior to movement onset in the self-paced conditions and was larger and earlier in the alternating compared to the repetitive condition. The BP component was absent in the externally triggered condition. In TBI patients, the BP was greatly reduced and no difference between the alternating-repetitive conditions was detected; in contrast, only small differences were present in the controls for the negative slope (NS) and MP components and no difference for the reafferent positivity (RAP) component. A dipole analysis indicated the supplementary motor area and the premotor area as the likely generators of BP and NS' components, respectively. Gradientrecalled echo magnetic resonance imaging allowed the detection of a number of small hypointense lesions primarily located in the frontal lobes, as in diffuse axonal injury. This pattern of results indicates a selective deficit in motor preparation and a relatively spared pattern of activation during and following movement in these patients. Imaging data appear generally consistent with the pattern of MRCPs observed in the patient group. Implications of these results for the problem of slowness in TBI patients are discussed.

Adult↗

PubMed2001

Influence of the radial and vertical dimensions on lateral neglect.

The influence of radial (near-far) and vertical (upper-lower) dimensions on lateral visuo-spatial neglect was studied using two horizontal line-bisection tasks (one motor and one perceptual). A group of 15 patients with neglect and a group of 14 right-brain damaged patients without neglect were examined. This latter group was used to define the range of variability in line-bisection performance that was independent of neglect. For the radial dimension, some neglect patients showed greater errors in far space than in near space (for both stimuli presented in the upper and lower space). Fewer patients showed the opposite pattern (i.e., greater errors for near-space stimuli). These near-far asymmetries were present for both the motor and perceptual conditions and showed a good degree of intra-individual consistency. This finding contradicts the hypothesis that the motor component is critical for yielding such asymmetry. For the vertical dimension, the results indicated that neglect patients make more bisection errors for lower-space stimuli than for upper-space stimuli. This vertical asymmetry was nearly always confined to stimuli in near space. Asymmetries along the vertical dimension were present for both perceptual and motor conditions, although intra-individual consistency was low. When perceptual and motor conditions were directly compared, several neglect patients showed greater errors in the perceptual than in the motor task.

Aged↗

PubMed2001

Large errors in the perception of vertically are generated by luminance borders (integrated across space) not by subjective borders.

The 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.

Adult↗

PubMed2000

Patterns of attentional impairment following closed head injury: a collaborative European study.

A comprehensive assessment of both selective (focused attention, divided attention) and intensive (alertness and vigilance) attentional processes was performed on 106 patients with closed head injury using a computerised battery for the evaluation of attention. All patients were tested at least five months after their accident. A high percentage of patients were pathological in tests mapping the selective components of attention while only a minority were impaired on tests mapping the intensive components of attention. Three different subgroups of patients with consistent performance patterns were evidenced. The psychometric characteristics of the battery and its possible clinical usefulness are discussed.

Adult↗

PubMed1999

Eye movement patterns in linguistic and non-linguistic tasks in developmental surface dyslexia.

Ten subjects who could be reliably assessed as surface dyslexics were selected on the basis of a large test battery. Eye movements in non-linguistic and linguistic tasks were studied in these subjects. Stability of fixation on a stationary stimulus was examined. Performance of dyslexics was no different from that of an age-matched control group. Similarly, no difference was observed between the two groups when they were requested to saccade to a rightward or leftward target. On the other hand, while reading short passages, dyslexics showed an altered pattern of eye movements with more frequent and smaller rightward saccades as well as longer fixation times. The reading pattern was analysed by eye tracking. Numerous fixations were used to read a single word in a fragmented way. Longer words showed a higher number of fixations. Overall, it was concluded that surface dyslexia is not associated with oculo-motor dysfunction and the study of eye movements in reading reveals the processing through orthography-to-phonology conversion characteristic of surface dyslexia. The importance is stressed of examining selected groups of subjects in the psychophysiological study of dyslexia.

Adolescent↗

PubMed1999

Hierarchical organisation in perception of orientation.

