Abstract
In a simple detection task, where the target can appear to either side of fixation, a background of randomly moving dots is added to the display. On some trials, the dots on one side of the display slowly start to move coherently away from a core location, giving an impression of looming motion. When motion coherence reaches 100% prior to the target being presented, participants show an advantage of up to 80 ms at detecting the target when it appears at the center of the looming motion than when it appears in the field opposite to the looming motion. This RT advantage has been named Loom Cueing (LC, von Mühlenen & Lleras, 2003, Psychonomics). In this study, we tested the effects of motion coherence on LC. In Experiment 1, we used three levels of motion coherence: 100%, 50% and 25%. LC was observed at all three levels of coherence, but the magnitude of the effect decreased substantially as motion coherence decreased (64 ms, 27 ms and 18 ms, respectively for 100%, 50% and 25% coherence levels). In Experiment 2, we measured participants' ability to detect the looming motion at several coherence levels, from 0% to 100%. Participants' ability to detect the looming motion increased linearly with increasing levels of coherence between 25% and 75% and asymptote afterwards. In Experiment 3, we tested whether LC would still be observed at very low levels of motion coherence and whether LC would occur below the coherent-motion detection threshold. LC was obtained, but only at coherence levels above the coherent-motion threshold. Finally in Experiment 4, we tested whether being aware of the looming motion would affect LC. Three coherence levels were used (6%, 12% and 25%). LC was observed at all three levels, regardless of whether participants were aware of the coherent motion or not. Possible mechanisms involved in LC are discussed.
NSF, SNF