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Christa van Mierlo, Eli Brenner, Stefan Louw, Jeroen Smeets; Are latency differences between slant cues visible in the online control of our movement?. Journal of Vision 2008;8(6):831. doi: 10.1167/8.6.831.
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When we place a cup on a table we not only need to traverse the distance between the cup and the table, but also make sure that at the end of the movement the cup has the same orientation as the table. We estimate both distance and orientation with binocular and monocular cues, which are processed independently with different neural latencies. This latency difference might become relevant if information is changing, such as during ones' movements. Movements can be corrected at short latency to a change in the environment. Are such corrections the sum of corrections to changes in the individual cues or a full reaction in response to the first indication of a change? To investigate this, we created a virtual environment in which subjects had to place a cylinder on a virtual surface. The slant of the virtual surface could change right after movement onset and was either simultaneously in binocular disparity and monocular cues or only in one of the cues. Subjects' adjustment might be based on the latest estimate of slant or on detecting the transient in surface orientation. We therefore removed the transient on half of the trials by blocking vision for 100 ms before the slant change. Subjects corrected their movement to accommodate the changed surface slant. This correction was 55 ms faster for monocular cues than for binocular disparity. Removing the transient delayed the response to the monocular cues by 80 ms, without affecting the response to the binocular cue. Corrections to slant changes happening simultaneously in both cues were the sum of corrections to changes in the individual cues. So we have access to the monocular transient and to monocular and binocular slant, but simply use the first one signaling a change when we have to adjust an ongoing movement.
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