Biomedical subjects

M Gangitano

Publications and source records attributed to M Gangitano.

12 recordsLinked to original sources

PubMed1998

Haptic information differentially interferes with visual analysis in reaching-grasping control and in perceptual processes.

We used an interference paradigm in order to study integration between haptic and visual information in motor control and in perceptual analysis. Subjects either reached and grasped a visually presented sphere or matched its size with their left hand while manipulating with their right hand another sphere whose size could be smaller or greater. In four experiments haptic analysis of the manipulated sphere could be either automatically incorporated with or explicitly dissociated from visual analysis. In a fifth experiment reaching-grasping and matching were executed with the right hand, whereas manipulation was executed with the left hand. Manipulation with the right hand influenced finger shaping during grasping with the left hand when the sizes of the two objects were different. Interference was observed mainly in those experiments in which haptic analysis could be automatically integrated with visual analysis. In the matching task, no effect was observed. Finally, manipulation with the left hand did not produce any interference effect on reaching-grasping and matching executed by the right hand. The results of the present study suggest that somesthetic information is integrated with visual information only in sensorimotor transformations. In addition, they support the notion that the left hemisphere together with the right hemisphere is involved in the control of left hand reaching-grasping movements.

Adult↗

PubMed1998

Implicit visual analysis in handedness recognition.

In the present study, we addressed the problem of whether hand representations, derived from the control of hand gesture, are used in handedness recognition. Pictures of hands and fingers, assuming either common or uncommon postures, were presented to right-handed subjects, who were required to judge their handedness. In agreement with previous results (Parsons, 1987, 1994; Gentilucci, Daprati, & Gangitano, 1998), subjects recognized handedness through mental movement of their own hand in order to match the posture of the presented hand. This was proved by a control experiment of physical matching. The new finding was that presentation of common finger postures affected responses differently from presentation of less common finger postures. These effects could be not attributed to mental matching movements nor related to richness in hand-finger cues useful for handedness recognition. The results of the present study are discussed in the context of the notion that implicit visual analysis of the presented hands is performed before mental movement of one's hand takes place (Parsons, 1987; Gentilucci et al., 1998). In this process, hand representation acquired by experience in the control and observation of one's and other people's hand gestures is used. We propose that such an immediate recognition mechanism belongs to the class of mental processes which are grouped under the name of intuition, that is, the processes by which situations or people's intentions are immediately understood, without conscious reasoning.

Adult↗

PubMed1998

Visual distractors differentially interfere with the reaching and grasping components of prehension movements.

In the present study we addressed the issue of how an object is visually isolated from surrounding cues when a reaching-grasping (prehension) movement towards it is planned. Subjects were required to reach and grasp an object presented either alone or with a distractor. In five experiments, different degrees of elaboration of the distractor were induced by varying: (1) the position of the distractor (central or peripheral); (2) the time when the distractor was suppressed (immediately or delayed, with respect to stimulus presentation); and (3) the type of distractor analysis (implicit or explicit). In addition, we tested whether the possible effects of the distractor on reaching-grasping were due to the use of an allocentric reference centered on it. This was obtained by comparing the effects of the distractor with those of a stimulus, the target of a placing movement successive to the reaching-grasping. The results of the five experiments can be summarized as follows. The necessary condition for an interference effect on both the reaching and the grasping components was the central presentation of the distractor. When the information on the distractor could be immediately suppressed, an interference effect was observed only on the grasp component. In the case of delayed suppression, an effect was found on the reaching component. Finally, when an overt analysis of the distractor was required, the interference effect disappeared. Two main conclusions have been drawn from the results of the present study. First, comparison between properties of the target and surrounding cues is performed by two independent processes for reaching and grasping an object. The process for the grasp relies more on allocentric cues than that for the reach. Second, when surrounding stimuli are automatically analyzed during visual search of the target, the process of visuo-motor transformation can incorporate their features into the target. In contrast, overt analysis of surrounding stimuli is performed separately from that of the target. Finally, the data of the present study are discussed in support of the premotor theory of attention.

Adult↗

PubMed1998

Right-handers and left-handers have different representations of their own hand.

The visual control of our own hand when dealing with an object and the observation of interactions between other people's hand and objects can be involved in the construction of internal representations of our own hand, as well as in hand recognition processes. Therefore, a different effect on handedness recognition is expected when subjects are presented with hands holding objects with either a congruent or an incongruent type of grip. Such an experiment was carried out on right-handed and left-handed subjects. We expected that the different degree of lateralisation in motor activities observed in the two populations [J. Herron, Neuropsychology of left-handedness, Academic Press, New York, 1980.] could account for the construction of different internal hand representations. As previously found [L.M. Parsons, Imaged spatial transformations of one's hands and feet, Cogn. Psychol., 19 (1987) 178-241.], in order to identify handedness, subjects mentally rotated their own hand until it matched with the presented one. This process was confirmatory, being preceded by an implicit visual analysis of the target hand. Presentation of hands holding objects with congruent or incongruent types of grip influenced handedness recognition at different stages in right-handed and left-handed subjects. That is, the mental rotation stage was affected in right-handed subjects, whereas the initial phase of implicit hand analysis was affected in left-handed subjects. We suggest that in handedness recognition, left-handers relied more on a pictorial hand representation, whereas right-handers relied more on a pragmatic hand representation, probably derived from experience in the control of their own movements. The use of different hand representations may be due to differential activation of temporal and premotor areas.

