File:PremotorTheoryOfAttention Fig2.jpg

The figure reports an example of the experimental paradigm used by Sheliga, Riggio, and Rizzolatti (1995) to support the premotor theory of attention. The basic assumption was that if visuospatial attention involves an activation of oculomotor circuits, then this activation should influence an overt oculomotor response. In contrast, if attention is not related to oculomotion, there is no reason why such an influence should occur. The basic experimental situation was similar to that used in experiments on meridian effect (see Figure 1). Participants were instructed to fixate a central cross and to pay attention to one of the possible stimulus locations according to the cue. The major difference was that the measured variable was not a manual response but a vertical saccade directed to a box located below or above the fixation point. Specifically, the visual display comprised three filled and two empty boxes. The three filled boxes were arranged horizontally. The two empty boxes were located above and below the central filled box. The central box was the fixation box. The cue was a thin line attached to this box, indicating the left box if pointing left, the right box if pointing right, the central box if pointed up. The stimulus consisted in a white vertical line across one of the filled boxes. In response to stimulus presentation, participants had to make a vertical saccade directed to one of the empty boxes, according to instructions. The figure shows all saccadic responses from one representative participant. Left side. Saccadic trajectories in response to imperative stimulus in the left box (upper panel), in the central box (middle panel), in the right box (lower panel). Right side. Mean horizontal deviation of saccades with imperative stimulus presented in the left box (upper panel) or in the right box (lower panel) after point-by-point subtraction of the mean horizontal deviation of saccades with the imperative stimulus presented in the central box (abscissa: horizontal deviation; ordinate: time). Main results showed that saccade trajectory deviated contralaterally to stimulus location, in particular the strength of the deviation was greater when trials were valid, that is when active attention was on the locus of imperative stimulus presentation. Finally, the deviation was present also when the imperative stimulus consisted not in a visual one, but in a computer-generated sound presented centrally, demonstrating that the deviation of response saccades doesn’t depend from the location of visual stimulus presentation.