According to Rock [1990, in The Legacy of Solomon Asch (Hillsdale, NJ: Lawrence Erlbaum Associates)], hierarchical organisation of perception describes cases in which the orientation of an object is affected by the immediately surrounding elements in the visual field. Various experiments were performed to study the hierarchical organisation of orientation perception. In most of them the rod-and-frame-illusion (RFI: change of the apparent vertical measured on a central rod surrounded by a tilted frame) was measured in the presence/absence of a second inner frame. The first three experiments showed that, when the inner frame is vertical, the direction and size of the illusion are consistent with expectancies based on the hierarchical organisation hypothesis. An analysis of published and unpublished data collected on a large number of subjects showed that orientational hierarchical effects are independent from the absolute size of the RFI. In experiments 4 to 7 we examined the perceptual conditions of the inner stimulus (enclosure, orientation, and presence of luminance borders) critical for obtaining a hierarchical organisation effect. Although an inner vertical square was effective in reducing the illusion (experiment 3), an inner circle enclosing the rod was ineffective (experiment 4). This indicates that definite orientation is necessary to modulate the illusion. However, orientational information provided by a vertical or horizontal rectangle presented near the rod, but not enclosing it, did not modulate the RFI (experiment 5). This suggests that the presence of a figure with oriented contours enclosing the rod is critical. In experiments 6 and 7 we studied whether the presence of luminance borders is important or whether the inner upright square might be effective also if made of subjective contours. When the subjective contour figure was salient and the observers perceived it clearly, its effectiveness in modulating the RFI was comparable to that observed with luminance borders.

Adult↗

PubMed1997

Developmental surface dyslexia is not associated with deficits in the transient visual system.

Deficits of the transient visual system have been reported in unselected groups of dyslexics. The aim of this study was to examine whether this finding holds when subjects with a specific type of developmental reading disorder (surface dyslexia) are considered. Ten Italian children were examined. They all presented the characteristic markers of surface dyslexia: slow and laborious reading with errors in tasks which cannot be solved with a grapheme-phoneme conversion (i.e., homophones). Contrast sensitivity thresholds to phase-reversal gratings were within normal limits for most subjects both for stimuli presented centrally and in the right parafovea. This indicates that developmental surface dyslexia is not associated with a deficit in the transient system. In contrast, sensitivity to high spatial frequency stationary stimuli was reduced.

Adolescent↗

PubMed1997

Vertical neglect: behavioral and electrophysiological data.

Both behavioral and electrophysiological methods were used to assess altitudinal neglect. In the first experiment, 100 patients with neglect completed Albert's Barrage test. Most omissions were present in the lower left quadrant. In 16 patients, visual evoked potentials to stimuli in the four quadrants were separately recorded (Exp. 2). Latencies in the lower left quadrant were longer than those in the other quadrants. A third experiment provided electrophysiological normative data from 13 young normal subjects. Overall, the results showed that both the horizontal and vertical dimensions of space are affected in neglect patients.

Adult↗

PubMed1997

Frame-of-reference and hierarchical-organisation effects in the rod-and-frame illusion.

Two 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.

Adult↗

PubMed1996

Facilitatory effect of neglect rehabilitation on the recovery of left hemiplegic stroke patients: a cross-over study.

A study of the effect of specific training for visual neglect on the recovery of motor and functional impairment in stroke patients is reported. Two groups of right hemisphere stroke patients with hemispatial neglect and one group without neglect were assessed by means of three functional and neurological scales (Rivermead Mobility Index, Barthel Index, Canadian Neurological Scale). Three evaluations were made at 0, 2 and 4 months from the beginning of physical rehabilitation. During the first 2 months of physical rehabilitation one of the two groups of neglect patients was randomly assigned to specific training for neglect, and the second group to a general cognitive intervention; during the final 2 months of rehabilitation the types of training were switched in the two groups. The non-neglect patients improved steadily during physical rehabilitation. In contrast, the functional recovery of the two neglect groups was time-locked to the period of the specific training for neglect. At the time of admission, the two neglect groups performed at the same level; after 2 months of rehabilitation, the group with neglect training showed higher functional recovery than the group with only general cognitive intervention. When the latter group received neglect training, there was no longer any difference between the two neglect groups. This pattern was present for both of the functional scales used but not for the neurological scale. Motor and functional recovery of stroke patients with neglect seems to be significantly improved by the simultaneous presence of a treatment specifically focused on neglect.

