Biomedical subjects

C Umiltá

Publications and source records attributed to C Umiltá.

3 recordsLinked to original sources

PubMed1989

Splitting visual space with attention.

If a right-left spatial compatibility effect is observed, it can be maintained that the space has been segmented into right- and left-side parts. The present study aimed at showing a spatial compatibility effect (and, by implication, a right-left subdivision of space) solely attributable to the orienting of attention. Five groups of 8 normal subjects were required to give right-left discriminative responses to stimuli presented within one of six empty boxes arranged in a horizontal row. Reaction times and errors were recorded. The first two experiments showed that a right-left grouping of the boxes occurred regardless of whether subjects' fixation was kept at the intermediate position (Experiment 1) or at one extremity (Experiment 2) of the row. In Experiments 3 and 4, subjects' attention was not aligned with a fixed position but was moved, through peripheral cues, from trial to trial and positioned between different pairs of adjacent boxes. The results showed that the display was again subdivided into two regions and that the reference point for the right-left subdivision was the focus of attention. In Experiment 5, eye position was instrumentally monitored, and subjects' attention was directed by central cues. The results confirmed that the focusing of attention leads to a right-left partitioning of space, with the boundary at the locus of focal attention. In conclusion, we demonstrated, by employing a right-left spatial compatibility paradigm, that directing attention to a position in space brings about a right-left perceptual organization that predominates over that provided by the other egocentric reference axes.

Adult↗

PubMed1987

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.

Attention↗

PubMed1987

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.

Attention↗