Temporal integration of visual information is affected by fast spatial grouping

Sensory information is integrated over space and time, determining both the content and time of our visual experience. Here we tested how spatial integration of elementary features affects temporal integration across the visual field. An array of 16 equidistant small sinusoidal gratings was presented on a virtual circle centered on the fixation point. The gratings were randomly split in two halves, and each half group was presented sequentially. Test stimuli were created by omitting one grating, and participants had to detect these tests in a sequential 2AFC paradigm. To measure the time course of temporal integration, we varied the duration of the first group of gratings (10–160 ms) and inter-stimulus interval between the two groups (ISI, 0–40 ms). The contrast of the first group was adjusted to match the perceived contrast of the second group. We compared two spatial conditions: the gratings’ orientations were either aligned with the virtual circle in both groups (forming a collinear contour), or the gratings’ orientations were aligned in one group and orthogonal in the other group (forming an interrupted contour). Increasing the ISI decreased performance, but more surprisingly, increasing the duration of the first group also decreased performance (see also DiLollo, 1977, Nature). The two effects were not additive: performance decreased faster with an increase in ISI than duration. Interestingly, detection of the missing element was better when both parts of the display contained gratings forming collinear, rather than with interrupted contours. The interaction between the duration of the display and ISI on performance is inconsistent with temporal integration being an output of a fixed or sliding temporal window integrating information over time. Furthermore, the effect of relative similarity of gratings suggests an interaction between a fast spatial grouping and temporal integration across the visual field, further informing models of temporal integration.