Visual similarity modulates visual size contrast.

Perception is relational: object properties are perceived in comparison to the spatiotemporal context rather than absolutely. This principle predicts well known contrast effects: For instance, the same sphere will feel smaller after feeling a larger sphere and larger after feeling a smaller sphere (the Uznadze effect). In a series of experiments, we used a visual version of the Uznadze effect to test whether such contrast effects can be modulated by organizational factors, such as the similarity between the contrasting inducer stimulus and the contrasted induced stimulus. We report that this is indeed the case: size contrast is attenuated for inducer-inducing pairs having different 3D shapes, orientations, and even - surprisingly - color and lightness, in comparison to equivalent conditions where these features are the same. These findings complement related work in revealing basic mechanisms for fine-tuning local interactions in space-time in accord to the global stimulus context.

Listening to action-related sentences modulates the activity of the motor system: a combined TMS and behavioral study.

Transcranial magnetic stimulation (TMS) and a behavioral paradigm were used to assess whether listening to action-related sentences modulates the activity of the motor system. By means of single-pulse TMS, either the hand or the foot/leg motor area in the left hemisphere was stimulated in distinct experimental sessions, while participants were listening to sentences expressing hand and foot actions. Listening to abstract content sentences served as a control. Motor evoked potentials (MEPs) were recorded from hand and foot muscles. Results showed that MEPs recorded from hand muscles were specifically modulated by listening to hand-action-related sentences, as were MEPs recorded from foot muscles by listening to foot-action-related sentences. This modulation consisted of an amplitude decrease of the recorded MEPs. In the behavioral task, participants had to respond with the hand or the foot while listening to actions expressing hand and foot actions, as compared to abstract sentences. Coherently with the results obtained with TMS, when the response was given with the hand, reaction times were slower during listening to hand-action-related sentences, while when the response was given with the foot, reaction times were slower during listening to foot-action-related sentences. The present data show that processing verbally presented actions activates different sectors of the motor system, depending on the effector used in the listened-to action.

Modulation of inhibition of return by type and number of dynamic changes of the cue.

Inhibition of return (IOR) is a response delay when the target is preceded by an irrelevant stimulus (cue) at the same location. In a previous study, we investigated the separate and joint effects on IOR of cue onset and offset. IOR was much greater when cue onset was followed by cue offset (on-off cue) than when the cue was a single event (on or off cues). The aim of the present study was to test whether the greater IOR with an on-off cue is due to the presence of two cue events. Three experiments were conducted. In Experiment 1 we replicated, with a different delay between cue onset and offset, the finding that IOR is greater with an on-off cue than with a single cue event. In Experiments 2 and 3, we used cues formed by two events. In Experiment 2, an on-off cue was compared with an off-on cue, whereas in Experiment 3 an on-on cue was compared with an off-off cue. Results showed that the magnitude of IOR did not simply depend on the number of cue events occurring before the target. IOR was greater with two different events than with two identical events and greater when was preceded by an off-event than an on-event. Therefore, IOR was greatest with an on-off cue, which likely also benefited from a gap effect. Possible mechanisms underlying IOR were discussed.

Inhibitory and facilitatory effects of cue onset and offset.

The response speed to a visual target is modulated by the position of previous events (cues) even if their position is not predictive of the target position. The modulation has been considered biphasic, with an early facilitatory and a later inhibitory component. We conducted three experiments that investigated the importance of the onset and offset features of the cue for the facilitatory and inhibitory effects and estimated their separate and joint effects. The two possible target locations, one in the right and one in the left visual field, were indicated by two empty boxes, and the cue consisted of the onset and/or offset of an arrowhead located just under one of the two boxes. Different time intervals were used between cue and target. Subjects were instructed to ignore the cue and to respond to the target (a cross inside one of the two boxes). The data showed only consistent effects of inhibition (inhibition of return) with the long intervals, but the pattern was different depending on the cue type. The amount of inhibition was much greater when the onset of the cue was followed by its offset. Apparently, inhibition of return depended on the dynamic changes of the cue.

The relationship between central cues and peripheral cues in covert visual orientation.

