Índices de confort PMV, PPD y TSV

Left intraparietal sulcus

-38 - 3 8 52 4.5 V ision Touch -42 - 4 0 52 -36 - 3 6 48 3.5 4.1 Left superior occipital

gyrus -22 - 8 8 32 3.9 V ision Touch -22 - 8 8 32 -22 - 9 0 3.9 2.1 Left occipito-tem poral

junction -50 - 8 0 12 2.9 V ision Touch -52 - 8 0 10 -50 - 8 2 14 2.4 2.4

Attend LEFT

Right superior occipital

gyrus 26 - 8 2 32 3.5 V ision Touch 24 - 8 8 32 26 - 8 0 32 2.6 3.0 Right occipito-tem poral

junction 4 6 - 7 4 2 3.8 V ision Touch 48 - 7 4 2 42 - 7 2 6 3.5 2.4

Table II.3.1. reports co-ordinates and statistics for the bimodal areas observed in Experiment 3. W hile

the intraparietal sulcus continued to show contralateral modulation only in the left hemisphere, both occipital areas were showing a contralateral effect in both hemispheres. These right hemisphere modulations were not observed in Experiment 1 and 2.

A third activation did not survive the criteria imposed here, but was clearly predicated by the results of Experiment 1 and 2. This was the occipito temporal junction. This area showed a bimodal effect in Experiment 1 but did not activate in Experiment 2. My interpretation was that this area did not activated in Experiment 2 because o f the lack of experience of the visual task. In Experiment 3 subjects experienced again the visual task. The association between vision and touch should therefore be reinstated and a bimodal modulation was expected. In fact, the left occipito-temporal junction showed a

E. M acaluso Cross-modal Spatial Attention

below threshold modulation at x,y,z = -50 -8 0 12 (Z-value = 2.9; p = 0.002). Both simple main effects were significant at p-uncorrected < 0.05. As expected the two occipital areas also showed a main effect of attending vision over touch.

A ttention to the left hemifield:

Experiment 3 revealed, for the first time, some contralateral activation in the right hemisphere. These were found at the right occipito-temporal junction and right superior occipital gyrus. The activations were symmetrical in respect o f the two observed in the left hemisphere for attention to the left versus attention to the right (see Fig. II.3.3).

Bim odal

Attend RIG H T Attend LEFT

T

^ 3

„

T t y

L

^ IT

R

P

N

c

Figure II.3.3. show s the contralateral effects observed in the occipital lobe. The S PM -(Z } threshold is set at p-uncorr=0.01, so that the sub-threshold cluster in the left m iddle occipital gyrus also appears on the section (y=-80). T he plots show the rC B F for the activations in the right hem isphere, where contralateral m odulations were observed for the first tim e in this experim ent. In both the left and the right hem ispheres, m odulations were independent o f the attended m odality (bim odal effects).

The right superior occipital maxima was at x,y,z = 26 -8 4 32 (Z-value = 3.5). The occipito-temporal maxima was at x,y,z = 32 -6 0 2 (Z-value = 4.0), with a second peak more lateral and posterior (x,y,z = 46 -7 4 2; Z-value = 3.8). As for Experiment 1, both clusters showed a main effect of vision over touch.

Spatial modulation observed only when attention was directed to one modality

As for the other experiments, the effect of one factor (attending left versus right) which applied only for one level of the other factor (attention to vision or touch) was determined by testing for a simple effect of attended side (at a threshold of p = 0.001, in the presence of an interaction (at p = 0.05). As in experiment 1 and 2, no areas in the right hemisphere showed contralateral spatial modulation. In the left hemisphere, I replicated the finding of the previous two experiments: The superior occipital gyrus was modulated only in the context of attention to vision, while the post-central gyrus was modulated only when attention was directed to the tactile stimuli (Table II.3.2).

Vision:

As in Experiment 1 the left superior occipital gyrus (BA 19) showed a strong contralateral spatial modulation when subjects attended the visual stimuli (Fig. n.3.4.a). The maxima for the simple main effect was found at x,y,z = -24 -8 6 26 (Z-value = 4.5), the maxima of the interaction was at x,y,z = -26 -8 6 24 (Z-value = 2.7). The activation was lateral to the small cluster that showed a common effect for both attention to vision

E. M acaluso Cross-m odal Spatial Attention

and touch, and extended into the sulcus lunatus. The pattern of activation of the left superior occipital lobe agreed with what was found in Experiment 1: a strong modulation during the visual task, and a weaker, but consistent, modulation during the tactile task. The clusters showing unimodal and bimodal effects were, in both experiments, adjacent.

Touch:

The test for unimodal modulation in Experiment 3 revealed a single cluster in the left post-central gyrus (Fig. II.3.4.b). The simple main effect of attending right versus attending left during the tactile task was found at x,y,z = -36 -3 4 48 (Z-value = 4.1), the maxima of the interaction was at x,y,z = -32 -3 2 44 (Z-value = 2.9). The rCBF plot shows that the spatial effect was much stronger during the tactile task than during the visual task. The plot shows also a weak modulation when volunteers attended to the visual stimuli, but at the plotted voxel the simple main effect in vision ([aRV]-[aLV]) did not reach significance at p-uncorrected = 0.05. However, comparing figures II.3.2.a and II.3.4.b it appears clear that the intraparietal (bimodal) and the post-central (only touch) were adjacent. Again, this replicated what was observed in Experiment 1 and 2, where unimodal and bimodal responses were found in nearby areas of the anterior parietal lobe.