The
Ternus Effect is an illusion involving
apparent motion. In this classical version, two frames are alternated, with or without a temporal gap (an
interstimulus interval or ISI) between them. In both frames, a central disk is presented with a lateral disk whose position alternates between left and right.
In this illusion, the length of the ISI determines the type of motion seen: the lateral disk is perceived as jumping between its left and right positions at short ISIs (referred as
element motion), while the 2 disks are perceived as moving together from side to side at long ISIs (referred as
group motion). At intermediate ISIs (40-50 ms), the motion appears
bistable.
With the sliders you can explore the effect by controlling the duration of the temporal gap between the 2 frames, as well as the size and separation of the disks.
This example of apparent motion may constitute a
third-order motion that relies on a higher-level, attentional long-range motion process that performs
feature tracking.
References:
Ternus (1926)
Experimentelle untersuchungen über phanomenale identitat (Experimental investigations of phenomenal identity). Psychologische Forschung 7(1):81-136
Pantle & Picciano (1976)
A multistable movement display: Evidence for two separate motion systems in human vision. Science 193(4252):500-502
Kramer & Yantis (1997)
Perceptual grouping in space and time: Evidence from the Ternus display. Perception and Psychophysics 59(1):87-99
Scott-Samuel & Hess (2001)
What does the Ternus display tell us about motion processing in human vision. Perception 30:1179-1188
Wallace & Scott-Samuel (2007)
Spatial versus temporal grouping in a modified Ternus display. Vision Research 47(17):2353–2366