Adult↗

PubMed1998

Influence of automatic word reading on motor control.

We investigated the possible influence of automatic word reading on processes of visuo-motor transformation. Six subjects were required to reach and grasp a rod on whose visible face the word 'long' or 'short' was printed. Word reading was not explicitly required. In order to induce subjects to visually analyse the object trial by trial, object position and size were randomly varied during the experimental session. The kinematics of the reaching component was affected by word presentation. Peak acceleration, peak velocity, and peak deceleration of arm were higher for the word 'long' with respect to the word 'short'. That is, during the initial movement phase subjects automatically associated the meaning of the word with the distance to be covered and activated a motor program for a farther and/or nearer object position. During the final movement phase, subjects modified the braking forces (deceleration) in order to correct the initial error. No effect of the words on the grasp component was observed. These results suggest a possible influence of cognitive functions on motor control and seem to contrast with the notion that the analyses executed in the ventral and dorsal cortical visual streams are different and independent.

Acceleration↗

PubMed1997

Eye position tunes the contribution of allocentric and egocentric information to target localization in human goal-directed arm movements.

Subjects were required to point to the distant vertex of the closed and the open configurations of the Müller-Lyer illusion using either their right hand (experiment 1) or their left hand (experiment 2). In both experiments the Müller-Lyer figures were horizontally presented either in the left or in the right hemispace and movements were executed using either foveal or peripheral vision of the target. According to the illusion effect, subjects undershot and overshot the vertex location of the closed and the open configuration, respectively. The illusion effect decreased when the target was fixated and when the stimulus was positioned in the right hemispace. These results confirm the hypothesis that both egocentric and allocentric information are combined in order to encode target position in space. When movements are directed to foveal targets, decreasing effects of allocentric cues, as shown by decreasing the illusion effect, could be due to enhanced efficiency of the egocentric system. That is, information on eye position when target is fixated can be used to precisely establish its spatial relations with the body. In addition, a more accurate analysis of allocentric information is hypothesized when the target is positioned in the left hemispace. In other words, our data confirm the notion that the right cerebral hemisphere is involved in space representation.

Adult↗

PubMed1997

Tactile input of the hand and the control of reaching to grasp movements.

The role of tactile information of the hand in the control of reaching to grasp movements was investigated. The kinematics of both reaching (or transport) and grasp components were studied in healthy subjects in two experimental conditions. In one condition (control condition) subjects were required to reach and grasp an object that could have two sizes and that could be located at two distances from the viewer. In the other condition (anaesthesia condition) the same movements were executed, but anaesthesia was provided to the subjects' fingertips. In both conditions vision of the hand was prevented during movement. Anaesthesia affected mainly the kinematics of the first phase of grasping, that is, the finger-opening phase. This phase was lengthened and maximal finger aperture increased. In contrast, the duration of the successive phase (finger-closure) was poorly modified. The reaching component was also impaired by anaesthesia. Although the total extent of hand path and the spatial relations between the finger aperture and closure phases did not change between the two conditions, hand path variability increased. This occurred during transport deceleration phase and after the increase in variability of finger path. In addition, the whole movement was slowed down. The results of the present experiment suggest that tactile signals at the beginning and at the end of movement can be used to compute grasp time and to optimise grasp temporal parameters. Alternatively, signals from tactile receptors can be involved in encoding the position sense of the fingers. When this input is lacking, the control of grasp and in particular that of finger-opening phase can be impaired. Finally, the effect of the grasp impairment on the reaching component supports the notion that the coordination between reaching and grasping involves the whole temporal course of the two components.

Adult↗

PubMed1997

Planning an action.

