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Kinematics of reaching-grasping movement towards stimuli of three different sizes located at two different distances were studied in one monkey (Macaca nemestrina). Transport and manipulation components were analyzed using the ELITE system. Transport time, peak velocity and deceleration phase of velocity were influenced by stimulus size, whilst acceleration phase remained unmodified. Peak velocity clearly increased with distance, while transport time remained constant (isochrony ). The main parameters of manipulation component were all influenced by stimulus size but they did not vary with distance. A comparison with kinematic data obtained from human subjects was made.

The display was composed of four boxes, horizontally aligned above the fixation point. In Experiment I, each box was cued by a digit shown at fixation. In Experiment II there were only two numeric cues, signalling the inner or the outer boxes, depending on the experimental condition. The subject was instructed to orient attention to the cued box, and to respond to the imperative stimulus as fast as possible, wherever it appeared. By using four time interval (SOAs), we tried to determine the route covered by attention movements. In Experiment I, with the shortest SOA (100 msec), it was shown that attention does not reach the cued box through a direct path. Rather it moves first on the inner boxes, thereafter focusing on the cued location. The same results were obtained in Experiment II, where the cue directed attention to the inner boxes. When the external boxes were cued, however, this trend was not observed.

In this experiment, two rows of four boxes, one above and the other below the fixation point, were displayed on a computer monitor. A cognitive numeric cue indicated one of the four external boxes, where the attention was to be directed. Stimuli, however, could occur in any of the eight boxes. The subject was instructed to respond to the imperative stimulus as fast as possible, regardless of its location. Four time intervals between cue and stimulus presentation (SOAs) were employed in order to disclose the route along which attention is moved. With the shortest SOA (100 msec) an indication that attention movements follow the cartesian/orthogonal axes was shown.

Lateralized presentations of verbal stimuli yield faster reaction times in the right visual field-left hemisphere, whereas nonverbal stimuli yield faster reaction times in the left visual field-right hemisphere. However, the problem of how lateral asymmetries in response latency are determined is still unsolved. The hypothesis of an absolute functional specialization of the two hemispheres suggests that information presented in the visual field connected with the unspecialized hemisphere has to travel along a less direct pathway, implying a crossing through the forebrain commissures, to reach the processing center. The hypothesis of a relative functional specialization assumes that stimuli are processed by the hemisphere contralateral to the field of presentation but speed of processing varies as a function of hemispheric specialization. The present study tried to find empirical evidence in favor of one of the two hypotheses. Choice reaction times to lateralized verbal stimuli were studied in normal subjects. In half of the trials the subjects had to carry out a concomitant task known to interfere selectively with mechanisms responsible of the organization of the responses of the left hemisphere. Both with and without concomitant task reaction times were significantly faster in the right visual field-left hemisphere. While the concomitant task produced an overall lengthening of reaction time, it did not affect interhemispheric asymmetry. This finding was discussed as evidence in favor of the absolute specialization hypothesis.

The effect of unilateral surgical ablations of lateral part of inferior parietal lobule (area 7b) has been studied in the macaque monkey. The following neurological deficits were found: 1) A hemi-inattention for tactile stimuli applied to the hemiface and hand contralateral to the lesion; 2) A hemi-inattention for visual stimuli in the contralateral peripersonal space; 3) A reluctance to use the contralateral arm; 4) A mild and transient deficit in mouth grasping movements towards stimuli contralaterally presented; 5) Postural abnormalities of the hand contralateral to the lesion. It is proposed that area 7b is involved in the perception of the peripersonal space and in the organization of movements towards stimuli presented in that space.

Subpial unilateral ablations of the postarcuate cortex (area 6) were performed in four macaque monkeys. After the operation the animals showed a tactile contralateral neglect and a visual neglect for stimuli presented in the space immediately around the contralateral hemiface, they tended to use the hand ipsilateral to the lesion and their mouth and face movements in response to contralateral stimuli were disorganized. No primary motor deficits were described. With time there was a marked recovery of the symptomatology, but the preference for using the ipsilateral hand and extinction of the contralateral stimuli were present until the animals' death. The deficits after the postarcuate cortex are discussed with reference to previous electrophysiological data.

Simple reaction times to lateralized visual stimuli were studied in normal subjects while they were carrying out a concomitant task. The concomitant task consisted in the exploration of a visual maze presented in the middle of a screen. Regardless of the hand used, the concomitant task produced a specific lengthening of the responses to stimuli located in the left visual field. It is concluded that the right hemisphere plays a major role in the organization of ocular movements during active exploration of visual environment.

