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Manfred Fahle, Michael Morgan, Volker Diehl, Karoline Spang; An fMRI correlate of perceived 3-dimensional structure from purely temporal information. Journal of Vision 2002;2(7):115. doi: https://doi.org/10.1167/2.7.115.
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© ARVO (1962-2015); The Authors (2016-present)
The Pulfrich effect, i.e. the perception of depth from delaying the input to one eye by means of a grey filter, allows the production of 3 dimensional structure without changing the spatial layout of a stimulus. We used modifications of this effect in order to study which parts of human cortex are most strongly activated when 3 dimensional structure emerges. Three types of stimuli were presented in a 1.5 tesla Siemens Vision scanner: a) stationary dots; b) dots moving in random directions; c) a checkerboard consisting of different grey levels modulated sinusoidally over time (cf. Morgan & Fahle, Vision Research 40 (2000), 1667–1675). Observers tried to decide what predominant motion direction they perceived, when either looking straight at the (moving) stimuli or else with a neutral density filter in front of their dominant eye. Without the filter, any predominance of motion direction is purely subjective, but delaying the input to one eye creates “spatio-temporal disparities” similar to the Pulfrich effect. With the filter in front of the right eye, dots moving to the right appear in front of the horopter, while those moving to the left appear behind. Mean results of so far 4 observers (Brain Voyager, GeneralLinearModel) show no strong effect of the filter for stationary targets. However, for both dynamic stimuli, looking through the filter decreases activity in V1, while activity increases in a circumscribed area in inferior temporal cortex. Hence, this area seems to be involved in the computation of structure from (pseudo) stereoscopic information.
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