Four experiments were conducted to compare valid and invalid cue conditions for peripheral and central cues. Experiments 1, 3, and 4 used reaction time (RT) as the dependent variable. Experiment 2 used a threshold measure. Peripheral and central cues were presented on each trial. The peripheral cue was uninformative in all experiments. The central cue was informative in Experiments 1 and 2, where it predicted stimulus side on 70% of the trials. Experiment 3 included 50% and 100% central-cue prediction conditions as well as the 70% treatment. Experiment 4 included 60%, 75%, and 90% central-cue prediction conditions. The effects of the central and peripheral cues were independent and additive in all four experiments, indicating that: (1) both cue types can act simultaneously, and that the relationship between them is additive under the conditions used in these experiments, (2) informativeness is not a necessary condition for attentional effects with peripheral cues, and (3) covert visual orientation influences sensory thresholds and RT in similar ways. The results of Experiments 3 and 4 demonstrated that the facilitation associated with peripheral cues was insensitive to manipulations which demonstrate that subjects use the informational value of the central cue to direct voluntary attention. The results are discussed with reference to two issues; first, the proposition that central and peripheral cues exert their influence on performance in independent information-processing stages, following the additive factor method, and, second, the problems raised for additive factors method when cues elicit both an "explicit" response-regarding the presence or absence of a specified letter-and an "implicit response"-involving the planning and possible execution of eye and hand movements.

Effects of spatial attention on directional manual and ocular responses.

The aim of the present study was to investigate how spatial attention influences directional manual and saccadic reaction times. Two experiments were carried out. In experiment 1 subjects were instructed to perform pointing responses toward targets that were located either in the same or the opposite hemifield with respect to the hemifield in which an imperative stimulus was presented. In experiment 2, they were instructed to make saccadic or pointing responses. The direction of the responses was indicated by the shape of the imperative stimulus. Reaction time (RT), movement time, and, in experiment 2, saccadic trajectory were measured. The imperative stimulus location was either cued (endogenous attention) or uncued. In the latter case the imperative stimulus presentation attracted attention (exogenous attention). The main results of the experiments were the following: First, exogenous attention markedly decreased the RTs when the required movement was directed toward the imperative stimulus location. This directional effect was much stronger for pointing than for ocular responses. Second, endogenously allocated attention did not influence differentially RTs of pointing responses directed toward or away the attended hemifield. In contrast, endogenous attention markedly favored the saccadic responses when made away from the cued hemifield. Third, regardless of cueing, the direction of movement affected both pointing and saccadic reaction times. Saccadic reaction times were faster when the required movement was directed upward, while manual reaction times were faster when the movement was directed downward. Fourth, lateralized spatial attention deviated the trajectory of the saccades contralateral to the attention location. This pattern of results supports the notion that spatial attention depends on the activation of the same sensorimotor circuits that program actions in space.

Orienting of visual attention in Alzheimer's disease: its implication in favor of the interhemispheric balance.

Visual attention in dementia of Alzheimer's disease (AD) has not been investigated as extensively as memory or language. The aim of this research was to study the orienting of attention in patients with AD (which temporo-parietal areas are primarily affected) compared with patients with Parkinson-Dementia, Parkinson's disease, and normal controls, using the Posner paradigm. Subjects were instructed to respond by pressing a response key after the appearance of a target at the same location (valid trial) or at the opposite location (invalid trial) indicated by a central cue (arrow). According to the experimental procedure developed by Posner, it has been hypothesized that parietal lobes are involved in "disengagement operation" (when attention has to move from one location to another in the controlateral field). Results showed no differences between AD and the other groups and between left and right hemifield. In conclusion, the authors did not find any sign of difficulty with disengagement, and results are discussed in terms of Kinsbourne's interpretation of a balance between hemispheres.

Spatial attention-determined modifications in saccade trajectories.

Normal subjects were required to make horizontal or vertical saccades at the presentation of visual or acoustic imperative stimuli. The locations of visual imperative stimuli were orthogonal to the required saccade. Before stimulus presentation the subjects were cued about its location and instructed to allocate attention to it without moving the eyes. The main aim of the experiment was to establish whether the trajectory of horizontal saccades would be modified by spatial attention. The results showed that, with respect to the condition in which attention was on the horizontal meridian, the allocation of attention to the upper hemifield determined a downward saccade deviation, while the allocation to the lower hemifield determined an opposite deviation. The data strongly support the view that spatial attention and saccade programming share the same neural substrates.

Spatial attention and eye movements.

We previously showed that when attention is allocated to the right or left of the fixation point, saccades directed to targets located above or below the fixation point deviate contralateral to the attention locus. In the present study, we examined how general this phenomenon is and whether the amount of saccade deviation depends on the location of attention with respect to that of the saccade target. Three experiments were carried out. In experiment 1 the location of the imperative stimulus was uncued. Its presentation exogenously directed attention to its location. In experiment 2 the location of the imperative stimulus was cued by a central cognitive cue. In this experiment attention was endogenously directed to the imperative stimulus location before its presentation (expectancy paradigm). In experiment 3 all stimulus boxes contained a possible imperative stimulus at the display presentation. A central cue, presented subsequently, indicated which of them had to be used for the saccade. In this experiment attention was endogenously directed to the imperative stimulus, but after its presentation (no-expectancy paradigm). The results showed that, regardless of how attention was directed to the imperative stimulus, the vertical saccades deviated contralateral to the attention location. The deviation was larger when attention was in the upper field and the saccade was directed upward ("same hemifield" condition) than when attention was in the upper field and the saccade was directed downward ("opposite hemifield" condition). The same relationship between the "same hemifield" condition and "opposite hemifield" condition was found when attention was in the lower field. Saccadic reaction times (SRTs) were shortest in experiment 2 and longest in experiment 3. In experiment 2, SRTs of the "same hemifield" condition were significantly longer than those of the "opposite hemifield" condition. Taken altogether, these results strongly support the notion that attention allocation in space leads to an activation of oculomotor circuits, in spite of eye immobility. The possible mechanisms responsible for saccade deviations and for greater saccade deviations when attention is in the same hemifield as the programmed ocular saccade are discussed.

Orienting of attention and eye movements.

According to the premotor theory of attention, the mechanisms responsible for spatial attention and the mechanisms involved in programming ocular saccades are basically the same. The aim of the present experiments was to test this claim. In experiment 1 subjects were presented with a visual display consisting of a fixation point and four boxes arranged horizontally and located above the fixation cross. Two of the boxes were in the left visual hemifield, two in the right. A fifth box was located on the vertical meridian below the fixation cross. Digit cues indicated in which of the upper boxes the imperative stimulus was most likely to appear. Subjects were instructed to direct attention to the cued box and to perform a saccadic eye movement to the lower box on presentation of the imperative stimulus. The trajectory of the saccades deviated contralateral to the hemifield in which the imperative stimulus was presented. This deviation was larger when the hemifield where the imperative stimulus was presented was the cued one. In experiment 2, the visual display consisted of five boxes forming a cross. The central box served as a fixation point. The cue was a small line, linked to the central box, pointing to different directions and indicating where the visual imperative stimulus would appear. In 50% of trials, the imperative stimulus was a visual stimulus presented either in one of the lateral boxes or in the central one. In the remaining 50% of trials, the imperative stimulus was a non-lateralised sound. Half the subjects were instructed to make a saccade to the upper box at the presentation of the visual imperative stimulus and to the lower box at the presentation of the acoustic stimulus. Half the subjects received the opposite instructions. The results confirmed that the saccades deviate contralateral to the hemifield of stimulus presentation in the case of visual imperative stimuli. Most importantly, they showed that the saccades deviate contralateral to the cued hemifield, also in the case of acoustic imperative stimuli. Experiment 3 was similar to experiment 2. It confirmed the results of that experiment and showed that slow ocular drifts, which are observed in the time interval between cue and imperative stimulus presentation, cannot explain the ocular deviations. Taken together, the experiments demonstrate that spatial attention allocation leads to an activation of oculomotor circuits, in spite of eye immobility.

[Facilitating and inhibiting effects of the orientation of attention using peripheral cues]. / Effetti facilitatori e inibitori dell' orientamento dell'attenzione con segnali periferici.

The attentional field resulting from the presentation of peripheral cues; which were either informative or non informative about the position of the imperative stimulus, was studied. Different time intervals between cue and stimulus (120, 300, 600 ms) were used. The results showed facilitation of the response with the informative cue and inhibition with the non informative cue. This happened for the longest cue-stimulus intervals and when the position of the cue and the position of the stimulus were congruent. Also order of cue presentation (i.e., either informative followed by the non informative cue or vice versa) proved important in producing facilitatory and inhibitory effects.

[Recall of the proper names of persons: effect of age and the modality of access]. / Rievocazione dei nomi propri di persona: effetto dell'eta' e della modalità di accesso.

