Volume 19, Issue 5, 1979, Pages 491–500

Perception of continuity in stroboscopic motion: A temporal frequency analysis

  • University of Durham, Department of Psychology, Science Laboratories, South Road, Durham DH1 3LE,England


A target moving periodically in discrete spatial steps, so as to be seen in horizontal apparent motion, is perceived as being shifted in depth if each step occurs slightly later in one eye than in the other. This apparent-motion version of the Pulfrich stereophenomenon can be understood if the momentary visual direction of the target is determined during an integration period that is sufficiently long to include more than one spatial step. It can be predicted that the depth effect will be reduced when the temporal interval between successive spatial steps of the target exceeds a critical value which is greater than the integration period. This is so, and the critical value is in the region of 30–50 msec. It may be further predicted that this critical value will be decreased as a function of light adaptation, and this was also verified. These results cannot be accounted for by a simple monocular delay model. The present analysis of the depth-by-delay effect suggests a more general treatment of apparent motion, which can be considered to be indistinguishable from continuous motion to the extent that the visual system shows low-pass temporal frequency filtering.


On présente au sujet par intermitance un cible qui se déplace horizontalement, dont l'interval inter-présentation (IFI) varie entre 10, 30 et 50 msec. Lors de chaque présentation de la cible chaque oeil reçoit un stimulus indépendent: l'interval entre ces deux stimuli (retard inter-oculaire, IOD) varie entre 0.1 × IFI et 0.9 × IFI. Ce retard a pour effet d'ajouter un mouvement en profondeur au mouvement horizontal apparent de la cible. La sensibilitédes sujetsàla profoudeur deˆcroit en fonction de l'interval inter-preˆsentation, aussi bien qu' en fonction du niveau de l'adaptationàla lumière. On discute les méchanismes d'un “interpolation de position” lors de la perception de movement stroboscopique.