Adjustment of Collinearity of Laterally Moving,Vertically Separated Lines Reveals Compression of Subjective Distance as a Function of Aperture Size and Speed of Motion

We have investigated the effects of the size of the aperture and the speed of motion of a pair of laterally moving vertical lines on the precision with which subjects were able to adjust the spatial position of these moving lines so as to achieve subjective collinearity. The reference line moved laterally across the whole computer display (14.4 deg) while the upper line (that was vertically separated from the reference one by 0.64 – 2.56 deg) appeared in a central aperture of varying horizontal width (0.62 – 1.9 deg). In each trial subjects shifted the aperture line leftwards and/or rightwards until it seemed collinear with the ‘permanently’ moving line. In order to achieve subjective collinearity the aperture line had to be shifted towards the direction of motion from the position that would have satisfied physical collinearity. The size of these shifts (up to 0.124 deg) was a monotonically increasing function of the speed of motion and a monotonically decreasing function of the diameter of the aperture. The results point to the compression of subjective space-time as a monotonically decreasing function of the spatiotemporal availability of the aperture stimulus. The longer the exposure of the aperture stimulus, the more its perception ‘caught up’ the initial delay compared with the perception of the moving reference stimulus. We may postulate a relative acceleration of establishing subjective conscious representation with increasing temporal availability of the stimulus. Similarities with the Fröhlich effect and tandem effect are discussed.