Reading the Clock in Different Ways - Separation of the Cortical Representations of Attention to Angles and Attention to Colours

Abstract:
The functional and anatomical separation of specific attentional mechanisms requires tasks in which the stimuli are kept constant across the conditions in order to exclude the effects of changes of the physical stimulus. In the present study, this was achieved by presenting subjects with the same set of clocks, while varying the discrimination tasks they had to perform. The change of blood oxygen dependent (BOLD) signal, measured by functional magnetic resonance imaging, was used as a measure of the activity of different cortical areas. The stimulus consisted of clocks with a yellow face and either yellow or white hands showing different times. Subjects were asked to press a button on an optic fibre answer box when the two hands formed an angle of 60° or less (angle discrimination) or when the hands were white (colour discrimination). Eye movements were recorded in separate electrooculography sessions. During the discrimination of angles the superior parietal lobule showed a significantly higher activation than during colour discrimination. Colour discrimination was accompanied by a significant BOLD signal increase in the inferotemporal cortex, particularly the fusiform gyrus. There was no significant difference in eye movements between the different task and control conditions. This implies that the superior parietal activation during angle discrimination represents a selective mechanism for spatial attention, while the inferotemporal activation during colour discrimination represents a modulation specific for attention to colours.