Wallace J M, Scott-Samuel N E, 2005, "Grouping in the Ternus display: Identity over space and time" Perception 34 ECVP Abstract Supplement
Grouping in the Ternus display: Identity over space and time
J M Wallace, N E Scott-Samuel
In the classical Ternus display, the 'group' or 'element' motion percepts reflect biases towards within-frame or across-frame grouping (Kramer and Yantis, 1997 Perception & Psychophysics 59 87 - 99; He and Ooi, 1999 Perception 28 877 - 892). With variable ISIs, spatially continuous internal element structure biases within-frame grouping (Alais and Lorenceau, 2002 Vision Research 42 1005 - 1016). Using a novel configuration of the Ternus display with no ISI, we investigated spatiotemporal grouping by manipulating internal structure of the stimulus elements across space and time. Each of five stimulus frames consisted of three elements (Gabors, SD 0.25 deg, 2 cycles deg-1 carriers): two central elements to either side of a fixation dot, plus one outer element alternating left to right. They were subjected to the following: (i) each stimulus frame was temporally subdivided, with carrier orientation oscillating back and forth about vertical on alternate subdivisions through angles varying from 0° to 90° across trials; (ii) each stimulus frame was subdivided into three frames alternating in orientation through 90° (central elements) or through an additional 0° to 45° range (outer elements); (iii) stimuli as for (ii), but outer elements oscillated with a delay ranging from 0 to 100 ms. Observers reported their percept: element or group motion. We found (i) an increased number of subdivisions in each stimulus frame gave more group motion: temporal contiguity influenced within-frame grouping; (ii) larger orientation differences between central and outer elements gave more element motion (thresholds around 30°): spatial contiguity influenced across-frame grouping; (iii) longer delays gave more element motion (thresholds around 40 ms): temporal contiguity influenced across-frame grouping. Thus both spatial and temporal factors can interact to influence the percept of the Ternus display. These interactions have implications for perceptual grouping in Ternus displays, suggesting more complex dynamics than pure spatial interactions, and also challenge short-range/long-range accounts.
[Supported by BBSRC.]
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