Cerebrovascular Disorders↗

PubMed1996

Eye movement patterns in reading as a function of visual field defects and contrast sensitivity loss.

Saccadic eye movements during reading were examined as a function of the side of visual field cut and the impairment of visual contrast sensitivity Five patients with various visual field defects were compared to five age-matched controls. Patients with right visual field defect showed an increase in the number of rightward saccades and a decrease in their amplitude, and patients with left visual field defects showed a pattern more similar to that of the control subjects. Two patients showed a selective deficit in the range of medium-high spatial frequency; they were the only patients to show a lengthening of mean fixation time during reading. These results indicate selective effects on reading depending on primary sensory defects. The clinical relevance of these findings is briefly discussed.

Adult↗

PubMed1995

Modulation of the rod-and-frame illusion by additional external stimuli.

The presence of an additional external upright frame was studied in three experiments to separate the role of visuovestibular, global, and local mechanisms in the rod-and-frame illusion (RFI). In the first experiment, carried out in a dark room, the external frame surrounded a large tilted frame. Rod-setting errors to the vertical were abolished with the additional-frame condition (at 22 degrees inner-frame tilt) confirming earlier findings. However, small, residual direct (at 11 degrees inner-frame tilt) and indirect effects (at 33 degrees inner-frame tilt) were still present, indicating the persistence of global visual processing. In the second experiment, the RFI in the dark was compared with the RFI with the lights on. Turning the light on abolished the effect at 22 degrees and 33 degrees frame tilt; however, a small direct effect was maintained at 11 degrees frame tilt. These two studies indicate that the addition of veridical vertical information abolishes the effect owing to visuovestibular mechanisms. In the third experiment, a small rod and frame was used with the lights on (a condition abolishing visual-vestibular interaction). In the case of a small gap between the rod and the inducing frame (a condition which maximises local processing), the effect of the outer upright frame was negligible; this indicates that the additional frame had no effect on local processing. In the case of a large gap (a condition which minimises local processing), the external square reduced the illusion, indicating its modulating effect on visual global processing. Overall, an upright external frame exerts a differential influence depending on which mechanisms contribute most to the RFI in a given experimental condition.

Adult↗

PubMed1995

Visual factors affecting the rod-and-frame illusion: role of gap size and frame components.

In two studies the effect of the distance between the tip of the rod and the frame sides (gap) in the rod-and-frame (RF) illusion was examined and the effect of a full-square condition was compared with that of two different frame amputations. In both studies, there were more rod-setting errors in the direction of the tilt of the inducing figure with a small gap than with a large one. These findings are consistent with the idea that in the case of small gap size local interactions contribute to determining the RF illusion. The actual length of the rod was varied in order to keep the gap constant across different frame tilts; therefore these findings cannot be due to the co-variation between gap size and frame tilt which is typical of standard apparatuses. The effect of frame amputations was compared to the full-square condition. According to Wenderoth and Beh, amputations that maintain the two orthogonal contours of the square produce the typical angular function of the RF illusion. This prediction was confirmed in both studies. However, results indicate that the full square has a stronger illusory effect in the case of a small degree of tilt of the inducing stimulus, irrespective of gap size. It is suggested that this 'square superiority' effect is related to global, not local, mechanisms. To pursue Wenderoth and Beh's observations, amputations close to the vertical meridian were used in one experiment and those close to the horizontal meridian in the second experiment. Contrary to predictions, these conditions produced overlapping results.

Adult↗

PubMed1995

Selective reading slowness in a traumatic patient with impairment in basic visual processes.

Following a closed-head injury, G.M., a 17-year-old male, showed a reading disturbance in the absence of other cognitive deficits. G.M.'s reading was exceedingly slow, although virtually error free. Analysis of his disorder indicated an inability to read words presented tachistoscopically to the left (spared) visual field. Therefore the reading deficit cannot be interpreted as simply due to the visual field reduction (hemianopic alexia). Reading speed was clearly affected by word length, a finding typical of letter-by-letter reading. Both behavioral and psychophysical testing indicated a selective reduction of visual discrimination and detection (particularly in the range of high spatial frequency information) in portions of the left hemifield which appeared spared upon perimetric examination. Overall, it is suggested that the reading deficit, phenomenologically similar to that of other letter-by-letter readers, can be interpreted as due to a combination of basic visual perturbations: visual field cut with macular splitting and deficit of processing of high spatial frequency information.

