Different groups of healthy subjects performed duration judgment tasks on various types of visual stimuli. In the first two experiments visual stimuli were constituted by digit pairs (1 and 9), presented in the centre of the screen or in the right and left space. In a third experiment visual stimuli were constituted by black circles. The duration of the reference stimulus was fixed at 300 ms. Subjects had to indicate the relative duration of the test stimulus compared with the reference one. The main results showed that, regardless of digit magnitude, duration of stimuli presented in the left hemispace is underestimated and that of stimuli presented in the right hemispace is overestimated. On the other hand, in midline position, duration judgments are affected by the numerical magnitude of the presented stimulus, with time underestimation of stimuli of low magnitude and time overestimation of stimuli of high magnitude. These results argue for the presence of strict interactions between space, time and magnitude representation on the human brain.
Thursday, March 20, 2008
Relativity of space, time and magnitude representation in our brains
Here are some simple and elegant experiments that shows how relativistic our time sense is. Our two cerebral hemispheres expand (right hemisphere) or contract (left hemisphere) time perception when acting alone, and then let magnitude cues in the stimulus influence perceived time when acting together. Vicario et al. investigated whether duration judgments of digit visual stimuli were biased depending on the side of space where the stimuli were presented (i.e. to which hemisphere) and on the magnitude of the stimulus itself: