Cortical areas involved in imagery and haptic exploration of object size

Human neuroimaging studies indicate that the primary visual cortex (V1) of sighted individuals is involved in haptic exploration of objects, even when visual information is not available. However, it remains unknown which object properties are processed in V1 during tactile tasks (e.g., size, shape, etc.). Here, we investigated whether haptic exploration of object size is processed in V1 despite the lack of online visual input, and whether activation in this area might be due to visual imagery. To this aim, we tested 22 right-handed participants in a slow-event related fMRI study in which participants explored the size of three rings or imagined them. Therefore, the experimental design consisted of a two by three factorial design with two tasks (Haptic, Imagery) and three stimulus sizes (Small, Medium, Large). Participants were blindfolded during the training and fMRI session, and did not see the stimuli until the end of the experiment. The results of univariate analysis revealed that haptic exploration of the rings elicits activation in frontal and parietal areas, as expected by the nature of the task, as well as in V1. Visual imagery induces activation in the premotor cortex and V1. Further, the activation in V1 is higher for the haptic than imagery task. These results confirm and extend previous findings by showing that V1 is involved in haptic exploration of objects in absence of online visual inputs, and that this univariate effect cannot be explained merely with visual imagery. Since activation levels were comparable for the three differently sized rings across the whole brain, we will use multivoxel pattern analysis to examine whether and where in the brain we can decode object size during imagery and haptic tasks, as well as across conditions.