Accumulation processes of time, space and numerosity : an fMRI study

Abstract

The underlying neuronal processes of the perception of time, space and other magnitudes are subject to intense scientific debate. Furthermore, mutual interactions between the perception of different dimensions are widely reported, but the origin of such crossdimensional interference effects is still not well understood. This thesis investigates time, space and numerosity judgements as well as their cross-dimensional influence on a behavioural and neuronal level within a navigational context. Participants underwent fMRI imaging while being passively moved forward along a virtual path that was covered with randomly appearing dots. After each trial, participants were asked to make judgements about the trial duration, distance covered or numerosity of items on the floor, allowing for a simultaneous observation of behavioural and neuronal effects. Behavioural results revealed a correlation between time and space judgement precision as well as a bidirectional interference only between these two dimensions, but not for numerosity. Analyses of the neuroimaging data identified the right IFG as a commonly activated area during the perception of all three dimensions and MT/V5 bilaterally as being uniquely activated during numerosity trials. Mirroring the behavioural results, activation patterns of time and space trials were indistinguishable by MVPA but could be decoded from numerosity trials, predominantly in MT/V5 as well as in the IPS bilaterally (time vs. numerosity). The findings suggest that the interference between travel time and traveled distance could be mediated by neuronal computations of movement speed on the basis of visual optic flow information. Furthermore, the results add to the body of evidence that the crossdimensional interference effects between time and space are based on overlapping neuronal representations.