The experiment was conducted to investigate, by using kinematic parameters, the influence of the type of prehension on the transportation component in reaching-grasping movements. The main question was whether the transportation component is influenced by the type of prehension besides the distance of the object. The experiment was carried out on eight subjects who performed reaching-grasping movements toward objects located at different distances. Two types of prehension were examined: whole hand prehension and precision grip. The following kinematic parameters of the transportation component (wrist movement) were studied: movement times, profiles of velocity and accelerations. Our results have shown that the transportation component is affected by the two factors. However the kinematic parameters were influenced differently by the distance and the type of prehension. Our conclusion is that, although distance and type of prehension affect the transportation component, they are computed separately in programming this component.

Horseradish peroxidase conjugated with wheat germ agglutinine was injected in restricted parts of the postarcuate cortex in the macaque monkey. Anterograde and retrograde transport was found in the parietal and frontal lobes. In the parietal lobe two areas were marked: the antero-lateral part of area 7 and the superior bank of the sylvian fissure. In the frontal lobe the marked areas were the precentral motor cortex, the supplementary motor area and the gyrus cinguli. The intrinsic connections within the postarcuate cortex were rich and widespread. The hand representation was connected anterogradely and retrogradely with the mouth representation and anterogradely with the leg representation; the mouth representation was connected both ways with the hand representation but not with the leg area. The richness of intrinsic connections in the postarcuate cortex supports the suggestion that this area is involved in the organization of sequential motor acts.

Single neurons and polispike activity were recorded from the superior colliculus of anesthetized, behaving monkeys. In agreement with previous findings neurons of the superficial layers responded exclusively to visual stimuli. In the intermediate layers most neurons were oculomotor, although some of them showed also a visual receptive field. No neurons responding to tactile or auditory stimuli were found. Occasionally the discharge of an oculomotor neuron increased if the ocular movement was triggered by a visual or an acoustical stimulus. Rare tacticle and auditory neurons were recorded in deep layers. However their receptive fields were difficult to map and their responses lacked the precision of the responses of the specific acoustic and tactile areas. Electrical stimulation of the SC produced contralateral eye and head movements, the threshold being high in the superficial layers and low in the intermediate and deep ones. In the deep layers complex limb and trunk movements could be also elicited. In conclusion, in contrast with carnivores and other mammals, the primate superior colliculus appears to be dominated by the visual modality.

Simple reaction time to a lateralized visual stimulus was studied in normal subjects while they were carrying out a concomitant task. The concomitant task consisted in a flexion of a single finger or pairs of finger at the middle joint. Regardless of the hand used the concomitant tasks produced a specific lengthening of responses to stimuli located in the left visual field. It is concluded that isolated finger movements, separate from a sequence of movement, are function of the right hemisphere.

Choice reaction times of two lateralized unstructured visual stimuli located within the same (right or left) visual hemifield were studied in subjects with hands crossed and uncrossed. The subjects were instructed to respond with their right or left hand depending on the position of the stimulus. In one experimental condition they have to use their right hand for responding to the right light and their left hand for responding to the left light. In another experimental condition the reverse arrangement was used. The two light stimuli were presented, one at a time and 3 degrees apart, in both visual fields. Thus, the analyzed factors were: hand position (crossed or uncrossed), responding hand (right or left), field of presentation (right or left), and relative position of the light stimulus (right or left). The main finding of the present study was that spatial compatibility effects were present even when both stimuli were presented within the same visual field. That means that the factor determining which hand is faster in responding is the relative position of the two stimuli and of the two hands and not the position of the stimuli with reference to the vertical meridian.

Simple reaction times to lateralized unstructured visual stimuli were studied in normal subjects while they were carrying out a concomitant task. In one task strings of four digits, randomly chosen from 1 to 9, were acoustically presented to the subjects who had to repeat them at the end of each presentation, in a second task again strings of four digits were presented and the subjects were asked to pay attention to the stimuli without memorizing them. In order to compel the subjects to listen carefully to the stimuli, in the second experiment, intermixed with the digits, a letter was occasionally presented and the subjects had to repeat it. It was found that the memory task facilitates reaction times mediated by the left hemisphere, whereas no hemispheric differences were found in the purely attentional task.