Adolescent↗

PubMed1995

Effectiveness of neglect rehabilitation in a randomized group study.

The effectiveness of neglect rehabilitation training has been studied in two randomly selected groups of right brain-damaged patients. All patients proved heminattentive on a standard battery 2 months or more after the CVA. One group received 2 months of treatment immediately after admission to a clinic, and the other group received only general cognitive stimulation for the same amount of time. At the end of this period a comparison showed significant improvement in the first group, based on a standard test battery and a functional scale. The second group was then given rehabilitation training for neglect for the same amount of time and obtained similar improvement. It is concluded that the rehabilitation program produces significant results, which generalize to situations similar to those of everyday life. The importance of the duration of training on the generalization of learning is briefly discussed with reference to previous negative reports in the literature.

Aged↗

PubMed1995

Local and global visual mechanisms underlying individual differences in the rod-and-frame illusion.

The role of local and global visual mechanisms in individual differences in the rod-and-frame (RF) effect was investigated. Field-dependent observes, selected on the basis of Witkin and Ash's (1948) classical procedure, were submitted to the small RF test (Coren & Holy, 1986). Four frame tilts and two gap sizes were used. As expected, direct effects (i.e., rod settings in the direction of frame tilt) were observed at small degrees of frame tilt, while indirect effects (i.e., rod settings in the direction opposite that of frame tilt) were observed at larger frame tilts. Field-dependent observers showed larger direct effects in the case of the small gap. Indirect effects were comparable in both field-dependent and field-independent subjects, regardless of gap size. Following the model proposed by Wenderoth and Johnstone (1987), these findings indicate that low-level visual mechanisms, responsible for local orientation interactions, have a different gain in field-dependent and field-independent individuals. In contrast, global visual mechanisms, presumably acting by means of long-range mechanisms, do not distinguish between these two subgroups.

Adult↗

PubMed1993

The gap between rod and frame influences the rod-and-frame effect with small and large inducing displays.

The role of the spatial separation between the ends of a rod and a frame's inner edge (gap) in modulating the rod-and-frame effect (RFE) has been studied here with frames subtending either large or small retinal angles. With a large frame, rod settings were always in the direction of frame tilt (direct effects) and varied inversely with gap size. With a small frame, rod settings were in the direction of frame tilt for tilts between 7.5 degrees and 15 degrees; with larger frame tilts, rod settings in the direction opposite that of the frame were observed (indirect effects). Increasing gap size produced a tendency toward negativity (away from frame tilt). Consequently, direct effects were larger for small gaps, while the opposite was true for indirect effects. Overall, these results point to the importance of gap size in modulating the RFE, for both large and small displays.

Adult↗

PubMed1992

The role of frame size on vertical and horizontal observers in the rod-and-frame illusion.

The rod-and-frame illusion was used to examine a proposed distinction between the mechanism responsible for frame effects on rod-adjustment errors with large displays and the mechanism responsible for errors with small displays. It was suggested that visual-vestibular mechanisms are involved only when the rod is surrounded by a large tilted frame. Errors in the perceived vertical with small frame would instead be due to purely visual mechanisms. To examine this dual process model, we compared errors at small and large frame when the body was vertical or horizontal. There is evidence to suggest that tilting the body affects visual-vestibular interactions, but there is no reason to expect that body tilt would affect intravisual interactions. Hence, we hypothesized that body tilt would increase errors for large frame, but not for small frame. Eight subjects were tested in four different conditions, corresponding to the combination of two body orientations (vertical versus horizontal) and two frame sizes (47.5 versus 10.5 deg of visual angle). Fourier analysis of data was performed. Repeated measures ANOVA tested the hypothesis about frame size and body orientation. The hypothesis was not confirmed. More specifically, we found that tilting the body increased errors for the small frame as well as for the large frame. The interaction between frame size and body orientation was not significant. Results are discussed in relation to the proposed dual-process model.

Adult↗