Visual feature integration: how long can it last?

Spatiotemporal features are integrated along motion trajectories. For example, when a central line is followed by pairs of flanking lines, two motion streams diverging from the center are perceived. The central line is rendered invisible by the subsequent flanking lines. Surprisingly, if the invisible central line, but none of the later lines, is offset, the entire stream appears offset. Further, if one of the flanking lines is offset in the opposite direction, the two offsets integrate and cancel each other out – given the offsets are presented within the same temporal window, lasting for up to 450ms. Here, we asked what determines this duration. Observers discriminated the perceived offset of the motion streams. In line with most models of decision making, one might expect that the window terminates as soon as sufficient evidence about the offset is accumulated. However, this is not what we found. When we presented either a large offset at the first line or smaller offsets at the following lines, all in the same direction, the duration of the integration windows was identical. However, when we increased the processing load by adding two additional offsets, which canceled each other out, the window duration increased slightly. Lastly, by varying the ISI between the lines, we found that absolute time determines the window duration but that the number of lines does not. We propose that perception is a series of discrete frames, which depends mainly on absolute time, potentially on the processing load, but not on stimulus evidence. [SNF n 320030_176153 / 1 “Basics of visual processing: from elements to figure”.]