The motor control of a sequence of two motor acts forming an action was studied in the present experiment. The two analysed motor acts were reaching-grasping an object (first target) and placing it on a second target of the same shape and size (experiment 1). The aim was to determine whether extrinsic properties of the second target (i.e. target distance) could selectively influence the kinematics of reaching and grasping. Distance, position and size of both targets were randomly varied across the experimental session. The kinematics of the initial phase of the first motor act, that is, velocity of reaching and hand shaping of grasping, were influenced by distance of the second target. No kinematic difference was found between movements executed with and without visual control of both hand and targets. These results could be due to computation of the general program of an action that takes into account extrinsic properties of the final target. Conversely, they could depend on a visual interference effect produced by the near second target on the control of the first motor act. In order to dissociate the effects due to second target distance from those due to visual interference, two control experiments were carried out. In the first control experiment (experiment 2) subjects executed movements directed towards spatial locations at different distances from the first target, as in experiment 1. However, the near second target was not presented and subjects were required to place the object on an arbitrary near position. Distance of the second (either real or arbitrary) target affected the reaching component of the first motor act, as in experiment 1, but not the grasp component. In the second control experiment (experiment 3), the pure visual interference effect was tested. Subjects were required to reach and grasp the object and to lift it in either presence or absence of a second near stimulus. No effect on the initial phase of the first motor act was observed. The results of the this study suggest a dissociation in the control of reaching and grasping, concerning not only visual analysis of extrinsic properties of the immediate target but also visual analysis of the final target of the action. In other words, the notion of modularity for the motor control can be extended to the construction of an entire action.

Adult↗

PubMed1996

On orienting the hand to reach and grasp an object.

Subjects were required to reach and grasp a parallelepiped, the position, orientation and size of which were varied. The kinematics of reaching and grasping movements was studied in full vision and in no vision conditions. Both direction and movement amplitude of reaching were affected by object orientation. Conversely, both the time course of finger axis orientation and the angular displacement of the hand at wrist were influenced by object position. These results were not modified by the absence of visual control. Finger aperture during grasping was affected by both object size and orientation. This latter result was not due to a distorted size perception, as shown by a control matching experiment. Taken together, the results of the present study suggest the integration between distal and proximal components during reaching and grasping.

Adult↗

PubMed1996

Transient topographical amnesia and cingulate cortex damage: a case report.

Transient topographical amnesia (TTA) is the temporary inability to find one's way in familiar or unfamiliar surroundings due to the inability to use well known environmental landmarks for route finding. The syndrome has not been described as having any obvious aetiology and has been thought to be caused by a vascular deficit in right hemispheric structures which are crucial for topographic recognition, i.e. parietal association and parahippocampal cortex. The patient described in the present study complained of several critical episodes of TTA and tonic rigidity of the left limbs. Neuropsychological assessment was normal except for a deficit in spatial memory tasks. Magnetic resonance (MR) imaging of the brain showed an angioma at the border of areas 24d and 23 of the right cingulate cortex. Because area 23 is strategically located in a network that links the parietal associative (area 7a) and parahippocampal cortices, and because these cortical areas are involved in topographical orienting processes, we suggest that a transient functional inactivation of the network caused by epileptic discharges spreading from the damaged cingulate cortex towards the parahippocampal and parietal association cortex could account for the spatial disorder. Similar discharges spreading from area 24d towards the primary motor cortex and/or the spinal cord could account for the episodes of tonic rigidity of the left limbs.

Amnesia↗

PubMed1996

The IHS classification criteria for migraine headaches in adolescents need minor modifications.

The operational and diagnostic criteria for migraine and all other headache disorders released in 1988 by the International Headache Society are universally considered reliable and exhaustive. These criteria, however, cannot be considered as satisfactory for population-based studies on migraine prevalence, especially if adolescents are the subjects of the study. Using these diagnostic criteria, we conducted an epidemiological study in order to assess the prevalence of migraine headache in a student population aged 11 to 14 years. Our survey made it possible to code IHS 1.1 (migraine without aura) in 2.35%, IHS 1.2 (migraine with aura) in 0.62%, IHS 1.7 (migrainous disorders not fulfilling migraine criteria) in 1.52%, and IHS 13 (headache not classifiable) in 1.38% of the examined pupils. In adolescents, the low prevalence estimates of migraine headache coded IHS 1.1 and the relatively high prevalence estimates of headaches coded IHS 1.7 and IHS 13 have appeared to be a consequence of the rigidity of some operational diagnostic criteria of the recent IHS classification rather than of the geographical, environmental, or socioeconomical peculiarities of the cohort. Therefore, in order to improve the reliability and the exhaustiveness of the IHS classification by increasing its sensitivity, we believe that minor modifications of the diagnostic criteria are necessary. Within these revised criteria, the subitem "moderate or severe intensity" of pain headache should become mandatory, whereas the lower limit of the criterion "duration of pain" should be reduced to 1 hour.

Adolescent↗

PubMed1994

Monosymptomatic presentation of type I Arnold-Chiari malformation: report of two cases.

Two cases of type I ACM are described, one of which presented with dizziness in late childhood (case 1), the other with mild intention tremor in adulthood (case 2). Cerebellar ectopia should be considered in monosymptomatic patients even in the absence of other symptoms and signs of C.N.S. dysfunction. Magnetic resonance imaging of the craniocervical junction should be performed because it may be diagnostic for type I ACM.

Adolescent↗