Aging is associated with phenomena of slowing down of cognitive processes and impairment of neuropsychological performances. Elderly people also report difficulty in the retrieval of proper names. Verbal fluency (VF) tests are particularly effective for the identification of even slight mental impairments. In this experiment we utilized the usual tests of VF for semantic categories and letters of the alphabet together with three new tests of VF for first names, differing in mode of access. The first mode was free recall, the second mode was semantic (first names beginning with a particular letter), and the third mode was autobiographical (first names of relatives). There were 3 experimental groups: young people with high education level, elderly people with high education level and elderly people with low education level. The aim of our work was to verify whether aging modifies the performance in the VF tests, particularly in the three first name VF tests. No difference was found between the groups of young and elderly people with high education level. The comparison between the two groups of elderly people, with high and low education level, showed that significant differences were present in some but not in all of the VF tests. While the two groups clearly differed in semantically oriented tests, no difference could be detected in the test oriented to episodic memory. This result seems to be inconsistent with the hypothesis that aging affects mainly episodic memory.

[Orientation of attention in the visual space]. / Aspetti dell'orientamento dell'attenzione nello spazio visivo.

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.

Movements of attention in the three spatial dimensions and the meaning of "neutral" cues.

Six experiments were conducted to examine the effect of various attentional manipulations on reaction time to visual stimuli. The first three experiments compared the responses to stimuli presented in the depth (Experiment 1), along the horizontal (Experiment 2), and vertical (Experiment 3) meridians in a valid condition (stimulus presented in the cued position), an invalid condition (stimulus presented in the alternative position to the cued position) and a neutral condition (no information on stimulus position). The most interesting result was the demonstration that attention can be moved along the sagittal plane in the absence of vergence eye movements and that when attention is focused on a certain point, unattended points between this point and the observer (i.e. near points) are responded faster than unattended points beyond it (i.e. far points). In the frontal plane no asymmetry was found between the responses to unattended points above or below the fixation, whereas a certain, albeit non-constant, advantage was present for unattended stimuli on the right of the fixation point in respect to those on the left of it. The second series of experiments was similar to the first one, except that a new situation was introduced in which the fixation point was cued and stimuli could appear either in correspondence to it or in a peripheral position (invalid condition with attention at the fixation point). The results showed that in this new situation the responses to unattended stimuli are much longer than they are under neutral conditions, and as long as they are under conventional invalid condition. It is suggested that the so called neutral condition is a condition of diffuse attention and an attempt is made to explain it in terms of a premotor theory of attention.

Reorienting attention across the horizontal and vertical meridians: evidence in favor of a premotor theory of attention.

Stimuli presented in a non-attended location are responded to much slower than stimuli presented in an attended one. The hypotheses proposed to explain this effect make reference to covert movement of attention, hemifield inhibition, or attentional gradients. The experiment reported here was aimed at discriminating among these hypotheses. Subjects were cued to attend to one of four possible stimulus locations, which were arranged either horizontally or vertically, above, below, to the right or left of a fixation point. The instructions were to respond manually as fast as possible to the occurrence of a visual stimulus, regardless of whether it occurred in a cued or in a non-cued location. In 70% of the cued trials the stimulus was presented in the cued location and in 30% in one of the non-cued locations. In addition there were trials in which a non-directional cue instructed the subject to pay attention to all four locations. The results showed that the correct orienting of attention yielded a small but significant benefit; the incorrect orienting of attention yielded a large and significant cost; the cost tended to increase as a function of the distance between the attended location and the location that was actually stimulated; and an additional cost was incurred when the stimulated and attended locations were on opposite sides of the vertical or horizontal meridian. We concluded that neither the hypothesis postulating hemifield inhibition nor that postulating movement of attention with a constant time can explain the data. The hypothesis of an attention gradient and that of attention movements with a constant speed are tenable in principle, but they fail to account for the effect of crossing the horizontal and vertical meridians. A hypothesis is proposed that postulates a strict link between covert orienting of attention and programming explicit ocular movements. Attention is oriented to a given point when the oculomotor programme for moving the eyes to this point is ready to be executed. Attentional cost is the time required to erase one ocular program and prepare the next one.

Right hand superiority in serial recall of tactile stimuli.

The fingertips of right and left hand of normal subjects (right-handed male) were stimulated at random. After intervals of 0.3, 1.0, 3.0 and 6.0 seconds, an acoustic or tactile signal set off the response of the subject. The response was the ordered reproduction of the tactile sequence given to the subject. The results show a greater efficiency of right hand, a better recall of the first serial positions and of the last one but no difference depending on whether the recall signal is acoustic or tactile. The results are discussed and new hypotheses are formulated.