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R. J. Babu, S. J. Leat, E. L. Irving; Time to Collision of Looming Targets With Single and Dual Visual Tasks. Invest. Ophthalmol. Vis. Sci. 2008;49(13):759. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The ability to estimate time to collision (TTC) is important in tasks such as driving and hazard avoidance. This study investigates 1) the effect of speed and eccentricity of looming targets in estimating TTC, 2) the difficulty of dual visual tasks in estimating TTC and 3) the role of eye movements in estimating TTC in dual visual tasks.
Ten adult participants were assigned to 2 single and 3 dual visual task conditions in which they estimated the TTC of targets looming at 3 different speeds at 10° and 20° eccentricities. Eye movements were allowed in all but one of the single task conditions. In dual task conditions, the primary task was to keep an enlarging black square within the confines of an outer dashed square and an inner white square in the central visual field. The secondary task was to estimate the TTC of a looming target in the periphery. In the three dual task conditions the difficulty of the central task was varied by changing the speed at which the black square enlarged (High 40msec refresh rate, Medium 70msec refresh rate, and Mixed-combination of 40 and 70msec refresh rates). Eye movements were recorded using a video based eye tracker. The dwell time (DT %), number of fixations (FP %) and the number of saccades to the central location were calculated.
There was a significant effect of speed of the looming target (p<0.05) in estimating TTC . There was a significant difference between the estimation of TTC with and without eye movements. In dual task conditions, TTC estimation was not affected by the difficulty of the central task nor the eccentricity of the looming target. This lack of differences between the dual task conditions could be explained by significant differences found in eye movement patterns, specifically in the central location. When the black (primary) target enlarged rapidly (40msec refresh rate), the dwell time (48.30±7.70) and the number of fixations (41.99±6.51) were significantly higher than in the medium (DT: 39.68±10.91, FP: 37.65±6.75) and the mixed condition (DT: 41.99±9.84, FP: 36.91±7.98).
The ability to estimate TTC is affected by the speed of the looming target. Furthermore, eye movements play an important role in judging TTC in both single and dual task scenarios. Studying eye movement patterns can be a valuable tool for determining the difficulty level of dual visual tasks.
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